Optical pick-up apparatus

1. An optical pick-up apparatus comprising:

an optical modular device having first and second light sources for emitting light beams of different power levels;

a photo-refractive crystal device disposed on the optical path between said optical modular device and a recording medium for coupling the powers of the light beams emitted from said two light sources; and

an objective lens disposed on the optical path between said photo-refractive crystal device and said recording medium for focusing the light beams emitted from said light sources on said recording medium.

2. The optical pick-up apparatus as claimed in claim 1 , wherein said optical modular device comprises:

a substrate;

a mount fixed on said substrate;

said first and second light sources installed on opposing sides of said mount, each emitting a light beam of a predetermined power level;

a photo-detector installed on said mount for receiving a light beam which is reflected from said recording medium;

a housing having an opening in the upper portion thereof; and

an optical path changing unit installed at said opening of the housing for changing the path of an incident light beam.

3. The optical pick-up apparatus as claimed in claim 2 , wherein said optical modular device further comprises first and second photo-detectors, which are installed on the upper surface of said substrate to detect radiant powers of light beams emitted from said first and second light sources, respectively.

4. The optical pick-up apparatus as claimed in claim 2 , wherein said optical path changing unit comprises:

first hologram elements provided with first and second patterns which diffract and transmit incident light beams from said first and second light sources, respectively; and

second hologram elements installed adjacent said first hologram elements and provided with third and fourth patterns which diffract and transmit incident light beams from said objective lens onto said photo-detector.

5. The optical pick-up apparatus as claimed in claim 2 , further comprising a converging lens which is disposed between the optical path changing means and the photo-refractive crystal device and converges incident light beams.

6. The optical pick-up apparatus as claimed in claim 1 , wherein the photo-refractive crystal device is formed of a material selected from the group consisting of BaTiO 3 , Bi 12 SiO 20 , LiNbO 3 , KNbO 3 , GaAs and SBN.

7. The optical pick-up apparatus as claimed in claim 1 , wherein the power level of the light beam emitted by the first light source is 10 mW.

8. The optical pick-up apparatus as claimed in claim 1 , wherein the power level of the light beam emitted by the first light source is 20 mW.

9. The optical pick-up apparatus as claimed in claim 1 , wherein the power level of the light beam emitted by the second light source is 5 mW.

10. An optical pick-up apparatus comprising:

an optical modular device having at least two light sources for emitting light beams of different power levels;

a photo-refractive crystal device disposed on the optical path between said optical modular device and a recording medium for coupling the powers of the light beams emitted from said two light sources; and

an objective lens disposed on the optical path between said photo-refractive crystal device and said recording medium for focusing the light beams emitted from said light sources on said recording medium.

11. An optical module comprising:

first and second light sources for emitting light beams of different optical characteristics;

an optical path changing unit for changing through diffraction the path of incident light beams whereby a light beam impinging on said optical path changing unit on substantially a same optical path as a light beam from said optical path changing unit is separated from said light beam from said optical path changing unit within said optical module; and

a photo - detector which detects said light incident on, and subsequently separated by, said optical path changing unit.

12. The optical module as claimed in claim 11 , wherein said optical path changing unit comprises:

a hologram element which diffracts and transmits incident light beams from outside optical module unit.

13. The optical module as claimed in claim 11 , wherein said optical path changing unit comprises:

first hologram elements provided with first and second patterns which diffract and transmit incident light beams from said first and second light sources, respectively; and

second hologram elements installed adjacent said first hologram elements and provided with third and fourth patterns which diffract and transmit incident light beams from said objective lens onto said photo - detector.

14. The optical module as claimed in claim 11 , further comprising:

a substrate;

said first and second light sources located on said substrate;

a photo - detector installed on said substrate for receiving a light beam which is received from said optical path changing unit; and

a housing.

15. An optical pick- up apparatus comprising:

first and second light sources for emitting light beams of different optical characteristics;

an optical path changing unit for changing through diffraction the path of incident light beams whereby a light beam impinging on said optical path changing unit on substantially a same optical path as a light beam from said optical path changing unit is separated from said light beam from said optical path changing unit within said optical module;

an objective lens disposed in the optical path between said optical path changing unit and the designed location of a recording medium for focusing the light beams emitted from said light sources on said recording medium; and

a photo - detector which detects light reflected from said recording medium.

16. The optical pick- up apparatus as claimed in claim 15 , wherein said optical path changing unit comprises:

a hologram element which diffracts and transmits incident light beams from said objective lens onto said photo - detector.

17. The optical pick- up apparatus as claimed in claim 15 , wherein said optical path changing unit comprises:

first hologram elements provided with first and second patterns which diffract and transmit incident light beams from said first and second light sources, respectively; and

second hologram elements installed adjacent said first hologram elements and provided with third and fourth patterns which diffract and transmit incident light beams from said objective lens onto said photo - detector.

18. The optical pick- up apparatus as claimed in claim 15 , further comprising:

a substrate;

said first and second light sources located on said substrate;

a photo - detector installed on said substrate for receiving a light beam which is reflected from said recording medium; and

a housing.