Optical switch

Details Optical switch Optical switch

1997-04-08

2000-07-18

Pascal, Leslie

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

359127, 359138, H04J 1400, H04J 1402, H04J 1408

Patent

active

060915242

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to the handling of optical telecommunications signals in digital form. More particularly it is concerned with optical signals in a time division multiplex format and on the separation of channels for supply to different terminal equipment. In many cases, one channel is removed and replaced by a new signal.
Optical telecommunication is particularly attractive because of the high speed of optical systems. In fact, optical systems have developed to the stage where it is difficult, sometimes impossible, to design electrical or electronic circuitry which is capable of matching the operating speeds of the fastest optical systems. In such fast systems it is appropriate or necessary that the signal processing be carried out by all optical equipment.
As mentioned above, this invention is particularly concerned with optical signals in time division multiplexed format. In such a format it is possible that each individual channel may be slow enough for processing in high speed electronic equipment but the multiplex may be too fast. For example, if four channels are multiplexed the bit rate of the multiplex will be four times the bit rate of each individual channel. Thus if each channel is operating at only 75%, of the maximum speed available electronically the multiplex will be operating at 3 times the limit. In such a system it is clearly necessary that the multiplex be handled optically whereas the individual channels can be processed electronically.
It is appropriate to distinguish between two versions of time division multiplex format. These two versions are conveniently designated as "byte interleaved" and "bit interleaved". The byte interleaved format is more familiar than the bit interleaved. Each "byte" comprises a plurality of bits, usually 8, and the byte represents a unit of transmission. In the case of digitised analogue signals, e.g. digitised audio or digitised video, each byte represents a single sample of the analogue signal. In the case of data transmission each byte usually represents a single symbol of the data, e.g. an alphanumeric character. In the byte interleaved version of time division multiplex format each slot of the multiplex relates to its own channel and it contains one byte relating to that channel.
The bit interleaved version of the time division multiplexed format is less familiar and each slot contains only one bit. The signals will normally consist of bytes as described above but each byte is spread over a plurality of slots (instead of the more usual version wherein the whole byte is contained in one slot). As mentioned above, a byte usually consists of 8 bits and, therefore, in bit interleaved format such a byte is spread over 8 slots.
"Electronic Letters" 30 (1994) Feb. 3, 1994 at pages 255 and 256 describes a laboratory experiment which demonstrated an all-optical time division multiplex to wavelength division multiplex conversion using four wave mixing in a semiconductor optical amplifier. The discussion is limited to demultiplexing and nothing is said about the removal and replacement of a channel.


SUMMARY OF THE INVENTION

This invention relates to techniques for the handling of high speed optical telecommunications signals.
This invention, which is more fully defined in the claims, relates to time division multiplex format, and replacing the removed channels by new signals modulated with local data;
The invention also includes methods of handling optical telecommunications signals in time divisional multiplex format.
The invention is based upon applying wavelength modulation to optical signals which are already modulated with data in a time division multiplex format. The modulation applies characteristic wavelengths to different channels of the multiplex. For example, to achieve the separation a primary wavelength is applied to all channels except selected channels and a complementary wavelength is applied to the selected channels. Having applied the wavelength modulation, the channels are separated by a suitable network o

REFERENCES:
patent: 5612805 (1997-03-01), Fevier et al.
patent: 5742415 (1998-04-01), Manning et al.
patent: 5754714 (1998-05-01), Suzuki et al.
Summerfield et al., "All-Optical TDM to WDM Conversion in a Semiconductor Optical Amplifier", Electronics Letters, vol. 30, No. 3, Feb. 1994, pp. 255-256.
Patrick et al., "Bit-rate Flexible All-Optical De-Multiplexing Using a Nonlinear Optical loop Mirror", Proceedings of the 19th European Conference on Optical Communication, vol. 2, Sep. 1993, pp. 281-284.
Morioka et al., "All-Optical Kerr Switching Techniques and Applications", IEEE Global Telecommunications Conference & Exhibition, vol. 2, Dec. 1990, pp. 1311-1317.
Blow et al., "Nonlinear Loop Mirrors for All Optical Switching", OSA Proceedings on Photonics in Switching, vol. 16, Mar. 1993, pp. 203-206.
Alexander et al., "A Precompetitive consortium on Wide-Band All-Optical Networks", Journal of Lightwave Technology, vol. 11, No. 5/6, May 1993, pp. 714-732.
Jinno et al., "Nonlinear Sagnac Interferometer Switch and its Applications", IEEE Journal of Quantum Electronics, vol. 28, No. 4, Apr. 1992, pp. 875-882.

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