Laser diode uses for optical disks

Summary form only given, as follows. Semiconductor lasers are key devices in optical disks. Optical properties of transverse mode-controlled diode lasers, such as far-field beam pattern, output power, spectrum, astigmatism, polarization, lifetime, and temperature dependencies for these characteristics are presented in this paper. Their use in optical heads has been improved in three respects: (1) Longitudinal mode instability causes noise in the output power. Therefore an appropriate length between the diode and theoretical disk was determined. (2) For diode laser recording, beam profile conversion from an elliptic to a circular profile was accomplished by using two prisms without optical loss. (3) The objective lens was actuated radially and vertically for tracking and focusing, instead of actuating it wholly. This has several advantages, such as easier laser diode cooling, high speed data recording and playback, and simple objective lens configuration. A means to reduce tracking offset error, due to radial displacement of an objective lens, is discussed.