OPTICAL FILTER ELEMENT

PURPOSE:To provide the optical filter element which performs the wavelength separation of signal light of a desired wavelength component from signal light containing plural wavelength components to a narrow band, eliminates defects of a conventional optical filter, and holds a steep cut-off characteristic without varying a transmission characteristic with an angle of incidence. CONSTITUTION:Luminous flux in a random polarized state is split by polarization separating elements 1 and 5 into two parallel pieces of luminous flux, at least one of which is passed through polarization rotating elements 2 and 4 to match the polarizing directions of the two pieces of luminous flux with each other; and they are made incident on a filter which has a rotating mechanism, one of the two pieces of luminous flux is passed through a polarization rotating element, and then the two pieces of luminous flux are multiplexed through a polarization separating element to eliminate variation in the transmission characteristic even if the input luminous flux changes in polarization.