Method and system for detecting loss of signal in wavelength division multiplexed systems

A system for detecting a fiber cut on a fiber having at least one fiber amplifier between a monitor point and the fiber cut, said system comprising:

• circuitry for generating a compensating channel;
• and
• circuitry for detecting the power ratio between the generated compensating channel and a spectral band having approximately the same gain as the compensating channel;
• said compensating channel circuitry and said detection circuitry being coupled to the fiber so that a cut at any location along the fiber is detected.

A wavelength division multiplex system comprising:

• at least two node elements interconnected by a working and a standby fiber;
• a plurality of amplifiers in said fibers;
• and
• means for determining a fiber cut in one of said fibers, said means comprising means for comparing the power ratio between a marker wavelength on said one fiber and a nearby spectral band.

A wavelength division multiplex system comprising:

• at least two node elements interconnected by a working and a standby fiber;
• a plurality of erbium doped amplifiers in said fibers;
• means for determining a fiber cut in one of said fibers, said means comprising means for comparing the power ratio between a marker wavelength on said one fiber and a nearby spectral band;
• and
• wherein said marker wavelength is provided by the erbium doped amplifiers.

A wavelength division multiplex system comprising:

• at least two node elements interconnected by a working and a standby fiber, said node elements being arranged in a point-to-point configuration;
• a plurality of amplifiers in said fibers,
• means for determining a fiber cut coupled to one of said fibers, said means comprising means for comparing the power ratio between a marker wavelength on said one fiber and a nearby spectral band;
• and
• means responsive to said determining means for switching from said working to said standby fiber.