Patent ID: 7020398

Claim:
A dispersion slope equalizer for compensating signal distortion caused by dispersion slope of a transmission line when transmitting lightwaves with plural wavelength signals in the transmission line characterized by comprising: N (N: natural number) waveguides, N output wavelength demultiplexer and/or N input wavelength multiplexer, and N group delay controllers; said N waveguides being connected to outputs of said wavelength demultiplexer and/or inputs of said wavelength multiplexer; in said group delay controllers, one of inputs and an output of transversal-form optical circuits being set on said N optical waveguides; the transversal-form optical circuit being provided with a first waveguide for one of inputs and M (M: natural number, M≧2) directional couplers for coupling M waveguides with said first waveguide at M different positions, and said M waveguides, after being coupled with said first waveguide, being multiplexed by a multiplexer into a second output waveguide; wherein control parts of a waveguide refractive index for effecting phase control of said waveguides are provided between said directional couplers and said multiplexer, and in respective ones of said directional couplers, or between said directional couplers and said multiplexer, and semipermanent phase shift is achieved by applying local heating and quenching for a photoelastic effect to said control parts of said waveguide refractive index.