Optical system for detecting data signal and tracking error signal including polarizing optical element

Abstract

In an optical system, reflected light from the disk is diffracted by a hologram optical element, and received by an optical detector. A focusing error signal is detected from −1st-order diffracted light of the hologram optical element. A tracking error signal by the differential phase method, a tracking error signal by a push-pull method and the data signal recorded on the disk are detected from +1st-order diffracted light of the hologram optical element. A diffraction efficiency of the +1st-order diffracted light is higher than a diffraction efficiency of the −1st-order diffracted light.

1 . An optical system comprising:
 a light source;   an object lens for focusing emitted light from the light source onto an optical recording medium;   first optical separating means which is provided between the light source and the object lens and which separates an optical path of reflected light from the optical recording medium, from an optical path of the emitted light from the light source;   second optical separating means which separates the reflected light from the optical recording medium via the first optical separating means into a first group of light and a second group of light; and   an optical detector for receiving the first group of light and the second group of light;   wherein an optical signal strength of the first group of light is larger than an optical signal strength of the second group of light; and wherein:   the first optical separating means and the second optical separating means are an integrated polarizing hologram optical element,   the polarizing hologram optical element transmits the emitted light from the light source and diffracts the reflected light from the optical recording medium, and   the first group of light is +1st-order diffracted light of the polarizing hologram optical element while the second group of light is −1st-order diffracted light of the polarizing hologram optical element.   
   
   
       2 . An optical system as claimed in  claim 1 , wherein:
 the polarizing hologram optical element is divided into four regions by two divided lines respectively in parallel with a radial direction and a tangential direction of the optical recording medium, and   directions of lattices or pitches of the lattices of the four regions are different from each other.   
   
   
       3 . An optical system as claimed in  claim 1 , wherein:
 a phase distribution of lattices in the polarizing hologram optical element is formed in a step-like shape of four levels,   when phase differences of light transmitting through the two contiguous levels for ordinary light and extraordinary light are designated respectively by notation φo and φe and widths of the lattices of a 1-st stage through a 4-th stage are respectively designated by notations p/2-w, w, p/2-w and w, φo is substantially equal to 0, φe is substantially equal to   π/2 and w/p falls within the range of 0<w/p<0.25 or 0.25<w/p<0.5, and   the emitted light from the light source is incident on the polarizing hologram optical element as the ordinary light while the reflected light from the optical recording medium is incident on the polarizing hologram optical element as the extraordinary light.   
   
   
       4 . An optical system as claimed in  claim 1 , wherein:
 a phase distribution of lattices in the polarizing hologram optical element is formed in a step-like shape of four levels,   when phase differences of light transmitting through the two contiguous levels for ordinary light and extraordinary light are designated respectively by notations φo and φe and widths of the lattices of a 1-st stage through a 4-th stage are respectively designated by notations p/2-w, w, p/2-w and w, φo is substantially equal to π/2, φe is substantially equal to 0 and w/p falls within the range of 0<w/p<0.25 or 0.25<w/p<0.5, and   the emitted light from the light source is incident on the polarizing hologram optical element as the extraordinary light while the reflected light from the optical recording medium is incident on the polarizing hologram optical element as the ordinary light.