Optical pickup compatible with a digital versatile disk and a recordable compact disk using a holographic ring lens

Abstract

An optical pickup apparatus compatible with at least two types of optical recording media, using light beams having respective different wavelengths for recording and reading information, the optical pickup apparatus including two laser light sources to emit light beams having the different wavelengths, a holographic lens including a holographic ring to transmit the light beams incident in an inner region of the holographic ring, and to diffract a specific light beam among the light beams emitted from the laser light sources incident in an outer region relative to the inner region, an objective lens to focus the light beams passed through the holographic ring lens on the respective information recording surfaces of the two types of the optical recording media, optical elements to alter optical paths of the light beams reflected from the information recording surfaces of the optical recording media to corresponding photodetectors.

1. An objective lens to form beam spots using light beams of respectively different wavelengths, the objective lens comprising:
 an inner region including an optical center of the objective lens; 
 a holographic region surrounding said inner region and comprising a plurality of steps disposed on a lens surface of the objective lens; and 
 an outer region surrounding said holographic region, 
 wherein
 said inner region transmits the light beams, 
 said holographic region diffracts a second one of the light beams, and 
 the outer region transmits a first one of the light beams. 
 
 
     
     
       2. The objective lens according to  claim 1 , wherein a first focal plane on which a first portion of the second light beam incident on said holographic region is focused coincides with a second focal plane on which a second portion of the second light beam incident on said inner region is focused. 
     
     
       3. The objective lens according to  claim 1 , wherein said holographic region further comprises grooves to diffract the second light beam. 
     
     
       4. An objective lens for an optical pickup, the objective lens comprising:
 a holographic region having a plurality of concentric ring-shaped steps formed on a lens surface of the objective lens, 
 wherein the objective lens has a wavelength dependence such that two light beams having corresponding different wavelengths and an identical diffractive order form appropriate different wavefronts corresponding to reproducing and/or recording information from and/or to corresponding two kinds of optical recording media having respectively different thickness. 
 
     
     
       5. The objective lens according to  claim 4 , further comprising an inner region surrounded by said holographic region, wherein a first focal plane on which a first portion of the second light beam incident on said holographic region is focused coincides with a second focal plane on which a second portion of the second light beam incident on said inner region is focused. 
     
     
       6. The objective lens according to  claim 4 , wherein said holographic region includes grooves to diffract the light beam. 
     
     
       7. An objective lens to form beam spots of different sizes using corresponding first and second light beams of respectively different wavelengths, the objective lens comprising:
 an inner region including an optical center of the objective lens which has an optical property optimized to focus the first light beam onto a first optical recording medium of a first thicknesses and to focus the second light beam onto a second optical recording medium of a second thickness other than the first thickness; and 
 a diffractive region surrounding said inner region and comprising an optical property optimized so as to selectively diffract the first and second light beams as a function of wavelength so as to change a numerical aperture of the objective lens. 
 
     
     
       8. The objective lens of  claim 7 , wherein, to adjust the numerical aperture as the function of the wavelength, the diffractive region:
 selectively diffracts the first light beam having a first wavelength so as to not be focused on the first optical recording medium, and 
 selectively allows the second light beam of a second wavelength to be focused on the second recording medium. 
 
     
     
       9. The objective lens of  claim 8 , wherein the diffractive region selectively diffracts the first light beam as first order light. 
     
     
       10. The objective lens of  claim 9 , wherein the diffractive region comprises a blazed type hologram. 
     
     
       11. The objective lens of  claim 9 , wherein the diffractive region comprises grooves formed in stepwise depths. 
     
     
       12. The objective lens of  claim 7 , wherein the diffractive region is optimized to selectively diffract the first and second light beams so as to reduce spherical aberration of the first and second light beams when focused on the first and second optical recording media as the function of the wavelength. 
     
     
       13. The objective lens of  claim 7 , wherein the diffractive region is optimized to selectively diffract the first and second light beams such that the numerical aperture of the objective lens is greater for the second optical recording medium than for the first optical recording medium. 
     
     
       14. The objective lens of  claim 13 , wherein the diffractive region diffracts the first light beam of a first wavelength so as to not be focused on the first optical recording medium. 
     
     
       15. The objective lens of  claim 14 , wherein the diffractive region allows the second light beam of a second wavelength to be focused on the second optical recording medium. 
     
     
       16. The objective lens of  claim 15 , wherein the diffractive region is disposed on an optical surface having the inner region. 
     
     
       17. The objective lens of  claim 16 , wherein the optical surface is optimized with respect to the first and second light beams to be received prior to being reflected from the first and second optical recording media. 
     
     
       18. The objective lens according to  claim 7 , wherein a first focal plane to which a first portion of the second light beam incident on the diffractive region is directed coincides with a second focal plane to which a second portion of the second light beam incident on the inner region is directed. 
     
     
       19. The objective lens according to  claim 7 , wherein the diffractive region further comprises grooves optimized with respect to the second light beam so to maximize first order light and to minimize zero th  order light. 
     
     
       20. An objective lens for use in focusing light beams on optical recording media of different thicknesses, comprising:
 an inner region which directs the light beams having corresponding wavelengths to be focused on the corresponding optical recording media having respectively different thicknesses; and 
 a diffractive region having a wavelength dependence such that the light beams are selectively diffracted so as to adjust a numerical aperture of the objective lens. 
 
     
     
       21. The objective lens of  claim 20 , wherein the diffractive region diffracts one of the light beams having one of the wavelengths so as to reduce spherical aberration when recording and/or reproducing with respect to a corresponding one of the optical recording media. 
     
     
       22. The objective lens of  claim 21 , wherein:
 the one optical recording medium is a compact disk, and 
 the diffractive portion diffracts the one light beam as first order light so as to reduce the spherical aberration with respect to the compact disk. 
 
     
     
       23. The objective lens of  claim 22 , wherein:
 another optical recording medium is a digital versatile disk, and 
 the diffractive portion allows another light beam of another wavelength other than the one wavelength to be directed to the digital versatile disk so as to record and/or reproduce with respect to the digital versatile disk together with a portion of the another light beam focused by the inner region. 
 
     
     
       24. The objective lens of  claim 20 , wherein the diffractive portion diffracts one of the light beams as first order light so as to adjust the numerical aperture of the objective lens in order to record and/or reproduce with respect to a corresponding one of the optical recording media. 
     
     
       25. The objective lens of  claim 20 , wherein a first focal plane on which a first portion of one light beam incident on the diffractive region is directed coincides with a second focal plane on which a second portion of the one light beam incident on the inner region is directed. 
     
     
       26. The objective lens of  claim 20 , wherein a first focal plane on which a first portion of one light beam incident on the diffractive region is directed does not coincide with a second focal plane on which a second portion of the one light beam incident on the inner region is directed such that a spherical aberration is reduced at the second focal plane and the numerical aperture is adjusted according to the wavelength of the one light beam. 
     
     
       27. The objective lens of  claim 26 , wherein a third focal plane on which a first portion of another light beam incident on the diffractive region is directed coincides with a fourth focal plane on which a second portion of the another light beam incident on the inner region is directed. 
     
     
       28. An optical system for use in focusing light beams on optical recording media of different thicknesses, comprising:
 an optical element; and 
 an objective lens, 
 wherein the optical element comprises:
 an inner region which directs the light beams having corresponding wavelengths to be focused by the objective lens on the corresponding optical recording media having respectively different thicknesses; and 
 a diffractive region having a wavelength dependence such that the light beams are selectively diffracted so as to adjust a numerical aperture of the objective lens. 
 
 
     
     
       29. The optical system of  claim 28 , wherein the diffractive region diffracts one of the light beams having one of the wavelengths so as to reduce spherical aberration when recording and/or reproducing with respect to a corresponding one of the optical recording media. 
     
     
       30. The optical system of  claim 29 , wherein:
 the one optical recording medium is a compact disk, and 
 the diffractive portion diffracts the one light beam as first order light so as to reduce the spherical aberration with respect to the compact disk. 
 
     
     
       31. The optical system of  claim 30 , wherein:
 another optical recording medium is a digital versatile disk, and 
 the diffractive portion allows another light beam of another wavelength other than the one wavelength to be directed through the objective lens to the digital versatile disk so as to record and/or reproduce with respect to the digital versatile disk together with a portion of the another light beam which passed through the inner region and the objective lens. 
 
     
     
       32. The optical system of  claim 28 , wherein the diffractive portion diffracts one of the light beams as first order light so as to adjust the numerical aperture of the objective lens in order to record and/or reproduce with respect to a corresponding one of the optical recording media. 
     
     
       33. The optical system of  claim 28 , wherein a first focal plane on which a first portion of one light beam incident on the diffractive region is directed by the objective lens coincides with a second focal plane on which a second portion of the one light beam incident on the inner region is directed by the objective lens. 
     
     
       34. The optical system of  claim 28 , wherein a first focal plane on which a first portion of one light beam incident on the diffractive region is directed by the objective lens does not coincide with a second focal plane on which a second portion of the one light beam incident on the inner region is directed by the objective lens such that a spherical aberration is reduced at the second focal plane and the numerical aperture is adjusted according to the wavelength of the one light beam. 
     
     
       35. The optical system of  claim 34 , wherein a third focal plane on which a first portion of another light beam incident on the diffractive region is directed by the objective lens coincides with a fourth focal plane on which a second portion of the another light beam incident on the inner region is directed by the objective lens. 
     
     
       36. An objective lens for an optical pickup, the objective lens comprising at least one holographic region so as to selectively transmit data with respect to disks of different thicknesses using light beams, wherein the at least one holographic region comprises a plurality of gratings on the objective lens, at least one part of the at least one holographic region transmits the light beams for use in transmitting the data with respect to the disks of different thicknesses, and at least one other part of the at least one holographic region diffracts one of the light beams so as to adjust a numerical aperture of the objective lens for use in transmitting the data with respect to the disks of different thicknesses. 
     
     
       37. An optical pickup for use with recording media, comprising:
 a light source to emit light beams of different wavelengths; 
 an objective lens comprising at least one holographic region, the at least one holographic region comprising a plurality of gratings on the objective lens; and 
 an optical detector to detect the light beams after reflection from the recording media and after having passed through the objective lens, 
 wherein:
 at least one part of the at least one holographic region transmits the light beams, and 
 at least one other part of the at least one holographic region diffracts one of the light beams. 
 
 
     
     
       38. An objective lens for an optical pickup for selectively diffracting at least one of plurality of light beams, the lens comprising
 a first surface which focuses the plurality of light beams; and   a second surface adjacent to the first surface and having a diffractive pattern to diffract at least one of the plurality of light beams, wherein the diffractive pattern comprises a holographic pattern.   
     
     
       39. The objective lens of claim 38, wherein:
 the first surface includes an inner portion of the lens, and   the second surface is on a periphery of the first surface.   
     
     
       40. The objective lens of claim 38, wherein the first surface does not include the diffractive pattern. 
     
     
       41. The objective lens of claim 38, wherein the diffractive pattern is configured to selectively diffract one of the plurality of light beams. 
     
     
       42. An objective lens for an optical pickup for selectively diffracting at least one of plurality of light beams, the lens comprising
 a first surface which focuses the plurality of light beams; and   a second surface adjacent to the first surface and having a diffractive pattern at a location where a numerical aperture of the objective lens is higher than a predetermined numerical aperture value so as to diffract at least one of the plurality of light beams.   
     
     
       43. The objective lens of claim 42, wherein the predetermined numerical aperture value is 0.3. 
     
     
       44. The objective lens of claim 42, wherein the first surface does not include the diffractive pattern. 
     
     
       45. The objective lens of claim 42, wherein the diffractive pattern is configured to selectively diffract one of the plurality of light beams. 
     
     
       46. The objective lens of claim 42, wherein the diffractive pattern comprises a holographic pattern. 
     
     
       47. An objective lens for an optical pickup for correcting a spherical aberration caused by one of plurality of light beams, the lens comprising
 a first surface which focuses the plurality of light beams; and   a second surface adjacent to the first surface and having a diffractive pattern which diffracts the plurality of light beams and which is disposed to correct the spherical aberration of at least one of the plurality of the one light beams, wherein the diffractive pattern comprises a holographic pattern.   
     
     
       48. The objective lens of claim 47, wherein the first surface does not include the diffractive pattern. 
     
     
       49. The objective lens of claim 47, wherein the diffractive pattern is configured to selectively diffract one of the plurality of light beams. 
     
     
       50. An objective lens for an optical pickup for correcting a spherical aberration caused by one of plurality of light beams, the lens comprising
 a first surface which focuses the plurality of light beams and has a curved surface curving from an apex; and   a spherical aberration correction pattern formed below the apex so as to correct the spherical aberration of the one light beam.   
     
     
       51. The objective lens of claim 50, further comprising a second surface on a periphery of the first surface and having the spherical aberration correction pattern. 
     
     
       52. The objective lens of claim 50, wherein the first surface does not include the spherical aberration correction pattern. 
     
     
       53. The objective lens of claim 50, wherein the spherical aberration correction pattern is configured to selectively diffract one of the plurality of light beams. 
     
     
       54. The objective lens of claim 50, wherein the spherical aberration correction pattern comprises a holographic pattern. 
     
     
       55. A method of selectively focusing first and second light beams of respectively different wavelengths using an objective lens to form corresponding beam spots of different sizes, the method comprising:
 receiving an emitted one of the first and second light beams at an inner region of the objective lens, the inner region including an optical center of the objective lens which has an optical property optimized to focus the first light beam onto a first optical recording medium of a first thicknesses and to focus the second light beam onto a second optical recording medium of a second thickness other than the first thickness; and   receiving the emitted one of the first and second light beams at a diffractive region surrounding said inner region, the diffractive region comprising an optical property optimized so as to diffract at least one of the first and second light beams as a function of wavelength so as to correct for spherical aberrations on the first and second optical recording media, wherein the diffractive region comprises a holographic pattern.   
     
     
       56. The method of claim 55, wherein the inner region does not include a diffractive region. 
     
     
       57. The method of claim 55, wherein the diffractive pattern is configured to selectively diffract the first and second light beams. 
     
     
       58. A method of selectively focusing light beams on optical recording media of different thicknesses using an objective lens, the method comprising:
 receiving an emitted one of the light beams at an inner region of the objective lens, the inner region having an optical property which directs the light beams having corresponding wavelengths to be focused on the corresponding optical recording media having respectively different thicknesses; and   receiving the emitted one of the light beams at a diffractive region, the diffractive region having a wavelength dependence such that the light beams are diffracted so as to correct for spherical aberrations due to the different thicknesses of the optical recording media, wherein the diffractive region comprises a holographic pattern.   
     
     
       59. The method of claim 58, wherein the inner region does not include the diffractive region. 
     
     
       60. The method of claim 58, wherein the diffractive pattern is configured to selectively diffract the light beams. 
     
     
       61. A method of manufacturing an objective lens, the method comprising forming a diffractive pattern on a portion of a surface of the objective lens without forming the diffractive pattern on another portion of the surface such that the another portion focuses a plurality of light beams, and the formed diffractive pattern has an optical property to selectively diffract one of the plurality of light beams, wherein the forming comprises etching a hologram having grooves on the surface as the diffractive surface. 
     
     
       62. A method of manufacturing an objective lens, the method comprising forming a diffractive pattern on a portion of a surface of the objective lens without forming the diffractive pattern on another portion of the surface such that the another portion focuses a plurality of light beams, and the formed diffractive pattern has an optical property to selectively diffract one of the plurality of light beams, wherein the forming comprises molding a hologram having grooves on the surface as the diffractive surface.