| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical head device which changes a light quantity converged on an optical recording medium even though an emission light quantity from a semiconductor laser used as a light source is not changed. SOLUTION: A phase modulation element is provided with a pair of transparent substrates which hold a liquid crystal layer in between, and electrodes for applying a voltage to the liquid crystal layer are formed on the surfaces facing the liquid crystal layer of the transparent substrates, respectively. At least one electrode is patterned in the shape of a grating so that part of emitted light passing through the liquid crystal layer is diffracted during a voltage application to change a light quantity of 0-th order diffracted light which condenses on an optical recording medium in recording information and in reproducing the information. This phase modulation element 125 is placed in the optical path between a semiconductor laser 121 being a light source and an objective lens 126. |
