Optical: systems and elements – Optical frequency converter
Reexamination Certificate
2002-12-23
2004-03-23
Lee, John D. (Department: 2874)
Optical: systems and elements
Optical frequency converter
C385S016000, C385S024000
Reexamination Certificate
active
06710913
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wavelength-conversion, and more particularly, to a technique for implementing wavelength-interchanging cross-connect architectures with wave-mixing frequency translation devices.
BACKGROUND OF THE INVENTION
Wavelength-conversion is an important attribute of all-optical metropolitan area networks. Wave mixing enables cost-effective wavelength-conversion through bulk or band conversion, where many channels at distinct frequencies are simultaneously frequency-converted, in a common device. Two native forms of wave mixing are difference-frequency generation and four-wave mixing. For both forms of conversion, an incoming channel at frequency f is converted to an outgoing channel at frequency (n−1)&pgr;−f, where &pgr; is the pump frequency, and n is the order of the wave-mixing process. For difference-frequency generation and four-wave mixing the order of the mixing process is respectively n=2, and n=3. It is possible to provide other non-native forms of wave-mixing frequency-conversion, with arrays of native wave-mixing devices. An example of non-native wave-mixing conversion is frequency-translation, where channels are frequency-shifted by a constant amount independent of the input channel frequency. Wave-mixing translation is achieved with two cascaded difference-frequency conversions that use different pump frequencies.
With wave mixing, it is possible to build non-blocking all-optical cross-connects that provide wavelength-conversion, with few converters. These architectures are usually multistage and comprise of many planes, and many stages of 2×2 space-switches.
A Twisted Benes architecture is based on a modification of a Benes architecture with difference-frequency converters. The Twisted Benes architecture is rearrangeable and uses O(FW) wave-mixing converters, where a given converter may simultaneously process up to O(W) channels. In Twisted Benes networks, for any connection, the worst case number of cascaded frequency-conversions is O(log
2
W).
Although it is based on bulk frequency-conversion, the Twisted Benes architecture has many limitations. First, it is only rearrangeable, implying that rerouting is needed at high load. Second, there is no cost-effective way to extend it with more planes into a strictly non-blocking network (e.g. into a Cantor network). Third, it does not offer any substantial reduction in the required number of wavelength-converters, when it is compared to more conventional designs with dedicated converters. Finally, in Twisted Benes networks, for a given connection, the worst case number of cascaded frequency-conversions of O(log
2
W) is large.
Other architectures of wave-mixing cross-connects have been proposed. These architectures are based on wave-mixing frequency-translation instead of difference-frequency generation. They enable the design of wave-mixing nodes with Benes, or any other multi-log topology. The converter requirements are between O(1) and O(F), per stage and per plane. With this architecture, it is possible to build strictly non-blocking networks with O(F log
2
W log
2
(FW)) wave-mixing converters (using a Cantor topology), instead of O(FW) wavelength-converters. However, like Twisted Benes networks, these binary wave-mixing translation networks are built with 2×2 elements. For this reason they are potentially limited by large impairments, given the worst-case number of cascaded frequency-conversions of O(log
2
W).
In view of the foregoing, it would be desirable to provide a technique for wave-mixing frequency translation which overcomes the above-described inadequacies and shortcomings. More particularly, it would be desirable to provide a technique for all-optical wavelength-conversion that uses wave-mixing frequency translation in an efficient and cost effective manner.
SUMMARY OF THE INVENTION
According to the present invention, a technique for selectively frequency translating channels in a system having W frequencies and one or more b×b switching elements is provided. In one particular exemplary embodiment, the technique may be realized as a method comprising selectively directing a channel operating at a respective one of the W frequencies based at least in part upon the respective frequency of the channel and shifting the respective frequency of the selectively directed channel by an amount defined by ±db
i
&Dgr;f, wherein d=0, 1, . . . , b−1, &Dgr;f is an optical frequency spacing between adjacent optical channels, and i=0, 1, . . . log
b
W−1.
In accordance with further aspects of this particular exemplary embodiment of the present invention, wherein the channel is a first channel and the selectively directed channel is a first selectively directed channel, the technique may include selectively directing a second channel operating at another respective one of the W frequencies based at least in part upon the respective frequency of the second channel, wherein the respective frequency of the second selectively directed channel is the same as the respective frequency of the first selectively directed channel after it has been shifted.
In another particular exemplary embodiment, the inventive technique may be realized by a method for wave-mixing frequency translation in a network, comprising one or more stages, and one or more b×b switching elements connecting a number, F, of waveguides. The method may comprise selectively directing an incoming channel, incoming on a respective incoming waveguide x
j
, operating at a frequency f
i
, to an inter-stage connection module; and permuting the incoming channel to a respective outgoing waveguide x
j+d
. The method may further comprise shifting the frequency f
i
by an amount defined by f
i−db
s−&phgr;
, where s is an index of a stage of the one or more stages, 0≦j≦(F−1), d=y
s−&phgr;
−z
0
, W is a number of frequencies per waveguide, z
&phgr;−1
. . . z
0
is the b-ary representation of j, y
&ohgr;−1
. . . y
0
in the b-ary representation of i and &phgr;=log
b
F.
In accordance with further aspects of this particular exemplary embodiment of the present invention, wherein the incoming channel is a first channel and the selectively directed incoming channel is a first selectively directed incoming channel, the method may further include selectively directing a second incoming channel operating at another respective one of the W frequencies based at least in part upon the respective frequency of the second incoming channel, wherein the respective frequency of the second selectively directed incoming channel is the same as the respective frequency of the first selectively directed incoming channel after it has been shifted.
In another particular exemplary embodiment, the invention may be realized by an apparatus for selectively frequency translating channels in a system having W frequencies. The apparatus may comprise one or more b×b switching elements for selectively directing a channel operating at a respective one of the W frequencies based at least in part upon the respective frequency of the channel. The apparatus may also comprise one or more frequency devices for shifting the respective frequency of the selectively directed channel by an amount defined by ±db
i
&Dgr;f, wherein d=0, 1, . . . , b−1, &Dgr;f is an optical frequency spacing between adjacent optical channels, and i=0, . . . log
b
W−1.
In accordance with further aspects of this particular exemplary embodiment of the present invention, wherein the channel is a first channel and the selectively directed channel is a first selectively directed channel, and wherein the one or more b×b switching elements selectively direct a second channel operating at another respective one of the W frequencies based at least in part upon the respective frequency of the second channel, the respective frequency of the second selectively directed channel is the same as the res
Dasylva Abel C.
Kodaypak Prasad
Montuno Delfin Y.
Sindile Pia
Yao Zhonghui
Hunton & Williams LLP
Lee John D.
Nortel Networks Limited
LandOfFree
Technique and apparatus for wave-mixing frequency... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Technique and apparatus for wave-mixing frequency..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Technique and apparatus for wave-mixing frequency... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3253783