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d2:laser_servo [2019/10/24 09:39]
Michael Radunsky [Lock Guard]
d2:laser_servo [2020/07/28 12:18] (current)
Michael Radunsky [Back-panel Section]
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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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 ** Aux: Bipolar / Aux: Unipolar (2-position slider switch) ** ** Aux: Bipolar / Aux: Unipolar (2-position slider switch) **
  
-This 2-position slider switch is only accessible by removing the right side panel (see above) and sets whether the AUXILIARY OUTPUT SERVO is unipolar or bipolar. It is factory set to be bipolar so the auxiliary output can range from -12 V to +12 V.  For some applications such as driving a PZT, limiting the voltage range to positive values is necessary.  When this switch is in the unipolar mode, the auxiliary output ranges from -0.5 V to +12 V. Additionally, when in Ramp->Aux mode and Aux: Unipolar, the ramp is centered at ~3.5V instead of 0V.+This 2-position slider switch is only accessible by removing the right side panel (see above) and sets whether the AUXILIARY OUTPUT SERVO is unipolar or bipolar. It is factory set to be bipolar so the auxiliary output can range from -10 V to +10 V.  For some applications such as driving a PZT, limiting the voltage range to positive values is necessary.  When this switch is in the unipolar mode, the auxiliary output ranges from -0.5 V to +10 V. Additionally, when in Ramp->Aux mode and Aux: Unipolar, the ramp is centered at ~3.5V instead of 0V.
  
 **Ramp Master / Slave (Jumper)** **Ramp Master / Slave (Jumper)**
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 **Absolute Jump TTL (BNC)** **Absolute Jump TTL (BNC)**
  
-When asserted HIGH (5V) while in LOCK mode, ABSOLUTE JUMP takes the Laser Servo out of lock and conveys the voltage on LASER JUMP AMPLITUDE to the SERVO OUTPUT.  Thus, a 1 V input to LASER JUMP AMPLITUDE applies 1 V  to SERVO OUTPUT.  ABSOLUTE JUMP is useful when one wants to control the voltage on the integration stages of the loop filter, or for zeroing the integrators during auto-locking routines. When returned to LOW (0V), the loop filter is reengaged. Engaging or disengaging the ABSOLULTE JUMP is achieved in under 400 μs.+When asserted HIGH (5V) while in LOCK mode, ABSOLUTE JUMP takes the Laser Servo out of lock and conveys <color black/yellow>the negative</color> of the voltage on LASER JUMP AMPLITUDE to the SERVO OUTPUT.  Thus, a 1 V input to LASER JUMP AMPLITUDE applies -1 V  to SERVO OUTPUT.  ABSOLUTE JUMP is useful when one wants to control the voltage on the integration stages of the loop filter, or for zeroing the integrators during auto-locking routines. When returned to LOW (0V), the loop filter is reengaged. Engaging or disengaging the ABSOLUTE JUMP is achieved in under 400 μs.
  
-When asserted HIGH (5V) while in RAMP mode, ABSOLULTE JUMP applies a DC offset equal to the LASER JUMP AMPLITUDE to the ramp signal at SERVO OUTPUT. When asserted LOW while in RAMP mode, the ramp signal is DC balanced.+When asserted HIGH (5V) while in RAMP mode, ABSOLUTE JUMP applies a DC offset equal to -1*(LASER JUMP AMPLITUDEto the ramp signal at SERVO OUTPUT. When asserted LOW while in RAMP mode, the ramp signal is DC balanced.
  
-When disconnected, ABSOLULTE JUMP is low. +When disconnected, ABSOLUTE JUMP is low. 
  
 **Relative Jump TTL (BNC)** **Relative Jump TTL (BNC)**
  
-When asserted HIGH (5 V) while in LOCK mode, RELATIVE JUMP engages a sample-and-hold circuit and takes the Laser Servo out of lock. The voltage on the SERVO OUTPUT is the sample-and-hold value summed in with the LASER JUMP AMPLITUDE. For example, if the laser is locked and the SERVO OUTPUT is -200 mV, then engaging the RELATIVE JUMP and putting 300 mV on the LASER JUMP AMPLITUDE will make the SERVO OUTPUT 100 mV (-200 mV + 300 mV).  This feature is useful for jumping the laser relative to its current lock point (say +200 MHz from a locked transition). When returned to LOW (0 V), the loop filter is reengaged, enabling the laser to be relocked to its original position (by setting LASER JUMP AMP to zero before returning the trigger to TTL low), or to a new lock point (by asserting the trigger low with the LASER JUMP AMP still at a non-zero value). (See [[http://www.vescent.com/jumping-lock-point-d2-125-reconfigurable-servo/|application note here]].) Engaging or disengaging the RELATIVE JUMP is achieved in under 400 μs.+When asserted HIGH (5 V) while in LOCK mode, RELATIVE JUMP engages a sample-and-hold circuit and takes the Laser Servo out of lock. The voltage on the SERVO OUTPUT is the sample-and-hold value summed in with <color black/yellow>the negative</color> of the LASER JUMP AMPLITUDE. For example, if the laser is locked and the SERVO OUTPUT is -200 mV, then putting <color black/yellow>+</color>300 mV on the LASER JUMP AMPLITUDE and engaging the RELATIVE JUMP will set the SERVO OUTPUT to -200 mV + (<color black/yellow>-</color>300 mV) = -500 mV.  This feature is useful for jumping the laser relative to its current lock point (say +200 MHz from a locked transition). When returned to LOW (0 V), the loop filter is reengaged, enabling the laser to be relocked to a new lock point (by asserting the trigger low with the LASER JUMP AMP still at a non-zero value). (See [[http://www.vescent.com/jumping-lock-point-d2-125-reconfigurable-servo/|application note here]].)  Or the laser can be relocked to its original position (by setting LASER JUMP AMP to zero before returning the trigger to TTL low). Engaging or disengaging the RELATIVE JUMP is achieved in under 400 μs.
  
 When asserted HIGH (5V) while in RAMP mode, RELATIVE JUMP applies a DC offset equal to the LASER JUMP AMPLITUDE to the ramp signal at SERVO OUTPUT. When asserted LOW (0V) while in RAMP mode, the ramp signal is DC balanced. When asserted HIGH (5V) while in RAMP mode, RELATIVE JUMP applies a DC offset equal to the LASER JUMP AMPLITUDE to the ramp signal at SERVO OUTPUT. When asserted LOW (0V) while in RAMP mode, the ramp signal is DC balanced.
d2/laser_servo.1571935147.txt.gz · Last modified: 2019/10/24 09:39 by Michael Radunsky