Patent
1988-11-21
1990-12-11
Lee, John D.
350 9620, G02B 626
Patent
active
049765051
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an optical switch and in particular, but not exclusively, to optical cross-point switches using D cross-section optical fibres.
An optical switch selectively transmits or does not transmit light from an input optical waveguide to an output optical waveguide. In the past various proposals and attempts have been made to provide such switches by interposing a material having selectively variable optical properties between the input and output optical waveguide so that light from the input optical waveguide can be selectively coupled to the output optical waveguide by selectively changing the properties of the material upon the application of an electrical field to it.
Another approach is to form a cross-point switch by locating a pair of optical fibres so that they cross each other diagonally but slightly apart. The optical fibres are chosen such that when they are pressed together an optical signal travelling in one fibre is coupled to the other, i.e. switched from the one optical fibre to the other. This is exemplified by the arrangements shown in the Patent Abstracts of Japan Vol 7, no. 168 (P-212)(1313) 23rd July 1983 (abstract of JP-A-58 199 304) and in the Patent Abstracts of Japan Vol 7, no. 196 (P-219)(1314) Aug. 26th 1983 (abstract of JP-A-58 95 701).
It is known to employ an electrostatic field to deflect an optical fibre supported at only one end so that the free end is moved into or out of abutting alignment with another optical fibre, the alignment being achieved by a V-groove into which the fibre is deflected as, for example in GB 1,598,334.
According to this invention an optical switch comprises an input and an output optical waveguide, one of which is an optical fibre mounted to be capable of movement towards and away from the other, and an electrode arranged to subject the one optical waveguide to an electrostatic field whereby application of an electrical potential to the electrode causes the optical fibre to move in a direction to enable or prevent optical coupling between the waveguides and hence operation of the switch, the optical fibre having a cross-section such that it is most flexible in said direction.
Because the fibre in the switch according to the present invention is most flexible in the direction of movement into and out of coupling relationship with the other waveguide it is less likely to be deflected laterally by the electrostatic field than a symmetrical optical fibre thereby reducing the strict tolerances required during manufacture.
The input and output optical waveguides may be biased towards one another so that the switch is biased into the ON state and then be operated and turned OFF when an electrical potential is applied to the electrodes to move the one optical waveguide away from the other. However, more usually, the input and output optical waveguides are biased away from one another so that the switch is biased into the OFF state and is then turned ON by the application of an electric potential to the electrode to move the input and output optical waveguides together.
The one optical fibre may have an electrically conducting coating and have an electrical potential applied to it so that it is attracted towards or repelled by the electrode. However, it is preferred that the one optical waveguide is entirely electrically non-conducting and the optical switch includes more than one electrode to provide a non-uniform electrostatic field, the one optical waveguide being caused to move towards the region of highest electrostatic field density and so move towards or away from the other waveguide to enable or prevent optical coupling between them. In this case the one optical waveguide may be coated with a material having a high dielectric constant, for example a polymer material such as poly acrylonitride, phenolic resin, elastomers, celluloid, and nylon.
The optical switch may include two or more output waveguides and, in this case, the switch by movement of the one optical waveguide between the two or more output waveguides is capable of esta
REFERENCES:
patent: 4493528 (1985-01-01), Shaw et al.
patent: 4798435 (1989-01-01), Fujiwara et al.
patent: 4805038 (1989-02-01), Seligson
Cassidy Stephen A.
Yennadhiou Peter
British Telecommunications public limited company
Lee John D.
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