OPTICAL FILTER

摘要

PROBLEM TO BE SOLVED: To achieve an optical filter whose transmittance can be changed at a high speed.

SOLUTION: An optical waveguide (18) includes a quantum well inter-subband transition optical waveguide structure which absorbs a TM wave by inter-subband transition and causes cross phase modulation on a TE wave. Reflecting films (20 and 22) are provided on the incidence side and the emission side of the optical waveguide (18) to constitute a Fabry Perot resonator. A polarization multiplexer (24) multiplexes signal light (28) of the TE wave and control light (30) of the TM wave, and multiplexed light is made incident on the optical waveguide (18) through the reflecting means (20). A polarizing beam splitter (26) on the emission side separates the signal light (32) and the control light (34) from light emitted from the optical waveguide (18).

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