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d2:laser_servo [2019/07/15 22:50] – [Laser Lock Troubleshooting] Michael Radunskyd2:laser_servo [2020/03/16 22:21] – [Description] Michael Radunsky
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 The D2-125 Reconfigurable Laser Servo contains a tunable PI<sup>2</sup>D loop filter for tight locking to an error signal. The error signal is either an amplified version of the Error Input signal (side-lock mode) or an amplified version of a demodulated Error Input (optional peak-lock mode). In both modes, a DC Offset is summed to the error signal, allowing the user to select the zero-crossing and thus the lock point. The error signal can also be inverted via a front-panel switch. Additionally, the Laser Servo has an internal ramp generator for sweeping the output and computer control functionality to make and break lock and directly control the output voltage.  The D2-125 Reconfigurable Laser Servo contains a tunable PI<sup>2</sup>D loop filter for tight locking to an error signal. The error signal is either an amplified version of the Error Input signal (side-lock mode) or an amplified version of a demodulated Error Input (optional peak-lock mode). In both modes, a DC Offset is summed to the error signal, allowing the user to select the zero-crossing and thus the lock point. The error signal can also be inverted via a front-panel switch. Additionally, the Laser Servo has an internal ramp generator for sweeping the output and computer control functionality to make and break lock and directly control the output voltage. 
  
-The main component in the Reconfigurable Laser Servo is the PI<sup>2</sup>D loop filter, which means that the feedback has standard proportional (P), integral (I), and differential (D) feedback with a second integral feedback (I) providing the  PI<sup>2</sup>D transfer function. The double integration is used to boost gain at low frequencies.  With integrator frequencies tunable from 2 MHz down to 10 Hz, the Laser Servo can be optimized to a wide variety of plants and servo loops. With the Peak Lock option, the Laser Servo can demodulate a provided 4 MHz dither signal to enable slope-detection for locking to signal minimas and maximas. The Laser Servo can be used to lock a laser's current or PZT to an interferometer or an optical transition. With peak-lock, the Laser Servo can perform Pound-Drever-Hall (PDH) locking to an optical cavity. The Reconfigurable Laser Servo uses basic voltage inputs and outputs.  As a result, it can be used with lasers or with any voltage-tunable device with an error signal.+The main component in the Reconfigurable Laser Servo is the PI<sup>2</sup>D loop filter, which means that the feedback has standard proportional (P), integral (I), and differential (D) feedback with a second integral feedback (I) providing the  PI<sup>2</sup>D transfer function. The double integration is used to boost gain at low frequencies.  With integrator frequencies tunable from 2 MHz down to 10 Hz, the Laser Servo can be optimized to a wide variety of plants and servo loops. With the Peak Lock option, the Laser Servo can demodulate a provided 4 MHz dither signal to enable slope-detection for locking to signal minima and maxima. The Laser Servo can be used to lock a laser's current or PZT to an interferometer or an optical transition. With peak-lock, the Laser Servo can perform Pound-Drever-Hall (PDH) locking to an optical cavity. The Reconfigurable Laser Servo uses basic voltage inputs and outputs.  As a result, it can be used with lasers or with any voltage-tunable device with an error signal.
  
 The Laser Servo can be unlocked by a computer (via TTL control) to jump the output voltage to a set voltage difference from the current lock point, or to a specific voltage. This feature can be used to jump the laser frequency a known distance away and then relock to the original or a new lock point frequency. This feature can be used for auto-locking or relocking routines.  The Laser Servo can be unlocked by a computer (via TTL control) to jump the output voltage to a set voltage difference from the current lock point, or to a specific voltage. This feature can be used to jump the laser frequency a known distance away and then relock to the original or a new lock point frequency. This feature can be used for auto-locking or relocking routines. 
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 Located at the top of the front panel, the monitor section contains 6 BNC outputs for monitoring various signals used by the Laser Servo. The logic of the monitors is shown in <imgref image1>.  Open a {{d2:d2-125:d2-125_monitor_logic.pdf|pdf of this image }}. Located at the top of the front panel, the monitor section contains 6 BNC outputs for monitoring various signals used by the Laser Servo. The logic of the monitors is shown in <imgref image1>.  Open a {{d2:d2-125:d2-125_monitor_logic.pdf|pdf of this image }}.
  
-<WRAP center round box 420px><imgcaption image1|Monitor output logic>{{ d2:d2-125:d2-125_monitor_logic.jpeg?400|}}</imgcaption></WRAP>+<WRAP center round box 420px><imgcaption image1|Monitor output logic>{{ d2:d2-125:d2-125_monitor_logic.jpeg?600|}}</imgcaption></WRAP>
  
 **Error In** **Error In**
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 **Ramp Master / Slave (Jumper)** **Ramp Master / Slave (Jumper)**
  
-This jumper is only accessible by removing the right side panel (see above) and sets whether the ramp input is in master or slave mode. It is factory set to be in MASTER MODE. In SLAVE MODE (jumper off) the RAMP signal is generated externally and input through the back panel RAMP I/O port. In MASTER MODE (jumper on) the ramp is generated internally and is sent out to the RAMP I/O port for driving other D2-125 Laser Servos configured in SLAVE MODE.+This jumper is only accessible by removing the right side panel (see above) and sets whether the ramp input is in master or slave mode. It is factory set to be in MASTER MODE. In SLAVE MODE (jumper off) the RAMP signal is generated externally and input through the back panel RAMP I/O port. In MASTER MODE (jumper on) the ramp is generated internally and is sent out to the RAMP I/O port for driving other D2-125 Laser Servos configured in SLAVE MODE.   
 + 
 +The amplitude of the slave ramp is about -5x of the master ramp input (at slave Ramp Amp maximum).  The DC offset is applied after amplification.
  
 ====Lock Guard==== ====Lock Guard====
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 <WRAP center round box 400px> <WRAP center round box 400px>
 |  **C**  |  **B**  |  **A**  |  ** Hold Time**  |  **N+1 Relock Time**  | |  **C**  |  **B**  |  **A**  |  ** Hold Time**  |  **N+1 Relock Time**  |
-|0ff|0ff|0ff|  60 µs  |  150 µs  | +|Off|Off|Off|  60 µs  |  150 µs  | 
-|0ff|0ff|0n|  125µs  |  300 µs  | +|Off|Off|On|  125µs  |  300 µs  | 
-|0ff|On|0ff|  250 µs  |  600 µs  | +|Off|On|Off|  250 µs  |  600 µs  | 
-|0ff|0n|0n|  500 µs  |  1.25 ms  | +|Off|On|On|  500 µs  |  1.25 ms  | 
-|0n|0ff|0ff|  1 ms  |  2.5 ms  | +|On|Off|Off|  1 ms  |  2.5 ms  | 
-|0n|0ff|0n|  2 ms  |  5 ms  | +|On|Off|On|  2 ms  |  5 ms  | 
-|0n|On|0ff|  4 ms  |  10 ms  | +|On|On|Off|  4 ms  |  10 ms  | 
-|0n|0n|0n|  8 ms  |  20 ms  |+|On|On|On|  8 ms  |  20 ms  |
 </WRAP> </WRAP>
  
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 If you are having problems locking the laser, it is a good idea to not use the AUXILIARY SERVO OUTPUT as this complicates the system. Once you get the locking to work properly, you can reconnect this cable. If you are having problems locking the laser, it is a good idea to not use the AUXILIARY SERVO OUTPUT as this complicates the system. Once you get the locking to work properly, you can reconnect this cable.
  
-<imgref factory_settings> shows the nominal corner settings for locking the Vescent D2-100 to atomic spectroscopy.  If all else fails, return to these setting, turn down the gain and try again.+<imgref factory_settings> shows and <tabref factory_setting> lists the nominal corner settings for locking the Vescent D2-100 (or a Photodigm TOSA) to atomic spectroscopy.  If all else fails, return to these setting, turn down the gain and try again.
  
 <WRAP center round box 400px><imgcaption factory_settings|Factory settings for locking a D2-100> <WRAP center round box 400px><imgcaption factory_settings|Factory settings for locking a D2-100>
-{{ {{ d2:d2-125:factory_settings_red.png?direct&400 |}} |}}</imgcaption></WRAP>+{{ {{ d2:d2-125:factory_settings_red.png?direct&700 |}} |}}</imgcaption></WRAP> 
 + 
 +<WRAP center round box 60%><tabcaption factory_setting |D2-125 locking D2-100 or TOSA> 
 +| **Corner**                                                       | **Value**       | **Units**  | 
 +| First Integrator (high freq.)                                    | low freq.       |       | 
 +| First Integrator (low freq.)                                     | 10              | Hz         | 
 +| Second Integrator (high freq.)                                   | low freq.       |       | 
 +| Second Integrator (low freq.)                                    | 500             | Hz         | 
 +| Differential (high freq.)                                        | OFF       |       | 
 +| Differential (low freq.)                                         | 100              | kHz         | 
 + 
 +</tabcaption></WRAP>
  
  =====D2-125 Stand-alone Test=====  =====D2-125 Stand-alone Test=====
d2/laser_servo.txt · Last modified: 2021/12/17 01:58 by 127.0.0.1