Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1997-09-02
2001-10-09
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06301031
ABSTRACT:
TECHNICAL FIELD
This invention relates to optical communication systems which incorporate wavelength division multiplexing, and demultiplexing functions. More particularly, this invention relates to an optical interconnection apparatus for use within such communication systems that has improved wavelength-channel tracking and alignment capabilities.
BACKGROUND OF THE INVENTION
As generally depicted in
FIG. 1
, optical wavelength multiplexing and demultiplexing have been accomplished in the past by using an interconnection apparatus having a plurality of closely spaced input waveguides
2
communicating with the input of a star coupler
4
. The output of the star coupler
4
communicates with an optical grating
6
comprising a series of optical waveguides, each of the waveguides differing in length with respect to its nearest neighbor by a predetermined amount. The grating
6
is connected to the input of a second star coupler
8
, the outputs
9
of which form the outputs of the switching, multiplexing, and demultiplexing apparatus. Examples of such interconnection apparatuses are disclosed in U.S. Patents 5,002,350 and 5,136,671, which are expressly incorporated by reference herein.
The overall design, and particularly the geometry, of such an interconnection apparatus may be such that a plurality of separate and distinct wavelengths each launched into a separate and distinct input port of the apparatus will all combine and appear on a predetermined one of the output ports. In this manner, the apparatus performs a multiplexing function. A similar apparatus may also perform a demultiplexing function. In this situation, an input wavelength is separated from the others and directed to a predetermined one of the output ports of the apparatus. An appropriate selection of input wavelength also permits switching between any selected input port to any selected output port. Accordingly, these devices are generally referred to as frequency routing devices and more specifically wavelength division multiplexers (WDM).
Ideally, the individual wavelength-channel positions, as measured by the center point of the passband, of the WDMs and the associated transmitter(s) should be aligned to a predefined wavelength grid, referenced herein as &lgr;
0
, &lgr;
1
, &lgr;
2
, &lgr;
3
, . . . , &lgr;
n
. Unfortunately however, in practice, the wavelengths of both the transmitter(s) and WDM channels drift with time and/or have initial fabrication errors. Such drifting or fabrication errors each result in the wavelengths of the respective optical devices to not be aligned as desired and thus adversely affect the operation of that device within a communication system. At present, either fabrication error and/or variances during operation can cause WDM components themselves to often exhibit about a 0.1 nm or 10 GHz shift or tolarance within a 100 GHz system while a transmitter may often exhibit about twice that amount of offset or about 20 GHz in a 100 GHz system. Furthermore, to be effectively used in the increasingly demanding optical communication systems of today where WDM systems are going to smaller channel spacings, i.e., less than about 50 GHz, and large channel counts, i.e. greater than or equal to about 32 channels, improvement is needed in the ability to provide appropriate wavelength-channel tracking and alignment in a WDM system and integrated device.
To date, devices have typically used what may be referred to as a “set and forget” scheme. In other words, existing devices have simply relied on the passband width of the WDM and/or transmitter(s) being large enough to tolerate any and all of the wavelength inaccuracies that may be present due to at least the reasons set forth above. In such a system, the wide WDM passband requires large channel spacing and also significantly limits the number of channels that can be effectively used in that communication system.
SUMMARY OF THE INVENTION
The present invention relates to an optical apparatus that has improved wavelength-channel tracking and alignment capabilities. More specifically, an optical apparatus includes an optical splitter/combiner device which receives optical signals. At least some portion of the optical signals from an output of the splitter/combiner is tapped or diverted into a detecting device which includes a wavelength selective device and has a detector connected to at least one of its outputs. The detector evaluates at least one selected characteristic about the optical signal on a predetermined channel and cooperates with a feedback link between the evaluated signal channel to controllably affect the selected characteristic for at least one of the optical signals received into the optical apparatus.
Alternative embodiments of the present invention incorporate optical devices having the improved wavelength-channel tracking and alignment capabilities into various components of any well known type of communications system such as a point-to-point communications system and/or Add-Drop optical networks.
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patent: 5136671 (1992-08-01), Dragone
patent: 5311347 (1994-05-01), Kubo et al.
patent: 5387992 (1995-02-01), Miyazaki et al.
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patent: 5493625 (1996-02-01), Glance
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patent: 6134036 (2000-10-01), Andreozzi et al.
“Optical FDM Transmission Technique” by Nosu et al, IEEE, p. 1305, Fig. 10, 1987.*
Nosu et al., publication “Optical FDM Transmission Technique”, p. 1305, 1987 IEEE.
Agere Systems Optoelectronics Guardian Corp.
Pascal Leslie
Phan Hanh
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