Compound holographic optical element with two superposition hologram patterns for converging and diffracting a light beam

摘要

Not more than one compound holographic optical element is provided on an optical path starting from a semiconductor laser chip and arriving at a photo detector via an optical disk. A hologram pattern of this compound holographic optical element is the superposition of a first hologram pattern, converging a laser beam emitted from the semiconductor laser chip onto the optical disk, and a second hologram pattern, diffracting the laser beam reflected at the optical disk toward the photo detector and changing it into a focusing beam. This single holographic optical element not only realizes the convergence of the laser beam onto the optical disk and/or the photo detector and the differentiation of going and returning optical paths but reduces the size and production cost of the optical pick-up apparatus.