Patent ID: 7619959

Claim:
An optical head comprising: a light source; a light focusing means for focusing a light beams emitted from the light source onto an optical recording medium; a beam splitting means for making the light beam emitted from the light source and return light coming from the optical recording medium via the light focusing means travel along different light paths; a light detecting means for detecting the return light coming from the optical recording medium via the beams splitting means; and an optical-coupling efficiency varying means provided between the light source and the beam splitting means, the optical-coupling efficiency varying means adapted to vary an optical-coupling efficiency that is a ratio of an amount of light focused on the optical recording medium with a total amount of light emitted from the light source; an optical-coupling efficiency detecting means for detecting an optical-coupling efficiency varied by the optical-coupling efficiency varying means, an irradiation light power detecting means for detecting a part of the power of the light beam for irradiation to the optical recording medium, an optical power controlling means for controlling the power of the light beam from the light source on the basis of the power of the light beam detected by the irradiation light power detecting means, power to keep constant the power of the light beam for irradiation to the optical recording medium, and in the state that the power of the light beam for irradiation to the optical recording medium by the optical power controlling means is constant, the optical-coupling efficiency detecting means detects optical-coupling efficiency varied when optical-coupling efficiency is changed by the optical-coupling efficiency varying means, the optical-coupling efficiency varying means changes the optical-coupling efficiency according to the optical-coupling efficiency varied that the optical-coupling efficiency detecting means detected.