Vescent Photonics D2 Series User manual

Offset Phase
Lock Servo
Vescent Photonics, Inc.
www.vescentphotonics.com
4865 E. 41st Ave
Denver, CO 80216
Phone [phone]
Fax [phone]

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 Jul 11, 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. Offset Phase Lock Servo
Model No. D2-135
Document Revision: 2
1.1. Description
The D2-135 Offset Phase Lock Servo (OPLS) locks the frequency and phase of the input beat-note to a
(multiple of the) reference frequency. The beat-note is typically generated by overlapping two lasers (a
master laser and a slave laser), whose interference forms a beat-note, which is a measurement of the
frequency difference (or offset) between the two lasers. The beat-note is either input as an electrical signal
via an SMA electrical connector (D2-135-SMA) or as an optical signal via a fiber (D2-135-FC). The
reference frequency can be sourced internally from voltage controlled oscillator ( CO) or an externally
from a user-input frequency reference. The output of the OPLS adjusts the frequency of the slave laser to
lock the frequency offset between the two lasers.
The beat-note input to the OPLS can be divided by N = 8, 16, 32, or 64 -- as set by the user – before its
frequency and phase is compared to the reference frequency. The locked frequency offset is given by the
formula:
Offset = N x Reference Frequency.
By adjusting either the reference frequency or N, the frequency difference between the lasers can be
precisely adjusted. The offset frequency is adjustable from 250 MHz to up to 10 GHz.
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Vescent Photonics D2 Series Product Manual
A schematic of the OPLS, along with the D2-150 Heterodyne module is shown in Figure 1.The key
component in the OPLS is a phase-frequency detector (PFD). The PFD compares the phase and frequency
of the divided-by-N beat-note to the reference frequency. The PFD outputs a signal proportional to the
phase difference between the two input frequencies when there are no phase-slips between the two
signals. This output provides a true phase-lock error signal. When there are phase slips, the PFD acts as a
frequency comparator, aiding initial lock-up and enabling the OPLS to function as a frequency offset lock
for laser sources with significant phase noise such as DFB and DBR laser diodes. The output of the PFD
is fed to a charge pump and finally to the loop filter, where it is then fed back to the slave laser to control
the frequency of the beat-note.
The loop filter has user-adjustable proportional-integral-differential (PID) feedback and an additional
high-frequency roll-off frequency. Tuning the values of the PID loop filter allow the user to optimize the
feedback to the laser for best offset locks. This is further discussed in Section 1.7.
The OPLS can be controlled via the front-panel, or with a computer via a 9 pin D-sub connector and BNC
connections on the back of the OPLS. In this way, the frequency offset can be jumped and tuned via an
external computer.
The D2-150 Heterodyne Module is designed for use the with D2-135-FC.
1.2. Options
The D2-135 comes in two different versions:
•D2-135-SMA – SMA input of the electrical beat-note
•D2-135-FC-800 – Fiber-input of optical beat-note for wavelengths 750nm – 870nm
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Figure 1: Schematic of the D2-135 Offset Phase Lock Servo and
D2-150 Heterdyne Module

Vescent Photonics D2 Series Product Manual
The D2-135-SMA requires an electrical signal input between 10 and -10 dBm of power.
The D2-135-FC-800 includes a 10 GHz GaAs high-speed photo-detector for converting the input optical
beat-note into a electrical beat-note. The maximum optical input power is 1 mW. Warning input powers
over 1mW of optical power can damage the OPLS. A minimum of 50 μW of power in the optical beat-
note is required1.
1 Note the power in the beat-note is not the same as total power. Because the optical input uses multi-mode fiber, the
spatial mode overlap between the two lasers is not guaranteed. If the overlap between the two lasers is poor, there
can be very little power in the beat-note despite large optical power.
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Vescent Photonics D2 Series Product Manual
1.3. Specifications
Value Units
Min Offset Fre uency2<250 MHz
Max Offset Fre uency Min: 9, Typical: 103GHz
VCO drift 500 ppm/°C
PFD Noise4-213 dBc/Hz
ωI (Integral/Prop. zero) 4,8,16,32,64,125,250,500 kHz
ωD (Proportional/diff. zero) 16,32,64,125,250,500,1000,off kHz
ωHF (high freq. cutoff pole) 0.25, 0.5, 1,2,4,8,16,off MHz
Electronics Input / Output Impedance 50 Ω
User Adjustable Gain50 -50 dB
Max Electronic Beat-Note Input (D2-135-SMA) 10 dBm
Min Electronic Beat-Note Input (D2-135-SMA) -10 dBm
Max Optical Beat-Note Input (D2-135-FC) 1 mW
Min Optical Beat-Note Input (D2-135-FC)650 μW
2 Low frequency beat-notes are possible with the D2-135-SMA provided the low-frequency beat-note is a square-
wave and not sine-wave input and that the loop bandwidth ~10 times lower than your reference frequency.
3 Maximum Offset Frequency depends on power of input beat-note signal.
4 See Section 1.8. for a full description
5 Not including internal gain compensation for N divider. See Section 1.6. for more details.
6Approximate value as exact value depends on wavelength of the light and spatial overlap between the lasers.
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