MXPA97006594A - An optical capture using an opt phase plate - Google Patents

Abstract

The present invention relates to an optical pickup apparatus having compatibility with a recordable compact disc (CD-R) and a digital video disc (DVD) using one of a first light and a second light according to a recording medium for be used In the optical pickup apparatus, the laser light sources emit a first light having a relatively short length for the DVD and a second light having a long wavelength for the CD-R, respectively. An objective lens has a predetermined focal length according to the position of an information recording surface on the DVD. An optical path control unit controls the path of the light so that the light emitted from one of the laser light sources is directed to the objective lens and the light emerging from the objective lens is directed to the optical detection unit. A phase deflection unit which is located between the optical path control unit to the objective lens, thereby reducing the size of a beam impact which is formed at the position of the information recording surface in the CD

Description

AN OPTICAL CAPTURE USING AN OPTICAL PHASE PLATE BACKGROUND OF THE INVENTION The present invention relates to an optical pickup apparatus which can record and read information on and from a digital video disc (DVD) and a recordable compact disc (CD-R), respectively. The recording medium for recording and reading information such as video, audio or data arc, a disk, a card or a tape. Among them, the disk type is used mainly. Recently, in the field of optical disc apparatus, a laser disk (LD), a compact disc (CD) and a digital video disc (DVD) have been developed. Such an optical disk includes a plastic or glass medium having a certain thickness along an axial direction for which the light is incident, and a signal recording surface in which the information is recorded and located in the plastic medium. or glass. Therefore, a high density optical disc system expands a numerical aperture of an objective lens in order to increase a recording density, and uses a short wavelength light source of 635 nm or 650 nm. Accordingly, the high density optical disc system can record or read signals on or from a digital video disc, and can also read signals from a CD. However, to be compatible with a recent type of a CD, that is, a recordable CD (CD-R), light having a wavelength of 780 nm must be used. This is due to the registration feature of the CD-R registration medium. As a result, using light of wavelengths of 780 nm and 650 nm in an individual optical sensor, it becomes very important for the compatibility of the DVD and the CD-R. A conventional optical pickup to be compatible with the DVD and CD-R will be described in the following with reference to Figure 1. Figure 1 shows an optical pickup using two laser diodes as light sources for a DVD and a CD- R and an individual objective lens. Figure 1, the optical pickup uses laser light having a wavelength of 635 nm when playing a DVD and uses laser light having a wavelength of 780 nm when recording and playing a CD-R. The light having the wavelength of 635 nm emitted from a light source 1 of the laser diode passes through a collimating lens 2 and a bias beam splitter 3 and then goes to an interference filter type prism 4. The light having the wavelength of 780 nm emitted from a laser diode light source 11 passes through a collimating lens 12, a beam splitter 13 and a converging lens 14 and then goes to prism 4, which converges the light that has the wavelength of 790 nm. An optical system that has such a structure is called a "finite optical system". The prism 4 transmits light having a wavelength of 635 nm reflected from the polarization beam splitter 3, and reflects the light converged by the converging lens 14. As a result, the light from the light source 1 is incident towards a quarter-wave plate 5 in the shape of the parallel beam by the collimating lens 2, while the light from the light source 11 is incident towards a plate 5 of fourth wave in the shape of the divergent beam by the convergent lens 14- and the prism 4. The light transmitted through the quarter-wave plate 5 is incident towards a target lens 7. The objective lens 7 is designed to be focused on a signal recording surface on a DVD 8 having a thickness of 0.6 mm, by which light of 635 nm wavelength emitted from the light source 1 is focused on the signal recording surface on the DVD 8. Therefore, the light reflected from the signal recording surface of the DVD 8 contains information recorded on the signal recording surface. The reflected light is transmitted through the polarization beam splitter 3, and is then incident to a light detector 10 to detect the optical information. If the finite optical system described in the above is not used, when the 780 nm wavelength light emitted from the light source 11 is focused on the signal recording surface on the CD-R 9 which is 1.2 mm thick using the objective lens 7 described in the above, spherical aberration is generated due to the difference in thickness between the DVD 8 and the CD-R 9. In more detail, the spherical aberration is due to the fact that the distance between the signal recording surface of the CD-R 9 and the lens The target is further away than that between the signal recording surface of the DVD 8 and the objective lens 7, along an optical axis. To reduce such spherical aberration, a construction of the finite optical system including the converging lens 14 is required. Using the variable aperture 6 to be described later with reference to Figure 2, the wavelength light of 780 nm forms an optimized beam impact on the signal recording surface of the CD-R 9. The wavelength light 780 nm reflected from the CD-R 9 is reflected by the prism 4 and then the beam splitter 13, to be detected in the light detector 15. The variable aperture 6 of Figure 1 has a thin film structure as shown in Figure 2 which can selectively transmit the rays of the incident light to the region no more than the numerical aperture (NA) of 0.6 which coincides with the diameter of lens 7 objective. That is, the variable aperture 6 is divided into two regions based on the NA of 0.45 with respect to an optical axis. Between the two regions, a first region 1 transmits both wavelengths of 635 nm and 780 nm of light and a second region 2 totally transmits light of wavelength of 635 nm and fully reflects light of wavelength of 780 nm . Region 1 has the numerical aperture of 0.45 or less, and region 2 is an outer region of region 1 and is coated by a thin dielectric film. Region 1 is comprised of a thin quartz film (SIO2) in order to eliminate the optical aberration generated by region 2 of the coated dielectric thin film. Using the variable aperture 6, the 780 nm wavelength light transmitted by the region 1 having the NA of 0.45 or less forms an appropriate beam impact for the CD-R 9 on the signal recording surface thereof. In this way, Figure 1 of the optical pickup uses an optimal light impact when a disc mode is changed from DVD 8 to CD-R 9. Accordingly, Figure 1 of the optical pickup is compatible to use the CD-R. However, the optical pickup of Figure 1 as described above must form a "finite optical system" with respect to the wavelength light of 780 nm in order to eliminate the spherical aberration generated when a DVD and a CD-R. As well as, due to the thin optical film, that is to say, the dielectric thin film which is formed in the region 2 having the NA of 0.45 or more, an optical path difference is generated between the light transmitting the region 1 that has the NA of 0.45 or less and the one that transmits the region 2 that has the NA of 0.45 or more. To eradicate this difference, it is necessary to form a thin optical film in region 1. Due to this reason, the coating quartz is formed in region 1 and a thin multilayer film is formed in region 2. However, such a process The manufacturing process does not only become complicated, but also the thickness adjustment of the thin film must be carried out precisely in units of "μm". In this way, it has been difficult to mass produce the optical pickup.

BRIEF DESCRIPTION OF THE INVENTION It is an object of the present invention to provide an optical pickup apparatus which is compatible for a digital video disc and a recordable compact disc by eliminating a spherical aberration using a phase plate. To carry out the above object of the present invention, there is provided an optical pickup apparatus for at least two optical recording means, which are different in distance from an optical pickup to the information recording surfaces and uses light from different wavelengths for recording and reading information, the optical acquisition apparatus comprising: laser light sources for emitting a first light having a relatively shorter wavelength and a second light having a relatively longer wavelength, respectively; an objective lens having a predetermined focal length in which the objective lens focal point according to the first light coincides with the position of the information recording surface in the first optical recording medium having the information recording surface close to the objective lens; optical detection means; means for controlling an optical path so that the light emitted from the laser light sources is directed to the objective lens and the light exiting the objective lens is directed to the optical detection means; and the phase deflection means, coupled between the optical path control means and the objective lens, to deflect the phase of the second light coming from the optical path control means towards the objective lens, thereby reducing the size of a beam impact which is formed at the position of the information recording surface in the second optical recording medium having the information recording surface farthest from the objective lens for the second light focused by the objective lens; wherein one of the first and second light is used in accordance with the optical recording medium to be used.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments are described with reference to the drawings in which: Figure 1 is a view of a conventional optical pickup using two laser diodes as light sources for a digital video disc (DVD) and a compact disc recordable ( CD-R) and an individual objective lens; Figure 2 is a view for explaining a variable aperture shown in Figure 1; Figure 3 is a view showing an optical system of an optical pickup according to a preferred embodiment of the present invention; Figure 4 shows a phase plate unit and an annular screen objective lens shown in Figure 3; Figure 5 is a view showing an optical system of an optical pickup according to another preferred embodiment of the present invention; Figure 6 shows an annular screen objective lens having a phase plate function as shown in Figure 5; Figures 7A and 7B are views showing the combined structure of a phase plate and a variable aperture according to the present invention; Figure 8 is a graphical diagram showing the effect of reducing an impact size and a lateral lobe according to the present invention; Figure 9 is a graphical diagram showing the characteristics of a servo focus signal during the reproduction of a CD-R disc; Figure 10 is a graphical diagram showing the phase variation of the light according to the depth of the groove in the phase plate; and Figure 11 is a graphical diagram showing the variation of diffraction efficiency of diffracted light of zero order that corresponds to the groove depth of the variable aperture according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Preferred embodiments of the present invention will be described in the following in more detail with reference to the accompanying drawings. Figure 3 shows an optical system of an optical pickup according to a preferred embodiment of the present invention. With reference to Figure 3When a laser diode light source 31 operates, the 650 nm wavelength light emitting in the divergent form from the light source 31 is reflected sequentially and transmitted by a first bias beam splitter 32 and a second divider 33 of polarization beams. The light transmitted by the second divisor 33 of polarization beams is incident to a collimating lens 34. When a laser diode light source 40 operates, the 780 nm wavelength light that is emitted in the divergent form from the light source 40 is reflected by the second polarization beam splitter 33 and then, is incident to the lens 34 collimator. The collimating lens 34 collimates the incident light from the second polarization beam splitter 33 to be parallel with an optical axis perpendicular to the surface of a variable aperture, and the collimated light is selectively transmitted in wavelength through the aperture 35. variable. With reference to Figures 7A and 7B, the variable aperture has a region 3 for transmitting both wavelengths of 780 nm light and wavelengths of 650 nm light and a region 4 for transmitting only wavelength light of 650 nm. Region 4 has a hologram structure. The hologram structure includes a reticular diffraction portion whose diffraction efficiency is maximized with respect to the light of wavelength of 780 nm that has no diffraction order zero and whose diffraction efficiency is 100% with respect to the light of longitude wavelength of 650 nm that has zero-order diffraction. Therefore, light of 650 nm wavelength can be transmitted without diffraction by the hologram structure. With reference to Figure 11 showing the diffraction efficiency of the diffracted light of zero order corresponding to the depth of the groove of the reticular diffraction portion, when the depth of the groove is 3.8 μm, the wavelength light of 650 nm has the diffraction efficiency of 100% as shown in a solid line that overlaps with the "++" symbol. and the wavelength light of 780 nm has the diffraction efficiency of 0% as shown in a solid line that overlaps with a circle. Therefore, the region 4 of the variable aperture 35 is designed with the cross-section of the diffraction having the groove depth of 3.8 μm. In this mode, the NA of 0.5 is used to divide the regions 3 and 4. Therefore, the region 3 is a portion that has the NA of 0.5 or less, and the region 4 is a portion that has the NA of more of 0.5. Thus, according to the embodiment of the present invention, the light transmitting the portion having the NA of not more than 0.6 that coincides with the diameter of the objective lens 37 is selectively transmitted in regions 3 and 4 of the aperture 35 variable according to the wavelengths. The variable aperture shown in Figure 7B which is constructed with a hologram pattern of an asymmetric configuration, eradicates a feedback noise produced by light proceeding to an optical detection portion. The light that the variable aperture transmits is transmitted to a phase plate 36 to be described later with reference to Figure 4, and is then incident on an objective lens 37 with annular shield. The objective lens 37 according to the present invention is designed to be focused on an information recording surface of the DVD 8. If the phase plate 36 of the present invention is not used, the size of the light impact formed on the surface CD-R 9 information record becomes 1.8 μm or more when the disc currently in use from DVD 8 to CD-R 9 is changed. However, since the conventional size of the light impact which is used in the CD-R 9 is generally 1.4 μm, the information can not be recorded or read from the CD-R 9 by means of the light impact having the size of 1.8 μm. Thus, the present invention uses the phase plate 36 in order to reduce the size of the light impact so that the information can be recorded or read on or from the CD-R 9. The phase plate 36 is, as shown in FIG. Figure 3, positioned between the variable aperture and the objective lens 37. The phase plate 36 includes an annular groove 361 which is concave inward from the surface close to the variable aperture 35 and has a predetermined width and depth. The annular groove 361 is manufactured by injection or molding using a metal mold or engraving, in which the depth D is determined by following equations (1) and (2) below. 2 r? Vd / r -2.t d /? '-2m') .t. . . (1) tr nd /? -2; r d /? = (2m-l) 7r. . . (2) Here, m is an integer, n 'and n mean a refractive index at wavelength A' (650 nm) and A (780 nm), respectively. In the above equations (1) and (2), if m '= 3 and m = 2, the depth D of the annular groove 361 becomes approximately 3.9 μm. The phase plate 36 having the annular groove 361 of depth D deflects the phase of the wavelength light of 780 nm by 180 ° and diverts the light phase of 650 nm by 360 °, when the light proceeds to the objective lens 37 from the variable aperture. Figure 10 is a graphical diagram showing the phase variation of two wavelengths according to the depth D of the annular groove 361 in the phase plate 36, in which a solid line represents the phase variation with respect to the light of wavelength of 650 nm and a dotted line represents that with respect to the light of wavelength of 780 nm. When D is 3.9 μm, the light of wavelength of 780 nm has the phase of 180 ° and the light of 650 nm has the phase of 360 °. In this way, the wavelength light of 780 nm which is phase shifted by 180 ° has a substantially super-resolution effect and passes through an aperture compared to the case when the phase plate 36 is not used. . By the phase plate 36, the size of the light impact formed on the information recording surface on the CD-R 9 is reduced to a degree at which it can be registered or read on or from the CD-R 9, for so the spherical aberration is eliminated. The phase plate 36 can be modified into a projection shape having a predetermined width and height projection outwardly from the surface near the variable aperture. Since such modification is apparent to someone who has skill in the art and who knows the function of the phase plate, the detailed description thereof will be omitted. The objective lens 37 for which the light transmitted by the phase plate 36 is incident, includes an annular screen portion 371 as shown in Figure 4. The annular screen portion 371 shieldes part of the light transmitted by the region 3. In this way, the spherical aberration due to the exchange of the DVD 8 to the CD-R 9 is reduced, and it increases a sensitivity of a focus signal error in a servo focus system (not shown).

The light reflected from the information recording surface of the DVD 8 or CD-R 9 proceeds to the light detection lens 38 from the objective lens 37, and is focused on the light detector 39 by the light detection lens 38 . In this way, the apparatus of Figure 3 can record or read information on or from both DVD 8 and CD-R 9. Figure 6 shows an objective lens 47, which is constructed by combining a phase plate 36 and a lens 37. objective of Figure 3 in an individual unit. Figure 5 shows an optical system of an optical pickup having such objective lens 47. The objective lens 47 of Figure 6 includes an annular slot 471 which is concave inwardly from the surface close to the variable aperture 35 and has a predetermined width and depth. The objective lens 47 recorded with such an annular slot 471 deflects the phase of the wavelength light of 780 nm by 180 ° as in the phase plate 36 and diverts the phase of the wavelength light of 650 nm by 360 ° . In this way, between the 780 nm wavelength light incident to the objective lens 47 from the variable aperture 35, the light diffracted by the annular slot 471 serves to decrease the spherical aberration with respect to the CD-R 9. The slot 471 annuls eliminates the spherical aberration when the DVD 8 is exchanged with the CD-R 9. Consequently, the small-sized beam impact is formed on the information recording surface in such a way that the information can be recorded or read in or from the CD-R 9 with respect to the light of wavelength of 780 nm. The optical pickup of Figure 5 includes a single unit 49 combining a light source 491 with a light detector 493 for light of wavelength of 780 nm, in addition to a light source 31, a light detection lens 51 and a light detector 53 for light of wavelength of 650 nm. The optical pickup of Figure 5 further includes a hologram-type beam splitter 48 for the light leaving the light source 491 of the unit 49 and the incident light to the light detector 493. Since the construction and operation of the apparatus of Figure 5 is apparent to a person skilled in the art who can fully understand the apparatus of Figure 3 through the explanation described in the foregoing, the detailed description thereof will be omitted. The annular groove 471 formed in the objective lens 47 as shown in Figure 6, can be modified into a projection shape which projects outwardly from the objective lens surface 47 and has a predetermined width and depth. Figure 7 is a view showing an individual structure combining a phase plate with a variable aperture according to the present invention. With reference to Figure 7, a region of phase variation contained in the region having the NA of 0.5 or less has a ring-shaped structure. Such region of phase variation performs the same function as that of phase plate 36, the detailed description thereof will be omitted. Figure 8 is a graphical diagram showing a reduction efficiency of an impact size and a lateral lobe. In Figure 8, a curve (a) indicates when an optical pickup optimized by a DVD is used for a CD-R, in which the impact size formed on the information recording surface of the CD-R is 1.53 μm. A curve (b) indicates when an optical pickup apparatus according to the present invention is used, in which the impact size is 1.33 μm. A curve (c) indicates when a conventional optical sensor is used for a CD-R, in which the impact size is 1.41 μm. It can be observed from Figure 8 that the optical pickup apparatus according to the present invention reduces the size of the impact by approximately 8% compared to the conventional optical pickup. Also, since the size of the lateral lobe is smaller in the period of disc registration and reproduction, it can be seen that a quantity of light in the peripheral portion of the impact which is called a lateral lobe is reduced with respect to an optical sensor that It has a desirable optical characteristic. Figure 9 shows that the optical pickup apparatus according to the present invention has an excellent characteristic with respect to the focus signal servo during CD-R playback when the optical pickup apparatus detects an optical signal in the form of astigmatism , through a relatively lower graph. The embodiments described in the foregoing have been described with the structure including a variable aperture, a phase plate and an annular screen objective lens. However, only by using a phase plate, the spherical aberration is reduced due to the exchange of the disk and an appropriate optical impact can be formed for the CD-R on the information recording surface. The modalities described in the above have been described together with an infinite optical system which is constructed by the lens 34 collimator. However, the present invention can be applied to a finite optical system which does not have a collimator lens that is located between a beam splitter and a target lens, which is apparent to one skilled in the art. As described above, the optical pickup apparatus according to the present invention utilizes a phase plate. Accordingly, the present invention can provide an optical pickup which is used compatibly by a DVD and CD-R with an individual objective lens, without using a conventional optical apparatus which creates a problem in the manufacturing process. While only certain embodiments of the invention have been specifically described herein, it will be apparent that numerous modifications can be made to them without departing from the spirit and scope of the invention.

Claims (24)

1. An optical acquisition apparatus for at least two optical recording means, which are different in distance from an optical sensor to the information recording surfaces and use light of different wavelengths to record and read information, the acquisition apparatus optics which is characterized in that it comprises: laser light sources for emitting a first light having a relatively short wavelength and a second light having a relatively long wavelength, respectively; an objective lens having a predetermined focal length, in which the objective lens focal point according to the first light coincides with the position of the information recording surface in the first optical recording medium having the recording surface of information close to the objective lens; optical detection means; means for controlling an optical path so that the light emitted from the laser light sources is directed to the objective lens and the light exiting the objective lens is directed to the optical detection means; and the phase deflection means, located between the optical path control means and the objective lens, to deflect the phase of the second light coming from the optical path control means towards the objective lens, thereby reducing the size of a beam impact which is formed at the position of the information recording surface in the second optical recording medium having the information recording surface which is placed beyond the objective lens for the second light-focused by the objective lens; wherein one of the first and second lights is used in accordance with the optical recording medium to be used.

2. The optical pickup apparatus according to claim 1, characterized in that the phase deflection means is a phase plate that includes two regions which have different thickness from a surface of the phase plate which is relatively farther from the medium of optical path control.

3. The optical pickup apparatus according to claim 2, characterized in that a region having a thin thickness of the phase plate is a portion for deflecting the phase of the second light, and includes a groove, having a width and a depth predetermined which is concave inwardly from the surface of the phase plate relatively close to the optical path control means.

4. The optical pickup apparatus according to claim 3, characterized in that the thin region has a shape of concentric circles with respect to the optical axis of the objective lens.

5. The optical pickup apparatus according to claim 3, characterized in that the groove has an optical depth to deflect the phase of the first light by a degree of 360 and diverts the phase of the second light by a degree of 180.

6. The optical pickup apparatus according to claim 2, characterized in that a region having a thin thickness of the phase plate is a portion for deflecting the phase of the second light, and includes a projection having a predetermined width and height. which projects outwardly from the surface of the phase plate relatively close to the optical path control means.

7. The optical pickup apparatus according to claim 6, characterized in that the thick region has a shape of concentric circles with respect to the optical axis of the objective lens.

8. The optical acquisition apparatus according to claim 6, characterized in that the projection has an optical height to deflect the phase of the first light by a degree of 360 and to divert the phase of the second light by a degree of 180.

9. The optical pickup apparatus according to claim 2, characterized in that the phase plate is manufactured by one of the engraving, injection and molding operations.

10. The optical pickup apparatus according to claim 1, characterized in that the phase deflection means is fabricated by engraving a slot having a predetermined width and depth, which is concave inward from the surface of the relatively close objective lens. to the optical path control means.

11. The optical acquisition apparatus according to claim 1, characterized in that the phase deflection means has a shape of a projection having a predetermined width and height, which projects outwards from the surface of the phase plate relatively close to the optical path control means.

12. The optical pickup apparatus according to claim 1, characterized in that the phase deflection means has the same curvature as that of the objective lens and is coupled with an objective lens surface which is relatively close to the optical path control means. .

13. The optical pickup apparatus according to claim 1, characterized in that it has a small size structure, in which one of the first and second lights is appropriately selected and other components are used consistently when one optical recording medium is changed to the other optical recording medium.

14. The optical acquisition apparatus according to claim 1, characterized in that one of the laser light sources and the optical detection means are integrated as a single unit.

15. The optical pickup apparatus according to claim 1, further characterized in that it comprises the variable aperture means which is located between the optical path control means and the phase deflection means, which has a first region for transmitting both of the first and second lights entering from the optical path control means and a second region to transmit only the second light introduced therefrom, wherein the first and second regions have the same optical axis as that of the objective lens.

16. The optical pickup apparatus according to claim 15, characterized in that the second region of the variable aperture means is to be constructed as a structure of a diffraction grating pattern.

17. The optical pickup apparatus according to claim 15, characterized in that the phase deflection means and the variable aperture means are constructed as a single unit in which the phase deflection means is formed within the first region of the medium of variable aperture.

18. The optical pickup apparatus according to claim 15, characterized in that the objective lens comprises at least a portion of an annular screen for shielding the part of the light which is transmitted by means of the first region.

19. The optical pickup apparatus according to claim 10, characterized in that the phase deflection means and the variable aperture means are constructed as a single unit in which the phase deflection means is formed within the first region of the variable opening means.

20. An optical acquisition apparatus for at least two optical recording means, which are different in distance from an optical sensor to the information recording surfaces and use light of different wavelengths to record and read information, the optical pickup apparatus which is characterized in that it comprises: 20 laser light sources for emitting a first light having a relatively short wavelength and a second light having a relatively long wavelength, respectively; an objective lens having a predetermined focal length, in which the focal point of the objective lens according to the first light 25 matches the position of the information recording surface in the first optical recording medium having the information recording surface close to the objective lens; optical detection means; means for controlling an optical path so that the light emitted from the laser light sources is directed to the objective lens and the light exiting the objective lens is directed to the optical detection means; and variable aperture means, located between the optical path control means and the objective lens, having a first region for transmitting both of the first and second lights introduced from the optical path control means and a second region for transmitting only the second light introduced therefrom, wherein the first and second regions have the same optical axis as that of the objective lens; wherein one of the first and second lights is used in accordance with the optical recording medium to be used.

21. The optical acquisition apparatus according to claim 20, characterized in that the second region of the variable aperture means is constructed as a structure of a diffraction grating pattern.

22. The optical acquisition apparatus according to claim 20, characterized in that the objective lens comprises at least a portion of an annular screen for shielding the part of the light which is transmitted by means of the first region.

23. The optical pickup apparatus according to claim 22, further characterized in that it comprises the phase deflection means, located between the variable aperture means and the objective lens, for deflecting the phase of the second light coming from the variable aperture means. to the objective lens, so reducing the size of the beam impact which is formed in the position of the information recording surface in the second optical recording medium that has the information recording surface which is located beyond of the objective lens by the second light focused with the objective lens.

24. The optical pickup apparatus according to claim 23, characterized in that the phase deflection means and the variable aperture means are constructed as a single unit in which the phase deflection means is formed within the first region of the medium of variable aperture.