Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1997-06-17
2001-01-16
Pascal, Leslie (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06175433
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to a bit rate converter for communication systems and more specifically to an optical bit rate converter for high speed communication systems.
BACKGROUND OF THE INVENTION
An optical bit rate converter is an important component for communication and computing systems such as ultra-high speed, time division multiplexed (TDM) multi-access networks. In TDM multi-access networks, the network bus may operate at a rate of 100 Gb/s. However, the data processing may be performed electronically. The electronic device receiving the ultra-high speed (on the order of 100 Gb/s) optical data stream will require a receiver node to buffer the incoming ultra-high speed optical data stream, rate convert the optical data to electronic rates (approximately 100 MHz-10 GHz), and detect and process the data. Optical bit rate converters are useful for rate-converting ultra-high speed optical data streams to lower rate optical data streams that can be detected and processed electronically.
One method for performing rate conversion known to the prior art is to demultiplex every K
th
bit of an N bit long optical data packet, K and N being relatively prime. As used herein, a set of numbers is “relatively prime” when the greatest common divisor of all the numbers in the set is equal to one. Further, as used herein, the term data pattern means the series of bits being converted and includes but is not limited to blocks and packets of data. The time required to rate convert an entire pattern of optical data using this demultiplexing method is substantially NKT
b
, where N is the length of the fundamental data pattern, K is an integer, and T
b
is the bit period (inverse of the bit rate) of the original optical data stream being rate-converted. This known demultiplexing method, with K≠(mN+1), where m is a whole number, however, scrambles the data bits of the original optical data pattern and requires further processing to reconstruct the original data pattern. In another known demultiplexing method, in addition to scrambling bits, only certain bits of data are selected from the original optical data stream and the rest of the bits are ignored. This demultiplexing method does not maintain all the bits of the original optical data stream in the rate-converted data stream.
In general, known bit rate converters utilize electronic or electro-optic devices, such as electronic memory. The bandwidth of these electrical devices limits the data rate of the optical data streams which can be rate-converted.
What is desired then is a rate converter which converts ultra-high speed optical data streams to lower rate optical data streams. The present invention permits such functionality.
SUMMARY OF THE INVENTION
The invention relates to an optical bit rate converter for high speed communication systems. The optical bit rate converter converts an ultra-high speed optical data stream to a lower rate optical data stream. In one embodiment, the optical bit rate converter converts the ultra-high speed optical data stream to a lower rate optical data stream that can be detected and processed electronically. The optical bit rate converter includes a buffer presenting a repeating optical data bit pattern, an optical sampler presenting an optical sampling bit stream, and an optical correlator. The optical correlator has a first input in communication with the output of the buffer and a second input in communication with the output of the optical sampler. The optical correlator produces a rate-converted optical data bit steam at its output in response to the repeating optical data bit pattern produced by the buffer and the optical sampling bit stream produced by the optical sampler. In one embodiment, the buffer generates the repeating optical data bit pattern. In another embodiment, the buffer has a data input and stores an optical data bit stream received from a high speed optical data source. In this embodiment, the buffer generates the repeating optical data bit pattern in response to the stored optical data bit stream. In yet another embodiment, the buffer is an optical memory. In another embodiment, the optical bit rate converter time dilates the repeating optical data bit pattern received from the buffer. In still another embodiment, the optical bit rate converter demultiplexes the repeating optical data bit pattern received from the buffer.
The invention also relates to a method for rate converting an ultra-high speed optical data stream to a lower rate optical data stream. The method includes the steps of providing a repeating optical data bit pattern, providing an optical sampling bit stream, correlating the repeating optical data bit pattern with the optical sampling bit stream, and producing a rate-converted optical data bit stream in response to the correlation. In one embodiment, the method rate converts an ultra-high speed optical data stream to a lower rate optical data stream that can be detected and processed electronically. In another embodiment, the method rate converts the repeating optical data bit pattern via demultiplexing. In yet another embodiment, the method rate converts the repeating optical data bit pattern via time dilation. In one embodiment, the method further includes the step of filtering the correlated repeating optical data bit pattern and optical sampling bit stream to remove the optical sampling bit stream.
The present invention has the technical advantage of accurately rate converting an ultra-high speed optical data bit stream to a lower rate optical data bit stream. In one embodiment, the present invention has yet the further advantage of maintaining the original sequence of the bits of the original ultra-high speed optical data stream in the rate-converted data stream without requiring further processing.
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Barry Richard A.
Finn Steven G.
Hall Katherine L.
Moores John D.
Patel Naimish S.
Fish & Richardson P.C.
Massachusetts Institute of Technology
Pascal Leslie
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