POLARIZATION CONVERSION ELEMENT

摘要

The present invention provides a polarization conversion element that is capable of converting linear polarization having wavelength included in a prescribed wavelength range to radial polarization. The polarization conversion element(1) includes a phase reversal element(2) and a polarization plane rotation element(3). The polarization plane rotation element(3) includes a liquid crystal layer(30) and two transparent electrodes(33)(34). The liquid crystal layer(30) has a plurality of regions (30a to 30h) disposed along circumferential direction with the intersection point of the polarization plane rotation element(3) and the optical axis (OA) as the center with alignment directions different from each other. When electric voltage in accordance with the wavelength of linear polarization incident on the polarization plane rotation element (1) is applied between the two transparent electrodes(33)(34), each region rotates the polarization plane of the polarization component transmitted by each region so as to be parallel to the radial direction with the intersection point as the center, and thus converts linear polarization to radial polarization. The phase reversal element(2) reverses, among the first and the second annular portions alternately disposed along the radial direction with the optical axis (OA) as the center, the phase of light incident on the first annular portion relative to the phase of light incident on the second annular portion. The present invention can be utilized for, e.g., an optical pickup apparatus, a laser processing machine, or a laser microscope.