The object of the present invention is to provide a compact dispersion slope equalizer by which it is possible to simultaneously recover distorted waveforms of WDM signals by dispersion slope of DSF or NZ-DSF at 1.55 µm band, and to compensate for the dispersion of various fiber transmission lines having various dispersion values and variation of dispersion value caused by the temperature change or the like. WDM signals distorted by the dispersion slope of the fiber are introduced into an input waveguide (1, 20), and are demultiplexed by a wavelength demultiplexer (2, 21) into each wavelength component, and pass through lattice-form optical circuits (4-1 to 4-N), transversal-form optical circuits (23-1 to 23-N), or the combination of these circuits. The dispersion slope of the signals is compensated for by these circuits. The recovered signals are multiplexed by a wavelength multiplexer (5, 24), and the multiplexed light is outputted at an output waveguide (6, 25). Arrayed-waveguide gratings can be used as the wavelength demultiplexer and multiplexer. Also, cascaded configuration of Mach-Zehnder interferometers, bulk-type optical filters, or fiber-type (or waveguide-type) gratings in series can also be used as the wavelength demultiplexer and multiplexer.
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