Optical pickup and information reproducing apparatus

摘要

An optical pickup (PU) for reading information recorded on information tracks of a recording medium (1) by using a main light beam and a subsidiary light beam includes a diffraction device (6) for diffracting an original light beam to generate the main light beam and the subsidiary light beam. The main light beam is applied to a reading track which is one of the information tracks on which the information to be read is recorded. The subsidiary light beam is applied to the information track adjacent to the reading track. The diffracting device (6) is made of an optical material having coefficient of linear expansion p, which is determined as follows: $$ $ where\; lambda\; 0\; is\; a\; wavelength\; of\; the\; original\; light\; beam\; at\; a\; design\; temperature,\; DELTA\; lambda\; is\; an\; amount\; of\; a\; change\; of\; the\; wavelength\; of\; the\; original\; light\; beam\; per\; unit\; temperature,\; DELTA\; tmax\; is\; a\; predetermined\; permissible\; amount\; of\; a\; change\; of\; an\; ambient\; temperature,\; L0\; is\; a\; spacing\; between\; an\; irradiation\; position\; of\; the\; subsidiary\; light\; beam\; and\; an\; irradiation\; position\; of\; the\; main\; light\; beam\; at\; the\; design\; temperature,\; and\; DELTA\; Lmax\; is\; a\; predetermined\; permissible\; amount\; of\; a\; change\; of\; the\; spacing.\mathop{\mathrm{image}}$$$