LIQUID CRYSTAL ELEMENT AND OPTICAL PICKUP OPTICAL SYSTEM

摘要

A liquid crystal element (14) includes a first transparent electrode layer (146) which drives a first liquid crystal layer (144) and a second transparent electrode layer (147).  The first transparent electrode layer (146) applies voltage to the first liquid crystal layer (144) so as to have a portion which assigns a phase difference substantially periodically changing along the radial direction of the laser beam within a range not smaller than -h? and not greater than +h? (wherein, h is an integer satisfying h = 1; and ? is a design wavelength), to a laser beam passing through the liquid crystal element (14), and which assigns a phase difference h? between laser beams transmitting through adjacent transparent electrodes of the first transparent electrode layer (146).  The second transparent electrode layer (147) applies voltage to the first liquid crystal layer (144) so that the first liquid crystal layer (144) assigns a phase difference substantially continuously changing along the radial direction of the laser beam, to the laser beam passing through the liquid crystal element (14).