Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-12-08
2001-08-28
Schuberg, Darren (Department: 2872)
Optical waveguides
With optical coupler
Particular coupling structure
C385S017000, C385S037000
Reexamination Certificate
active
06282344
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to star couplers for routing optical signals through optical communication systems. More specifically, the invention relates to optical coupler combinations having overlapped star couplers with at least one input waveguide and at least one output waveguide for guiding optical signals to and through the coupler combination.
2. Description of the Related Art
Photonic Lightguide Circuits (PLCs) are components used in optical communication systems for routing optical signals through the systems to enable optical communication. PLCs typically comprise substrate materials, typically glass or silicon but oftentimes other more exotic materials. Lithographic means and processes are used to produce optical structures and subcomponents such as waveguides near the surface of the substrate. Light is guided near the surface region of the substrate where optical signals can be routed through the PLC. The optical subcomponents on the PLCs optically process the light traversing the surface of the substrate so that the PLC can perform the particular function for which it is designed. One such optical component is an optical N×M coupler. In the past, optical couplers have taken up a large amount of “real estate” in the PLC and have also been limited with respect to the number of channels that can be routed through the couplers since they are physically less able to handle many input waveguides having different channel frequencies. Thus, current optical couplers for PLCs are not optimally functional for use in modern, dense wavelength division multiplexed (DWDM) optical communication systems.
It has been known to place two N×M star couplers in the PLC to provide stable, low-loss connections between them, particularly in Dragone routers which are a well-known type of PLC. The N×M star couplers are made by N input waveguides arrayed along a circular arc that is approximately centered about a second arc. On the second arc M output waveguides are approximately centered about the central waveguide end of the first circular arc. Personnel of the assignee of the present invention have developed a wafer having two overlapped star couplers to create two Dragone routers each consisting of a pair of star couplers on a single wafer, and wherein the Dragone router on the wafer with the best performance is utilized while the other is discarded or ignored. This overlapping of couplers did not, however, produce a PLC wherein the overlapped couplers could be used simultaneously and instead the couplers were overlapped merely to maximize the probability that at least one highly functional Dragone router would be created during the fabrication process.
Other methods have been proposed for producing a plurality of working routers by folding or overlapping routers to save space on a wafer. See T. Brenner et al., Electronics Letters, Vol. 32, 18 (Aug. 29, 1996). However, the couplers of Brenner et al. are not intended to be used simultaneously but, rather, are designed to produce multiple routers that are then individually cleaved or diced from the wafer to produce a plurality of separate PLCs with independent star couplers.
There exists a long-felt need in the art, recognized by the inventors of the present invention, for PLCs that include overlapped N×M star couplers so that optical signals in the PLC can be routed over one another without interfering with each other. Furthermore, PLCs of this type should maximize the utilization of space on a wafer, thereby conserving and better utilizing the available real estate thereon. Moreover, the use of overlapped N×M star couplers in PLCs should promote the capability to make more compact DWDM routers with smaller inter-channel wavelength spacings. Such needs have not heretofore been satisfied or achieved in the art.
SUMMARY OF THE INVENTION
The aforementioned long-felt needs are met, and problems solved, by overlapping coupler combination PLCs provided in accordance with the present invention for routing optical signals within an optical communication system. The coupler combination PLCs comprise first and second couplers that overlie each other each having planar slab waveguides for distributing the optical signals through the couplers. The first and second couplers each further comprise at least one input waveguide connected to input regions of the first and second couplers for guiding the optical signals to the planar slab waveguides, and each further comprise at least one output waveguide connected to output regions of the first and second couplers for guiding the optical signals out of the couplers. In a preferred form of the invention, the coupler combination forms a Dragone router wherein each of the output waveguides of the first coupler are optically connected to each of the input waveguides of the second coupler, and the output waveguides of the first coupler are disposed at an angle with respect to the input waveguides of the second coupler. This angle helps create path length differences amongst the optical connections leading between the first and second couplers and favors the optical signals of a particular wavelength entering particular inputs of the first coupler to be constructively coupled to particular outputs of the second coupler.
The coupler combinations of the present invention maximize use of the area of a wafer on which the PLC is fabricated, thereby increasing the manufacturing efficiency in constructing the PLC with a given amount of functionality and reducing the cost of the inventive coupler combination. Furthermore, by overlapping individual couplers and disposing the output waveguides at an angle with respect to the input waveguides as herein described, it is possible to control the constructive interference of the optical signals traversing through the individual waveguides. And, by creating a progressive path length difference of about at least one integral wavelength amongst the optical connections as a result of the angular orientation of the waveguides, a clean, highly constructive signal may be passed out of the PLCs of the present invention within the optical communication system in which the PLC is to be utilized. This allows a Dragone router to be constructed with high resolution in a limited amount of space and to provide high integrity optical communication of signals which is especially advantageous in DWDM systems having many signal channels spaced as little as 25 GHz apart. Such results have not heretofore been achieved in the art. These and other features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.
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R. Adar, C. Henry, C. Dragone. R. C. Kistler and M. Milbrodt. Broad-Band Array Multiplexers Made with Silica Waveguides on Silicon (2/93)Journal of Lightwave Technologyvol. 11, No. 2 pp. 212-219
Bergmann Ernest Eisenhardt
Bogert Gail Ann
Agere Systems Optoelectronics Guardian Corp.
Schuberg Darren
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