Method and apparatus for maintaining incident optical signal having low degree of polarization in specific state of polarization

An optical circuit includes a light source having a low degree of polarization, an input section connected to the light source, and an output section connected to the input section. The input section has an optical waveguide incapable of maintaining a state of polarization. The output section has at least one optical waveguide having no branches. The optical waveguide having no branches has, in at least part thereof, an optical waveguide capable of maintaining a state of polarization.