Information recording and reproducing apparatus

An information recording and reproducing apparatus comprising:

• a radiation light source;
• a collimator receiving a light beam emitted from said radiation light source and turning the light beam into substantially parallel light;
• a light beam convergence member receiving the substantially parallel light and focusing the substantially parallel light on an information carrier;
• a light beam branching member that is located between said radiation light source and said collimator, 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 collimator 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 (n±¼ 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 (n±¼ 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.

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 polarization-branching member that is located between said radiation light source and said light beam convergence member, branching the light beam by polarization;
• a variable wave plate located between said light beam polarization-branching member and said light beam convergence member;
• a photo detector receiving the light beam branched by said light beam polarization-branching member and outputting a current according to an incident light quantity;
• and
• an output level judging member judging whether an output of said photo detector is larger or smaller than a predetermined value;
• wherein a phase difference of said variable wave plate is switched according to a judgement of said output level judging member,
• the phase difference of said variable wave plate is switched between substantially (n) times a used wavelength and substantially (n±¼ 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 (n±¼ 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.

An information recording and reproducing apparatus comprising:

• a radiation light source;
• a collimator receiving a light beam emitted from said radiation light source and turning the light beam into substantially parallel light;
• a light beam convergence member receiving the substantially parallel light and focusing the substantially parallel light on an information carrier;
• a light beam polarization-branching member that is located between said radiation light source and said collimator, branching the light beam by polarization;
• a variable wave plate located between said collimator and said light beam convergence member;
• a photo detector receiving the light beam branched by said light beam polarization-branching member and outputting a current according to an incident light quantity;
• and
• an output level judging member judging whether an output of said photo detector is larger or smaller than a predetermined value;
• wherein a phase difference of said variable wave plate is switched according to a judgement of said output level judging member,
• the phase difference of said variable wave plate is switched between substantially (n) times a used wavelength and substantially (n±¼ 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 (n±¼ 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.

An information recording and reproducing apparatus comprising:

• a first radiation light source;
• a second radiation light source;
• a dual wavelength branching member receiving a first light beam and a second light beam emitted from said first radiation light source and said second radiation light source and directing the first and second light beams in a predetermined direction;
• a light beam convergence member receiving the first and second light beams emitted from said dual wavelength branching member and focusing the first and second light beams on an information carrier;
• a variable wave plate located between said dual wavelength branching member and said light beam convergence member;
• a first photo detector and a second photo detector receiving the light beam branched by said dual wavelength branching member and outputting a current according to an incident light quantity;
• and
• an output level judging member judging whether an output of said first and second photo detectors is larger or smaller than a predetermined value;
• wherein a phase difference of said variable wave plate is switched according to a judgement of said output level judging member,
• the phase difference of said variable wave plate is switched between substantially (n) times a used wavelength and substantially (n±¼ wavelength) times the used wavelength, wherein n is an integer, and
• a light quality received by each of said first photo detector and said second 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 one or both of said first photo detector and said second 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 (n±¼ wavelength) times the used wavelength when the light quantity received by one or both of said first photo detector and said second photo detector is more than 50% of the light quantity that has been stored, wherein n is an integer.