Patent ID: 6912362

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, comprising: N (N: natural number) waveguides, N output wavelength demultiplexer and/or N input wavelength multiplexer, and K (K: natural number, K<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 or both of input/output parts of lattice-form optical circuits being set on said N waveguides; said lattice-form optical circuits having two waveguides interleaved with at least two directional couplers; and said two waveguides being designed so that optical path lengths between said directional couplers are different; wherein control parts of waveguide refractive index for effecting phase control of said waveguides are provided between respective ones of said directional couplers and in respective ones of said directional couplers, or between respective ones of said directional couplers, and semipermanent phase shift is achieved by applying local heating and quenching for a photoelastic effect to said control parts of waveguide refractive index.