KR100268385B1 - Focusing optical system of parabolic mirror and high density optical recorder - Google Patents

Abstract

A parabolic converging optical system and a high-density optical recording / reproducing apparatus using the same are made of a parabolic optical system having a high numerical aperture by using a converging optical system to enable high-density optical recording and reproducing of a disc with an optical system of optical pickup employing the parabolic mirror. The focused optical system of the present invention has a conical parabolic surface having an outer circumferential surface showing a parabola curve of y = kx ² on the xy plane and an exit surface cut perpendicular to the optical axis at the point of focus (0,1 / 4k). By the light, the inside is transparent to the laser to be used, and the upper part is connected to the cylindrical material having the same diameter as the diameter of the parabolic mirror as it is, and in the center of the upper surface is the conical concave shape of the v-shaped cross section. It is manufactured so as to block incident light around the optical axis. In addition, the material of the parabolic mirror has a refractive index of 2 or more to increase the numerical aperture, wind the coil around the parabolic mirror, and apply a reflective film to the outer circumferential surface of the parabolic mirror to be inserted into the air slider of the hard disk drive (HDD). Therefore, the present invention enables high-density optical recording and reproducing, and provides an effect that can replace the HDD.

Description

Focusing optical system of parabolic mirror and high density optical recorder

The present invention relates to a focused optical system of a parabolic mirror and a high density optical recording and reproducing apparatus using the same.

Generally, for high density recording and reproduction of an optical disc, grooves and lands are formed on an optical disc substrate, and a recording film is deposited thereon. An optical system of a conventional optical pickup for recording and reproducing information on such an optical disc will be described with reference to FIG.

The optical system of the optical pickup shown in FIG. 1 injects a laser beam of a predetermined wavelength emitted from the light source unit 11 into a half mirror 12. Light transmitted through the half mirror 12 is incident on the objective lens 13. The objective lens 13 focuses the light emitted from the light source unit 11 onto the signal recording surface of the optical disc 14. Therefore, the light reflected from the signal recording surface of the optical disc 14 contains the information recorded on the signal recording surface. The reflected light is again reflected by the partial reflection mirror of the half mirror 12 to reach the light receiving portion 15. The light receiving unit 15 is provided with an optical system capable of detecting a focus error and a tracking error. Here, the extracted error signal is amplified and used to drive the actuator 16.

은 레이저광의 파장(λ)과 대물렌즈(13)의 개구수(N.A)와 다음의 수학식 1과 같은 관계가 있다.In the optical recording and reproducing apparatus composed of the optical system of the conventional optical pickup, the optical recording density depends on the beam diameter at the focal point of the objective lens 13. Beam diameter

Is related to the wavelength? Of the laser light, the numerical aperture NA of the objective lens 13, and the following equation (1).

은 650㎚정도가 된다.Where n is the refractive index of the medium and θ is the angle of incidence of the outermost circumferential ray, the beam diameter when the wavelength λ is 650 nm and the numerical aperture NA is 0.6

Is about 650 nm.

In terms of recording density, it can be seen that the size of the recording mark is limited to the wavelength. Therefore, among the various methods for increasing the recording capacity of the optical recording and reproducing apparatus, the basic is to reduce the size of the condensing spot by reducing the wavelength of light used and increasing the numerical aperture (N.A) of the objective lens used. A focusing optical system for reducing the size of the focusing spot by increasing the numerical aperture will be described with reference to FIG. 2.

The focusing optical system shown in FIG. 2 uses a near field to reduce the size of the condensing spot, and the conventional aspherical lens 21 and the spherical lens 22 also called a solid immersion lens (SIL) are used. Equipped. When using this focused optical system as the objective lens of the optical disk, the sled 23 moves the spherical lens 22 with respect to the surface of the disk 24, and the distance between the spherical lens 22 and the disk 24 is 100 nm. Keep below. The aspherical lens 21 refracts the laser light emitted from a light source (not shown), and the spherical lens 22 condenses the laser light refracted by the aspherical lens 21 to the inside of the surface located toward the disk 24. . The surface of the spherical lens 22 in which the laser light is focused forms a near field, and as a result, information is recorded on or read from the disk 24 through the near field.

In the case of having the refractive index 'n' of the medium constituting the spherical lens 22, the angle at which the laser light is collected inside the spherical lens 22 is increased and the wavelength of the laser light is reduced to λ / n. The numerical aperture N.A also rises to N.A / λ. Therefore, the size of the light spot finally formed inside the surface of the spherical lens 22 is proportional to NA / n. As a result, the spot size is determined by using the refractive index n of the medium of the spherical lens 22. Can be reduced.

Since the numerical aperture NA of the objective lens is about 0.6 and the refractive index n of the glass-impregnated lens SIL is about 2, the total numerical aperture is 1.2, that is, the optical system shown in FIG. Doubled, the recording density can achieve four times its square value. For example, the current level of optical recording technology can record 5 gigabytes (GB) of information on one surface of a 12cm optical disk. Capacity can be achieved.

However, the above recording capacity is not much larger than the recent magnetic recording technology, and when the optical system of the optical pickup employing such a focused optical system is applied to the optical disk drive, the lens size is much larger than that of the magnetic head. It was difficult to attach to the air slider.

Accordingly, an object of the present invention is to provide a focusing optical system of a parabolic mirror manufactured in such a small size that the recording capacity can be increased while being inserted into the air slider of an optical disk drive in view of the above-mentioned problems.

Another object of the present invention is to provide a high-density optical recording and reproducing apparatus, which is composed of an optical pickup optical system employing the above-mentioned parabolic converging optical system, and enables high-density optical recording and reproduction on a disk.

1 is a view showing an optical system of a conventional optical pickup.

2 is a diagram for explaining a conventional focusing optical system.

3 is a view for explaining a focusing optical system of the parabolic mirror according to an embodiment of the present invention.

4 is a view showing an example modified to fit the focusing optical system of the parabolic mirror of FIG.

5 is a view showing an optical system of optical pickup employing a focused optical system of the parabolic mirror of FIG.

6 is a partial structural diagram of a high density optical recording and reproducing apparatus composed of the optical system of FIG.

FIG. 7 shows an example in which the converging optical system of the parabolic mirror of FIG. 3 is modified to be suitable for use in a magneto-optical disk.

8 is a view showing an example of coating a reflective film on the parabolic mirror of FIG.

<Explanation of symbols for main parts of drawing>

30: parabolic mirror 31: incident surface

33: exit surface 35: V groove

51 laser light source 53 collimating lens

55: half mirror 57: total reflection prism

59: optical disk 61: light receiving unit

63: Boy coil motor 65: Optical component support plate

67: leaf spring 69: air slider

The focusing optical system of the parabolic mirror according to the present invention for achieving the above object, in the focusing optical system for focusing the incident laser light to the optical recording medium, in the conical shape, the parabolic outer peripheral surface, the incident surface located on the light source side, And an emission surface positioned on the optical recording medium, and focusing the laser light source incident from the incident surface on the outer circumferential surface to focus at the center position of the emission surface so that a focal point is formed at the center position of the emission surface. do.

The high-density optical recording and reproducing apparatus of the present invention for achieving another object of the present invention has a conical shape, having a parabolic outer circumferential surface, an entrance surface located on the light source side, and an exit surface located on the optical recording medium side, and the focus is on the above. And an optical pickup optical system employing a parabolic converging optical system that totally reflects a laser light source incident from the incident surface at the outer circumferential surface so as to be formed at the center position of the exit surface and focuses at the center position of the exit surface. And recording and reproducing the signal on the optical recording medium through an optical system.

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

Referring to FIG. 3, the converging optical system 30 according to the exemplary embodiment of the present invention is a parabolic mirror in the shape of a parabolic curve that satisfies the following Equation 2 when viewed on an x-y plane.

The parabolic converging optical system 30 has a conical shape, the outer peripheral surface of the optical material along the parabolic curve of Equation 2 above, the exit surface 31 located on the light source (not shown) and the exit located on the optical disk (not shown) The face 33 is provided. The focal point F of the parabolic mirror is processed to be located at the center of the exit surface 33. The laser light incident from the incident surface 31 is totally reflected at the outer circumferential surface to face the focal point F. As shown in FIG. At this time, the incident angle of the light beam incident on the parabolic mirror is larger than the critical angle, so that total reflection is performed even without the reflection coating. Here, the focal point F is the position of the coordinate (0,1 / 4k) on the xy plane, and the emission surface 33 is cut off perpendicularly to the optical axis at the point of the focal point F, and the coordinate (-1 / 2k) , 1 / 4k) and (1 / 2k, 1 / 4k) are the same as the plane cut along the line AA ', the radius is 1 / 2k, the diameter is 1 / k. The diameter and height of the incident surface 31 are determined by BB ', which is the position of any two points (-a, ka ² ) and (a, ka ² ) on the curve. At this time, the length (L) of the parabolic mirror 30 is the following equation (3), the diameter of the incident surface 31 is determined to a value of 2a.

For example, when the value of k is "2" and the length L is 1 mm, the coordinate of the focal point F is (0,1 / 8), and the diameter of the exit surface 33 is 0.5. It will be mm, and the diameter of the incident surface 31 will be 1.5 mm. The size of the parabolic converging optical system 30 may be mounted on an air slider used to allow a magnetic head of a hard disk drive (HDD) to rise to a predetermined height from a disk surface when the magnetic disk is rotated. It is small enough.

FIG. 4 is an example modified to fit the focusing optical system 30 of the parabolic mirror. Since the size is too small and inconvenient to handle, the cylinder region having a cylindrical shape having the same diameter as the diameter of the parabolic mirror is incident on the incident surface ( 31) Eliminate inconveniences during assembly by connecting the upper part as it is. Here, the cylinder region plays no optical role. In the center of the upper surface, the cross section is processed into a concave concave shape in the shape of a "v" shape to form a "v" shape groove 35. This is because the laser light incident within the radius of the emission surface 33 around the optical axis is reflected by the parabolic mirror 30 and thus fails to form the focal point F, thereby blocking such a ray. The " v " groove 35 of the parabolic mirror 30 scatters incident light around the optical axis so that it can be prevented from acting as a noise in the future optical recording. The energy of the laser light canceled by the v-groove 35 is determined by the area ratio of the incident surface 31 and the exit surface 33, which is only 11% of the total incident energy, for example. High light efficiency can be maintained.

Looking at the performance of such a parabolic mirror 30, since the maximum incident angle is 90 degrees given by the light reflected at the AA 'point of Figure 3, when the material having a refractive index of 2 is used, the numerical aperture (NA) is 2 It can be seen that the conventional optical system shown in FIG. 2 is very large compared to the numerical aperture (NA) 1.2.

The following Table 1 shows the exit face 33 diameter, the incident face 31 diameter, the length L of the parabolic surface portion, and the light efficiency according to the k value.

Table 2 shows the refractive index according to the material of the parabolic mirror (30).

As shown in Table 2 above, when the focusing optical system 30 of a parabolic mirror is made of a material having a refractive index of 2.7, such as a cubic Sic, and used in an optical system of an optical pickup, the optical disk drive is composed of about 100 GB on a 12 cm optical disk. Information can be recorded and reproduced. In addition, since the volume, or weight, of the parabolic mirror 30 is very small, it is possible to perform very fast position tracking due to less load when transferring the air slider radially.

FIG. 5 shows an optical system of a general optical pickup employing the converging optical system 30 of FIG. In FIG. 5, the laser light emitted from the laser light source 51 of the predetermined wavelength is collimated by the collimating lens 53 so as to be parallel to the optical axis of the collimating lens 53, and then enters the half mirror 55. The half mirror 55 transmits the incident laser light toward the total reflection prism 57. The total reflection prism 57 reflects the laser light incident from the half mirror 55 to the incident surface 31 of the parabolic mirror 30 which is a focusing optical system. The parabolic mirror 30, which is a focusing optical system, exhibits the optical characteristics described with reference to FIG. 3 with respect to the laser light incident from the total reflection prism 57, and as a result, the light spot is located at the focal point F of the exit surface 33. Is formed. The distance between the focusing optical system and the disk 59 is maintained by the air bearing, which is less than 0.1 mu m. The light spot formed at the focal point F is deformed by the signal recording surface of the disk 59, and the reflected light indicating such deformation is reflected by the total reflection prism 57 and the half mirror 55 in turn, and then the light receiving portion 61 To pass.

FIG. 6 is a partial structural diagram of a high density optical recording and reproducing apparatus composed of the optical system of FIG. 5, and the optical system configuration of the optical pickup of FIG. Referring to FIG. 6, the parabolic mirror 30 is inserted into the optical axis of the air slider 69 supported by the leaf spring 67, in which the exit surface must exactly match the lower surface of the slider 69. . And the other optical component is to be assembled on the optical component support plate (65). In addition, the leaf spring 67 and the optical component support plate 65 are connected to the shaft of the voice coil motor 63 to enable the optical disk 59 to move in the radial direction. The laser light emitted from the light source portion formed by the laser light source 51 and the collimating lens 53 passes through the half mirror 55, is reflected by the total reflection prism 57, proceeds downward, and is inserted into the air slider 69. It reaches the parabolic mirror 30 and eventually reaches the optical recording surface coated on the optical disk 59. According to the characteristics of the optical recording surface, the laser light whose light amount or polarization direction is changed is reflected and reaches the light receiving portion 61 through the total reflection prism 59 and the half mirror 55. The air slider 69 is automatically floated to a height of about 0.1 μm by the flow of air generated on the surface by the rotation of the optical disk 59, so that the focus control as in the prior art is not necessary.

FIG. 7 is an example modified to fit the focused optical system 30 of the parabolic mirror 30 to be used for a magneto-optical disk. The coil 71 is installed to cause a vertical magnetic field at the focal point F of the parabolic mirror 30. . The coil 71 winds up the periphery of the outer circumferential surface of the parabolic mirror 30 and fixes it using the adhesive 73. In addition, in order to prevent light leakage by adhesion of the adhesive 73 or the coil 71, as shown in FIG. 8, the reflective film 81 may be coated around the outer circumferential surface of the parabolic mirror 30.

The optical disk drive as shown in FIG. 6 constituting the optical system of the optical pickup employing the condensing optical system according to the present invention in a general hard disk drive is obvious to those skilled in the art, and thus, further detailed description thereof will be omitted.

As described above, the parabolic converging optical system and the high-density optical recording / reproducing apparatus using the same can insert and install a parabolic converging optical system having a high numerical aperture of a material having a refractive index of 2 or more in an air slider of a hard disk drive. It is possible to record and play high density of about 100GB on 12cm optical disk, and it is possible to perform very fast position tracking because it takes less load when transporting air slider radially.

Claims (15)

A focusing optical system for focusing incident laser light onto an optical recording medium, the conical shape includes a parabolic outer circumferential surface, an entrance surface located on the light source side, and an exit surface located on the optical recording medium side, and the focusing surface is the output surface. A parabolic confocal optical system for totally reflecting a laser light source incident from the incidence surface on the outer circumferential surface to focus at a center position of the outgoing surface to be formed at a center position of the incidence surface. The focusing optical system of claim 1, wherein the outer circumferential surface is an optical material following a parabolic curve of the following equation. y = kx ² The focusing optical system of claim 1, wherein the emission surface is formed to be cut perpendicular to the optical axis at a focal point. The focusing optical system of claim 2, wherein the position of the focal point is a point of coordinates (0, 1/4/4). The focusing optical system of claim 4, wherein the emission surface has a radius of 1 / 2k and a diameter of 1 / k. The converging optical system of claim 1, wherein the parabolic mirror is too small in size to remove inconvenience during assembly, and has a cylindrical shape having a diameter equal to the diameter of the parabolic mirror without any optical role. . The converging optical system of claim 6, wherein the parabolic mirror has a groove having a “v” shaped cross section at the center of the upper surface to block incident light around the optical axis. The focusing optical system of claim 1, wherein the parabolic mirror has a maximum incident angle of 90 degrees. The focusing optical system of claim 1, wherein the parabolic mirror has a refractive index of 2 or more. An optical recording and reproducing apparatus, having a conical shape, having a parabolic outer circumferential surface, an entrance surface located on a light source side, and an exit surface located on an optical recording medium side, from the entrance surface such that a focal point is formed at a center position of the exit surface. And an optical pickup optical system employing a parabolic converging optical system for totally reflecting the incident laser light source from the outer circumferential surface to focus at the center position of the exit surface, and recording and reproducing a signal on an optical recording medium through the optical system of the optical pickup. An optical recording and reproducing apparatus. The parabolic mirror according to claim 10, wherein the parabolic mirror which is the converging optical system can be mounted on an air slider used for use in a hard disk drive, such that the magnetic head of the hard disk drive floats to a predetermined height on the disk surface when the magnetic disk is rotated. Optical recording and reproducing apparatus manufactured in a small size. 12. The optical recording and reproducing apparatus according to claim 11, wherein the parabolic mirror which is the focusing optical system is inserted on the optical axis of the air slider. 13. The optical recording and reproducing apparatus according to claim 12, wherein the exit surface of the parabolic mirror coincides with the lower surface of the air slider. 14. The optical recording and reproducing apparatus according to claim 13, wherein the parabolic mirror is wound around a coil and inserted into an air slider so as to cause a vertical magnetic field at a focus when used in a magneto-optical recording medium. 15. The optical recording and reproducing apparatus according to claim 14, wherein the parabolic mirror coats a reflective film around to prevent leakage of light by adhesion of the coil.

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