U.S. patent number RE41,840 [Application Number 11/332,804] was granted by the patent office on 2010-10-19 for method and apparatus for maintaining alignment of a laser diode with an optical fiber.
Invention is credited to Richard A. Booman, Ernest Charles Gilman, Edward L. Hershberg, Dana L. Patelzick.
United States Patent |
RE41,840 |
Gilman , et al. |
October 19, 2010 |
**Please see images for:
( Certificate of Correction ) ** |
Method and apparatus for maintaining alignment of a laser diode
with an optical fiber
Abstract
A method and apparatus for maintaining an alignment of a laser
diode with an optical fiber is disclosed. A mounting plate is made
of a first material, and mounted on the mounting plate is a first
substrate made of a second material. A semiconductor laser, with a
light emitting side, is mounted on the first substrate. Separated
from the first substrate by a predetermined distance is a second
substrate made of a third material, and mounted on the second
substrate is an optical fiber. The optical fiber is mounted, such
that, the optical fiber is adjacent to and aligned with the light
emitting side of the semiconductor laser. The first, second, and
third materials making up the mounting plate, the first substrate,
and the second substrate respectively, facilitate maintenance of
the alignment between the optical fiber and the light emitting side
of the semiconductor laser.
Inventors: |
Gilman; Ernest Charles
(Beaverton, OR), Patelzick; Dana L. (West Linn, OR),
Hershberg; Edward L. (Portland, OR), Booman; Richard A.
(Lake Oswego, OR) |
Family
ID: |
30001171 |
Appl.
No.: |
11/332,804 |
Filed: |
January 12, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
09896128 |
Jun 29, 2001 |
06679636 |
Jan 20, 2004 |
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Current U.S.
Class: |
385/90; 385/88;
385/92; 385/147; 385/93; 385/94; 385/89; 372/36; 372/45.01;
385/91 |
Current CPC
Class: |
G02B
6/4202 (20130101); G02B 6/4238 (20130101) |
Current International
Class: |
G02B
6/36 (20060101) |
Field of
Search: |
;385/88-94,147
;372/36,45.01 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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03142892 |
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Jun 1991 |
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JP |
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03-142892 |
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Jun 1991 |
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JP |
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Other References
Office Action, issued in U.S. Appl. No. 09/896,128, mailed Jan. 24,
2003. cited by other .
Notice of Allowance, issued in U.S. Appl. No. 09/896,128, mailed
Sep. 25, 2003. cited by other.
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Primary Examiner: Sanghavi; Hemang
Attorney, Agent or Firm: Schwabe, Williamson & Wyatt,
P.C.
Claims
What is claimed is:
1. An apparatus comprising: a mounting plate comprising a first
material; a first substrate mounted on the mounting plate, the
first substrate comprising a second material; a semiconductor laser
mounted on the first substrate, the semiconductor laser having a
light emitting side; a second substrate mounted on the mounting
plate and separated from the first substrate by a predetermined
distance, the second substrate material including a shelf formation
above the mounting plate, the second substrate comprising a third
material; and an optical fiber mounted on the second substrate, the
optical fiber being adjacent to and aligned with the light emitting
side of the laser, wherein the first, second and third materials
being complementary in thermal characteristic to facilitate
maintenance of the alignment between the optical fiber and the
light emitting side of the laser.
2. The apparatus of claim 1, wherein the first material is a
conductor of heat.
3. The apparatus of claim 1, wherein the first material comprises
at least one of a CuW alloy, a CuMo alloy, and pure Mo.
4. The apparatus of claim 1, wherein the first material comprises a
thermal conductivity value: the thermal conductivity value being at
least 160 W/m.sup.2K/m; and the thermal conductivity value being no
more than 185 W/m.sup.2K/m.
5. The apparatus of claim 1, wherein the first material comprises a
coefficient of thermal expansion (CTE) value, and the CTE being
linear and measured at 20.degree. C.: the CTE value being at least
6.1 .mu.m/m.degree. C.; and the CTE value being no more than 7.36
.mu.m/m.degree. C.
6. The apparatus of claim 1, wherein the first material comprises a
thermal conductivity value: the thermal conductivity value being at
least 140 W/m.sup.2K/m; and the thermal conductivity value being no
more than 175 W/m.sup.2K/m.
7. The apparatus of claim 1, wherein the first material comprises a
CTE value, and the CTE value being linear and measured at
20.degree. C.: the CTE value being at least 6.5 .mu.m/m.degree.
C./; and the CTE value being no more than 7.2 .mu.m/m.degree.
C.
8. The apparatus of claim 1, wherein the first material comprises a
thermal conductivity value of 138 W/m.sup.2K/m.
9. The apparatus of claim 1, wherein the first material comprises a
CTE value of 5.35 .mu.m/m.degree. C., and the CTE value being
linear and measured at 20.degree. C.
10. The apparatus of claim 1, wherein the second material is a
conductor of heat.
11. The apparatus of claim 1, wherein the second material comprises
at least one of an AIN and BeO.
12. The apparatus of claim 1, wherein the second material comprises
a thermal conductivity value: the thermal conductivity value being
at least 90 W/m.sup.2K/m; and the thermal conductivity value being
no more than 170 W/m.sup.2K/m.
13. The apparatus of claim 1, wherein the second material comprises
a CTE value, and the CTE value being linear and measured at
20.degree. C.: the CTE value being at least 4.2 .mu.m/m.degree. C.;
and the CTE value being no more than 4.3 .mu.m/m.degree. C.
14. The apparatus of claim 1, wherein the second material comprises
a thermal conductivity value of 248 W/m.sup.2K/m.
15. The apparatus of claim 1, wherein the second material comprises
a CTE value of 6.4 .mu.m/m.degree. C., and the CTE being linear and
measured at 20.degree. C.
16. The apparatus of claim 1, wherein the third material is a
thermally insulating material.
17. The apparatus of claim 1, wherein the third material is an
aluminum oxide.
18. The apparatus of claim 1, wherein the third material comprises
a thermal conductivity value of no more than 28 W/m.sup.2K/m.
19. The apparatus of claim 1, wherein the third material comprises
a CTE value of no more than 7.4 .mu.m/m.degree. C., and the CTE
being linear and measured at 250.degree. C.
20. The apparatus of claim 1, wherein the apparatus is an optical
networking module.
21. The apparatus of claim 1 wherein the optical fiber is mounted
upon the shelf formation of the second substrate material.
22. An apparatus comprising: a mounting plate, the mounting plate
comprising a first material; a first substrate mounted on the
mounting plate, the first substrate comprising a second material;
an semiconductor laser mounted on the first substrate, the
semiconductor laser having a light emitting side; a second
substrate mounted on the mounting plate substantially in contact
with the first substrate, the second substrate material including a
shelf formation above the mounting plate, the second substrate
comprising a third material; and an optical fiber mounted on the
second substrate, the optical fiber being adjacent to and aligned
with the light emitting side the laser.
23. The apparatus of claim 22, wherein the first material comprises
at least one of a CuW alloy, a CuMo alloy, and pure Mo.
24. The apparatus of claim 22, wherein the first material comprises
a thermal conductivity value: the thermal conductivity value being
at least 160 W/m.sup.2K/m; and the thermal conductivity value being
no more than 185 W/m.sup.2K/m.
25. The apparatus of claim 22, wherein the first material comprises
a coefficient of thermal expansion (CTE) value, and the CTE being
linear and measured at 20.degree. C.: the CTE value being at least
6.1 .mu.m/m.degree. C.; and the CTE value being no more than 7.36
.mu.m/m.degree. C.
26. The apparatus of claim 22, wherein the first material comprises
a thermal conductivity value: the thermal conductivity value being
at least 140 W/m.sup.2K/m; and the thermal conductivity value being
no more than 175 W/m.sup.2K/m.
27. The apparatus of claim 22, wherein the first material comprises
a CTE value, and the CTE value being linear and measured at
20.degree. C.: the CTE value being at least 6.5 .mu.m/m.degree.
C./; and the CTE value being no more than 7.2 .mu.m/m.degree.
C.
28. The apparatus of claim 22, wherein the first material comprises
a thermal conductivity value of 138 W/m.sup.2K/m.
29. The apparatus of claim 22, wherein the first material comprises
a CTE value of 5.35 .mu.m/m.degree. C., and the CTE value being
linear and measured at 20.degree. C.
30. The apparatus of claim 22, wherein the second material
comprises at least one of an AIN and BeO.
31. The apparatus of claim 22, wherein the second material
comprises a thermal conductivity value: the thermal conductivity
value being at least 90 W/m.sup.2K/m; and the thermal conductivity
value being no more than 170 W/m.sup.2K/m.
32. The apparatus of claim 22, wherein the second material
comprises a CTE value, and the CTE value being linear and measured
at 20.degree. C.: the CTE value being at least 4.2 .mu.m/m.degree.
C.; and the CTE value being no more than 4.3 .mu.m/m.degree. C.
33. The apparatus of claim 22, wherein the second material
comprises a thermal conductivity value of 248 Wm.sup.2K/m.
34. The apparatus of claim 22, wherein the second material
comprises a CTE value of 6.4 .mu.m/m.degree. C., and the CTE being
linear and measured at 20.degree. C.
35. The apparatus of claim 22, wherein the third material is an
aluminum oxide.
36. The apparatus of claim 22, wherein the third material comprises
a thermal conductivity value of no more than 28 W/m.sup.2K/m.
37. The apparatus of claim 22, wherein the third material comprises
a CTE value of no more than 7.4 .mu.m/m.degree. C., and the CTE
being linear and measured at 250.degree. C.
38. The apparatus of claim 22 wherein the apparatus is an optical
networking module.
39. The apparatus of claim 22 Wherein the optical fiber is mounted
upon the shelf formation of the second substrate material.
.Iadd.40. An apparatus, comprising: a mounting plate, the mounting
plate comprising a first material; a first substrate mounted on the
mounting plate, the first substrate comprising a second material; a
laser device mounted on the first substrate, the laser device
having a light emitting side; a second substrate mounted on the
mounting plate, the second substrate material including a shelf
formation above the mounting plate, the second substrate comprising
a third material; and an optical fiber mounted on the second
substrate, the optical fiber being aligned with the light emitting
side of the laser device..Iaddend.
.Iadd.41. The apparatus of claim 40, wherein said laser device
comprises a semiconductor laser..Iaddend.
.Iadd.42. The apparatus of claim 40, wherein said second substrate
is substantially in contact with said first substrate..Iaddend.
.Iadd.43. The apparatus of claim 40, wherein said first and second
substrates are separated by a predetermined distance..Iaddend.
.Iadd.44. The apparatus of claim 40, wherein said first material
comprises a conductor of heat..Iaddend.
.Iadd.45. The apparatus of claim 40, wherein the first, second and
third materials are complementary in thermal characteristic to
facilitate maintenance of the alignment between the optical fiber
and the light emitting side of the laser device..Iaddend.
.Iadd.46. The apparatus of claim 40, wherein said second material
comprises a conductor of heat..Iaddend.
.Iadd.47. The apparatus of claim 40, wherein said optical fiber is
mounted on said shelf..Iaddend.
.Iadd.48. The apparatus of claim 40, wherein said optical fiber is
mounted adjacent to said light emitting side of said laser
device..Iaddend.
Description
FIELD OF INVENTION
The invention relates to the field of optical components. More
specifically, the invention relates to maintaining alignment of a
laser diode with an optical fiber.
BACKGROUND OF THE INVENTION
An important aspect of optical components, such as optical
components used in telecommunications and data communications
technology (i.e., lightwave communications), is the alignment of a
light source with a light transmission medium. For example, a
semiconductor laser aligned with an optical fiber. Because the
light emitted from the semiconductor laser is transmitted via the
optical fiber, the alignment between the semiconductor laser and
the optical fiber is an important aspect of the optical
components.
The alignment of the semiconductor laser with the optical fiber is
commonly referred to as coupling. The efficiency of the
transmission of power from one medium to another (i.e.,
semiconductor laser to optical fiber) is commonly referred to as
coupling efficiency.
Prior to operation, aligning a semiconductor laser with an optical
fiber may have low coupling efficiencies, approximately 10%
corresponding to a loss in power of approximately 10 decibels. The
low coupling efficiencies may be attributable to factors such as
size and shape differences in spot sizes between the semiconductor
laser and the optical fiber, absorption, reflectance, scattering,
tolerances of the components and alignment methods involved, and so
forth. With so many factors contributing to low coupling
efficiencies, a great deal of effort is expended to increase the
coupling efficiencies and reduce the loss in power.
Efforts to increase the coupling efficiencies may involve focusing
the light from the semiconductor laser to the optical fiber,
modifying the optical fiber end, through which the optical fiber
receives the light, reducing the tolerances, and so forth.
Additionally, certain thermal methods of attaching the optical
fiber on an optical fiber mounting block may affect the alignment.
The efforts involved in increasing the coupling efficiencies and
reducing the power loss often correspond to increases in costs,
complexity, and size. As a result, once a desired coupling
efficiency is achieved, maintaining the desired coupling efficiency
is important. However, maintaining the desired coupling efficiency
during operation is difficult.
During operation, maintaining the desired coupling efficiency can
be difficult due to many factors. One factor, in particular, is the
thermal characteristics of materials involved in the optical
components.
For example, the semiconductor laser may have a temperature
characteristic, whereby, during operation, as the temperature of
the semiconductor laser increases, the required operating current
of the semiconductor laser also increases. In order to control the
temperature of the semiconductor laser, the semiconductor laser may
be mounted on a heatsink, where the heatsink conducts heat away
from the semiconductor laser at a rate corresponding to the thermal
conductivity of the material of the heatsink. Because the heatsink
absorbs the heat from the semiconductor laser, the heatsink
increases in temperature, as well. Subsequently, the heat in the
heatsink, itself, must be removed or the rate at which the heat is
transferred from the semiconductor laser to the heatsink will
decrease, and ultimately stop.
Additionally, the alignment between the semiconductor laser and the
optical fiber may change due to thermal properties of the heatsink,
such as the coefficient of thermal expansion (CTE). The CTE is a
thermal property of a material describing dimensional changes
corresponding to temperature changes in the material.
One method for removing the heat from the semiconductor laser may
involve an active heat removal device, such as, a Peltier effect
device. Due to size constraints of optical components, active heat
removal methods result in increased complexity and cost.
As described above, due to the many factors affecting coupling
efficiencies, changes in alignment, due to thermal properties of
the optical components, may result in power loss between the
semiconductor laser and the optical fiber.
BRIEF DESCRIPTION OF DRAWINGS
The invention is illustrated by way of example and not by way of
limitation in the figures of the accompanying drawings, in which
the like references indicate similar elements and in which:
FIG. 1 illustrates an example of an assembly of optical components,
where an alignment between a semiconductor laser and an optical
fiber is maintained utilizing thermal properties of various
materials, in accordance with one embodiment of the present
invention; and
FIG. 2 illustrates an example of an assembly of optical components,
where an alignment between a semiconductor laser and an optical
fiber is maintained utilizing thermal properties of various
materials, in accordance with an alternate embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
In the following description, various aspects of the invention will
be described. However, it will be apparent to those skilled in the
art that the invention may be practiced with only some or all
described aspects. For purposes of explanation, specific numbers,
materials and configurations are set forth in order to provide a
thorough understanding of the invention. However, it will also be
apparent to one skilled in the art that the invention may be
practiced without the specific details. In other instances,
well-known features are omitted or simplified in order not to
obscure the invention.
Various operations will be described as multiple discrete steps in
turn, in a manner that is most helpful in understanding the
invention. However, the order of description should not be
construed as to imply that these operations are necessarily order
dependent. In particular, these operations need not be performed in
the order of presentation.
In various embodiments of the invention, an improved way of
maintaining alignment between a semiconductor laser and an optical
fiber is facilitated. This and other advantages will be evident
from the disclosure.
FIG. 1 illustrates an example of an assembly of optical components,
where an alignment between a semiconductor laser and an optical
fiber is maintained utilizing thermal properties of various
materials, in accordance with one embodiment of the present
invention. Shown in FIG. 1 is an assembly of optical components
100, such as optical components used in telecommunications and data
communications technology (i.e., lightwave communications). The
assembly 100 includes a mounting plate 110 having a substantially
flat surface 112 for mounting various substrates and components,
including optical, electronics, and opto-electronic components. The
mounting plate 110 is of a material, which is a good conductor of
heat and electrically conductive. For example, the material for the
mounting plate 110 may be a copper (Cu) and tungsten (W) alloy such
as, but not limited to, CuW alloys with varying alloy percentages
ranging from 10%-5% Cu and 90%-85% W, respectively. The material
for the mounting plate 110 may also be Cu and Molybdenum (Mo)
alloys such as, but not limited to, CuMo alloys with varying alloy
percentages ranging from 15%-20% Cu and 85%-80% Mo, respectively.
Another material for the mounting plate 110 may also be of pure
Mo.
Some of the thermal properties, in particular, for the mounting
plate 110 materials include thermal conductivity and coefficient of
thermal expansion (CTE). For the CuW alloys, thermal conductivity
values may range from 160-185 watts per meter squared Kelvin per
meter (W/m.sup.2K/m). The coefficient of thermal expansion for the
CuW alloys may range from 6.1-7.36 microns per meter degree Celsius
(.mu.m/m.degree. C.) linear measured at 20.degree. C. For the CuMo
alloys, the thermal conductivity values may range from 140-175
W/m.sup.2K/m with CTE values ranging from 6.5-7.2 .mu.m/m.degree.
C. linear at 20.degree. C. For pure Mo, the thermal conductivity
value may be 138 W/m.sup.2K/m with a CTE value of 5.35
.mu.m/m.degree. C. linear at 20.degree. C.
Additionally shown in FIG. 1, is a first substrate 115 mounted on
the surface 112 of the mounting plate 110. Mounted on the first
substrate 115 is a semiconductor laser 117 having a light emitting
side 119. The first substrate 115 is of a material, which is a good
conductor of heat but electrically insulating. For example, the
material for the first substrate may be an aluminum (Al) based
ceramic such as, but not limited to, Aluminum Nitride (AIN) with
varying purity levels ranging from 98%-99%. The material for the
first substrate may also be an oxide of beryllium such as, but not
limited to, Beryllia (BeO) with a purity of 99.5%.
Some of the thermal properties, in particular, for the first
substrate 115 materials also include thermal conductivity and CTE.
For the AIN ceramics ranging from 98%-99% purity, the thermal
conductivity values may range from 90-170 W/m.sup.2K/m. The CTE for
the AIN ceramics ranging from 98%-99% purity may range from 4.2-4.3
.mu.m/m.degree. C. linear measured at 20.degree. C. For Beryllia
(BeO) with a purity of 99.5%, the thermal conductivity value may be
248 W/m.sup.2K/m with a CTE value of 6.4 .mu.m/m.degree. C. linear
at 20.degree. C.
Also mounted on the surface 112 of the mounting plate 100 is a
second substrate 120. The second substrate 120 is separated from
the first substrate 115 by a predetermined distance 122 along the
surface 112 of the mounting plate 110. As will be described in more
detail below, the predetermined distance 122 facilitates isolation
of heat within the second substrate 120. The second substrate 120
is of a material, which is a good insulator of heat and also
electrically insulating. For example, the material for the second
substrate 120 may be an aluminum (Al) based ceramic such as, but
not limited to, aluminum oxide (Al.sub.2O.sub.3), also commonly
referred to as Alumina, with a purity of 99.9%.
Some of the thermal properties, in particular, for the second
substrate 120 material also include thermal conductivity and CTE.
For Alumina with a purity of 99.9%, the thermal conductivity value
may be 28 W/m.sup.2K/m. The CTE for the Alumina with a 99.9% purity
is 7.4 .mu.m/m.degree. C. linear measured at 250.degree. C.
In one embodiment shown in FIG. 1, an optical fiber 130 is mounted
on the second substrate by a predetermined quantity of solder
material 127 on an optical fiber attachment area 125. The solder
material 127 may be of a preformed type and placed on the second
substrate 120. The optical fiber 130 is placed on the solder
material 127 and is oriented such that a light input end 131 is
adjacent to and aligned with the light emitting side 119 of the
semiconductor laser 117 mounted on the first substrate 115. Once a
desired alignment is achieved, the solder material 127 is heated to
a predetermined temperature to melt the solder material 127. The
heating may be facilitated by applying a variety of methods, such
as, but not limited to, applying a current to resistive material
included in the optical fiber attachment area 125 with the solder
material 127. Subsequently, if the current is removed from the
optical fiber attachment area 125, the optical fiber attachment
area cools back to ambient temperature, re-solidifying the solder
material 127. Another example may be a method involving applying
heat from coherent and incoherent infrared sources and the
like.
Furthermore, because of the heat that may be introduced to the
optical fiber attachment area 125, in the embodiment shown in FIG.
1, the optical fiber attachment area 125 comprises a shelf
formation above the mounting plate 110. The shelf formation further
facilitates isolation of heat within the second substrate 120. The
shelf formation may be formed by reducing the thickness of the
second substrate 120, in and around the area of the optical fiber
attachment area 125 (i.e., below), while maintaining horizontal
alignment on the top surface of the second substrate 120.
The shelf formation also helps to decrease the thermal mass of the
second substrate 120 thereby isolating any heat within a small
confined area. Additionally, the small confined area facilitates
rapid heating, while reducing the amount of latent heat that may be
present in the second substrate 120.
When the melted solder material 127 is allowed to re-solidify, the
re-solidified solder material 127 attaches the optical fiber 130 to
the second substrate 120. The predetermined temperature will depend
upon the material used for the solder. The solder material 127 may
be of any type of low melting point solder, such as, but not
limited to, an alloy of lead and tin (PbSn) with a melting point
below that of 240.degree. C. Alternatively, the solder material 127
may be of any type of high melting point solder, commonly known as
stiff solder, such as, but not limited to, an alloy of gold and tin
(AuSn) with a melting point of approximately 280.degree. C.
Utilizing the above described thermal properties of the materials
for the mounting plate 110, the first substrate 115, the second
substrate 120, and the arrangement of the substrates 115 & 120,
the desired alignment between the semiconductor laser 117 and the
optical fiber 130 is maintained.
Prior to operation, a factor that may affect the alignment is the
heat applied to the second substrate 120 during the mounting of the
optical fiber 130. In one embodiment, because the second substrate
120 increases in temperature to melt the solder ball 127, the
selected material for the second substrate 120 has a low thermal
conductivity and a low CTE, or at least a CTE measurable at
relatively high temperatures. These thermal properties help prevent
heat transfer from the second substrate 120 to the first substrate
115. Additionally, the combination of the relatively low melting
point of the solder material 127 with the low CTE of the material
for the second substrate 120, allows for very small, if not
negligible, dimensional changes in the second substrate 120.
However, if the heat applied to melt the solder material 127,
during the mounting of the optical fiber 130, is allowed to
transfer to the first substrate 115, the dimensions of the first
substrate 115 may change.
The dimensional change is based at least upon the thermal
properties of the material of the first substrate 120, such as, but
not limited to the thermal conductivity and the CTE. The change in
the first substrate 115 causes the position of the semiconductor
laser 117 mounted on the first substrate 115 to move, thereby
affecting the alignment between the semiconductor laser 117 and the
optical fiber 130. In order to minimize any heat transfer from the
second substrate 120 to the first substrate 115, the second
substrate 120 is separated from the first substrate 115 by the
predetermined distance 122 along the surface 112 of the mounting
plate 110. The predetermined distance may be any distance required
to minimize heat transfer, such as, but not limited to, 0.5
millimeter because heat transfer occurs more readily through
conductive rather than convective heat transfer.
During operation, a factor that affects the alignment between the
semiconductor laser 117 and the optical fiber 130 is the beat
generated by the operation of the semiconductor laser 117. The
effect on the optical alignment has, in turn, a detrimental effect
on the coupling efficiency. Because of the detrimental effects of
heat on optical components, the heat generated by the semiconductor
laser 117 is removed.
The heat generated by the semiconductor laser 117 is transferred to
the first substrate 115, where the first substrate acts as a
heatsink. In turn, the beat from the first substrate 115 is
transferred to the mounting plate 112, where the heat may be
further removed. The rate, at which the heat is transferred from
one component to another is based at least upon the thermal
properties of the components, such as, but not limited to, the
thermal conductivity. Additionally, as the heat is transferred into
a component, the component may dimensionally change based at least
upon the thermal properties of the material of the component, such
as, but not limited to, the CTE. Utilizing the thermal properties
of the materials of the components, the alignment between the
semiconductor laser 117 and the optical fiber may be maintained
during operation.
In one embodiment, the material for the mounting plate 110 is a
good conductor of heat, such as, but not limited to, an alloy of
10% Cu and 90% W. An example of a 10%Cu and 90%W alloy may be a
material known as Thermkon.RTM. 62 supplied by CMW, Inc. of
Indianapolis, Ind. Thermkon.RTM. has a thermal conductivity value
of 160 W/m.sup.2K/m and a CTE of 6.1 .mu.m/m.degree. C., as
information provide by CMW, Inc.
Mounted on the mounting plate 110 made of the good conductor of
heat, is the first substrate 115 made of a material that is also a
good conductor of heat, such as, but not limited to an AIN ceramic
substrate of 99% purity. The 99% AIN ceramic material may be a
material known as AN 160 supplied by MarkeTech International of
Port Townsend, Wash. The AN 160 has a thermal conductivity value of
155 W/m.sup.2K/m and a CTE of 4.3 .mu.m/m.degree. C., as
information provided by MarkeTech International. Mounted on the
first substrate 115 is the semiconductor laser 117. The
semiconductor laser 117 may be of any type of semiconductor lasers
known in the art, such as, but not limited to, the semiconductor
lasers from the family fabricated in gallium aluminum arsenide
(GaAlAs), and so forth.
Mounted on the mounting plate 110 made of Thermkon.RTM. and
adjacent to the first substrate 115 made of AN 160, the second
substrate 120 a material that has a low thermal conductivity, such
as, but not limited to, a ceramic material of aluminum oxide
(Al.sub.2O.sub.3). The aluminum oxide may be a material known as
Alumina with a thermal conductivity value of 28 W/m.sup.2K/m and a
CTE of 7.4 .mu.m/m.degree. C. Additionally, mounted on the second
substrate 120 made of Alumina, is the optical fiber 130. As
previously described, the optical fiber 130 may be attached to the
second substrate 120 by the solder material 127. The light input
end 131 is adjacent to and aligned with the light emitting side 119
of the semiconductor laser 117 mounted on the first substrate
115.
It should be appreciated by those skilled in the art that the
mounting of the substrates 115 & 120 onto the mounting plate
110 may be achieved by utilizing adhesives, including solder, that
complement the thermal properties of the materials of the
substrates 115 & 120 and the mounting plate 110. Additionally,
mounting the semiconductor laser 117 onto the first substrate 115
may be achieved by utilizing adhesives that complement the thermal
properties of the materials of the first substrate 115 and the
semiconductor laser 117. Furthermore, the adhesives utilized may be
thin enough to have very little or no appreciable affects on the
thermal properties of the materials. For the purposes of describing
the present invention, the adhesives used may be either
complementary materials or thin enough to have very little or no
appreciable affects on the thermal properties of the optical
components.
The combination of the materials in the one embodiment is based at
least upon the thermal properties of the materials. Alumina, the
material for the second substrate 120 having a thermal conductivity
value of 28 W/m.sup.2K/m, helps to thermally isolate any heat
applied to the second substrate. As previously described, prior to
operation, heat may be applied to the second substrate 120 during
the mounting of the optical fiber 130 to the second substrate
120.
During operation, AIN ceramic, the material for the first substrate
115 having a thermal conductivity value of 155 W/m.sup.2K/m, helps
to transfer heat generated by the semiconductor laser 117 away from
semiconductor laser 117. In turn, an alloy of 10% Cu and 90% W, the
material for the mounting plate 110 having a thermal conductivity
value of 160 W/m.sup.2K/m, helps transfer heat from the first
substrate 115 away from the substrate 115.
The thermal conductivity values of the first substrate 115 and the
mounting plate 110 are relatively high as compared to the second
substrate 120. As previously described, the thermal conductivities
of the first substrate 115 and the mounting plate 110 are selected
to transfer heat at a high rate from the semiconductor laser 117 to
prevent detrimental heat effects of an increase in temperature to
the operation of the semiconductor laser 117.
However, the detrimental effects of loss in coupling efficiency,
due to changes in alignment between the semiconductor laser 117 and
the optical fiber 130, is controlled by utilizing the thermal
properties of CTE of the materials. In the one embodiment, the
mounting plate 110 has a CTE of 6.1 .mu.m/m.degree. C. linear at
20.degree. C. Mounted on the mounting plate 110 is the first
substrate 115 having a CTE of 4.3 .mu.m/m.degree. C. linear at
20.degree. C. Also mounted on the mounting plate 110 is the second
substrate 120 having a CTE of 7.4 .mu.m/m.degree. C. linear at
250.degree. C. Because of the high temperature requirements for the
CTE of the second substrate 120, the second substrate 120 may be
considered dimensionally stable, as compared to the mounting plate
110 and the first substrate 115, at the operating temperatures of
the semiconductor laser 117.
Any dimensional changes that may occur due to the rise in
temperature of the mounting plate 110 will have a very small affect
on the alignment because both the first substrate 115 and the
second substrate 120 relatively close CTEs. Because of the
closeness of the CTEs of the first substrate 115 and the second
substrate 120, dimensional changes in the two substrates 115 &
120 due to heating are minimized. For example, during operation,
because the CTEs of the first substrate 115 and the second
substrate 120 are relatively close, the minimized dimensional
change may be no more than plus or minus 0.049 micrometers, which
may be within optical fiber to semiconductor laser alignment
specifications.
As a result, selecting materials with predetermined thermal
properties, and arranging the materials in a predetermined manner
facilitate maintaining alignment between a semiconductor laser and
an optical fiber. Additionally, heat generated by the semiconductor
laser is removed passively (i.e., without the need for active
cooling).
FIG. 2 illustrates an example of an assembly of optical components,
where an alignment between a semiconductor laser and an optical
fiber is maintained utilizing thermal properties of various
materials, in accordance with an alternate embodiment of the
present invention. Shown in FIG. 2, the first substrate 115 is
mounted on the mounting plate 110. Additionally, the first
substrate 115 has the semiconductor laser 117. In FIG. 2, the
second substrate 120 located in a position that is substantially in
contact with the first substrate 115. However, the second substrate
120 has thermal features 210 & 211, and in one embodiment, the
thermal features 210 are variations of slots (i.e., oval shaped
holes in the second substrate 120).
As shown, a first thermal feature 210 is located adjacent to one
side of the optical fiber attachment area 125 and at the interface
of the first substrate 115 and the second substrate 120. The first
thermal feature 210 is a half slot shape occupying approximately
50% of the surface area immediately adjacent the optical fiber
attachment area 125. Furthermore, the first thermal feature 210 is
shaped in such a way as to allow for contact between the first
substrate 115 and the second substrate 120 beyond either end of the
first thermal feature 210.
A second thermal feature 220 is located adjacent to the other side
of the optical fiber attachment area 125. The second thermal
feature is a full slot occupying approximately 50% of the surface
area immediately adjacent the optical fiber attachment area
125.
The thermal features 210 & 220 help to isolate any heat
retained in the optical fiber attachment area 125 from the first
substrate 115. As previously described, prior to operation, the
optical fiber attachment area 125 may have heat from the melting of
the solder material 127. This heat is isolated from being,
conducted to the first substrate 115 where it may detrimentally
affect the alignment between the semiconductor laser 117 and the
optical fiber 130. Because the material of the second substrate 120
has a low thermal conductivity, the heat for melting the solder
material 127 may be retained for a time based at least upon the
rate at which heat is transferred out of the optical fiber
attachment area 125 (i.e., latent heat).
Furthermore, as shown in FIG. 2, the optical fiber attachment area
125 comprises of a shelf formation. As previously described, the
shelf formation helps to decrease the thermal mass of the second
substrate 120 thereby further isolating any heat within a small
confined area.
During operation, the thermal features 210 & 220 help prevent
latent heat from the optical fiber attachment area 125 to be
transferred to the first substrate 115. As previously described,
heat from the semiconductor laser 117 has detrimental effects on
the alignment between the semiconductor laser 117 and the optical
fiber 130, and therefore, additional heat from the second substrate
120 will have even more detrimental effects.
As a result, providing certain mechanical features to the selected
materials with predetermined thermal properties, and arranging the
materials in a predetermined manner further facilitate maintaining
alignment between a semiconductor laser and an optical fiber. In
one embodiment, the alignment method of the present invention is
used in an optical networking module, with integrated protocol
processing and unified software control. Such module is the subject
matter of co-pending application number .[.<to be
inserted>.]. .Iadd.09/861,002.Iaddend., entitled "An Optical
Networking Module Including .[.Integrated.]. Protocol Processing
and Unified Software Control", filed on May 18, 2001.Iadd., now
issued as U.S. Pat. No. 6,567,413, .Iaddend.and assigned to the
same assignee as the present invention. The application is hereby
fully incorporated by reference.
Although the invention had been described and illustrated in
detail, it is to be understood that the same is by way of
illustration as an example only and is not to be taken by way of
limitation.
Thus, an improved way of maintaining alignment between a
semiconductor laser and an optical fiber is disclosed.
* * * * *