Patent ID: 8620155

Claim:
An optical noise monitor for monitoring noise in an optical signal, comprising: an optical transmitter for receiving at least a portion of said optical signal; a device arranged to extract a reflected optical signal comprising a portion of said optical signal back-reflected by stimulated Brillouin scattering in said optical transmitter; and a photodetector for receiving said reflected optical signal; wherein said optical transmitter scatters said optical signal by stimulated Brillouin scattering; wherein, when the noise in the optical signal is above a Brillouin threshold, efficiency of power transfer to a Stokes wave is reduced and a strength of said reflected optical signal received by said photodetector is inversely proportional to a level of noise in said optical signal; and wherein said monitor is configured (i) to identify that noise is present in said optical signal based on a reduction in the strength of said reflected optical signal received by said photodetector, or (ii) to determine said level of noise in said optical signal based on the strength of said reflected optical signal received by said photodetector.