Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2001-07-13
2003-07-15
Lester, Evelyn A (Department: 2873)
Optical waveguides
With optical coupler
Plural
C385S014000, C385S015000, C385S031000, C385S033000, C385S037000, C385S047000, C385S129000, C385S130000, C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06594415
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wavelength division multiplexing and, more particularly, to wavelength division multiplexing/demultiplexing devices employing patterned optical components.
BACKGROUND OF THE INVENTION
Optical communication technology relies on wavelength division multiplexing (WDM) to provide increased bandwidth over existing installed fiber, as well as newly deployed fiber installations. Several technologies exist to provide the technical solution to WDM: array waveguide gratings (AWG's), fiber Bragg grating based systems, interference filter based systems, Mach-Zehnder interferometric based systems, and diffraction grating based systems, to name a few. Each system has advantages and disadvantages over the others.
Diffraction grating based systems have the advantage of parallelism, which yields higher performance and lower cost for high channel count systems. One drawback to traditional diffraction grating based systems, however, is an insertion loss that rises quickly and monotonically as the source illumination drifts off of the center of the desired communication channel wavelength. That is, traditional diffraction grating based systems invariably suffer from a variation in transmission efficiency across a wavelength channel. This variation in transmission efficiency with wavelength creates deleterious effects on modulated signals. For analog signals it creates harmonic distortion, for digital signals it increases the bit-error-rates at higher modulation bandwidths.
Also, most traditional diffraction grating based systems have an inherently gaussian-shaped passband profile. Such a gaussian-shaped passband profile is generally very narrow with a single peak and steep passband edges. Thus, even when a communication channel drifts off of its center wavelengths by only a slight amount, signal coupling with a receiving fiber is often severely detrimentally affected.
One attempt to alleviate at least one aspect of the above-described shortcomings is described by D. Wisely in “High Performance 32 Channel HDWDM Multiplexer with 1 nm Channel Spacing and 0.7 nm Bandwidth”, SPIE, Vol. 1578, Fiber Networks for Telephony and CATV (1991). In this paper, Wisely suggests that a microlens may be employed at the end of an input fiber in a WDM device so as to widen the gaussian-shaped passband profile of the WDM profile. That is, by widening the gaussian-shaped passband profile of the WDM device, there is less susceptibility to wavelength drift in communication channels. However, widening the gaussian-shaped passband profile of a WDM device may increase the chances of channel crosstalk. Thus, a tradeoff determination must be made when deciding whether or not to implement the above-described technique of Wisely.
Another attempt to alleviate at least one aspect of the above-described shortcomings is described by Martin et al. in U.S. Pat. No. 6,084,695. In this patent, Martin et al. suggest that a converging lens array, which is disclosed to be a planar microlens array with an index gradient, may be used to increase the width of elementary bands, and thereby increase the ratio between the width of elementary bands and the distance separating the central wavelengths of adjacent elementary bands in a multiplexer/demultiplexer device. Each microlens in the planar microlens array corresponds to a respective input/output fiber, which is placed directly in the focal point of its corresponding microlens. Thus, the apparent diameter of a beam exiting/entering the core of an input/output fiber as seen by a dispersion element or grating of the multiplexer/demultiplexer devices is the diameter of the beam as it is incident upon a corresponding microlens, and not the actual diameter of the beam as it exits/enters the core of the input/output fiber. That is, the width of each elementary band as seen by the dispersion element or grating of the multiplexer/demultiplexer device is increased without increasing the distance separating the central wavelengths of adjacent elementary bands.
However, as with the Wisely reference described above, the widening of elementary passbands as disclosed by Martin et al. may increase the chances of channel crosstalk. Also, Martin et al. disclose that an additional fiber (not shown) is required once for each channel wavelength or once for the multiplexed output beam of the multiplexer/demultiplexer device to attenuate the peak of each passband and thereby flatten each passband. Furthermore, Martin et al. disclose that the spacing between the input/output fibers, as well as the spacing between microlenses, is equal so as to allow for a much simpler implementation of the multiplexer/demultiplexer device. However, Martin et al. additionally disclose that this equal spacing of the input/output fibers and the microlenses is achieved only through the use of a prism, which compensates for wavelength spacing non-linearity due to dispersion laws of the dispersion element or grating. Thus, a tradeoff determination and additional device complexities are encountered when deciding whether or not to implement the above-described multiplexer/demultiplexer device of Martin et al.
While no other known attempts have been made to alleviate one or more aspects of the above-described shortcomings, it is presumed that such other attempts, if made, would also require certain tradeoffs to be made and/or complexities to be added. Thus, in view of the foregoing, it would be desirable to provide a WDM device which overcomes the above-described inadequacies and shortcomings with minimal or no tradeoffs or additional complexities.
OBJECTS OF THE INVENTION
The primary object of the present invention is to provide wavelength division multiplexing/demultiplexing devices which overcome the above-described inadequacies and shortcomings with minimal or no tradeoffs or additional complexities.
The above-stated primary object, as well as other objects features, and advantages, of the present invention will become readily apparent to those of ordinary skill in the art from the following summary and detailed descriptions, as well as the appended drawings. While the present invention is described below with reference to preferred embodiment (s), it should be understood that the present invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present invention as disclosed and claimed herein, and with respect to which the present invention could be of significant utility.
SUMMARY OF THE INVENTION
According to the present invention, improved wavelength division multiplexing/demultiplexing devices are provided. In the case of an improved wavelength division multiplexing device having a diffraction grating for combining a plurality of narrowband optical beams into a multiplexed, polychromatic optical beam, wherein the plurality of narrowband optical beams are received from a corresponding plurality of optical sources and the multiplexed, polychromatic optical beam is transmitted to a corresponding optical receiver, the improvement comprises employing a plurality of patterned optical input components corresponding to the plurality of narrowband optical beams and the plurality of optical sources for introducing a first patterned phase delay into the plurality of narrowband optical beams, wherein each of the plurality of patterned optical input components has an effective focal length such that each of the plurality of optical sources is disposed substantially inside the effective focal length of a corresponding one of the plurality of patterned optical input components. The improvement also comprises employing a patterned optical output component corresponding to the multiplexed, polychromatic optical beam and the optical receiver for introducing a second patterned phase delay into the multiplexed, polychromatic optical beam, wherein the patterned optical output component has an
Cappiello Gregory G.
Dueck Robert H.
Confluent Photonics Corporation
Dinh Jack
Hunton & Williams
Lester Evelyn A
LandOfFree
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