Vescent Photonics D2 Series Manual de usuario
Reconfigurable
Laser Servo
Vescent Photonics, Inc.
www.vescentphotonics.com
4865 E. 41st Ave
Denver, CO 80216
Phone (303)-296-6766
Fax (303)-296-6783
info@vescent.com
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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