Patent ID: 6584059
Filing Date: 2003-06-24
Classification: G11B

Abstract:
An information recording and reproducing apparatus comprising:a radiation light source; a light beam convergence member receiving a light beam emitted from said radiation light source and focusing the light beam on an information carrier; a light beam branching member that is located between said radiation light source and said light beam convergence member, branching the light beam; a photo detector receiving the light beam branched by said light beam branching member; and a variable wave plate located between said light beam branching member and said light beam convergence member; wherein the phase difference of said variable wave plate is switched between substantially (n) times a used wavelength and substantially (nÂ±Â¼ wavelength) times the used wavelength, wherein n is an integer, and a light quantity received by said photo detector with respect to the information carrier without any birefringence is stored in advance, and then the phase difference of said variable wave plate is set at substantially (n) times a used wavelength when a light quantity received by said photo detector at the time of recording and reproducing is less than 50% of the light quantity that has been stored, and the phase difference of said variable wave plate is set at substantially (nÂ±Â¼ wavelength) times the used wavelength when the light quantity received by said photo detector is more than 50% of the light quantity that has been stored, wherein n is an integer.