Vescent D2 Series User manual

DBR
Laser Module
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 Jun 10, 2008

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
Stage 2 Temperature of DBR Laser Diode >15°C and <40°C
Laser Diode Current 180mA

Vescent Photonics D2 Series Product Manual
1. DBR Laser Module
Model No. D2-100
1.1. Description
The DBR laser module is comprised of a distributed feedback (DBR) laser diode in a precision
temperature-controlled housing with beam conditioning optics and an optical isolator. DBR laser diodes
are fabricated with the feedback grating patterned directly over the gain section of the diode. They are
highly immune to vibrations and by virtue of a very short cavity (~ 1 mm), they can be current tuned over
more than 50 GHz. The result is a robust laser capable of very fast servo control for easy locking to
atomic transitions. The module contains no moving parts or piezo-electrics and is therefore inherently
robust and rugged.
DBR lasers have 2-3 times larger temperature and current tuning coefficients as compared to external-
cavity diode lasers. escent carefully controls these parameters with two stages of temperature control
and a precision low-noise current controller with fast servo input.
The DBR laser is collimated by a 0.55 NA lens mounted to a movable plate for pointing adjustments.
The module also comes with a 35 dB optical isolator and a pair of anamorphic prisms. (Note that prior to
fiber coupling we recommend a second stage of isolation.)
The temperature controllers use an 8-pin circular connector on the back of the DBR subassembly. The
injection current connection to the laser diode is through an SMA connector also on the back of the DBR
subassembly.
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Vescent Photonics D2 Series Product Manual
The DBR laser chip is contained in a thermal package allowing temperature control between 0° to 50° C.
escent can replace the package if it exceeds its lifetime.
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Figure 1: The DBR laser module.
Anamorphic
pris ms
Stage 1
TEC
DFB
assy
Anamorphic
pris ms
Isolator
Stage 1
TEC
DFB
ass y
Lens set
screw
access
Anamorphic
pris ms
Stage 1
TEC
DFB
assy
Anamorphic
pris ms
Isolator
Stage 1
TEC
DFB
ass y
Lens set
screw
access
Figure 2: Exploded view of the DBR subassembly.
Laser pkg
Feedthru
TEC
Laser holder
DFB on c-mount
Coverplate w window
Collimation lens
Lens plate
Lock Sc rews
DFB housing
Lens plate
adjustment screws
(0.050” Allen)
Laser pkg
Feedthru
TEC
Laser holder
DFB on c-mount
Coverplate w window
Collimation lens
Lens plate
Lock Sc rews
DFB housing
Lens plate
adjustment screws
(0.050” Allen)

Vescent Photonics D2 Series Product Manual
1.2. Specifications
Min. Typical Ma . Units
Wavelength 780.24 nm
Output power 30 40 50 mW
Beam diameter 0.8 1.1 1.7 mm
(1/e2 dia.)
Polarization Horizontal
Optical isolation 35 dB
Operating current 150 180 mA
Threshold Current 40 50 70 mA
Temperature range
Stage 1, housing
Stage 2, laser
15
0
20
15
40
50 (1)
°C
Temperature stability See Laser Controller,
Model No. D2-105
Safety Class 3B
Beam height 0.95 inches
Total package Size
(L x W x H) 3.75 x 4 x 2 inches
1.3. Inputs, Outputs, and Controls
Vertical and horizontal pointing
The vertical and horizontal alignment of the laser system is factory set and should not need
adjustment. However, if your specific application requires it or the system is misaligned, the
DBR subassembly has adjustments to steer the beam for alignment to the spectroscopy module or
other modules. The beam pointing is adjusted by loosening the three lock screws ½ turn past the
crack point and adjusting the x and y positioning setscrews on the top and left side (facing out
along the laser beam) of the module (see Figure 3). For more detailed instructions, see section
1.4.
1Operation above 40° C can reduce the lifetime of the laser diode
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Vescent Photonics D2 Series Product Manual
Beam Conditioning
The collimation of the output beam is set at the factory and should not be adjusted unless
absolutely necessary. Remove the isolator subassembly from the baseplate with the 4 screws
accessible from the bottom. The locking set screw on the right side of the DBR subassembly can
then be loosened and the lens repositioned with a 9 mm spanner wrench (Thorlabs, SPW301).
Tighten the locking screw and reattach the isolator subassembly.
Laser diodes all have astigmatism, which means the horizontal and vertical axis have different
foci. escent uses a powerful asphere with a short focal length and an anamorphic prism pair to
create a small diameter circular beam. This reduces the costs of the isolator and other downstream
modules by reducing the clear aperture requirements. While the aspheres and anamorphic prisms
produce a circular beam, astigmatism dictates that a single lens will not simultaneously collimate
both orthogonal axes of the beam with the result that in the far field the beam is again elliptical.
The far-field pattern is the most important for ascertaining the quality of the diode output. The
near-field pattern often shows stray light from the diode waveguide and ASE that doesn’t
propagate as part of the primary beam. However, aberrations and beam clipping due to an
insufficient lens NA will show up as fringes-on the far field pattern. escent has taken care in
the design of the DBR laser module to keep aberrations and clipping to a minimum, resulting in a
clean beam in the far field.
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Figure 3: Lock screws and beam pointing controls.
Lock Screws
Horizontal adj.
ertical adj.
Lock Screws
Horizontal adj.
ertical adj.

Vescent Photonics D2 Series Product Manual
Cable Connector
The connections to the TECs and thermisters are made to an 8-pin circular connector. The pin
definitions are:
Pin Signal
1 TEC1+
2 TEC1-
3 Rth-1
4 Rth1-RTN
5 TEC2+
6 TEC2-
7 Rth2
8 Rth2-RTN
NOTE: Earlier models use a push-pull connector for the 8-pin connector to the DBR module. To remove
take care to apply opposition forces with the thumb and forefinger knuckles against the housing.
Excessive force could displace the output beam and require realignment.
Laser Current (SMA)
Current is provided to the DBR chip through an SMA connector. The central conductor of the
SMA connects to the laser anode, and the shield connects to the laser cathode. This is a direct,
unprotected connection to the DBR chip, so care must be taken to avoid ESD damage.
1.4. Aligning the DBR Laser Module
The module should not need adjustments, but if necessary the following procedure can be used to fine
tune the beam positioning.
1. Loosen the three locking screws on the back of the DBR module ½ turn past the crack point.
2. With a 0.050” Allen driver, adjust the vertical adjustment setscrew on the top of the DBR housing
to level the beam.
3. Adjust the horizontal adjustment 4-40 set screw on the left side of the DBR housing (See Figure
3).
4. Alternatively, use the spectroscopy module as a beam target. Place the spectroscopy module as
far down the table as possible, bolt it down, and center the beam to the input hole.
5. Gently retighten the three locking screws.
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