Patent ID: 6396603
Filing Date: 2002-05-28
Classification: H04B,H04J

Abstract:
A circuit for monitoring the stability of wavelengths of light signals in an optical communications system employing wavelength division multiplexing (WDM) and having a wavelength stabilization circuit, comprising:a plurality of channel transmitters each having a laser diode for generating a light signal at a particular frequency under the control of a laser diode driver; a WDM device for multiplexing said wavelengths by wavelength division; a Fabry-Perot filter having resonant frequencies continuously arranged with given free spectral ranges according to specified central frequencies for the channels to resonate an output of said WDM device; a photodetector for converting output light signals of said Fabry-Perot filter into corresponding electrical signals; and a quadrature phase shifter for shifting a phase of an output signal of said photodetector by 90Â°; each of said channel transmitters further comprising: an oscillator for generating a dither signal of a frequency specified for a particular channel; a first phase sensitive detector (PSD) for effecting a phase sensitive detection of said dither signal and an output signal of said photodetector to generate an error signal corresponding to a first derivative signal of an Airy function; a first low pass filter (LPF) for filtering said error signal to generate a first detected direct current voltage having a level representing a deviation of the output signal of said photodetector from said central frequency; an adder for adding said dither signal and the first detected voltage to generate a bias signal supplied to said laser diode driver; a second PSD for effecting a phase sensitive detection of said dither signal and an output of said quadrature phase shifter to generate an intensity signal representing an intensity of a light signal transmitted by said WDM device; a second LPF for filtering said intensity signal to generate a second detected direct current voltage; and the monitor circuit monitoring said first and second detected voltages so as to indicate whether or not said wavelength of the light signal is stabilized based on said first and second detected voltages.