Patent ID: 7280216

Claim:
An apparatus for measuring the wavelength of an input light beam, the apparatus comprising: an optical waveguide having an input port and two output ports, the optical waveguide defining first and second optical paths which operate to direct light from the input port to the first and second output ports, respectively, and which have physical path lengths which differ by a preset amount to yield a first optical length difference therebetween, wherein the two output ports are located in a common plane normal to the direction of propagation of the central light rays emitted therefrom and are separated by a separation distance such that light exiting the optical waveguide through the two output ports forms, at an observation plane disposed at a second distance from the two output ports, a fringe pattern whose configuration at the observation plane is a function of the wavelength of the input light beam; a photo detector adapted to generate one or more detection signals in response to said fringe pattern; and a processor responsive to said detection signals and operative; to determine an average period of the fringes evidenced by said detection signals and the phase of a selected fringe evidenced by the detection signals; to determine an exact order number of the light to a reference point on said photo detector based on the average period and phase; to determine an optical delay of said first optical length difference at said reference point; and to divide said optical delay by said exact order number to get the wavelength of the input light beam.