Patent ID: 6931165

Claim:
A variable polarization plane rotator for rotating a polarization plane of linearly polarized light, comprising: a first phase difference variable element that has an optical axis in the same direction as, or at a 90 degree angle relative to, a polarization direction of an input light beam, and applies, to the light beam being transmitted, a variable phase difference between a polarization component parallel to said optical axis and a polarization component perpendicular to said optical axis; a second phase difference variable element that has an optical axis at a ±45 degree angle relative to the optical axis of said first phase difference variable element, and applies, to the light beam being transmitted, a variable phase difference between the polarization component parallel to said optical axis and the polarization component perpendicular to said optical axis; a first phase difference adjustment section that adjusts such that the variable phase difference of said first phase difference variable element becomes 90 degrees depending on the wavelength of said input light beam; and a second phase difference adjustment section that adjusts the variable phase difference of said second phase difference variable element, wherein after being transmitted through said second phase difference variable element said input light beam is made into an elliptically polarized light or a circularly polarized light, the elliptically polarized light or the circularly polarized light being thereafter transmitted through said first phase difference variable element, to thereby be made into a linearly polarized light, so that the polarization plane of said input light beam is rotated by an angle corresponding to the phase difference applied by said second phase difference variable element.