Planar lightwave circuit type variable optical attenuator

摘要

A planar lightwave circuit type variable optical attenuator has waveguides formed on a substrate. The variable optical attenuator comprises an input waveguide, a first optical coupler, a second optical coupler, two arm waveguides connecting said first optical coupler to said second optical coupler, phase shifters placed on said two arm waveguides for controlling phase difference between two light beams propagating trough said two arm waveguide with a thermooptic effect, and an output waveguide. Each of said first optical coupler and said second optical coupler is a directional coupler having a region in which said two arm waveguides are brought in close proximity to each other, and a length of said arm waveguides is designed to be equal to an integer multiple of an optical beat length obtained by dividing a used optical wavelength by the waveguide birefringence.