Optical unit

An optical unit comprising:

• a filter member that separates transmitted light;
• and
• a photodetector having a plurality of light receiving elements,
• wherein the filter member includes:
• a light transmissive substrate;
• a plurality of protrusions formed with a first metallic material on one surface of the substrate;
• and
• a metal film formed by a second metallic material having a higher refractive index than the first metallic material, so as to cover the one surface of the substrate along with the plurality of protrusions,
• the plurality of protrusions are disposed such that the metal film located between adjacent protrusions serves as a diffraction grating and incident light that is incident the filter member from an other side of the photodetector propagates inside the protrusions as an evanescent wave,
• at least one of a grating pitch of the diffraction grating, a height of the protrusions and a thickness of the metal film is set, such that a wavelength of light transmitted through the filter member changes for each portion, to a different value for each of the portions, and
• the photodetector is disposed such that each of the plurality of light-receiving elements receives light transmitted through the filter member.