KR100421498B1 - Optical pickup device for different kinds of optical disks - Google Patents

Abstract

PURPOSE: An optical pickup device for different kinds of optical disks is provided to change a path of an optical beam according to a kind of an optical disk, and to use objective lenses having different apertures, to irradiate the optical beam on information recording surfaces of different kinds of optical disks, thereby exactly accessing the optical disks. CONSTITUTION: A light source(12) generates an optical beam to be irradiated on the first and second information recording surfaces(10A,10B) of optical disks(10). The first objective lens(14A) having the first predetermined apertures focuses the optical beam to be irradiated on the first information recording surface(10A). The second objective lens(14B) having the second predetermined apertures focuses the optical beam to be irradiated on the second information recording surface(10B). An optical detector(16) converts the optical beam into an electrical signal. An LCD unit(18) selectively changes polarized properties of the optical beam. An adaptive beam splitter(20) transmits the optical beam to one of the objective lenses(14A,14B), and transmits the optical beam to the optical detector(16).

Description

Optical pickup device for different optical discs

The present invention relates to an optical pickup apparatus for optically accessing an optical disc, and more particularly, to an optical pickup apparatus for heterogeneous optical discs for accessing different types of optical discs.

Recently, optical discs have been referred to as Digital Video Disks ("DVDs") having a larger recording capacity than conventional Compact Disks ("CDs") due to continuous development efforts to increase recording capacity. Has been developed. A DVD has a higher recording density (i.e. track density) than a CD and a shorter distance from the surface of the disc to the information recording surface. In fact, DVD has a distance of 0.6 mm from the surface of the disc to the information recording surface, while CD is 1.2 mm. Because of this, it is difficult for an optical pickup device for DVD to record / reproduce information on a CD, which is spherical aberration caused by a change in the distance between the surface and the information recording surface of the optical disc, and coma aberration and decoupling due to tilting of the optical disc. This is caused by astigmatism or the like caused by focus.

Spherical aberration causes the intensity of the main lobe of the light beam by the information recording medium area to be relatively large compared to the intensity of the side lobe by the area other than the information recording medium, thereby causing interference between information tracks. Coma aberration and astigmatism differential destabilize the optical system and degrade optical characteristics. These spherical aberrations (SA), coma (CA) and astigmatism (DA)

SA = (Δd / 8) · ((n ² -1) / n ³ ) NA ⁴ ----------------- (Equation 1)

CA = (Δd / 2) · ((n ² -1) SinθCosθ / (n ² -Sin ² θ) ^5/2 ) NA ³ --- (Equation 2)

DA = (l / 4√3), NA ² , NA ² , △ Z ------------------ (Equation 3)

Where Δd is the change in distance between the surface and the information recording surface on the optical disc, n is the refractive index, NA is the numerical aperture of the objective lens, ΔZ is the amount of defocus, and θ is the tilt of the optical disc.

In the above formula (1), it is assumed that the refractive index n of the optical disk is 1.54, the wavelength λ of a wide range is 0.65 탆, the aperture ratio of the objective lens is 0.6, and the distance between the surface of the optical disk and the information recording surface is 0.6 mm. . In this case, spherical aberration difference between the surface of the CD and the DVD and the information recording surface when spherical aberration-based optical pickup device plays a CD whose surface and information recording surface is 1.2 mm while maintaining the aperture ratio of the objective lens as it is. The average wavefront aberration is 0.43 lambda by 0.6 mm.

On the other hand, when the aperture ratio of the objective lens is changed to 0.35, the spherical aberration becomes 0.048 lambda, which is an average value of wavefront aberration, and the astigmatism caused by defocus is corrected so that it does not exist at 31.67 lambda. It is below the standard (Marechal's Criteron).

In addition, in the above formula (2), the tilt amount of the optical disk also has a tolerance of 2 times or more than that of the conventional CD due to the change of the aperture ratio, thereby stabilizing the optical system. However, the increase in the aperture ratio results in an increase in spherical aberration, and conversely, a decrease in the aperture ratio causes a beam spot to be irradiated to the optical disk to be large. As a result, a change in the aperture ratio of the objective lens results in a change in the signal-to-noise ratio (S / N). Therefore, the aperture ratio of the objective lens is in the range of 0.25 to 0.38.

According to the above theory, the optical pickup apparatus can access both CD and DVD when the diameter of the light beam from the light source is adjusted by using objective lenses having different numerical apertures.

Accordingly, an object of the present invention is to provide an optical pickup apparatus for heterogeneous optical disks capable of accurately accessing all kinds of optical disks of different types.

In order to achieve the above object, there is provided a fan pickup apparatus for a heterogeneous optical disk according to the present invention, a light source for generating a fan beam to be irradiated to the optical disk, a first objective lens having a first predetermined numerical aperture for converging the light beam to be irradiated to the fan disk; A second objective lens having a second predetermined numerical aperture for connecting the light beam to be irradiated to the optical disc, optical detection means for converting the light beam reflected by the optical disc into an electrical signal, and the light beam from the light source according to the type of the optical disc; And optical path separation means for transmitting to either one of the second objective lenses and for transmitting the light beam from the optical disc via the first and second objective lenses toward the light detecting means.

Other objects and advantages of the present invention in addition to the above objects will become apparent from the following description of the preferred embodiments with reference to the accompanying drawings.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying FIG. 1.

Referring to FIG. 1, a light source 12 for generating a light beam to be irradiated onto the optical disc 10 and a pop beam from the light source 12 are directed to the first or second information recording surfaces 10A and 10B of the optical disc 10. Referring to FIG. An optical pickup apparatus for a heterogeneous optical disc according to an embodiment of the present invention, which includes a focusing unit 14 for focusing and a photodetector 16 for converting a light beam reflected by the optical disc 10 into an electrical signal, is shown. have. The first information recording surface 10A of the optical disk 10 is an information recording surface of a DVD and the second information recording surface 10B of the optical disk 10 is an information recording surface of a CD or CD-R. The first information recording surface 10A is located at a depth thinner from the surface of the optical disc 10 than the second information recording surface 10B. The light source 12 may be a vertical sunfun beam of polarization characteristics flowing in a uniaxial direction with respect to an ellipse (that is, a TE wave called "S wave") or a horizontal linearly polarized beam of polarization characteristics with a long axis direction with respect to an ellipse. , A so-called TM wave). In the present invention, the light beam generated by the light source 12 is referred to as "vertical linearly polarized beam" for convenience. In addition, the focusing unit 14 focuses the light beam in the form of a spot on the first information recording surface 10A or the second information recording surface 10B in accordance with an optical path traveling from the light source 12 toward the optical disk 10. For this purpose, the focusing unit 14 includes first and second objective lenses 14A and 14B located side by side with respect to the radial direction of the optical disc 10. The first objective lens 14A is formed to have a relatively large numerical aperture of about 0.6 so as to connect the fang beam from the light source 12 in the form of a spot on the first information recording surface 10A of the optical disc 10. On the other hand, the second objective lens 14B is formed to have a relatively small numerical aperture of " 0.25 to 0.35 " to focus the light beam from the light source 12 in the form of a spot on the second information recording surface 10B. The first objective lens 14A is installed to be in line with the light source 12 and the optical disk 10, while the second objective lens 14B is positioned next to the first objective lens 14A. In addition, the first and second objective lenses 14A and 14B are integrally formed. Next, the electrical signal output from the photodetector 16 carries information recorded on the first or second information recording surfaces 10A and 10B of the optical disc 10.

The optical pickup device for heterogeneous optical discs includes a spectrometer 20 located between the light source 12, the focusing unit 14, and the photodetector 16, and a liquid crystal unit 18 located between the light source 12 and the spectrometer 20. ) And a λ / 4 plate 22 located between the spectroscope 20 and the focusing unit 14. The liquid crystal unit 18 is installed so as to be in line with the first objective lens 14A of the focusing unit 14 so that the spectrometer 20 is separated from the light source 12 in accordance with the disc mode signal CB / DVD from the control line 11. Selectively change the fungal light characteristic of the light beam traveling toward That is, the liquid crystal unit 18 spectrographs a vertical linear polarization range (S wave) from the light source 12 when a high logic disk mode signal (CD / DVD) indicating that the optical disk 10 to be accessed is DVD is input. Pass it straight toward (20). When a low logic disk mode signal (CD / DVD) indicating that the optical disk 10 to be accessed currently is a CD or CD-R is input, the liquid crystal unit 18 generates a vertical linearly polarized beam (S wave) from the light source 12. Is converted into a horizontal linear light beam (P wave). On the contrary, when the horizontally polarized beam P-wave is generated from the light source 12 on the liquid crystal unit 18, the horizontal linearly polarized beam P-wave is selectively selected according to the logic value of the disc mode signal CD / DVD. It can also be converted to a vertical linearly polarized beam (S wave).

In addition, the spectroscope 20 transmits the light beam toward the first objective lens 14A or the second objective lens 14B of the focusing unit 14 according to the polarization characteristic of the light beam from the liquid crystal unit 18 and at the same time as the first objective lens 14B. Alternatively, the light beams from the second objective lenses 14A and 14B are transmitted to the photodetector 16. To this end, the spectroscope 20 is installed in a straight line with the liquid crystal unit 18 and the first objective lens 14A, and is perpendicular to the photodetector 16 and the liquid crystal unit 18 or the first objective lens 4A. 20 A of 1st reflective surfaces, and the 2nd reflective surface 20B provided so that the 2nd objective lens 14B and the 1st reflective surface 20A may be perpendicular | vertical. The first reflective surface 20A passes the vertical linearly polarized beam S wave from the liquid crystal unit 18 directly toward the first objective lens 14A, while the horizontal linear polarized beam P wave from the liquid crystal unit 18 is passed. Is reflected toward the second reflecting surface 20B. In addition, the first reflective surface 20A passes the vertical linearly polarized beam S wave from the second reflective surface 20B to the photodetector 16 as it is, and the horizontal linearly polarized beam P from the λ / 4 plate 22. Waves) toward the photodetector 16. To this end, the first reflective surface 20A is formed of a PBS coating film. On the other hand, the second reflecting surface 20B reflects the horizontal linearly polarized light beam (P wave) from the first reflecting surface 20A toward the second objective lens 14B and λ / 4 from the second objective lens 14B. The vertical linearly polarized beam S wave via the plate 22 is reflected to travel to the photodetector group 16 via the first reflective surface 20A. To this end, the second reflecting surface 20B is formed of a total reflection material film. As a result, the first reflecting surface 20A selectively transmits or reflects the light beam according to the polarization characteristic, and the second reflecting surface 20B reflects the light beam irrespective of the polarization characteristic.

Further, the λ / 4 plate 22 has a vertical linearly polarized beam (S wave) traveling from the first reflective surface 20A toward the first objective lens 14A, and the second objective lens from the second reflective surface 20B. A horizontal linearly polarized beam (P wave) traveling toward 14B) is converted into a circularly polarized beam. In detail, the λ / 4 plate 22 converts the vertical linearly polarized beam S wave from the first reflective surface 20A into a left-rotating circularly polarized beam and the horizontal linearly polarized beam P wave from the second reflective surface 20B. ) Is converted into a right-handed circularly polarized beam, respectively. The left rotating circularly polarized beam via the first objective lens 14A is turned into a right rotating circularly polarized beam when reflected by the first information recording surface 10A of the optical disk 10. Similarly, the right rotating circularly polarized beam via the second objective lens 14B is turned into a left rotating circularly polarized beam when reflected by the first information recording surface 10B of the optical disc 10. Further, [lambda] / 4 plate 22 has a right rotating circularly polarized beam from the first objective lens 14A as a horizontal linearly polarized beam (P wave) and a left rotating circularly polarized beam from the second objective lens 14B. Convert to (S wave). In contrast, the λ / 4 plate 22 converts the vertical linearly polarized beam S wave from the first reflecting surface 20A into the right rotating circularly polarized beam and the horizontal linearly polarized beam P wave from the second reflecting surface 20B. To the left rotating circularly polarized beam, the left rotating circularly polarized beam from the first objective lens 14A to the crystal linearly polarized beam (P wave), and the right to rotating circularly polarized beam from the second objective lens 14B, to the vertical linearly polarized beam S Par). This can be achieved by changing the optical axis of the λ / 4 plate 22. As a result, when the vertical linearly polarized beam is output from the liquid crystal unit 18, the light beam is focused on the first information recording surface 10A of the optical disc 10 by the first objective lens 14A so that the DVD can be accessed accurately. . When the vertical linearly polarized beam is output from the liquid crystal unit 18, the light beam is focused on the second information recording surface 10B of the optical disc 10 by the second objective lens 14B so that the CD and the CD-R are correctly accessed. do.

Finally, the optical pickup device for heterogeneous optical discs includes a collimator 24 positioned between the liquid crystal unit 18 and the spectrometer 20, and a sensor lens positioned between the photodetector 16 and the spectrometer 20. , 26). The collimating lens 24 causes the divergent light beam from the liquid crystal unit 18 to travel in parallel to the first reflecting surface 20A of the spectrometer 20. The sensor lens 26 focuses the light beam incident in parallel from the first reflecting surface 20A of the spectrometer 20 on the surface of the photodetector 16. In this regard, the collimating lens 24 and the sensor lens 26 prevent the leakage of the light beam to improve the light sensitivity of the optical pickup device to a certain level or more.

As described above, the optical pickup apparatus for heterogeneous optical discs according to the present invention changes the path of the optical beam according to the type of the optical disc and uses an objective lens having a numerical aperture different from each path, thereby spotting the optical beam on the information recording surfaces of the heterogeneous optical discs. Investigate in form. Accordingly, the optical pickup apparatus for heterogeneous optical discs provides an advantage of accurately accessing all kinds of different types of fan discs (ie, CD, CD-R and DVD).

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

1 is a diagram schematically showing the structure of an optical pickup apparatus for heterogeneous optical disks according to an embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

10: optical disc 10A: first information recording surface

10B: second information recording surface 12: light source

14: focusing unit 14A: first objective lens

14B: second objective lens 16: photodetector

20: spectroscope 20A: first reflective surface

20B: second reflecting surface 22: lambda / 4 plate

24: collimating lens 26: sensor lens

Claims (6)

An optical pickup apparatus for heterogeneous optical discs having a first information recording surface and a second information recording surface, A light source for generating a light beam to be irradiated to the first and second information recording surfaces of the optical disc; A first objective lens having a first predetermined numerical aperture that focuses the light beam to be irradiated from the light source to the first information recording surface of the optical disc; A second objective lens having a second predetermined numerical aperture for focusing the light beam to be irradiated onto the second information recording surface of the optical disc from the light source; Light detecting means for converting the light beam reflected by the first information recording surface or the second information recording surface of the optical disk into an electrical signal; Control polarization converting means for selectively changing the polarization characteristic of the light beam from the light source in accordance with the first information recording surface or the second information recording surface of the optical disk; The light beam from the control polarization converting means is transmitted to either one of the first objective lens and the second objective lens according to its polarization characteristic, and is reflected from the first information recording surface or the second information recording surface of the optical disc, and thus the first beam is reflected. Or an adaptive beam splitter for transmitting a light beam passing through a second objective lens toward the light detecting means. The method of claim 1, The adaptive beam splitter, A first reflection surface positioned between the first objective lens, the light detection means, and the control polarization conversion means to selectively reflect the light beam according to the polarization characteristic of the light beam; Positioned in alignment with the light detecting means and the first reflective surface to reflect the light beam reflected by the first reflective surface toward the second objective lens and the light beam from the second objective lens towards the second reflective surface And a second reflecting surface to make an optical pickup device for heterogeneous optical disks. The method of claim 2, And a λ / 4 plate positioned between the adaptive beam splitter and the first and second objective lenses to convert a light beam traveling from the adaptive beam splitter toward the first and second objective lenses into a circularly polarized beam. An optical pickup apparatus for heterogeneous optical disks, characterized in that one. The method of claim 3, wherein The light source generates a vertical linearly polarized beam, The control polarization converting means converts the vertical linearly polarized beam to be irradiated onto the first information recording surface or the second information recording surface of the optical disc into a horizontal linearly polarized beam, The first reflecting surface passes the vertical linearly polarized beam and reflects the horizontal linearly polarized beam, The λ / 4 plate is characterized in that the vertical linearly polarized beam is a right rotating circularly polarized beam, the horizontal linearly polarized beam is a left rotating circularly polarized beam, the leftly rotating circularly polarized beam is the vertical linearly polarized beam, and the rightly rotating circularly polarized beam is the horizontal linearly polarized beam. An optical pickup apparatus for heterogeneous optical disks, characterized in that it is changed to a beam. The method according to any one of claims 2 to 4, And said first reflecting surface is formed by a PBS coating film. The method of claim 1, A sensor lens positioned between the light path separating means and the light detecting means to condense a light beam to be incident from the light path separating means toward the light detecting means; And a collimating lens positioned between said light source and said optical path separating means to parallel a light beam traveling from said fang source to said optical path separating means.