Patent ID: 8457489

Claim:
A method for controlling the center wavelength of a narrow band WDM optical channel transmitting device in a WDM network, the method including: (a) coupling the optical channel signal created by the optical channel transmitting device into a near end of an optical channel waveguide, a remote end of the optical channel waveguide being coupled to a channel port of an optical multiplexing device, wherein the channel port defines a wavelength transmission band and the optical multiplexing device is designed such that the optical channel signal is included in an optical WDM signal output at a WDM port of the optical multiplexing device; (b) periodically modulating the center wavelength of the optical channel signal with a predetermined modulation frequency and amplitude to produce a modulated optical channel signal having a bandwidth narrower than the bandwidth of the wavelength transmission band; (c) at the near end of the optical channel waveguide, detecting the optical power of a reflected portion of the optical channel signal as a function of time, and creating a corresponding electrical reflection signal, wherein the reflected portion of the optical channel signal comprises either, (i) a first type reflected signal produced by a first type device which exhibits a relatively low reflectivity at the center wavelength of the optical channel signal and a sharply increasing reflectivity aside from the center wavelength, or (ii) a second type reflected signal produced by a second type device which exhibits a relatively high reflectivity at the center wavelength of the optical channel signal and a sharply decreasing reflectivity aside from the center wavelength, the second type device being coupled to the optical path of the WDM signal output from the WDM port of the optical multiplexing device by means of a splitting device which directs a portion of the optical WDM signal to the second type device; (d) creating from the electrical reflection signal an electrical monitoring signal corresponding to the power included in the fundamental modulation frequency components of the detected reflected portion of the optical channel signal; and (e) controlling the center wavelength of the optical channel signal such that the electrical monitoring signal is minimized when the reflected portion of the optical channel signal comprises the first type reflected signal, and controlling the center wavelength of the optical channel signal such that the electrical monitoring signal is maximized when the reflected portion of the optical channel signal comprises the second type reflected signal.