U.S. patent application number 09/822207 was filed with the patent office on 2001-09-13 for electro-opto mechanical assembly for coupling a light source or receiver to an optical waveguide.
Invention is credited to Jewell, Jack, Kaluzhny, Mikhail, Moore, Andrew, Swirhun, Stanley.
Application Number | 20010021287 09/822207 |
Document ID | / |
Family ID | 23258161 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010021287 |
Kind Code |
A1 |
Jewell, Jack ; et
al. |
September 13, 2001 |
Electro-opto mechanical assembly for coupling a light source or
receiver to an optical waveguide
Abstract
A novel electro-opto-mechanical assembly is provided. The
electro-opto-mechanical assembly comprising: a first wafer, the
wafer having a top and bottom surface; at least one optical element
disposed on one surface of the first wafer; at least one discrete
opto-electronic transducer element disposed on the bottom surface
of the first wafer and in optical communication with the optical
element; and an optical waveguide; wherein the first wafer and the
optical element form an optical relay which relays light between
the discrete opto-electronic transducer and the optical waveguide
and thereby forms an efficient optical coupling between the
discrete opto-electronic transducer and the optical waveguide.
Inventors: |
Jewell, Jack; (Boulder,
CO) ; Swirhun, Stanley; (Boulder, CO) ;
Kaluzhny, Mikhail; (Boulder, CO) ; Moore, Andrew;
(Broomfield, CO) |
Correspondence
Address: |
Ajay A. Jagtiani
Jagtiani & Associates
Democracy Square Business Center
10379-B Democracy Lane
Fairfax
VA
22030
US
|
Family ID: |
23258161 |
Appl. No.: |
09/822207 |
Filed: |
April 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09822207 |
Apr 2, 2001 |
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09323204 |
Jun 1, 1999 |
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6243508 |
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Current U.S.
Class: |
385/14 ;
385/49 |
Current CPC
Class: |
G02B 6/4249 20130101;
G02B 6/4232 20130101; G02B 6/4292 20130101; G02B 6/4246 20130101;
G02B 6/423 20130101; G02B 6/4206 20130101 |
Class at
Publication: |
385/14 ;
385/49 |
International
Class: |
G02B 006/26 |
Claims
What is claimed:
1. An electro-opto-mechanical assembly comprising: a first wafer,
said wafer having a top and bottom surface; at least one optical
element disposed on said top surface of said first wafer; at least
one discrete opto-electronic transducer element disposed in
communication with said bottom surface of said first wafer and in
optical communication with said optical element; and an optical
waveguide; wherein said first wafer and said optical element form
an optical relay which relays light between said discrete
opto-electronic transducer and said optical waveguide and thereby
forms an efficient optical coupling between said discrete
opto-electronic transducer and said optical waveguide.
2. The assembly recited in claim 1, wherein said first wafer
comprises a material selected from the group consisting of glass,
plastic, sapphire, crystal, ceramic, metal, and semiconductor.
3. The assembly recited in claim 2 wherein said semiconductor
material is selected from the group consisting of GaP, GaAs, InP,
and Si.
4. The assembly recited in claim 1, wherein said optical element is
selected from the group consisting of refractive lenses, GRIN
lenses, diffractive lenses, holographic lenses, and gratings.
5. The assembly recited in claim 1, wherein said optical element
has a conic constant between and including -2 to 1.
6. The assembly recited in claim 1, wherein said optical element
further comprises an optical coating disposed on said optical
element.
7. The assembly recited in claim 1, further comprising electrical
contacts disposed on said bottom surface of said first wafer
8. The assembly recited in claim 1, wherein said first wafer has a
thickness of between 50 and 2,000 .mu.m.
9. The assembly recited in claim 1, wherein said transducer is
affixed to said first wafer by a solder.
10. The assembly recited in claim 9, wherein said solder is in the
form of a self-aligning solder bump.
11. The assembly recited in claim 9, wherein said solder is
indium.
12. The assembly recited in claim 1, wherein said transducer is
affixed by a conductive epoxy.
13. The assembly recited in claim 1, further comprising a fill
material between said first wafer and said transducer.
14. The assembly recited in claim 13, wherein said fill material
and said wafer have substantially similar refractive indexes.
15. The assembly recited in claim 13, wherein said fill material is
a two-part optical silicone.
16. The assembly recited in claim 1, further comprising an
antireflective coating on said first wafer and between said
transducer and said optical waveguide.
17. The assembly recited in claim 1, further comprising a micro
rough surface on said first wafer and between said transducer and
said optical waveguide.
18. The assembly recited in claim 1, further comprising a raised
portion of said first wafer that is disposed above said transducer
and said optical waveguide.
19. The assembly recited in claim 1, further comprising a passive
alignment feature disposed in said top surface of said first
wafer.
20. The assembly recited in claim 1, further comprising a second
wafer having a top and bottom surface, said second wafer being
disposed between said first wafer and said waveguide and said
bottom of said second wafer being proximal to said top of said
first wafer.
21. The assembly recited in claim 20 wherein said second wafer
comprises a material selected from the group consisting of glass,
plastic, sapphire, crystal, ceramic, metal and semiconductor.
22. The assembly recited in claim 21 wherein said semiconductor
material is selected from the group consisting of GaP, GaAs, InP,
and Si.
23. An electro-opto-mechanical assembly comprising: a first wafer,
said wafer having a top and bottom surface; an optical waveguide
proximal to said top surface of said first wafer; a second wafer
having a top and bottom surface, said second wafer being disposed
between said first wafer and said waveguide and said bottom of said
second wafer being proximal to said top of said first wafer; at
least one optical element disposed on said bottom surface of said
second wafer; and at least one discrete opto-electronic transducer
element disposed in communication with said bottom surface of said
first wafer and in optical communication with said optical element;
wherein said first wafer, said second wafer and said optical
element form an optical relay which relays light between said
discrete opto-electronic transducer and said optical waveguide and
thereby forms an efficient optical coupling between said discrete
opto-electronic transducer and said optical waveguide.
24. The assembly recited in claim 23, wherein said second wafer has
a thickness of between 50 and 2,000 .mu.m.
25. An electro-opto-mechanical assembly comprising: a first wafer,
said wafer having a top and bottom surface; at least one optical
element disposed on said bottom surface of said first wafer; at
least one discrete opto-electronic transducer element disposed in
communication with said bottom surface of said first wafer and in
optical communication with said optical element; and an optical
waveguide; wherein said first wafer and said optical element form
an optical relay which relays light between said discrete
opto-electronic transducer and said optical waveguide and thereby
forms an efficient optical coupling between said discrete
opto-electronic transducer and said optical waveguide.
26. An electro-opto-mechanical assembly comprising: a first wafer,
said wafer having a top and bottom surface; at least first and
second optical elements disposed on said top surface of said first
wafer; at least first and second discrete opto-electronic
transducer elements disposed on said bottom surface of said first
wafer and in optical communication with respective said first and
second optical elements; and at least first and second optical
waveguides; wherein said first wafer and said first optical element
form an optical relay which relays light between said first
discrete opto-electronic transducer and said first optical
waveguide and thereby forms an efficient optical coupling between
said first discrete opto-electronic transducer and said first
optical waveguide; and wherein said first wafer and said second
optical element form an optical relay which relays light between
said second discrete opto-electronic transducer and said second
optical waveguide and thereby forms an efficient optical coupling
between said second discrete opto-electronic transducer and said
second optical waveguide.
27. The electro-opto-mechanical assembly recited in claim 26,
further comprising a lens layer disposed on said top surface of
said first wafer, said lens layer for forming said optical
elements.
28. The electro-opto-mechanical assembly recited in claim 26,
further comprising a circuit layer disposed on said bottom surface
of said first wafer, said circuit layer for providing electrical
communication to said discrete opto-electronic transducers.
29. The electro-opto-mechanical assembly recited in claim 28,
wherein a portion of said circuit layer absorbs some of a light
beam emitted from said first discrete opto-electronic transducer to
function as a monitor for said first discrete opto-electronic
transducer.
30. The electro-opto-mechanical assembly recited in claim 1,
wherein said first wafer has first and second lateral dimensions,
said discrete opto-electronic transducer has third and fourth
lateral dimensions, and wherein said least either said third or
fourth lateral dimension is smaller than said either of said first
or second lateral dimension.
31. The electro-opto-mechanical assembly recited in claim 23,
wherein said first wafer has first and second lateral dimensions,
said discrete opto-electronic transducer has third and fourth
lateral dimensions, and wherein said least either said third or
fourth lateral dimension is smaller than said either of said first
or second lateral dimension.
32. The electro-opto-mechanical assembly recited in claim 25,
wherein said first wafer has first and second lateral dimensions,
said discrete opto-electronic transducer has third and fourth
lateral dimensions, and wherein said least either said third or
fourth lateral dimension is smaller than said either of said first
or second lateral dimension.
33. The electro-opto-mechanical assembly recited in claim 26,
wherein said first wafer has first and second lateral dimensions,
said first discrete opto-electronic transducer has third and fourth
lateral dimensions, and wherein said least either said third or
fourth lateral dimension is smaller than either of said first or
second lateral dimension.
34. An electro-opto-mechanical assembly comprising: a first wafer,
said wafer having a top and bottom surface; at least first and
second optical elements disposed on said top surface of said first
wafer; at least first and second discrete opto-electronic
transducer elements disposed on said bottom surface of said first
wafer and in optical communication with respective said optical
elements; at least first and second optical waveguides; and means
for reducing crosstalk between at least two of said discrete
opto-electronic transducer elements from said first wafer; wherein
said first wafer and said first optical element form an optical
relay which relays light between said first discrete
opto-electronic transducer and said first optical waveguide and
thereby forms an efficient optical coupling between said first
discrete opto-electronic transducer and said first optical
waveguide; and wherein said first wafer and said second optical
element form an optical relay which relays light between said
second discrete opto-electronic transducer and said second optical
waveguide and thereby forms an efficient optical coupling between
said second discrete opto-electronic transducer and said second
optical waveguide.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application makes reference to the following co-pending
U.S. patent application: U.S. App. No. 08/905,938, entitled "Device
for Coupling a Light Source or Receiver to an Optical Waveguide,"
filed Aug. 5, 1997. This application is hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to connectors, and
more particularly to a connector for passively aligning a light
source or detector to an optical waveguide such as a fiber optic
cable or bundle.
[0004] This invention is made with government support under
contract number FC 49620-97-C-0039, awarded by the Ballistic
Missile Defense Organization. The government may have certain
rights in this invention.
[0005] 2. Description of the Prior Art
[0006] Communication systems are now being developed in which
optical waveguides such as optical fibers are used as conductors
for modulated light waves to transmit information. These fibers may
be utilized for long distance communication networks, fiber to the
home networks, wide area networks, or local area networks.
[0007] The communication networks used comprise at least a
connector between the optical waveguide and a detector or light
emitter. A detector converts the signal from the light waves to an
electrical signal which may be used by conventional electrical
devices such as a computer. A light emitter, on the other hand,
performs the opposite function. It converts an electrical signal
into an optical signal. A generic term of either a light emitter or
a detector is an "optoelectronic transducer."
[0008] This application addresses the means and efficiency of
optical coupling between an optical waveguide and an optoelectronic
transducer. For single mode fibers, high efficiency coupling into
the waveguide requires: 1) close matching of the sizes of the light
beam and the waveguide; 2) close matching of the angular extent of
the light beam with the acceptance angle of the waveguide; and 3)
close positional alignment between the light beam and the
waveguide. Furthermore, real world effects, such as temperature
changes, may change the alignment. For this reason, many commercial
couplers compromise efficiency for slight positional tolerances.
For example, the light beam may be focused to a spot smaller than
the waveguide with the inevitable result that some light will be
lost in the waveguide. For multimode fibers, these alignment
considerations may be relaxed considerably.
[0009] The prior art has also addressed the alignment problem by
actively aligning the above elements. The major disadvantage of
active alignment is the cost associated with this process. For
example, for a device to be actively aligned, the light source
needs to be turned on and the other elements must be aligned with
the light source while the device is activated. By using this
approach, one must carefully align each device produced. Obviously,
this is not preferable if one is to mass-produce these
elements.
[0010] Numerous patents teach active alignment as discussed above.
For example, U.S. Pat. No. 4,204,743, by Etaix, discloses an
actively aligned connector for coupling an optical fiber to a light
emitter or receiver. This reference teaches the use of a truncated
cone in order to facilitate contacting of the emitter or receiver
without being obstructed by electrical connections to the emitter
or receiver. This device is activated to align the emitter with the
optics. Additionally, this device is very intolerant to off-axis
alignment of the optical lenses.
[0011] U.S. Pat. No. 4,307,934, by Palmer, discloses a packaged
fiber optic module that utilizes two oppositely oriented convex
lenses to transmit light between a light source and a fiber bundle.
Because of the use of this particular construction, the distance
between the fiber bundle and its associated convex lens is critical
since the lens functions to focus the light beam generated by the
light source. Thus, it is essential that active alignment be
utilized in this device. Additionally, this device is very
intolerant to off-axis alignment of the optical lenses.
[0012] U.S. Pat. No. 4,687,285, by Hily et al, discloses a packaged
fiber optic module that utilizes two oppositely oriented
plano-convex lenses in combination with a ball lens to transmit
light between a light source and a fiber bundle. As may be seen,
the axis of each lens must be in perfect alignment for this system
to function properly. Therefore, this device is very intolerant to
off-axis alignment of the optical lenses. This reference also
teaches the use of an adhesive to allow the ball lens to be
manipulated during the active alignment process.
[0013] U.S. Pat. No. 4,687,285, by Haberland et al, discloses a
packaged fiber optic module that has an active alignment
positioning means. In addition, this reference teaches the use of a
single spherical or cylindrical lens for focusing a light beam from
a fiber optic cable onto a detector. As may be seen in FIG. 8, it
is critical to align this spherical lens to the cable in order to
achieve coupling between the cable and the detector. Thus, this
device is very intolerant to off-axis alignment of the optical
lenses.
[0014] U.S. Pat. No. 4,711,521, by Thilays, discloses a terminal
device for an optical fiber. A mechanical guiding operation, by
means of a pin, is used to actively position a ball lens with
respect to a fiber optic cable end. The ball lens utilized by this
reference must be the same order of magnitude as the exit aperture,
e.g., 80 to 100 microns for the ball lens and 200 microns for the
aperture. This is an essential to allow precision alignment.
Therefore, this device is very intolerant to off-axis alignment of
the optical lens with the aperture.
[0015] U.S. Pat. No. 4,753,508, by Meuleman, discloses an optical
coupling device that utilizes a reflective cavity to provide
optical coupling between a fiber cable and a light emitter. A
spherical lens is aligned with the optical axis of the fiber cable
and is disposed outside of the reflective cavity. Precision active
alignment of the spherical lens to the fiber cable is essential for
the operation of this device. Therefore, this device is very
intolerant to off-axis alignment of the optical lens.
[0016] U.S. Pat. No. 5,347,605, by Isaksson, discloses an
optoelectronic connector that is actively aligned. To perform this
alignment, a mirror is provided which is journaled and is adjusted
to provide maximum coupling efficiency while the light source is
active.
[0017] U.S. Pat. Nos. 5,537,504, and 5,504,828, both by Cina et
al., disclose a transducer, a spherical lens and an optical fiber
cable in axial alignment with one another. This is accomplished by
activating the transducer and aligning the spherical lens with
respect to the fiber cable. Once this is done, the position of the
laser and lens is fixed by heating an epoxy layer. In addition, the
spherical lens is provided with different surfaces, one for
collimating light and one for introducing a spherical aberration
that compensates for lens position. Precision active alignment of
the spherical lens to the fiber cable is essential for the
operation of this device. Therefore, this device is very intolerant
to off-axis alignment of the optical lens, even with the second
surface of the spherical lens.
[0018] U.S. Pat. No. 4,842,391, by Kim et al., discloses an optical
coupler that utilizes two spherical lenses between a laser diode
and a fiber cable. As may be seen, active alignment is provided by
a set of screws which is used to actively align the optical
elements to increase coupling efficiency.
[0019] U.S. Pat. Nos. 4,265,511 and 4,451,115, both issued to Nicia
et al. disclose the use of two ball lenses for coupling optical
fibers. In a similar fashion, U.S. Pat. No. 5,175,783, by Tatoh,
discloses a similar structure. These patents disclose the concept
of carefully aligning each fiber in a tube to a precise axial and
distance position with respect to its respective ball lens.
Therefore, these devices are very intolerant to off-axis alignment
of the optical lens.
[0020] Other patents which disclose active alignment of a lens to a
fiber cable include: U.S. Pat. No. 5,526,455, by Akita et al.; U.S.
Pat. Re 34,790, by Musk; U.S. Pat. No. 5,073,047, by Suzuki et al.;
U.S. Pat. No. 4,824,202, by Auras; U.S. Pat. No. 4,818,053, by
Gordon et al.; U.S. Pat. No. 4,790,618, by Abe; U.S. Pat. No.
5,452,389, by Tonai et al.; and U.S. Pat. No. 4,752,109, by Gordon
et al. Precision active alignment of the lens to the fiber cable is
essential for the operation of these devices. Therefore, these
devices are very intolerant to off-axis alignment of the optical
lens to the light source.
[0021] The prior art has addressed this issue of off-axis alignment
of the fiber cable and the light source. For example, U.S. Pat. No.
5,566,265, by Spaeth et al., discloses a module for bi-directional
optical signal transmission. In this device, a plano-convex lens is
aligned with the optical axis of a fiber cable and a beam splitter
is aligned with a edge emitting light source. By adjusting the beam
splitter in relation to the plano-convex lens, one may correct for
off axis alignment of the light source and the fiber cable. In a
similar fashion, U.S. Pat. No. 5,463,707, by Nakata et al.,
discloses the use of a barrel lens instead of a plano-convex lens.
U.S. Pat. No. 5,546,212, by Kunikane et al., discloses the use of a
prism instead of a beam splitter. U.S. Pat. No. 5,074,682, by Uno
et al., discloses the use of a Grin rod lens instead of a beam
splitter.
[0022] The prior art also addresses the issue of utilizing
conventional TO Cans in opto-mechanical assemblies. These patents
generally address the use of a laser diode in a TO Can which is
aligned to a mechanical structure which partially houses the Can.
Examples of U.S. Pat. Nos. which discuss these structures include:
5,239,605 by Shinada; 5,274,723 by Komatsu; 5,526,455 by Akita et
al.; 4,639,077 by Dobler; 5,046,798 by Yagiu et al.; 5,495,545 by
Cina et al.; 5,692,083 by Bennett; 5,440,658 by Savage; and
5,548,676 by Savage. None of these references provide any teaching
as to how to integrate the opto-electronic transducer into the
package and provide wafer scale assembly of the package.
[0023] Finally, the prior art has addressed micro-mechanical
structures utilized in an opto-mechanical package. These patents
generally address the use of a semiconductor or ceramic material
base for an opto-electronic transducer. Examples of U.S. Pat. Nos.
which discuss these structures include: 4,733,932 by Frenkel et
al.; 5,362,976 by Suzuki; 5,485,021 by Abe; 5,566,264 by Kuke et
al.; 5,734,771 by Huang; and 5,500,540 by Jewell et al. and
5,266,794 by Olbright et al.
SUMMARY OF THE INVENTION
[0024] It is therefore an object of the present invention to
provide an opto-mechanical assembly that may be manufactured on a
semi-wafer scale.
[0025] It is a further object of the present invention to provide
an opto-mechanical assembly that provides easy optical coupling
between a light source/detector and a fiber.
[0026] It is a further object to provide an opto-mechanical
assembly where the waveguide insertional losses are low.
[0027] It is yet another object to provide an opto-mechanical
assembly which may meet very stringent specifications for use in
special environments, for example, under water or in gases of
composition which may damage a light source.
[0028] It is yet another object to provide for significantly
reduced optical aberrations generated by the opto-mechanical
assembly.
[0029] It is yet another object to provide an opto-mechanical
assembly that has the ability to withstand moderate temperature
cycles of approximately 200.degree. C.
[0030] In all of the above embodiments, it is an object to provide
an opto-mechanical assembly that has a small number of components
and high endurance against a connecting/disconnecting operation and
which can be aligned easily.
[0031] In all of the above embodiments, it is a further object to
provide an opto-mechanical assembly that has the ability to
tolerate lateral and angular misalignment of the light
source/detector and fiber.
[0032] According to one broad aspect of the present invention,
there is provided an electro-opto-mechanical assembly comprising: a
first wafer, the wafer having a top and bottom surface; at least
one optical element disposed on the top surface of the first wafer;
at least one discrete opto-electronic transducer element disposed
in communication with the bottom surface of the first wafer and in
optical communication with the optical element; and an optical
waveguide; wherein the first wafer and the optical element form an
optical relay which relays light between the discrete
optoelectronic transducer and the optical waveguide and thereby
forms an efficient optical coupling between the discrete
opto-electronic transducer and the optical waveguide.
[0033] According to another broad aspect of the present invention,
there is provided an electro-opto-mechanical assembly comprising: a
first wafer, the wafer having a top and bottom surface; an optical
waveguide proximal to the top surface of the first wafer; a second
wafer having a top and bottom surface, the second wafer being
disposed between the first wafer and the waveguide and the bottom
of the second wafer being proximal to the top of the first wafer;
at least one optical element disposed on the bottom surface of the
second wafer; and at least one discrete opto-electronic transducer
element disposed in communication with the bottom surface of the
first wafer and in optical communication with the optical element;
wherein the first wafer, the second wafer and the optical element
form an optical relay which relays light between the discrete
optoelectronic transducer and the optical waveguide and thereby
forms an efficient optical coupling between the discrete
opto-electronic transducer and the optical waveguide.
[0034] According to yet another broad aspect of the present
invention, there is provided an electro-opto-mechanical assembly
comprising: a first wafer, the wafer having a top and bottom
surface; at least one optical element disposed on the bottom
surface of the first wafer; at least one discrete opto-electronic
transducer element disposed in communication with the bottom
surface of the first wafer and in optical communication with the
optical element; and an optical waveguide; wherein the first wafer
and the optical element form an optical relay which relays light
between the discrete opto-electronic transducer and the optical
waveguide and thereby forms an efficient optical coupling between
the discrete opto-electronic transducer and the optical
waveguide.
[0035] According to yet another broad aspect of the present
invention, there is provided an electro-opto-mechanical assembly
comprising: a first wafer, the wafer having a top and bottom
surface; at least first and second optical elements disposed on the
top surface of the first wafer; at least first and second discrete
opto-electronic transducer elements disposed on the bottom surface
of the first wafer and in optical communication with respective the
first and second optical elements; and at least first and second
optical waveguides; wherein the first wafer and the first optical
element form an optical relay which relays light between the first
discrete opto-electronic transducer and the first optical waveguide
and thereby forms an efficient optical coupling between the first
discrete opto-electronic transducer and the first optical
waveguide; and wherein the first wafer and the second optical
element form an optical relay which relays light between the second
discrete opto-electronic transducer and the second optical
waveguide and thereby forms an efficient optical coupling between
the second discrete opto-electronic transducer and the second
optical waveguide.
[0036] According to yet another broad aspect of the present
invention, there is provided an electro-opto-mechanical assembly
comprising: a first wafer, the wafer having a top and bottom
surface; at least first and second optical elements disposed on the
top surface of the first wafer; at least first and second discrete
opto-electronic transducer elements disposed on the bottom surface
of the first wafer and in optical communication with respective the
optical elements; at least first and second optical waveguides; and
means for reducing crosstalk between at least two of the discrete
opto-electronic transducer elements from the first wafer; wherein
the first wafer and the first optical element form an optical relay
which relays light between the first discrete opto-electronic
transducer and the first optical waveguide and thereby forms an
efficient optical coupling between the first discrete
opto-electronic transducer and the first optical waveguide; and
wherein the first wafer and the second optical element form an
optical relay which relays light between the second discrete
opto-electronic transducer and the second optical waveguide and
thereby forms an efficient optical coupling between the second
discrete opto-electronic transducer and the second optical
waveguide.
[0037] Other objects and features of the present invention will be
apparent from the following detailed description of the preferred
embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] The invention will be described in conjunction with the
accompanying drawings, in which:
[0039] FIG. 1 is a cross sectional view of an opto-mechanical
assembly constructed in accordance with a preferred embodiment of
the invention;
[0040] FIG. 2a is a back view of a wafer microlens chip showing
patterned electrical connections for the opto-mechanical assembly
of FIG. 1;
[0041] FIG. 2b is a back view of lead frame connectors associated
with the patterned electrical connections of FIG. 2a;
[0042] FIG. 3 is a cross sectional view of a laser mounting
utilized in an alternate embodiment of the opto-mechanical
assembly;
[0043] FIG. 4 is a cross sectional view of an optical system used
for coupling a multimode waveguide;
[0044] FIG. 5 is a cross-sectional view of an alternative
embodiment of the opto-mechanical assembly of FIG. 1, which
illustrates a refractive lens system used to couple a single mode
waveguide to a light source;
[0045] FIG. 6 is a cross-sectional view of an alternative
embodiment of the opto-mechanical assembly of FIG. 1, which
illustrates a diffractive lens system used to couple a single mode
waveguide to a light source;
[0046] FIG. 7 is a cross-sectional view of an alternative
embodiment of the opto-mechanical assembly of FIG. 1, which
illustrates an ion-diffused planar micro lens system used to couple
a single mode waveguide to a light source;
[0047] FIG. 8 is a cross-sectional view of an alternative
embodiment of the opto-mechanical assembly of FIG. 1, which
illustrates a hybrid assembly used to couple an optical waveguide
to a light source;
[0048] FIG. 9 is a cross-sectional view of a transceiver assembly
constructed in accordance with a preferred embodiment of the
invention;
[0049] FIGS. 10a, 10b and 10c are cross-sectional views of the
mounting structure for attaching a VCSEL to the lens of FIGS. 1, 5
through 9, 13, and 16 through 19;
[0050] FIGS. 11 and 12 are plots of laser offset v. coupling
efficiency for select lenses;
[0051] FIG. 13 is a cross-sectional view of an alternative
embodiment of the opto-mechanical assembly of FIG. 1, which
illustrates an integrated lens and housing assembly which is used
to couple an optical waveguide to a light source;
[0052] FIG. 14 is an isometric view of a microlens wafer having a
plurality of opto-mechanical assemblies as illustrated in FIGS. 1,
5 through 9 and 13;
[0053] FIG. 15 is a block diagram of the steps associated with the
construction of the opto-mechanical assemblies as illustrated in
FIGS. 1, 5 through 9 and 13;
[0054] FIG. 16 is a cross-sectional view of a transceiver assembly
constructed in accordance with an alternate embodiment of the
invention;
[0055] FIG. 17 is a cross-sectional view of an OSA or transceiver
assembly constructed in accordance with an alternate embodiment of
the invention;
[0056] FIG. 18 is a planar view of the transceiver of FIGS. 9, 16,
and 17; and
[0057] FIG. 19 is a cross sectional view of an opto-mechanical
assembly constructed in accordance with yet another embodiment of
the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0058] Before describing the invention, it is essential to provide
definitions to terms that are used in the description of the
invention. The first of these terms is an optical waveguide.
[0059] For the purposes of this patent application, an "optical
waveguide" is a system of material boundaries or structures for
guiding an optical wave. Such waveguides include, but are not
limited to, single mode optical fibers, multi-mode optical fibers,
semiconductor waveguides, dielectric waveguides, single mode
polymer waveguides, and multimode polymer waveguides and optical
connectors.
[0060] A single mode optical fiber (SMF) is a fiber optic cable in
which only the lowest order bound mode (which may consist of a pair
of orthogonal polarized fields) may propagate at the wavelength of
interest. Generally, SMF has a waveguide in core diameter of
.about.8 .mu.m for wavelengths in the 1300 to 1600 nm range. It
should be appreciated that the diameter of the SMF may vary while
still utilizing the teachings of the present invention.
[0061] A multi-mode optical fiber (MMF) is a fiber optic cable that
will allow more than one bound mode to propagate. Typically, MMF
has a waveguide in core diameter of .about.50 .mu.m or more.
Several types of MMF are of particular interest to this invention.
One type of fiber is plastic fiber having a core diameter of 100
.mu.m, 125 .mu.m or 250 .mu.m. Another type of fiber is a 50 .mu.m
or 62.5 .mu.m diameter glass fiber.
[0062] It should be understood that while specific fibers have been
discussed above, the inventive concept may be applied to any SMF,
MMF, or any waveguide including all discussed above. It should be
appreciated that a particular design technique used for a MMF may
not function for a SMF due to the tolerance differences between the
fibers. A design technique for a SMF will usually function in an
MMF environment, but may be more costly than techniques designed
for an MMF.
[0063] For the purpose of this application, a wafer is defined as a
material having substantially parallel and planar surfaces. An
optical wafer is a wafer that has at least a region which is
composed of a substantially optically transparent material which
for the purposes of this application means any material which
allows at least 10% transmission of light at a wavelength of
interest. It should be appreciated that the term "wafer" may
represent a whole wafer as illustrated in FIG. 14 or any portion
thereof such as in FIG. 1. The term "semi-wafer" refers to the use
of an optical wafer and discrete optoelectronic transducer elements
affixed together.
[0064] For the purpose of this application, an "optoelectronic
transducer" is a generic term for an optoelectronic device which
either converts electrical energy to optical energy, or optical
energy to electrical energy, or both.
[0065] With reference to the Figures, wherein like references
characters indicate like elements throughout the several views and,
in particular, with reference to FIG. 1, an opto-mechanical
assembly 10 is illustrated. In order to understand how the
opto-mechanical transducer was formed and the novelty associated
with this formation, one should refer to FIG. 15 which is a block
diagram of the formation process for the opto-mechanical assembly
of FIG. 1. In order to avoid confusion, we will first describe the
case for the MMF embodiment since this embodiment has fewer
restrictions than the SMF embodiment.
[0066] As may be seen from block 100, a first optical wafer
substrate 12 is formed. This first wafer 12 may be formed by any
means known in the art or may be commercially purchased from Schott
or AXT. Optical wafer substrate 12 may be glass, plastic, sapphire,
crystal, ceramic, semiconductor or any other material known in the
wafer processing art. The preferred material is glass because of
the optical characteristics, commercial availability, and the large
variety of characteristics available, such as thermal expansion
matching with other materials. The use of plastic is desired due to
the ease of use in molding and low cost. In addition, the use of
plastic allows for easier thermal matching between the wafer and
the opto-mechanical assembly housing. The use of semiconductor
material, such as, but not limited to GaP, GaAs, or Si, may be
desired for improved heat dissipation, for thermal matching with an
opto-electronic transducer, for fabricating electronic circuitry,
or so that the entire fabrication process may be expedited by
growing a light source directly on optical wafer 12. Additionally,
sapphire may be the preferred material for wafer 12 because of its
ruggedness and the possibility of forming silicon-on-sapphire (SOS)
circuits.
[0067] Turning back to FIG. 15, the next step in the process is the
production of optical elements 24 such as microlenses on optical
wafer 12. For convenience, we have defined each optical wafer 12 as
having a top and bottom planar surface 16, 18 respectively. In a
preferred embodiment, optical elements 24, for example, refractive
lenses, are formed on top planar surface 16. This may be
accomplished by spinning photoresist on top surface 16 of optical
wafer 12 and patterning pancakes of this photoresist. Finally, the
photoresist pancakes are then melted to form optical elements 24
such as microlenses. Shapes of optical elements 24 are determined
by varying the relationship between the diameter of the pancake and
the thickness of the pancake as well as the viscosity of the
photoresist. Refractive microlenses may be produced by other
techniques such as replication by molding or by a gray-level
photoresist process. It should be appreciated that holograms may be
utilized.
[0068] In an alternative embodiment, one may pattern holes through
a masking layer on top surface 16 of optical wafer 12 and diffuse
ions in these holes. This changes the refractive index of wafer 16
in select regions 54 localized near the holes as illustrated in
FIG. 7. This technique is effective in making a gradient index
(GRIN) lens. Finally, diffractive and/or holographic lenses may
also be constructed.
[0069] It should be appreciated that coatings 25 may be applied to
optical elements 24 after their formation on optical wafer 12. The
significant advantage to this approach is that the cost of
manufacturing each individual optical element 24 is reduced since
the process is performed on a wafer level. Optical elements 24 that
may be formed by the processes discussed above and by other
processes, include, but are not limited to: microlenses, reflectors
(partial or total).
[0070] For MMF embodiment, it may be beneficial to introduce
defocus in optical elements 24. It should be appreciated that the
introduction of these optical distortions are generally not desired
in the SMF embodiment. The benefit to utilizing these distortions
in the MMF embodiment include, but are not limited to: reduced
optical feedback into optoelectronic transducer 26 resulting from
reflections from fiber 32, and reduced sensitivity to alignment
variations.
[0071] The shape of optical element 24 may be optimized as may be
seen in FIG. 11 and 12. For example, the conic constant cc=0
describes a spherical lens, cc=-1 is an asphere, cc=+1 is another
asphere. As may be seen, for the cases simulated and illustrated,
it is preferable to have a cc.ltoreq.0.
[0072] In a similar fashion, second wafer substrate 14 may be
constructed. It should be appreciated that optical wafers 12 and 14
may be of different material or may be constructed from the same
material. Optical wafer 14 has top and bottom surfaces 20, 22
respectively. In an alternate embodiment, optical wafer 14 would
have optical elements 24' fabricated on bottom surface 22 while
wafer 12 would not have optical elements 24. In this manner, the
optical elements 24' may be further separated along an optical axis
from optoelectronic transducer 26. Additionally, processing of
optical wafer 12 may be conducted independently of optical wafer
14. In yet another embodiment, optical elements 24 and 24' will be
present as illustrated in FIG. 5. It should be appreciated that
having optical elements 24, 24' on both optical wafers 12 and 14
would preferably be associated with SMF applications as illustrated
in FIGS. 5 and 6. Preferably, if optical wafer 12 is thick enough,
e.g., FIGS. 1, 8, 9, and 13, optical elements 24 may be disposed on
optical wafer 12 in a MMF application. An optical coating 25' may
be placed on optical element 24', for example, to reduce or
increase reflections from optical element 24. It should be
appreciated that optical elements 24 and 24' may be the same type
or different optical elements.
[0073] Turning back to FIG. 1, there are two optical axes
illustrated. The first optical axis 28 is associated with
optoelectronic transducer 26 and the second optical axis 30 is
associated with waveguide 32. As may be seen in FIG. 1, axes 28 and
30 may be in lateral and/or angular misalignment. This is due to
minor misalignments of elements of the opto-mechanical assembly 10.
As may be seen, optical elements 24 or 24' may compensate for this
minor misalignment to allow for efficient optical coupling between
optoelectronic transducer 26 and waveguide 32.
[0074] An important feature of this invention is the ability to
have efficient optical coupling between waveguide 32 and
optoelectronic transducer 26, despite misalignment between optical
axes 28 and 30. This feature is better illustrated in FIG. 4, which
is discussed below.
[0075] As discussed above, optical wafer 12 may be processed
independently of optical wafer 14. As may be seen in FIG. 2a,
electrical connections such as common contact 34 may be patterned
on bottom surface 18 of optical wafer 12. This has the added
advantage of providing electrical access to the side of
optoelectronic transducer 26 which faces optical wafer 12 as
illustrated in FIGS. 2a and 3. Photodiode contact 36 and
optoelectronic transducer contacts 38 are also provided to complete
electrical circuits to photodiode 40 and optoelectronic transducer
26, respectively.
[0076] Protective epoxy 42 is utilized to attach optical wafers
12,14 as well as provide a space around optical element(s) 24, 24'
there between. For example, this may allow the device to have an
air gap with a refractive index of 1.0, between optical wafers 12
and 14 which have a refractive index of 1.5 and 1.5 respectively.
Optical elements 24 and 24' typically have a refractive index of
1.5. It should be appreciated that while an air gap is disclosed in
the preferred embodiment, any material may be placed in this gap so
long as there is a difference in refractive indices between the
material utilized and optical element 24 or 24' of at least 0.2.
Epoxy 42 may be applied by a silk screening process which has a
tolerance of .about.10 .mu.m. In a preferred embodiment, optical
wafers 12,14 are mounted together by epoxy 42 to form a unitary
structure before dicing.
[0077] Optoelectronic transducer 26 is attached mechanically and
electrically to optical wafer 12 by either a conductive epoxy or
solder bump bond or by other means as illustrated as step 106 in
FIG. 15. FIGS. 10a through 10c illustrate the use of any of these
means. For a solder bump bond, this process may be accomplished by
a "pick and place machine" which would provide an alignment
tolerance of, for example, 3-25 .mu.m while a self aligned solder
bump process may provide a tolerance of .about.2 .mu.m or even
less. This same process may be used for affixing an optional
monitoring photodiode 40, however its alignment usually does not
need to be as accurate as optoelectronic transducer 26. A major
improvement over prior art devices is the ability to utilize
individual transducers 26 and photodiodes 40 as illustrated in FIG.
14. In prior art devices, these transducers were utilized on a
wafer scale and there was no ability to use an individual
transducer on a transducer wafer without manipulating the entire
transducer wafer. Additionally since one lateral dimension of
transducer 26 is smaller than one lateral dimension of wafer 12 (in
this case, the lateral dimension between dicing lines on wafer 12),
this assures that one is not utilizing well known wafer to wafer
processes. Another advantage of the present invention is that the
transducers may be pre-sorted before being mounted onto optical
wafer 12. Also the wafer used to fabricate transducers 26 is
efficiently utilized since the transducer wafer (not shown) does
not need to include area-using elements such as circuitry. The
present invention places non-transducer functionality such as
circuitry on the less costly optical wafer 12.
[0078] As may be seen in FIG. 1, an electrical spacer 58 may be
provided so as to allow contacts 39; for example, lead frame
contacts, ceramic chip contacts, flex circuit contacts, or any
other electrical contacts; to be in planar level across assembly
10.
[0079] As shown in FIG. 14, an automated probe test may be utilized
to test the sub-packages at this point. It should be appreciated
that the testing is preferably conducted at the wafer level, ie.,
before optical wafers 12, 14 are diced into individual components
and housed. Finally, it should be appreciated that the step of
testing the sub-assemblies at the wafer level is optional but would
provide significant efficiency, cost reductions, and increased
assembly process control.
[0080] Finally, the sub-assemblies are separated to form
independent units that are then incorporated into a housing 52.
This step is illustrated in FIG. 15 as block 110. Separation of
sub-assemblies is performed preferably by sawing or any other
method know in the semiconductor separation art.
[0081] Turning now to step 112, the independent units are packaged
into housing or encapsulant 52. It should be appreciated that
encapsulant 52 may be constructed of any material and is designed
to provide structural integrity to the elements enclosed therein.
It is preferred that optical wafer 14 have an alignment recess 59
so that waveguide 32 may be passively aligned to optical wafer
14.
[0082] Now that the basic structure of the Electro-Opto-Mechanical
Assembly 10 has been described, it is essential to discuss some of
the more critical features of the invention such as the physical
positional relationships of optoelectronic transducer 26, waveguide
32 and optical elements 24. It is necessary to discuss the
following relationships in detail: the distance "d" between optical
elements 24 and waveguide 32; the distance between transducer 26
and optical elements 24, the lateral displacements between the
optical axis 28 of waveguide 32 and optical axis 28' of transducer
26; the angular displacement between the optical axis 28 of
waveguide 32 and optical axis 28" of transducer 26; the length of
waveguide 32; and the size of optical elements 24 in relationship
to transducer 26.
[0083] Turning now to FIG. 4, we will now discuss the positioning
of waveguide 32. Instead of using conventional object-image
position for optoelectronic transducer 26 and waveguide 32,
respectively, a MMF is positioned relative to the image position i
and the back focal plane f. The optimal MMF distance "d" is defined
by the type and radius optical element 24, the angle of the beam
emitting from or incident upon optoelectronic transducer 26 and
other factors such as back reflection from waveguide 32, width or
diameter of fiber core 50, and sensitivity to lateral displacement
of optical axis 28 and optical axis 28'. This position may be found
experimentally or by simulation. Once the optimum position is
determined, the present invention allows for passive alignment to
achieve this same goal and thus eliminate the need for active
alignment which is generally required in the prior art devices.
[0084] For clarity, like elements have been provided with like
reference numerals except that a prime has been added to each
reference numeral where there is a slight difference in the
particular element in this embodiment.
[0085] FIG. 4 shows the light beam paths for 3 cases: perfect
alignment of axis 28 is illustrated by beam path 44; lateral
displacement of optoelectronic transducer 26' is illustrated by
beam path 44' and axis 28'; and tilt of optoelectronic transducer
26" is illustrated by beam path 28" and axis 28". Due to the short
focal length of optical element 24 and the relatively large fiber
core diameter 50 of waveguide 32, tilts on the order of degrees
have negligible effect in the MMF embodiment. It has been found
that for MMF applications the maximum tilt of optoelectronic
transducer 26" may be as high as 10 degrees without adverse impact
on assembly 10 and 5 degrees for the SMF embodiment. Additionally,
the maximum lateral displacement for MMF applications has been
found to be >50 .mu.m for the MMF embodiment and 2 .mu.m for the
SMF embodiment. The negligible effect of lateral displacement may
be visualized in FIG. 4 by the near coincidence of beams 44 and
44", especially in the region near the back focal plane f.
[0086] A model based on the beam wave front propagation using
commercial software (GLAD 4.5) has been developed to simulate and
analyze the proposed optical design for a multimode fiber having a
parabolic graded index core of 62.5 .mu.m and 50 .mu.m in diameter.
The fiber model was analyzed to find the propagation length
necessary for accurate coupling efficiency estimation. It was found
that the major power loss (more than 95% of total losses) happens
over very short length of waveguide 32, e.g., 2 to 5 mm (2-5
pitches). The propagation length 2.5 mm was chosen for waveguide 32
to determine coupling efficiency.
[0087] A typical value of optical plastic/glass refractive index of
1.5 was chosen for the initial simulation with a 62.5 .mu.m core
fiber. The size of optical element 24 and distances from transducer
26 to optical element 24, and from optical element 24 to waveguide
32 were approximated and varied in the simulation to achieve best
system performance.
[0088] In FIG. 4, transducer 26' has been provided with a lateral
offset and has optical beam path 44' associated with this offset.
As may be seen, beam paths are in approximate alignment, especially
near the back focal plane f, due to optical element 24. By
utilizing optical element 24, transducer 26' may have a lateral
offset of as much as 50 .mu.m before optical coupling with
waveguide 32 is significantly affected in the MMF embodiment. This
is shown in FIGS. 11 and 12. This is accomplished by optical
element 24 refocusing beam path 44' onto the core of waveguide 32
as illustrated in FIG. 4. It is preferable that optical element 24
have a radius of curvature of 300 .mu.m or less in order to assure
that the diameter and position of beam 44' at waveguide 32 will be
appropriate for effective optical coupling with such a large
lateral offset. For larger diameter fibers, e.g., plastic optical
fibers, the maximum lateral offset is larger in approximate
proportion to the ratio of the fiber diameters.
[0089] Turning now to FIGS. 11 and 12, the coupling efficiency for
several lenses having radii which vary from 150 .mu.m to 200 .mu.m
and having various conic constants are displayed. FIG. 11
corresponds to the molded lens embodiment illustrated in FIG. 13
while FIG. 12 corresponds to the wafer lens structure illustrated
in FIG. 8. As may be seen, from the figures, a radius of 175 .mu.m
provides better coupling than 150 .mu.m or 200 .mu.m radii, and a
150 .mu.m radius provides better coupling than 200 .mu.m. Thus, the
optimal radius of curvature is between 150 .mu.m and 175 .mu.m.
Similarly, the optimal conic constant is between 0 and -1. It is
clear from these figures that the coupling efficiency change is
less than 10% for a 40 .mu.m lateral offset of transducer 26 for an
optical element 24 optimized for these conditions. Optical element
24 may be further optimized by forming its surface modified by even
higher-order aspheric coefficients.
[0090] The designs are also very tolerant to optical element 24
radius and optical element 24 shape variation. For example, a 10%
variation in the radius of optical element 24 and a significant
change in optical element 24 shape (conic constant from -1 to 0)
leads to little variation in coupling efficiency.
[0091] Turning now to FIGS. 10a through 10c, the bonding of
transducer 26 to optical wafer 12 is illustrated. The process of
mounting and bonding a transducer 26 with its active side down onto
a patterned surface, such as optical wafer 12, is referred to as
flip-chip bonding. Most lasers, including VCSELs, are not flip-chip
bonded. Rather, the substrate side is bonded to a flush surface
such as that of a TO-header. FIGS. 3 and 10a through 10c illustrate
a close-up view of a flip-chip bonded VCSEL. If a self-aligned
solder-bump bonding is used, transducer 26 typically stands about
50 .mu.m off the surface of optical wafer 12 due to the large
thickness of the solder bumps. Self-aligned solder-bump bonding has
a distinct advantage over other bonding methods and is the
preferred method in this invention. Due to surface tension in the
solder in its liquid state, transducer 26 will actually be pulled
into alignment with the photolihgraphically defined solder bump
pads. For typical pad dimensions of about 50 .mu.m, this means that
as long as the transducer 26 chip is placed within about 25 .mu.m
of its desired position, the self alignment of the solder bonding
process will pull the transducer 26 to within about 2 .mu.m of the
desired position. Use of smaller size pads require more accurate
initial placement, produce more accurate alingment, and have
reduced stand-off height, in approximate proportion to the pad
size. This passive self alignment is a tremendous benefit to the
overall alignment budget and greatly reduces the lateral
displacement discussed above.
[0092] The selection of the appropriate solder is not an
inconsequential issue as well. When boding many chips to a common
substrate, it is important that the chips do not fall off or move
significantly while subsequent chips are being mounted. This will
affect the choice of bonding materials. For example, a pure-indium
solder is soft enough to "tack" with very light pressure and
therefore a chip may be placed on wafer 12 with low likelihood of
slippage. Thus, the characteristics for a suitable solder is one
that will allow "tacking" to occur with little pressure and may be
flowed at a temperature that will not affect wafer 12. In assembly
10, transducers 26, transducers 26' and photodiodes 40 would be
mounted first, using an indium or other appropriate solder to take
advantage of the passive self-aligning process. Then, a single
heating of the entire optical wafer 12 might be used to align and
bond all the traducers 26, transducers 26', and photodiodes 40.
Then other chips could be mounted, for example with a conductive
epoxy, which uses a lower temperature for setting. A more advanced
process could incorporate a laser micro-welder to bond each chip as
it is placed.
[0093] The one drawback to the self-aligned solder bonding process
is the displacement between the surface of transducer 26 and
optical wafer 12. This displacement raises the issues of a
contaminant inside the beam of transducer 26, reflection feedback
into transducer 26 as illustrated in FIG. 10a by optical rays 62.
FIGS. 3, 10b, and 10c illustrate some options that may be used to
reduce feedback effects to transducer 26. A promising solution to
the contaminant and reflection problem is to fill the space, after
bonding, with a material 60 whose refractive index matches that of
wafer 12 as illustrated in FIG. 3. Materials are available for this
purpose, such as a two-part optical silicone sold by Shin-Etsu.
Another solution to this problem is to provide an antireflective
coating 64 on optical wafer 12 as illustrated in FIG. 10b. In
addition, or by itself, the surface of optical wafer 12 may be
provided with a micro-rough surface 66 at least below transducer
26. This surface 66 is provided to scatter reflection and thus
prevent coherent feedback into transducer 26. Yet another solution
to this problem is to construct a raised dielectric mesa 68 and or
a raised portion 70 of wafer 12. The mesa 68 and/or raised portion
70 effectively reduces the gap between transducer 26 and wafer 12.
In this manner, the possibility of contamination and the
detrimental effects of reflection feedback are reduced or
eliminated. Finally, it should be appreciated that any of these
options, in combination or alone, may be incorporated into any
embodiment of the invention discussed above or below.
[0094] Now that the preferred embodiment has been discussed,
alternate embodiments shall be described below. For clarity, like
elements have been provided with like reference numerals except
that a prime has been added to each reference numeral where there
is a slight difference in the particular element in this
embodiment. The following discussion will focus on the differences
between the elements of this embodiment and that of the preferred
embodiment.
[0095] Turning now to FIGS. 8, 9, 13 and 16, alternate embodiments
of electro-opto-mechanical assembly 10 are illustrated.
Specifically, FIG. 8 illustrates a hybrid assembly used to couple
optical waveguide 32 to optoelectronic transducer 26. In this
embodiment, a passive alignment feature 72 is provided for wafer 12
which mates with a passive alignment feature 74. In this
embodiment, only one wafer 12 is used. Additionally, waveguide 32
is secured via a receptacle 76 having passive alignment features 74
disposed at one end. Receptacle 76 may be affixed to housing 52 by
any means known in the art such as mechanical clips. Preferably,
Receptacle 76 or connector 82 would be a MT-RJ fiber ferrule 82
fitting to alignment pins 84 as illustrated in FIG. 16. Receptacle
76 and connector 82 may be constructed of any material but would
preferably be made from molded plastic.
[0096] Turning now to FIG. 9, a cross-sectional view of a duplex
assembly is provided. As may be seen, this figure duplicates FIG. 8
and adds a second channel which may preferably be used as a
receiver or as a second transmitter. Alternatively, both channels
may be used as receivers. The invention readily extends to, and
includes, any number of channels, such as 12 channels or even
more.
[0097] Turning now to FIG. 13, a cross-sectional view of an
integrated lens and housing assembly is illustrated. In this
embodiment, housing 52' is formed from molded plastic or any other
malleable material which transmits light. As may be seen housing
52' has an integrated lens 25'. In addition, recess 78 is formed in
housing 52' to allow for mounting of transducer 26. Finally,
housing 52' is provided with outwardly tapered flanges 80 that
engage waveguide 32. It should be appreciated that flanges 80 need
not be taped to be utilized in conjunction to the teachings of the
present invention.
[0098] Turning now to FIG. 16, a transceiver assembly constructed
in accordance with an alternate embodiment of the invention. This
device is similar to that described in FIG. 9 in basic operation.
This device has a different mounting structure for waveguides 32.
Optical sub-assembly 81 comprises a solid piece with pins 84
precisely held in bores 86, wafers 12 and 14, transducers 26,
contacts 39, etc. Fiber ferrule or connector 82 is another solid
piece containing fibers 32 and 32' and counterbores 87 for
precisely engaging pins 84. Wafer 14 could be just about any
material including silicon, glass, or even a piece of metal, e.g.
copper, with bores 86 and vias or voids 88 stamped through it or a
lead-frame metal with etched features.
[0099] Turning now to FIG. 17, an optical sub-assembly (OSA) or a
transceiver 114 is illustrated. It comprises optoelectronic
transducers 26, 26' and contacts 39 and may contain spacers 58. OSA
or transceiver 114 also comprises connector 116 which is preferably
a single piece of molded plastic which contains alignment pins 84,
and includes spaces 118 which typically comprise air. It may also
contain alignment receptacles 120, for precise alignment to
alignment features 122. In the event that alignment receptacles 120
and alignment features 122 are not used, spaces 118 may be used for
alignment to lenses 24. Spaces 118 and/or alignment receptacles 120
may be complete vias completely traversing connector 116, or they
may be small air spaces, with plastic which fills regions 124 and
126, respectively. In the event that alignment receptacles 120 and
alignment features 122 are used, and air spaces 88 are desired to
be complete vias or voids 88, it is not necessary for region 128 to
be filled with plastic, i.e., a single via or void 88 could be
formed in which regions 126 and 128 comprise air. The preferred
embodiment however has alignment receptacles 120 and alignment
features 122, and regions 124, 126 and 128 are plastic filled as
illustrated. Alignment features 122 may be formed in the same
formation process as lenses 24, and may be larger than lenses 24 to
increase mechanical robustness.
[0100] An additional and optional feature or wafer 12 is that it
may contain one or more layers on either side which may comprise
materials different from that of wafer 12. Lens layer 130 may be
used if the material of wafer 12 is not well-suited for forming
microlenses 24. For example, sapphire may be desired to comprise
wafer 12, however it is very difficult to etch and therefore it may
be difficult to form lenses 24 integral to it. In this case,
several options exist. Lenses 24 may simply comprise a photoresist
or other material which is allowed to melt, thereby forming lenses
24. One disadvantage of this structure is that the materials which
may be melted so are typically not thermally, mechanically, or
chemically robust. Suitable choices of materials and/or higher
temperature melting may help this situation. Another choice is to
form a layer 130 of tough material such as spin-on-glass (SOG), and
then form microlenses 24 by the usual process of melting material
such as photoresist followed by etching the resulting pattern into
layer 130. Additionally, a circuit layer 132 is illustrated.
[0101] Circuit layer 132 may be used to increase functionality in
wafer 12. In a preferred embodiment, circuit layer 132 comprises
deposited silicon in a polycrystalline or crystalline state. In
some embodiments, a region of circuit layer 132 absorbs a portion
of light beam emitted from transmitting optoelectronic transducer
26. With suitable contacts, these regions may form a monitor for
transducer 26, which replaces the functionality of monitor 40
illustrated in FIG. 16 and other Figures. This monitor has the
advantage of sampling the entire beam, rather than just a portion.
It may be desirable to remove a portion of circuit layer 132,
leaving void 133, in order to maximize the efficiency of receiving
optoelectronic transducer 26'.
[0102] OSA or transceiver 114 may comprise additional components to
increase functionality. For example, driver circuit 144 may drive
transmitting optoelectronic transducer 26, and/or amplifier 146 may
amplify the signals from receiving optoelectronic transducer 26'.
With sufficient transmit and receive functionality, OSA 114
comprises a transceiver. Driver circuit 144 and/or amplifier 146
may be bonded to wafer 12 with bump bonds, such as bump bond 148
for transducer 26, or they may be wirebonded or they may be
mechanically and electrically attached by other means.
Alternatively, drive and receive functionality may be implemented
in circuitry directly in circuit layer 132. In a preferred
embodiment, wafer 12 is sapphire, circuit layer 132 is
silicon-on-sapphire (SOS), and the functions of monitoring the
output of transmitting optoelectronic transducer 26, driving
transducer 26, and amplifying the output of receiving
optoelectronic transducer 26', are all integrated into circuitry
formed in circuit layer 132.
[0103] FIG. 17 shows adjacent connector 116' which may be formed
integral to connector 116. A plurality of connectors 116 may be
formed integral to each other and on which wafer (chips) 12 may be
placed while still intact. This would simplify the assembly
process. Connector 116 may also comprise light barrier 150 to
minimize light reflected from lens 24 from reaching receiving
optoelectronic transducer 26'
[0104] Turning now to FIG. 18, an exemplary planar view of the
electrical contacts for transceiver assembly 114 is illustrated. It
should be appreciated that this view may also represent assemblies
in FIGS. 9 and 16 as well. For simplicity, the arrangements of
various components are described to correspond most closely with
the arrangement of FIG. 17. As may be seen, optoelectronic
transducer 26 is exemplified by a VCSEL having contact 166. A VCSEL
driver chip 144 comprises, for example, a silicon CMOS circuit.
Transmit power contact 168 and transmit ground contact 170 may
optionally comprise spacers 58 shown in FIGS. 16 and 17. Monitoring
photodiode 40 corresponds with photodetectors having a contact 172.
Amplifier 146 may comprise a silicon CMOS circuit, or it may
comprise, for example, a GaAs circuit and may be integrated with
optoelectronic component 26' on the same chip. Receive power
contact 176 and receive ground contact 178 may optionally also
comprise spacers 58.
[0105] Now that we have discussed MMF embodiments, we shall now
discuss other embodiments of the invention in a SMF context. As
discussed above, tighter tolerances are required for the SMF
embodiment and thus any teaching provided for the SMF embodiment
may be incorporated into the MMF embodiment.
[0106] Turning now to FIG. 5, an alternate embodiment for the
illustrates a refractive lens system used to couple single mode
waveguide 32' to a transducer 26. In this embodiment, there is an
optical element 24' that is disposed on surface 22 of optical wafer
14.
[0107] FIG. 6 illustrates a diffractive lens system used to couple
a multi mode or single mode waveguide to a light source. The only
substantive difference in this embodiment from that illustrated in
FIG. 1 is that optical elements 24 and 24' are diffractive lenses
24 and 24'.
[0108] FIG. 7 illustrates an ion-diffused planar microlens system
used to couple a single mode waveguide to a light source. In this
embodiment, optical element 24 or optical element 24' is formed by
diffusing ions 90 into wafer 12 or wafer 14 or both.
[0109] FIG. 19 shows yet another embodiment of the invention.
Electro-opto-mechanical assembly 180 comprises wafer 182, on which
optical element 184 resides on bottom surface 18, i.e., on the same
side of wafer 182 as optoelectronic transducer 26. Due to this
configuration, the distance between optoelectronic transducer 26
and optical element 184 is quite small, and determined by the
standoff heights of bump bonds 148. This distance is typically 10's
of micrometers compared to the typical distances of 100's of
micrometers of embodiments described earlier. This means that
optical element 184 may be quite small, typically less than 50
.mu.m in diameter. Its fabrication is simpler and more accurate
than that of optical elements of embodiments described earlier, and
the optical aberrations are smaller. In most cases, the thickness
of wafer 182 is on the order of 100 .mu.m, significantly less than
that of wafers 12 described earlier. Due to the reduced dimensions
of electro-opto-mechanical assembly 180, any movements due to
temperature or other changes are reduced approximately in
proportion to the dimensions. The increased accuracy in
electromechanical assembly 180 makes it a viable candidate for
coupling to SMF over varying environmental conditions. The
advantage of this embodiment over a simpler butt-coupled
arrangement is that optical element 184 transforms the beam of a
transmitting transducer 26 to make it better suited for coupling
into the waveguide. For example, optoelectronic transducer 26 may
comprise a VCSEL whose beam has an NA of 0.2, while the SMF has an
accepting NA of about 0.1. In this case, appropriately configured
optical element 184 would reduce the NA of the beam to about 0.1 at
the waveguide end.
[0110] It is to be appreciated that there the invention described
thus far is readily extendable to many alternative configurations.
For example, the invention includes transmitting and/or receiving
modules which comprise more than one transmitting and/or receiving
element. In FIGS. 9, 16 and 17, optoelectronic transducers 26 and
26' could comprise a VCSEL and photodetector, respectively, as
described, or they could both comprise VCSELs, or they could both
comprise photodetectors. Furthermore, there could be more than 2 of
such optoelectronic transducers in a single assembly. For example,
one assembly may comprise an array of 1.times.12 transmitting
elements, and another assembly may comprise an array of 1.times.12
receiving elements. A single assembly may comprise any number of
transmitting and/or receiving elements.
[0111] While the various optoelectronic transducers are described
as having their emitting (or receiving) surfaces facing the wafers
on which they are mounted, it is also possible for emitters or
receivers to have their emitting or receiving surfaces opposite the
wafers on which they are mounted.
[0112] Additionally, it is possible for either type of element to
be arranged in any form of array, for example 1-dimensional or
2-dimensional. FIG. 14 shows elements mounted to a microlens wafer
in a 2-dimensional array. The dicing lines may be chosen to dice
out single elements, rows of elements with any number of elements,
or 2-dimensional arrays of elements with any number of elements.
The spacing between adjacent elements in FIG. 14 may be uniform as
shown, or elements could be clustered to optimize manufacturing
efficiency for arrays.
[0113] While all of the above embodiments disclose the use of a
waveguide 32, it should be appreciated that the teachings of this
invention are not limited to the need for this waveguide. In other
words, the invention has applications in pointers, bar code
scanners, disk drives, CD-ROM drives as well as the communications
assembly described above.
[0114] Although the present invention has been fully described in
conjunction with the preferred embodiment thereof with reference to
the accompanying drawings, it is to be understood that various
changes and modifications may be apparent to those skilled in the
art. Such changes and modifications are to be understood as
included within the scope of the present invention as defined by
the appended claims, unless they depart therefrom.
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