KR100360267B1 - High resolution lens and information recording devide using it - Google Patents

Abstract

The present invention relates to an ultra-high resolution lens and an information recording apparatus using the same, which is a condenser lens for condensing light incident from a light source, wherein one surface of the lens is a flat surface, the other surface is a curved surface, and the curved surface has a center vertex. Except for the other part is coated with a reflective material, the incident light is incident through the planar portion of the lens, the center portion of the curved portion of the lens provides an ultra-high resolution lens, characterized in that the parabolic surface, and using the same Provide an information recording apparatus.

Description

Ultra high resolution lens and information recording device using the same {HIGH RESOLUTION LENS AND INFORMATION RECORDING DEVIDE USING IT}

The present invention relates to an ultra high resolution lens and an information recording apparatus using the same.

Resolution in a microscope, line width in semiconductor exposure equipment, and storage density in an information storage device are directly related to the degree of light convergence, that is, the spot size of the light. The smaller the light spot, the higher the resolution, the line width of the semiconductor circuit can be reduced, and the information storage density of the information recording apparatus can be increased. The size of the light spot depends on the wavelength of the light, the light convergence angle of the lens, the diameter of the incident beam, and the refractive index of the medium on which the spot is formed, and can be expressed as follows.

d = 0.6λ / n * sinθ

Where d is the diameter of the spot, λ is the wavelength of light, n is the refractive index, and θ is the convergence angle. Therefore, to reduce the light spot, it is necessary to reduce the wavelength, increase the refractive index, and increase the convergence angle. However, the size of the light spot is limited to half the wavelength of light used due to the diffraction limit of the light.

Several methods have been proposed to overcome diffraction limits and obtain smaller light spots. In order to reduce the wavelength of light, the wavelength of 600 nm can be reduced to about 400 nm by using blue laser light. It has also been proposed to reduce spots by using lenses with large refractive indices. A representative example thereof is a solid immersion lens (hereinafter referred to as SIL).

1 shows an optical system used for an information recording apparatus, which is composed of a hemispherical SIL 12 and a primary condensing lens 10, the SIL being adjacent to the surface of the recording medium 14. 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. Light incident on the primary condenser lens is refracted and enters the SIL. Since the focus of the primary condenser lens is at the center of the planar portion of the SIL, the incident light is collected at the center of the SIL planar portion.

The light convergence angle θ is determined by the numerical aperture of the primary condensing lens, and the refractive index n is determined by the material of the SIL. The maximum refractive index of the material used as the SIL is about 2.2, and the sinusoidal value sinθ of the convergence angle due to the numerical aperture of the primary condenser lens can be up to 0.7. Therefore, when light having a wavelength λ of 632 nm is used, the minimum spot size that can be realized by SIL is about 246 nm.

In order to record data (bits) on the disc using the SIL, as shown in FIG. 2, the SIL 20 is brought close to the surface of the recording medium 22 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 a bit 24 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, the optical system using SIL can overcome the diffraction limit of light and reduce the light spot, but has the following problems.

In general, as shown in FIG. 3, the optical lens 30 generates an aberration 32 in which light is not collected at one point. The aberration has a characteristic that the higher the magnification of the lens is, the larger the magnification is. 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, since the hemispherical SIL using the near field must be close to the recording medium or the measurement object, there is a risk of collision. Since the base of the SIL has a diameter of about 1 mm and the distance between the SIL and the recording medium should be maintained at about 50 nm, the SIL is inclined slightly with respect to the medium because of the relatively large plane (20,000 times the diameter gap) compared to this interval. If you lose, you'll crash.

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 addition, when contaminants such as dust intervene in the minute gap between the SIL and the recording medium, there is a problem that spots are difficult to be formed by blocking the light path.

Accordingly, an object of the present invention is to provide an optical system that does not require a primary condenser lens. Another object of the present invention is to reduce the risk of collision between the lens and the recording medium in the near field information recording apparatus. In addition, the present invention solves the difficulty in forming spots by blocking the path of light when contaminants such as dust intervene in the minute gap between the lens and the recording medium.

1 is a schematic diagram showing a conventional information recording apparatus using SIL.

2 is a schematic diagram illustrating data recording by SIL.

It is a schematic diagram explaining the aberration by a lens.

4A and 4B are a cross-sectional view and a plan view showing an ultra high resolution lens of the present invention.

Figure 5 is a schematic diagram showing the path of light in the ultra-high resolution lens of the present invention.

6 is a schematic diagram showing a movement path of light incident on a parabolic surface.

7 is a schematic diagram illustrating total reflection between two media having different refractive indices.

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

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

FIG. 10 is a cross-sectional view illustrating that a focus is formed on a recording medium in the embodiment of FIG. 9.

11 is a schematic diagram illustrating an information recording method using the ultra high resolution lens of the present invention.

12 is a plan view schematically showing a part of the information recording apparatus.

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

40: Super high resolution lens 41: Curved surface of the lens

42: plane of the lens 43: reflective material

44: center vertex of curved surface 45: measured object or recording medium

46: Parallel light 91: The top surface of the lens

92: Edge of the lower surface of the lens 93: Center of the lower surface of the lens

The ultra-high resolution lens of the present invention is characterized in that one side of the lens is a plane, the other is a curved surface, and the curved surface is coated with a reflective material except for the center vertex. The incident light is incident through the planar part of the lens, and the incident light is reflected by the reflective material of the curved part, and is totally reflected at the planar part to collect at the vertex of the center of the curved surface of the lens. In the curved portion of the lens, the center portion is preferably flat and the edge is curved. This form allows the focal point of the lens to be formed below the lens bottom.

The curved surface may be spherical or aspherical, and in order to reduce aberration, it is preferable that it is a parabolic surface.

Since the lens of the present invention can obtain high resolution without the need for a separate condenser lens, the lens can be reduced in size in various applications. In addition, even if the surface of the lens is in close proximity to other objects, there is a small risk of collision with the surface of the object to cause damage. The present invention can be applied to various fields such as an optical information recording apparatus.

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

4A shows an ultra high resolution lens according to an embodiment of the present invention. 4B shows the underside of the lens shown in FIG. 4A. As shown in the figure, the ultra-high resolution lens 40 according to the exemplary embodiment of the present invention has one surface 42 in a flat surface and the other surface 41 in a curved surface. The reflective surface 43 is coated on the curved surface so that light is not transmitted and is reflected, and the central peak 44 near the curved surface does not coat the reflective material as a light exit portion. The object to be measured or the recording medium 45 is positioned close to the lower surface of the lens, that is, the curved surface.

The movement path of light incident on the lens is shown in FIG. 5. The parallel light 46 incident on the lens 40 passes through the plane 42 of the upper portion of the lens and is reflected by the curved surface 41. The light reflected from the curved surface is incident to the plane again. If the incident angle is greater than the critical angle, the light incident from the curved surface to the plane is totally reflected and then incident to the curved surface again. After parallel light enters the plane of the lens and undergoes several reflections inside the lens, the object to be measured or the recording medium 45 through the light exit portion of the vertex 44 of the lens without the reflective material 43 coated thereon. Is passed on.

If the curved surface of the lens is a parabolic surface, the aberration can be reduced. Referring to FIG. 6, which shows the parabolic mirror 50, when parallel light is incident on the parabolic surface 53 coated with a reflective material, the incident light 55 is reflected from the parabolic surface 53 due to the characteristics of the parabolic surface 53. Gathered at Thus, unlike ordinary optical lenses, the aberration of the parabolic lens coated with the reflective material is ideally zero. Since the aberration becomes zero, the condensing performance of the lens is improved.

7 illustrates the total reflection of light. As shown, total reflection of light is a phenomenon that occurs when light travels from a medium having a large refractive index to a small medium. Looking at the incident light 63 on the left, it can be seen that some of the light is transmitted but some is reflected when the medium 1 (60) having a large refractive index is advanced to the medium 2 (61) having a refractive index smaller than the medium 1. The incident light 64 on the right side does not proceed from the medium 1 (60) to the medium 2 (61). In this case, it can be seen that the incident angle is larger than the incident light on the left side, and the incident angle at which total reflection can occur is called a critical angle. That is, the light traveling from the medium having a large refractive index to the medium has a small amount of transmitted light and reflected light when the incident angle is small, but when the incident angle becomes larger than the critical angle, all incident light is reflected like reflection on the mirror surface. The critical angle of total reflection is related to the refractive index of the medium and is determined as follows.

θ = arc sin (1 / n)

θ represents the critical angle and n represents the refractive index of the medium.

8 illustrates an ultra high resolution parabolic lens according to an embodiment of the present invention. As shown, the incident parallel light 46 passes through the planar portion 42 of the lens 40 and is reflected from the parabolic surface 41 coated with the reflective material 43 to face the focal point 47 of the parabolic surface. When light propagates toward the focal point of the parabolic surface is incident at a large angle to the planar portion 42 of the lens, the light is reflected back to the parabolic surface 41 by the total reflection described above. By total reflection, the parabolic focal point is formed at the vertex 49 in the center of the parabolic plane which is a symmetrical position with respect to the plane. Therefore, light incident in parallel to the lens is collected at the parabolic vertices.

9 illustrates another embodiment of the present invention. The upper surface 91 of the lens is flat and the lower surface is basically curved. The difference from the above embodiment is that the lower surface of the lens is cut out partly. In other words, the lower edge 92 of the lens is curved, and the center 93 is flat. The bottom surface is coated with a reflective material, and the center apex of the bottom surface is not coated with a reflective material. This structure has a position 93 at which the focal point of the lens is formed below the lens bottom surface as compared with the previous embodiment. The optical system using the near field is very close to the recording medium or the object to be measured, and the area where the focus of light is formed in the optical system is exposed to the atmosphere. If contaminants such as dust enter the area where focus is formed, light is blocked. Since the size of the light spot is a very small size of less than a micrometer, even if fine dust is intervened on the optical path, most of the light is blocked, which can cause a big problem in recording information or measuring an object. In the embodiment of FIG. 9, since the position where the focus of the light is formed is lower than the bottom surface of the lens, the light is blocked by the contaminant.

FIG. 10 shows that the lens shown in the embodiment of FIG. 9 is adjacent to the recording medium. A protective film 103 is formed on the surface of the recording medium 102, and a recording layer 104 is formed below it. Since the focus of the lens 100 is formed below the bottom surface of the lens, the focus may be formed on the recording layer of the recording medium. That is, the air layer between the lens and the recording medium is not in focus, so that the focal point is formed under the surface of the recording medium. Therefore, even if foreign matter such as dust is interposed between the recording medium and the lower surface of the lens, the light does not have a great influence on the focus formation.

In the near field optical recording apparatus, since the recording layer must exist very close to the optical spot, the thickness of the recording layer protective film of the recording medium must be very thin. If the protective film is thin, light spots are formed on the surface of the recording medium, and the temperature of the recording layer on the surface of the recording medium becomes high. Therefore, the lubricating film of the recording layer can be easily damaged. However, the lens of the form cut out of the bottom surface of the present invention can prevent a large increase in the temperature of the recording layer because light spots can be formed under the surface of the recording medium even if the thickness of the protective film is increased.

The ultra high resolution lens of the present invention can be used in various technical fields. 11 illustrates an information recording method using the ultra high resolution lens of the present invention. As shown, when the recording medium 132 is close to the bottom surface of the lens 131 by about 50 nm, the light energy 133 incident from the light source (not shown) to the lens is transferred to the medium surface by the optical near field effect. Light energy heats the local region 134 on the surface of the medium. Bits may be formed on the surface of the media by local heating. That is, data can be recorded. 12 schematically shows a part of the information recording apparatus. The information recording apparatus is composed of a recording medium 144 and a head portion. The head portion is composed of a suspension 142, a suspension support 141, and a head slider 143. The lens of the present invention is mounted on the slider to be in close proximity to the recording medium. The slider floats at intervals of several tens of nanometers from the surface of the recording medium due to air pressure during the high speed rotation of the recording medium. Although not shown, the apparatus includes a light source for supplying light to the lens.

In addition, the present invention can be used not only for the optical information recording device but also for measuring devices, semiconductor equipment, etc., and can be used for various purposes in combination with various light supply means.

As described above, according to the present invention, it is possible to record near-field light information using only one lens without a separate light collecting lens. Since the condenser lens of a large magnification is unnecessary, the deterioration of condensing performance due to aberration can be prevented. In addition, since the underside of the lens is curved, the risk of collision with the surface of the recording medium can be reduced. In addition, the use of only a single lens makes the device small in volume and simple, thus facilitating manufacture. In particular, even if a contaminant such as dust enters the minute gap between the lens and the recording medium, the light path is not blocked, and light spots may be formed below the surface of the recording medium, thereby greatly improving the reliability of the near field information recording apparatus. Can be.

Claims (8)

A condenser lens for condensing light incident from a light source, One side of the lens is a flat surface, the other side includes a curved surface, the surface including the surface is coated with a reflective material other than the central vertex, Incident light is incident through the planar portion of the lens, The center of the curved portion of the lens is a super high resolution lens, characterized in that the flat surface and the edge. The ultra high resolution lens according to claim 1, wherein the curved surface of the edge of the curved portion of the lens is spherical. The ultra-high resolution lens according to claim 1, wherein the curved surface of the edge at the curved portion of the lens is a parabolic surface. The ultra-high resolution lens of claim 1, wherein the light incident through the planar portion of the lens is reflected by the reflective material of the curved portion, and is totally reflected at the planar portion. The ultra-high resolution lens of claim 1, wherein the light incident through the planar portion of the lens is reflected by the reflective material of the curved portion, and is totally reflected by the planar portion to collect at a vertex at the center of the curved portion. A device for recording information using light, A slider for mounting a condensing lens, a suspension connected to the slider, a suspension support for supporting the suspension, and a head for recording or reproducing information on a recording medium; Including a light source for generating light, One side of the condenser lens is a plane, and the other side includes a curved surface, and the surface including the curved surface is coated with a reflective material except for a central vertex. Incident light generated from the light source is incident through the planar portion of the lens, And the center portion of the curved portion of the lens is flat and the edge is curved. 7. An information recording apparatus according to claim 6, wherein said slider does not have a separate condenser lens. The information recording apparatus according to claim 6, wherein the curved surface of the edge of the curved portion of the lens is a parabolic surface.