Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-05-28
2001-04-10
Pascal, Leslie (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06215573
ABSTRACT:
TECHNICAL FIELD
This invention relates to an optical receiver for an optical communications system for transmitting coded optical signals, comprising an optical detector unit and an optical filter device connected ahead of the optical detector unit and comprising a periodic filter with a periodic transfer function. The invention also relates to an optical filter device for use in an optical communications system for transmitting coded optical signals, comprising a periodic filter with a periodic transfer function. The invention further relates to a method of operating this communications system comprising the steps of coding the signal in a transmitter by means of a transmitter filter and decoding it and converting it to an electric signal in a receiver by means of a periodic filter and detector unit, respectively.
BACKGROUND OF THE INVENTION
In a paper by L. Möller, “An Optical CDMA Method Based on Periodic Spectrum Encoding”, presented at the Thirteenth Annual Conference on European Fibre Optic Communications and Networks, Brighton, England, 1995, pp. 178-181, an asynchronous transmission system is described which uses a CDMA (code-division multiple access) method based on periodic spectrum encoding. In that system, the code words used for gaining access are implemented by different transfer functions of periodic filters. The method uses a particular periodic spectral filtering technique for broadband optical signal sources. An information signal can be received and processed in a receiver only if the periodicities of the filter transfer functions of the transmitter and receiver match.
In the communications system described, crosstalk occurs when two or more transmitters with filter transfer functions that are contiguous to each other in the tuning range are transmitting simultaneously.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical receiver for a communications system of the above kind wherein crosstalk between transmitters contiguous to each other in the tuning range is reduced. Further objects are to provide an optical filter device for use in such an optical communications systems as well as a method of operating this communications system.
These objects are attained by a receiver for an optical communications system for transmitting coded optical signals, comprising an optical detector unit and an optical filter device connected ahead of the optical detector unit and comprising a periodic filter with a periodic transfer function, wherein the filter device additionally comprises a prefilter with a transfer function by which the optical frequency spectrum of the signal can be changed in such a way that its cosine transform is limited to a predeterminable range of a tuning curve showing the total received power when tuning the periodic filter.
The objects are further attained by an optical filter device for use in an optical communications system for transmitting coded optical signals, comprising a periodic filter with a periodic transfer function, wherein the device includes an additional prefilter having a transfer function by which the optical frequency spectrum of the signal can be changed in such a way that its cosine transform is limited to a predeterminable range of a tuning curve showing the total received power when tuning the periodic filter.
The objects are still further attained by a method of transmitting coded optical signals in an optical communications system, comprising the steps of coding the signal in a transmitter by means of a transmitter filter and decoding it and converting it to an electric signal in a receiver by means of a periodic filter and a detector unit, respectively, wherein prior to the conversion, the signal is filtered by means of a prefilter with a transfer function which changes the optical frequency spectrum of the signal in such a way that its cosine transform is limited to a predeterminable range of a tuning curve showing the total received power when tuning the periodic filter, respectively. Further advantageous features of the invention are defined in the dependent claims.
The invention has the advantage that the number of transmitters that can transmit simultaneously and independently of each other without creating crosstalk is greater than in prior-art systems.
Another advantage is that even if the filter transfer functions of the transmitter and receiver deviate from respective nominal transfer functions, no crosstalk will occur.
REFERENCES:
patent: 4561119 (1985-12-01), Epworth
patent: 5293548 (1994-03-01), Siebert
patent: 5371354 (1994-12-01), Domon et al.
patent: 5389778 (1995-02-01), Shinomiya
patent: 5654814 (1997-08-01), Ouchi
patent: 5742418 (1998-04-01), Mizutani
patent: 5784506 (1998-07-01), Pfeiffer
patent: 6088144 (2000-07-01), Doerr
patent: 4206555 (1992-09-01), None
patent: 0622913 (1994-11-01), None
patent: 0670641 (1995-09-01), None
“An Optical CDMA Method Based on Periodic Spectrum Encoding” by L. Moller, Conference on European Fibre Optic Communications and Networks, England, 1995 pgs 178-181.
Alcatel
Bello Agustin
Pascal Leslie
Ware Fressola Van der Sluys & Adolphson LLP
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