Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making named article
Reexamination Certificate
1998-05-07
2001-02-13
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making named article
C385S049000, C385S039000, C385S088000, C385S052000
Reexamination Certificate
active
06187515
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a monolithically integrated optical microbench system for coupling optical energy between optical devices and a method for producing the same by using the anisotropic etch characteristics of m-V semiconductors where one orthogonal etch direction provides a natural channel for fiber positioning and the other orthogonal etch direction provides a reflecting surface for the redirection of optical energy between a fiber or waveguide and optical devices.
2. Description of the Prior Art
Compact and simple optical coupling systems for micro-optical devices are essential in optical communication systems. In addition, simplified assembly processes in packaging micro-optical coupling systems are very important in manufacturing low cost and reliable systems. An increasingly popular method for the coupling of optical energy between optical devices and systems is through the use of fiber and micro-optical lenses. Fiber provides an efficient transfer medium between optical devices by providing improvements in coupling efficiency and communication lag. Micro-optical lenses provide additional coupling efficiency by focusing divergent optical energy output from an optical fiber end. Present optical coupling systems use a variety of coupling schemes to obtain efficient coupling between micro-optical devices.
The publication “Packaging Technology for a 10-Gb/a Photoreceiver Module”, by Oikawa et al., Journal of Lightwave Technology Vol. 12 No. 2 pp.343-352, February 1994 discloses an optical coupling system containing a slant-ended fiber
10
secured in a fiber ferrule
12
where the fiber ferrule
12
is welded to a side wall
14
of a flat package
16
and a microlens
18
is monolithically fabricated on a photodiode
20
where the photodiode
20
is flip-chip bonded to the flat package
16
, as illustrated in FIG.
1
. An optical signal
22
enters horizontally and is reflected vertically at the fiber's
10
slant-edge. The microlens
18
then focuses the optical signal
22
on the photodiode's
20
photosensitive area.
In the Olkawa publication, maintaining alignment between the fiber and the photodiode chip is essential for optimal coupling of the optical signal. Misalignment can occur as a result of mechanical stress to the fiber ferrule or thermal fluctuations of the entire system. In an attempt to overcome these factors, complex assembly and fabrication techniques are used. The fiber attachment is a complex ferrule attachment which seeks to optimize the mechanical strength of the attachment and therefore minimize the effects of fiber displacement Because the photodiode chip is flip-chip bonded on the flat package a complex bonding machine is required for high-precision alignment. Finally, in order to provide a high optical coupling efficiency wide misalignment tolerances must be built in to the photodiode chip during fabrication to compensate for both displacement by the fiber attachment and deformation by temperature fluctuation.
Disclosed in U.S. Pat. No. 5,346,583 is a monolithic coupling system for optical energy transfer between a microlens and a fiber, as illustrated in FIG.
2
. The configuration disclosed in patent '583 contains at least one preshaped photoresist (PR) microlens
24
formed on a surface
33
of a substrate
34
by standard photolithography steps and on an opposing surface
31
of the substrate
34
an optical fiber guide
26
is formed through standard photolithography steps. The fiber guide
26
is used to mount an optical fiber
28
such that the central axis
30
of the optical fiber
28
is substantially coincident with the central axis
32
of the PR microlens
24
. While the proximity of the fiber
28
to the microlens
24
allows for efficient coupling of optical energy between the fiber
28
and an optical device, there are some significant disadvantages. First, the system is not very compact because of the orientation of the fiber
28
to the surface
31
of the substrate
34
. More importantly, the PR microlens
24
cannot withstand variable temperature cycles and long-term reliability of the system would be an issue.
In many cases external lenses are used to couple optical energy between optical fibers or waveguides and optical devices. Examples of such coupling techniques are disclosed in U.S. Pat. Nos.: 5,247,597; 4,653,847; 4,433,898; 4,875,750; and 5,343,546. Using external microlenses makes coupling extremely complex and in most cases unreliable.
As discussed, present optical coupling systems use a variety of coupling schemes to obtain efficient coupling between micro-optical devices. However, these schemes use many components, require a complicated assembly process, and are not compact. In addition, these components are typically made of different materials and have different thermal expansion coefficients. These differences can cause optical misalignment during temperature changes, which are common in military and space applications. Furthermore, when using discrete bulk optical components, the complexity of the assembly process is increased because there are more individual components to align. The greater the complexity the more assembly costs are increased and reliability decreased.
Based on techniques known in the art for optoelectronic coupling schemes, a monolithic optical microbench system for coupling optical energy between a fiber or a waveguide and an optical device is highly desirable.
SUMMARY OF THE INVENTION
It is an aspect of the present invention to provide a monolithic optical microbench system for the coupling of light between optical devices which includes a substrate wafer having a crystal plane; a mirror etched in the crystal plane of the substrate wafer; and a groove etched on a side of the substrate wafer intersecting the crystal plane of the mirror.
It is also an aspect of the present invention to provide a method for producing a monolithic optical microbench for the coupling of light between optical devices. The method comprises the steps of providing a substrate wafer having a first opposing surface, a second opposing surface, a first crystal plane, and a second crystal plane; lapping the entire first opposing surface of the substrate wafer and polishing the entire first opposing surface of the substrate wafer; coating a first layer of photoresist material over the entire first opposing surface of the substrate wafer and coating a second layer of photoresist material over the entire second opposing surface of the substrate wafer; baking the first opposing surface and the second opposing surface of the substrate wafer; providing a first mask to the first opposing surface and a second mask for the second opposing surface of the substrate wafer; selectively aligning the first mask to the first opposing surface and the second mask to the second opposing surface of the substrate wafer; exposing the first opposing surface of the substrate wafer coated with the first layer of photoresist material to a light source to form a first photoresist mask and exposing the second opposing surface of the substrate wafer coated with the second layer of photoresist material to a light source to form a second photoresist mask; developing the first opposing surface and the second opposing surface of the substrate wafer; etching the first opposing surface and the second opposing surface of the substrate wafer; removing the first photoresist mask and cleaning the first opposing surface of the substrate wafer and removing the second photoresist mask and cleaning the second opposing surface of the substrate wafer; and finally, metallizing the entire substrate wafer.
REFERENCES:
patent: 4349410 (1982-09-01), Stupp et al.
patent: 4354898 (1982-10-01), Coldren et al.
patent: 4433898 (1984-02-01), Nasiri
patent: 4464458 (1984-08-01), Chow et al.
patent: 4613398 (1986-09-01), Chion et al.
patent: 4653847 (1987-03-01), Berg et al.
patent: 4875750 (1989-10-01), Spaeth et al.
patent: 4923564 (1990-05-01), Bilakanti et al.
patent: 5073003 (1991-12-01), C
Anderson Eric R.
Rezek Edward A.
Strijek Ronald L.
Tran Dean
Angebranndt Martin
TRW Inc.
Yatsko Michael S.
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