Optical waveguides – Accessories – External retainer/clamp
Reexamination Certificate
2001-07-19
2003-03-18
Field, Lynn (Department: 2839)
Optical waveguides
Accessories
External retainer/clamp
C385S134000, C385S030000
Reexamination Certificate
active
06535685
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention generally pertains to structures and methods exploiting silicon processing technology for accomplishing both arcuate and straight segment shapes of path trajectory for an optical fiber within a groove across a surface of a supporting substrate. It particularly applies when the surface region of side-polish on the fiber is generally co-planar with the silicon surface containing the groove and the arcuate path within the groove lies in a plane that is parallel to the normal to the silicon surface. It applies to single-mode optical fibers as well as optical fibers that are not single-mode.
An objective of this invention is to improve the yield and lower the cost of manufacture for precision side-polished fiber optic components.
There are no prior art methods, structures, apparatuses, or devices published or on the market for utilizing precision silicon processing technology to achieve ultra-precise alignments of interacting side-polished fiber optics as when joining two side-polished fibers face to face against their side-polished areas. What is known in the related prior art deals with implementation of single fibers that are side-polished to implement two-port photonic functions requiring no side-by-side critical alignment to other fibers. This prior art is taught in U.S. Pat. No. 5,809,188 “Tunable optical filter or reflector” and U.S. Pat. No. 5,781,675 “Method for preparing fiber-optic polarizer”, both by Tseng.
Tseng's patents teach the use of V-grooves etched in a 100 surface of a silicon crystal substrate and having a continuously varying groove depth. Note that “100” refers to crystal orientation as defined by Miller indices as generally known in the field of crystallography and silicon processing. Tseng's patents teach how such a continuous arcuate groove achieves both a) an arcuate path for guiding the fiber along an arcuate path trajectory and b) precise control of the remaining side-wall thickness left along a controlled length of the arcuate, side-polished fiber that is bound within the groove.
Tseng's patents teach methods to achieve superior precision in groove dimensions and consequent control of remaining, polished, sidewall thickness to a fiber held within a silicon V-groove. Using this technique, the cross-sectional shape of a groove running parallel to the 110 direction is that of a “V-shape”, wherein the side-walls of the “V-shape” are 111 planes. This technique works well because the 111 etch direction has a significantly slower etch rate than any other direction. A continuous change in groove depth is used to achieve an arcuate path with a long radius of curvature for holding a fiber and thereby guiding the fiber itself into an arcuate path trajectory.
But a disadvantage exists with attempting to achieve a precise groove depth with Tseng's technique. If the groove was of constant depth (and width), the side-walls would indeed be 111 planes, and since they are the slowest to etch, the cross-section would be precisely determined by width of the etch mask. However, Tseng teaches the use of a smoothly curved groove depth (and width) thereby causing the side-walls to be determined by a very large set of 111 planes intersecting the groove. This makes the groove depth at the shallowest point harder to define by etch-rate and etch-time, since the etchant can attack the groove-forming substrate from directions other than just the 111 direction.
Another shortcoming of the above cited Tseng inventions is that the length of the side-polished area is strongly a function of the radius of curvature of the arcuate path of the fiber. In order to achieve a shorter length to a side-polish on a fiber, it then becomes necessary to use a shorter radius of curvature. The current invention overcomes this disadvantage by utilizing a straight middle portion of path trajectory. At the ends of the straight portion, the current invention uses either short-radius, arcuate, portions of path length, or portions of groove that are deeper in the substrate. This can make the side-polish length more a function of the length of the straight portion and less a function of the particular fiber-path radius or radii used within the end portions. This also allows two such fibers to be joined face-to-face against their side-polished areas to create optical couplers wherein the interaction length of coupling can be selected or adjusted. With the current invention, this adjustment can be accomplished more precisely either by design specification of the length of the straight middle portion of the groove or by shifting one fiber relative to the other along the direction parallel to the groove axes. This is because the arcuate end portions can be made relatively short compared to a path determined by a single radius of curvature.
No prior art teaches methods, structures, apparatuses, or devices for achieving an arcuate fiber trajectory by using a few steps in mask pattern width or by few incremental steps between portions of the groove wherein each portion has a constant depth. And no prior art teaches use of either arcuate or stepped grooves to achieve an arcuate fiber trajectory having a long straight portion in the middle. And no prior art teaches use of a groove that has a midportion that is of constant width and depth joined with end portions that increase in depth with transitions parallel to crystal planes.
Additional prior art on positioning of fiber optics on substrates is found in the technology of Microelectronic Mechanical Systems (MEMS). One reference to such technology is that of “MEMS Packaging for Micro Mirror Switches”, by L. S. Huang, S. S. Lee, E. Motamedi, M. C. Wu, and C. J. Kim, Proc. 48th Electronic Components & Technology Conference, Seattle, Wash., May 1998, pp. 592-597. But this prior art does not teach the use of arcuate groove shapes or arcuate fiber trajectories, since a single V-groove of constant width and depth cannot alone shape an arcuate path for an optical fiber.
Another aspect of using a groove to guide the path shape of a fiber is that continuous contact between a fiber and a groove with either a straight or arcuate trajectory is susceptible to contamination in the form of a particulate or a film. Mechanical interference with such contamination can alter the accuracy and/or precision of the trajectory (i.e. shape) of the fiber. For example, a contaminating particle or film positioned between a surface of the groove and the surface of the fiber it guides can perturb the position of the fiber from precisely following the contour of the groove.
What is needed are structures and methods that can utilize a combination of groove features, using length-wise portions that each have constant width and constant depth to better exploit the dimensional controls achievable with photolithography and etching to guide an optical fiber along a straight or arcuate trajectory. The current invention provides these structures and methods, provides better determination of interaction length for couplers (and other 4-port fiber optic components) and reduces susceptibility to fiber mis-alignment caused by particulate or film contamination on either the groove surface(s) or on the surface of the fiber.
BRIEF SUMMARY OF THE INVENTION
Certain objects, advantages and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the methods and structures (or apparatuses or devices) and combinations particularly pointed out in the appended claims.
The objects of the invention are principally five-fold: a) to provide methods and structures to accomplish a precise and accurate fiber trajectory or path within a groove in the surface of a crystal substrate for creating a side-polished optical fiber wherein a portion of the fiber path is straight, b) to cause the length of side-
Field Lynn
Zarroli Michael C.
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