Patent ID: 7333210

Claim:
A control unit for controlling a wavelength of light from a tunable laser, said control unit comprising: a wavelength tuner for providing information of a desired wavelength; a coupler for tapping a portion of light from the tunable laser; and an apparatus for measuring an actual wavelength of said portion of light, including: an optical device having an input port for receiving said portion of light from said coupler, two output ports, beam splitting means for splitting said portion of light received by said input port into first and second beams, and first and second optical paths configured to have different optical lengths and to direct said first and second beams to said two output ports, respectively, wherein said two output ports are separated by a first distance such that said first and second beams exiting said two output ports form a fringe pattern at an observation plane disposed at a second distance from said two output ports; a photo detector for receiving an image of said fringe pattern at said observation plane and generating one or more detection signals responsive thereto; and a processor for receiving said detection signals, for analyzing said detection signals to determine said actual wavelength of said portion of light, for receiving said information of said desired wavelength from said wavelength tuner, for calculating an error value representing a difference between said desired wavelength and said actual wavelength and for sending a control signal commensurate with said error value to the tunable laser to tune the tunable laser.