Abstract: An optical demultiplexer that separates, for each signal wavelength, signal light a plurality of wavelengths of which is multiplexed, the optical demultiplexer including: an antireflection film disposed at on an incident surface of a glass block; filters disposed on an emission surface of the glass block, the filters transmit light of a wavelength predetermined for each signal wavelength included in the signal light and reflect light of a wavelength other than the transmitting wavelength toward the incident surface; and a reflection film disposed on the incident surface of the glass block, wherein processing to reduce reflection of the reflection light into the glass block is applied on an optical path of the reflection light reflected by the filter disposed at an end away from the antireflection film.

Abstract: An optical demultiplexer that separates, for each signal wavelength, signal light a plurality of wavelengths of which is multiplexed, the optical demultiplexer including: an antireflection film disposed at on an incident surface of a glass block; filters disposed on an emission surface of the glass block, the filters transmit light of a wavelength predetermined for each signal wavelength included in the signal light and reflect light of a wavelength other than the transmitting wavelength toward the incident surface; and a reflection film disposed on the incident surface of the glass block, wherein processing to reduce reflection of the reflection light into the glass block is applied on an optical path of the reflection light reflected by the filter disposed at an end away from the antireflection film.