Laser beams respectively emitted from a SHG blue laser unit and a red
semiconductor laser unit that have photo detectors respectively are turned
into parallel lights by a collimator lens and then coupled by a dielectric
multi-layer film mirror so as to be propagated on the same optical axis.
The dielectric multi-layer film mirror is configured so as to transmit
light with a wavelength of 500 nm or shorter and reflect light with a
wavelength of 500 nm or longer for both P wave and S wave. The lights that
are transmitted and reflected by the dielectric multi-layer film mirror
pass through a polarizing hologram and a phase variable wave plate and are
focused on an optical disk by an objective lens. In this manner, a simple
configuration can realize a compatibility with many types of optical disks
and a stable signal detection even when using a polarizing optical
detection system.
