Disclosed is a lens for light collection for total reflection for a front
monitor photodiode (PD) in an optical pick-up device. The optical pick-up device
includes a light source provided with a holographic unit adapted to diffract a
light beam, an optical disc arranged in front of the light source and adapted to
allow data to be written thereof or to be read therefrom, a monitor photodiode
arranged in front of the light source in a diagonal direction with respect to the
light source, the monitor photodiode serving to monitor a laser power of the light
source, and a lens for light collection arranged between the light source and the
monitor photodiode and adapted to converge a first-order diffracted beam outputted
from the holographic unit and to apply the converged first-order diffracted beam
to the monitor photodiode. The optical pick-up device can achieve an enhancement
in the efficiency of utilizing a main beam, namely, a zero-order diffracted beam,
an improvement in optical characteristics, and an improvement in the axial distance
between the light source and the monitor PD.
