Light emitting device, optical pickup apparatus and method for manufacturing the same

Abstract

In the present invention, to improve CD read/write characteristics having poor image height characteristics, a third light emitting source emitting a third laser beam for CD is disposed on an optical axis of an objective lens. Thereby, the third laser beam emitted from the third light emitting source travels along the optical axis of the objective lens, thus generating no coma aberration in the third laser beam. Furthermore, in the present invention, a second light emitting source emitting a second laser beam for DVD and a first light emitting source emitting a first laser beam for BD are disposed across the third light emitting source. Thereby the phase propagation directions of coma aberrations in the first and second laser beams coincide with each other. Adjustment of the coma aberration in one of the laser beams enables the coma aberration in the other laser beam to be adjusted.

1 . A light emitting device emitting a plurality of laser beams used for reading or writing on optical recording media through an objective lens, the light emitting device comprising:
 a first light emitting source configured to emit a first laser beam;   a second light emitting source configured to emit a second laser beam having a wavelength longer than that of the first laser beam; and   a third light emitting source configured to emit a third laser beam having a wavelength longer than those of the first and second laser beams, wherein   the third light emitting source is disposed closest to an optical axis of the objective lens, the first light emitting source is disposed at one side of the third light emitting source, and the second light emitting source is disposed at the other side of the third light emitting source.   
     
     
         2 . The light emitting device according to  claim 1 , wherein
 the first light emitting source is included in a first light emitting chip,   the second and third light emitting sources are included in a second light emitting chip different from the first light emitting chip, and   the first and second light emitting chips are mounted on the same mounting plane so that the first light emitting chip comes close to the third light emitting source in the second light emitting chip.   
     
     
         3 . The light emitting device according to  claim 2 , wherein
 the first light emitting source and the second light emitting source are arranged symmetrically about the third light emitting source.   
     
     
         4 . The light emitting device according to  claim 1 , wherein
 the first laser beam is in a blue-violet wavelength range of 400 to 420 nm,   the second laser beam is in a red wavelength range of 645 to 675 nm, and   the third laser beam is in an infrared wavelength range of 765 to 805 nm.   
     
     
         5 . An optical pickup apparatus applying a laser beam to an optical recording medium and detecting the laser beam reflected by the optical recording medium, comprising:
 a light emitting device according to any one of  claims 1  to  4 ;   a first light receiver configured to receive the first laser beam reflected by one of the optical recording media; and   a second light receiver configured to receive the second laser beam and the third laser beam each reflected by one of the optical recording media.   
     
     
         6 . The optical pickup apparatus according to  claim 5 , further comprising:
 a three-wavelength compatible objective lens compatible with all the wavelengths of the first to third laser beams and having such a characteristic that a phase direction of coma aberration generated in the second laser beam and a phase direction of coma aberration generated in the third laser beam are opposite to each other.   
     
     
         7 . A method for manufacturing an optical pickup apparatus, comprising:
 a first step of positioning a light emitting unit including a first light emitting chip emitting a first laser beam and a second light emitting chip emitting a second laser beam and a third laser beam which are different in wavelength from the first laser beam;   a second step of preparing a first light receiver having a first light receiving region and a second light receiving region, and positioning the first light receiver so that the second laser beam is applied to the center of the first light receiving region and the third laser beam is applied to the center of the second light receiving region; and   a third step of preparing a second light receiver having a third light receiving region separately from the first light receiver, and positioning the second light receiver so that the first laser beam is applied to the center of the third light receiving region.   
     
     
         8 . The method for manufacturing an optical pickup apparatus, according to  claim 7 , wherein
 the second step includes the steps of:   emitting the second laser beam from the light emitting unit, determining a position of the first light receiver in the travelling direction of the second laser beam so that a spot shape of the second laser beam becomes circular, and determining a position of the first light receiver in a direction orthogonal to the travelling direction of the second laser beam so that the second laser beam is applied to the center of the first light receiving region; and   emitting the third laser beam from the light emitting unit and positioning the first light receiver by rotating the first light receiver around the center of the first light receiving region so that the third laser beam is applied to the center of the second light receiving region.   
     
     
         9 . The method for manufacturing an optical pickup apparatus, according to  claim 8 , wherein
 the third step includes   emitting the first laser beam from the light emitting unit, determining a position of the second light receiver in the travelling direction of the first laser beam so that a spot shape of the first laser beam becomes circular, and determining a position of the second light receiver in a direction orthogonal to the travelling direction of the first laser beam so that the first laser beam is applied to the center of the third light receiving region.