Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1999-12-08
2001-07-03
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S031000, C385S033000, C385S088000, C385S089000, C385S024000, C359S199200, C359S199200
Reexamination Certificate
active
06256436
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical wavelength demultiplexer mainly for use in wavelength-division-multiplexed optical communications.
2. Description of the Related Art
Heretofore, optical wavelength demultiplexers mainly for use in the art of wavelength-division-multiplexed optical communications comprise a single optical fiber, a collimator lens, a diffraction grating, and a one-dimensional array of photodetectors. In the optical wavelength demultiplexers, the optical fiber is positioned at the focal point of the collimator lens. Light emitted from the optical fiber is converted by the collimator lens into parallel light that is applied to the diffraction grating which is Littrow-mounted. The diffraction grating demultiplexes the light with its chromatic dispersion capability and applies the demultiplexed light rays to the collimator lens, which focuses the light rays on the photodetectors in respective channels.
Another type of optical wavelength demultiplexer comprises a concave diffraction grating, a single optical fiber disposed at the focal point of the concave diffraction grating, and a one-dimensional array of photodetectors. Light emitted from the optical fiber is reflected and demultiplexed by the concave diffraction grating into light rays that are focused on the photodetectors in respective channels.
If the number of demultiplex channels is to increase, then the photodetector array will require an increased number of photodetectors. Since the photodetector array will have an increased width, it will be difficult to design aberrations of the collimator lens.
One optical wavelength demultiplexer provides a single input capability. If an optical wavelength demultiplexer system with two or more input capabilities is needed, then it is necessary to provide as many optical wavelength demultiplexers as the required number of input capabilities. Since each of the optical wavelength demultiplexers has the diffraction grating and the collimator lens, or the concave diffraction grating, which is expensive, the overall optical wavelength demultiplexer system is highly expensive.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical wavelength demultiplexer which is small in size and low in cost and which has a single diffraction grating and a single collimator lens or a single concave diffraction grating that is shared by two or more input capabilities for achieving a required optical wavelength demultiplexing function.
According to an aspect of the present invention, there is provided an optical wavelength demultiplexer comprising at least two optical fibers, a two-dimensional array of photodetectors arranged in as many rows as the number of optical fibers and as many columns as the number of demultiplex channels, a collimator lens, and a diffraction grating for demultiplexing a light ray emitted from each of the optical fibers into the demultiplex channels, any one of the optical fibers and a central line of one of the rows which corresponds to the any one of the optical fibers being spaced equal distances from an optical axis of the collimator lens.
The optical fibers and the two-dimensional array of photodetectors may be disposed on a focal plane of the collimator lens, and axially symmetric with respect to the optical axis of the collimator lens. Specifically, the optical fibers and the two-dimensional array of photodetectors may be disposed on a front focal plane of the collimator lens, and the diffraction grating may comprise a planar diffraction grating disposed on a back focal plane of the collimator lens.
According to another aspect of the present invention, there is provided an optical wavelength demultiplexer comprising at least two optical fibers, a two-dimensional array of photodetectors arranged in as many rows as the number of optical fibers and as many columns as the number of demultiplex channels, and a concave diffraction grating for demultiplexing a light ray emitted from each of the optical fibers into the demultiplex channels, any one of the optical fibers and a central line of one of the rows which corresponds to the any one of the optical fibers being spaced equal distances from an optical axis of the concave diffraction grating.
The optical fibers and the two-dimensional array of photodetectors may be disposed on a focal plane of the concave diffraction grating, and axially symmetric with respect to an optical axis of the concave diffraction grating.
According to still another aspect of the present invention, there is provided an optical wavelength demultiplexer comprising at least two optical fibers, a two-dimensional array of photodetectors arranged in as many rows as the number of optical fibers and as many columns as the number of demultiplex channels, and a focusing and demultiplexing element for focusing and demultiplexing a light ray emitted from each of the optical fibers into the demultiplex channels, any one of the optical fibers and a central line of one of the rows which corresponds to the any one of the optical fibers being conjugate to each other with respect to the focusing and demultiplexing element.
Any one of the optical fibers and a central line of one of the rows which corresponds to the any one of the optical fibers may be spaced equal distances from an optical axis of the focusing and demultiplexing element.
A light ray emitted from any one of the optical fibers is demultiplexed by the planar or concave diffraction grating into light rays, which are applied to a corresponding row of photodetectors to produce output signals in the respective demultiplex channels. The planar diffraction grating and the collimator lens, or the concave diffraction grating is shared by the at least two optical fibers which provide input capabilities. The optical wavelength demultiplexer may be relatively small in size and low in cost.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.
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Healy Brian
Nippon Sheet Glass Co., Ltd
Schwegman Lundberg Woessner & Kluth P.A.
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