Vescent Photonics D2 Series User manual

Reconfigurable
Laser Servo
Vescent Photonics, Inc.
www.vescentphotonics.com
4865 E. 41st Ave
Denver, CO 80216
Phone [phone]
Fax [phone]
[e-mail]

General Warnings and Cautions
The following general warnings and cautions are applicable to this instrument.
WARNING
This instrument is intended for use by qualified personnel who
recognize shock hazards or laser hazards and are familiar with
safety precautions required to avoid possible injury. Read the
instruction manual thoroughly before using to become familiar
with the instrument’s operations and capabilities.
CAUTION
There are no serviceable parts inside the instrument. Work
performed by persons not authorized by escent Photonics may
void the warranty.
CAUTION
Although ESD protection is designed into the instrument,
operation in a static-fee work area is recommended.
WARNING
To avoid electrical shock hazard, connect the instrument to
properly earth-grounded, 3-prong receptacles only. Failure to
observe this precaution can result in severe injury or death.
WARNING
Do not clean outside surfaces of any escent Photonics products
with solvents such as acetone. Front panels on electronics
modules may be cleaned with a mild soap and water solution.
Do not clean optics modules.

Limited Warranty
escent Photonics warrants this product to be free from defects in materials and workmanship for a period of one year
from the date of shipment. If this product proves defective during the applicable warranty period, escent Photonics, at
its option, either will repair the defective product without charge or will provide a replacement in exchange for the
defective product. The customer must notify escent of the defective product within the warranty period and prior to
product return. The customer will be responsible for packaging and shipping the defective product back to escent
Photonics, with shipping charges prepaid.
escent Photonics shall not be obligated to furnish service under this warranty from damage caused by service or repair
attempts made without authorization by escent Photonics; from damage caused by operation of equipment outside of
its specified range as stated in either the product specification or operators manual; from damage due to improper
connection to other equipment or power supplies.
This warranty is in lieu of all other warranties including any implied warranty concerning the suitability or fitness of
the product for a particular use. escent Photonics shall only be liable for cost of repairs or replacement of the
defective product within the warranty period. escent Photonics shall not be liable for any damages to persons or
property resulting from the use of the product or caused by the defect or failure of this product. escent Photonics'
liability is expressly limited to the warranty set out above. By accepting delivery of this product, the purchaser
expressly agrees to the terms of this limited warranty.
escent Photonics
Printed Nov 27, 2012

Absolute Maximum Ratings
Note: All modules designed to be operated in laboratory environment
Parameter Rating
Environmental Temperature >15°C and <30°C
Environmental Humidity <60%
Environmental Dew Point <15°C

Vescent Photonics D2 Series Product Manual
1. Reconfigurable Laser Servo
Model No. D2-125
Document Revision: 5
1.1. Description
The D2-125 Reconfigurable Laser Servo contains a tunable PI2D 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, an optional temperature controller, 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 PI2D 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 PI2D 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
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Vescent Photonics D2 Series Product Manual
optimized to a wide variety of plants and servo loops. With the Peak Lock option, the Laser Servo can
demodulate a system-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 has an internal sweep generator to sweep the laser frequency prior to lock. It also
optionally contains a temperature control circuit to maintain constant temperature for the Spectroscopy
Module (D2-110) or other TEC-controlled environments.
1.1.1. Options
The D2-125 can be purchased with five options1:
•-PL – Peak Lock option
•-T – Temp stabilization option
•-RC – Ramp Offset option
•-IP-X – Internal Power (where X=100 AC, 120 AC, or 230 AC)
•-LG – Lock Guard option
The Peak Lock option generates a 4 MHz dither signal that can be used to modulate the laser current. The
amplitude and phase of this modulation can be adjusted via front panel controls. The Error Signal input
will be demodulated relative to the dither signal which will generate a derivative of the input Error Signal.
This derivative signal will be used to lock the laser to a minima or maxima of the input Error Signal. This
is often referred to as peak-locking. If purchased with the Peak Lock option, the Laser Servo can still be
used in side-lock mode. A front panel 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 Temp option is designed for use with the escent Spectroscopy Module (D2-110). It provides power
(±12 ) to the photo-detector board and stabilizes the module's temperature via the TEC's and a thermistor
in the D2-110 module. In this manual, sections that are only relevant to the Temp stabilization Lock
option are printed in blue.
The Ramp Offset option provides the user with two front-panel knobs to adjust the voltage of the center
of the ramp. Without this option, the ramp is always centered at 0 and when the servo goes from unlock
mode to lock mode, it engages the integrators starting from 0 . With the Ramp Offset option, the user
can turn Ramp Offset knobs (coarse and fine) to adjust the center of the ramp and the initial voltage point
from which the servo begins integrating. This option is typically not used when Servoing escent DBR
lasers as this functionality is redundant with the current adjust knobs on the D2-105 Laser Controller.
1 Not all combinations of options are available. For example, the “-T” option cannot be combined with the “-IP”
option. Please contact sales for details.
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Vescent Photonics D2 Series Product Manual
This option is recommend for Servoing PZT-based external-cavity lasers where the PZT amplifier (if
used) does not have an offset knob. In this manual, sections that are only relevant to the Ramp Offset
option are printed in green.
The Internal Power option removes the 9-pin power connector used to connect power between escent
electronics modules and provides a power entry module for powering the module via main AC lines. The
input voltage, 100 AC, 120 AC or 230 AC, is specified in the option. Note, with this option, the D2-
125 cannot be powered via the D2-005 Power Supply, the D2-001 break-out or from any other escent
electronics modules. Additionally, this module will not be able to power other escent electronics
modules; the -IP option makes the Laser Servo completely stand-alone. In this manual, sections that are
only relevant to the Internal Power option are printed in orange.
The Lock Guard option provides a relocking feature that detects if the primary servo output has changed
its value too quickly, and if this is detected, the servo disengages the lock and reengages the lock with the
servo output set to its value prior to the unlock event. More details can be found in the Lock Guard
Controls section on page 18. In this manual, sections that are only relevant to the Lock Guard option are
printed in purple.
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Vescent Photonics D2 Series Product Manual
1.2. Specifications
Value Units
Input and Output Impedan e 50 Ω
Output Voltage ±10
Input Voltage Noise2<5 n /√Hz
Max Input Voltage DC Level2±500 m
Max Input Voltage Signal Amplitude2±500 m
Bandwidth3>10 MHz
Proportional Gain (ref to DC Error)
Proportional Gain (ref to Input Error)
-40 to +32
-66 to +6 dB
First Integrator Off, 10 Hz, 20 Hz, 50 Hz, 100 Hz, 200 Hz,
500 Hz, 1 kHz, 2 kHz, 5 kHz, 10 kHz,
20 kHz, 50 kHz, 100 kHz, 200 kHz
Se ond 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 Gain4Integral: 500 μs to 5 sec
Laser Freq. Jump
Input Impedance 10 kΩ
Jump Time <400 μs
Ramp Amplitude (Max) ±5
Ramp Frequen y 500 Hz
Dither Frequen y (-PL only) 4 MHz
RF Output Max Amplitude (-PL only)2 60 m
2 Referenced to 50Ω load
3 Oscillation frequency when Laser Servo locked to itself in proportional mode.
4 Gain referenced to Primary Servo Output.
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Vescent Photonics D2 Series Product Manual
1.3. Inputs, Outputs, and Controls
1.3.1. Monitor Se tion
Located at the top of the front panel, the monitor section contains 6 BNC outputs for monitoring various
signals used by the Laser Servo.
Error In
In SIDE LOCK mode, the ERROR IN monitor is a buffered and filtered version of the ERROR
INPUT. In PEAK LOCK mode, the ERROR IN monitor is a buffered and filtered version of the
demodulated signal from ERROR IN. In both modes, the monitor has a 300 kHz low-pass filter.
DC Error
The signal from ERROR IN (after demodulation if in PEAK LOCK mode) is amplified by 26 dB
(x20). The amplified signal is summed with both the DC OFFSET as set on the front panel and
the back-panel DC OFFSET INPUT. The DC ERROR is passed through a low pass filter with a
roll off of 200 kHz, so that high frequency noise does not obfuscate the signal. The DC level 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.
11
Figure 1: Schematic drawing of the front and back panels.

Vescent Photonics D2 Series Product Manual
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 estimates of the laser line-width. The
bandwidth of the AC ERROR is limited by the preceding amplifier stages to greater than 20
MHz.
Servo Out
The SER O OUT monitors the correction signal that is fed back to the laser, SER O OUTPUT.
The signal is the output from the tunable loop filter.
Ramp
The RAMP MON is a monitor for the actual ramp signal sent to the SER O OUTPUT when the
laser is in RAMP mode.
Ramp TTL
The RAMP TTL is a trigger synchronous with the ramp. It is usually used to trigger an
oscilloscope while sweeping the SER O OUTPUT. The RAMP TTL signal is also available on
the back panel as a dedicated trigger output.
1.3.2. Front Panel
Power (LED indi ator)
All electronic modules have a blue LED power indicator on the top right side of the front panel
control section. The LED requires +15 and -15 in order to light.
Lo k Mode (two-position swit h) –PL only
When set to the PEAK LOCK position, this switch routes the ERROR IN to a FM demodulation
circuit that extracts the error signal, which is then passed to the Loop Filter circuit. In the SIDE
LOCK position, the demodulation circuit is bypassed and the signal is fed directly to the Loop
Filter circuit. Additionally, the RF OUTPUT is disabled in SIDE LOCK.
Ramp Amp (1-turn knob)
The RAMP AMP sets the amplitude of the internal ramp generator. The maximum ramp
amplitude is ±5 . The ramp is either applied to the SER O OUTPUT at 500 Hz or to the
AUXILIARY SER O OUTPUT at 50 Hz. The user can select between these options using a
DIP switch accessible via the side panel.
Phase (25-turn trimpot) –PL only
When purchased as part of a complete laser system, the PHASE control is set at the factory and
generally will not require further adjustment. The PHASE control 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 signal at RF OUTPUT.
When purchased as part of a complete laser system, it is set at the factory and generally will not
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Vescent Photonics D2 Series Product Manual
require further adjustment. When used with the D2-105 Laser Controller, the RF OUTPUT
should be connected to the Laser Controller's RF INPUT to modulate the laser current.
Error Input (BNC)
This is the input for the error signal. In SIDE LOCK mode, the signal is amplified by 26 dB and
summed with the DC OFFSET and DC OFFSET INPUT (back panel). In PEAK LOCK mode,
the ERROR INPUT is demodulated by the dither frequency and is then amplified by 26 dB and
summed with the DC OFFSET and DC OFFSET INPUT (back panel). In both modes the
amplified signal can be seen with the DC ERROR MONITOR and the AC ERROR MONITOR.
RF Output (BNC) –PL only
The RF OUTPUT signal is the 4 MHz dither or FM modulation signal. When used with the
D2-105 Laser Controller, it should be connected to the RF INPUT on the Laser Controller. In
SIDE LOCK mode the dither to the RF OUTPUT is turned off.
Gain Sign (two-position swit h)
The GAIN SIGN reverses the sign of the signal input from ERROR INPUT and should be used
if the desired lock-point has the wrong slope (loop is providing positive feedback instead of
negative feedback). Switching GAIN SIGN will invert the pattern seen at DC ERROR. When
triggering an O-scope with the RAMP TTL signal on a positive edge, the Laser Servo locks to a
zero crossing with a positive slope.
Laser State (three-position swit h)
The lock switch has three positions. The lowest is the RAMP, which connects the internal ramp
to the SER O OUTPUT causing the laser to sweep. The amplitude of the sweep is controlled
with RAMP AMP knob. In the center position (UNLOCK) the ramp is disconnected and zero
volts is output to SER O OUTPUT. In the top position (LOCK) the loop filter is engaged.
DC Offset (10-turn potentiometer)
The DC OFFSET knob adds a DC offset to the DC ERROR MONITOR signal. Since the servo
locks to the point where the DC ERROR MONITOR reads 0 , adjusting the DC OFFSET
changes the lock point.
Coarse Gain (seven-position swit h)
The COARSE GAIN sets the overall proportional gain of the circuit without changing the
location of any zeros 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. This can
sometimes result in setting the gain too high because the DC ERROR MONITOR filters high
frequencies and thus hides some of the gain peaking with high gain. To precisely set the gain,
look at the noise with a spectrum analyzer through the AC ERROR MONITOR.
Fine Gain (1-turn knob)
The FINE GAIN control adjusts the proportional gain by +6 to -6 dB.
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Vescent Photonics D2 Series Product Manual
Servo Output
The SER O OUTPUT is a voltage output to control the frequency of the laser. When the Laser
Servo is used with the D2-105 Laser Controller, the SER O OUTPUT is connected to the
CURRENT SER O INPUT on the Laser Controller. The SER O OUTPUT is the output from
the loop filter when in LOCK mode, zero volts when in UNLOCK mode, and a DC balanced
triangle wave when in RAMP mode. The ramp can be shifted with respect to 0 if the -RC ramp
centering option has been purchased.
Auxiliary Servo Output
The AUXILIARY SER O OUTPUT is generated from integrating the SER O OUTPUT. Its
purpose is to supply a correction signal to drive the SER O OUTPUT to zero. When used with
escent DBR lasers and the D2-105 Laser Controller, the AUXILIARY SER O OUTPUT can
be connected to the TEMP SER O IN to adjust the laser diode temperature to keep the feedback
laser current constant. Similarly, AUXILIARY SER O OUTPUT can drive a PZT on an
external-cavity laser diode to keep the laser diode current constant. See AUXILIARY SER O:
GAIN SIGN and AUXILIARY SER O: GAIN in section 1.3.3 for information on setting the
gain and and gain sign of the AUXILIARY SER O OUTPUT.
Ramp Offset Coarse -RC only
Coarse adjust to the center of the ramp signal and the DC oltage output in UNLOCK mode.
This can be used when driving systems other than the D2-100 which require unipolar input (such
as a laser with PZT-driven tuning elements.)
Ramp Offset Fine -RC only
Fine adjust to the center of the ramp signal and the DC oltage output in UNLOCK mode.
Spe tros opy Temp Control –T only
This is an 8-pin connector (HR25-7TR-8SA) that connects to the Spectroscopy Module, D2-110.
The connector provides power to the Spectroscopy Module's photo-detector and connects the
Module's thermistor and TEC to the Laser Servo's temperature controller. The pin definitions are
listed below where Rth and Rth_Rtn are the two ends of the thermistor.
Pin Signal
1 TEC+
2 TEC-
3 +15
4 Rth_Rtn
5 Rth
6 -15
7 NC
8 GND
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Vescent Photonics D2 Series Product Manual
1.3.3. Right Side Panel
15
Figure 2: TOP: Picture of right-side panel. BOTTOM: schematic of
the configurable transfer function and its user-controls.

Vescent Photonics D2 Series Product Manual
The feedback loop is defined by the Gain vs Frequency plot shown above. ωI, ωPI and ωD define three
zeros in the transfer function. ωI and ωPI are the frequencies where the first and second integrators
respectively switch from having integral gain to having proportional gain. ωD is the frequency where the
gain switches from proportional to differential. ωI, ωPI and ωD are controlled by two rotary switches,
where the upper switch is used to select higher frequencies, and the lower switch is used for selecting the
lower frequencies. The upper switch must be in the “low freq” position to engage the lower switch.
NOTE Adjusting the loop filter poles and zeros while locked may result in loss of lock. If this happens,
unlock laser before adjusting poles and zeros and relock laser after adjustment.
First Integrator (TOP)
Sets the frequency of the first integrator (ωI). This knob only selects higher-frequency positions
(2 kHz – 200 kHz). To set ωI to lower frequencies, this knob must be placed in the LOW FREQ
position.
First Integrator (BOTTOM)
Sets the frequency of the first integrator (ωI). This knob only selects the lower-frequency
positions (10 Hz – 1 kHz) and is only active if the FIRST INTEGRATOR (TOP) knob is in the
LOW FREQ position. To turn off the integrator, this knob must be placed in the OFF position
and the FIRST INTEGRATOR (TOP) knob must be in the LOW FREQ position.
Se ond Integrator (TOP)
Sets the frequency of the second integrator (ωPI). This knob only selects the higher-frequency
positions (20 kHz – 2 MHz). To set ωPI to lower frequencies, this knob must be placed in the
LOW FREQ position.
Se ond Integrator (BOTTOM)
Sets the frequency of the second integrator (ωPI). This knob only selects the lower-frequency
positions (100 Hz – 10 kHz) and is only active if the SECOND INTEGRATOR (TOP) knob is in
the LOW FREQ position. To turn off the integrator, this knob must be placed in the OFF position
and the SECOND INTEGRATOR (TOP) knob must be in the LOW FREQ position.
Differential (TOP)
Sets the frequency of the differentiator (ωD). 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 ωD to lower frequencies, this knob must be placed in the LOW FREQ position.
Differential (BOTTOM)
Sets the frequency of the differentiator (ωD). This knob only selects the lower-frequency
positions (500 Hz – 100 kHz) and is only active if the DIFFERENTIAL (TOP) knob is in the
LOW FREQ position.
Differential Gain (25-turn trimpot)
Sets the maximum differential gain. 25-turn trimpot adjusts the gain from 5dB to 15dB.
Auxiliary Servo: Gain (25-turn trimpot)
This trimpot sets the gain for the AUXILIARY SER O OUTPUT.
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Vescent Photonics D2 Series Product Manual
Sele tor DIP Swit h Array:
Ramp->Aux / Ramp->Servo (2-position slider swit h)
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 SER O OUTPUT or the AUXILIARY SER O
OUTPUT. It is factory set in the Ramp->Servo position. When Ramp->Servo is selected, the
ramp is a ~500Hz triangle wave and when Ramp->Aux is selected the ramp is ~50Hz. Ramp-
>Aux would be selected, for instance, when using a PZT-driven ECDL laser. Additionally, when
using The Absolute Jump TTL or the Relative Jump TTL, the output jump is placed on the same
channel as gets the ramp signal. The other signal (SER O OUTPUT or AUXILIARY SER O
OUTPUT) is held at its current value.
Aux Gain: + / Aux Gain - (2-position swit h)
This switch is only accessible by removing the right side panel (see above). This switch sets the
gain sign for the AUXILIARY SER O OUTPUT.
Aux Gain: Low / Aux Gain: High (2-position swit h)
This switch is only accessible by removing the right side panel (see above). This switch sets a
40dB attenuator for the AUXILIARY SER O OUTPUT loop gain when set to Aux Gain: Low.
17
Figure 3: Certain rarely used controls are only accessible by removing the right-
side panel, as shown in the figure above.

Vescent Photonics D2 Series Product Manual
Aux: Bipolar / Aux: Unipolar (2-position slider swit h)
This 2-position slider switch is only accessible by removing the right side panel (see above) and
sets whether the AUXILIARY OUTPUT SER O is unipolar or bipolar. It is factory set to be
bipolar so the auxiliary output can range from -12 to +12 . 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 to +12 . Additionally, when in
Ramp->Aux mode and Aux: Unipolar, the ramp is centered at ~3.5 instead of 0 .
Ramp Master / Slave (Jumper)
This jumper is only accessible by removing the right side panel (see previous page) and sets
whether the ramp input is in master or slave mode. It is factory set to be in MASTER MODE. In
SLA E 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 SLA E
MODE.
Lo k Guard Controls (DIP Swit h Array) - LG Only
Disabled / Enabled
This 2-position slider switch is only accessible by removing the right side panel (see above) and
sets whether the Lock Guard routine is engaged or not. When engaged, an AC-coupled (RC ≈ 10
μs) window comparator monitors the SER O OUTPUT to detect fast changes in the output. If
the servo output changes more than the value set by R202 and measured at T3, the Lock Guard
routine is engaged. The Lock Guard will set the SER O OUTPUT to the value it held
immediately before the detected unlock event, wait for the Hold Time (see below for setting the
Hold Time) and then re-engage the lock. If the SER O OUTPUT jumps again after this relock
attempt, the relock routine will attempt a second relock, but only after the Settle Time (see below
for setting the Settle Time) has passed since the previous relock attempt.
Mode A,B,C
These three 2-position slider switches are only accessible by removing the right side panel (see
above) and set the Hold Time and Settle Time described above. The 3 positions of A,B,C form a
binary scale factor given by the table below:
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Vescent Photonics D2 Series Product Manual
A B C Hold
Time
Settle Time
Off Off Off 60 µs 150 µs
On Off Off 125µs 300 µs
Off On Off 250 µs 600 µs
On On Off 500 µs 1.25 ms
Off Off On 1 ms 2.5 ms
On Off On 2 ms 5 ms
Off On On 4 ms 10 ms
On On On 8 ms 20 ms
The ideal delay used will depend on your system and loop bandwidth. Generally, faster detection
of an unlock event and slower Hold and Settle Time is ideal, however, sometimes the system
needs time to stabilize after a large correction and these settings enable the user to adjust how
long to wait to let the system stabilize before re-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 positives when the system remains locked but the SER O OUTPUT is
moving quickly to respond to a challenge.
1.3.4. Back-panel Section
Power I/O (9-pin D-sub)
The power to each electronics module is through a 9-pin D-sub connector through escent
provided power bridge cable. The pin outs are shown in the following figure:
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Vescent Photonics D2 Series Product Manual
Absolute Jump TTL (BNC)
When asserted HIGH (5 ) 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 SER O
OUTPUT. Thus, a 1 input to LASER JUMP AMPLITUDE applies -1 to SER O
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 (0 ), the loop filter is reengaged with the integrator initially at the value input
at LASER JUMP AMPLITUDE. Engaging or disengaging the ABSOLULTE JUMP is achieved
in under 400 μs.
When asserted HIGH (5 ) while in RAMP mode, ABSOLULTE JUMP applies a DC offset
equal to the LASER JUMP AMPLITUDE to the ramp signal at SER O OUTPUT. When
asserted LOW while in RAMP mode, the ramp signal is DC balanced.
When disconnected, ABSOLULTE JUMP is low.
Relative Jump TTL (BNC)
When asserted HIGH (5 ) while in LOCK mode, RELATI E JUMP engages a sample-and-hold
circuit and takes the Laser Servo out of lock. The voltage on the SER O OUTPUT is the sample-
and-hold value summed in with the LASER JUMP AMPLITUDE. For example, if the laser is
locked and the SER O OUTPUT is -200 m , then engaging the RELATI E JUMP and putting
300 m on the LASER JUMP APPLITUDE will make the SER O OUTPUT 100m (-200 m
+ 300 m ). 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 ), the loop filter is reengaged,
enabling the laser to be relocked to its original position (by setting LASER JUMP AMP to zero),
or to a new lock point determined by the value at LASER JUMP AMPLITUDE. Engaging or
disengaging the RELATI E JUMP is achieved in under 400 μs.
When asserted HIGH (5 ) while in RAMP mode, RELATI E JUMP applies a DC offset equal
to the LASER JUMP AMPLITUDE to the ramp signal at SER O OUTPUT. When asserted
LOW (0 ) while in RAMP mode, the ramp signal is DC balanced.
When disconnected, RELATI E JUMP is low.
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