LASER DIODE TO FIBER COUPLERS.qxd
219 Westbrook Rd, Ottawa, ON, Canada, K0A 1L0 Toll Free: 1-800-361-5415 Tel:(613) 831-0981 Fax:(613) 836-5089 E-mail: [email protected]
LASER DIODE TO FIBER COUPLERS
OZ Optics offers a complete line of laser diode to fiber
couplers, offering optimum coupling in a small, rugged
package. They may be purchased prealigned, with the
diode already in place, or as a kit that can be assembled
by the customer using their own diode. The complete
assembly procedure is quite straightforward, and can be
done in less than twenty minutes. Assembly and operating
instructions are available in a video cassette, showing the
alignment process. The video is available in both North
America and European (PAL) versions. In addition, a
complete alignment kit is available, which includes the
collimating wrench, multimode fiber assembly, centering
lens, and video instructions.
female receptacle, such as NTT-FC, or AT&T-ST, etc. at
the output end. This allows the user to connect any optical
fiber with a matching male connector to the diode. Pigtail
style laser diode to fiber couplers are also offered, with the
fiber pigtailed directly onto the coupler. Pigtail style laser
diode to fiber couplers provide higher coupling efficiencies
than receptacle style couplers, as well as better stability,
and lower backreflection levels. The output fiber can also
be terminated with different output connectors.
Diode source couplers are available for a variety of diode
case sizes, and for diode wavelengths from less than
630nm to greater than 1550nm. These source couplers
work with multimode, singlemode, and polarization
maintaining fiber. Should the diode ever fail, it can be
easily replaced while using the rest of the coupling optics.
The source coupler can then be realigned for optimum
coupling. This is one of the main advantages of using the
OZ Optics tilt adjustment technique.
Laser diode to fiber couplers are available in different
diameters. The standard diameter package is 0.79 inches
in diameter. This size fits most diode types, and is
available for both receptacle style and pigtail style
couplers. For the best coupling efficiencies choose the
larger, 1.3 inch diameter housing, which supports larger
and higher quality lenses. This housing size is also used
with large diode case sizes, such as H1 package sizes.
For pigtail style source couplers, a smaller 0.59" diameter
housing is available for diode can sizes 9.0mm in diameter
or smaller. For diodes with can diameters of 5.6mm or
less, a miniature 0.5" diameter tilt adjustable housing is
possible.
There are two versions of tilt adjustable laser diode to fiber
couplers; receptacle style couplers, and pigtail style
couplers. Connector receptacle style couplers have a
One misconception about tilt adjustable laser diode
couplers is the belief that the number of tilt and
lockingscrews make the coupler sensitive to temperature
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09/99 OZ Optics reserves the right to change any specifications without prior notice.
or vibration. In fact, tilt adjustable source couplers can be
used over a temperature range of -25°C to 60°C, and have
been vibration tested. Higher temperature versions are
available on request.
OZ Optics also offers a special, low cost, miniature
pigtail style laser diode to fiber couplers for OEM
applications. These packages use just a single lens to
couple light from the laser diode into the fiber. They do not
use OZ Optics tilt adjustment technique. This package
features a compact, rugged housing, at a significantly
lower cost. The housing diameter is typically 10mm.
Coupling efficiency into singlemode and multimode fibers is
typically 10 percent and 35 percent, respectively.
A variety of options are available for laser diode to fiber
couplers. One such option is a coupler with a built in
isolator. Isolators can reduce the effects of backreflection
by up to 60dB. This is done by using coated optics and
angled polished fibers. This is very useful for applications
where the intensity and wavelength stability of the output
light from the diode is critical.
Self contained systems are available in both a pocket size
casing, as well as a miniature pen size housing. Both
receptacle style and pigtail style systems are available. OZ
Optics can also provide fiber pigtailed collimators for your
system.
OZ Optics has in stock a selection of laser diodes. In
addition we can package customer specified laser diodes.
OZ Optics also provides laser diode power supplies and
drivers, as well a thermoelectric Peltier coolers. Please
refer to the Fiber Optic Stable Source & TE Cooled Laser
Diode Housing Data Sheet.
OPERATING PRINCIPLE
Another option for laser diode to fiber couplers is a blocking
screw to attenuate the output beam. This allows the user
to precisely control the output power entering the fiber,
without having to change the diode current. Another option
is laser diode to fiber couplers with polarizer or polarization
Rotator in the middle.
Laser Diode to Fiber Coupler with
Polarization Rotator in the middle
LIGHT SOURCES
OZ Optics also has available self contained laser diode to
fiber delivery systems, with battery operated power
supplies. AC to DC converters are also available. These
systems provide a compact, portable source of light to
attach to an optical fiber for test and measurement
systems. They are used in a variety of applications,
including fault detection, laser acupuncture, fluorescence
measurements, etc.
Laser diode to fiber couplers with tilt adjustment use a two
stage process to couple light from the laser diode into the
fiber. In the first stage, the output light from the diode is
collimated with a collimating lens. The distance between
the diode and the collimating lens is easily adjusted with a
collimator wrench, then locked with a radial set screw. The
collimated beam is then coupled into the fiber with a
second lens, using OZ Optics' patented tilt alignment
technique. The focal lengths of the collimating and
coupling lenses are carefully selected to transform the
optical properties of the laser diode light to match the mode
field pattern of the fiber as closely as possible. Coupling
efficiencies of over 50 percent into singlemode fiber, and
80 percent into multimode fibers, can be achieved with
certain diodes with the correct choice of lenses. Coupling
efficiencies into singlemode fibers better than 80% are
possible with certain diodes by correcting the diode
astigmatism and the ellipticity of the diode output with a
miniature cylindrical type lens. Contact OZ Optics for
further information about this technique.
Before building a laser diode to fiber coupler, OZ Optics
has to choose an appropriate lens combination to
maximize coupling efficiency. To do so, we need to know
the following laser diode characteristics: (1) Diode
wavelength (2) Output power (3) Diode can size (4) Emitter
dimensions (5) Far field divergence angles (6)
Astigmatism. In addition, the diode selected should exhibit
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good pointing stability over time.
SPECIFICATIONS
Coupling Efficiency:
Backreflection levels:
Wavelength range:
Operating temperature:
Output extinction ratios:
75% to 85% for multimode fibers, 35%-55% for singlemode (SM) or polarization maintaining (PM)
fibers. Coupling efficiencies greater than 75% into SM or PM fibers are also possible for certain
diodes.
Typically -15dB for receptacle style versions, and either -25dB, -40dB, or -60dB for pigtail style
versions. (-60dB is available for 1300nm and 1550nm only.)
600nm to 1600nm.
-20°C to +60°C.
Typically greater than 20dB for PM fibers. 30dB versions are available on request for 1300 and
1550nm only
ORDERING INFORMATION
When ordering laser diode to fiber couplers, please specify the laser diode characteristics (diode type, angular beam profile,
housing dimensions, etc.). If possible, please fax us the diode manufacturer's specification sheet before ordering. For pigtail
style laser diode to PM fiber couplers please indicate whether you wish to align the slow axis or the fast axis of the PM fiber with
respect to the diode output. The OZ Optics standard is to align the PM fiber such that the diode output is transmitted along the
slow axis of the fiber.
Part Number
HULD-AX-W-F-C
LDPC-0A-W-a/b-F-LB-X-JD-L-C
VIDEO-01-NTSC (or PAL)
MMJ-X1-50/125-3-0-1
LDC-21 (or LDC-21A)
ALIGN-0X-NTSC (or PAL)
Where:
Description
Laser diode to fiber source coupler with connector receptacle.
Pigtail style laser diode to fiber source coupler.
Video instructions for using OZ Optics' components. Please indicate whether an
American (NTSC) or European (PAL) standard video is required.
One meter long multimode jumper assembly for performing initial alignment of
singlemode laser to fiber couplers.
Alignment wrench for adjusting the laser diode collimation.
Alignment kit for laser diode to singlemode fiber source couplers, containing a
collimating wrench, a multimode jumper assembly, written instructions, and instructional
video. Please indicate whether an American (NTSC) or European (PAL) standard video
is required.
A is the diameter of the diode package. (Use 1 for the standard 0.79" diameter package size, 2 for the higher
performance 1.3" diameter package, 3 for compact 0.59" diameter, and 4 for the miniature 0.50" diameter. Note that
due to limitations in the size of the diode being used, not all package sizes are available for every diode.)
X is the receptacle type for connector style laser diode to fiber source couplers. For pigtail style laser diode to fiber
couplers, it refers to the male connector on the fiber end (3 for FC, 5 for SMA 905, 8 for AT&T-ST, SC for SC
connectors, etc. Use X for unterminated fibers for pigtail style laser diode to fiber couplers.)
W is the laser diode wavelength in nm;
a/b are the fiber core and cladding diameters, respectively, in microns;
F is the type of fiber being used (S for singlemode, M for multimode, P for polarization maintaining fiber);
C is the desired coupling efficiency (35%, 45% or 75% typical efficiencies for singlemode couplers, 75% typically for
multimode fibers). Note that due to limitations in the diode optical characteristics, not all of the coupling efficiencies
listed are possible with every diode. Contact OZ Optics for further technical help.
LB is the desired backreflection level for pigtail style laser diode to fiber couplers. (25, 40 or 60 dB typically);
JD is the fiber jacket type (1 for uncabled fiber, 3 for 3 mm OD loose tube kevlar, 3A for 3mm OD armored cable, and
5A for 5mm armored cable);
L is the fiber length in meters;
Options: If OZ Optics is to supply the laser diode, then add the term "-LD" to the part number. If you require a power supply
as well, then add the term "-PS" to the part number. For a blocking screw, add the term "-BL" to the part number. Add “-PO”
to the part number for parts only, if customer wants to do the alignment. Add “-DR” to the part number for laser diode driver
circuit.
APPLICATION EXAMPLES
1. A pigtail style laser diode to fiber coupler is needed to couple light from a 1300nm laser diode into a PM fiber. The output
fiber is to be one meter long, cabled with 3.0mm kevlar cable, and with an NTT-FC connector on the end. The backreflection
level is to be less than 40dB. A coupling efficiency of 45% is desired. The slow axis of the fiber is to be aligned with the
polarization axis of the output light from the diode. The customer wants OZ Optics to supply the laser diode and a power supply
for the diode. OZ Optics' part number: LDPC-01-1300-9/125-P-40-3-3.0-1-45-LD-PS.
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QUESTIONS AND ANSWERS
Q: Does the diode chip have to be centered with
respect to the outer diode housing?
Q: What type of laser diode should I choose for my
application?
A:
A: Normally, the choice of laser diode wavelength, output
power, line width, and modulation rate will drive your
choice in choosing a laser diode. The remaining
information can be found from the diode
manufacturer's data sheets. In choosing between
similar diodes, keep the following points in mind:
Diode can size: Ideally, the can dimensions should
be as small as possible. The critical dimension is the
distance between the laser diode chip and the outside
of the optical window on the can. For maximum
flexibility, this distance should be less than or equal to
1.1mm. Diodes with longer separations can be used,
but this means using longer focal length lenses, which
will affect the package size.
Emitter Dimensions: The smaller the emitter area is,
the easier it is to couple the light into a fiber. Most
diodes have emitting areas of the order of one to three
microns in size. It is usually easy to get good coupling
efficiency into a singlemode fiber with this chip size.
However some diodes, particularly very high power
diodes, have much larger dimensions (100 microns,
for instance). These diodes can only be efficiently
coupled to multimode fibers with similar core sizes.
Far field divergence angles/Astigmatism: These
two properties are closely related. Ideally, the
divergence angles should be as small as possible.
Typical divergence angles are about 10° by 30°.
Furthermore, the difference between the two angles,
which is limited by the diode's astigmatism, should be
as little as possible.
Pointing Stability: Some diodes show changes in
the pointing direction of their output over time. This
could be a serious problem when coupling the laser
diode output into a singlemode fiber. Contact the
diode manufacturer for information about their diode's
specifications.
Q: Is there any way to achieve greater than the 45%
coupling efficiency normally specified for a
singlemode laser diode to fiber coupler?
A:
Q: Can the level of backreflected light going back
into the laser diode cavity be reduced without
having to use an isolator?
Yes. In certain cases a cylindrical microlens can be
added to the laser diode to reduce the astigmatism
and aspect ratio. Coupling efficiencies of up to 80
percent have been achieved using this method.
However, this usually means removing the diode can
from the diode. The can is then soldered back on.
Contact OZ Optics for more information on this
technique.
Q: I have a laser diode mounted on an open chip
carrier. How can I use a laser diode to fiber
coupler with it?
A:
The laser diode chip must first be attached to a laser
diode holder. The laser diode and laser diode holder
can then be attached to the collimating lens assembly
and focusing optics.
OZ Optics has several different type of laser diode
holders already in stock, and custom diode holders
can be manufactured to meet your needs. Contact
OZ Optics for further information.
Q: I want to convert the output from a laser diode
into a Gaussian beam. Can I do this without using
cylindrical lenses or anamorphic prisms?
A:
Q: If the diode fails, do I have to throw out the whole
assembly?
A: No. This is one of the main advantages of the OZ
Optics adjustable tilt design. The lenses and optical
fibers can be easily reused. Simply put the new diode
into a new laser diode holder, collimate it using the old
collimating lens assembly, and focus the collimated
beam into the fiber using the old focusing optics.
No. This is one of the advantages of the OZ Optics
design. There is no need for tight tolerances on the
diode chip location. Any offset in the lateral position
of the laser diode chip can be easily compensated for
at the focusing optics, using the patented tilt
adjustment technique.
Yes.
Couple the light into a singlemode or
polarization maintaining fiber using a laser diode to
fiber coupler. The fiber acts as an excellent spatial
filter, giving an almost ideal Gaussian output beam.
Wavefront distortion can be as low as l/50. The fiber
output can then be easily collimated using a lens. OZ
Optics offers a wide variety of fiber optic collimators
for this purpose.
Q: Can optical amplifiers be pigtailed as well as laser
diodes?
A:
Yes. Optical amplifiers emit a little light in both
directions when operated at low currents. This light
can be collimated, then coupled into an optical fiber.
By doing this on both sides of the coupler, the
amplifier can be pigtailed.
A: Yes. First, the laser diode chip should be positioned
slightly off center with respect to the collimating lens
assembly. This prevents reflections from traveling
straight back into the cavity. Secondly, The input end
of the fiber can be polished at an angle. Finally, the
output end of the fiber can be angle polished, or index
matching gel can be used on the output end of the
fiber.
By combining these techniques, typical
backreflection levels of up to -40dB can be achieved.
In addition, backreflection levels as low as -60 dB are
possible by applying an AR coating to the fiber tips.
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