Holographic optical element for an optical disk head with spot-size detection servo optics

A CGH construction of a holographic optical element (HOE) for an optical disk head with spot-size detection by means of superimposing two Fresnel zone plates is studied. Optimum parameter values for the ratio of segment to grating pitch (duty) and grating height are clarified from the viewpoint of total light power efficiency in the round trip optical system. The influences of higher-order diffracted beams near the first-order diffracted beams used to get signals on signal detection are shown to be small. The HOEs with almost optimum parameter values are fabricated and the desired diffracted spots, the expected total light power efficiency, and the small influence of higher-order diffracted beams are observed.