Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1999-06-18
2001-11-20
Bovernick, Rodney (Department: 2874)
Optical waveguides
With optical coupler
Plural
C385S014000, C385S033000, C385S037000, C359S199200, C359S199200
Reexamination Certificate
active
06321001
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related generally to an optical communication system, and more particularly to an optical communication system employing grating couplers to provide wavelength division multiplexed data.
2. Description of the Prior Art
Telecommunication systems have employed an optical fiber as the transmission medium. Recent advancements in telecommunications, however, have placed a heavy demand on the total amount of data that can be optically transmitted on a single optical fiber.
For this reason, techniques to multiplex several wavelength channels, each carrying unique data, on to a single optical waveguide, such as a dielectric slab or an optical fiber, have been sought. To achieve wavelength division multiplexing (WDM) it is necessary to couple each wavelength into and out of the optical waveguide without compromising the data carried by the other wavelengths. Adding to this challenge is the constraint that the wavelengths need to be closely spaced so as to all fit within a relatively narrow gain spectrum.
Presently there are commercial wavelength division multiplexed products on the market that utilize for example, array waveguide grating structures, dichroic mirror assemblies, and wavelength selective fiber optic couplers. The products that use these approaches have been refined to yield a performance level that is acceptable for some limited applications. Each approach, however, introduces some compromises in performance. More particularly, in the array waveguide grating approach, such as described in U.S. Pat. No. 5,136,671 by Dragone, a free-space coupling region is fed by an array of individual channeled waveguides that use constructive interference to direct light of a specific wavelength from one waveguide to another waveguide. The constructive interference process is controlled by the propagation path lengths of each waveguide in the coupling array. These path lengths must be accurately maintained to within a fraction of a wavelength of light, and thus this approach requires a high degree of temperature control. In the dichroic mirror assembly approach, light is reflected off wavelength selective mirrors made from multiple dielectic coatings that pass a narrow portion of the optical spectrum and reflect all the remaining portions of the spectrum. The transmitted light of a specific wavelength is coupled to a specific optical output while the other wavelengths are reflected to impinge upon other dichroic mirrors that are designed to pass these wavelengths and couple these wavelengths to their unique optical outputs. To make and assemble dichroic mirrors is extremely complex. In the wavelength selective fiber optic couplers, light of a particular wavelength interacts with an adjacent waveguide within the coupler for the appropriate optical interaction length so as to completely couple over into this adjacent waveguide. The light at other wavelengths remains in the original waveguide and is extracted by another wavelength selective coupler. This approach requires a separate coupler in the optical fiber for each wavelength that is multiplexed. This requires either multiple optical fiber connections or fusion splicing which complicates the manufacturing process. Consequently, the known prior art approaches invoke a high degree of complexity to implement.
What is needed, therefore, is an improved optical system with a single optical waveguide that readily accommodates additional wavelengths for communicating data in a wavelength division multiplexed manner.
SUMMARY OF THE INVENTION
A wavelength division multiplexed optical communication system is disclosed. The system is particularly suited for simultaneous broadcast capability and includes an optical waveguide having a plurality of gratings, each defining a node and serving to Bragg diffract incident light. A first grating is disposed at a first node and couples by Bragg diffraction impinging light at a plurality of preselected wavelengths into the waveguide which propagates the coupled light therethrough. A portion of the propagated light is outcoupled and emitted by a second and a third grating which Bragg diffract and outcouple a portion of the light in directions corresponding to each of the preselected wavelengths. A plurality of coplanar optical sources are disposed proximate the first node, each transmitting an optical signal at a preselected wavelength to the first grating. Optical detectors are disposed proximate the second and the third nodes. Each detector is positioned in a direction to detect a preselected wavelength of the emitted light that corresponds to a transmitted preselected wavelength.
The foregoing and additional features and advantages of this invention will become apparent from the detailed description and accompanying drawing figures below. In the figures and the written description, numerals indicate the various elements of the invention, like numerals referring to like elements throughout both the drawing figures and the written description.
REFERENCES:
patent: 4441181 (1984-04-01), Winzer et al.
patent: 4864310 (1989-09-01), Bernard et al.
patent: 5136671 (1992-08-01), Dragone
patent: 5784184 (1998-07-01), Alexander et al.
Bovernick Rodney
Doan Jennifer
Keller Robert W.
TRW Inc.
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