Detection of stress applied to an optical fiber
AssigneeBritish Telecommunication public limited company
InventorsGodfrey R. Hill, Ian W. Stanley, Kenneth I. White
Life of this patent
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Abstract
Shocks or sudden stresses caused by attempts to tap into an optical fiber network are detected by monitoring the "speckle pattern" produced by intermodal interference at the output of a multimode fiber. The fiber is a single mode optical fiber communication link through which a monitoring beam having a wavelength at which the fiber supports multiple propagation modes is also transmitted.
Claims10
Monitoring apparatus for detecting movement of an optical fibre comprising:
- an optical demultiplexer coupled to said optical fibre for demultiplexing electromagnetic signals at a first and a second wavelength (.lambda..sub.1, .lambda..sub.2),
- the electromagnetic signals at said first wavelength (.lambda..sub.1) propagating in a single mode of the fibre,
- the electromagnetic signals at said second wavelength (.lambda..sub.2) propagating in a plurality of modes of the fibre, and
- means for detecting changes in an interference pattern produced by the interaction of the plurality of modes at the second wavelength (.lambda..sub.2).
An optical communications system comprising:
- an optical demultiplexer couple to an optical fibre for demultiplexing electromagnetic signals at a first and a second wavelength .lambda..sub.1, .lambda..sub.2),
- the electromagnetic signals at said first wavelength (.lambda..sub.1) propagating in a single mode of the fibre,
- the electromagnetic signals at said second wavelength (.lambda..sub.2) propagating in a plurality of modes of the fibre,
- means for detecting changes in an interference pattern produced by the interaction of the plurality of modes at the second wavelength (.lambda..sub.2),
- a first optical transmitter coupled to the optical fibre for transmitting data signals at the first wavelength (.lambda..sub.1), and
- a second optical transmitting means coupled to the optical fibre for transmitting an optical signal at the second wavelength (.lambda..sub.2).
A method of monitoring an optical communications system in which data-carrying electromagnetic signals at a first wavelength (.lambda..sub.1) are conveyed in a single mode of an optical fibre comprising:
- transmitting an electromagnetic signal along the optical fibre at a second wavelength (.lambda..sub.2) at which the optical fibre supports propagation in a plurality of modes;
- selectively extracting only the electromagnetic signals at the second wavelength (.lambda..sub.2) from the optical fibre;
- and
- detecting changes in the interference pattern produced by the interaction of the plurality of modes at the second wavelength (.lambda..sub.2).
Dependencies are inferred from the claim text.