Apparatus and method for monitoring signal-to-noise ratio in...

Details Apparatus and method for monitoring signal-to-noise ratio in... Apparatus and method for monitoring signal-to-noise ratio in...

2007-05-15

2007-05-15

Pascal, Leslie (Department: 2613)

Optical communications

Diagnostic testing

Determination of communication parameter

C398S202000, C329S306000

Reexamination Certificate

active

10636385

ABSTRACT:
A high-sensitivity signal-to-noise ratio (SNR) determining apparatus measures the in-band SNR of an optical data signal by detecting and demodulating the optical signal and analyzing a narrow bandwidth of the resulting electrical data spectrum at half the data clock frequency, or more generally, a predetermined frequency equal to a multiple M of one-half the clock frequency, fclk/2, where M is an integer equal to or greater than one, may be used. When the optical signal is a WDM signal, a tunable filter isolates a single channel for detection. The detected electrical signal is subjected to both an in-phase and quadrature narrowband RF demodulation using a local oscillator at precisely half the clock frequency. Using this technique, the magnitude of the data portion of the optical signal becomes the in-phase component and the magnitude of the noise present in the optical signal becomes the quadrature component. The ratio of the two demodulated signal components (in-phase and quadrature) is proportional to the SNR of the detected signal. The technique is inherently narrowband and offers very high sensitivity and does not require an optical pre-amplifier.

REFERENCES:
patent: 3035231 (1962-05-01), Woods et al.
patent: 4466108 (1984-08-01), Rhodes
patent: 5881107 (1999-03-01), Termerinac et al.
patent: 6775521 (2004-08-01), Chen

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