Patent ID: 8611750

Claim:
An apparatus comprising: a plurality of optical transmitters coupled to a fiber; a signal generator coupled to the optical transmitters and configured to provide a single pilot tone to the optical transmitters; an optical splitter coupled to the fiber, positioned within a feedback loop between the fiber and the optical transmitters, and having a first output and a second output; an etalon filter positioned within the feedback loop and coupled to the first output; an optical-to-electrical (O/E) converter coupled to the etalon filter and the first output, wherein the O/E converter is configured to convert an output of the etalon filter and the second output to electrical signals; and a processor coupled to the O/E converter, wherein the processor is configured to: compute a quadrature component as an imaginary component of a frequency-domain output of the etalon filter divided by the second output in the frequency domain; and adjust a wavelength for each of the optical transmitters to lock the wavelengths based on a magnitude and a sign of the quadrature component.