Abstract: An optical wavelength selective device includes a waveguide grating unit to separate input beam signals with different wavelengths into a plurality of output beam signals, each of which has a different wavelength span and is output from a different channel region of the waveguide grating unit; a polarization splitting unit to split each of the output beam signals into a first polarized beam with a first polarization and a second polarized beam with a second polarization different from the first polarization; a birefringence control member to control the first polarized beam to undergo a different refractive effect than the second polarized beam when the first and second polarized beams pass through the birefringence control member under a first voltage applied thereto; and a reflection member configured to reflect the first and second polarized beams output from the birefringence control member back to the birefringence control member.

Abstract: A variable optical attenuator includes a collimating unit that collimates an incident light beam, a polarization splitting member that separates the collimated light beam into a first polarized light beam having a first polarization and a second polarized light beam having a second polarization, a birefringence control unit through which the first and second polarized light beams pass, the birefringence control unit including a liquid crystal cell having a birefringence is controlled by a voltage or current, wherein the birefringence of the liquid crystal cell is substantially zero when no voltage or current is applied thereto, and a reflection member that reflects the first and second polarized light beams output from the birefringence control unit. The variable optical attenuator has high stability, high precision, and low volume.