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.