Optical pickup employing a hologram-laser-photodiode unit

In this paper we review the holographic optical element technology applied to compact disc (CD), digital versatile disc (DVD) and mini disc (MD) picku ps. Using this technology, the number of optical components and the size an d weight of a CD pickup are successfully reduced and its reliability is imp roved, because many functions of the optical components are integrated into a hologram-laser-photodiode unit. For DVD application, the focus detection for a dual-layer disk and the differential phase detection (DPD) method ar e realized by the hologram technology. Our unique two-segment DPD method sh ows more stable characteristics than the conventional DPD method. An integr ated MD hologram pickup is also developed with an optical waveguide device that functions in magneto optical (MO) signal detection.