KR100393772B1 - Optics for optical recording and reproducing system - Google Patents

Abstract

The present invention relates to an optical system for an optical recording and reproducing system, comprising: an incident portion to which a beam generated from a light source is incident, a first reflecting surface on which an incident beam is reflected, and a reflecting material is coated to reflect from the first reflecting surface A first lens having a second reflecting surface on which the reflected beam is reflected again, and a lens positioned near the center of the lower end of the first lens and converging light transmitted from the second reflecting surface to pass through the first reflecting surface An optical system for an optical recording and reproducing system including two lenses is provided. According to the present invention, it is possible to manufacture an ultra-thin optical recording and reproducing system capable of high-density information recording and storage and having a very small thickness and volume.

Description

Optical system for optical recording and reproducing system {OPTICS FOR OPTICAL RECORDING AND REPRODUCING SYSTEM}

The present invention relates to an optical system for an optical recording and reproducing system, and more particularly, to an optical system for an optical recording and reproducing system capable of reducing the thickness and volume of a lens and recording ultra-high density information.

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 the absolute limit of the resolution due to the diffraction phenomenon 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 a perspective view showing a conventional near field optical recording system 10. In the deck 18, a central portion of the disk 11, which is a recording medium, is mounted on the spindle motor (not shown) so as to be rotatable, and a recording and reproducing apparatus is provided on the other side of the inside. The floating head slider 12 is supported by the suspension arm 14 on the upper surface of the disk, and one side of the suspension arm is connected to the pickup 17. A voice coil motor (VCM) 16 is installed below the pickup to allow the pickup to rotate at an angle within a certain range. On the other hand, a fixed arm 13 is supported on the upper surface of the head slider from the pickup, and a prism 15 is provided at the end of the fixed arm. Light generated by the light source (not shown) of the pickup part is changed in the prism, passes through a lens (not shown) 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.

FIG. 2 is an enlarged schematic view of an optical system mounted on a head slider in the system of FIG. 1, which is composed of a hemispherical solid immersion lens (SIL) 22 and a primary condenser lens 21. The SIL is spherical in shape with a top surface spherical and a bottom surface flat, and is installed so that the center of the flat portion of the SIL coincides with the focal point of the primary condensing lens. In the center of the lower plane of the. In order to record data (bits) on the disc using the SIL, as shown in FIG. 2, the SIL is brought close to the surface of the recording medium 23 at very small intervals, for example, at intervals of 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 the SIL, it is possible to overcome the diffraction limit of the 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.

An object of the present invention is to provide an optical system with a low aberration of a condenser lens and a very large convergence angle of light incident on the condenser lens, thereby improving 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 perspective view showing a conventional near field optical recording system.

FIG. 2 is an enlarged schematic view of an optical system mounted to a head slider in the system of FIG. 1.

3 is a cross-sectional view showing an embodiment of the present invention.

4 is a cross-sectional view showing another embodiment of the present invention.

FIG. 5 is a schematic diagram showing a state in which light incident from a light source is focused through the lens in the embodiment of FIG. 3.

6 is a partially enlarged view of the embodiment of FIG. 3.

7 is an enlarged schematic view of the head of the optical recording and reproducing system according to the present invention.

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

L1: First lens L2: Second lens

S1: entrance part S2: second reflection part

S3: First Reflector

In order to achieve the above object, the present invention provides an incident part to which a beam generated from a light source is incident, a first reflecting surface on which an incident beam is reflected, and a reflecting material is coated so that the beam reflected from the first reflecting surface is reflected again. A first lens having a second reflecting surface, and a second lens positioned near the center of the lower end of the first lens and focused on the light reflected from the second reflecting surface and passing through the first reflecting surface; An optical system for an optical recording and reproducing system is provided.

The first reflection surface may be formed as a curved surface having a large curvature with respect to the incident direction so that the incident beam is totally reflected, and may be reflected by coating a reflective material on the surface of the first reflection surface.

The first reflecting surface of the first lens is formed to have a similar curvature to the upper portion of the second lens so that the two lenses can be adjacent to each other as close as possible to the first reflecting surface. Preferably, the two lenses may be attached to each other at the boundary of the first reflecting surface to form one integrated lens.

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.

3 is a cross-sectional view showing an embodiment of the present invention, showing a first lens L1 as a condenser lens and a second lens L2 as a condenser lens mounted on a head (not shown) of an optical recording and reproducing system. The second lens is adjacent to the first lens and is substantially integrated. There is a very small space between the two lenses, the curvature of the two lenses are similar to each other in the region where the two lenses are adjacent. The first lens L1 includes an incidence part S1 through which light from a light source is incident, a second reflection part S2 formed on both sides of the incidence part, and a first reflection part S3 formed under the lens. It is composed.

Although the incident part S1 is concave in FIG. 3 when viewed from the direction of incidence of light, it may be designed in a flat or convex shape according to the purpose of use of the lens. The size of the incidence portion can be variously set according to the diameter of the incident beam and other design conditions of the optical system. When the incident part is concave, as shown in FIG. 3, even though the diameter of incident light is small, the incident part is diverged inside the lens to have the same effect as when the diameter of the incident beam is large.

The first reflection surface S3 is formed below the incident portion S1. It can be seen that the first reflecting surface is convex when viewed from the direction of incidence of light, unlike the incident portion. The first reflecting surface of the convex shape allows total reflection of the incident beam as described below. The central portion of the first reflective surface may be coated with a reflective material. When the reflective material is coated on the first reflecting surface, light that acts as a noise can be reduced by directly penetrating the first reflecting surface without being totally reflected among the incident light passing through the incident part, thereby improving data recording and reproducing efficiency. have. The first reflecting surface may have various curvatures in consideration of the convergence angle at which the incident beam is finally incident on the second lens, and may be formed as a spherical surface or an aspherical surface.

The second reflecting surface S2 is coated with a reflective material, and is convex when viewed from the incident direction of the incident beam. The second reflecting surface may have various curvatures in consideration of the convergence angle at which the incident beam is finally incident on the second lens, and may be formed as spherical or aspheric. However, it is preferable not to have the same curvature as the first reflecting surface.

The second lens is adjacent to the first lens, and the light incident on the first lens is finally focused on the lower surface of the second lens. The second lens is made of a material having a refractive index different from that of the first lens, and has a hemispherical shape.

4 shows an integrated lens in which a second lens L2 is attached to the center of the lower end of the first lens L1 as another embodiment of the present invention. An upper portion of the second lens is fitted to the first reflective surface S3 of the first lens. In this case, the upper curved surface of the second lens and the first reflective surface S3 of the first lens need not have the same curvature, and it is sufficient that the two lenses are attached so as to be integrated as one. In such an embodiment, the two lenses are integrated as one lens, which facilitates the alignment of the lenses in the optical recording and reproducing system. In particular, when recording and reproducing information on the surface of a recording medium, servos between bits or tracks are used. Servo is easy.

3 and 4, the total thickness (d of FIG. 3) of the two lenses is greatly reduced as compared with the lens unit of the conventional optical recording system. Specifically, 0.5 mm or less, Preferably, it is possible to reduce the thickness to 0.3 mm or less. Reduction of the lens thickness can reduce the height of the head (or slider) of the optical recording system, and thus can significantly reduce the thickness of the entire optical recording system. Specifically, it is possible to make the thickness of the whole system at least 7 mm or less, preferably in the range of 3 to 5 mm or less.

FIG. 5 is a schematic diagram showing a state in which light incident from a light source is focused through the lens in the embodiment of FIG. 3. The beam generated from the light source passes through the various optical systems perpendicularly to the incident part S1 of the first lens L1, is totally reflected by the first reflecting surface S3, and is reflected by the second reflecting surface S2. Next, the light penetrates the first reflective surface S3 and enters the second lens L2 at a large angle with the initial incident direction.

Since the incidence portion is concave, the initial incident beam is diverged larger in diameter to touch the first reflecting surface of the first lens.

The first reflective surface S3 of the first lens L1 has a convex shape having a larger curvature than the incident portion S1 when viewed in the incident direction, and has a material different in medium, that is, a thin air layer (or the second lens L2). Since the light is incident to the first reflection surface S3, most of the light incident on the first reflection surface S3 is totally reflected at an angle greater than or equal to the critical angle in the remaining area except for the central portion of the first reflection surface S3, and is incident on the second reflection surface S2.

The surface of the second reflecting surface S2 of the first lens L1 is coated with a reflective material, so that the second reflecting surface concave when viewed in the direction of incidence of light totally reflected from the first reflecting surface S3 ( In S2) all are reflected. The light reflected from the second reflecting surface S2 eventually passes through the first reflecting surface S3 and enters the upper portion of the second lens L2 to finally focus on the lower flat surface of the second lens.

In another embodiment, the focal point may be positioned below the lower surface of the second lens. In this case, a recording layer in which data is stored below the surface of the recording medium is formed so that the incident beam is focused on the recording layer.

Another feature of the present invention is that the spot size of the focused light can be reduced very small. 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.

In the present invention, as shown in the partial enlarged view of FIG. 6, the light 30, which has undergone total reflection and reflection from the first lens L1, is formed at a very large angle with respect to the initial incident direction of the incident beam. Incident on L2). Since the convergence angle θ of the incident beam becomes larger in the second lens, the numerical aperture can be increased, and thus, the beam spot focused on the light can be further reduced, thereby making it possible to record and reproduce ultra-high density information.

On the other hand, the present invention can be used for recording and reproducing information even when the diameter of the incident beam generated from the light source is small by varying the shape of the incident portion of the first lens. Referring to FIG. 7, it can be seen that the light 30 generated from the light source (not shown) is reflected through the prism 15 and incident on the lens. Since the incidence portion of the first lens L1 is concave, the incidence beam passes through the incidence portion and becomes larger in diameter to touch the reflective surface in a divergent state. This effect is the same as the case where the diameter of the initial incident beam is large, so that it is possible to use a beam having a small diameter. The diameter of the initial light from the light source is proportional to the diameter of the light incident on the lens. Therefore, when the diameter of the incident beam is small, the diameter of the initial light generated by the light source is reduced, and as a result, the incident beam having a small diameter can be used in the light source, thereby reducing the size and power loss of the light source.

The features of the present invention as described above not only enable the implementation of optical memory devices that require high integration in recent years, but also can be included in various applications by significantly reducing their size and thickness.

As described above, according to the present invention, it is possible to reduce the aberration of the condenser lens and to increase the convergence angle of the light focused on the condenser lens. Therefore, the condensing performance and the recording density are improved in the optical recording and reproducing system. In addition, the present invention reduces the volume and thickness occupied by the primary condenser lens and the condenser lens to facilitate assembly of the optical system and the entire system, and enables an ultra-thin optical recording and reproducing 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 (9)

A second reflecting surface having an incident portion to which the beam generated from the light source is incident, a first reflecting surface on which the incident beam is reflected, and a reflecting material coated to reflect the beam reflected from the first reflecting surface again; 1 lens, And a second lens positioned near the center of the lower end of the first lens and focusing the light reflected from the second reflection surface and passing through the first reflection surface. The first reflection surface is formed as a curved surface having a greater curvature than the second reflection surface Optical system for optical recording and playback system. The optical system for an optical recording and reproducing system according to claim 1, wherein the incidence portion is a concave curved surface, a flat surface, or a convex curved surface when viewed in the incident direction of the incident beam. The optical system for an optical recording and reproducing system according to claim 1, wherein the first reflecting surface is a convex curved surface when viewed in the incident direction of the incident beam. The optical system of claim 3, wherein an upper portion of the second lens is a curved surface having a curvature similar to that of the first reflective surface. The optical system for an optical recording and reproducing system according to claim 1, wherein the first reflecting surface is coated with a reflective material at a central portion thereof. The optical system for an optical recording and reproducing system according to claim 1, wherein the second reflecting surface is spherical or aspheric. The optical system of claim 1, wherein the second reflecting surface is coated with a reflective material. The optical system of claim 1, wherein the second lens is adjacent to a lower portion of the first reflecting surface of the first lens. The optical system for an optical recording and reproducing system according to claim 8, wherein the first lens and the second lens are attached to and integrated with each other at a boundary of the first reflecting surface.