Abstract: A variable optical attenuator in which a polarization beam splitter splits a beam incoming from the front into two linearly-polarized beams perpendicular to each other and separately outputs them to the back along first and second light paths. A Faraday rotator rotates a polarization plane of the two incoming linearly-polarized beams to an arbitrary angle by controlling a magnetic field to be applied to a Faraday element by a magnetism applying means and outputs them to the back. First and second analyzers arranged in the first and the second light paths and parallelly arranged perpendicular to these light paths are arranged in that order. The two analyzers have optical axes perpendicular to each other so that the optical axes are in the same direction as that of the polarization plane of the two linearly-polarized beams output from the polarization beam splitter.

Abstract: A disclosed optical element includes three or more sub-wavelength convexo-concave structures having pitches less than a wavelength of an incident light incident to the optical element and having groove depths equal to each other and a periodic structure having the three or more sub-wavelength convexo-concave structures, the pitch of the periodic structure greater than the wavelength of the incident light, in which a predetermined polarization direction of the incident light is diffracted mainly into a specific order.