US Patent 7333690 Evanescent waveguide couplers

A multi-port planar evanescent coupler having N inputs and M outputs, where both N and M are each no less than three, formed of combinations of at least one of at least one planar evanescent 2×2 coupler and at least one planar evanescent 3×3 coupler subunits, with phase shifting segments in selected waveguides disposed between the planar evanescent coupler subunits. The multi-port planar evanescent coupler can be used in phase measurement and detection devices, such as interferometers, optical receivers, and laser gyroscopes.