KR20070106361A - Recording/playback apparatus and medium - Google Patents

Abstract

A record playing device, and a recording medium are provided to manufacture a lens which is suitable for playing a record by using a near field, easily and to be used when the recording medium includes a protection layer and plural recording layers. A record playing device comprises a lens unit(40), a light receiving unit(60,70), and a control unit(90). The lens unit includes a near field forming lens and an objective lens compensating spherical aberration of the near field forming lens, and irradiates a beam emitted from a beam source, to a recording medium(50). Height of the circular near field forming lens is larger than a radius of a globe and smaller than a diameter thereof. The recording medium includes at least one recording layer and a projection layer blocking the recording layer from an outside. A refractive index of the protection layer is larger than the number of effective apertures for the lens unit irradiating the beam to the recording medium.

Description

Recording and playback apparatus and recording medium {Recording / playback apparatus and Medium}

1 is a schematic cross-sectional view showing a part of an optical pickup in a near field optical recording apparatus using a general near field.

Fig. 2 is a block diagram showing the structure of the optical pickup of the recording / reproducing apparatus constituting the first preferred embodiment of the present invention.

Fig. 3 is a schematic cross sectional view showing the lens portion together with the recording medium of the recording and reproducing apparatus constituting the first preferred embodiment of the present invention.

4A to 4C are cross-sectional views showing the near field forming lens constituting the recording and reproducing apparatus of the present invention.

5 is a correlation diagram showing a change in spherical aberration according to the change in thickness d of the near field forming lens.

6 is a schematic cross-sectional view of a lens unit including a near field forming lens and an objective lens that compensates for spherical aberration of the near field forming lens.

Fig. 7 is a block diagram showing the structure of the optical pickup of the recording / reproducing apparatus constituting the second preferred embodiment of the present invention.

Fig. 8 is a schematic cross sectional view showing a part of a recording medium of a recording / reproducing apparatus having an aberration compensating unit which constitutes a preferred embodiment of the present invention.

9 is an enlarged partial sectional view and a perspective view of a cross section of a recording medium.

* Description of the symbols for the main parts of the drawings *

10: light source 20, 30: separation synthesis unit

35: aberration compensation unit 40: lens unit

41: objective lens 42: near field forming lens

50: recording medium 51: recording layer

52: protective layer 53: spacer

60: first light receiver 70: second light receiver

80: signal generator 90: controller

100: optical system

The present invention relates to a recording / reproducing apparatus and a recording medium, and more particularly, to a recording / reproducing apparatus suitable for use in a near field and a recording medium used therein.

A recording and reproducing apparatus using light such as a laser beam records data on or reproduces recorded data using an optical disk such as a compact disc (CD) or a digital versatile disc (DVD) as a recording medium. The information recording medium used for this is actively researched for high density according to the demand for high quality video processing and the development of video extrusion technology. However, due to the optical and physical limitations caused by the conventional optical recording method or magneto-optical recording method, the recording capacity has not reached a satisfactory level.

In the above recording medium, the recording density may depend on the diameter of light irradiated onto the recording layer of the recording medium. In other words, the smaller the diameter of the focused light irradiated onto the recording medium, the higher the recording density. At this time, the diameter of the focused light is largely determined by two factors. One is the number of effective apertures (Numeric Aperture, NA), which is the performance of a lens used for focusing light, and the other is the wavelength of light focused to the lens.

Since the focused light increases the recording density as the wavelength is shorter, light having a shorter wavelength is used as a method for increasing the recording density. In other words, when blue light is used as compared with red light, the recording density can be further increased. However, when a general lens is used, there is a limit to reducing the diameter of the light because there is a diffraction limit of the light. Accordingly, a near field recording (NFR) device using near field optics capable of storing or reading information in units smaller than the wavelength of light has been developed.

1 is a simplified diagram partially showing a lens and a recording medium for irradiating light onto a recording medium in one embodiment of a near field optical recording device. As shown, the lens portion of the near field optical recording device may be configured such that the light focused by the objective lens 1 passes through the hemispherical lens 2 having a high refractive index. The light incident on the hemispherical lens 2 at an angle greater than or equal to the critical angle is totally reflected while exiting the hemispherical lens 2 having a high refractive index, and forms light having a fine intensity on the surface of the lens. That is, it forms an evanescent wave below the diffraction limit. The dissipation wave enables high resolution which was impossible due to the diffraction limit of the wavelength in the recording device using one lens. At this time, the hemispherical lens 2 and the recording medium 3 can be approached at very close intervals within 100 nm to form a near-field to store high-density bit information by the dissipation wave. In this case, the region forming the dissipation wave is called a near field, and in order to maintain the near field, the hemispherical lens 2 and the recording medium 3 preferably maintain an interval of 100 nm or less forming the near field. Here, for convenience, the area having the original wavelength out of the near field corresponding to the near field is called a far-field.

However, the prior art as described above has the following problems.

That is, there is a difficulty in manufacturing a lens suitable for the near field recording and reproducing apparatus which increases the recording density while minimizing the manufacturing error.

In addition, since the near field optical recording apparatus uses a dissipation wave having a very small wavelength, it is difficult to define a recording medium suitable for this.

In addition, when the recording medium used in the near field optical recording device includes a plurality of recording layers or has a protective layer on the surface, there is a problem that it is difficult to control the light irradiated onto the recording medium to be accurately irradiated onto each recording layer. .

Accordingly, the present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a lens suitable for a near field recording and reproducing apparatus, and a recording and reproducing apparatus having the lens.

Another object of the present invention is to provide a recording medium having a protective layer and a recording / reproducing apparatus which can use the recording medium.

It is another object of the present invention to provide a recording medium having a plurality of recording layers and a recording / reproducing apparatus which can use the recording medium.

According to a feature of the present invention for achieving the above object, the recording and reproducing apparatus of the present invention includes a near field forming lens and an objective lens for compensating spherical aberration of the near field forming lens to record light emitted from a light source. And a lens unit for irradiating the medium, a light receiving unit for receiving the reflected light after being irradiated to the recording medium, generating a signal corresponding to the received reflected light, and a control unit for generating a control signal through the generated signal. It features.

The near field forming lens may be a part of a spherical lens having a height greater than a radius of a sphere and smaller than a diameter, and the objective lens may have spherical aberration of the same size in the opposite direction to the spherical aberration of the near field forming lens.

The effective numerical aperture of the lens portion is preferably smaller than the refractive index of the protective layer of the recording medium used in the recording and reproducing apparatus. For example, when the near field forming lens is made of glass, the effective numerical aperture of the lens portion is preferably smaller than 1.85, which is smaller than the refractive index of the protective layer of the recording medium. More preferably, the effective numerical aperture of the lens portion is greater than or equal to 1.6 and less than or equal to 1.85.

The recording and reproducing apparatus may further include an aberration compensating unit for varying the position of the focal point irradiated from the lens unit to the recording medium. The aberration compensator may include a lens movable in at least one optical axis direction. For example, the first lens may include a fixed first lens and a second movable lens, and the second lens may be moved in an optical axis direction to change the path of the light.

The recording medium of the present invention is a recording medium used in a near field, and includes at least one recording layer and a protective layer for blocking the recording layer from the outside, wherein the refractive index of the protective layer is effective for the lens unit for irradiating light to the recording medium. It is characterized by being larger than the numerical aperture.

Here, the protective layer is provided on the surface of the recording medium and preferably has a thickness of 10 nm to 25 µm. The recording medium may further include a spacer between the recording layers or spaced apart from the recording layer and the protective layer. The thickness of the spacer is preferably 1 µm to 25 µm, and the refractive index of the spacer is also larger than the effective numerical aperture of the lens portion. In addition, the sum of the thickness of the protective layer and the spacer is preferably at most 25㎛.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of a recording / reproducing apparatus and a recording medium according to the present invention as described above will be described in detail with reference to the accompanying drawings. In adding reference numerals to the components of the following drawings, the same components are used the same reference numerals as much as possible even if they are displayed on different drawings.

In the recording and reproducing apparatus constituting the first preferred embodiment of the present invention, the optical pickup is configured as shown in FIG. The optical system 100 of the optical pickup includes the light source 10, the separation and synthesis units 20 and 30, the lens unit 40, and the light receiving units 60 and 70.

The light source 10 is preferably a laser or the like having good directivity. Therefore, the light source 10 is specifically a laser diode. The light emitted from the light source 10 to be irradiated onto the recording medium is preferably parallel light. Therefore, it can be configured to include a lens, such as a collimate, to parallel the path of light on the path of light emitted from the light source.

The separation synthesis units 20 and 30 separate portions of light incident in the same direction or synthesize paths of light incident in different directions. In the present embodiment, since the first separation synthesis unit 20 and the second separation synthesis unit 30 are provided, each of them will be described. The first separation synthesis unit 20 is a portion that passes a part of the incident light and reflects some of the incident light (in this embodiment, the first separation synthesis unit 20 is a non-polarized beam splitter, NBS). In addition, the second separation synthesis unit 30 is a portion that passes only polarization in a specific direction according to the polarization direction (in this embodiment, the second separation synthesis unit 30 is a polarized beam splitter (PBS)). For example, when using linear polarized light, the second separation composition part 30 may be configured to pass only the polarization component in the vertical direction and reflect the polarization component in the horizontal direction. Alternatively, it may be configured to pass only the polarization component in the horizontal direction and reflect the polarization component in the vertical direction.

The lens unit 40 is a portion for irradiating the recording medium 50 with the light emitted from the light source 10. Specifically, as shown in FIG. 3, the lens unit 40 includes a near-field forming lens 42 provided on a path through which the objective lens 41 and the light passing through the objective lens 41 enter the recording medium. It includes. That is, by providing a near field forming lens 42 having a high refractive index in addition to the objective lens 41, the numerical aperture of the lens unit 40 is increased to thereby form a dissipation wave.

Herein, the near field forming lens 42 will be described in detail as follows. The near field forming lens 42 is preferably a solid immersion lens (SIL). The near field forming lens 42 is formed by cutting a spherical lens, and the height of the formed lens is preferably larger than the radius of the spherical lens and smaller than the diameter. This will be described in detail with reference to the drawings of FIGS. 4 and 5 as follows.

4 shows an example of a near field forming lens 42 formed by cutting one end of a spherical lens, and FIG. 5 shows spherical aberration according to the thickness d of the cut near field forming lens 42.

By cutting one end of the spherical lens, as shown in FIG. 4, the near field forming lens 42 having various sizes d may be obtained. At this time, the spherical aberration according to the thickness of the near-field forming lens 42 is as shown in Figure 5 (spherical aberration in each case shown in (a), (b), (c) of Figure 4 is d1, d2) and at d3 respectively). As shown, there is no spherical aberration when the thickness of the near field forming lens 42 is d1 or d3, which is referred to as spherical aberration point. Therefore, by using the near-field forming lens 42 having a thickness without spherical aberration as shown in FIG.

However, the hemispherical lens shown in FIG. 4 (a) has a relatively low numerical aperture (NA). The numerical aperture (NA) means the performance of the lens, the numerical aperture (NA) is defined as nsin θ in the hemispherical lens of FIG. Where n is the refractive index of the medium through which light passes, and θ is the maximum value of the angle of light passing through the lens with the optical axis. That is, when the refractive index n or the angle θ of the medium is large, the numerical aperture NA becomes large and the resolution for identifying two adjacent points also increases.

On the other hand, the numerical aperture NA is defined as n ² sin θ in the ultra-spherical lens of 4 (c). Therefore, the ultra hemispherical lens of Fig. 4C has a larger numerical aperture NA than the hemispherical lens of Fig. 4A, and the ultra hemispherical lens is preferred in the near field recording / reproducing apparatus.

However, the ultra hemispherical lens shown in FIG. 4 (c) has a disadvantage in that it is difficult to manufacture. As shown in FIG. 5, the spherical aberration shows a sudden change in slope at the d3 position representing the hyperspherical lens. That is, the ultra hemispherical lens has a large error in spherical aberration if there is a manufacturing error in thickness. Therefore, since the hemispherical lens has to be cut to have an accurate thickness, manufacturing is difficult.

Therefore, as shown in Fig. 4 (b), it is necessary to manufacture and use the near field forming lens 42, which has a larger numerical aperture NA and is easier to manufacture than the hemispherical lens. In this case, spherical aberration of the near field forming lens 42 of FIG. 4B may be compensated using the objective lens 41.

FIG. 6 shows the lens unit 40 which compensates for the spherical aberration of the near field forming lens 42 having a thickness of about d2 as shown in FIG. 4 (b) by using the objective lens 41. The objective lens 41 is designed to have spherical aberration in the opposite direction of the same size as the manufactured near field forming lens 42. Through this, a spherical aberration-compensated, easy-to-manufacturing and large lens unit 40 can be configured. Here, as shown in FIG. 5, a lens having a thickness of about d2 varies along a gentle curve of spherical aberration according to a change in thickness, so that a manufacturing error range also has a small utility.

At this time, the effective numerical aperture NA _eff formed by the objective lens 41 and the near field forming lens 42 is limited when the recording medium has a protective layer. That is, in order to prevent the light irradiated to the recording medium 50 from total reflection at the protective layer of the recording medium 50, the effective numerical aperture NA _eff is preferably smaller than the refractive index of the protective layer. Here, the effective numerical aperture NA _eff means the numerical aperture of the entire lens portion 40 including the objective lens 41 and the near field forming lens 42.

Generally, the refractive index of the protective layer is about 1.6 at a wavelength of 405 nm when using a polycarbonate series. However, the refractive index of the protective layer is about 1.75 to 1.85 using an acrylate (Acrylate) series. That is, when considering the refractive index of the protective layer, the limit of the effective numerical aperture NA _eff corresponds to about 1.75 to 1.85. For example, when the near field forming lens 42 is glass (specifically, the LasF35 or LAM79 having a refractive index of 1.8 or more), the limit value of the effective numerical aperture NA _eff is 1.85. And within the range of the said limit value, the appropriate range of the effective numerical aperture NA _eff for forming the light beam of minimum diameter in the recording medium 50 is _1.6-1.85 .

On the other hand, the effective numerical aperture NA _eff is not limited by the refractive index of the recording medium 50 when the protective layer is not provided on the recording medium 50 so that the recording layer is provided on the surface. Therefore, the near field forming lens 42 can be manufactured using diamond or the like having a high refractive index, and in this case, the effective numerical aperture NA _eff becomes 2.0 or more.

The optical system 100 of the optical pickup including the lens unit 40 is preferably located very close to the recording medium 50. The concrete example will be described as follows. When the lens portion 40 (specifically referred to as a near-field forming lens) and the recording medium 50 are brought close to about 1/4 or less of the optical wavelength (that is, λ / 4), the inside of the lens portion 40 The generated dissipation wave maintains its properties and can be used for recording and reproducing. However, when the distance between the lens portion 40 and the recording medium 50 is greater than λ / 4 or more, the wavelength of the light loses the property of the dissipated wave and returns to the original wavelength. Therefore, in the recording and reproducing apparatus using the near field, the lens portion 40 is maintained so that the distance from the recording medium 50 does not exceed approximately [lambda] / 4. Is the limit of the near field.

In FIG. 2, the light receiving units 60 and 70 receive and photoelectrically convert reflected light to generate an electrical signal corresponding to the amount of reflected light. In the present exemplary embodiment, the light receiving unit includes a first light receiving unit 60 and a second light receiving unit 70 for receiving the separated reflected light, respectively.

The signal generator 80 uses the electrical signals generated by the first light receiver 60 and the second light receiver 70 to control the RF signal, the focus error signal FE, and the track error signal TE. ), And so on.

The controller 90 receives a signal generated by the signal generator 90 and generates a control signal. For example, a control signal for driving an actuator (not shown) for moving the lens unit 40 may be generated by receiving the focus error signal FE generated by the signal generator 90.

Hereinafter, in the pickup constituting the embodiment of the recording and reproducing apparatus, the operation in the optical system 100 will be described in detail based on the traveling direction of the light emitted from the light source 10 and other than the signal flow. .

The light emitted from the light source 10 is incident on the first separation synthesis unit 20, part of which is reflected, and part of the light is incident on the second separation synthesis unit 30. The second separating synthesis unit 30 passes the vertically polarized light component and reflects the horizontally polarized light component from the linearly polarized light (or vice versa). It is preferable that a polarization conversion surface (not shown) is further included on the path of the light passing through the second separation synthesis unit 30, and the polarization conversion surface will be described later in detail.

The light passing through the first separation and synthesis unit 30 is incident on the lens unit 40. The light incident on the objective lens 41 of the lens unit 40 passes through the near field forming lens 42 to form a dissipated wave. Specifically, light incident on the near field forming lens 42 at an angle equal to or greater than the critical angle is totally reflected at the surface of the lens and the surface of the recording medium 50. Light incident on the near field forming lens 42 at an angle not exceeding the critical angle is reflected on the recording layer of the recording medium 50. The dissipation wave generated in this process reaches the recording layer of the recording medium 50 to perform recording / reproducing.

The light reflected by the recording medium 50 again enters the second separation composition part 30 through the lens part 40. At this time, as described above, it is preferable that a polarization converting surface (not shown) is provided on the path incident to the second separation composition part 30. The polarization converting surface converts the polarization directions of the light incident on the recording medium 50 and the reflected light. For example, if a quarter wave plate (QWP) is used as the polarization converting surface, the quarter wave plate polarizes the light incident on the recording medium 50 to the left circle, and the reflected light proceeds in the reverse direction. Polarize. As a result, the reflected light passing through the quarter wave plate is converted in the polarization direction in a direction different from the incident light, and has a difference of 90 degrees from each other. Therefore, when only the horizontal polarization component is passed by the second separation synthesis unit 30, the incident light is reflected by the recording medium 50 to have a vertical polarization component when it is incident on the second separation synthesis unit 30 again. . Therefore, the reflected light of the vertically polarized light component is reflected by the second separating synthesis unit 30, and the reflected light is incident on the second light receiving unit 70.

On the other hand, in the recording and reproducing apparatus of the present embodiment, since the numerical aperture NA of the lens portion 40 is larger than 1, distortion occurs in the polarization direction of light in the process of being irradiated and reflected through the lens portion 40. That is, a part of the reflected light incident on the second separation compound part 30 has a horizontal polarization component due to the distortion in the polarization direction, and passes through the second separation compound part 30. The passed reflected light is incident to the first separation synthesis unit 20. The first separation synthesis unit 20 passes a part of the incident light and reflects the part. The light reflected by the first separation synthesis unit 20 is incident to the first light receiving unit 60.

The first light receiver 60 and the second light receiver 70 generate an electrical signal corresponding to the amount of reflected light received. The signal generator 80 generates an RF signal, a focus error signal FE, a track error signal TE, and the like by using the electrical signal generated by the light receiver. The controller 90 receives a signal generated by the signal generator 80 and generates a control signal. In this way, it is possible to control so that accurate data is recorded or reproduced in the recording and reproducing process.

In the recording and reproducing apparatus constituting the second preferred embodiment of the present invention, the optical pickup is constructed as shown in FIG. That is, in addition to the above-described first embodiment, aberration compensator 35 is further included. Description of the same parts as in the first embodiment will be omitted.

The aberration compensator 35 is a portion for varying the focus of light irradiated onto the recording medium 50. In the recording / reproducing apparatus using the near field, as described above, the lens portion 40 should be kept close to the recording medium 50. Therefore, it is difficult to directly move the lens unit 40 in the axial direction, and the above problem can be solved by using the aberration compensator 35.

The aberration compensator 35 is provided on the optical axis separately from the lens unit 40 and preferably includes at least one movable lens. In this specification, the aberration compensator 35 illustrated in FIG. 8 will be described as an example.

 The aberration compensator 35 is configured to be movable along the optical axis. The position at which light is irradiated onto the recording medium 50 in accordance with the movement of the aberration compensator 35 (for example, from 35a to 35b) moves from the first recording layer 51a to the second recording layer 51b. It is movable.

In this case, the aberration compensator 35 may include two lenses, wherein the first lens is fixed and the second lens may be movable as shown in FIG. 8. In addition, the aberration compensator 35 may be configured by combining a concave lens and a convex lens. The aberration compensator 35 may be modified in various ways.

That is, the position of the focal point irradiated to the recording medium 50 can be changed without changing the position of the lens portion 40 using the aberration compensator 35 as described above. This makes it possible to use the recording medium 50 having the multilayer recording layer even in the near field.

In the recording and reproducing apparatus using the near field, the recording medium used is very thin in thickness and a thin film type recording medium is required. Hereinafter, a recording medium that is suitable for the recording / reproducing apparatus of the present invention and can also be used in other recording / reproducing apparatus will be described in detail.

9 is a perspective view and a partial cross-sectional view showing a recording medium constituting a preferred embodiment of the present invention. As shown, the recording medium 50 according to the present invention preferably has at least one recording layer 51a, 51b, 51c (hereinafter, referred to as 51 in its entirety) and a protective layer 52 for blocking the recording layer from the outside. ) And spacers 53a and 53b spaced apart from each recording layer (hereinafter, all are denoted by 53).

The recording layer 51 preferably means a data processing layer in which data is recorded or reproduced by the light irradiated on the recording medium. The recording medium according to the present invention includes the first recording layer 51a, the second recording layer 51b, and the third recording layer 51c, which can triple the capacity of data to be processed. Here, the number of the recording layers 51 is not limited to this embodiment, and is included in the case where it is located within the depth of focus of the irradiated light.

Since the first recording layer 51a closest to the surface of the recording medium may be damaged due to disturbance, it is preferable to provide a protective layer 52 to block the recording layer 51a from the outside. .

The protective layer 52 is for blocking the recording layer 51 from the outside and may be formed by applying a cured resin or the like to the surface of the recording medium 50. In addition, a lubrication layer (not shown) may be further provided on the protection layer 52, and the protection layer 52 may be provided on each recording layer 51. Since the first recording layer 51a exposed to the outside is preferably cut off from the outside, the embodiment provided on the surface of the recording medium 50 is shown.

The thickness of the protective layer 52 is largely determined in consideration of two factors. First, the protective layer 51 as described above should have the minimum thickness possible. Therefore, the thickness of the protective layer 52 is preferably at least 10nm. The protective layer 52 is resistant to external pollutants when the thickness is 10 nm or more. Since the thinned recording medium 50 for use in the near field has no rigidity, there is a necessity to protect and maintain the shape by using a cartridge. Thus, in the embodiment of the present invention, the protective layer 52 is cured to minimize the recording medium. It can be configured to maintain the rigidity of.

Secondly, the thickness of the protective layer 52 is preferably determined in consideration of the range in which the movement of the lens portion 40 positioned near the recording medium 50 is permitted. As described above, in the recording and reproducing apparatus using the near field, the lens unit 40 and the recording medium 50 maintain a very close distance. More precisely, the preferred distance between the lens portion 40 and the recording medium 50 is about 1/4 of the light wavelength λ to be irradiated. For example, when blue light (a wavelength of approximately 450 to 500 nm) is used, light has a fine interval of about 100 nm.

However, in the process of recording or reproducing data on the recording medium 50, the position of the irradiated light needs to be changed continuously. That is, the horizontal movement of the lens unit 40 for searching the track or moving the track is essential. The horizontal movement of the lens unit 40 is not a big problem in the remote field recording / reproducing apparatus, but the near-field recording / reproducing apparatus has a slight deviation from the horizontal level due to the maintenance of minute intervals. There is a conflicting problem.

Therefore, the thickness of the protective layer 52 should be determined in consideration of the allowable range of the inclination of the lens unit 40, it is preferable not to exceed 25㎛. When the protective layer 52 having a thickness of 25 μm is provided, the range in which the lens unit 40 can be tilted without contacting the recording medium 50 is only 0.07 ° experimentally. This is in consideration of the maximum horizontal degree, when the protective layer 52 or more than the thickness is provided, the lens unit 40 is forced to collide with the recording medium.

Therefore, in consideration of the above factors, in the recording medium 50 of the present invention, the thickness of the protective layer 52 is preferably in the range of 10 nm to 25 mu m.

In addition, the refractive index of the material constituting the protective layer 52 is preferably larger than the effective numerical aperture NA _eff of the lens portion for irradiating light to the recording medium 50 of the present invention. This is to prevent total reflection as described above with reference to FIG. 2.

In the case of the recording medium 50 constituting an embodiment of the present invention including a plurality of recording layers 51, as shown in FIG. 2, spacers 53 spaced apart from each recording layer 51, respectively. It is preferable to have a.

When a plurality of recording layers 51 are included in one recording medium 50, the recording layer 51 is located very close to each other in the thin film type recording medium 50 used in the near field. In this case, each of the recording layers 51 may cause interference that interferes with each other's data processing in recording or reproducing data by using irradiated light. Therefore, it is preferable to place the spacers 53a, 53b between the respective recording layers 51a, 51b, 51c to block the interference. In the present invention, the number of spacers 53 positioned between the recording layers 51 is preferably one less than the number of recording layers 51.

The thickness of the spacer 53 is largely determined in consideration of three factors. First, the thickness of the spacer 53 is determined in a range where interference does not occur between the recording layers 51, and is preferably 1 µm or more. That is, the spacer 53 having a thickness of 1 μm or more can suppress the interaction between the layers, which can be below the current DVD level.

Secondly, as in the case of the protective layer 52 described above, it is preferable that the determination is made in consideration of the range in which the movement of the lens portion 40 located close to the recording medium 50 is permitted. As described above, as described above, the inclination of the lens unit 40 is considered. Therefore, it is preferable that the thickness of the spacer 53 also does not exceed a maximum of 25 μm.

Third, it is preferable to limit the thickness of the spacer 53 to a maximum of 25 μm and to limit the sum of the thicknesses of the protective layer 51 and the spacer 53 to a maximum of 25 μm. This ensures that the gap between the recording layer closest to the farthest recording layer in terms of light irradiation does not exceed the spherical aberration adjustable range.

On the other hand, in order to irradiate light to the first recording layer 51a, the second recording layer 51b, or the third recording layer 51c having different positions of focal point, the light path is incident on the optical path incident on the lens unit 40. It is necessary to provide an optical element such as the aberration compensator 35 (see FIGS. 7 to 8) described. At this time, the distance between the first recording layer 51a at the position closest to the incident surface and the third recording layer 51c at the furthest position can be corrected for spherical aberration by an optical element such as the aberration compensator 35. Should be provided in the range.

That is, as described above, the maximum value of the spacer 53 and the maximum value of the spacer 53 and the protective layer 52 are determined by setting the maximum value in the case of two recording layers 51 and the thickness of the recording medium 50. Can be limited so as not to deviate from the range where the spherical aberration correction is possible. Therefore, in consideration of the above factors, in the recording medium 50 of the present invention, the thickness of the spacer 53 is preferably in the range of 1 µm to 25 µm.

In addition, the refractive index of the material constituting the spacer 53 is preferably larger than the effective numerical aperture NA _eff of the lens portion 40 for irradiating light to the recording medium 50 of the present invention. This is to prevent light from totally reflecting by the spacers 53, as described above with respect to the protective layer 52.

In the recording medium 50 using the near field, since there is a limit in the wavelength used, the thickness of the recording medium 50 is gradually thinner and thinner. Therefore, the number of recording layers 51 included in the recording medium 50 needs to be limited. Preferably, as described above, the recording medium 50 of the present invention is configured such that the sum of the thicknesses of the protective layer 52 and the spacer 53 does not exceed 25 µm. Since the spacer 53 is preferably configured to have one less than the number of the recording layers 51, the number of the entire recording layers 51 and the thickness of the recording medium 50 can be limited.

The rights of the present invention are not limited to the embodiments described above, but are defined by the claims, and those skilled in the art can make various modifications and adaptations within the scope of the claims. It is self-evident.

In the recording / reproducing apparatus and recording medium according to the present invention as described in detail above, the following effects can be expected.

That is, there is an advantage that a lens suitable for recording and reproducing using a near field can be easily manufactured.

It is also an advantage to provide a recording medium suitable for use in a recording / reproducing apparatus using a near field.

It is also advantageous to provide a recording / reproducing apparatus that can be used even when the recording medium has a protective layer or a plurality of recording layers.

Claims (15)

A lens unit including a near field forming lens and an objective lens for compensating spherical aberration of the near field forming lens, for irradiating light emitted from a light source to the recording medium; A light receiving unit receiving light reflected after being irradiated to the recording medium and generating a signal corresponding to the received reflected light; And a control unit for generating a control signal based on the generated signal. The method of claim 1, wherein the near field forming lens, And a part of a spherical lens whose height is larger than the radius of the sphere and smaller than the diameter. The method of claim 1, wherein the objective lens, And a spherical aberration of the same magnitude in opposite directions to the spherical aberration of said near field forming lens. The effective numerical aperture of the lens unit according to claim 1, And a refractive index of the protective layer of the recording medium used in the recording and reproducing apparatus. The method of claim 4, wherein The near field forming lens is made of glass, and the effective numerical aperture of the lens portion is smaller than 1.85. The effective numerical aperture of the lens unit according to claim 5, A recording and reproducing apparatus, characterized by greater than or equal to 1.6 and less than or equal to 1.85. The recording and reproducing apparatus according to claim 1, And an aberration compensator for varying the position of the focal point irradiated from the lens unit to the recording medium. The method of claim 7, wherein the aberration compensation unit, And a lens movable in at least one optical axis direction. The method of claim 7, wherein the aberration compensation unit, And a first lens having a fixed position and a second movable lens, wherein the path of the light is changed by moving the second lens in an optical axis direction. A recording medium for use in a near field, comprising: at least one recording layer and a protective layer for blocking the recording layer from outside; And the refractive index of the protective layer is larger than the effective numerical aperture of the lens portion for irradiating light to the recording medium. The method of claim 10, wherein the protective layer, And a thickness of 10 nm to 25 탆 provided on the surface of the recording medium. The method of claim 10, wherein the recording medium, And a spacer spaced between the recording layers or spaced apart from the recording layer and the protective layer. The method of claim 12, wherein the thickness of the spacer, A recording medium, characterized in that 1 µm to 25 µm. The method of claim 12, wherein the refractive index of the spacer, And a larger than an effective numerical aperture of the lens portion. The method of claim 10, And the sum of the thicknesses of the protective layer and the spacer is at most 25 μm.

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