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Digilock 110

1. 7 3 Controller Parameter Adjustment and Optimization Once a suitable error signal is at hand the feedback loop can be closed and optimized The general working principle of the Proportional Integral Derivative PID controller is to minimize the deviation of a physical measure process variable from a selected set value by modifying the actuator drive Manipu lated variable accordingly The output of the controller is a weighted sum of the integral I proportional P and differential D paths scaled by the overall gain The digital PIDs in the DigiLock 110 allow for a precise and reproducible control of the gain settings The three contributions differ in their frequency dependence P The integral I part is given by the time integral of the error signal Therefore its gain increases to lower frequencies and it is responsible for the compensation of offset changes The residual devia tion of the error signal from zero respectively the difference between the physical measure and the set point decreases with increasing integral gain 2 The proportional P part has a flat frequency response and is limited by the bandwidth of the con trol loop A larger proportional gain Kp reduces the deviation from the set point and is limited by the onset of oscillations di The differential D part reacts on sudden changes to reduce deviations e g an over shoot in the transient response Its frequency response increases with frequency and is
2. Phase shift in degrees between the output and the reference signal Offset in units corresponding to the oscilloscope display The offset is substracted from the original signal Output channel to which the modulation is applied Turn ON OFF the modulation The modulation is automatically switched on for locking Therefore it only needs to be activated manually for the adjustment of the phase shift or in manual lock mode Channel that is used in the AutoLock display only available in Advanced Settings mode see Paragraph 6 2 5 5 NOTE Due to signal processing limitations it is recommended to optimize the lock with the demodulated lt LI out gt signal and not the modulated input signal see Paragraph 7 6 Page 20 Status 21 10 08 TOPTICA PHOTONICS 6 Operation Frontend 6 2 1 8 PDH Module rel PDH error signal a q UOISSILUSUDI J21 l l l I I l l detuning linewidth Figure 14 Left PDH Module Tab Right Error Signal generated with the Pound Drever Hall Modulation Technique The principle of operation is similar to the Lock In Module but the available modulation frequencies are higher and restricted to even fractions of 25 MHz 25 MHz 12 5 MHz 6 25 MHz 3 13 MHz 1 56 MHz Input Input source for the module Main in Aux in Mod set freq The desired modulation frequency in Hz Mod amplitude Peak to peak amplitude of the modulation signal in Volts Phase shift Phase
3. TOPTICA e Page 35 Status 21 10 08 Feedback Controlyzer DigiLock 110 600 400 200 200 LI error signal a u 400 600 120 80 IN i correct si unlocked 40 40 Sat Absorption Signal mV o 80 Figure 30 Polarity of PID Controller using Frequency Modulation The graph shows the characteristic distortions of the error signal as well as the saturated absorption signal of a top of fringe lock for different polarities The undistorted signal solid black is given for reference For the correct overall polarity dashed red the slope of the error signal at the peak is shallower while the peak itself is broader see boxed part of the graph In contrast for the wrong polarity dotted green the slope is steeper and the peak narrower If the overall sign is correct incorrect a resonance should become wider narrower as compared to the case of the controller being inactive The slope of the error signal e g in frequency modulation should become flatter steeper when the overall sign is correct incorrect If the overall gain is too high oscillations will be observed which will be either at the original position with multiple zero crossings or repelled from the original position with oscillations positive and or negative at different parts of the signal for correct and incorrect overall polarity respectively To suppress the oscillations reduce the overall gain Generally the change in slope as exp
4. able robustness against oscillations due to additional external disturbance and variations in the overall response The DigiLock 110 features a build in network analyzer see Paragraph 6 2 3 which can be used to analyze the frequency dependent amplitude and phase response of the actuators and control loop ele ments In particular it can be used to do an in loop analysis of the stability of the closed lock 7 4 Identification of Signal Polarity and Slope To support the AutoLock features the DigiLock 110 software frontend takes a consistent approach to the definition of the signal polarity of each controller and the slope of the error signal The polarity of the controller is used to match the action of the corresponding output to the direction of the scan It should be chosen such that an increased output acts in the same direction as an increase of the scan output Hence if the output of the controller is identical to the scan output the polarity is pos itive Otherwise the direction has to be determined for the particular actuator used For example if the DigiLock 110 scan module scans the laser via the Scan Control SC 110 and the output of PID 2 is also cho sen to be the SC 110 its polarity is trivially positive If the output of PID 1 is then directed to the current of the laser diode the polarity of the controller will deoend on the polarity of the laser diode as defined by the DCC 110 current control see Sys DC 110 manual for details I
5. 2 Di 2 Sd default not connected 40 k in Ver default not connected sion 1V1 px E E Aux in Precise in BCC laa Sum in AIO Tin AO 2in ook sk eas fark o 27M 1 0 50 Bandwidth value refers to signal path between lt Sum in gt and lt Main DIO in Output Resolution Sample Bandwidth Range 50 Ohm Comment Channel bit Rate Hz 3dB Hz V Driver Main out 100 M Backplane Sum of lt Sum in gt and Analog P branch 100 k 18k 6 5 amplification by 15 with SC110 AUX OUT SC110 out DCC ha TOOK packpiane DTC The 100k backplane AIO Toui ook Tek 65 No o AIO Zovi 100K default not connected Yes 6 6 Error out lt Main in gt lt Input Off pei de set gt Gain 2 bandwidth value refers to signal path between lt Main in gt and lt Error out gt TRIG DIO out 026 Mii teve 026 ve mee Ss Internal Resolution Sample Bandwidth Range Comment input offset 16 wok f 25 AnalogP 16 wok __ 08 o Table 7 CC Page 60 Ww PHOTONICS Status 21 10 08 9 Appendix 9 4 Pin Assignment of the DigiLock 110 Backplane Actual pins needed for normal operation of the DigiLock 110 Module are marked with a grey back ground color VG 64 a b c standard connector according to IEC 60603 2 22 A Mm0o0do0o0000000000000000000000000000 eS 0 00000000000000000000000000000060 Figure 57 VG 64 a b c Standard Connector O
6. AG TOPTICA PHOTONICS Status 21 10 08 Feedback Controlyzer DigiLock 110 Contents 1 The Feedback Controlyzer DigiLock 110 3 1 1 Package Contents J 1 2 Design and Operating Principle of the DigiLock 110 4 2 Safety Instructions and Warnings 6 2 1 General Safety Terms 6 2 2 Identification of Manufacturer 7 3 Operator Controls and Connections 8 3 1 Front Panel 8 3 2 Description of Front Panel Operator Controls and Connectors 9 3 3 Backplane Connections 10 4 Hardware Installation 10 5 Software Installation 11 5 1 System Requirements 1 5 2 USB Driver Installation 11 5 3 Control Software Installation 11 6 Operation Frontend 12 6 1 General User Interface 13 6 2 Functions 15 6 2 1 Scan and Lock 15 6 2 2 Controller Design 22 6 2 3 Network Analysis 23 6 2 4 System Setup 24 6 2 5 Settings 25 6 3 Display Area 29 6 3 1 Scope Mode 29 6 3 2 AutoLock Mode 30 6 3 3 Frequency Analysis Sl 6 4 Status Display 31 7 Notes on Feedback Control Loops with the DigiLock 110 32 7 1 Signal to Noise and Bandwidth Considerations 32 7 2 Frequency Modulation Techniques 32 7 3 Controller Parameter Adjustment and Optimization 33 7 4 Identification of Signal Polarity and Slope 34 7 5 Relock Feature 36 7 6 Signal Limitations in Analyzing the Locking Performance oF TOPTICA PHOTONICS Status 21 10 08 Feedback Controlyzer DigiLock 110 8 Application Examples 8 1 General System Setup 8 2 Doppler Free Saturation Spectrosco
7. Jumpers The DigiLock 110 module is shipped with a standard configuration of its inouts and outputs The internal jumpers allow to modify this configuration The table below shows all jumpers and their function For loca tion of the jumpers please see Figure 55 and Figure 56 Pos POs 2 Figure 54 Description of Jumper Positions Pos 1 is always near the angled corner Baseboard s o input out Foa JP 302 DCC 110 connected to open DAI JP 303 SC 110 out connected to closed DA2 Table 5 Baseboard Jumper Settings JP 300 DIC TOT connected to open DA3 Plug on board Jeg AUX In 50 Ohm connection to high Pos terminated Main in impedance JP 3 Precise In 50 Ohm connection to high open terminated Main in impedance JPS Sum in 50 Ohm connection to high Pos terminated Main in impedance impa homer closed open Feto JP Main in 50 Ohm high imped closed terminated ance Table 6 Plug on board Jumper Settings TOPTICA ELLA Page 9 Status 21 10 08 Feedback Controlyzer DigiLock 110 9 2 DigiLock 110 PCBs 9 2 1 Baseboard JP 302 JP 303 te x g OSEHU Son n 9ED BSPED o zi 3 ea St ba n J l esene amp b fa Bo 9 al ga 06 na ct usos 0 303 U305 C91 I Rao C3 Cc 8 i RI JP 301 G4 N mo Dow a C356 1304 360 6s R364 ao 8 g w pesca Laos i I R327 G04 R328 0 C321 nR
8. Smenn del Jisa ire Fossi a E Jooo Functions gt fsciiocu scio ou Dis p la y 450m 400m 350m i 300m i AutoLock Mode 250m 4 200m Sampling 150m Main in Y Display 100m E SC110 out Status 7 BA i 2 anaj u pon Figure 33 DigiLock 110 User Interface after Startup Here the laser is scanned across the saturated absorption lines of Rb at 780 24 nm see Paragraph 8 2 error out sum in Main out 0 000 Main in Biman out Grain cut grain cut Abano Figure 34 Graphical Overview of the Signal Path through the Controller System Setup 12 The System Setup function Figure 34 shows a block diagram of the control loop Here several options for the analog gain and offset as well as different filters for the lt Main in gt signal path can be set Their function and default setting are given in the following table The default values are a good starting point and can later be optimized for the specific application by the user Please refer to Paragraph 7 for further information TOPTICA Ce Page 41 Status 21 10 08 Feedback Controlyzer DigiLock 110 Inout offset offset to be subtracted from the input signal 0 0 V before digitalization to use the full resolution of the analog to digital converter ADC 2 V Table 3 Input Signal Path Settings CC Page 42 Ww PHOTONICS Status 21 10 08 8 Application Examples 8 2 Doppler Free Sa
9. a lamb dip of saturated absorption signal are illus trated in Figure 29 and Figure 30 respectively 5 Alternatively there are several optimization methods for PID controllers which mostly originate from slow temperature type controller applications The Ziegler Nichols method gives rule of thumb values derived from the proportional gain Kp osc where oscillation of fre QUENCY Voge Starts Kp 0 6 x Kpogse Ki 2 Kposc Yose Ki Kposc X Vosc 8 6 The overall polarity is given by the product of the PID controller polarity and the slope CC Page 34 Ww PHOTONICS Status 21 10 08 7 Notes on Feedback Control Loops with the DigiLock 110 0 10 Ci neg slope unlocked pos slope S oO DI Saturated Absoption Signal V o S 0 05 0 75 1 00 1 25 1 50 1 75 Scan V Figure 29 Polarity of PID Controller for Side of Fringe Lock The graph shows the characteristic distortions of the error signal of a side of fringe lock for dif ferent polarities The disolayed example is a zoom into the saturated absorption spectros copy of Rb The undistorted signal solid black is given for reference When the polarity is chosen to lock on a negative slope dashed red the negative slopes are shallower while the positive slopes are steeper The opposite is true for locking onto the positive slopes dotted green The traces have successively been exported from the scope display of the DigiLock 110 right click on scope graph
10. backplane and SC 110 on the grating piezo and via the lt Main out gt on the laser diode current mod DC CC Page 38 Ww PHOTONICS Status 21 10 08 8 Application Examples Initial setup CAUTION Make sure that the laser current is switched off while installing or exchanging the DigiLock 110 or any other module Take care of proper personal grounding while han dling the laser head e g when connecting cables la Switch OFF all modules in the DC 110 electronics to install the DigiLock 110 The DigiLock 110 pro vides the Scan Control SC 110 with a signal via the backplane Therefore the external control of the SC 110 has to be configured to DA2 by appropriately setting the jumpers dip switches on the SC 110 board For detailed description on the SC 110 please see the Sys DC 110 user manual 2 Make sure that the laser head is properly connected to the Temperature Controller DTC 110 and the Current Controller DCC 110 In these examples a DLpro extended cavity diode laser ECDL is used The same setup can equally well be realized with the DL 100 and translated to other diode based laser systems like the tapered amplifier TA 100 DLX 110 RockSolid and SHG 110 For the DL 100 laser head the corresponding connections are labelled as follows Pigro o commet O mod DC PEE DC coupled current feedback is used for the fast feed l l back in addition to the slow feedback to the piezo AC coupled fast current feedback can op
11. by the user Either the PID controller output is set to zero or its Current value is transferred to the offset value of its output channel The latter setting leads to the scan being centered at the last output value see Paragraph 6 2 5 1 for details TOPTICA Ce Page 47 Status 21 10 08 Feedback Controlyzer DigiLock 110 Signal Hold Ovid n Lockpoint tracker I RMS error ooo show ne No 1 zZ E Lei 21 8 21 8 22 SC110 out Figure 43 AutoLock Display after the lock has been triggered The yellow scatter plot indicates signal input and regulator output PID 2 Parameter optimization To obtain a good lock it is necessary to increase the gain settings of the PID controllers to the highest possible values without oscillations The RMS error value in the right panel quantifies the residual excur sions of the laser As PID 2 is only responsible for the low frequency components this controller can be left at moderate gains The performance of the lock is predominantly affected by the settings of PID 1 con nected to the fast actuator Mod input of the DLpro A helpful tool in the optimization process is the Frequency Analysis display see Figure 44 Here the result of the Fourier transformation of the sampled time signal is shown In our case select lt Main in gt as CH 1 The frequency scale has to be chosen according to the bandwidths of the experiment Typical bandwidth of the gratings are in
12. demodulation For the setup follow the initial steps 1 to 18 described above but choose lt LI out gt as input to the AutoLock module 21 To display the error signal switch to AutoLock Mode Set the scan frequency of the Scan Module to 10 Hz the output to lt SC 110 out gt and switch on the scan mann Ti 195 91k Jooo ooo Main out sali Hfmn Figure 45 Lock In Module with typical Parameters 22 Configure the parameters for the Lock In Module see Figure 45 The modulation set frequency Mod set freq has to be chosen depending on the spectral resonance A reasonable choice is about 1 10 of the characteristic linewidth In this example a frequency of about 100 kHz is used Due to the specific architecture of the DigiLock 110 only discrete frequencies are possible Type in the desired one and the system will automatically calculate the nearest one available Mod act freq 23 Turn on the modulation by pressing the Modulation button The second trace should now display the error signal derived from the frequency modulation The modulation amplitude is a trade off between the desired lock in signal strength and the allowed frequency modulation of the laser The larger the amplitude the larger the lock in signal but note that at the same time the fre quency modulation of the laser increases 90 Figure 46 shows the resulting scope display with optimized phase 10 This tradeoff can be eliminated by using an add
13. le TOPTICA Photonics AG guarantees the buyer that there will be no defects in the product based on defective material or processing for a period of 12 months from first delivery guarantee period Natural wear and tear as well as defects resulting from improper use or use contrary to the specifications from failure to observe operating instructions from insufficient maintenance and care or from modifications interventions or attempted repairs that are neither carried out nor authorized by TOPTICA Photonics AG are not covered by the guarantee 2 Unless expressively stated in the order acknowledgement or the invoice semiconductor light emitting devices like laser diodes tapered amplifier chips etc whether sold as single parts or integrated in systems are not covered by the guarantee di If a defect covered by the guarantee arises during the guarantee period TOPTICA Photonics AG shall rectify such defect within a reasonable period at its own discretion by repairing or replacing the product or the defective part 4 The guarantee period shall commence upon delivery of the product by TOPTICA Photonics AG or by a third party that obtained the product directly from TOPTICA Photonics AG for the purpose of selling it to the buyer The claim under the guarantee shall be excluded if the defect is not notified to TOPTICA Photonics AG in writing immediately after having been discovered and no later than one month after expiry of the guarantee period For
14. out Figure 17 System Setup Schematic of the high speed signal path inside the DigiLock 110 module Some parameters can only be set on this screen lt Main in gt input offset lt Main in gt gain invert signal all kinds of filters All parameters set here are automatically updated throughout the whole system The filters three low pass and one high pass are either configured via the corresponding input fields fc cut off frequency order of the filter function Alternatively pressing the filter symbol opens a screen which shows the simulation of the transfer function of the filter with the specified parameters By modify ing the parameters fc order you can change this transfer function Pressing OK confirms the parame ters and transfers them to the setup Note that the filters introduce additional phase lags and delays corresponding to the processing time The processing time for an active low pass filter is 2 order x 10 ns for an active high pass filter 1 order x 10 ns erre Page 24 Ww PHOTONICS Status 21 10 08 6 Operation Frontend 6 2 5 Settings The settings layer enables the user to access additional options of the DigiLock 110 It is divided into the following four tabs 6 2 5 1 PID On this tab all advanced parameters for the PID modules can be found PID1 and PID within Lock Window A Figure 18 PID Tab on the Settings Layer PID 1 and PID 2 keep PID value reset PID Sets the b
15. out gt To display the PDH error signal use the AutoLock Mode In the Scan Module set the scan frequency to 10 Hz and the output to lt SC 110 out gt z I me l a D 3 o000 1 cI mJ Tm ai SC110 out fi T go als Du 3 Figure 50 PDH Module with typical Parameters Phase and offset should be optimized to the specific setup 17a To obtain an error signal the modulation amplitude has to be set The amplitude is a trade off between the signal to noise ratio and the tolerated frequency modulation of the laser The larger the amplitude the larger the error signal and the frequency modulation of the laser Turn on the modulation and start to scan the laser with the Scan Module In Figure 51 the resulting scope display with optimized phase is shown 12 This trade off can be eliminated by using an additional electro optical modulator EOM in the locking beam path after splitting from the main beam Ce Page 54 Ww PHOTONICS Status 21 10 08 8 Application Examples Signal Hold Old d Lockpoint tracker 7 show aa scicout MIO Main in Y POH out a u 18 3 18 4 SC110 out Figure 51 AutoLock Display of the reflection signal of a Fabry Perot Cavity upper yellow trace with the 18a corresponding PDH Signal lower red trace The phase between the modulation and the reference signal has to be adjusted to obtain a large symmetric
16. please see Paragraph 7 4 Once locking is accomplished the parameters can be optimized see Paragraph Faol Figure 40 PID Setup for Locking to a Doppler free Rb Peak cz 9 Ce Page 46 Ww PHOTONICS Before the lock is initiated the lock point has to be selected by dragging the crosshairs in the AutoLock graph to the desired position When you drag the vertical line in the horizontal direction the crosshairs will follow the current trace Once chosen the crosshairs will automatically track the lock point while the laser might slowly drift To engage the lock click the right mouse button and choose PID Lock to slope from the context menu see Figure 41 Starting with the next trigger the trace captured is displayed in a different color here yellow while the held trace is visible here blue Once the lock point is reached the trace stops and the lock is activated Figure 42 shows the AutoLock display some seconds after the lock has been triggered The output of the controllers can be restricted using the Limit settings Paragraph 6 2 1 4 and 6 2 1 5 e g to about the scan range This helps to avoid destabilization of the laser by driving it far from the lock point especially during initial setup and optimization The colors of the traces can be changed by the user To restore the factory settings load the default profile Status 21 10 08 8 Application Examples Signal Hold Old Lockpoint tracker PID Lock to
17. shift in degrees between the output and the reference signal Offset Offset in units corresponding to the oscilloscope display The offset is substracted from the original signal Mod output Output channel to which the modulation is applied Modulation Turn ON OFF the modulation The modulation is automatically switched on for locking Therefore it only needs to be activated manually for the adjustment of the phase shift or in manual lock mode AutoLock Display Channel that is used in the AutoLock display only available in Advanced Settings mode see Paragraph 6 2 5 5 NOTE Due to signal processing limitations it is recommended to optimize the lock with the demodulated lt PDH out gt signal and not the modulated input signal see Paragraph 7 6 TOPTICA Ce Page 21 Status 21 10 08 Feedback Controlyzer DigiLock 110 6 2 2 Controller Design Gain gjo fisco g E go C rein out Magnitude 371 Figure 15 Controller Design This function visualizes the transfer function of the selected PID controller according to the parameters chosen The transfer function graph consists of two traces the magnitude and the phase which are plot ted versus the frequency It also includes filters and signal delay e g ADC conversion FPGA calcula tions This information is very helpful in designing the control loop to the frequency response of the actuators Selected PID PID controller to which
18. the parameter set belongs Get parameters Actual parameters of the selected PID are transferred to the controller design environment PID input Inout channel to the controller Main in Aux in LI out PDH out Gain Overall gain P Proportional gain I Integral gain cut off Frequency in Hz at which the integral part is limited only applies to PID 1 D Derivative gain PID output Output channel of the controller Send parameters Sends the above parameters to the selected PID controller see Para graph 6 2 1 Initial freq Start frequency of the simulation Final freq End frequency of the simulation Freq unit Units used on the frequency axis You can change these parameters and the transfer function graph will be updated automatically If you are satisfied with the displayed transfer function you can send the parameters to the selected PID con troller see Paragraph 6 2 1 CC Page 22 Ww PHOTONICS Status 21 10 08 6 Operation Frontend 6 2 3 Network Analysis T E a i l m i z Figure 16 Network Analysis In order to determine the dynamic behavior of a system it is a common strategy to perform a network analysis The result of such an analysis is the transfer function of the device under test DUT defined by the amplitude and phase values with respect to the frequency of the stimulus In particular it is possible to analyze the complete feedback loop comprising of frequen
19. 322 U309 R325 b a i as U31 C332 C i Rape c3 C35 a R356 C3430 C3240 C3130 u _ S20 R192 Ral C327 u310 a R331 i caog a R320 0 cf sgn R345 Do I cao ar R33 R342 a R3570 casa le ES J301 c355 a z 8 g 20 g gI 3 I x E i 5 N 5 sl 2 s seven ga E n mA aa g 4 g amp g aal a g amp A hO wiles dan F SG i th og ee 5 8 ft of am DA eq 413 cwo 2200 n N eztan Moe N SZINO Li Ra eda F fia g Q R314 J3 Sul Og OO NI amp U o gr O JP Figure 55 DigiLock 110 Jumpers on Baseboard TOPTICA PHOTONICS Page 58 Status 21 10 08 9 Appendix Plug On Board 9 2 2 JP 4 0 UKI azii OZ Ta zyn role Z Get JES JESI Ure JES DigiLock 110 Plug On Board Figure 56 Page 59 PHOTONICS TOPTICA Status 21 10 08 Feedback Controlyzer DigiLock 110 9 3 Specifications of Digilock 110 Connections Fower Supply Supply Voltage Supply Current 700 MA mievimod fn Supply Current 200 mA i a OA S Input Resolution Sample Bandwidth Range Input Comment Channel bit Rate Hz 3dB Hz V Impedance Ohm Main in 100 M 14 50 Input signal at lt Main in gt has to be between 3 5 V it can be shifted with the lt Input Offset gt and ampli fied with the input gain OM 200 E
20. 9 and the locking point is chosen to be at the rising slope of the second peak 71 9 22 22 3223 SC110 out Figure 39 85Rb D2 transitions at 780 nm The Crosshairs mark the currently selected locking point TOPTICA Ce Page 45 Status 21 10 08 Feedback Controlyzer DigiLock 110 To configure the PID controllers select the PID 1 PID 2 tab to access the corresponding parame ters see Figure 40 In AUtoLock operation the input channel of the PIDs is defined by the AutoLock input PID 1 is used for the high frequency feedback therefore its output channel is lt Main out gt which is connected to the modulation input of the laser PID 2 is used for large range low fre quency feedback to the piezo To prevent the controllers from mutual interaction the PID 1 fea tures an cut off frequency The cut off frequency defines the corner frequency below which the integral gain of the controller is limited A reasonable choice is in the order of 100 Hz The values of the gain parameters for the PIDs shown in Figure 40 are set in the corresponding tabs Their settings depend on the slope of the error signal and the actuator response For the given setup the error signal amplitude should be on the order of 100 mV_ In most cases the low fre quency feedback of PID 2 is sufficient to achieve a first lock It is advisable to start with conserva tive gain settings To find the correct settings of the sign for each PID controller
21. Digilock 110 Feedback Controlyzer Manual Manual M 031 Version 02 Copyright 2008 ToPTICA Photonics AG TOPTICA Photonics AG Lochhamer Schlag 19 D 82166 Graefelfing Munich Tel 49 89 85837 0 Fax 49 89 85837 200 email info toptica com http www toptica com October 2008 Subject to changes without notice Feedback Controlyzer DigiLock 110 Dear Customer welcome to the TOPTICA Community We have designed this product to be easy to use and reliable so that you can focus on your actual work Should you anyway have questions regarding its use or need advice on how to integrate it into your setup please do not hesitate to ask We will provide you with quick and competent help through our ser vice staff and product managers You can contact us in the following ways internet www toptica com In our support section you can find a list of frequently asked ques tions and a service contact form email service toptica com phone 49 89 85837 0 Please have your product ID serial number ready when contacting us so we can quickly retrieve all rele vant information from our databases We are constantly refining and improving our products and therefore highly valuate feedback from our customers We would therefore like to encourage you to let us know what you like about our products and of course also if there is something we could improve Best regards HO Harald Ellmann Service Manager TOPTICA Photonics
22. Digital Signals not used D 0 D 2 D 4 D 6 Analog Signals O On By OIN ki i Oni BR W Address Lines not used AW AW AW AR read write r w Indicated Parameter Photo Diode Channel 1 DCC Umax Channel 1 DCC 9a I TEC mox Channel 1 DTC Tmax Channel 1 DTC Inox Channel 1 DCC Tmin Channel 1 DTC 10c FE pe ISC 14c A 1 A 3 A 5 A 7 Address Enable AEN DCC Photo Diode Channel 2 CC Umax Channel 2 DIC TEC max Channel 2 DICI Tmax Channel2 DCC mag ChannelZ DTC Lnn GNannel 2 CEI ke cnanel2 DTC Tser Channel 2 CC las Channel 2 DTC Tact Channel 2 256 DTC lrec Channel 2 24c V ON 25c Power typ 6 8 V GND floating if no DCC 110 3A implemented 8C 9c Loc 16c 17C 18c 19c gt e N a i a 20c i n di cau eo _ Eom RES CS ST Ses ve ee Ea ee E ed 2 0 Ze 21c 226 lec Channel 1 DTC HV ON Power typ 6 8 V GND floating if no DCC 110 3A implemented HV Supply 26c HV Supply Error beep OTe Error LED on when GND Blink Reference GND 28a 28c Remote On Off low Power down Ure pa e Ver General supply lines Sti ___ __ _uu_mdmdy_up 0 i se Power typ 6 8 V floating if no 320 32C Power typ 6 8 V floating if no DCC 110 3A implemented DCC 110 3A implemented lines connected on backplane E TOPTICA Ce Page l Status 21 10 08 Feedback Controlyzer DigiL
23. Min and Max values When the signal leaves this window the out of lock state is detected and the output of the controller is frozen Once the signal has reentered the inner 80 window the system is considered to be locked again The time between detection of the out of lock state and the activation of the relock scan is defined by the relock delay as set in the Setting function 7 6 Signal Limitations in Analyzing the Locking Performance To analyze the performance of a lock based on a frequency modulation technique as provided by the PDH and LI modules it is highly recommended to use the demodulated signal lt PDH out gt or lt LI out gt to observe residual excursions in scope mode as well as using the frequency analysis tools As common to any digital signal sampling the DigiLock 110 oscilloscope shows effects of aliasing When the sampled signals have frequency components faster than half the sampling rate they will be folded into the frequency band from zero to this Nyquist frequency The sampling rate of the DigiLock 110 is automatically set to make full use of the number of acquired points Therefore in Scope and AutoLock mode the sampling rate is given by the number of points per trace 1000 divided by the time range cho sen According to the Nyquist theorem the sampling rate in the frequency analysis FFT is set to twice the selected maximum frequency Because of the aliasing effects it is hence irritating to look at the input s
24. Slot Slot 4 Slot 2 DigiLock110 Dee ITO Figure 5 DigiLock 110 installed in Supply Rack DC 110 CC Page 10 Ww PHOTONICS Status 21 10 08 5 Software Installation 5 Software Installation The installation of the USB driver and the control software requires administrator privileges Please uninstall any previously installed DigiLock 110 software as otherwise the installations may interfere Read the Readme html file located on the installation CD for up to date information about the current software version 5 1 System Requirements Processor x86 Platform e g Pentium Ill 4 M min 800 MHz recommended gt 1 2 GHz RAM min 256 MB recommended 512 MB Screen resolution min 1024 x 768 Operating System Windows XP SP2 Windows 2000 SP4 not tested with Windows Vista Interface 1 x USB 1 1 or USB 2 0 To view the user manual provided in the Help Menu installation of Adobe Acrobat Reader is necessary 5 2 USB Driver Installation The DigiLock 110 provides a USB connection to load the firmware and to control the module via the sup plied PC based software In order to communicate with the DigiLock 110 the USB driver has to be installed before the installation of the application software The driver is located in the directory Driv ers USB on the installation CD supplied with the DigiLock 110 module Run the exe file to install the driver on the PC After the driver is installed successfully connect the DigiLoc
25. The sign of PID 1 is defined by the polarity of the current controller DCC110 It is positive negative if the polarity of the DCC110 is negative positive respectively For details see Para graph 7 4 Gain Overall gain P Proportional gain I Integral gain cut off Frequency in Hz below which the integrator is limited D Derivative gain NOTE If the gain parameters are out of range an error message is displayed in the controller tab Output Output channel of the controller Limits Voltage values to which the PID output is limited relative to the offset of the output channel TOPTICA Ce Page 1 Status 21 10 08 Feedback Controlyzer DigiLock 110 General These parameters are intended to manually operate the controller In the AutoLock mode these parameters are set automatically Since the interactive AutoLock covers most standard locking situations the man ual options should only be needed in special cases Setpoint Setpoint of the controller Slope Sign of the slope to which the system is locked to Lock Turns the controller ON OFF Lock Window Use Lock Window This option specifies boundaries for the selected channel If the signal leaves the selected range Min Max the controller is disabled Relock This option is only available if the Use Lock Window checkbox is selected see above In case the Lock Window signal is out of bounds the relock option scans the output channel of the PID controller w
26. ay while the lock is triggered LI PDH Lock to nearest peak The background trace blue displays the last scan before The trace yellow captured dur ing the engagement of the lock stops at the selected lock point where the scan stops and the selected controllers are switched on CC Page 52 Ww PHOTONICS Status 21 10 08 8 Application Examples 8 3 Pound Drewer Hall Stabilization to a Cavity The second important application described here is the stabilization of a laser to a cavity with the Pound Drever Hall technique Figure 49 shows an overview of the setup used for a Pound Drever Hall stabiliza tion onto a cavity in reflection In this example the cavity is a FPI 100 Fabry Perot interferometer available from TOPTICA Photonics AG D Mon110 DC110 Connection via backplane Cavity FPI 100 PBC Polarizing Beam Cube 2 4 Quarter wave Plate Isolator Optical Isolator Figure 49 Experimental Setup of a Pound Drewer Hall PDH Stabilization to a Cavity Note that the modulation is directly added to the lt Main out gt channel of the DigiLock 110 Alternatively the modulation can be applied to the mod AC input of the DLpro The initial setup is the same as in the other examples see Paragraph 8 1 steps 1 to 12 Once the spectros copy signal is obtained the following steps are analogous to the case of the Doppler free absorption spectroscopy see Paragraph 8 2 steps 13 and 14 Figure 51 shows the expected signal for scan
27. ciently it is necessary to be familiar with the user interface Some helpful remarks are presented in the following Changing numeric input controls Set the focus on the desired numeric control left click on the field A cursor appears in the input field The digit to the left of the cursor can be incremented decremented with the up down arrow keys To select the desired digit use the arrow keys left right digit to modify DI OA mammal pma ee Engineering units All input fields in this software are capable of handling engineering units For example U micro 10 m milli 10 k kilo 108 M mega 10 Graph display Dynamic range scaling The axes of the graphs have a dynamic range scaling optimized for the data displayed If this behavior is not desired it can be turned on or off by clicking on the button marked in the figure below Autoscale off Time s Main in v PDH out 4 u Autoscale on Ce Page 13 Status 21 10 08 Feedback Controlyzer DigiLock 110 e Graph Display Setting the scale of a graph When the dynamic range scaling option is deactivated the limits of the scaling of an axis can be modified manually To change the lower upper limit click on the value in the graph and modify it by typing a new value upper limit lower limit e Description of controls To get information about a control move the mouse pointer across the desired control and a brief description app
28. cy discriminator detector controller and actuator How it works The stimulus signal of a certain frequency and amplitude travels through the DUT and generates a response signal These two signals are analyzed regarding their phase and amplitude relation and dis played with respect to the frequency of the stimulus Start freq Start frequency of the stimulus for the determination of the transfer func tion Stop freq Stop frequency of the stimulus for the determination of the transfer func tion of samples Number of measurement points between the start and stop frequency Mod amplitude Amplitude peak to peak of the stimulus signal Freq scaling Method to distribute the measurement points between the start and stop frequency logarithmic or linear Averaging Number of measurements to average for one resulting measurement value Mod source Output channel for the stimulus signal Signal input Inout channel for the response signal Show reference tracks Option to display the reference tracks saved before Show time signal during analysis Option to display the response signal in the scope unit during the mea surement the scope has to be selected manually by the user NOTE Any filters applied to the signal path see Figure 17 influence the measured transfer func tion too Ce Page 23 Status 21 10 08 Feedback Controlyzer DigiLock 110 6 2 4 System Setup o oo Main out fi fi f Main
29. e of the DigiLock 110 relies on a con sistent choice of polarity and slope the determination of which is discussed in Paragraph 7 4 Details on the Relocking and signal analysis features can be found in Paragraph 7 4 and 7 5 respectively 7 1 Signal to Noise and Bandwidth Considerations To take full advantage of the possible bandwidth of the control loop care should be taken to implement a true 50 Ohms wave guide and to avoid extra cable length in the signal path The fast inputs and out puts of the DigiLock 110 are 50 Ohms in the standard setting upon delivery Bandwidths and sampling rates of the inputs and outputs are listed in Table 7 Due to the limited gain bandwidth product in analog amplification a higher gain generally reduces the bandwidth In the DigiLock 110 the digital signal paths do not show this effect but instead every pro cessing step inherently contributes a fixed delay The implementation of extra filters e g low pass filters to clean up the error signal usually has a negative influence by introducing extra phase lag and should hence be avoided Improvements based on filfers Usually rely on a detailed analysis of the frequency response of the control loop and have to be carefully designed In case of the digital filters in the DigiLock 110 the phase lag is due to additional signal delay For most cases it is hence recommended to bypass the digital input filters in the System Setup Paragraph 6 2 4 To optimize the s
30. e values specified in the interface software The firm ware must be uploaded each time the DigiLock 110 is switched on If the module is already configured and running e g you already worked with the system but you closed down the interface software for a while the upload and reset are not necessary By activating this option the user is asked at startup whether a firmware upload should be per formed Modules included in the software that are not used in a specific application might distract the user Therefore the visibility status of some modules can be configured Figure 22 Visibility Tab on the Settings Layer Module and Function visibility Advanced Settings O TOPTICA PHOTONICS Show or hide the respective functions and modules Show or hide settings that give the user access to additional functional ity This functionality is not needed for standard operation scenarios The option is only recommended for experienced users Page 27 Status 21 10 08 Feedback Controlyzer DigiLock 110 6 2 5 6 Profiles NOTE Loading profiles is only possible if the PID controllers are off see Status display The user can save and load profiles A profile is a set of system parameters e g all settings of the different modules display settings etc Profiles are useful and save time if the user has to change between different control tasks Li Load profile al Save profile Figure 23 Load and Save Profiles If the u
31. ears CC Page 14 Ww PHOTONICS Status 21 10 08 6 Operation Frontend 6 2 Functions In the upper part of the screen all the available functions and options of the DigiLock 110 are displayed on different layers With the buttons on the left hand side you can select the desired function and then browse the corresponding options and parameters 6 2 1 Scan and Lock This function comprises all the modules needed for scanning and locking the laser 6 2 1 1 Scan Module SC110 out Figure 7 Scan Module The Scan Module is used to generate periodic waveforms with user adjustable parameters The signal can be directed to different output channels Signal type Type of the generated waveform sine triangle square or sawtooth Frequency Repetition frequency of the chosen waveform in Hz Amplitude Peak to peak amplitude in Volts Scan button Turn signal generation on off indicated by the green light Output Output channel to which the generated signal is directed 6 2 1 2 Offset Adjustment 52 3609 SCL10 out Figure 8 Offset Adjustment With the Offset Adjustment Module it is possible to view and change the DC voltage level of the selected output channel Offset Signal level in Volts Output Output channel to which the offset voltage applies TOPTICA Ce Page Is Status 21 10 08 Feedback Controlyzer DigiLock 110 6 2 1 3 AutoLock Figure 9 AutoLock The AutoLock tab is used in combina
32. ed as a moving aver age filter in the digital domain The first notch of such a filter is at the modulation frequency In order to reduce noise this first filter notch can be set to lower frequencies It has to be taken into account that a mov ing average filter introduces a linear phase shift to the output signal of the Ll Module At the first notch frequency the phase shift is 180 As a consequence lowering the filter frequency reduces the maximum available regulation bandwidth On this tab the settings for displaying the data can be chosen Figure 20 Display Tab on the Settings Layer Update rate FFT Window Scope average Freq analysis average Page 26 Status 21 10 08 Rate at which new data sets are displayed in the various graphs Window type used for fast fourier transformation FFT Number of averaged data sets if the avg option is used in the Scope Mode Number of averaged data sets if the avg option is used in the Fre quency Analysis Mode TOPTICA PHOTONICS 6 2 5 4 General 6 Operation Frontend General system settings can be accessed on this tab Figure 21 General Tab on the Settings Layer Ask to upload firmware at startup 6 2 5 5 Visibility By default the firmware of the DigiLock 110 is Uploaded at startup of the software This upload takes some seconds and resets the module During a module reset all analog output channels are set to 0 V before they are loaded with th
33. ehavior of the PID controllers when switching off the lock Both PID controllers can be set individually for AutoLock as well as Manual Mode Either the PID output is transferred to the offset value of its output or the PID output is simply set to zero In the first case the scan will be centered around the last output value which is suitable when the PID controller offset compensated an offset drift relock delay Sets the time that passes after the detection of the Lock Window out of lock state see Paragraph 6 2 1 3 until the relock scan Is activated DIO output port DIO output port function Configures the function of the DIO digital input output port when jum pered as output factory setting Four different modes are available manual operation PID 1 within Lock Window range PID 2 within Lock Window range PID 1 and PID 2 within Lock Window range Manual state When the function selector is in mode manual operation the state of the DIO output port can be set TOPTICA Ce Page 25 Status 21 10 08 Feedback Controlyzer DigiLock 110 6 2 5 2 LI PDH Figure 19 LI PDH Tab on the Settings Layer Modulation signal type First filter notch LI Module 6 2 5 3 Display Type of the waveform used for modulation and demodulation The Ll Module only works properly if a low pass filter is applied to the demodulated signal in order to filter frequency components located at the modulation frequency This filter is implement
34. error signal with steep slopes at the maximum of the spectral signal The sign of the error signal can be inverted by changing the phase by 180 The sign should be adjusted such that the lock in signal is the derivative of the input signal To find the optimum phase 19a 20a Change the phase value until you get the minimum signal at the carrier Then subtract 90 and you will get the maximum signal If you observe the wrong overall sign add or subtract 180 to the current phase value Once the phase is adjusted compensate for any residual offset at the corresponding control of the PDH Module and check the parameters of the PID controllers To find the correct settings of the sign for each PID controller please see Paragraph 7 4 For optimization of the PID parameters see Paragraph 7 3 Now you can position the crosshairs to either a peak or a valley and they will automatically track the lock point To initiate the lock perform a right mouse click to access the context menu and select between LI PDH Lock to nearest peak or LI PDH Lock to nearest valley The trace changes its color here from yellow to blue to show that the actual trace is captured in the background During the next scan the lock is triggered Figure 53 shows the AutoLock display while the lock is triggered The blue trace is the captured signal of the last scan The yellow trace is the scan during which the lock is triggered You can see that the trace stops at t
35. es The DigiLock 110 is designed to cover a large range of locking scenarios This paragraph describes step by step how to implement some of the most common ones with the DigiLock 110 NOTE This chapter assumes that the user has some basic knowledge of the laser system and the electronics involved For further information see the Sys DC 110 manual 8 1 General System Setup The general setup for the stabilization is shown in Figure 32 All locking schemes are based on a spectro scopic signal provided by the experimental setup which serves as a reference The DigiLock 110 is capa ble of supplying the scan to find the resonance and lock point derive the error signal and it provides the controllers for the feedback loop It can optionally generate an error signal by means of a frequency modulation technique Furthermore the graphical user interface supports both a user friendly auto lock mode as well as intuitive access to all locking parameters The integrated frequency analysis allows to optimize the regulators in advanced applications This section introduces the common setup for the different locking scenarios described in the following paragraphs DC DCC110 DTC110 Mon110 DC110 Connection via backplane Isolator current Experimental Setup Figure 32 Typical Setup for Laser Locking The signal from the photo detector PD is fed into the lt Main in gt input of the DigiLock 110 The two PID controllers act via the
36. f Use Lock Window checkbox is selected see above In case the Lock Window signal is out of bounds the relock option scans the output channel of the selected PID controller with the chosen values for frequency and amplitude waveform type is triangle Once the Lock Window signal is within the specified limits again the scan is turned off and the controllers are activated TOPTICA PHOTONICS 6 Operation Frontend 6 2 1 4 PID 1 IE h jj du aja f Tur Figure 10 PID 1 Controller The PID 1 is a standard PID controller with the special feature that the user can set a frequency below which the integral part is limited as illustrated by the transfer function Paragraph 6 2 2 This limitation of the integral part is important in case PID 1 is used together with PID 2 in one control system This prevents the controllers from integrating offsets in opposite directions NOTE In case the controller is not selected for AutoLock it can be used as an independent con troller Manual Mode Input Input source for the controller Main in Aux in LI out or PDH out Cannot be changed when the AutoLock for this controller is active Locked LED This indicator shows the status of the controller Sign In the typical setup the PID 2 output is directed to lt SC110 out gt and the PID 1 output to the current modulation input of the laser head In this case the PID 2 sign is positive
37. for legal disputes arising under or in connection with this guarantee request the above mentioned guarantee for the purchased products and herewith consent to the above mentioned Guarantee Conditions Model No Date Serial No Signature Date of Delivery Name Title To be completed by the buyer and returned to TOPTICA Photonics AG by mail or fax 49 89 85837 200 Version 01 02 05 Service and Technical Support Form amp TOPTICA PHOTONICS QM form F 008 Status of form 22 7 05 Page 1 of 1 Return to Sender TOPTICA Photonics AG Customer Service Lochhamer Schlag 19 D 82166 Graetelting Muenchen Germany FAX 49 89 85837 200 Return Authorization number RMA VB Betore goods are returned please ask the TOPTICA Customer Service for a RMA number Products model ID numbers S N Located on the back panel of the device S N S N Please give us a detailed description of your problems e g what the symptoms are and under which circumstances they occur Additional information e g modifications additional equipment etc Mains voltage V Hz Did you notice irregularities spikes etc 2 To be completed by the customer and returned to TOPTICA Photonics AG by mail or fax 49 0 89 85837 200
38. gher bandwidth error signal after mixing with the local oscillator LO The phase of the local oscillator has to be adjusted to obtain a large error signal with steep slopes at the maximum of the spectral signal The sign of the error signal can be inverted by changing the phase by 180 It should be adjusted such that the lock in PDD signal is the derivative of the input signal 1 Note that the analog preamplifiers in the DigiLock have a fixed bandwidth independent of the selected gain 2 Some details on the generation of the error signal by frequency modulation can be found in the SYS DC 110 manual in the corresponding chapters of LIR 110 and PDD 110 respectively CC Page 32 Ww PHOTONICS Status 21 10 08 7 Notes on Feedback Control Loops with the DigiLock 110 The optimum phase can be found by first adjusting to the minimum signal at a phase shift of 90 to the optimum setting l Change the phase value until you get the minimum signal close to the carrier Then subtract 90 to obtain the maximum signal d If you observe the wrong sign add or subtract 180 to the current phase value Note that the phase should always be adjusted on the local oscillator as implemented in the DigiLock 110 because any additional phase in the signal path deteriorates the control loop perfor mance Once the optimum phase is found and the offset is properly adjusted the control loop can be closed and the controller parameters can be optimized
39. hat an improvement of the lock relies on a corre spondingly high actuator and detection bandwidth NOTE In case the controller is not selected for AutoLock it can be used as an independent con troller Manual Mode P Proportional gain Sign Sign of the controller input signal General Slope Sign of the slope the system is locked to Lock Turns the controller ON OFF TOPTICA Ce Page 19 Status 21 10 08 Feedback Controlyzer DigiLock 110 6 2 1 7 Lock In Module lt i A E i in im cs DI rel L error signal a TT q UOISSILUSUDI Ja detuning linewidth Figure 13 Left Lock in Module Tab Right Error Signal generated with the Lock In Modulation Technique The Lock In Module can be used to generate an error signal for the PID controller with the Lock in modu lation demodulation scheme Since it generates the derivative of the original signal it allows the user to stabilize a system to a peak ora valley Input Mod set freq Mod act freq Mod amplitude Phase shift Offset Mod output Modulation AutoLock Display Input source for the module Main in Aux in The desired modulation frequency in Hz The actual modulation frequency in Hz Due to signal processing limitations only discrete modulation frequen cies are possible even fractions of 781 25 kHz The closest frequency is chosen automatically Peak to peak amplitude of the modulation signal in Volts
40. he selected peak After a while the yellow trace disappears and there is only a scatter plot left The interpretation of this plot and the optimization of the lock can be found in Paragraph 8 2 1 a Residual offsets in the demodulated error signal are mostly due to unintended intensity modulations that come with the phase modulation The output of the controllers can be restricted using the Limit settings Paragraph 6 2 1 4 and 6 2 1 5 e g to about the scan range This helps to avoid destabilization of the laser by driving it far from the lock point especially during initial setup and optimization TOPTICA Ce PAGE vs Status 21 10 08 Feedback Controlyzer DigiLock 110 PID Lock to slope LI PDH Lock to nearest peak LI POH Lock to nearest valley Unlock amp Restart scan Unlock imd x Clear Graph Export Data Export Simplified Image 18 3 18 3 SC110 out Figure 52 Initiating the automatic PDH Lock to a Valley Main in 18 2 18 3 SC110 out me no Hdd re no Had Signal Hold Old e Lockpoint tracker RMS error D Main in v il mi PoHout a u Sea Signal Hold Ovld mi Lockpoint tracker I RMS error Hi CH2 50110 out i Main in Y PDH out a u Figure 53 AutoLock display after triggering the lock LI PDH Lock to nearest valley Page 56 Status 21 10 08 TOPTICA Ww PHOTONICS 9 Appendix 9 Appendix 9 1 Internal
41. hown in Figure 36 TOPTICA Ce Page 43 Status 21 10 08 Feedback Controlyzer DigiLock 110 Signal Hold Ovyld cad n cH2 SC110 out xy Mode I gt RMS error show avg CH z a E om di Pai i m E A 190 OTTIS Tire 5 Main in 30m Time s Figure 36 Absorption Signal of a Doppler free Rb Spectroscopy Once the laser scans across the spectral feature two different locking schemes can be implemented using the AutoLock feature of the DigiLock 110 First locking to the side of a fringe is presented Para graph 8 2 1 then the use of frequency modulation demodulation to lock to a Maximum or minimum is explained Paragraph 8 2 2 8 2 1 Side of Fringe Locking We are now ready to use the AutoLock feature to lock the laser to the slope of a Doppler free absorption line AutoLock PID 1 PID 2 Analog P Input ALI out AutoLock controllers PID 1 PID 2 Analog P General MinMax Intense Use MinMax Intense Relock Channel main in Dest PIDI PID Max 21 00 Y Frequency SP Hz Min A 1 00 Amplitude 1 00 Vpp Figure 37 AutoLock Setup for the PID Controllers CC Page 44 Ww PHOTONICS Status 21 10 08 8 Application Examples 15 First the AutoLock is activated and the controllers PID 1 and PID 2 are selected by checking the corresponding boxes see Figure 37 PID 1 will handle the high frequencies by controlling the laser current via the mod
42. ignal to noise ratio of the input subtract the dc offset from the input signal by setting the input offset to the mean value as read from the oscilloscope display see Figure 17 The gain can now be increased to take advantage of the full 2 V range of the analog to digital converter 7 2 Frequency Modulation Techniques Frequency modulation techniques are applied to obtain a steep slope of the error signal at the lock point The typical spectroscopy signal in transmission or absorption consists of a resonance line e g a Lorenzian or Gaussian see application examples in Paragraph 8 To lock to the maximum of the reso nance a dispersive signal is needed which is generated by frequency modulation and subsequent demodulation There are two regimes depending on the choice of the modulation frequency with respect to the characteristic line width Dn of the resonance A modulation frequency vmodg smaller than Av leads to the derivative of the resonance signal as obtained from the Lock In Regulator cp Paragraph 00 A modulation frequency much larger than Av cp Pound Drever Hall Paragraph 8 3 will lead to an error signal and hence capture range that extends from one sideband to the other vo Vmod Vo Vmod The later situation is preferable and used in situations where the resonance is well isolated e g on a Fabry Perot cavity where no neighboring resonances spoil the signal In this case a higher modulation frequency also provides a hi
43. ignal with frequency modula tion applied On the other hand the non demodulated signal can serve as an example to discuss the possible effects observed In the frequency analysis the modulation frequency will be observed at a lower value i e modulus the sampling rate Fora sampling rate lower than the modulation frequency an undersampled oscillation will be observed i e a rather fast noisy signal that can breathe in amplitude from shot to shot This effect is well known from digital oscilloscopes In the case of the DigiLock 110 there is an additional effect to be observed for sampling rates well below the Nyquist frequency especially using PDH modulation Due to the complete synchrony of the sampling with the applied modulation the undersampled signal can show as a noisy line at a finite off set that varies from shot to shot Note that this is not an indication of the performance of the lock but merely an artifact of sampling the input signal including the applied modulation and explains why it is highly recommended to use the demodulated signal for analysis 7 By additionally applying the signal to the Aux input a low passed signal for analysis can be derived using the built in digital filter see Paragraph 6 2 4 TOPTICA Ce Page 3 Status 21 10 08 Feedback Controlyzer DigiLock 110 8 Application Examples There are numerous different schemes to stabilize lasers for example to atomic or molecular resonances and caviti
44. ith the chosen values for frequency and amplitude waveform type is triangle Once the Lock Window signal is again within the specified limits the scan is turned off and the controller is activated NOTE The tabs General Lock Window for the individual PID controller and the Analog P are only visible when the respective controller is not selected for AutoLock Manual Mode NOTE The turn off behavior of the PID controllers can be configured by the user see Paragraph 6 2 0 6 2 1 5 PID 2 f f ir f E7 fi Eg i gt gt Di on C rr Figure 11 PID 2 Controller The PID 2 controller is identical to PID 1 PID 2 does not have an integral cut off frequency because when combining two PID controllers this is only needed at the controller which has to drive the output with the higher bandwidth usually PID 1 Instead it comprises an additional low pass output filter see System Setup in Paragraph 6 2 4 NOTE In case the controller is not selected for AutoLock it can be used as an independent con troller Manual Mode Ce Page 18 Ww PHOTONICS Status 21 10 08 6 Operation Frontend 6 2 1 6 Analog P Figure 12 Analog P In order to overcome the signal delay introduced by digital signal processing the DigiLock 110 features a very fast analog path Its high bandwidth allows the experienced user to achieve further improvements in particularly demanding locking situations Note t
45. itional electro optical modulator EOM in the locking beam path after splitting from the main beam TOPTICA Ce Page 49 Status 21 10 08 Feedback Controlyzer DigiLock 110 Mod set freq modulation set frequency is the user selected 100 kHz modulation frequency Mod act freq modulation act frequency is automatically set to the automatically set nearest possible discrete frequency Mod amplitude amplitude of the modulation 0 01 Vip Phase shift phase shift of the local oscillator with respect to the to be optimized applied modulation see text Mod Output output to which the modulation is added Signal Hald Old al Lockpoint tracker RMS error RE O CH1 CH 2 SC110 out v Main in 4 LI out a u DC F 22 22 1 SC110 out Figure 46 AutoLock Display of the Doppler free Rb spectrum upper yellow trace with the correspond ing Lock in Signal lower red trace Note that the sign phase of the error signal is chosen to be the derivative of the absorption signal i e it is positive negative on positive negative slopes respectively 24 The phase between the modulation and the reference signal has to be adjusted to obtain a large error signal with steep slopes and zero crossings at the maxima of the spectral signal The sign of the error signal can be inverted by changing the phase by 180 The sign should be adjusted such that the lock in signal is the derivative of the input signal i e positive erro
46. k 110 module to the PC with the appropri ate USB cable The operating system will recognize the new hardware 5 3 Control Software Installation NOTE The Control Software will not work if the DigiLock 110 module has not been connected at least once to the PC before Control Software installation Start the program setup exe located in the folder Installer on the installation CD The installer will guide you through the installation process TOPTICA oo Page 11 Status 21 10 08 Feedback Controlyzer DigiLock 110 6 Operation Frontend NOTE This DigiLock 110 manual refers to the software version 1 1 3 40 Visit www toptica com for information about the most recent software version The DigiLock 110 frontend consists of two main areas and a status bar In the upper part of the screen the user can set the appropriate operation parameters for the chosen function The lower part is used to dis play various signals by the means of an oscilloscope or a spectrum analyzer DigiLock 110 SN 0101 3 Rb Spectro File View Help Functions PID1 PID2 Analogr ES frriangie dio E 195 31k A scio out _ Display Sampling Display Status Figure 6 DigiLock 110 Operation Frontend Example Autolock mode displaying a saturated absorption spectrum CC Page 12 Ww PHOTONICS Status 21 10 08 6 Operation Frontend 6 1 General User Interface To operate the software effi
47. k and Lock e Configurable relock e Integrated multi channel digital oscilloscope e Network analyzer e Spectrum analyzer e Controller simulation 1 1 Package Contents 1 DigiLock 110 plug in module 1 Installation CD containing software and drivers 1 DigiLock 110 manual color version is provided on the installation CD 1 USB cable 2 BNC SMB cables TOPTICA Oo Page 3 Status 21 10 08 Feedback Controlyzer DigiLock 110 1 2 Design and Operating Principle of the DigiLock 110 Error out QS Hi rs JP3 f Qur2 3 Aux in gt Precise in Figure 1 Schematic Block Diagram of the DigiLock 110 Module Page 4 Status 21 10 08 JP7 Sum in Main out f gt Aux out 6 gt AIO 1 6 gt AIO 1 6 gt DIO x TRIG FPGA Field Programmable Gate Array TOPTICA PHOTONICS 1 The Feedback Controlyzer DigiLock 110 Scan DDS 1 Module Offset Adjustment Output Command Interpreter LI Module Ea PDH Module DDS Direkt Digital Synthesizer LI Lock in PDH Pound Drever Hall ADC Analog to Digital Converter DAC Digital to Analog Converter FPGA Field Programmable Gate Array Modulation Input Figure 2 Schematic Block Diagram of the DigiLock 110 Functional Units and their Interaction Figure 3 Schematic Block Diagram of the Connections to the DC 110 Backplane TOPTICA Urra Page 5 Status 21 10 08 Feedback Controlyzer DigiL
48. lained earlier is easier to inter pret NOTE The AutoLock feature of the DigiLock 110 expects a consistent choice of the slope setting for all PID controllers involved see above Once the overall polarity is found a correction of the slope can be compensated by changing the polarity also 7 5 Relock Feature The basis of the relock feature of the DigiLock 110 is the out of lock detection It is based on a window comparator which is defined by the minimum and maximum bounds The laser is considered in lock when the signal of the selected channel is within these bounds 100 window Once the signal has left this window the corresponding PID controller is in hold state i e its output is frozen Reentering the com parator window takes into account a 10 hysteresis i e the input signal has to be within the 80 win dow see Figure 31 Once the signal has been within these bounds the PID controller is reactivated The time between the detection of the unlocked state and the activation of the relock scan can be set by the relock delay on the PID tab of the Settings function see Paragraph 6 2 5 1 The output channel fre erre Page 36 Ww PHOTONICS Status 21 10 08 7 Notes on Feedback Control Loops with the DigiLock 110 quency and amplitude of the relock scan are defined in the Lock Window tab of the AutoLock tab or the corresponding PID controller Mean Figure 31 Relock Window The relock window is defined by the
49. limited to higher fre quencies by the bandwidth of the control loop Since it provides a phase lead the differential D part can help to improve the phase response at higher frequencies which in turn allows to increase the gain on the and P parts Note that due to the high bandwidth transient response the differential part is also particularly prone to amplification of noise Before adjusting the parameters of the controllers the correct phase and polarity should be chosen for details see Paragraph 7 2 and 7 4 respectively To start select a low input gain and set all contributions P I D to zero Now increase the integral part until the system locks Generally speaking at this point the quality of the lock improves with increasing gain on the controller until the feedback loop starts to oscillate This is the case when the feedback loop reaches a gain of 1 at a 180 phase shift Therefore the usable bandwidth of many actuators e g piezos is limited by their characteristic frequencies In any case phase shifts due to finite bandwidths and signal propagation times in the control loop lead to phase lags which increase with frequency The appearance of oscillations can be observed in the oscil loscope display of the error signal see Paragraph 7 6 for details However the frequency analysis is bet ter suited because it is more sensitive and directly shows the resonance peak at its frequency Usually it is helpful to drive the system int
50. mplitude peak peak Output output to which the scan signal is added lt SC 110 our 1 The numerical values are guidelines and depend on the individual setup Table 2 DigiLock 110 Scan Module Settings The maximum scan range of the DigiLock 110 module is obtained in the following way 8 Choose lt SC 110 out gt in the Offset adjustment control box of the DigiLock 110 Control Software and set the Offset to 0 V gt Set the Offset adjust ten turn potentiometer on the SC 110 front panel to half the available output range 5 which corresponds to an output voltage of 75 V The DigiLock 110 software can now access the full output range 0 150 V 10 All the relevant signals can be analyzed through the DigiLock 110 computer interface However the DigiLock 110 also provides a trigger output TRIG which can be used for monitoring with an auxiliary external oscilloscope CAUTION The SC 110 output can deliver high voltages up to 150 V Please make sure that your oscilloscope has suitable inputs Now all the hardware is set up and the system can be completely controlled by the DigiLock 110 soft ware 11 The photodetector signal connected to the Main in 4 connector on the DigiLock 110 front panel can be examined in the scope mode shown in the lower part of Figure 33 CC Page 40 Ww PHOTONICS Status 21 10 08 8 Application Examples DigiLock 110 SN 01013 Rb Spectro FA File View Help Functions Grande
51. n this case the polarity of PID 1 has to be opposite to the polarity of the laser diode The polarity of the controller output for any actuator can be figured out by comparing the signals of the scan output with the change observed while scanning the controller output To determine the result ing effect one can look at a characteristic part of the error signal e g close to the lock point or use the wavemeter reading if available The slope is defined by the lock point given by the display during scan It is automatically chosen in AutoLock mode If the controller is used in manual mode the user can define the lock point by selecting the corresponding slope direction A general method to verify the correct overall polarity is to compare the signals during scan with the controller switched on and off while using just the proportional part To do so only activate the PID con troller in question Set the integrator and differentiator parts to zero and the P part and overall gain to some finite value e g 10 Use the System setup input offset see Paragraph 6 2 4 to center the signal around zero Switch on the PID controller while scanning across the characteristic lock point Increase the proportional part and or overall gain until you see a significant distortion of the signal To check the observed effect you can compare with the cases of the other polarity and the controller being switched off The cases of side of fringe locking and locking to
52. nd its mean value The following shortcuts AutoLock Mode only allow a more convenient operation CTRL lt arrow left gt increases the offset of the x channel by scanrange 0 1 CTRL lt arrow right gt decreases the offset of the x channel by scanrange 0 1 CTRL lt arrow down gt increases the scanrange of the x channel to scanrange 1 2 CTRL lt arrow up gt decreases the scanrange of the x channel to scanrange 1 2 CC Page 30 Oo rrorones Status 21 10 08 6 Operation Frontend 6 3 3 Frequency Analysis Signal Hold Old aig TE 1 500 kH He a C E Mean RMS error l l show avg CHI CH 2 Frequency Hz it LI out a u Main in Y 0 50k 100k 150k 200k 250k 300k 350k 400k 450k 500k Frequency Hz Figure 27 Frequency Analysis Display The frequency analysis displays the fast fourier transform FFT of the signal The functionality is similar to the scope mode but in the frequency domain NOTE The selected frequency range defines the sampling rate of the signal used for the FFT CH 1 Signal displayed on channel 1 CH2 Signal displayed on channel 2 Hold Freezes the trace for this channel Ovid Indicates whether the selected channel was at its limits during the last acquisition f scale Frequency span displayed on the frequency axis Within this range 500 measurement points are calculated from a time signal of 1000 measure ment points sample rate 2 x f scale Show Shows or hides the trace A
53. ning across a resonance of the cavity It can directly be used for side of fringe locking analogous to Para graph 8 2 1 15a To generate the error signal for locking to the maximum of the resonance use the PDH Module The PDH Module provides a number of higher modulation frequencies in the MHz range In the case of the cavity with well separated modes modulation frequencies much larger than the char acteristic linewidth combine steep slopes with a large capture range To activate the PDH Module check the box on the corresponding tab TOPTICA e Page 53 Status 21 10 08 Feedback Controlyzer DigiLock 110 The parameters of the PDH Module are analogous to the LI Module and are listed in the following table Mod set freq modulation set frequency can be selected for a set of 12 5 MHz 5 discrete modulation frequencies Mod amplitude amplitude of the modulation 0 1 Vppl Phase shift phase shift of the local oscillator with respect to the 0 to be optimized applied modulation see text Mod Output output to which the modulation is added lt Main out gt Table 4 Note that the capture range is given by the modulation frequency but a larger modulation amplitude is needed with increasing modulation frequency For standard applications a modulation frequency of 12 5 MHz or less is preferred because at 25 MHz the analog electronics bandwidth additionally reduces the signal strength 16a Set the input of the AutoLock Mode to lt PDH
54. nufacturer name and address serial number article number compliance with CE standards are given by the identification label i Lochhamer Schlag 19 i Top aie D 32166 Graefelfing Made in Germany Product ID No 3 DigiLock 110_1V0_01001 Size 46mm x 25 mm Color Silver black Location Rear Panel of the plug in module TOPTICA TEA Page 7 Status 21 10 08 Feedback Controlyzer DigiLock 110 3 Operator Controls and Connections 3 1 Front Panel Figure 4 Front Panel of the DigiLock 110 1 ON OFF switch and indicator 6 Main out 11 General purpose digital input LED high speed analog output output 2 Precise analog input 7 Avuxout 12 Trigger output high speed analog output 3 Auxin 8 Sum input 13 USB connector high speed analog input 4 Mainin 9 General purpose analog high soeed analog input input output 2 5 Error output 10 General purpose analog input output CAUTION All high speed inputs are 50 Ohm terminated and all high speed outputs including Trigger output 12 are able to drive 50 Ohm loads CC Page 8 Ww PHOTONICS Status 21 10 08 3 Operator Controls and Connections 3 2 Description of Front Panel Operator Controls and Connectors 1 ON OFF Switch ON OFF Switch for the e Switch and LED DigiLock 110 module x Precise analog input Precision analog input SMB connector 3 Aux in high speed analog input High speed analog SMB connector input 4 Mainin high speed analog inp
55. o oscillation and note the characteristic frequencies for reference A simple parameter adjustment is obtained in an iterative process l Set the integral gain K to a finite value all others to zero and increase the overall gain until the system locks 2 Alternate between increasing the proportional Kp and the integral gain K each until the feedback loop oscillates then reduce the gains until the oscillation definitely stops Standard optimization procedures set the proportional Kp gain to about half the value at which oscillation starts S Alternate between increasing the differential Kp and the integral K gain each until the feedback loop just oscillates increase one and the other until the oscillation will not stop by further increase At that point reduce the gain until the oscillation definitely stops 3 In analog controller circuits the integral part is sensitive to persistent DC deviations of the error signal e g internal IC offsets Therefore the integral gain K should always be kept at a finite setting to reduce residual offsets 4 Ifthe system does not lock check the polarity i e try the opposite polarity or consult Paragraph 7 4 TOPTICA ELLA Page 33 Status 21 10 08 Feedback Controlyzer DigiLock 110 Note that the optimized parameters depend on the slope of the error signal at the current lock point and the actuator response Therefore there is usually a trade off between a good locking result and a reason
56. ock 110 10 Guarantee and Service To obtain information concerning factory service contact your local distributor or TOPTICA Photonics AG directly On the following pages you find the Guarantee Registration Form and the Service and Technical Support Form Please fill in the Guarantee Registration Form immediately after you have received your device and return it to TOPTICA Photonics AG by mail or fax In case your device has to be returned to TOPTICA Photonics AG for service or technical support first call TOPTICA Photonics AG for a Return Authorization Number which you should use as a reference in your shipping documents and mark clearly on the outside of the shipping container Then fill in the Service and Technical Support Form and return it to TOPTICA Photonics AG together with the device Please spec ify the problems with the device as detailed as possible CC Page 62 Ww PHOTONICS Status 21 10 08 Guarantee Registration Form amp TOPTICA PHOTONICS QMform F 015 sttsorform 22 02 08 return to sender TOPTICA Photonics AG Customer Service Lochhamer Schlag 19 D 82166 Graefelfing Munich Germany FAX 49 89 85837 200 Guarantee Conditions The products of TOPTICA Photonics AG are produced with the greatest possible care using high quality components and are checked in detail before being delivered Therefore as the manufacturer TOPTICA Photonics AG gives a guarantee of durability according to the following terms
57. ock 110 2 Safety Instructions and Warnings 2 1 General Safety Terms The following safety terms are used in this manual The DANGER heading in this manual explains danger that could result in personal injury or death The CAUTION heading in this manual explains hazards that could damage the instrument In addition instrument DANGER CAUTION DANGER DANGER DANGER DANGER DANGER CAUTION CAUTION Page 6 Status 21 10 08 a NOTE heading provides information to the user that may be beneficial in the use of the Before operating the DigiLock 110 plug in module please read this manual carefully to prevent from damage to the electronics connected diode lasers and injury to persons The following safety instructions must be followed at all times The electrical units should not be operated in a hazardous environment Any plug in module should only be opened by trained personnel Before exchanging and opening any module the Sys DC 110 Supply Electronics must be switched off and discon nected from the mains supply Do not look into the beam from the laser diode under conditions which exceed the limits specified by the United States Food and Drug Administration Department of Health and Human Services Center for Devices and Radiological Health 21 CFR 1040 10 and 2 CFR 1040 11 Take precautions to eliminate exposure to a direct or reflected beam It is essential to check the adjusted paramete
58. ppears and there is only a scatter plot left The interpretation of this plot and the optimization of the lock can be found in Paragraph 8 2 1 For optimization of the PID parameters see Paragraph 75 11 The output of the controllers can be restricted using the Limit settings Paragraph 6 2 1 4 and 6 2 1 5 e g to about the scan range This helps to avoid destabilization of the laser by driving it far from the lock point especially during initial setup and optimization Cae Page 5 Status 21 10 08 Feedback Controlyzer DigiLock 110 Signal Hold Ovid PID Lock to slape LI i PDH Lock to nearest peak Lockpoint tracker LI PDH Lock to nearest valley Unlock amp Restart scan RMS error oo show CH il ia O Export Data CH in a Export Simplified Image 50110 out Ca n i Clear Graph amp m we ano 11 Main in N ouau TIMBA 22 SC110 out Figure 47 Initiating the automatic LI lock to a Peak Select the lock point by positioning the crosshairs When the Lockpoint tracker is on it snaps to the nearest peak or dip and if the laser drifts the lock point is tracked automatically Acti vate the lock by selecting LI PHD Lock to nearest peak valley from the context menu Signal Hold Old a 4 w Lockpoint tracker E RMS error Sg 4m show Main in ne no 1 Manin fr TSO 22 22 1 SC110 out Figure 48 AutoLock Displ
59. py 8 2 1 Side of Fringe Locking 8 2 2 Top of Fringe Locking Lock In 8 3 Pound Drewer Hall Stabilization to a Cavity 9 Appendix 9 1 Internal Jumpers 92 DigiLock 110 PCBs 9 2 1 Baseboard 9 2 2 Plug On Board 9 3 Specifications of DigiLock 110 Connections 9 4 Pin Assignment of the DigiLock 110 Backplane 10 Guarantee and Service Status 21 10 08 38 38 43 44 49 33 57 oF 58 57 60 61 62 TOPTICA PHOTONICS Feedback Controlyzer DigiLock 110 1 The Feedback Controlyzer DigiLock 110 Stabilized lasers see an increasing number of applications in research and development To meet the dif ferent requirements a number of locking techniques have been developed So far the different schemes require a corresponding set of adapted electronics The DigiLock 110 integrates fast analog and digital electronics into a versatile general purpose locking module Its Up to date digital hardware allows to implement the scan generator PID controllers and optional frequency modulation techniques all into one plug in module Together with a graphical user interface running on a PC the module facilitates the procedure of laser locking enormously and provides features to analyze and optimize the control system DigiLock 110 features e Generation of scan waveforms e Two separate PID controllers e Lock in error signal generator e Pound Drever Hall PDH error signal generator e Computer assisted hardware zoom e Automatic lock Clic
60. r signal on positive signal slope and vice versa To find the optimum phase e Change the phase value until you get the minimum signal e Then subtract 90 and you will get the maximum signal e If you observe the wrong sign add or subtract 180 to the current phase value To set the lock point i e the zero crossing of the error signal any residual offset can be compensated by setting the offset in the Lock In Module to the value observed in the scope display CC Page 50 7 72 Status 21 10 08 8 Application Examples 25 Once the phase is adjusted turn off the modulation of the Lock In Module Check the parameters of the PID controllers Now you can position the crosshairs to either a peak or a valley and it will automatically track the lock point To find the correct settings of the sign for each PID controller please see Paragraph 7 4 26 To initiate the lock perform a right mouse click to access the context menu and select between LI PDH Lock to nearest peak or LI PDH Lock to nearest valley The trace changes its color here from yellow to blue to show that the actual trace is captured in the background During the next scan the lock is triggered Figure 48 shows the AutoLock display while the lock is triggered The blue trace is the captured signal of the last scan The yellow trace is the scan during which the lock is triggered You can see that the trace stops at the selected peak After a while the yellow trace disa
61. rs of the supply units before switching on the modules Therefore the operator must make sure that the ON OFF switches of the modules are in position OFF before the Key Switch of the DC 110 monitor Unit is switched to position ON In particular pay attention to the Imax limitation the POS NEG switch and the CURRENT POWER switch of the Current Control DCC 110 As long as the ON OFF switches are set to position OFF the laser diode is short circuited by the relay integrated in the Toptica Diode Laser Head The user must not open the Diode Laser Supply Electronics Sys DC 110 or any of the plug in modules during operation Internal tuning as well as the replacement of components may only be carried out by authorized and specially trained service personnel Under certain cir cumstances there may be dangerous voltages even if the device is disconnected from the mains supply Special precautions are necessary if the Diode Laser Supply Electronics Sys DC 110 is to be operated in surroundings of high electro magnetic radiation such as close to a plasma dis charge Please refer to TOPTICA Photonics AG for technical support Please assure with particular care that the electrical safety conditions are met especially concerning the high voltage outputs Also carefully read the instruction for operation of the Supply Rack DC 110 before using the device TOPTICA PHOTONICS 2 Safety Instructions and Warnings 2 2 Identification of Manufacturer Ma
62. ser saves a profile all system parameters are recorded To load a profile a dialog window opens in which the desired parameters can be selected to be imported see Figure 24 Open DigiLock Profile LiLabVIEW DigiLock FrontendiFrofiles O DigiLock_defaulk pro 14 04 2008 12 50 Figure 24 Dialog Window to select the Profile Source File and the Parameters to be imported erre Page 28 Ww PHOTONICS Status 21 10 08 6 Operation Frontend 6 3 Display Area The lower part of the screen shows three different displays that are accessible through the buttons on the left hand side 6 3 1 Scope Mode Signal Hald Ovid CH i a Timescale SH SEE xy Mode I Mean FEE RMS error 169 0 show awg ET d CH2 Time 5 Main in v LI out a u z m 30m Time s Figure 25 Scope Mode Display Two channel digital oscilloscope to display different available system signals CH 1 Signal displayed on channel 1 CH2 Signal displayed on channel 2 CH x Signal on the x axis Only available in x y mode Hold Freezes the trace for the respective channel Ovid Indicates whether the signal has reached the limits of the channel dur ing the last acquisition Timescale Timescale displayed on the time axis Mean Mean value calculated from the trace for CH 1 and CH 2 RMS error RMS value calculated from the difference between the displayed trace and ifs mean value Show Shows or hides the trace Avg Option
63. slope RMS error ae LI PDH Lock to nearest peak show LI POH Lock to nearest valley o Unlock amp Restart scan Unlock Clear Graph f eve a Mainin v MISE Export Data LI out a u EMEEN Export Simplified Image me mo 11 a le E E m 21 9 22 SC110 out Y Figure 41 Initiating the AutoLock to a slope of the absorption signal 620m Signal Hold Old 600m 70 al 580m 65 e roe 560m 60 Lockpoint tracker II 540m K i RMS error Oo o show 520m 30 45 500m 40 450m Main in me gno x 35 460m 33 scuoout v Ql 440m Di Manin E Bente LI out a u a E 20 400m 15 mie RO 380m 10 2 21 9 22 22 2 22 2 SC110 out Figure 42 Autolock Display while the lock is engaged PID lock to slope 20 After some time the yellow trace disappears and a scatter plot is left which indicates both the input signal y axis and the current output of the PID 2 which in this case coincides with the scan see Figure 43 on the x axis The calculated rms deviation from the setpoint value displayed in the right panel can be used to optimize the lock To turn the lock off perform a right mouse click in the AutoLock graph and select either Unlock to just release the lock or Unlock amp Restart scan to release the lock and immediately start scanning again The behavior of the output value of the PID controllers when switching off the lock can be configured
64. t DTC 110 Tset not jumpered by default The assignment of the DA lines to the respective parameter is fixed inside the DigiLock 110 module Be sure that the jumpers of the corresponding modules are set Table 1 according to the table above For detailed information please see the appropriate para graphs in the Sys DC 110 manual 4 Hardware Installation The DigiLock 110 module is designed as a plug in module for the TOPTICA DC 100 or DC 110 supply rack Before installation switch off all other modules and disconnect the supply rack from the mains supply The DigiLock 110 can be plugged into any slot of a 19 or 12 rack except the one reserved for the DC 110 Mon on the right Make sure that no module other than the SC 110 uses the DA 2 analog backplane line By default the DigiLock 110 communicates via DA 2 with the SC 110 If you do not need this functionality you can disconnect DA 2 from the backplane by removing the appropriate jumper see Paragraph 9 1 As described in Paragraph 9 3 the DigiLock 110 can read the DCC 110 lact and DTC 110 Tact parame ters via the backplane This readout only works for modules installed on channel 1 of the rack slot 2 3 and 6 It is recommended to install the DigiLock 110 in slot 6 see Figure 5 For further information on the arrangement of the modules please see the Sys DC 110 manual uu ISS TTT AAAARA A FM N ElL Slot 3 Slot 3 Slot CTO elem ale Bee TO Mon
65. terface software after startup All parameters of the DigiLock 110 can be reset by loading the default profile Functions Setup gt Load profile For the standard installation the default profiles can be found at e Documents and Settings lt User Name gt Application Data Toptica DigiLock Pro files DigiLock_default pro for English Windows setup e Dokumente und Einstellungen lt User Name gt Anwendungsdaten Toptica DigiLock Pro files DigiLock_default pro for German Windows setup TOPTICA e Page 37 Status 21 10 08 Feedback Controlyzer DigiLock 110 The laser frequency can be adjusted to the desired resonance by several means with increasing preci sion e Coarse tuning in the 0 1 nm range usually only required for the initial setup can be achieved by modifying the angle of the grating with the fine thread screw e Change the current and if necessary the temperature of the laser to tune the frequency and achieve single mode operation e The built in piezo allows mode hop free scanning of the laser over several 10 GHz The DigiLock 110 generates the scan signal that drives the piezo using the SC 110 as a high voltage amplifier The output is the sum of the voltage specified in the DigiLock 110 software and the offset of the SC 110 The SC 110 offset can hence additionally be used to scan the laser ba In the Scan Module of the DigiLock 110 you can choose the parameters for the scan signal gener ation Amplitude scan a
66. the purpose of rectifying a defect covered by the guarantee the product or the relevant part shall be sent to TOPTICA Photonics AG at the expense and risk of the buyer The product shall be returned at the expense and risk of TOPTICA Photonics AG 5 No claims may be derived from this guarantee other than claims for rectification of the defects falling within the scope hereof in accordance with the present terms In particular the buyer is not entitled under this guarantee to claim damages or a reduction in price from TOPTICA Photonics AG or to rescind the contract Potential more far reaching claims of the buyer against its seller shall not be affected by this guarantee 6 Important The obligation of TOPTICA Photonics AG under this guarantee is subject to the condition that the buyer gives his her express consent to them by sending the signed duplicate of this form to TOPTICA Photonics AG immediately after delivery also truthfully indicating the model number the serial number and the date on which the product was delivered Te The buyer may not assign claims under this guarantee to third parties without the prior written consent of TOPTICA Photonics AG 8 This guarantee is governed by substantive German law to the exclusion of the provisions of the UN Convention on Contracts for the International Sale of Goods CISG The Regional Court Landgericht Munich shall be the court of exclusive international local and subject matter jurisdiction
67. the range of a few kHz while the DC modulation input has bandwidths of a few 100 kHz Turn off the autoscale function of CH 1 because normally a high DC offset is present and therefore small signal amplitudes may not be observed Choose the appropriate amplitude range by setting the upper bound of the y axis see Paragraph 6 1 to resolve all peaks in the frequency spec trum as desired Signal Hold Gld cH1 6 Em e 2 5 MHz 426 d show avg ne ano 1 Pi Ml ANI M M W i 0 200k 400k 600k 800k 1M 1 2M 1 4M 1 6M 1 8M 2M 2 2M Frequency Hz i o We hath itl h A hh Mt ntl ul Asa re Miah Figure 44 Frequency Analysis of the Photodiode Signal at lt Main in gt In this example the frequency analysis clearly shows the onset of an oscillation at about 600 kHz due to high gain settings To improve the lock performance you can now increase the gain of the P and D parts of the PID in turn to values well below the point at which the control loop starts to oscillate The strategy for optimizing the P and D parameters is described in Paragraph 7 3 CC Page 48 Ww PHOTONICS Status 21 10 08 8 Application Examples 8 2 2 Top of Fringe Locking Lock In To lock the laser to a maximum of the Doppler free absorption signal a zero crossing slope is generated by frequency modulation The Lock In Module uses a modulation frequency smaller than the character istic resonance width to obtain the derivative of the absorption signal by
68. tion with the AutoLock Mode display see Paragraph 6 3 2 in the lower part of the screen Thismode combines the controllers and enables the user to interactively search for the desired locking point select it and lock the system click and lock In addition several options are available to detect out of lock states and to relock the system Checkbox Input AutoLock controllers General Setpoint Lock Lock Window Use Lock Window Relock Page 16 Status 21 10 08 Activation deactivation of the AutoLock Signal input used for the controllers Main in Aux in LI out and PDH out In AutoLock mode the inputs of both PIDs PID 1 PID 2 are set accor ding to this selection Once selected for AutoLock the input channels of the controllers can not be modified any longer in the corresponding tabs After the automatic lock has been engaged via the interactive mode the controllers have a given setpoint This setpoint can be modified here for all of the selected controllers simultaneously Initiates the AutoLock procedure and releases the lock respectively This option specifies boundaries for the selected channel If the signal leaves the selected range Min Max the controllers associated with the AutoLock feature are on hold They are reactivated when the signal is back in the selected range taking into account a 10 hysteresis for further details see Paragraph 7 5 This option is only available i
69. tionally be mod AC bias t used for feedback or modulation at high frequencies in the MHz range CAUTION Check the maximum current Imax of the current controller DCC 110 to prevent damage of the laser diode To do so turn on the key switch but leave the modules and laser switches off and check the Imax setting on the DC 110 Monitor Unit 3 Connect the output of the Scan Control SC 110 to the piezo of the ECDL Since the DigiLock 110 provides the scan capability set the trigger switch on the front panel of the SC 110 to position ext external 4 The fast feedback via the Main out 6 SMB connector of the DigiLock 110 is applied to the DC coupled modulation input of the DLpro 5 The output of the photodetector is connected to the Main in 4 connector of the DigiLock 110 CAUTION To allow for high bandwidth the Main in 4 connector of the DigiLock 110 is jumpered in the factory settings as a 50 Ohm input Check that the photodetector amplifier can drive the 50 Ohm input Alternatively the input can be jumpered to high impedance see Paragraph 9 1 6 When all connections are established switch ON the DigiLock 110 connect the USB port to the PC and start the software Afterwards turn on the Temperature and Current Control DTC 110 and DCC 110 as well as the SC 110 After a few minutes the laser will thermally stabilize Adjust the parameters ler and Tet in order to get stable single mode cw operation Figure 33 shows the user in
70. to average consecutive scans of a channel the number of traces for the average can be set in the Advanced Settings see Para graphi 6 2 5 3 Ce Page 29 Status 21 10 08 Feedback Controlyzer DigiLock 110 6 3 2 AutoLock Mode Signal Hold Old Lockpoink tracker O Mean 209 6m 150 0 Rmseror 158 6m MI 00 i a __ show cHi 5C110 out v E rm Pl i Main in VW LI out a u 17 18 SC110 out Figure 26 AutoLock Mode Display This display is used in conjunction with the AutoLock tab in the upper part of the screen In this mode the user can handle two major tasks e Search the desired point to lock to via panning and zooming the displayed signal e Initiate the locking procedure with the help of the context menu CH 1 Can not be modified Input signal chosen in the AutoLock tab see Figure 9 CH x Can not be modified Signal displayed on the x axis Output signal of the Scan Module Hold Freezes the trace Ovid Indicates whether the selected channel was at its limits during the last acquisition Lockpoint tracker After choosing the desired lock point signal level for side of fringe lock or peak valley lock in case of LI or PDH the crosshairs automatically fol low this lock point even if the signal is drifting or the user changes the off set Mean Mean value calculated from the trace for CH 1 and CH 2 RMS error RMS value calculated from the difference between the displayed trace a
71. turation Spectroscopy After realizing the initial setup in Paragraph 8 1 this section describes the stabilization to an atomic transi tion by Doppler free saturation spectroscopy of Rb Figure 35 shows the experimental setup DC DCC110 DTC110 Mon110 DC110 Connection via backplane R oS Gas Cell Rb Cs Figure 35 Experimental Setup for Doppler free Saturation Spectroscopy Once the Doppler free saturation spectroscopy is adjusted and the laser is tuned to the appropriate transition the photodetector signal at the Main in connector 4 in Figure 4 can be optimized by scan ning the laser wavelength across the desired resonance 13 To scan the laser with the piezo use the Scan Module control box of the DigiLock 110 Control Soft ware Select lt SC 110 out gt as output set the signal type to triangle the frequency to 10 Hz and the amplitude in the order of 10 Volts Depending on the laser this corresoonds to several GHz of fre quency tuning Switch on the scan by pressing the button Scan 14 The scope mode provides a two channel oscilloscope and is a general tool to view a variety of signals of the DigiLock To display the spectroscopy signal use a timescale of 50 ms corresponding to the 10 Hz scan frequency choose lt Main in gt as CH 1 and lt SC 110 out gt as CH 2 The scope trig gers on the rising slope of the internal scan ramp The signal expected after the adjustment will look similar to the one s
72. ulation option in the laser head whereas PID 2 will be responsible for the lower frequencies by controlling the piezo voltage As input channel select lt Main in gt where the photo detector signal enters the module In AutoLock operation the input channel chosen in the AutoLock tab is taken as input for all the selected controllers 16 To use the AutoLock features change the display from Scope Mode to Auto Lock Mode The x axis of the display is the output of the Scan Module and the y axis is the corresponding value of the selected AutoLock input channel In the AutoLock mode the software will actually perform a hardware zoom and pan i e modify the scan amplitude of the Scan Module and the offset of the corresponding output channel according to the dis played x axis To graphically and interactively magnify the part of the absorption spectrum in the vicinity of the desired lock point Select the x axis Zoom tool see Figure 38 place the cursor left of the desired x value hold the left mouse button move the mouse to the right of the desired x value and release the left mouse button Zoom out Zoom in Figure 38 Available Tools for the Graph Displays To increase the scan range again use the Zoom out tool The graph will zoom as long as you press the left mouse button To shift the soectrum to the left or right i e modifying the offset use the Pan tool In our example the Rb D2 transitions at 780 nm are used Figure 3
73. ut Versatile high ninni Gc SMB connector analog input 5 Error output Output of the error sig a AN e SMB connector nal Main in Input off set x Gain 2 6 Main out high speed analog Versatile high speed output analog output e SMB connector 7 Aux out high speed analog High speed analog 1 V 50 output output e SMB connector 8 Sum input Signal input is added to 1V 50 e SMB connector Main out 9 General purpose analog input General purpose ana Input 12 5V Input 47k output 2 log input output OUTOUT 26 5 V Output high e SMB connector 10 General purpose analog input General purpose ana Input 12 5V Input 47k output 1 log input output Output 6 5 V Output high e SMB connector 11 General purpose digital input General purpose digital O V 2 6 V TTL Input 47k output input output Output 50 e SMB connector 12 Trigger output Trigger output O V 2 6 V TIL 50 e SMB connector 13 USB connector Connector for Com outer Control TOPTICA Oo Page 9 Status 21 10 08 Feedback Controlyzer DigiLock 110 3 3 Backplane Connections The DigiLock 110 module is capable of accessing several analog signals on the backplane of the Sys DC 110 rack On the one hand analog signals can be set in order to remote control other modules see Table below On the other hand actual parameters of modules can be read DCC 110 laet JIG nes Bere DCC 110 set not jumpered by default SC 110 Offset jumpered by defaul
74. vg Option to average consecutive frequency spectra of a channel the number of traces for the average can be set in the Advanced Settings see Paragraph 6 2 5 3 Mean Mean value calculated from the time signal for CH 1 and CH 2 RMS error RMS value calculated from the difference between the time signal and its mean value 6 4 Status Display On the bottom of the window the status bar displays the current state of the most important modules sys tem messages and a progress bar used for time Consuming processes Figure 28 Status Display Ce Page 3 Status 21 10 08 Feedback Controlyzer DigiLock 110 7 Notes on Feedback Control Loops with the DigiLock 110 The DigiLock 110 is a Universal module to realize different locking scenarios It provides two PID controllers means for frequency modulation techniques as well as tools for analyzing the lock This Paragraph is indented as a starting point for more detailed information on the implementation of control loops and their optimization For application examples see Paragraph 8 Before discussing the adjustment of the controller parameters Paragraph 7 3 it is helpful to consider a few signal path issues Paragraph 7 1 Frequency modulation is necessary to generate an error signal for top of fringe locking It also offers advantages in terms of insensitivity with respect to amplitude modulation and frequency noise and can provide a larger capture range Paragraph 7 2 The AutoLock mod

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