KR100438571B1 - Lens for optical recording and reproducing system - Google Patents

Abstract

The present invention includes an incident part to which a beam generated from a light source is incident, a first reflecting surface formed of an aspherical surface and reflecting an incident beam; A second reflection surface formed as an aspherical surface and reflecting the beam reflected from the first reflection surface again; An optical lens including a converging portion located at the center of the first reflecting surface and converging light reflected from the second reflecting surface, wherein the incidence portion has a vertex at a lower portion and a portion other than the vertex is formed as an aspherical surface; An optical lens for an optical recording and reproducing system is provided.

Description

Optical Lens for Optical Recording and Playback System {LENS FOR OPTICAL RECORDING AND REPRODUCING SYSTEM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical lenses for optical recording and reproducing systems, and more particularly to optical lenses for near field recording systems with low light loss and high aperture.

An optical recording medium or a magneto-optical recording medium must have a small bit (or recording mark) size and a narrow track width to have a high density recording capacity. However, since the spot size of the light condensed on the recording medium to form a bit in the recording film of the recording medium is limited by the diffraction limit, there is a limit in improving the recording density.

In light of the trend of large-capacity information, new optical recording / reproducing methods are required to overcome the limitations of existing optical recording / reproducing methods. In recent years, research on near field recording / reproduction using near field, which is expected to significantly improve recording capacity, has been increasing.

The principle of near field optical recording and reproduction is as follows. Light entering the lens at an angle greater than or equal to the critical angle is totally reflected when traveling from a dense refractive index to a small one. At this time, due to total reflection of light, light of very small intensity exists on the surface of the lens, which is called an evanescent wave or dissipation wave. Using this evernet wave, it is possible to achieve high resolution, which is impossible because of the diffraction limit, which is an absolute limit of resolution due to diffraction of light in the far-field. The near field optical recording and reproducing optical system totally reflects the light in the lens to generate an Evernet wave on the surface of the lens, and records and plays back by coupling the Evernet wave and the recording medium.

1 is an enlarged cross-sectional view of an optical system mounted on a head slider in an optical recording system, which is composed of a hemispherical solid immersion lens (SIL) 12 and a primary condensing lens 11. The SIL has a spherical shape with a top surface of a sphere and a bottom surface of a hemispherical shape, and is installed so that the center of the flat portion of the SIL coincides with the focus of the primary condenser lens. Thus, the light 14 incident on the primary condensing lens is refracted and collected at the center of the lower planar portion of the SIL. In order to record data (bits) on the disc using the SIL, as shown in FIG. 1, the SIL is brought close to the surface of the recording medium 13 at very small intervals, for example, about 10 to 70 nm. In this proximity, an optical near field phenomenon occurs in which a part of the primary energy focused on the lower surface of the SIL is transferred to the recording medium. This near field phenomenon makes it possible to record or reproduce data on the recording medium surface. For example, the energy delivered from the SIL heats part of the surface of the record carrier, causing local phase changes. This phase change forms bits on the surface of the recording medium. That is, to record information. When reading the recorded information, the property of reflectance is changed at the locally changed phase. When light of low intensity is incident through the SIL, and the intensity of the light reflected from the surface of the recording medium and output through the SIL is measured by the optical sensor, the reflectance varies depending on the presence or absence of the bit, so that information can be read.

As described above, in the optical system using SIL, it is possible to overcome the diffraction limit of light and reduce the light spot, but there are the following problems.

In general, an optical lens generates an aberration in which light does not collect at a point, and this aberration has a characteristic that the higher the magnification of the lens is, the larger it becomes. Since an optical system using SIL requires a large-scale primary condenser lens, the aberration of the primary condenser lens greatly degrades the primary condensing performance of the optical system.

In addition, the data recording / reproducing apparatus using SIL requires a primary condenser lens, which makes the device bulky and complicated, and makes it difficult to assemble the entire data storage device and the primary condenser lens. In particular, there is a limit in reducing the height of the head slider on which the lens is mounted, and it is difficult to manufacture an ultra-thin optical recording and reproducing system that can be mounted on a portable device or the like.

In addition, the convergence angle θ of the focused light is determined by the numerical aperture of the focusing lens, which is a factor that determines the spot size of the incident light. The existing SIL has a limit to increase θ, so the spot of the focused light is limited. It is difficult to reduce the size anymore.

In addition, as the numerical aperture becomes larger, it becomes difficult to control the thickness tolerance and alignment between the SIL and the objective lens. If the thickness and alignment of the focusing lens and the objective lens are not accurately controlled, the operation of the optical recording apparatus will be adversely affected.

An object of the present invention is to provide an optical system with a low aberration of a focusing lens and a very large convergence angle of light incident on the focusing lens, thereby improving light condensing performance and recording density in an optical recording and reproducing system.

In addition, an object of the present invention is to reduce the volume and thickness occupied by the primary condenser lens and the focusing lens to facilitate the assembly of the optical system and the entire system, and to enable an ultra-thin optical recording and reproducing system.

Other objects and features of the present invention will appear in detail from the following specific examples and claims.

1 is a cross-sectional view showing a SIL of a conventional near field optical recording system.

2A is a cross-sectional view showing an embodiment of an optical lens according to the present invention.

2B is a cross-sectional view showing a comparative example in which the incidence portion of the lens is spherical.

3A is a graph showing the intensity distribution of light at the converging portion of the optical lens of the present invention.

3B is a graph showing the intensity distribution of light of SIL.

Figure 4 is a cross-sectional view showing another embodiment of the present invention, shows a lens formed in the shape of a cone with a modified incidence portion.

5 is a cross-sectional view showing another embodiment of the present invention, showing an embodiment in which a step is formed on the lower surface of the lens.

6 is a cross-sectional view showing another embodiment of the present invention, in which the lens lower surface is a convex aspherical surface.

7 is a cross-sectional view showing another embodiment of the present invention, in which the lens lower surface is a concave aspherical surface.

8 is a cross-sectional view showing another embodiment of the present invention, and shows an embodiment in which protrusions are formed on the lens periphery.

9 is a perspective view showing an example of an optical recording system using the optical lens of the present invention.

*** Explanation of symbols for main parts of drawing ***

21a: entrance part 22a: first reflection surface

23a: second reflective surface 24: convergence unit

25: incident beam

In order to achieve the above object, the present invention includes an incident portion to which the beam generated from the light source is incident, and a first reflecting surface formed as an aspherical surface and reflecting the incident beam; A second reflection surface formed as an aspherical surface and reflecting the beam reflected from the first reflection surface again; An optical lens including a converging portion located at the center of the first reflecting surface and converging light reflected from the second reflecting surface, wherein the incidence portion has a vertex at a lower portion and a portion other than the vertex is formed as an aspherical surface; An optical lens for an optical recording and reproducing system is provided.

The incidence part may have an inverted cone shape having a triangular cross section, and may have a vertex at the lower part of the incidence part, and a portion other than the lower part may have a deformed cone shape formed as an aspherical surface.

The first reflection surface and the second reflection surface are preferably formed as an aspherical surface, the shape of the first reflection surface can be variously modified depending on the conditions of the system in which the lens is used.

The optical lens of the present invention can suppress the light loss caused by the light incident on the lens is not used for optical recording and reproduction, and the optical system required for the near field optical recording system with only a focusing lens without an objective lens. Can be implemented to significantly reduce the size and thickness of the system. Therefore, the present invention not only enables the implementation of an optical memory device requiring high integration, but also can be applied to various applications by significantly reducing its size and thickness.

The optical system of the present invention is applicable not only to the optical recording and reproducing system using the near field, but also to the system using the existing far-field.

In optical recording systems, the information storage density has a direct relationship to the extent to which light is used for recording, i.e. the spot size of the beam. The smaller the beam spot, the higher the data storage density. The size of the beam spot depends on the wavelength of light used, the light convergence angle of the lens, the diameter of the incident beam, and the refractive index of the medium in which the spot is formed. It can be expressed in the same way.

d ∝ λ / NA, NA = n * sinθ

Where d is the diameter of the beam spot, λ is the wavelength of light, NA is the numerical aperture of the lens, n is the refractive index of the lens, and θ represents the convergence angle of the incident beam. Therefore, in order to reduce the beam spot, the wavelength should be reduced or the numerical aperture should be increased, and in order to increase the numerical aperture, the refractive index or the convergence angle should be increased.

According to the present invention, the spot size of light can be reduced very small by reducing the convergence angle of light converging on the focusing lens.

2A is a cross-sectional view showing an embodiment of an optical lens according to the present invention. An incident part 21a is formed at the center of the lens upper surface to which the light 25 generated by the light source is incident. The incident part of the lens shows an inverted triangle in cross section, but is actually formed in a cone shape. The lower surface of the lens is a first reflection surface 22a in which light passing through the incident part is first reflected, and the curved surface around the incidence portion of the upper surface of the lens is a second reflection surface 23a in which light reflected from the first reflection surface is secondarily reflected. )to be. The light passing through the inverted cone-shaped incidence portion 21a proceeds toward the bottom of the lens without the light converging to the center of the lens bottom, that is, near the edge of the first reflecting surface 22a coated with the reflective material. After reflecting from the first reflecting surface 22a, it is reflected back from the second reflecting surface 23a coated with the reflective material and finally concentrated on the converging portion 24a located at the center of the lower surface of the lens. The light concentrated on the convergence part magneto-magnetically interacts with the surface of the recording medium (not shown) near the lower surface of the lens and records or reproduces the data.

If the incident part 21a of the upper surface of the lens is not a conical shape as in the present invention, but is a spherical surface as shown in FIG. 2B, the following problem may occur. Light passing through the incidence portion 21 of the upper surface of the lens is emitted to each part of the lower surface of the lens according to the curved surface of the incidence portion 21. Although some of the emitted light travels near the edge of the lower surface of the lens, the light 25 ′ of the center region of the incident beam 25 is formed by the first reflection surface 22 of the lower surface of the lens and the first upper surface of the lens. Unlike the reflection on the two reflecting surfaces 23 and being concentrated on the converging portion 24 at a large angle of incidence, the light proceeds directly to the converging portion 24 on the lower surface of the lens. As such, the light proceeding to the converging portion 24 without undergoing the reflection process has a small incident angle, so that the numerical aperture becomes small (e.g., the numerical aperture becomes smaller than 1). It becomes large and acts as a noise also in an optical signal. Therefore, the optical recording system using the lens as shown in Figure 2b is the loss of the light amount during recording and playback increases the light efficiency, and to compensate for this light loss requires a light source of higher output system The size of the manufacturing cost increases.

However, in the optical lens of the present invention as shown in FIG. 2A, since the incidence portion 21a is conical, all the light passes through the first reflecting surface 22a and the second reflecting surface 23a without any light loss. By concentrating on the converging portion 24a in a state larger than 1, light having a small spot size and noise free reaches the recording medium.

The optical lens of the present invention forms the second reflecting surface 23a as an aspheric surface. In general, in spherical lenses, spherical aberrations in which light does not converge to a point occur, and the spherical aberration causes a large spot of collected light. The larger the spot size of the converging light, the smaller the recording density of the optical recording system. Since the second reflecting surface 23a is an aspherical surface, the lens of the present invention can eliminate spherical aberration, and thus can reduce the spot of converged light.

On the other hand, the lens of the present invention having a conical incidence portion is superior to conventional SIL in light intensity of converging light. FIG. 3A shows the intensity of light at the converging portion 24a of the optical lens of the present invention, and it can be seen that the intensity of light at the center is very large and the distribution width d is also very small. On the other hand, referring to Figure 3b, in the case of SIL can be seen that the intensity of light in the center is small and the distribution width (d) is also very wide. The intensity and distribution of light converging on the lens depends mainly on the size of the light incident from the light source. In the present invention, even if the size of the light incident from the light source is small, the lens incident portion 21a can reflect all the light without light loss and concentrate the lens converging portion 24a, and the size of the incident portion 21a of the lens Since light having a large numerical aperture can be converged to the lower surface of the lens even if it is small, the intensity of light condensed on the lower surface of the lens can be increased and the distribution of the intensity can be narrowed. This result can greatly improve the recording density of the optical recording system and improve the reliability of signal processing.

4 is a cross-sectional view showing yet another embodiment of the present invention. In this embodiment, the incidence portion of the lens has a modified cone shape. More specifically, the lower part of the incidence part 21b has a vertex, and the part other than the vertex has a bell shape similar to a cone formed as an aspherical surface. The incident part 21b of this type has an angle where the incident light reaches the first reflecting surface 22b or the first reflecting surface 22b when compared with the incident part 21a as shown in FIG. 2A. It is easy to control the area of light.

5 is a cross-sectional view showing yet another embodiment of the present invention. In the present embodiment, a step 26 is formed on the bottom surface of the lens. The light concentrated through the incidence portion 21c and finally concentrated at the converging portion 24c on the lower surface of the lens interacts photoelectrically with the recording medium, and the surface of the recording medium and the lower surface of the lens are flush with each other due to shaking of the optical recording system. If it is not maintained, it may be inclined, causing physical defects on the surface of the recording medium or changing the distance between the recording medium and the lens, making it difficult to transmit an optical signal. When the step 26 is formed in the light converging portion 24c of the lower surface of the lens, the area between the lower surface of the lens and the surface of the recording medium is greatly reduced, thereby solving the above problems. In particular, the formation of the step 26 on the lower surface of the lens is particularly required when the lower surface of the lens is formed into a concave surface with respect to the recording medium surface as described later.

The lens of this embodiment includes a first reflecting surface 22c and a second reflecting surface 23c, and each reflecting surface is coated with a reflecting material so that the light passing through the incident part 21c is reflected twice. After undergoing the process, the light is focused on the converging portion 24c at a large angle of incidence. As described above, the second reflecting surface 23c is preferably formed as an aspheric surface, and in order to eliminate spherical aberration, the first reflecting surface 22c is preferably formed as an aspheric surface.

6 is a cross-sectional view showing another embodiment of the present invention, in which both of the first reflecting surface 22d and the second reflecting surface 23d of the lens are aspherical surfaces, in particular, the lower surface of the lens, that is, the first reflecting surface 22d is The converging portion 24d is formed at the lowest central portion by being formed convex with respect to the recording medium surface. This type of lens advantageously maintains the distance between the surface of the recording medium and the lower surface of the lens, and can prevent the surface of the recording medium from contacting the lower surface of the lens even when the optical recording system is shaken.

Fig. 7 shows another embodiment in which the first reflecting surface is formed as an aspherical surface, wherein the first reflecting surface 22e, which is the lower surface of the lens, is formed as a concave surface with respect to the recording medium surface. As in the present embodiment, the lens having the concave shape of the first reflecting surface 22e can make the incident angle of the light condensed on the converging portion 24e larger than the above-described embodiments, thereby enabling high numerical aperture and thus light. The spot size can be reduced as much as possible. On the other hand, in this embodiment, it can be seen that the step 26 is formed on the lower surface of the lens to prevent the lower surface of the lens and the surface of the recording medium. However, unlike illustrated in the drawings, a step may not be formed on the lower surface of the lens by changing the concave shape of the lower surface of the lens.

8 shows an embodiment in which the protrusion 27 is formed at the edge of the lens periphery as another embodiment of the present invention. In an optical recording system, a focusing lens is generally mounted on a slider. If a projection is formed at the periphery of the lens, the focusing lens is easily mounted on the sulfider. In the example of FIG. 8, the incident part 21f, the first reflecting part 22f, the second reflecting part 23f, and the converging part 24f are shown to be the same as in the above-described embodiment of FIG. Applicable to all the embodiments.

The optical lens of the present invention described above is mounted on an optical recording system and used for optically recording and reproducing information. An optical recording system using the optical lens of the present invention will be described. 9 is a perspective view showing an example of the near field optical recording system 30. In the deck 38, a central portion of the disk 31, which is a recording medium, is mounted to be rotatable and mounted on a spindle motor (not shown), and a recording and reproducing apparatus is provided on the other side of the inside. The floating head slider 32 is supported by the suspension arm 33 on the upper surface of the disk, and one side of the suspension arm is connected to the pickup 37. A voice coil motor (VCM) 36 is installed below the pickup unit to allow the pickup unit to rotate at a predetermined range of angles. On the other hand, a fixed arm 34 is supported on the upper surface of the head slider from the pickup, and a prism 35 is provided at the end of the fixed arm. Light generated by a light source (not shown) of the pickup part is reversed in the prism, passes through the lens 39 mounted on the head slider, and finally enters the disk surface. It is possible to record or reproduce the optical information by the interaction of the incident light with the disk surface. In the drawings, the size of the head slider, the position of the lens, and the size of the head slider are larger than they are. The optical lens of the present invention may be variously modified in the above embodiments, and may be applied to various photooxyoxysystems.

As described above, according to the present invention, the optical lens can suppress light loss due to noise acting on the lens rather than being used for optical recording and reproduction. In addition, it is possible to reduce the aberration of the focusing lens and to increase the convergence angle of the light focused on the focusing lens. Therefore, the condensing performance and the recording density are improved in the optical recording and reproducing system. In addition, the present invention can implement the optical system required for the near field optical recording system with only one focusing lens without an objective lens, and can significantly reduce the size and thickness of the system, thereby facilitating the assembly of the optical system and the entire system, and ultra-thin optical recording and reproduction. Enable the system. Therefore, it is possible to implement a high density memory device that can be mounted on portable electronic devices such as mobile phones and PDAs.

Claims (10)

An incident part to which the beam generated from the light source is incident, a first reflecting surface formed as an aspherical surface and reflecting the incident beam; A second reflection surface formed as an aspherical surface and reflecting the beam reflected from the first reflection surface again; An optical lens including a converging portion located at the center of the first reflecting surface and converging light reflected from the second reflecting surface, wherein the incidence portion has a vertex at a lower portion and a portion other than the vertex is formed as an aspherical surface; Optical lenses for optical recording and reproducing systems. delete delete delete 2. The optical lens of claim 1, wherein the first reflecting surface is flat with respect to the recording medium surface. delete 7. The optical lens of claim 6, wherein the first reflecting surface is convex with respect to the recording medium surface. 7. The optical lens of claim 6, wherein the first reflecting surface is concave with respect to the recording medium surface. The optical lens for an optical recording and reproducing system according to claim 1, wherein the converging portion has a step below the first reflecting surface. 2. An optical lens for an optical recording and reproducing system as set forth in claim 1, wherein an edge of said lens periphery is formed.