KR100404084B1 - Lens for optical recording and reproducing system - Google Patents

Abstract

According to the present invention, an incidence part is formed at the center of the upper surface of the lens, and a reflection surface is formed around the incidence portion. The periphery is a transmissive surface, the lower surface of the lens is a paraboloid, the center of the parabolic surface is a flat surface, the part except the flat surface of the parabolic surface is composed of a lower lens which is a reflective surface, the lower and lower lenses of the upper lens The upper surface of the contact with each other, the bonding surface between the two lenses provides an optical lens for optical recording and reproducing system, characterized in that the reflecting means is formed in the center.

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 improve the condensing performance and recording density in an optical recording and reproducing system by providing an optical system with a low aberration of the focusing lens and a large convergence angle of light incident on the focusing lens.

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 example of a parabolic mirror.

2B is a cross-sectional view showing an example of a parabolic lens.

Figure 2c is a cross-sectional view showing an embodiment of the parabolic lens according to the present invention.

3 is a cross-sectional view showing an embodiment of the annular beam forming lens according to the present invention.

4A is a cross-sectional view showing an example of combining the lenses of the present invention.

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

5 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 ***

40: incident beam 41a: upper lens 41a

42a: lower lens 43: incident part

45: Slope part 46: Parabolic surface

47a: Reflective material 48: Flat surface

49: convergence point

According to the present invention, an incidence part is formed at the center of the upper surface of the lens, and a reflection surface is formed around the incidence portion. The peripheral portion is a transmissive surface, the lower surface of the lens is a paraboloid (paraboloid), the center of the parabolic surface is a flat surface, the portion of the parabolic surface except the flat surface is composed of a lower lens which is a reflective surface,

The lower surface of the upper lens and the upper surface of the lower lens are in contact with each other, and the bonding surface between the two lenses is provided with an optical lens for an optical recording and reproducing system, characterized in that formed in the center.

The incident part of the upper lens is indented in the center of the lens upper surface, and the incident light diverges to the lower surface of the upper lens. The emitted light is reflected from the lower surface of the upper lens and travels to the reflective surface around the incident portion of the upper lens upper surface.

The reflecting surface around the incidence portion of the upper lens is inclined at a constant angle so that the reflected light propagates to the lower lens in a direction parallel to the initial incident beam, ie, in a direction perpendicular to the upper surface of the lower lens.

At the center of the bonding surface between the upper lens and the lower lens, an air layer or a reflective material is formed as a reflecting means at the center.

On the flat surface in the center of the parabolic surface of the lower lens, a point where the focal point of the parabolic surface is symmetrical with respect to the lower lens upper surface is located. Light incident on the lower lens is first reflected at the parabolic surface, secondly at the upper surface of the lower lens, and then converges to all the symmetry points.

In the optical recording and reproducing system using the optical lens of the present invention, the incident light of the upper lens proceeds to the incident part of the upper lens and finally converges on the flat surface of the lower lens and photomagnetically interacts with the recording medium located close to the lower surface of the lens. Done.

Since the lower surface of the lower lens is formed as a parabolic surface, it is possible to eliminate the spherical aberration of the light that finally converges, and to minimize the spot size of the light used for optical recording and reproduction.

In the optical lens of the present invention, the light incident on the lens due to the cone-shaped incidence portion formed on the upper lens is not used for optical recording and reproducing, so that the optical loss can be suppressed from occurring. In addition, the optical system required for the near field optical recording system may be implemented using only a focusing lens without an objective lens, thereby significantly reducing 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 general, in spherical lenses, spherical aberrations in which light does not converge to one point occur. Due to such spherical aberration, the light passing through the lens increases in spot size converged at the focus. The larger the spot size of the converging light, the smaller the recording density in the optical recording system.

In the present invention, to eliminate spherical aberration by using a parabolic lens instead of a spherical lens. 2A is a schematic diagram showing a cross section of a parabolic mirror. The parallel beams 22 incident on the parabolic mirror 20a all converge at the focal point 24a of the parabolic surface due to the characteristics of the parabolic mirror. In this case, the converged light has no spherical aberration, and therefore the spot of light becomes very small.

The present invention applies the characteristics of such a parabolic mirror to form a parabolic lens as one component. 2B is a cross-sectional view showing an example of a parabolic lens. The bottom surface 20b of the parabolic lens is coated with a reflective material so that all light incident to the bottom surface is reflected. If, as shown in the figure, the light reflected from the lower surface of the lens is reflected back from the lens upper surface 21, a point inside the lens symmetrical with the focal point of the parabolic surface with respect to the upper surface of the lens (hereinafter referred to as a convergence point) 24b. Will gather all together. At the convergence point 24b, the light of very small spot without spherical aberration is concentrated like the light converged at the focus of the parabolic mirror in FIG. 2A. However, the parabolic lens shown in the drawing needs a means for the incident light reflected from the lower surface of the lens to be reflected again and concentrated at the convergence point inside the lens.

FIG. 2C shows a parabolic lens provided with reflecting means on the upper surface of the lens according to the present invention. The difference from the parabolic lens shown in FIG. 2B is that the reflective material is coated at the center of the lens upper surface 21 and the flat surface 25 is formed at the center of the lower surface of the lens. The reflective material on the upper surface of the lens reflects light 22 incident on the lens from the lower surface of the lens 20c coated with the reflective material, and then is reflected on the upper surface of the lens. The light, which has undergone two reflection processes, is concentrated at the convergence point 24c on the lower surface of the lens without spherical aberration. In FIG. 2B, the convergence point is present inside the lens, but in FIG. 2C, the central portion of the lower surface of the lens is flattened so that the convergence point is positioned on the lower surface of the lens. This parabolic lens allows the incident light to converge at the convergence point located on the lower surface of the lens so that the light passing through the lens in the optical recording system is within a very small distance, for example, within a few nanometers on the surface of the recording medium. Get close.

However, in the parabolic lens illustrated in FIG. 2C, only the light at the edge of the light incident from the light source is incident, and the central light 22 ′ is not incident into the lens by the reflective material on the upper surface of the lens. Therefore, a considerable amount of light generated from the light source is lost, and the light efficiency is lowered. If the parabolic lens is provided with means for converting light generated from a light source into an annular beam, it is possible to concentrate all the light without spherical aberration at the convergence point without light loss. To this end, the present invention includes, as another component, a means for forming an annular beam in addition to the parabolic lens.

3 is a cross-sectional view showing an example of the annular beam forming lens according to the present invention. The incident part 33 is formed in the center on the lens upper surface, and the periphery 31 is inclined by a fixed angle. The inclined portion is coated with a reflective material. The lower surface of the lens is a flat surface and a reflective material 35 is coated on the center thereof. The incident part has an inverted triangle shape in cross section, but is actually formed in a cone shape and has a vertex 34 formed at the lower center thereof.

The light 30a incident to the lens vertically from the light source is all reflected by the reflecting material 35 on the lower surface of the lens and incident to the inclined region 31 on the upper surface of the lens, and then reflected and lowered in parallel to the initial incident direction. It passes through the left and right regions 32 of. As a result, the light passing through the incident part of the lens passes through the two reflection processes and passes through the lens as an annular light 30b in the center.

In the annular beam forming lens of FIG. 3, the light incident on the lens does not go back to the outside, but all the light passes through the lower surface of the lens. The angle of the inclined portion 31 and the inclined portion 33 on the upper surface of the lens is appropriately adjusted so that the light passing through the lower surface of the lens is perpendicular to the lower surface of the lens, that is, the annular parallel beam 30b.

As shown in the figure, the incidence portion may have a cross section of the inclined portion 34 in a curved line rather than a straight line in order to change the diffusion angle of light passing through the incidence portion. If the cross section of the inclined portion is curved, the inclined portion may be formed into a spherical or aspherical surface similar to a cone.

The annular beam thus formed can be used as a means for supplying an annular parallel beam to the parabolic lens of the present invention described in FIG. 2C.

An embodiment in which the annular beam forming lens and the parabolic lens are combined is shown in FIG. 4A. The embodiment of the present invention shown in the drawing is composed of an upper lens and a lower lens, the upper lens 41a is an annular beam forming lens, and the lower lens 42a corresponds to a parabolic lens. The lower surface of the upper lens is in contact with the upper surface of the lower lens, and the reflective material 47a is formed at the center on the surface where the two lenses contact. The light 40 generated from the light source passes vertically through the incident part 43 of the upper lens and then is reflected by the reflective material on the lower surface of the upper lens and reflected by the inclined portion 45 of the upper lens upper surface. After two reflections, the incident beam passes through the lower surface of the upper lens in parallel with the angle of incidence and enters the lower lens as an annular light. Light incident on the lower lens is reflected by touching the parabolic surface 46, which is a lower surface of the lower lens, and reflected again by the reflecting material 47a on the upper surface of the lower lens, converging point 49 positioned on the flat surface 48 in the center of the lower lens. Is focused on). Light concentrated at the convergence point has no spherical aberration, so the spot of light is very small. The present invention can provide an optical lens for an optical recording system in which the beam size is small and a separate objective lens is not required by the combination of the upper lens forming the annular beam and the parabolic lens forming the light without spherical aberration.

The convergence angle of the light in the lens may be increased according to the size of the lens, specifically, the angle of the incidence portion and the inclination portion of the upper lens, the shape of the parabolic surface of the lower lens, and the like. Therefore, it is possible to further reduce the numerical aperture of the lens to reduce the spot size of light as much as possible.

On the other hand, the light passing through the incident part 43 and finally concentrated at the converging part 49 on the lower surface of the lower lens interacts with the recording medium (not shown) located close to the lower surface of the lens. If the surface of the recording medium and the lower surface of the lens are inclined due to the shaking of the system, the surface of the recording medium may be inclined, and the surface of the recording medium may have a physical defect or the distance between the recording medium and the lens may be difficult to transmit the optical signal. In the present invention, the flat surface 48 of the lower surface of the lower lens reduces the area where the lens lower surface and the surface of the recording medium come close to each other.

Another embodiment of the combination of the upper lens forming the annular beam and the parabolic lens forming the light without spherical aberration will be described with reference to FIG. 4B.

As in the embodiment of FIG. 4A, the lower surface of the upper lens and the upper surface of the lower lens are in contact with each other. In contrast to FIG. 4A, an air layer 47b is formed at the center of the bonding surface of the upper lens and the lower lens. Such an air layer totally reflects light incident from the upper lens or the lower lens into the air layer without a reflective material. The light passing through the incident part of the upper lens is totally reflected by the air layer 47b and reflected back from the inclined portion 45 of the upper lens, and then is incident vertically into the lower lens. Total reflection at 47b) and finally converge at convergence point 49.

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. 5 is a cross-sectional view showing an example of a near field optical recording system.

In the deck (not shown), the central portion of the disc 59, which is a recording medium, is mounted to the spindle motor 58 so as to be rotatable. The other side of the deck is provided with a recording and reproducing apparatus. The light generated from the light source 51 passes through the collimator lens 52 and is converted into a parallel beam and then passes through the beam splitter 53 and through the optical path converting means 56 through the optical lens 57 of the present invention. It reaches the surface of the recording medium in the state of convergence with light of diameter. The light reflected from the recording medium passes through the lens 57 and the light path is changed by the change means, and then proceeds from the beam splitter to the sensor lens 54 to finally reach the light sensing means 55.

Although the size of the lens is relatively large in the figure, it is actually mounted on the head part (not shown) in a very small size in the system, and the lens and the recording medium are closely spaced at very fine intervals of several nanometers. Since the size and weight of the lens is very small, the servo of the lens is very easy in the present system, and the lens of the present invention can be applied to both the integrated pickup and the separate pickup. 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, 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. In addition, the weight of the head portion can be reduced, and the incident pupil of the light source can be made small, so that power consumption of the driving means and the system as a whole can be greatly reduced. 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)

The upper part of the lens is formed with an incident part through which light is incident from the outside, a reflecting surface is formed around the incident part, and a peripheral part of the lower surface of the lens is an upper lens which is a transmission surface through which light is transmitted; The periphery of the upper surface of the lens is a transmissive surface, the lower surface of the lens is a paraboloid (paraboloid), the center of the parabolic surface is a flat surface, except for the flat surface of the parabolic surface is composed of a lower lens, which is a reflective surface, An optical lens for an optical recording and reproducing system, characterized in that the lower surface of the upper lens and the upper surface of the lower lens are in contact with each other, and a reflecting means is formed at the center of the bonding surface between the two lenses. The optical lens for an optical recording and reproducing system according to claim 1, wherein the incidence portion of the upper lens is a form in which the lens upper surface is indented in a cone shape. The optical lens for an optical recording and reproducing system according to claim 1, wherein the reflecting surface around the incident portion of the upper lens is inclined at a constant angle. The optical lens of claim 1, wherein the lower surface of the upper lens and the upper surface of the lower lens are flat surfaces. The optical lens for an optical recording and reproducing system according to claim 1, wherein an air layer is formed at the center of the bonding surface between the upper lens and the lower lens as reflecting means. The optical lens for an optical recording and reproducing system according to claim 1, wherein the bonding surface between the upper lens and the lower lens is coated with a reflective material at the center thereof as a reflecting means. The optical lens for an optical recording and reproducing system according to claim 1, wherein a point in which the parabolic surface is symmetrical with respect to the upper surface of the lower lens is positioned on a flat surface in the center of the parabolic surface of the lower lens. The optical lens for an optical recording and reproducing system according to claim 1, wherein the light incident on the upper lens is converted into an annular beam and incident on the lower lens. The optical lens of claim 8, wherein light incident from the upper lens to the lower lens is incident perpendicularly to an upper surface of the lower lens.