Wavelength selective switch, variable dispersion compensator, optical transmission apparatus, and optical transmission system

A variable dispersion compensator comprising:

• an optical system configured to collect input light input from an input side in a one-dimensional direction;
• an optical component having two parallel planes opposite to each other, one of the parallel planes being formed with an irradiation window and a first reflection surface, the other of the parallel planes being formed with a second reflection surface, the light collected in the one-dimensional direction by the optical system entering between the first reflection surface and the second reflection surface through the irradiation window, the entered light being multi-reflected on each of the reflection surfaces and a part of the reflected light being transmitted and emitted through the second reflection surface, the parallel planes serving as a wavelength demultiplexer configured to form light fluxes traveling in different directions depending on wavelengths by using interference of the emitted light from the second reflection surface;
• a reflector configured to reflect the light fluxes each having the demultiplexed wavelength, the light fluxes being emitted to different directions from the second reflection surface of the optical component, such that the light fluxes return to the optical component and are output from the output side;
• a light source configured to generate monitor light having at least a wavelength included in the input light;
• a monitor light input unit configured to input the monitor light generated by the light source to the variable dispersion compensator from the output side of the variable dispersion compensator;
• a monitor light extraction unit configured to extract the monitor light input from the output side of the variable dispersion compensator by the monitor light input unit, the monitor light being propagated in a direction opposite to a propagation direction of the input lights each having the demultiplexed wavelength in the variable dispersion compensator and being output to the input side of the variable dispersion compensator;
• and
• a monitor configured to monitor the monitor light extracted by the monitor light extraction unit.