Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1999-03-02
2001-03-20
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S039000, C385S024000, C385S046000, C359S199200
Reexamination Certificate
active
06205273
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to optical devices and, more particularly, to waveguide grating routers.
BACKGROUND OF THE INVENTION
Waveguide grating routers in conventional lightwave systems are used as optical switches, multiplexers, demultiplexers, detectors, add/drop filters, one by N (1×N) and N by one (N×1) splitters and N by N (N×N) arrays. Typically, such waveguide grating routers include an interconnection apparatus having a plurality of closely spaced input waveguides communicating with an input of a star coupler. An output of the star coupler communicates with an optical grating comprising a series of optical waveguides in which each of the grating waveguides differ in length with respect to its nearest neighbor by a predetermined fixed amount. The optical grating is further connected to an input of a second star coupler, the outputs of which form outputs of the switching, multiplexing, and demultiplexing apparatus. Waveguide grating routers are also frequently referred to as “frequency routing devices” and are further described in U.S. Pat. No. 5,002,350, issued Mar. 26, 1991 to C. Dragone, entitled “Optical Multiplexer/Demultiplexer” (hereinafter “Dragone 1”) and U.S. Pat. No. 5, 136,671, issued Aug. 4, 1992 to C. Dragone, entitled “Optical Switch, Multiplexer, and Demultiplexer” (hereinafter “Dragone 2”), both of which are hereby incorporated by reference.
A known characteristic of these waveguide grating routers is that they do not efficiently provide a predetermined composite amplitude spectrum for each of the output signals that may comprise many wavelengths or frequencies. Rather, these routers tend to attenuate signals in outer waveguides more than signals in the inner waveguides. Thus, the amplitude response of the router across the spectrum of wavelengths in the waveguides is nonuniform.
Attempts have been made to design a waveguide grating router with a uniform composite amplitude spectrum, yet prior designs have proven to be inefficient in deriving a predetermined composite amplitude spectrum, such as a uniform output spectrum, or such designs suffer severe loss. For example, one method uses a “loop-back” optical path with the waveguide grating router. “Loop-back” optical path connections are connections from the output signal fed back into a predetermined input port as described in an article entitled “Loss Imbalance Equalization of Arrayed Waveguide Grating Add-Drop Multiplexer,” written by Osamu Ishida, et. al., that appeared in Electronics Letters, Vol. 30, No. 14, Jul. 7, 1994. However, this method has not been effective to equalize loss in waveguide routers.
Another method used for achieving a uniform output spectrum averages the waveguide grating router loss over the cascaded routers by shifting the port connections between adjacent routers, as described in an article entitled “Loss Imbalance Equalization in Arrayed Waveguide Grating (AWG) Multiplexer Cascades” written by Osamu Ishida, et al., that appeared in Journal of Lightwave Technology, Vol. 13, No. 6, Jun. 1995. However, such a system suffers severe loss due to the cascading of routers.
Still another method to achieve greater channel uniformity was described in an article entitled “Waveguide Grating Router with Greater Channel Uniformity” written by J. C. Chen and C. Dragone, that appeared in Electronics Letters, Vol. 33, No. 23, pp. 1951-2, Nov. 6, 1997. The method disclosed therein, which is incorporated by reference herein, uses auxiliary waveguides between adjacent grating arms in a waveguide grating router. Although such a system does not add loss, it also does not provide a predetermined composite amplitude spectrum, such as a uniform output spectrum. Specifically, the auxiliary waveguides simply help to shape the radiation pattern of the star coupler within the waveguide grating router to reduce channel non-uniformity. Thus, there is a need for a more effective means of providing a waveguide grating router having a predetermined composite amplitude spectrum thereby reducing the complexity of lightwave systems.
SUMMARY OF THE INVENTION
A waveguide grating router having a predetermined composite amplitude spectrum is achieved in accordance with the principles of the present invention by introducing loss into the waveguide grating router's waveguides. When the desired predetermined composite amplitude spectrum is a uniform amplitude spectrum, this same loss can produce loss equalization by the complete elimination of gain nonuniformity in all the output signals. The invention however is not limited to the production of a flat amplitude spectrum. For example, the predetermined composite amplitude spectrum may be sinusoidal, triangular, stepwise discrete, sloped, logarithmic, etc.
According to one aspect of the invention, a waveguide grating router is provided that includes at least one input waveguide and a plurality of output waveguides. A variable loss element is introduced to a predetermined group of output waveguides to produce a predetermined composite amplitude spectrum of the output signals.
According to another aspect of the invention, a waveguide grating router is provided that includes a plurality of input waveguide and a plurality of output waveguides. The variable loss element is introduced loss to a predetermined group of both input and output waveguides to yield output signals that exhibit the predetermined composite amplitude spectrum. In both types of waveguide grating routers, loss may be introduced in a variety of ways, including varying the cross-section of an input waveguide with respect to that of an output waveguide.
REFERENCES:
patent: 4737002 (1988-04-01), Boucouvalas
patent: 5002350 (1991-03-01), Dragone
patent: 5136671 (1992-08-01), Dragone
patent: 5243672 (1993-09-01), Dragone
patent: 5357589 (1994-10-01), Brown, Jr. et al.
patent: 5881199 (1999-03-01), Li
patent: 5953467 (1999-09-01), Madsen
patent: 5982960 (1999-11-01), Akiba et al.
O. Ishida et al, “Loss-Imbalance Equalisation of Arrayed Waveguide Grating Add-Drop Multiplexer”, Electronics Letters, vol. 30, No. 14, Jul. 7, 1994, pp. 1160-1162.
J. C. Chen et al, “Waveguide Grating Routers With Greater Channel Uniformity”, Electronics Letters, vol. 33, No. 23, Nov. 6, 1997, pp. 1951-1952.
O. Ishida et al, “Loss-Imbalance Equalization in Arrayed-Waveguide-Grating (AWG) Multiplexer Cascades”, Journal of Lightwave Technology, vol. 13, No. 6, Jun. 1995, pp. 1155-1163.
Brosemer J. J.
Lucent Technologies - Inc.
Pak Sung H.
Sanghavi Hemang
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