A dispersion-slope compensator including a feedback-type optical filter constituted by a looped optical line; an input-and-output optical line which inputs and outputs optical signals; and optical couplers which couples the looped optical line and the input-and-output optical line at two or more positions so that a Mach-Zehnder interferometer is formed by a portion of the looped optical line and a portion of the input-and-output optical line which are located between two of the optical couplers. A portion of the optical path realizing an MZI arm which constitutes the Mach-Zehnder interferometer is spatially separated from the other portions of the optical path so that the optical length of the MZI arm can be variably adjusted, and an amount of compensation for dispersion slope can be variably set.

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> Charging device, and process cartridge and image forming apparatus using the charging device

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