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Vescent Photonics D2-125, Manual

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Vescent Photonics D2-125 Manual Download Page 14

Last update: 2021/03/02 17:06

d2:laser_servo https://www.vescent.com/manuals/doku.php?id=d2:laser_servo

https://www.vescent.com/manuals/

Printed on 2021/04/17 23:32

Absolute Jump TTL (BNC)

When asserted HIGH (5V) while in LOCK mode, ABSOLUTE JUMP takes the Laser Servo out of lock and
conveys the negative 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, ABSOLUTE JUMP applies a DC offset equal to
-1*(LASER JUMP AMPLITUDE) to the ramp signal at SERVO OUTPUT. When asserted LOW while in RAMP
mode, the ramp signal is DC balanced.

When disconnected, ABSOLUTE JUMP is low.

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 negative of the LASER JUMP AMPLITUDE. For example, if the laser is locked and
the SERVO OUTPUT is -200 mV, then p300 mV on the LASER JUMP AMPLITUDE and engaging
the RELATIVE JUMP will set the SERVO OUTPUT to -200 mV + (-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

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 disconnected, RELATIVE JUMP is low.

Ramp TTL

Same as the front panel signal. The RAMP TTL is a trigger synchronous with the ramp. It is used to
trigger an oscilloscope while sweeping the SERVO OUTPUT.

Summary of Contents for D2-125

Page 1: ...e feedback has standard proportional P integral I and differential D feedback with a second integral feedback I providing the PI 2 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 de...

Page 2: ... switch controls whether the D2 125 PL is in side lock or peak lock mode When in side lock mode the modulation demodulation circuitry is disabled In this manual sections that are only relevant to the Peak Lock option are printed in red The Internal Power option removes the 9 pin power connect used to connect power between Vescent electronics modules and provides power entry module for powering the...

Page 3: ... Hz 1 kHz 2 kHz 5 kHz 10 kHz 20 kHz 50 kHz 100 kHz 200 kHz Second Integrator Off 100 Hz 200 Hz 500 Hz 1 kHz 2 kHz 5 kHz 10 kHz 20 kHz 50 kHz 100 kHz 200 kHz 500 kHz 1 MHz 2 MHz Differential Off 500 Hz 1 kHz 2 kHz 5 kHz 10 kHz 20 kHz 50 kHz 100 kHz 200 kHz 500 kHz 1 MHz 2 MHz 5 MHz 10 MHz Differential Gain 5 to 15 dB Auxiliary Servo Output Gain 5 Integral 500 μs to 5 s Laser Freq Jump Jump Time 400 μs ...

Page 4: ...manuals Printed on 2021 04 17 23 32 Fig 2 Schematic drawing of the front and back panels of the D2 125 Monitor Section 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 figure 3 Open a pdf of this image ...

Page 5: ...vel of the DC ERROR sets the lock point and can be adjusted with the DC OFFSET knob When locked the Laser Servo acts to drive the DC ERROR to zero AC Error The AC ERROR monitors the same signal as the DC ERROR except there is no low pass filter and the signal is coupled through a high pass filter to remove DC components 10 Hz It is designed for spectrum analysis and is also useful for coarse estimat...

Page 6: ...l adjusts the phase between the dither signal at RF OUTPUT and the local oscillator used to demodulate the signal coming in to ERROR INPUT It is used to maximize the demodulated DC ERROR signal while the laser is sweeping across the desired transition s or lock points The dither frequency is 4 MHz Dither Amp 25 turn trimpot PL only The DITHER AMP control is used to set the amplitude of the dither ...

Page 7: ...he COARSE GAIN sets the overall proportional gain of the circuit without changing the location of any corners or poles in the loop filter transfer function Relative to the DC ERROR MONITOR the Coarse Gain adjusts the gain from 0dB to 60dB The overall loop gain controlled by both the COARSE GAIN and the FINE GAIN should be set around the point that minimizes the RMS noise on the DC ERROR MONITOR Thi...

Page 8: ... user with two front panel knobs to adjust the voltage of the center of the ramp When the Ramp Offset is zeroed the ramp is centered at 0 V and when the servo goes from unlock mode to lock mode it engages the integrators starting from 0 V The user can adjust the Ramp Offset knobs coarse and fine to define the center of the ramp and the initial voltage point from which the servo begins integrating The ...

Page 9: ...equencies The upper switch must be in the low freq position to engage the lower switch NOTE Adjusting the loop filter corners while locked may result in loss of lock If this happens unlock laser before adjusting poles and corners and relock laser after adjustment NOTE The triangle embedded in the rounded side of each click switch points to the selected value First Integrator TOP Sets the frequency ...

Page 10: ...nd the FIRST INTEGRATOR TOP knob must be in the LOW FREQ position Differential TOP Sets the frequency of the differentiator ƒD This knob only selects the higher frequency positions 200 kHz 10 MHz and can turn off the differential by placing the switch in the OFF position To set ƒD to lower frequencies this knob must be placed in the LOW FREQ position Differential BOTTOM Sets the frequency of the differe...

Page 11: ...der switch This 2 position slider switch is only accessible by removing the right side panel see above and sets whether the ramp is applied to the SERVO OUTPUT or the AUXILIARY SERVO OUTPUT It is factory set in the Ramp Servo position When the Ramp Servo is selected the ramp is a 500 Hz triangle wave and when Ramp Aux is selected the ramp is 50 Hz Additionally when using The Absolute Jump TTL or t...

Page 12: ...hether 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 ...

Page 13: ...the user to adjust how long to wait to let the system stabilize before engaging the lock R202 Trimpot The R202 trimpot sets the size of the window comparator described above The size of the window can be measured by the voltage on T3 A smaller window means that the servo is more sensitive to unlock events and detects them quicker however if the window is too small the servo may detect false positi...

Page 14: ... the Laser Servo out of lock The voltage on the SERVO OUTPUT is the sample and hold value summed in with the negative of the LASER JUMP AMPLITUDE For example if the laser is locked and the SERVO OUTPUT is 200 mV then putting 300 mV on the LASER JUMP AMPLITUDE and engaging the RELATIVE JUMP will set the SERVO OUTPUT to 200 mV 300 mV 500 mV This feature is useful for jumping the laser relative to it...

Page 15: ...E is an analog signal that is used to jump the frequency of the diode laser See preceding sections on RELATIVE JUMP and ABSOLUTE JUMP for a full explanation Laser Lock Troubleshooting Most laser locking problems can be attributed to the following Gain set too high or too low Reduce the coarse and fine gain all the way and try locking Increase the coarse gain by one click at a time Gain sign wrong t...

Page 16: ...gnetic fields can affect the transfer function of the spectroscopy error signal in a negative way making locking difficult If using the D2 110 Spectroscopy Module and a D2 100 laser make sure the laser module is at least three inches away from the spectroscopy module In some cases strong magnetic fields can emanate from the optics table if magnetic clamps are in use If you are having problems locking t...

Page 17: ... wave at 500 Hz 1 In Unlock mode 2 Should be 0 V Could be offset by the Ramp Center 1 In Lock mode 3 Should be 0 V Could be offset by either the Ramp Center or DC Offset 1 If D2 125 rails return to Unlock mode switch the Gain Sign from to or vice versa and retry 10 In Lock mode turn up gain At some point the Servo Out should oscillate at something close to 11 10 MHz depending on the specific corner se...

Page 18: ...vescent com manuals doku php id d2 laser_servo https www vescent com manuals Printed on 2021 04 17 23 32 From https www vescent com manuals Product Manuals Permanent link https www vescent com manuals doku php id d2 laser_servo Last update 2021 03 02 17 06 ...

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