Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1998-12-29
2001-04-10
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Input/output coupler
C385S015000, C359S199200
Reexamination Certificate
active
06215929
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a dispersion compensating waveguide (DCW), which has the property of introducing frequency dispersion in transmitted optical waves and is generally used for compensating unwanted dispersion in a transmission path usually comprising fibre. The invention further relates to an optical transmission system incorporating a dispersion compensated waveguide.
Typically the waveguide will comprise dispersion compensating fibre ((DCF).
In order that a required dispersion be introduced, without a requirement for unduly long lengths of dispersion compensating fibre, the fibre may be highly doped, e.g. germania doped silica. Whether or not it is highly doped, it is usual to cut or otherwise select an appropriate length to select a dispersion value, which is somewhat inflexible. If more than one wavelength is being used in the transmission of information, there will be an inevitable trade-off in throughput resulting from selecting an optimum length to suit all the wavelengths used.
It would be also desirable if losses could be compensated independently of the compensation of dispersion, or so as to enable use of dispersion compensating fibre to be more flexible.
SUMMARY OF THE INVENTION
A particular arrangement to be described below as being helpful in understanding the invention proposes the provision of Bragg gratings in the dispersion compensating fibre, and makes use of the reflected signals from the gratings. The incident signal traverses selectively different lengths of the dispersion compensating fibre according to the dispersion required by the appropriate positioning of the grating along the dispersion compensating fibre.
If various selected dispersions are required, a prior method is to use dispersion compensating fibres of different lengths, or to cut down from a starting length. This embodiment uses reflection gratings at intervals such that different (double—) lengths of the dispersion compensating fibre can be selected for traversal by the signal, and hence different dispersions can be selected. The selection would be achieved in practice by splicing or writing a grating into the fibre at the required length down the fibre.
In the specification of U.S. Pat. No. 5,404,413 there was proposed an optical circulator with three ports. The first and third ports were connected to optical fibre systems. The second port was connected to a dispersion compensating fibre and return means. A signal passed through the dispersion compensating fibre twice, thus permitting the use of shorter compensating fibres than previously.
The following description and drawings disclose a previously proposed arrangement and, by means of examples, the invention which is characterised in the appended claims, whose terms determine the extent of the protection conferred hereby.
REFERENCES:
patent: 5404413 (1995-04-01), Delavaux
patent: 5410624 (1995-04-01), Morkel
patent: 5574810 (1996-11-01), Byron et al.
patent: 5608562 (1997-03-01), Delavaux et al.
patent: 5701188 (1997-12-01), Shigematsu et al.
patent: 6072811 (2000-06-01), Fermann et al.
patent: 0 485 100 (1992-05-01), None
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patent: 0 732 819 (1996-09-01), None
Font Frank G.
Lee Mann Smith McWilliams Sweeney & Ohlson
Nguyen Sang Hoang
Nortel Networks Limited
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