Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1999-05-13
2001-07-17
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S033000, C385S037000, C385S046000
Reexamination Certificate
active
06263127
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to multiwave optical routers for use in wavelength division multiplexed (WDM) systems and, more particularly, to a router combining free-space and guided wave optics to increase the number of wavelength channels that can be handled by such routers.
BACKGROUND OF THE INVENTION
Wavelength division multiplexed (WDM) transmission systems currently use integrated optical arrayed waveguide routers (AWRs) to multiplex individual wavelength signals onto a single fiber and to demultiplex the signals received over a fiber. However, as the number of channels used in WDM transmission systems increases, suitable AWRs become increasingly difficult to design and fabricate. Some of the difficulties involved are forming flat passbands, and suppressing the interchannel crosstalk from the many output lines. Using today's technology, it should be possible to manufacture an 128 channel router with a 50 GHz spacing, but further increases to the channel count will probably require a new approach.
What is desired is a technique for increasing the number of channels that can be used in WDM transmission systems.
SUMMARY OF THE INVENTION
In accordance with the method and apparatus of the present invention, we describe a router combining free-space and guided wave optics to increase the number of channels used in WDM transmission systems by a factor of five or more. We have recognized that the partial demultiplexing characteristic of an arrayed waveguide router (AWR) can, advantageously, be combined with a free-space optical router to fully demultiplex an input WDM signal. The two-stage router can be used to obtain output wavelength signals in either one- or two- dimensional arrays.
More particularly, in accordance with our invention, an optical apparatus comprises an optical arrayed waveguide router (AWR) for receiving at an vinput wavelength division multiplexed (WDM) signal having M wavelength channels, M>1, and a one dimensional array of N outputs, 1<N<M, for outputting the WDM signals from the AWR, each output n, where 1≦n≦N, including a partially demultiplexed signal having a plurality of wavelength channels n, n+N, n+
2
N, . . . n+{M/N−1}N of the WDM signal. A free-space optical wavelength channel demultiplexer receives each of the partially demultiplexed signal channels and produces therefrom M wavelength channels, each of the M wavelength channels being outputted at a different one of M outputs.
According to other aspects of our invention, the free-space optical wavelength channel demultiplexer may be implemented using a combination of one or more lenses and a transmissive or a reflective grating. Other features of our invention enable the M outputs to terminate in a one-dimensional array of fibers or a two-dimensional array of fibers or mirror elements. According to another aspect, each-mirror element of an array of mirror elements is independently controlled to reflect its associated wavelength back through the apparatus to a originating AWR or to a second AWG to implement switching or other control of the demultiplexed wavelength signals.
REFERENCES:
patent: 6144783 (2000-11-01), Epworth et al.
Dragone Corrado Pietro
Ford Joseph Earl
Caccuro John A.
Lucent Technologies - Inc.
Palmer Phan T. H.
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