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US 4,070,091 AGranted
Optical fibre with enhanced security
AssigneeNorthern Telecom Limited
InventorsJohn Charles Wood Taylor, Felix Paul Kapron
Life of this patent
Estimating the term…
Abstract
An optical fibre has a light conducting core surrounded by first and second cladding layers of sequentially lower refractive index. A data-carrying signal can be propagated in the core and a monitoring signal--of a higher modal order than the data signal--can be propagated in the core and first cladding layer. Any attempt to rap the fibre and abstract data information results in aberration of the monitor signal, which can be detected. The monitor signal can be such that resolvable signals cannot be obtained from the data channel by a tap.
Claims14
An optical fibre comprising:
- a light conducting core having a predetermined minimum refractive index and forming a first light conducting path;
- a first, light conducting, cladding layer surrounding said core and having a constant refractive index lower than said minimum refractive index of said core and forming with said core a second light conducting path;
- a second cladding layer over said first cladding layer and having a constant refractive index lower than the refractive index of the first cladding layer;
- whereby a first signal will propagate only in the core and a second signal will propagate in both the core and the first, light conducting, cladding layer.
1 more element
Dependencies are inferred from the claim text.