PLANAR LIGHTWAVE CIRCUIT TYPE VARIABLE OPTICAL ATTENUATOR

摘要

A waveguide type variable light attenuator having a small polarization dependent loss. A polarization mode coupling is permitted to be -25dB or below by setting a waveguide birefringent index (absolute value) at first and second optical coupler sections at 3.5x10^-4 or more, and influence of polarization dependent loss due to the polarization mode coupling at a cross port of the first and second optical couplers is suppressed. In addition or merely, an arm waveguide length may be designed to be an integral multiple of a beat length obtained by dividing a wavelength of a using light by a waveguide birefringent index.