Objective optical element and optical pickup apparatus

Abstract

An objective optical element of an optical pickup apparatus has a magnification m 1 satisfying the following formula for a light flux of the wavelength λ 1 : − 1/7≦m 1 ≦− 1/25 and |m 1 |<|M 1 , where M 1 is an optical system magnification from the first light source to the first optical information recording medium for a light flux of the wavelength λ 1 . The objective optical element comprises a common region and an exclusive region. The exclusive region includes an exclusive diffractive structure having a function to suppress an increase of spherical aberration due to a raise of atmospheric temperature. A light flux of a wavelength λ 2 having passed through the exclusive diffractive structure intersects with the optical axis at a position different from the position of the converged light spot formed on the information recording plane of the second optical information recording medium.

1 - 114 . (canceled) 
   
   
       115 . An objective optical element for use in an optical pickup apparatus which is provided with a first light source of a wavelength λ 1 , a second light source of a wavelength λ 2  (λ 1 <λ 2 ), and the objective optical element,
 wherein the objective optical element converges a light flux from the first light source onto an information recording plane of a first optical information recording medium through a protective substrate having a thickness t 1  so that recording and/or reproducing information is conducted for the first optical information recording medium and the objective optical element converges a light flux from the second light source onto an information recording plane of a second optical information recording medium through a protective substrate having a thickness t 2 (t 1 ≦t 2 ) so that recording and/or reproducing information is conducted for the second optical information recording medium,   wherein the objective optical element comprises on at least one surface:   a common region through which the light flux having the first wavelength λ 1  and the light flux having the second wavelength λ 2  pass in common so as to form a converged light spot on the information recording plane of the first optical information recording medium and on the information recording plane of the second optical information recording medium, respectively; and   an exclusive region through which the light flux having the first wavelength λ 1  passes so as to form a converged light spot on the information recording plane of the first optical information recording medium and the light flux having the second wavelength λ 2  passes so as not to form a converged light spot on the information recording plane of the second optical information recording medium,   wherein the exclusive region comprises an exclusive diffractive structure having a function to suppress an increase of spherical aberration due to a raise of atmospheric temperature when the light flux having the first wavelength λ 1  having passed through the exclusive diffractive structure is converged on the information recording plane of the first optical information recording medium,   wherein the common region comprises a common diffractive structure having a correcting function to reduce a difference between a first spherical aberration when the light flux of the first wavelength λ 1  having passed through the common diffractive structure is converged on the information recording plane of the first optical information recording medium through the protective substrate having the thickness t 1  and a second spherical aberration when the light flux of the second wavelength λ 2  passing through the common diffractive structure is converged on the information recording plane of the second optical information recording medium through the protective substrate having the thickness t 2  by the change of the diffractive function caused in accordance with a wavelength difference between the first wavelength λ 1  and the second wavelength λ 2 , and   wherein the common region does not comprise a diffractive structure having a function to suppress an increase of spherical aberration due to a raise of atmospheric temperature.   
   
   
       116 . The objective optical element of  claim 115 , wherein the exclusive diffractive structure suppresses the increase of spherical aberration which a change of refractive index of the objective optical element causes due to the raise of atmospheric temperature by utilizing a wavelength fluctuation of the light flux having the first wavelength λ 1  due to the raise of atmospheric temperature. 
   
   
       117 . The objective optical element of  claim 115 , wherein the light flux having the second wavelength λ 2  having passed through the exclusive structure intersects with the optical axis at a position different from the position of the converged light spot formed on the information recording plane of the second optical information recording medium. 
   
   
       118 . An optical pickup apparatus, comprising:
 a first light source of a wavelength λ 1 ;   a second light source of a wavelength λ 2  (λ 2 <λ 1 ); and   an objective optical element, wherein the objective optical element converges a light flux from the first light source onto an information recording plane of a first optical information recording medium through a protective substrate having a thickness t 1  so that recording and/or reproducing information is conducted for the first optical information recording medium and the objective optical element converges a light flux from the second light source onto an information recording plane of a second optical information recording medium through a protective substrate having a thickness t 2  (t 1 ≦t 2 ) so that recording and/or reproducing information is conducted for the second optical information recording medium;   wherein the objective optical element comprises on at least one surface:   a common region through which the light flux having the first wavelength λ 1  and the light flux having the second wavelength λ 2  pass in common so as to form a converged light spot on the information recording plane of the first optical information recording medium and on the information recording plane of the second optical information recording medium, respectively; and   an exclusive region through which the light flux having the first wavelength λ 1  passes so as to form a converged light spot on the information recording plane of the first optical information recording medium and the light flux having the second wavelength λ 2  passes so as not to form a converged light spot on the information recording plane of the second optical information recording medium,   wherein the exclusive region comprises an exclusive diffractive structure having a function to suppress an increase of spherical aberration due to a raise of atmospheric temperature when the light flux having the first wavelength λ 1  having passed through the exclusive diffractive structure is converged on the information recording plane of the first optical information recording medium,   wherein the common region comprises a common diffractive structure having a correcting function to reduce a difference between a first spherical aberration when the light flux of the wavelength λ 1  having passed through the common diffractive structure is converged on the information recording plane of the first optical information recording medium through the protective substrate having the thickness t 1  and a second spherical aberration when the light flux of the second wavelength λ 2  passing through the common diffractive structure is converged on the information recording plane of the second optical information recording medium through the protective substrate having the thickness t 2  by the change of the diffractive function caused in accordance with a wavelength difference between the first wavelength λ 1  and the second wavelength λ 2 , and   wherein the common region does not comprise a diffractive structure having a function to suppress an increase of spherical aberration due to a raise of atmospheric temperature.   
   
   
       119 . The optical pickup apparatus of  claim 118 , wherein the exclusive diffractive structure suppresses the increase of spherical aberration which a change of refractive index of the objective optical element causes due to the raise of atmospheric temperature by utilizing a wavelength fluctuation of the light flux having the first wavelength λ 1  due to the raise of atmospheric temperature. 
   
   
       120 . The optical pickup apparatus of  claim 119 , wherein the light flux having the second wavelength λ 2  having passed through the exclusive structure intersects with the optical axis at a position different from the position of the converged light spot formed on the information recording plane of the second optical information recording medium.