Digital versatile disc read-only disc, rewritable disc and compact disc compatible optical pickup with a two-wavelength laser diode unit

We have developed an optical pickup with a two-wavelength laser diode unit which can read all the compact disc (CD) and digital versatile disc (DVD) family, including DVD rewritable discs (DVD-RAMs). To enable DVD-RAMs to be read, it is necessary to increase the light power efficiency of the optical system and to reduce the so-called track-crossing noise. This paper discusses several approaches to designing an optical system using a monolithic two-wavelength laser diode, and describes our experimental results and compatible reading of DVD read-only discs (DVD-ROMs), DVD-RAMs, and CDs using an optical pickup with a two-wavelength laser diode unit.