JP2003323738A - Optical recording/reproducing unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide optical reproducing arrangement that widens the tolerance level of assembly errors, condenses light with accuracy that could not be achieved in assembly, uses near-field light or light generated by interference between modes to the maximum for enabling high-density optical recording, has superior reliability of signal detection, and can safely record and reproduce data. <P>SOLUTION: The optical recording/reproducing unit includes a focus variable lens that is installed in a light path at a area, where emitted light from a light source is detected by a photodetector; and a focus distance adjusting means for adjusting the focus of the focus-variable lens, by applying an electric field to maintain optimum focusing distance. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus, and more particularly to an optical recording / reproducing apparatus for recording or reproducing data at a super high density using an optical or near-field optical effect.

[0002]

2. Description of the Related Art As one of data recording / reproducing methods, there is a method of recording / reproducing on / from a recording medium using light. As a typical example of such an optical recording method, 2 pieces of compressed image information according to MPEG2 are recorded on one side of an optical disk having a diameter of 12 cm.
DVD systems have been commercialized because of the demand for recording for more than an hour. According to the DVD standard, the storage capacity of the disc is 4.7 GB on one side, and the track density is 0.74.
The line density is 0.267 μm / bit. Hereinafter, a DVD based on this standard will be referred to as a current DVD.

The reproduction of information recorded on an optical disc such as a DVD is performed by using an optical head. In the optical head, a light beam emitted from an LD (laser diode) is focused by an objective lens into a series of pits on a track of an optical disc. The light beam reflected by the optical disk is condensed on the photodetector by the condenser lens, and a reproduction signal is obtained. The reproduction signal from this photodetector is input to the reproduction signal processing system, and the data is decoded. In the DVD standard, the wavelength of the LD in the optical head is 0.65 μm and the numerical aperture NA of the objective lens is 0.6.

Optical discs are required to have higher densities and higher speeds. For example, a high-definition DVD system capable of recording high-definition video for 2 hours or more on one side of a disc having a diameter of 12 cm, as compared with the current DVD system. Is currently under development. The storage capacity required for high-definition DVD is 1
It is 5GB / side, which is 3.19 (= 1 compared to the current DVD.
5 / 4.7) times higher density is required. High definition DVD
As a technique for increasing the density of an optical disc for realizing the above, there is a reduction in beam spot. The size of the beam spot is proportional to the wavelength of the laser and inversely proportional to the numerical aperture of the objective lens. An optical disk collects laser light with a lens optical system and irradiates it on a recording medium, and the spot diameter of this laser is an important parameter for determining the size of a recording mark. However, in such a method, it is impossible to make the spot diameter of the light equal to or smaller than the wavelength of the laser light source due to the diffraction limit of the light. For example, in a high-definition DVD system, an optical system having a blue laser (wavelength 0.41 μm) and an objective lens with a numerical aperture of 0.6 is regarded as promising, and the beam spot area is the same as the beam spot area in the current DVD system. 1 is 0.397. That is,
The density increase of the optical disc achieved by the reduction of the beam spot is 2.52 (= 1 / 0.397) times,
In order to achieve the high-definition DVD storage capacity, in addition to the reduction of the beam spot, it is about 1.25 times (up to 3.2 / 0.39).
Higher density of 7) is required.

On the other hand, the recording capacity required for a high-definition DVD is 15 GB / surface or more, but in order to reproduce this capacity within 2 hours, a data transfer rate of at least 2 MBPS or more is required. When used as a ROM for a computer, a high-speed read / write speed of 200 MBPS is required for stream reproduction and 200 MBPS or higher for random reproduction.

Therefore, in recent years, optical recording using near-field light has attracted attention as a method for achieving high density of an optical disk device. For example, Applied Physycs Leters, 61
Vol. 2, pp. 142-144 (Applied Physycs Le
ters, Vol. 62, No. 2, pp. 142-14
4, 1992) (hereinafter referred to as Conventional Example 1), the tip of the optical fiber is processed into a cone shape, and a probe in which the tip is covered with a metal coating except the region of several tens nm is manufactured. An example has been reported in which a recording mark having a diameter of 60 nm is recorded and reproduced on a platinum / cobalt multilayer film by controlling the position by mounting on a precision actuator using a piezoelectric element. In this prior art example 1, a probe is used in which the tip of the optical fiber is processed into a cone shape, and the tip of the tip is covered with a metal coating except for a region of several tens nm.

As another conventional example, Applied Ph
ysycs Leters, Vol. 73, No. 15, pp. 2078-208
Page 0 (Applied Physycs Leters, Vol. 73, No.
15, pp. 2078-2080, 1998) (hereinafter referred to as Conventional Example 2), a recording layer, a protective layer, and a nonlinear optical material layer are provided on an optical disk substrate, and the nonlinear optical material layer is used as a mask for the near field. A method of generating light for recording and reproducing has been proposed. In the second embodiment, a polycarbonate optical disk substrate is provided with a SiN protective layer and Ge.
A recording layer of ₂ Sb ₂ Te ₅ and a protective layer of Sb are stacked and vapor-deposited, and a laser beam is incident from the substrate side to obtain a diameter of 9
An example of recording and reproducing a recording mark of 0 nm has been reported.

On the other hand, there are the following documents as the prior art of the electro-optical lens. As one of them, JP-A-6-1485
In Japanese Patent No. 80, both sides of a rectangular parallelepiped PLZT facing each other are described.
A distributed index type one-dimensional electro-optical lens having a structure in which a striped electrode is formed along the optical axis has been proposed. Since this electro-optic lens uses the horizontal effect of PLZT,
The direction of the applied electric field is orthogonal to the optical axis. Therefore, when it is desired to have a two-dimensional lens effect in the x and y directions, 1
It is necessary to stack two dimensional lenses. When a voltage is applied to the opposing stripe electrodes, an electric field distribution is generated inside PLZT. At the same time, a refractive index distribution corresponding to the electric field distribution is generated due to the electro-optic effect. By appropriately selecting the rectangular parallelepiped shape of the PLZT and the width and length of the stripe electrode, the square distribution of the refractive index is generated inside the PLZT, and the focus of the lens can be changed.

[0009]

When the near-field light is applied to the optical recording as in the above-mentioned conventional example 1, it is generated by a probe having a sharpened tip of an optical fiber or a minute opening provided in a flat slider. Near-field light has been used.
However, as a property of the near-field light, when the distance between the minute aperture that generates the near-field and the recording layer is increased, the light intensity is rapidly attenuated and the light is diverged, so that the spot diameter is rapidly increased. There is. Therefore, it is necessary to always keep the distance between the aperture and the recording layer to be 10 nm or less, and it is very precise to
Moreover, a high-precision pickup actuator for controlling the optical head at high speed is required. The actuator is controlled using magnetic force by a magnetic field normally generated by a magnet coil. In particular, the optical head itself is a volume, and is heavy, and in order to be controlled by an electromagnet,
You have to drive a coil of thick and heavy metal wire,
It is difficult to control the drive at an extremely high speed. Therefore, when the optical disc rotates at a high speed, the actuator cannot control the optical head, and the light spot irradiated on the recording layer becomes large. In such a state, the signal output from the photodetector for signal detection in the optical pickup has a light spot larger than a bit, so that read waveforms of adjacent bits are added to both sides of the read waveform. Become. Therefore, the signal output from this optical pickup suffers intersymbol interference from adjacent bits, and it becomes difficult to independently detect only the necessary bit information with high sensitivity. In the worst case, the head itself may come into contact with the medium and destroy the surface of the medium, making it difficult to record or reproduce data.

In addition, when the actuator used in the optical disk of the conventional example 1 is applied to the near-field optical disk device, various problems occur. Regarding the accuracy required for the pickup of the near-field optical disk device, since the head forms a spot below the light diffraction limit, each optical component is required to have a position accuracy below the light diffraction limit. But,
It is actually difficult to assemble each optical component with accuracy less than the diffraction limit of light. For example, the focal length cannot be adjusted after assembling a collimator lens, a condenser lens, etc., which causes an offset due to the lens assembly in the optical axis direction, making it difficult to generate a smaller spot in the near field. Becomes Also, if the wavelength of the laser light source changes due to some reason such as temperature change during use, or the current focal length of the lens changes due to aging of optical components, a near-field optical pickup will form a minute spot below the diffraction limit. Therefore, it is difficult to realize a high-density optical disk reproducing device.

According to the second conventional example, a recording layer, a protective layer, and a non-linear optical material layer are provided on an optical recording medium, and the non-linear optical material layer is used as a mask to open a minute aperture to generate near-field light for recording. In the reproducing method, the optical system can record and reproduce by the same mechanism as the conventional optical disk. In this case, the optical disk substrate is provided with the same lands and grooves as in the conventional case, and the near field is generated by the minute aperture generated on the aperture mask by the objective lens or the like for the laser beam propagating in space to perform recording / reproduction. In this method, if the minute opening diameter formed by the Sb mask layer is 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording medium. However, this is a case where a light spot is focused on the mask layer with the same precision as the spot diameter, that is, with an accuracy of 50 nm or more, and the objective lens can be driven even if the same objective lens as that of an optical disc such as a conventional DVD is used. The electromagnet actuator is difficult to realize for the same reason as the drawback of the conventional example 1 described above.

Further, according to the above-mentioned conventional example 3, since the lateral electro-optical element is used, it becomes long in the optical axis direction,
It is difficult to apply it to a planar device such as an optical pickup. Also, when the focus is changed two-dimensionally, 1
Since two dimensional focus variable lenses must be prepared, the number of parts such as the cylindrical lens is large, and it takes time to assemble and adjust.

The present invention is intended to solve these problems, and by adjusting the error generated after the lens is assembled after the assembly, the allowable range of the assembly error can be expanded and the error which cannot be obtained by the assembly. Concentrates light with high accuracy and enables high-density optical recording by using the near-field light of the light or light generated by intermode interference to the maximum, reliable signal detection, and stable data recording or An object is to provide an optical recording / reproducing device capable of reproducing.

[0014]

In order to solve the above-mentioned problems, the light emitted from the light source is condensed and irradiated onto the surface of the optical disc to record information and to transmit the information from the optical disc. The optical recording / reproducing apparatus of the present invention reproduces information by detecting light or reflected light by a photodetector, or focusing in a signal detection optical system and detecting the focused light by the photodetector. A variable focus lens installed in the optical path until the light emitted from is detected by the photodetector, and a focal length adjustment means for adjusting the focus of the variable focus lens by applying an electric field so as to maintain the optimum focal length. Have. Therefore, since the focal length of the lens can be adjusted after assembly, the amount of offset caused by lens assembly in the optical axis direction can be minimized, which expands the allowable range of assembly error and Since light can be condensed with an accuracy that could not be obtained with, it is possible to realize an optical recording / reproducing apparatus capable of high-density optical recording, high signal detection reliability, and stable data recording / reproducing. Further, since the variable lens focal length adjusting means is provided, the wavelength of the laser light source changes due to some reason such as temperature change during use, and an error occurs in the current lens focal length due to aging of optical components. In such a case, since such an error can be detected and feedback controlled, it is possible to realize an optical recording / reproducing apparatus equipped with an optical pickup that is resistant to changes over time and that can always detect a signal with a small error. .

Further, by providing a slider-like near-field light emitter in the light spot forming means for forming a spot smaller than the diffraction limit of the light emitted from the light source on the recording surface of the optical disk, the near-field effect of light is obtained. Alternatively, it is possible to realize an optical recording / reproducing apparatus capable of performing high-density optical recording by making maximum use of the pseudo near-field effect, having high reliability of signal detection, and stably recording or reproducing data.

Further, since the variable focus lens is used as an objective lens for condensing the light emitted from the light source on the recording layer, the focus actuator becomes unnecessary, and the size and weight can be further reduced. As a result, the allowable range of the assembly error can be expanded, and the light can be condensed with the accuracy that could not be obtained by the assembly.

Further, since the variable focus lens is used as a collimator lens for collimating the light emitted from the light source, the collimate adjustment can be performed after the lens is assembled, which facilitates the collimate adjustment and allows accurate adjustment. It can be carried out. Further, since the collimated state can be always assembled, the allowable range of the assembly error can be expanded, and the light can be condensed with the accuracy which cannot be obtained by the assembly.

Further, since the variable focus lens is used as a condenser lens for condensing the transmitted light or the reflected light from the optical disk on the photodetector, the position of the condenser lens in the optical axis direction after the lens assembly is adjusted. Can make adjustments,
As a result, the allowable range of the assembly error can be expanded, and the light can be condensed with the accuracy that could not be obtained by the assembly.

The variable focus lens is formed of a vertical lens material base material exhibiting an odd-order electro-optical effect, and by applying an electric field from the outside, a refractive index distribution is generated inside the lens material base material to form a focus. Since it is an electro-optical lens that changes the vertical axis, it is composed of a vertical type material base material showing an electro-optical effect and a ring-shaped electrode formed on this base material, and a voltage is applied to the electrode. Thereby, the refractive index distribution can be smoothly generated inside the lens material base material. Further, since the material base material exhibiting the electro-optic effect of odd orders is used, the birefringence is zero when the applied voltage is zero, and the polarities of the applied voltage are positive birefringence and negative birefringence, respectively. Since it becomes positive and negative and the operating point voltage can be set to zero, it is possible to realize an optical recording / reproducing apparatus equipped with an optical pickup capable of performing control such as focus adjustment and tracking adjustment with a simple circuit.

Further, it is preferable to form a pattern electrode having a symmetrical shape with respect to the optical axis on the lens material base material. Further, it is preferable that the pattern electrode has a ring shape.

Further, since the lens material base material is formed of a complex oxide having a silenite structure, the focus can be largely changed at a low voltage due to a large first-order electro-optical effect.
It is possible to realize a compact and lightweight optical recording / reproducing device without requiring a large-scale booster circuit.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The optical recording / reproducing apparatus of the present invention comprises a variable focus lens installed in the optical path until the light emitted from the light source is detected by a photodetector, and a variable focus lens by applying an electric field. And a focal length adjusting means for adjusting the focal point to maintain an optimum focal length.

[0023]

1 is a schematic diagram showing the configuration of an optical recording / reproducing apparatus according to a first embodiment of the present invention. In the figure, the optical recording / reproducing apparatus of the present embodiment includes a laser light source (hereinafter referred to as LD) 11, a collimator lens 12, a deflection beam splitter (hereinafter referred to as PBS) 13, a variable focus lens 14, an objective lens 15, and a condenser. An optical head 10 including a lens 16 and a photodetector 17; an LD driver 20;
And a reproduction signal processing system 30.

The optical recording / reproducing apparatus of the present embodiment having such a configuration collimates the light emitted from the LD 11 with the collimator lens 12, and the collimated light is
Information is recorded by passing the light through the PBS 13 and the variable focus lens 14 and condensing the light with the objective lens 15 to irradiate the surface of the optical disc 40. Any light source may be used as long as it can be focused on the surface of the optical disk, but a laser light source having strong coherence is particularly preferable. On the other hand, with the recording of information,
The reflected light from the optical disc 40 is separated from the incident light by the PBS 13 after passing through the objective lens 15 and the focus variable lens 14, and is focused by the condenser lens 16, and the focused light is detected by the photodetector 17. A reproduction signal for reproducing information is detected and converted into decoded data by the reproduction signal processing system 30. As shown in FIG. 1, the light emitted from the LD 11 is disposed in the optical path until it is detected by the photodetector 17,
The variable focus lens that adjusts the focal length of the beam is a variable lens focal length adjusting means (not shown) that detects the deviation amount of the focal length and adjusts the focus of the variable focus lens to always keep the optimum focal length. Is provided.

FIG. 2 is a schematic view showing the arrangement of an optical recording / reproducing apparatus according to the second embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 1 indicate the same components. As a different configuration, the focus variable lens 14 is provided between the objective lens 15 and the optical disc 40, and the focal length is adjusted with respect to the beam spot condensed on the surface of the optical disc 40.

FIG. 3 is a schematic view showing the arrangement of an optical recording / reproducing apparatus according to the third embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 1 indicate the same components. As a different configuration, a variable focus lens 1 is provided between the LD 11 and the PBS 13.
4 is provided to adjust the collimation of the LD 11. Also, P
Only the objective lens 15 is provided between the BS 13 and the optical disc 40.

FIG. 4 is a schematic view showing the arrangement of an optical recording / reproducing apparatus according to the fourth embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 1 indicate the same components. As a different configuration, a variable focus lens 14 is provided between the PBS 13 and the photodetector 17, and the reflected light is condensed and adjusted on the photodetector 17. Further, only the objective lens 15 is provided between the PBS 13 and the optical disc 40.

FIG. 5 is a schematic view showing the arrangement of an optical recording / reproducing apparatus according to the fifth embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 1 indicate the same components. As a different configuration, only the variable focus lens 14 is provided between the PBS 13 and the optical disc 40, and the focal length is adjusted with respect to the beam spot focused on the surface of the optical disc 40. As shown in FIG. 6, a non-linear optical material layer provided with a recording layer, a protective layer, and a non-linear optical material layer on an optical disk substrate made of polycarbonate or the like is used as a mask to record a light spot smaller than the diffraction limit of light. It is generated in a layer and recorded and reproduced. In the example shown in FIG. 6, S is formed on the polycarbonate substrate 41.
An iN protective layer 42, a recording layer (phase change material) 45 such as Ge ₂ Sb ₂ Te ₅ , AgInSbTe, etc., and an Sb mask layer 43 were laminated and deposited. Here, Ge ₂ Sb ₂ Te ₅ and AgInSbTe have two states (crystal and amorphous) having different reflectances at room temperature. It can be crystallized or made amorphous by changing the conditions of the irradiation light, and the state can be freely changed.
Using this principle, it is possible to configure an optical memory that records data and reads the data according to the difference in reflectance.
High contrast S / N by using this material
It is possible to obtain an optical disk recording / reproducing apparatus which can obtain a reproduction signal with good quality and has a high recording holding capacity. Further, since silver is used for the recording layer 45, it has good adhesion to the substrate and excellent abrasion resistance. The respective film thicknesses are 20 nm for the SiN protective layer 42 above and below the recording layer, and 15 for the recording layer (phase change material) 45.
nm, Sb mask layer 43 is 15 nm, Sb mask layer 43
A SiN protective layer 44 having a thickness of 170 nm was laminated between the and the polycarbonate substrate 41. The recording layer 45 may be any material that produces contrast in transmitted light or reflected light when it is irradiated with light, so that not only a phase change material but also a magneto-optical material or a material exhibiting an electro-optical effect can be considered. . The contrast includes not only the difference in light intensity due to changes in absorbance and reflectance, but also contrast caused by changes in optical constants such as rotation of the polarization plane and changes in birefringence. At the time of recording, the laser beam focused by the variable focus lens 14 is incident on the Sb mask layer 43 from the substrate side as in the case of a normal optical disc. At this time, the Sb mask layer 43 in the region corresponding to the incident laser power becomes transparent and a minute opening is formed. At this time, the near-field light leaks into the recording layer from the formed minute opening, and a recording mark smaller than the light diffraction limit can be formed. For example, the small opening diameter formed by the Sb mask layer 43 is 5
When the thickness is 0 nm, the recording layer of the surface recording medium has about 5
It is possible to form a light spot of about 0 nm. By configuring a pickup using such an electro-optical lens, the focus of the lens can always be kept optimal, and high-density optical writing and reading can be performed using light that has been condensed to the limit.

An optical disc as shown in FIG. 7 is used as the surface recording type optical disc of the optical recording / reproducing apparatus. As shown in FIG. 7, a near-field light emitter, such as a protrusion or an aperture, provided on a near-field probe or a near-field slider head by providing a phase change material and a protective layer on an optical disk substrate made of polycarbonate or the like as an optical recording medium. The near-field light is generated by using such as recording and reproducing. In the example shown in FIG. 7, SiN protective layers 44 and 46 and a recording layer 45 of a phase change material are laminated and vapor-deposited on a polycarbonate optical disc substrate 41. For example, the respective film thicknesses are such that the SiN protective layers 44 and 46 above and below the recording layer 45 are laminated to 20 nm, and the recording layer 45 of the phase change material is laminated to 15 nm. Recording layer 45 of phase change material
Is a material that undergoes a phase change (crystal phase, amorphous phase, etc.) when irradiated with strong light for writing. If stable multiple phases can be reversibly changed, RAM
When it changes irreversibly, it can be used as a write-once recording medium. Further, any material may be used as long as the transmitted light or the reflected light produces contrast in a plurality of phases when irradiated with weak light for reading. At the time of recording, in the case of this example, near-field light or internal condensing type near-field light is incident from the recording layer side by a near-field protrusion or the like.
Light can enter from either the substrate side or the recording layer side of the medium, but FIG. 7 is a diagram when the near-field light enters from the recording layer side. The light emitted from the tip of the near-field generator becomes the near-field light once and enters the sample. The light passes through the recording layer and is emitted to the polycarbonate substrate side as propagating light. Recording marks smaller than the diffraction limit of light can be formed on the data recording layer. Therefore, in the optical recording / reproducing apparatus of the present invention, the electro-optical lens is used to constitute the pickup, so that the focus of the lens can always be kept optimum. For example, in the case of FIG. 7, since it is possible to accurately collect light on the near-field generator by using the electro-optical lens, the near-field light is generated by using the light condensed to the limit, and the high-density light is generated. Writing and reading are possible.

FIG. 8 is a diagram showing the structure and refractive index distribution characteristics of the variable focus lens used in the optical recording / reproducing apparatus of the present invention. As the variable focus lens used in the optical recording / reproducing apparatus of the present invention, an electro-optical lens as shown in FIGS. This electro-optical lens uses a lens lens material base material 51 that exhibits a vertical electro-optical effect, applies an electric field from the outside through a ring-shaped electrode 52, and inside the lens material base material 51 shown in FIG. A smooth refractive index distribution like the characteristic shown in c) is produced. For example, as shown in FIG. 9, a BSO crystal (B ₁₂ SiO ₂₀ ) is used as the lens material base material 5
1, and when a voltage is applied between the electrodes 52 facing each other, an electric field is generated in the Z-axis direction inside the lens material base material 51 sandwiched by the electrodes 52 facing each other, and as shown in (c) of FIG. Since the refractive index of the lower portion of the electrode is relatively reduced, the refractive index distribution can be formed as a square distribution in which the center is large and becomes weaker toward the edges. When collimated light is applied to such a lens material base material from one side, the light passing through the vicinity of the electrodes is refracted toward the center of the lens, so that condensed light can be produced. The shape of the electrode 52 is not limited to that shown in FIG. 8A in which ring-shaped electrodes are provided on both surfaces of the lens material base material, and the following shapes are effective.

First, the lens material base material 5 as shown in FIG.
The electrode 52 on 1 has a ring shape on one side, and the other surface is a circular or rectangular electro-optical lens as shown in FIGS. 10 (a) and 10 (b). When this plate electrode is made of a transparent electrode such as ITO, it becomes a transmissive electro-optical lens. Further, when an electrode that reflects light, for example, a metal electrode such as an aluminum vapor deposition film is used, a reflective electro-optical lens is formed. Further, as shown in FIG. 11, the ring-shaped electrode 52 is divided into four in the x direction and the y direction, and the electro-optical lens has a structure in which the voltage can be applied independently in the x direction and the y direction. This electro-optic lens has x-direction and y-direction.
By applying the voltage independently in the directions, the focus can be changed independently in the x direction and the y direction, so that astigmatism can be corrected. Further, by adjusting the voltage applied to each electrode, the focus position can be moved not only forward and backward but also left and right. It can be used to deflect light. That is, it can also be used for tracking adjustment. The shape of the electrode 52 is a double-sided view 1.
In addition to the four-divided electrode as shown in FIG.
There is a ring-shaped electrode 52 as shown in FIG. 10 or a simple flat plate electrode 52 as shown in FIGS. This flat plate electrode 52 is
When a transparent electrode such as O is used, it becomes a transmissive electro-optical lens. Further, when an electrode that reflects light, for example, a metal electrode such as an aluminum vapor deposition film is used, a reflective electro-optical lens is formed. In such an electro-optical lens, when an electric field is externally applied to the lens material base material 51 exhibiting a vertical electro-optical effect, a refractive index distribution is generated inside the lens material base material 51, and the focal position is arbitrarily continuous. It becomes a lens that can be changed. It is possible to make a flat focus variable lens that is thin in the optical axis direction and wide in the surface direction as compared with a horizontal variable focus lens based on the electro-optic effect. This shape is suitable for ultra-thin optical disk drives used for notebook PCs and the like. Further, by forming an electrode on the lens material base material exhibiting the electro-optic effect and applying a voltage, a refractive index distribution can be generated inside the lens material base material. The focal length can be continuously changed by changing the voltage value. The light can be manufactured so as to be transmitted through a place other than the electrode portion and need not be transparent, but it is also possible to transmit the light that is applied to the electrode portion by using a transparent electrode.

Further, by making the electrodes ring-shaped,
Since a two-dimensional refractive index distribution can be generated inside the lens material base material, a two-dimensional simultaneous focus variable lens in the x direction and the y direction can be realized with one lens.
Further, the focus can be changed independently in the x direction and the y direction for the purpose of correcting aberrations and the like. In this case, lenses in the x direction and the y direction can be formed on the same base material, and the positions of the lenses are the same in both directions. Therefore, even if the two-dimensional independent variable operation is performed, focusing of the focus and voltage control can be easily performed. Further, by using the vertical electro-optic effect, it becomes possible to increase the area of the lens, which was difficult with the electro-optic lens using the horizontal effect and the stripe electrode. Since an electro-optical lens having a structure in which no electrode is applied to the optical axis can be formed, in principle, a clean light collection without diffraction or scattered light can be achieved, which is optimal for an optical recording / reproducing apparatus.

A specific example of the present invention will be described in more detail. According to the distributed index type variable focus electro-optic lens using the vertical electro-optic effect shown in FIG. 8A, the lens material base material 5 is used.
1 is a Bi ₁₂ SiO ₂₀ single crystal substrate (1
5 mm × 15 mm × 1 mm). The electrode 52 is a ring-shaped transparent ITO electrode (diameter of the inner circle is 3 mm) formed on both sides of the substrate and facing each other. When a voltage is applied between the upper and lower ring-shaped electrodes, an electric field is generated in the substrate in the thickness direction (z-axis direction) of the material base material. Since the material base material is a vertical electro-optic crystal, the surface direction of the material base material (x-axis direction and y
Birefringence occurs during (axial direction). Now, assuming that the refractive index in the x-axis direction is small, the electric field in the z-axis direction is strong just below the electrode, and therefore the refractive index for transmitted light having a polarization plane in the x-axis direction is small. The central part of the material base material without electrodes still has a high refractive index. As shown in FIG. 8C, the material base material has a refractive index distribution of the convex lens due to the voltage application. When linearly polarized light having a plane of polarization in the x-axis direction is incident on such a material base material, the incident light is condensed at one point by the convex lens effect. On the contrary, since the refractive index in the y-axis direction becomes large, when linearly polarized light having a polarization plane in the y-axis direction is incident, the incident light diverges due to the concave lens effect. When the applied voltage is continuously changed from positive to negative, the focal length continuously changes, and it is possible to easily switch the convex lens to the concave lens by adjusting the voltage. He-Ne laser (wavelength: 633n) is used for the incident light.
m, beam diameter: about 1 mm), and this light is made incident on the electro-optical lens. An achromatic lens placed immediately in front of the electro-optical lens collects the light transmitted through the lens at one point (spot diameter: 20 μm). An aperture having a diameter of 25 μm was used to detect the focal position, and the aperture was moved from the vicinity of the lens focal point on the optical axis to the front and back, and the aperture position when the transmitted light intensity was maximized was obtained. When a voltage of 1.6 kV was applied to the electro-optical lens, the focus moved to the front by about 1 mm. The basic operation of the electro-optical lens was confirmed from the change of the focal position due to the voltage application.

Next, as a lens material base material exhibiting a vertical electro-optical effect, LiNbO ₃ and LiTaO _{3 having} a crystal point group of ₃ m, NH ₄ H ₂ PO ₄ (ADP) and KH ₂ PO having a crystal point group of 42 m are used. ₄ (KDP), α crystal (SiO ₂ ) of crystal point group 32, Bi ₁₂ SiO ₂₀ of crystal point group 23
(BSO), Bi ₁₂ GeO ₂₀ (BGO), ZnS, ZnTe with a crystal point group of 43 m,
There are single crystals and polycrystals that do not have central symmetry, such as Bi ₄ Ge ₃ O ₁₂ . This type of crystal exhibits a large first-order electro-optic effect (Pockels effect) and exhibits optimum characteristics in the present invention. In particular, BSO and BGO have a large electro-optic constant (Pockels coefficient γ ₄₁ ) of 10 ⁻¹² m / v or more, and the focus can be largely changed at a low voltage. Therefore, they are optimal material base materials in the present invention. Alternatively, a lens material base material that exhibits a second-order electro-optical effect (electro-optical Kerr effect) or a higher-order effect can be used.

By constructing a pickup using such an electro-optical lens, the focus of the lens can always be kept optimal, and high-density optical writing / reading can be performed by using the light condensed to the limit. .

FIG. 12 is a schematic view showing the arrangement of an optical recording / reproducing apparatus according to the sixth embodiment of the present invention. In the figure,
The same reference numerals as those in FIG. 5 indicate the same components. A slider 61 is provided as a different configuration. According to the optical recording / reproducing apparatus of this embodiment having such a configuration, the LD 11
The light emitted from the collimator is collimated by the collimator lens 12, and the collimated light is focused by the focus variable lens 14 to be condensed, and a near field such as a protrusion, a minute aperture, or a slit provided in the slider 61 is collected. Irradiate the generation area. Information is recorded by coupling the near-field light generated from the near-field generator onto the surface of the optical disc 40. For example, when the protrusion has a minute opening diameter of 50 nm, a light spot of about 50 nm can be formed on the recording layer of the surface recording medium. By configuring a pickup using such an electro-optical lens, the focus of the lens can always be kept optimal, and high-density optical writing and reading can be performed using light that has been condensed to the limit.

FIG. 13 is a schematic view showing the arrangement of an optical recording / reproducing apparatus according to the seventh embodiment of the present invention. In the figure,
The same reference numerals as those in FIG. 3 indicate the same components. A slider 61 is provided as a different configuration.

FIG. 14 is a schematic view showing the arrangement of an optical recording / reproducing apparatus according to the eighth embodiment of the present invention. In the figure,
The same reference numerals as those in FIG. 4 indicate the same components. A slider 61 is provided as a different configuration.

According to the optical recording / reproducing apparatus provided with such a slider, a protrusion, a minute opening, a slit, etc. for forming a spot smaller than the diffraction limit of light are provided inside the slider, whereby a near field is provided. Recording or reproduction is performed by generating light or an internally focused near-field light.

As shown in FIG. 15, a vertical lens material base material showing an odd-order electro-optical effect and a ring-shaped electrode formed on the lens material base material are used. Is applied, a refractive index distribution is smoothly generated inside the lens material base material. Since the lens material base material that exhibits the electro-optic effect of odd orders is used, the birefringence is zero when the applied voltage is zero, and the positive and negative birefringence causes the positive and negative polarities of the applied voltage. Since the operating point voltage can be set to zero, it is effective in control such as focus adjustment and tracking adjustment.
In particular, when a vertical lens material base material that exhibits an odd-order electro-optical effect is used, the refractive index of the electric field application portion can be increased or decreased by applying a positive or negative electric field. Therefore, when the value of the electrode voltage is changed from negative to positive,
Alternatively, the focal point of the lens can be continuously changed in the opposite manner. By configuring a pickup using such an electro-optical lens, the focus of the lens can always be kept optimal, and high-density optical writing and reading can be performed using light that has been condensed to the limit.

Further, according to the present invention, the lens material base material of the silenite structure complex oxide and the ring-shaped electrode formed on the lens material base material are used. By applying a voltage to the electrode, the lens material is formed. The refractive index distribution is smoothly generated inside the base material. As a silenite structure double oxide,
Particularly, Bi ₁₂ SiO ₂₀ (BSO), Bi ₁₂ GeO ₂₀ (BGO) and the like of the crystal point group 23 are useful. This type of crystal exhibits a large first-order electro-optical effect (Pockels effect) and exhibits optimum electro-optical characteristics in the present invention. By configuring a pickup using such an electro-optical lens, the focus of the lens can always be kept optimal, and high-density optical writing and reading can be performed using light that has been condensed to the limit.

It is needless to say that the present invention is not limited to the above embodiments, and various modifications and substitutions can be made within the scope of the claims.

[0043]

As described above, information is recorded by collecting the light emitted from the light source and irradiating it onto the surface of the optical disk, and detecting the transmitted light or the reflected light from the optical disk. The optical recording / reproducing apparatus of the present invention detects the light emitted from the light source by detecting the light from the light source, or by reproducing the information by causing the light detector to detect the focused light by focusing the light in the signal detection optical system. It has a variable focus lens installed in the optical path until it is detected by the container, and a focal length adjusting means for adjusting the focal point of the variable focus lens by applying an electric field so as to keep the focal length at an optimum focal length. Therefore, since the focal length of the lens can be adjusted after assembly, the amount of offset caused by lens assembly in the optical axis direction can be minimized, which expands the allowable range of assembly error and Since light can be condensed with an accuracy that could not be obtained with, it is possible to realize an optical recording / reproducing apparatus capable of high-density optical recording, high signal detection reliability, and stable data recording / reproducing. Further, since the variable lens focal length adjusting means is provided, the wavelength of the laser light source changes due to some reason such as temperature change during use, and an error occurs in the current lens focal length due to aging of optical components. In such a case, since such an error can be detected and feedback controlled, it is possible to realize an optical recording / reproducing apparatus equipped with an optical pickup that is resistant to changes over time and that can always detect a signal with a small error. .

In addition, the near-field effect of light is provided by providing the slider-like near-field light emitter in the light spot forming means for forming a spot smaller than the diffraction limit of the light emitted from the light source on the recording surface of the optical disk. Alternatively, it is possible to realize an optical recording / reproducing apparatus capable of performing high-density optical recording by making maximum use of the pseudo near-field effect, having high reliability of signal detection, and stably recording or reproducing data.

Furthermore, since the variable focus lens is used as an objective lens for condensing the light emitted from the light source on the recording layer, the focus actuator becomes unnecessary, and the size and weight can be further reduced. As a result, the allowable range of the assembly error can be expanded, and the light can be condensed with the accuracy that could not be obtained by the assembly. It is possible to follow high-speed movement when the slider slides or floats, and high-speed movement of the head itself becomes possible. In addition, since the number of mechanically movable parts is reduced, it is possible to realize an optical recording / reproducing device equipped with an optical pickup that is resistant to vibration and fluctuations in the internal air flow. Further, since the head itself can be made smaller and lighter, the operation of the head can be speeded up, the seek speed can be improved, and an optical recording / reproducing apparatus capable of accessing the recording / reproducing point on the medium at high speed can be realized. It is not necessary to provide an objective lens driven by an electromagnetic coil, the structure of the optical pickup can be simplified, and a high-speed and high-density optical recording / reproducing apparatus can be realized.

Further, since the variable focus lens is used as a collimator lens for collimating the light emitted from the light source, the collimate adjustment can be performed after the lens is assembled, which facilitates the collimate adjustment and allows accurate adjustment. It can be carried out. Further, since the collimated state can be always assembled, the allowable range of the assembly error can be expanded, and the light can be condensed with the accuracy which cannot be obtained by the assembly.

Further, since the variable focus lens is used as a condenser lens for condensing the transmitted light or the reflected light from the optical disk on the photodetector, the position of the condenser lens in the optical axis direction after the lens assembly is adjusted. Can make adjustments,
As a result, the allowable range of the assembly error can be expanded, and the light can be condensed with the accuracy that could not be obtained by the assembly.

The variable focus lens is formed of a vertical lens material base material exhibiting an odd-order electro-optical effect, and by applying an electric field from the outside, a refractive index distribution is generated inside the lens material base material and a focus is generated. Since it is an electro-optical lens that changes the vertical axis, it is composed of a vertical type material base material showing an electro-optical effect and a ring-shaped electrode formed on this base material, and a voltage is applied to the electrode. As a result, the refractive index distribution can be smoothly generated inside the lens material base material. Further, since the material base material exhibiting the electro-optic effect of odd orders is used, the birefringence is zero when the applied voltage is zero, and the polarities of the applied voltage are positive birefringence and negative birefringence, respectively. Since it becomes positive and negative and the operating point voltage can be set to zero, it is possible to realize an optical recording / reproducing apparatus equipped with an optical pickup capable of performing control such as focus adjustment and tracking adjustment with a simple circuit.

Further, it is preferable to form a pattern electrode having a symmetrical shape with respect to the optical axis on the lens material base material. Further, it is preferable that the pattern electrode has a ring shape.

Further, since the lens material base material is formed of a complex oxide having a silenite structure, the focus can be largely changed at a low voltage due to a large first-order electro-optical effect.
It is possible to realize a compact and lightweight optical recording / reproducing device without requiring a large-scale booster circuit.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an optical recording / reproducing apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a configuration of an optical recording / reproducing apparatus according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram showing a configuration of an optical recording / reproducing apparatus according to a third embodiment of the present invention.

FIG. 4 is a schematic diagram showing a configuration of an optical recording / reproducing apparatus according to a fourth embodiment of the present invention.

FIG. 5 is a schematic diagram showing a configuration of an optical recording / reproducing apparatus according to a fifth embodiment of the present invention.

FIG. 6 is a diagram showing an example of an optical disc.

FIG. 7 is a diagram showing another example of an optical disc.

FIG. 8 is a diagram showing a configuration and a refractive index distribution characteristic of a variable focus lens used in the optical recording / reproducing apparatus of the present invention.

FIG. 9 is a diagram showing a circuit for applying a voltage between opposing electrodes.

FIG. 10 is a diagram showing another configuration of the variable focus lens used in the optical recording / reproducing apparatus of the present invention.

FIG. 11 is a diagram showing still another configuration and refractive index distribution characteristics of the variable focus lens used in the optical recording / reproducing apparatus of the present invention.

FIG. 12 is a schematic diagram showing the structure of an optical recording / reproducing apparatus according to a sixth embodiment of the present invention.

FIG. 13 is a schematic diagram showing a configuration of an optical recording / reproducing apparatus according to a seventh embodiment of the present invention.

FIG. 14 is a schematic diagram showing the configuration of an optical recording / reproducing apparatus according to an eighth embodiment of the present invention.

FIG. 15 is a characteristic diagram showing the relationship between the applied voltage and the refractive index of the variable focus lens used in the optical recording / reproducing apparatus of the present invention.

[Explanation of symbols]

10: Optical head, 11; LD, 12; Collimating lens, 13; PBS, 14; Focus variable lens, 15; Objective lens, 16; Condensing lens, 17; Photodetector, 20; L
D driver, 30; reproduction signal processing system, 40; optical disc, 51; lens material base material, 52; electrode, 61; slider.

Continued front page    F-term (reference) 5D118 AA01 AA13 BA01 BB02 CA11                       CD02 CG02 DC16                 5D119 AA01 AA11 AA22 AA29 AA32                       AA39 BA01 BB01 BB02 BB04                       BB05 BB10 BB11 CA06 DA01                       DA05 EA02 EA03 EB02 EC02                       EC20 FA05 JA01 JA12 JA34                       JA42 JA54 MA06                 5D789 AA01 AA11 AA22 AA29 AA32                       AA39 BA01 BB01 BB02 BB04                       BB05 BB10 BB11 CA06 CA21                       CA22 CA23 DA01 DA05 EA02                       EA03 EB02 EC02 EC20 FA05                       JA01 JA12 JA34 JA42 JA54                       JA66 MA06

Claims (9)

[Claims] 1. Information is recorded by condensing light emitted from a light source and irradiating the light onto the surface of an optical disk, and a transmitted light or reflected light from the optical disk is detected by a photodetector, or In an optical recording / reproducing apparatus that reproduces information by focusing the light in the signal detection optical system and causing the photodetector to detect the focused light, until the light emitted from the light source is detected by the photodetector. 2. An optical recording / reproducing apparatus comprising: a variable focus lens installed in the optical path of 1. and a focal length adjusting means for adjusting the focus of the variable focus lens by applying an electric field so as to maintain an optimum focal length. 2. The optical recording according to claim 1, wherein a slider-like near-field light emitting body is provided in the light spot forming means for forming a spot smaller than the diffraction limit of the light emitted from the light source on the recording surface of the optical disc. Playback device. 3. The optical recording / reproducing apparatus according to claim 1, wherein the variable focus lens is used as an objective lens for condensing light emitted from a light source on a recording layer. 4. The optical recording / reproducing apparatus according to claim 1, wherein the variable focus lens is used as a collimating lens for collimating the light emitted from the light source. 5. The optical recording / reproducing apparatus according to claim 1, wherein the variable focus lens is used as a condenser lens for condensing transmitted light or reflected light from the optical disc on the photodetector. 6. The variable focus lens is formed of a vertical lens material base material that exhibits an odd-order electro-optical effect, and a refractive index distribution is generated inside the lens material base material by applying an electric field from the outside. The optical recording / reproducing apparatus according to claim 1, wherein the optical recording / reproducing apparatus is an electro-optical lens for changing a focus. 7. The optical recording / reproducing apparatus according to claim 6, wherein a pattern electrode having a shape symmetrical with respect to the optical axis is formed on the lens material base material. 8. The optical recording / reproducing apparatus according to claim 7, wherein the pattern electrode has a ring shape. 9. The optical recording / reproducing apparatus according to claim 6, wherein the lens material base material is formed of a complex oxide having a silenite structure.