To solve the problem that, in an optical pickup using a solid immersion lens (SIL), since a gap interval between an end face of the SIL and a surface of an optical disk is as narrow as several tens of nm, if there is relative tilting, the SIL and the optical disk may collide and a method for detecting a relative tilt angle in order to avoid the collision is being invented but according to a method using one beam, detection sensitivity of the tilt angle may be changed in the case of a multilayer optical disk including a plurality of information layers.
A plurality of beams are used to suppress a change in detection sensitivity of a tilt angle. Furthermore, even when a multilayer optical disk is irradiated with a plurality of beams, splitting to a detection system is performed closer to an objective lens system than a divergence change mechanism such as a beam expander, thereby easily separating a main beam and a sub beam and even in the case of the multilayer optical disk, the relative tilt angle can be detected stably.
MIZUNO SADAO
Daisuke Nagano
Kentaro Fujii