Optical: systems and elements – Diffraction – From grating
Reexamination Certificate
2001-02-02
2002-09-03
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Diffraction
From grating
C359S572000, C359S573000, C359S900000, C359S290000, C359S295000
Reexamination Certificate
active
06445502
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the field of communication systems, and more particularly to an apparatus and method operable to facilitate signal processing using variable blazed grating based elements.
BACKGROUND OF THE INVENTION
As optical systems continue to increase the volume and speed of information communicated, the need for methods and apparatus operable to facilitate high speed optical signal processing also escalates. Various devices and methodologies have been developed to provide numerous signal processing capabilities on optical signals. Some of these devices attempt to control a diffraction of an input optical signal to facilitate basic signal processing functions.
One such approach uses an optical switching device having a plurality of adjacent reflective strips disposed above a conductive inner surface. In one state of operation, the adjacent reflective strips remain in a single plane and substantially reflect optical signals received. In another mode of operation, alternate adjacent strips are pulled down parallel to the inner surface to create a bi-planar diffraction grating. The resulting two parallel planes of reflective strips create diffraction of the input optical signal in numerous directions. Diffracted portions of the input signal can be detected and used as a modified output signal.
This approach suffers from a number of deficiencies. For example, where a normal incident input signal is used, the power of the output signal is split equally between the two first order beams, which are diffracted in different directions. This results in difficulties maintaining two substantially equal outputs, because only a small portion of the diffracted signal can be recovered using a single detector or a single fiber. Recovering additional portions of the diffracted signal typically requires collecting diffracted portions traveling in numerous directions and recombining them. This approach typically results in additional system components, complexity and cost.
Another approach to diffraction based signal processing involves orienting a solid membrane diffraction grating at an angle to the incoming optical signal to cause a majority of the diffracted output signal to travel in one direction. Early variable blazed grating apparatus attempted to implement deformable membranes that could be selectively deformed to cause diffraction substantially in one direction. Supporting the membranes in these devices required use of an elastomeric substance under the entire membrane, which contacted the entire membrane. The combination of a large area membrane and a confining supporting material generally resulted in slow device operation and large required drive voltages.
Recently, variable blazed gratings have been used in spectral analyzers to improve the frequency sensitivity of those devices by directing high powered optical beams in specific directions. These devices use a series of adjacent slats (typically ranging from 50,000 nanometers to 80,000 nanometers in width) that are capable of rotating by a very small amount to direct low order diffraction modes in a specific direction. The high power of the incident beams in this application generally requires that the slats be constructed as wide as possible. The large width of the slats severely limits the blaze angle (less than two degrees) that can be obtained using this approach. In addition, the width of the slats significantly limits the frequency at which these devices can change states, and increases the drive voltage necessary to rotate the slats.
SUMMARY OF THE INVENTION
The present invention recognizes a need for a method and apparatus operable to economically facilitate high speed optical signal processing. In accordance with the present invention, an apparatus and method operable to facilitate optical signal processing are provided that substantially reduce or eliminate at least some of the shortcomings associated with prior approaches.
In one aspect of the invention, an apparatus operable to provide optical signal processing comprises an inner conductive layer comprising an at least substantially conductive material and a plurality of at least partially reflective mirror strips disposed outwardly from the inner conductive layer and operable to receive an input optical signal. None of the plurality of strips has a width greater than 40 microns and at least some of the strips are operable to undergo a partial rotation in response to a control signal, the partial rotation resulting in a diffraction of the input optical signal wherein a majority of the diffracted input signal is communicated in one direction.
In another aspect of the invention, a method of processing optical signals using a blazed grating comprises receiving an optical signal at a plurality of at least partially reflective mirror strips residing in a first position, none of the plurality of strips having a width of more than 40 microns. The method further comprises rotating the mirror strips by an angle THETA from the first position to create a plurality of diffracted signal portions. The majority of the diffracted signal portions are diffracted in one direction.
In still another aspect of the invention, an apparatus operable to provide optical signal processing comprises an inner conductive layer comprising an at least substantially conductive material and a plurality of at least partially reflective mirror strips disposed outwardly from the inner conductive layer and operable to receive an input optical signal. At least some of the strips are operable to undergo a partial rotation of more than two degrees in response to a control signal, the partial rotation resulting in a diffraction of the input optical signal wherein a majority of the diffracted input signal is communicated in one direction.
In yet another aspect of the invention, a method of processing optical signals using a blazed grating comprises receiving an optical signal at a plurality of at least partially reflective mirror strips residing in a first position. The method further comprises rotating the mirror from the first position to create a plurality of diffracted signal portions, the majority of the diffracted signal portions being diffracted in one direction, the strips having a maximum rotation angle that is greater than two degrees.
Depending on the specific features implemented, particular embodiments of the present invention may exhibit some, none, or all of the following technical advantages. One aspect of the present invention provides an effective and cost efficient mechanism for facilitating high speed signal processing using a diffraction based technology while reducing or eliminating at least some of shortcomings typically associated with diffraction based signal processing. For example, particular embodiments of the invention facilitate diffraction based signal processing that maintains good contrast ratios without requiring the additional beam collection and/or combining technology often associated with other approaches. In addition, implementing narrow strips compared to the wide slats used in other approaches facilitates a wide range of blaze angles, reduces the drive voltage required to rotate the strips, and increases the resolution of the resulting output signal by increasing the number of strips illuminated by the input beam.
The flexible operation of the invention facilitates its application in any number of signal processing applications, such as, variable attenuators, optical switches, optical add/drop multiplexers, and optical routers, to name a few. Moreover, the invention facilitates fabrication of arrays of variable blazed-grating based elements at a nominal incremental cost over that of producing a single element. This aspect of the invention facilitates construction of, for example, gain equalizers and wave-division add/drop multiplexers capable of processing numerous wavelengths for a small incremental cost over a single stage of elements. This provides significant cost savings in processing signals carrying information
Islam Mohammed N.
Kuditcher Amos
Baker & Botts L.L.P.
Celeste Optics, Inc.
Jr. John Juba
Spyrou Cassandra
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