Patent attributes
An optical information recording and reproducing apparatus includes a light source for emitting a light beam, a head unit, including an objective lens and a solid immersion lens, that allows a light beam from the light source to reach an optical recording medium as evanescent light, and a photodetector that detects returning light that returns from a bottom surface of the solid immersion lens for detecting a gap and a tilt between the optical recording medium and the solid immersion lens. The photodetector has a first section and a second section, along a direction in which the returning light is moved in the photodetector, when the solid immersion lens is driven in a tracking direction with respect to the optical recording medium. An area of the returning light in the first section and an area of the returning light in the second section is constant, even when the solid immersion lens is driven in the tracking direction. The photodetector is divided into two halves in the direction in which the returning light is moved when the solid immersion lens is driven in the tracking direction, and has divided sections that are parallel to the direction in which the returning light is moved. The divided sections are disposed inside the inner circumference of the returning light in a direction perpendicular to the direction in which the returning light is moved. The apparatus further includes a tilt control circuit to control the tilt on the basis of a light intensity obtained by the photodetector.
