U.S. patent application number 14/334839 was filed with the patent office on 2015-05-14 for device comprising weldbonded components.
The applicant listed for this patent is Corning Incorporated. Invention is credited to Venkata Adiseshaiah Bhagavatula, Roy Joseph Bourcier, Satish Chandra Chaparala, John Himmelreich.
Application Number | 20150131949 14/334839 |
Document ID | / |
Family ID | 42196573 |
Filed Date | 2015-05-14 |
United States Patent
Application |
20150131949 |
Kind Code |
A1 |
Bhagavatula; Venkata Adiseshaiah ;
et al. |
May 14, 2015 |
DEVICE COMPRISING WELDBONDED COMPONENTS
Abstract
A method of assembling optoelectronic and/or photonic
components, said method comprising: (i) providing at least two
optoelectronic and/or photonic components; (ii) aligning and
situating these components relative to one another and in close
proximity with one another so as to: (a) provide optical coupling
between these components; and (b) maintain the distance d between
the adjacent parts of these components, where d is 0 to 100 .mu.m;
(iii) adhering these components to one another with while
maintaining optical coupling therebetween; and (iv) laser welding
these components together while maintaining optical coupling
therebetween.
Inventors: |
Bhagavatula; Venkata
Adiseshaiah; (Big Flats, NY) ; Bourcier; Roy
Joseph; (Corning, NY) ; Chaparala; Satish
Chandra; (Painted Post, NY) ; Himmelreich; John;
(Horseheads, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Corning Incorporated |
Corning |
NY |
US |
|
|
Family ID: |
42196573 |
Appl. No.: |
14/334839 |
Filed: |
July 18, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12276786 |
Nov 24, 2008 |
8790483 |
|
|
14334839 |
|
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Current U.S.
Class: |
385/95 |
Current CPC
Class: |
B29C 65/1406 20130101;
G02B 6/4237 20130101; B29C 2035/0822 20130101; Y10T 428/269
20150115; B29C 2035/0827 20130101; B29C 65/1616 20130101; G02B
6/3801 20130101; B29C 65/16 20130101; B29C 66/21 20130101; B29C
65/484 20130101; Y10T 428/31551 20150401; B29C 65/4845 20130101;
B29C 65/72 20130101; B29C 66/3452 20130101; G02B 6/2551 20130101;
Y10T 428/31721 20150401; B29C 65/4835 20130101; B29C 65/4815
20130101; Y10T 428/31663 20150401; B29C 65/1619 20130101; G02B
6/4239 20130101 |
Class at
Publication: |
385/95 |
International
Class: |
G02B 6/255 20060101
G02B006/255 |
Claims
1. A device comprising: (i) at least two components situated
proximate to one another, each of said two components including at
least one optical element; (ii) said at least one optical element
of at least one of said at least two components being optically
coupled to at least one optical element of another one of said at
least two components; (iii) at least one welding spot, and at least
one spot of adhesive being situated at a periphery of the boundary
formed between the two components.
2. The device according to claim 1 wherein said adhesive is a UV or
heat curable adhesive, a thermoplastic adhesive, a thermosetting
adhesive, a cyanoacrylate, a polyurethane, a silicone, or a
polyimide.
3. The device according to claim 1 wherein said at least one
welding spot has a cross-section of 250 .mu.m to 1 mm.
4. The device according to claim 1 wherein said at least two
components are connected to one another by at multiple adhesive
spots and said adhesive spots are situated symmetrically with
respect to one another.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/276,786, filed on Nov. 24, 2008, the content of which
is relied upon and incorporated herein by reference in its
entirety, and the benefit of priority under 35 U.S.C. .sctn.120 is
hereby claimed.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to an improved
method of weldbonding, and more particularly to a method of
weldbonding photonic or electro-optical components, and to devices
comprising such weldbonded components.
[0004] 2. Technical Background
[0005] With rapidly increasing demand for photonic or
opto-electronic devices (for example lasers or LED based portable
or embedded projectors), one of the biggest challenges in
assembling these devices is connecting or joining various
components to one another to provide high optical coupling
efficiency between these components, and maintaining the
performance of the assembled device stable over time and during
temperature variations.
[0006] Laser welding has been used in a variety of applications in
the assembly of photonic components. During welding, the rapid
solidification of the welded parts and the associated material
shrinkage can lead to a relative movement between the pre-aligned
components (process induced misalignment). This is also referred to
as Post Weld Shift (PWS). The optical output power and/or optical
coupling efficiency between welded photonic or opto-electronic
components may be significantly reduced by PWS.
[0007] The use of combined adhesive bonding and welding has been
considered previously for aero and auto applications. In these
applications, large area metal sheets are glued and welded to
provide structural/strength characteristics. This process is
referred to as weldbonding. The adhesive is sandwiched between the
metal sheets and the welding is performed subsequently through the
sheets. The welding provides the benefits of instant strength and
high peel resistance, whereas the adhesive bonding provides fatigue
and vibration resistance and improved strength and durability. The
focus is on large area bonding and structural requirements, not on
high precision alignment, or optical coupling between components.
Thus, to our knowledge, the weldbonding art does not address
prevention of movement at the submicron level of the bonded parts
during the welding process.
SUMMARY OF THE INVENTION
[0008] According to one aspect of the invention a method of
assembling optoelectronic and/or photonic components, said method
comprising: (i) providing at least two optoelectronic and/or
photonic components; (ii) aligning and situating these
optoelectronic and/or photonic components relative to one another
and in close proximity with one another so as to: (a) provide
optical coupling between these components; and (b) maintain the
distance d between the adjacent parts of said components, where 0
.mu.m.ltoreq.d.ltoreq.100 .mu.m; (iii) adhering said components to
one another with adhesive by situating adhesive at a boundary
between these components and curing or solidifying the adhesive
while maintaining optical coupling therebetween; and (iv) laser
welding said components together. According to at least some
embodiments the laser welding is performed at the boundary line
between the two components. Preferably, the step of laser welding
creates at least one welding spot (i.e., weld bead) about 50 .mu.m
to 1 mm in diameter.
[0009] Preferably, the laser welding step produces less than 1
.mu.m shift, and more preferably less than 0.5 .mu.m shift in the
relative positions of the adjacent components.
[0010] Preferably the adhesive is characterized by modulus of
rigidity in the range of 5 GPa.ltoreq.R.ltoreq.100 GPa, and a cure
time between 1 sec and 90 sec. Preferably the adhesive's
contraction (i.e., linear shrinkage during curing) is less than 1
.mu.m during curing or solidification. For example, in some
embodiments, the thickness of the epoxy bond shrunk by less than
10%, and in some embodiments by less than 5%, and in some
embodiments by less than 1%. Preferably the adhesive is selected
from the UV or heat curable epoxies such as acrylates to facilitate
quick curing process and easy assembly process.
[0011] According to another embodiment of the present invention a
device comprises: (i) at least two components situated proximate to
one another, each of the two components including at least one
optical element (i.e., optical, electro-optical or photonic
element); (ii) at least one optical element of at least one of the
at least two components being optically coupled to at least one
optical element of another one of the at least two components; and
(iii) at least one welding spot, and at least one spot of adhesive
being situated at a periphery of the boundary formed between the
two components.
[0012] Advantageously, the method of assembling optical,
opto-electronic or photonic components into a package, according to
the embodiments of the present invention provides high yields, can
be done at a relatively low cost, and produces minimal (or no) post
weld shift(s) of these components.
[0013] Additional features and advantages of the invention will be
set forth in the detailed description which follows, and in part
will be readily apparent to those skilled in the art from that
description or recognized by practicing the invention as described
herein, including the detailed description which follows, the
claims, as well as the appended drawings.
[0014] It is to be understood that both the foregoing general
description and the following detailed description present
embodiments of the invention, and are intended to provide an
overview or framework for understanding the nature and character of
the invention as it is claimed. The accompanying drawings are
included to provide a further understanding of the invention, and
are incorporated into and constitute a part of this specification.
The drawings illustrate various embodiments of the invention and
together with the description serve to explain the principles and
operations of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1A and FIG. 1B is a schematic depiction of one
embodiment of the present invention;
[0016] FIGS. 2A and 2B are photographs of one embodiment of the
present invention;
[0017] FIG. 3A is another schematic depiction of one embodiment of
the present invention;
[0018] FIGS. 4A and 4B are photographs of another embodiment of the
present invention;
[0019] FIG. 5 is a graph showing temperature fluctuation and output
power fluctuation as a function of time, for a device of FIG.
4A;
[0020] FIG. 6 is a graph showing output power fluctuation during
ultrasonic vibration, as a function of time;
[0021] FIG. 7 is a schematic depiction of two components that are
being weldbonded together; and
[0022] FIG. 8 shows the measured mechanical displacements of the
axisymmetric surrogate test article schematically shown in FIG.
7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. Whenever possible, the
same reference numerals will be used throughout the drawings to
refer to the same or like parts. One embodiment of the device of
the present invention is shown schematically in FIG. 1, and is
designated generally throughout by the reference numeral 10. FIG.
2A is a photograph of an exemplary built device, and FIG. 2B
illustrates an enlarged area of the device 10 shown in FIG. 2A. The
device 10 includes: (i) at least two components 20 (e.g.,
optoelectronic and/or photonic components) situated proximate to
one another, each of these components including at least one
optical, photonic, or optoelectronic element 21 (which are referred
to herein as an optical element 21); (ii) at least one spot of
adhesive 23 (adhesive bead) situated at a periphery of the boundary
25 formed between the two components (iii) and at least one welding
spot 28 situated at a periphery of the interface or boundary 25
formed between the two components. The optical element 21 of at
least one of these two components is optically coupled to at least
one optical element 21 of the other component. Although the two
optical elements 21 are optically coupled to one another, they may
or may not be in physical contact with one another. Some examples
of optical elements 21 are: waveguides (fiber or planar), lenses,
lensed fibers, optical gratings, optical filters, optical couplers,
optical or opto-electronic switches, optical frequency doubling
crystals, laser diodes, and/or optical isolators. Preferably the
adhesive 23 is characterized by modulus of rigidity in the range of
5 GPa.ltoreq.R.ltoreq.100 GPa, and rapid curing rate (e.g., between
1 sec and 90 sec). Preferably the adhesive's contraction (i.e.,
linear shrinkage during curing) is less than 1 .mu.m during curing
or solidification. For example, in some embodiments, the thickness
of the epoxy bond shrunk by less than 10%, and in some embodiments
by less than 5%, and in some embodiments by less than 1%.
[0024] In accordance with some embodiments of the present
invention, a method of assembling optoelectronic and/or photonic
components 20 (also referred to as components herein), comprises
the steps of: (i) providing at least two optoelectronic and/or
photonic components 20; (ii) aligning and situating the components
20 relative to one another and in close proximity with one another
so as to: (a) provide optical coupling between these components;
and (b) maintain the distance d between the adjacent parts of these
components, where d is 0 (components are in physical contact with
one another) to 100 .mu.m; (iii) adhering or joining the two
components to one another with an adhesive 23 (e.g., UV or
temperature curable epoxy) by: (a) situating the adhesive 23 at a
boundary 25 between components 20, such that the two components are
in physical contact with the adhesive 23 and (b) curing or
solidifying the adhesive 23 while maintaining the optical coupling
between these components; and (iv) laser welding the components
together at the boundary 25 (e.g., along the periphery of the
boundary) to produce the assembled device 10. The laser welding
creates welding spot(s) 28, for example of 50 .mu.m to 1 mm in
cross-section (e.g., 200 .mu.m to 600 .mu.m in diameter).
Preferably a plurality of welding spots 28 (also referred herein as
weld spots) are created during the laser welding part of the
process. If the adhesive requires UV curing, (for example a UV
curable epoxy) the step of adhering the two components to one
another with the adhesive 23 includes the step of UV curing the
adhesive 23 to create a permanent bond between these components 20.
The optical alignment and/or optical coupling is maintained during
laser welding by the structural rigidity of the (solidified or
cured) adhesive 23. As used herein, the term "optical coupling"
means that the two components are aligned such that if (or when)
light is provided to an optical element of one of the two
components (e.g., first component), the light will enter into the
optical element of the other component and will then exit from the
optical element of this other component. Thus, the two components
or two optical elements may be optically coupled to one another
even when the light is not provided to an optical element of one of
the two components (e.g., to the first component), because they are
positioned and aligned such that the if light is provided, it will
couple from one of the elements to the other element.
Advantageously, the laser welding step produces less than 1 .mu.m
shift in position of either one of the two welded components.
Preferably, the two components 20 shift by no more than 1 .mu.m
relative to one another. Such small shifts do not significantly
interfere with optical coupling efficiency E or with optical output
power P, which (assuming that the input optical power is maintained
at the same level) is preferably maintained within 20% and even
more preferably within 10%, i.e., P.sub.2.gtoreq.0.8 P.sub.1 and
more preferably P.sub.2.gtoreq.0.9 P.sub.1 where P.sub.1 is the
optical power throughput before the laser welding step and P.sub.2
is to the optical power throughput after laser welding. Even more
preferably, P.sub.2.gtoreq.0.95 P.sub.1. This power change relates
to the post-weld shift and depends on the relative shifts between
the aligned optical elements and their optical beam
characteristics. In many optical, photonic or opto-electronic
devices of interest (for example, Laser Diodes and single mode
waveguides) the beam diameters are in the range of about 1 .mu.m to
about 10 .mu.m, and it is preferable to limit the PWS to submicron
levels to get less than 20%, and more preferably less than 10%
relative change from P.sub.1 to P.sub.2. The optical coupling
efficiency E is also maintained within 20%, preferably within 10%.
And more preferably within 5%. (E=Pout/Pin), where Pin is an input
optical power provided to an optical element of one of the two
components, and Pout is an output optical power provided by an
optical element of the other component.). Thus, it is preferable
that E.sub.2.gtoreq.0.8 E.sub.1 and more preferably
E.sub.2.gtoreq.0.9 E.sub.1 where E.sub.1 is the optical coupling
efficiency before the laser welding step and E.sub.2 is to the
optical coupling efficiency after laser welding. Even more
preferably, E.sub.2.gtoreq.0.95 E.sub.1.
[0025] According to some embodiments, the adhesive is an epoxy, and
the step of adhering the two (or more) components to each other
includes a step of changing rigidity of the epoxy 23 to create a
permanent bond between the two adjacent components 20. This can be
done, for example, by UV curing the applied adhesive 23 to make it
rigid, attaching it to both components. The adhesive 23 may be a
heat curable adhesive, which is applied in a liquid form, and
solidifies when exposed to heat. Alternatively an adhesive 23 may
be applied as a hot liquid which then solidifies (becomes more
rigid) when exposed to a room temperature. Preferably, the adhesive
changes its rigidity (solidifies or cures) within a few seconds
(e.g., 1 sec to 90 sec, 1 sec to 60 sec, or 5 sec to 45 sec) after
its application, thus bonding the two components together while
maintaining their alignment within the desired level.
[0026] According to some embodiments the method also includes steps
of: (i) measuring optical output power or optical coupling
efficiency between components 20 prior to joining them one to
another with said epoxy; and (ii) measuring optical output power or
optical coupling efficiency between components 20 while adhering
them one to another with epoxy 23. According to some embodiments
the method also includes steps of: (i) measuring optical output
power or optical coupling efficiency between components 20 prior to
joining them one to another with said epoxy; and (ii) measuring
optical output power or optical coupling efficiency between
components 20 while measuring optical output power, or coupling
efficiency between these components while laser welding them one to
another.
[0027] The optical coupling efficiency is defined as the ratio
between output optical power (Pout) out of the optical element of
the other component 20, and input optical power (Pin) out of the
optical element of the other component 20 (i.e., E=Pout/Pin), where
the two optical elements are optically coupled to one another.
Thus, the coupling efficiency E.sub.1 between the two components 20
prior to joining them one to another with the adhesive 23 is
E.sub.1=P.sub.1/Pin. Similarly, coupling efficiency Ec between said
components while curing or solidifying the adhesive 23 is
E.sub.C=Pc/ Pin. Similarly, coupling efficiency E.sub.2 between
these components while laser welding them one to another is
E.sub.2=P.sub.2/Pin.
[0028] For example, according to some embodiments the method also
includes the steps of (i) measuring optical output power P.sub.1,
or coupling efficiency E.sub.1 between the two components 20 prior
to joining them one to another with the adhesive 23; (ii) measuring
optical output power Pa, or coupling efficiency Ea between these
components while adhering them one to another with the adhesive 23;
(iii) measuring optical output power P.sub.C, or coupling
efficiency Ec between said components while curing or solidifying
the adhesive 23; (iv) measuring optical output power P.sub.2, or
coupling efficiency E.sub.2 between these components while laser
welding them one to another.
[0029] Preferably the method of assembling optoelectronic and/or
photonic components 20 further includes steps of: (i) measuring
optical output power P.sub.1 or the optical coupling efficiency
E.sub.1 between the two components 20 prior to adhering or bonding
them together with the adhesive 23; and (ii) utilizing the
mechanical strength and rigidity of the adhesive bond to maintain
optical output power P.sub.2, or the optical coupling efficiency
E.sub.2 between the two components 20 while laser welding the two
components to each other such that: (a) the optical output power
after welding is P.sub.2.gtoreq.0.8 P.sub.1, and preferably
P.sub.2.gtoreq.0.9 P.sub.1.; and/or optical coupling efficiency
E.sub.2.gtoreq.0.8 E.sub.1, and preferably E.sub.2.gtoreq.0.9
E.sub.1 Preferably, P.sub.2.gtoreq.0.95 P.sub.1, more preferably
P.sub.2.gtoreq.0.97 P.sub.1. Preferably, E.sub.2.gtoreq.0.95
E.sub.1, more preferably E.sub.2.gtoreq.0.97 E.sub.1.
[0030] According to some embodiments, laser welding is performed
utilizing a Nd:YAG laser with a wavelength of 1064 nm operated at
0.5 J to 2.5 J per weld spot, using a pulse width of 1 to 5
milliseconds, with a laser spot diameter of 250 .mu.m to 1 mm
(e.g., 450 .mu.m). However, laser welding can be performed with
other lasers, for example a CO.sub.2 laser with a wavelength of
10,600 nm, a frequency-doubled YAG with a wavelength of 532 nm, a
810 nm laser, or an IR laser operating in the 1.3 .mu.m to 1.5
.mu.m wavelength range.
[0031] The optical components 20 may be made of materials which can
be joined using laser welding, including metal (e.g., steel or
aluminum substrates), metal-ceramic composite material,
glass-ceramic material, glass or polymer materials. For example,
the adhesive 23 may be utilized to create bond between two metal
components, a metal component and a metal-ceramic composite
component, or two glass components. Laser welding is then
subsequently performed to weld the two bonded components together.
For example, two glass components can be laser welded to one
another after they have been adhered to one another so that the
desired alignment is maintained during and after laser welding.
[0032] Beneficially, one advantage of the method according to the
present invention is that it results in sub-micron shift between
the two welded components 20, creating only minimal change in
optical coupling efficiency between the welded components.
[0033] Thus, the method of weldbonding described herein
advantageously prevents movement of the bonded parts during the
welding process (any residual movement can be held at the submicron
level), which is especially advantageous for opto-electronic or
photonic applications.
[0034] More specifically, the adhesive bond provides the rigidity
to oppose stresses that would misalign the optoelectronic
subassemblies (components 20) during the subsequent laser welding
process. In order to prevent movement of the bonded parts relative
to one another during the welding process, the adhesive needs to
have (1) rigidity R to counter the forces of laser welding, where
preferably R>1 GPa, more preferably R>5 GPA, for example 10
GPa.ltoreq.R.ltoreq.50 GPa, 15 GPa.ltoreq.R.ltoreq.30 GPa, or 18
GPa.ltoreq.R.ltoreq.25 GPa; (2) negligible/low contraction
(shrinkage) C during curing to maintain the sub-micron alignment
during the initial epoxy tacking of the opto-electronic
sub-assemblies, wherein C<1 .mu.m (preferably C.ltoreq.0.5
.mu.m), and (3) rapid curing for low cost manufacturing. For
example, in some embodiments, the thickness of the epoxy bond
shrunk by less than 10%, and in some embodiments by less than 5%.
Thus, for example, if the original epoxy bead thickness was 20
.mu.m, after curing the epoxy bond thickness was not less than 19
.mu.m, which means that the epoxy thickness was reduced by less
than 5%. Preferably the curing time should be less than 90 sec,
more preferably no more than 60 sec (e.g., 10-60 sec), and even
more preferably less than 10 sec. Examples of epoxies that can be
used for this application include, but are not limited to, the
"Optocast" brand of filled epoxies (available, for example, from
Electronic Materials Inc. of Breckenridge, Colo.). This brand of
epoxy is a UV and/or heat curable one component epoxy with silica
filler material. Non-filled epoxy can also be used for this purpose
as long as the rigidity, cure time and contraction requirements are
met. Such materials include, for example, "Lens Bond" UV curable
epoxies (available from Summers Optical Inc. of Hatfield, Pa.).
These epoxies come in different viscosity ranges. For example, in
order to facilitate very thin bond lines or spots for the
adhesives, low viscosity adhesives with viscosity values in the
range of 50-500 centipoise can be utilized. These adhesives are
preferable when the distance between two components needs to be
small, for example d.ltoreq.5 nm. The low viscosity adhesives can
spread into the gap between the two components, providing more
surface contact. However if the low viscosity adhesive is a UV
curable adhesive, and spreads between the two components, it would
be hard to completely cure such adhesive, unless the components are
transparent. Furthermore, care has to be taken to not allow such
adhesives to contaminate optical element(s) or to interfere with
optical coupling by spreading into the optical path. Thus, high
viscosity adhesives, particularly filled epoxies with low
shrinkage, may be preferable, because these adhesives are less
likely to spread into the optical path, and less likely to
contaminate optical elements. The high viscosity adhesives may have
viscosity values in the range of 500 to 100000 centipoise. In the
following examples we have chosen to use adhesives of high
viscosity and applied these adhesives on outside of the interface
(or boundary) between the two components. High viscosity adhesives
may require to be applied in relatively large bead sizes to provide
more surface contact. The bead diameters, or bead widths for high
viscosity adhesives in the following examples are 1 mm to 3 mm, but
may be different, based on the required application.
EXAMPLES
[0035] The invention will be further clarified by the following
examples.
Example 1
[0036] According to one exemplary embodiment, two photonic
components 20 were assembled together to create a permanent bond
therebetween. (See FIGS. 1, 2A and 2B). More specifically, an
optical element 21A (in this example, an optical fiber) was mounted
on a metal substrate 22A, (in this example stainless steel 304
substrate) and glued to the substrate, forming a first photonic
component 20. Another photonic component 20 was made by mounting an
optical fiber 21B on another substrate 22B. Note that there is a
wedge W on one of the mating surfaces 20A of the first component
20. The two photonic components 20 were situated in close proximity
to one another such that when light was provided to the input end A
of optical fiber waveguide 21A, the light exited from the output
end B of optical fiber waveguide 21B. The two photonic components
20 were aligned for peak coupling (coupling that produces a maximum
output power measured at the exit end B of the optical fiber
waveguide 21B) band; and then glued in place using UV curable
adhesive (e.g., OPTOCAST.TM. 3415, available from Electronic
Materials, Inc., Breckenridge, Colo.) forming a "T" joint. Laser
welding was subsequently performed on the glued assembly. In this
exemplary embodiment we utilized a pulsed Nd:YAG laser operated
with a pulse width of 3 milliseconds, depositing an energy of
approximately 0.9 J per weld spot. In this exemplary embodiment,
the weld spot diameters d were approximately 450 microns. (See
FIGS. 1 and 2A, 2B for the welding spot locations.)
[0037] The adhesive placement should be such that adhesive does not
interfere with subsequent laser welding. In choosing the placement
of the adhesive 23, one should preferably take into account the
symmetry of the device design, such that any contraction of the
adhesive 23 would generate nearly equal and opposing forces that
cancel each other and minimize the relative shift between
components 20. For example, it may be preferable that adhesive
beads be placed equidistantly from a component's center, or
symmetrically around the perimeter of the smaller component. In
this exemplary embodiment the adhesive is a high viscosity
adhesive, and it is applied on outside the interface between the
components, in order to avoid possible wicking between components.
Thus, is preferable to utilize adhesives with viscosities greater
than 5000 centipoise, and more preferably greater than 50,000
centipoise (Cps). For example, Opticast 3415 has a viscosity value
of 100,000 Cps. The weld positions are also preferably selected for
symmetry and the production of counter balancing forces. The laser
pulse energy is preferably chosen such that each pulse produces a
residual force small enough to be easily withstood by the rigid
epoxy. Multiple weld spots are used to provide enough strength and
reliability under operating conditions.
[0038] In this exemplary embodiment we measured optical coupling
efficiency (optical output power) before and after the welding
step. We had found that the joined components 20 had excellent
coupling stability after the welding step. The change in the output
power measured as a result of post weld shift was less than 1%
(i.e., P.sub.2>0.99 P.sub.1). In the initial experiment, the
metal substrate thickness was 6 millimeters. Later, the substrate
thickness was modified to 1.5 millimeters and the experiment was
repeated. The change in the output power measured as a result of
post weld shift in thinner assemblies was less than 3% (i.e.,
P.sub.2>0.97 P.sub.1). Later, both of these assemblies (devices
10) were subjected to thermal cycling testing over temperature
ranges from about 20.degree. C. to about 85.degree. C. The optical
output power variation during the thermal cycling was less than 3%
(i.e., P.sub.2 changed by less than 3%), thus demonstrating
excellent athermal behavior of the device 10. We then subjected
both assemblies (devices 10) to ultrasonic vibration with heat
(50.degree. C.) and 100% humidity (ultrasonic bath environment).
Both devices 10 demonstrated 0.3% output power variation. More
specifically, FIG. 5 shows the athermal behavior of the completed
assembly shown in FIG. 4. FIG. 6 illustrates assembly performance
under heat, humidity and vibration conditions.
Example 2
[0039] The method of aligning components and gluing them in place
and performing laser welding can extended to different mating
surface geometries. In the above Example 1, the face of one of the
mating surfaces has a wedge. In this example, the surface is
changed such that there is no wedge and the whole assembly looks
like a "T" joint. (See FIG. 3 for the schematic drawing and FIGS.
4A and 4B for a photograph of the manufactured device 10). More
specifically, FIG. 4A illustrates a top view of the device 10 and
FIG. 4B illustrates a portion of the side view of the manufactured
device 10 of FIG. 4A. The average post-weld shift induced
throughput power variation was about 1.8% (i.e., P.sub.2>0.982
P.sub.1, including source fluctuations. In this exemplary
embodiment, thermal cycling of the manufactured device 10 resulted
in less than 2% variation (i.e., P.sub.2 varied by less than 2%).
This type of "T joint" geometry is preferred because each component
20 can be a simple rectangular block. Another advantage with such
T-Junction component assemblies is that, even with manufacturing
variations in sizes and tolerances, the weld joints will be
symmetric and thus apply opposed transverse weld forces. That is,
with balanced laser beam powers and placements, the resulting
symmetric weld locations (weld spot locations) apply equal and
opposite forces and to a large extent cancel each other, and the
remaining forces that need to be compensated by the rigid epoxy
bond are reduced.
[0040] Also, a preferred laser welding approach would involve using
multiple smaller pulses, which results in smaller welding spot
sizes. Smaller welding spots generally involve smaller forces that
are easier to counteract. Also, multiple welded areas would provide
redundancy during operation and hence would lead to more reliable
and durable devices. In this exemplary embodiment, the laser beam
welds were made in the center of the T-junction using two balanced
laser beams, because this laser weld configuration provides the
most symmetry in this exemplary device 10. Similar factors (e.g.,
device geometry, adhesive placement location, location and number
of weld spots) have to be taken into account for other device
geometries when weldbonding together optical, photonic or
electro-optical components 20.
[0041] The excellent stability (e.g., small PWS values, and good
optical coupling under different environmental conditions) obtained
using this method of assembly is believed to be primarily due to
the counter-force provided by the adhesive 23 to oppose the motions
caused by the rapid solidification of the molten material (e.g.,
metal, glass and/or glass ceramic). Another cause could be the
lever arm effect. The weld plane almost coincides with the plane of
two waveguides (the distance between the two waveguides 21A, 21B of
this embodiment is less than 5 microns). During cooling of the
welding spots 28, there could be rotational motions of the
sub-assemblies (optical components 20) which could result in the
translation of the waveguides 21A, 21B relative to one another. If
the weld plane was far removed from the optical coupling plane,
large lateral displacements could occur on the optical coupling
plane which would greatly reduce coupling efficiency. But, in the
examples described herein, the welding and optical coupling planes
are nearly coincident, and thus the translations would be
insignificant because the lever arm is small. Thus, it is
preferable, to have weld plane coincide or nearly coincide (i.e.,
preferably within 1 mm) with the plane that the optical elements
are situated on.
[0042] Although in the second example the two components 20 were in
physical contact with one another, this method was also shown to
work when there was an approximately 30 microns gap (d=30 .mu.m)
between the two mating surfaces of the two components, with similar
post weld shift performance.
Example 3
[0043] The present method of device assembly can also be applied to
axisymmetric devices. In this embodiment, stainless steel 304
device surrogates (i.e., components without optical elements) were
assembled with adhesives: some device surrogates were bonded using
three small beads of cyanoacrylate gel (such as Super Glue
Gel.RTM., The Original Super Glue Corporation, Rancho Cucamonga,
Calif.) while the other surrogates were made using a filled two
part epoxy (such as J-B Kwik.RTM., J-B Weld Company, Sulphur
Springs, Tex.). The cylindrically shaped metal substrate 22A
(surrogate component 20) used in this example (see FIG. 7) were
flanged, with a 45 degree taper and attached to the base surrogate
component 20' (metal substrate 22A). The bonded device surrogates
were clamped into our test fixturing and component displacements in
each device surrogate were monitored using three Philtec RC20 fiber
optic sensor displacement probes (Philtec, Annapolis, Md.). Other
probes may also be utilized. The bonded device surrogates were
welded with three beams oriented 120 degrees apart and inclined at
25 degrees from the ferrule centerline. The test configuration is
illustrated schematically in FIG. 7. A relatively low power laser
beam (in this example laser conditions were: 0.9 J per weld spot; 3
millisecond pulse width, and approximately 450 .mu.m welding spot)
was directed onto the interface between the two metal components.
After the components have been welded together, the lateral
post-weld shifts were measured. A typical test result from one of
these device surrogates adhesively bonded using cyanoacrylate gel
is shown in FIG. 8. This figure shows the measured mechanical
displacements of the axisymmetric surrogate test device shown in
FIG. 7. The three traces of FIG. 8 represent the output of the
three displacement sensors. In FIG. 8 the y axis units are .mu.m,
and the x-axis represents time, measured in seconds.
[0044] Advantageously, the present method of weldbonding offers
attractive features such as micron-level accuracy joining of
optical components, stability over temperature, and long term
device reliability. That is, because the weldbonding joint is
capable of holding the components 20 with submicron precision.
[0045] Advantageously, the method of assembling opto-electronic or
photonic components into a package, according to the embodiments of
the present invention, utilizes a modified weldbonding processes
that minimizes the post-weld shift to submicron levels, which makes
this method suitable for assemblies of photonic or opto-electronic
devices or packages.
[0046] It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention
without departing from the spirit and scope of the invention. Thus
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *