JP2001023182A - Device and method for positioning optical system, and recording/reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a positioning device of an optical system capable of preventing the contact between the optical system and an optical record medium in the case of forming a near field by shortening the distance between them. SOLUTION: An optical disk-driving device 100 that is one example of the positioning devices of an optical system is provided with an optical system for applying convergence light to an optical disk 51 by forming a proximity field at an area to the optical disk 51, an actuator for moving the optical system in a focus direction that orthogonally crosses the recording surface of the optical disk 51, and a control circuit 28 for reducing distance (air gap) between the optical system and the optical disk 51 from the outside of a region where the near field is formed toward the inside of the region in steps and further controlling the actuator for maintaining into the above region. The optical system in an optical head 1 is provided with an objective lens for converging light from a semiconductor laser and a solid immersion lens for converging the transmission light of the objective lens and applying it to the optical disk 51, and the numerical aperture NA of the optical system is larger than 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positioning apparatus and a positioning method for an optical system for irradiating convergent light onto an optical recording medium,
Further, the present invention relates to a recording / reproducing apparatus for recording or reproducing information by irradiating convergent light onto an optical recording medium.

[0002]

2. Description of the Related Art Optical devices include, for example, a recording / reproducing device for recording or reproducing information using an optical recording medium such as an optical disk, and an optical microscope. The cut-off spatial frequency fc in the optical device is determined by the numerical aperture (Nu) of the objective lens.
It is generally expressed by the following equation using the NA of the mercury aperture and the wavelength λ of the output light of the light source.

[0003]

Fc = 2NA / λ ...

The shorter the wavelength λ of light from a light source, the more
The higher the numerical aperture NA of the objective lens, the higher the resolution, the higher the recording density with the recording / reproducing apparatus, and the more detailed the observation with the optical microscope. As a method for increasing the numerical aperture NA of an objective lens, a near-field using a solid immersion lens (SIL: Solid Immersion Lens)
(Near-field) optical systems are known, and an optical system having a numerical aperture exceeding 1 is realized by this method.

[0005] References relating to near-field optics and solid immersion lenses include, for example, SM Man.
sfield, WR Studenmund, GS Kino, and K. Osat
o, "High-numerical-aperture lens system for optica
l storage, "Opt. Lett. 18, pp. 305-307 (1993) (hereinafter referred to as" Reference Document 1 "). Other references include, for example, HJ Mamin, BD Terris, an
d D. Rugar, "Near-field optical data storage," App
l. Phys. Lett. 68, pp. 141-143 (1996) (hereinafter referred to as “Reference Document 2”).

Note that USP 4183060 and USP 43
No. 00226 discloses that the distance between an optical disk and an electrode is detected by a capacitance sensor, but does not describe a near-field optical system and a solid immersion lens (SIL). Japanese Patent Application Laid-Open No. 8-212579 discloses an invention of an optical head and an optical recording medium. In this publication, an objective lens is held by a first lens holder, a solid immersion lens is held by a second lens holder, and a second lens holder and an optical disk are formed by using a conductive material for the second lens holder. It is disclosed that the position of a solid immersion lens is controlled based on the capacitance between them.

[0007]

In the near-field optical system, the distance (air gap) between the optical system and the optical recording medium is determined by a near-field in order to efficiently irradiate the optical recording medium with light. It must be kept within the region (near-field region). In particular, when the numerical aperture exceeds 1, if the air gap is larger than the above-mentioned region, the light intensity at the optical recording medium is considerably reduced due to multiple reflection and interference of light between the optical system and the optical recording medium. It is important to keep the gap in the region.

However, in order to realize an air gap in which a near field is formed, for example, an air gap of 500 nm or less (preferably an air gap of 100 nm or less), the initial value outside the region is changed to the final target value within the region. And optical system at once to optical recording medium (pull in)
Then, the optical system may come into contact with the optical recording medium due to overshoot, and the optical system and the optical recording medium may be impacted by this contact.

A first object of the present invention is to position an optical system capable of preventing contact between the optical system and the optical recording medium when forming a near field by shortening the distance between the optical system and the optical recording medium. It is to provide an apparatus and a positioning method.

A second object of the present invention is a recording / reproducing apparatus for recording or reproducing information by irradiating an optical recording medium with light from a light source via an optical system, and comprising an optical system and an optical recording medium. It is an object of the present invention to provide a recording / reproducing apparatus capable of preventing contact between an optical system and an optical recording medium when a near field is formed by shortening the distance.

[0011]

An optical system positioning apparatus according to the present invention comprises: an optical system for forming a near field with an optical recording medium and irradiating convergent light to the optical recording medium; An actuator for moving the optical system in a focus direction orthogonal to a recording surface of the medium, and a distance between the optical system and the optical recording medium is multi-stepped from outside the area where the near field is formed to inside the area. And a control circuit for controlling the actuator so as to maintain the actuator within the region.

In the positioning apparatus for an optical system according to the present invention,
Preferably, the control circuit sets the distance to an intermediate target value from an initial setting value outside the area, temporarily maintains the intermediate target value or substantially the intermediate target value, and sets the distance from the intermediate target value to the area. The actuator is controlled so as to approach the final target value in the above.

In the optical system positioning apparatus according to the present invention,
Preferably, the optical system includes a first lens having an objective lens for converging light and a solid immersion lens for converging light passing through the objective lens and irradiating the optical recording medium.
Or a second optical system in which the objective lens and the solid immersion lens are integrated.

In the optical system positioning apparatus according to the present invention,
More preferably, the optical recording medium is an optical disk, and the solid immersion lens has a central portion protruding at the surface facing the optical disk and its peripheral portion is flat, and the peripheral portion has A conductive film is formed,
The control circuit adjusts the distance by controlling the actuator based on a capacitance between the conductive film and the optical disc, by converging light passing through the objective lens and passing the light through the central portion.

In the positioning apparatus for an optical system according to the present invention,
For example, the numerical aperture of the optical system is greater than 1 and 3 or less, and the area where the near field is formed is in a state where the optical system and the optical recording medium are not in contact with each other and the distance is 5
The configuration may be a region of 00 nm or less.

In the method for positioning an optical system according to the present invention, the distance from the optical system that forms a near field with the optical recording medium and irradiates the optical recording medium with convergent light is controlled. An optical system positioning method, wherein the distance between the optical system and the optical recording medium is reduced in multiple stages from outside the region where the near-field is formed into the region,
Maintaining the distance within the region.

In the method for positioning an optical system according to the present invention,
Preferably, the step of shortening in multiple stages comprises:
Converting the initial value outside the region to an intermediate target value and maintaining the intermediate target value or substantially the intermediate target value; and setting the distance from the intermediate target value to a final target value within the region. And

In the method for positioning an optical system according to the present invention,
For example, the numerical aperture of the optical system is greater than 1 and 3 or less, and the area where the near field is formed is in a state where the optical system and the optical recording medium are not in contact with each other and the distance is 5
The configuration may be a region of 00 nm or less.

The recording / reproducing apparatus according to the present invention comprises: an optical system which forms a near field between a light source and an optical recording medium, converges light from the light source and irradiates the optical recording medium with the optical system; An actuator for moving the optical system in a focus direction orthogonal to the recording surface of the recording medium, and increasing a distance between the optical system and the optical recording medium from outside the area where the near field is formed to inside the area. A control circuit for controlling the actuator so as to shorten the phase and further maintain the actuator in the area; a motor for rotating the optical recording medium when recording and reproducing information; and recording information. An intensity modulation circuit for modulating the intensity of the light from the light source in accordance with the information to be recorded; and a detection circuit for detecting the recorded information from the light reflected by the optical recording medium when reproducing the information. And a circuit.

In the recording / reproducing apparatus according to the present invention, preferably, the control circuit sets the distance to an intermediate target value from an initial set value outside the area, or the intermediate target value or substantially the intermediate target value. And the actuator is controlled so as to approach the final target value in the area from the intermediate target value.

In the recording and reproducing apparatus according to the present invention, preferably, the optical system includes an objective lens for converging light from the light source and a solid for converging light passing through the objective lens and irradiating the optical recording medium with the light. A first optical system including an immersion lens, or a second optical system in which the objective lens and the solid immersion lens are integrated.

In the recording / reproducing apparatus according to the present invention, more preferably, the optical recording medium is an optical disk, and the solid immersion lens has a central portion protruding from a surface opposing the optical disk, and the solid immersion lens has an optical disk. A peripheral portion is flat, and a conductive film is formed on the peripheral portion, and the light passing through the objective lens is converged to pass through the central portion, and the control circuit controls a gap between the conductive film and the optical disc. The distance may be adjusted by controlling the actuator based on capacitance.

In the recording / reproducing apparatus according to the present invention, more preferably, the motor rotates the optical recording medium after the distance is maintained within the area.

In the recording / reproducing apparatus according to the present invention, for example,
The numerical aperture of the optical system is greater than 1 and 3 or less;
The region where the near field is formed is where the optical system and the optical recording medium are in a non-contact state and the distance is 500 nm.
The following areas may be used.

The control circuit controls the actuator so that the distance (air gap) between the optical system and the optical recording medium is shortened in multiple steps from outside the area where the near field is formed to inside the area. The distance between the system and the optical recording medium can be gradually reduced, and contact can be prevented. The control circuit temporarily maintains the distance as an intermediate target value from the initial setting value outside the area, and controls the actuator to approach the final target value in the area from the intermediate target value, thereby controlling the distance. In addition to being able to be shortened stepwise, the amount of this overshoot can be reduced when overshoot occurs, and the impact at the time of contact in the event of contact should be reduced.

[0026]

Embodiments of the present invention will be described below with reference to the accompanying drawings. An optical disk drive will be described as an example of an optical system positioning device according to the present invention.

Optical Head FIG. 1 is a diagram showing a configuration example of an optical head. The optical head 1 is attached to an optical pickup of the optical disk drive. The optical head 1 includes an objective lens 2, a solid immersion lens (SIL) 3, and a lens holder 4.
And an electromagnetic actuator 5.

The objective lens 2 is supplied with a laser beam LB from a semiconductor laser, which is a light source in the optical pickup, and converges the laser beam LB and supplies it to the solid immersion lens 3.

The solid immersion lens 3 converges the laser beam LB passing through the objective lens 2 and supplies the laser beam LB to the optical disk 51. This solid immersion lens 3 has a shape obtained by cutting a part of a spherical lens.
Generally, "Super Sphere SIL" or "Hyper Sphere
Called SIL. The solid immersion lens 3
The spherical surface is opposed to the objective lens 3, and the surface (bottom surface) opposite to the spherical surface is arranged to face the optical disk 51.

The lens holder 4 integrally holds the objective lens 2 and the solid immersion lens 3 in a predetermined positional relationship. When the laser beam LB parallel to the optical axis is incident on the objective lens 2, the solid immersion lens 3 converges the laser beam LB from the objective lens 2 to pass through the center of the bottom surface of the solid immersion lens 3. The optical disk 51 is irradiated with the passed laser beam LB. The objective lens 2 and the solid immersion lens 3 are arranged so that their optical axes coincide with each other, and the central portion is located on this optical axis.

The lens holder 4 has a conductive member, and a conductive film is formed on the bottom surface of the solid immersion lens 3 as described later. Are electrically connected via the solder 7.

The electromagnetic actuator 5 includes the lens holder 4
To move. The electromagnetic actuator 5 includes a focusing actuator (not shown) and a tracking actuator (not shown).
It has an actuator. The focusing actuator moves the lens holder 4 in a focus direction orthogonal to the recording surface of the optical disk 51, and holds the solid immersion lens 3 and the optical disk 51 at a predetermined distance. The tracking actuator moves the lens holder 4 in the radial direction (or the tracking direction) of the optical disk 51, and moves the solid immersion lens 3
Is held at the center of the track of the optical disc 51.

The solid immersion lens 3 is
The laser beam LB is designed to converge without aberration, and satisfies the condition of Stigmatic Focusing. The solid immersion lens 3 is set so that the recording surface of the optical disc 51 is focused on.
From the laser beam LB. The thickness t of the solid immersion lens 3 in the optical axis direction is represented by the following equation using the radius r and the refractive index n of the spherical lens.

[0034]

T = r × (1 + 1 / n)

According to Reference 2, the numerical aperture NA _eff of the optical system 10 including the objective lens 2 and the solid immersion lens 3 is equal to the numerical aperture NA of the objective lens 2.
_{Using obj} and the refractive index n of the solid immersion lens 3, it is expressed by the following equation.

[0036]

[ _Equation 3] NA _eff = n ² × NA _obj ...

In the present embodiment, as an example, the numerical aperture NA _obj of the objective lens 2 is set to 0.45, and the refractive index n of the solid immersion lens 3 is set to 1.83. In this case, according to the above equation, the numerical aperture NA _eff of the optical system 10 _{ 1.
It becomes 5. The wavelength λ of the laser beam LB is, for example, λ = 640 nm, and the air gap A is, for example, 0 <A ≦ 100 nm, preferably A ≒ 50 nm, for forming a near field.

The solid immersion lens FIG. 2 is a diagram showing a configuration example of a solid immersion lens. Solid immersion lens 3 is optical disk 5
1 has a diameter D = 1.5 mm, a central portion 3a protrudes, and a peripheral portion 3
b is flat. The projection of the central portion 3a has a height of about 2 μm and a diameter φ ≒ 40 μm.

The flat surface of the peripheral portion 3b is covered with a conductive film 6 of aluminum or the like formed by vapor deposition or the like, and the thickness of the conductive film is smaller than the height (about 2 μm) of the protrusion. . The conductive film 6 and a reflective film (recording film) such as aluminum of the optical disk 51 are formed by a solid immersion lens 3.
The capacitance Cg corresponding to the distance h between the flat surface of the optical disk 51 and the optical disk 51 is formed.

The capacitance Cg is expressed by the following equation using the facing area S between the peripheral portion 3b and the optical disk 51 and the interval h. The thickness of the conductive film is assumed to be negligibly small as compared with the interval h.

[0041]

Cg = ε ₀ × ε _r × S / h

Here, ε ₀ is a dielectric constant in a vacuum, and its value is 8.854 × 10 ⁻¹² F / m. ε _r is the relative dielectric constant, and its value is approximately 1 in air.

The facing area S is the diameter of the bottom surface D = 1.5.
mm, S = π × (D / 2) ² ≒ 1.767 ×
10 ⁻⁶ m ² . The interval h has a minimum value of 2 μm when the projection of the central portion 3a contacts the optical disk 51, that is, when the distance (air gap) A between the optical system 10 and the optical disk 51 is 0 nm. The interval h is such that the air gap A is 5
In the case of 0 nm, 100 nm, and 200 nm, they are 2.05 μm, 2.10 μm, and 2.20 μm, respectively.

Therefore, the air gap A is 0 nm, 5
Capacitance Cg at 0 nm, 100 nm, and 200 nm
Are about 7.82 pF and about 7.63, respectively, from the above equations.
pF, about 7.45 pF, and about 7.11 pF. As described above, since the capacitance Cg changes according to the air gap A, the air gap A can be detected using the capacitance Cg, and the servo control of the electromagnetic actuator 5 is performed using the capacitance Cg. Is performed, the air gap A can be set in the near-field region.

Further, since the central portion 3a of the opposing surface of the solid immersion lens 3 is protruded, and the peripheral portion 3b is formed with the conductive film 6 thinner than the height of the protrusion, the conductive film 6 is formed.
Can be prevented from approaching the optical disk 51 more than the central portion 3a and coming into contact with the optical disk 51. Also,
As shown in FIG. 1, since the conductive film 6 and the conductive lens holder 4 are electrically connected by the solder 7, wiring connection to the conductive film 6 can be easily performed via the lens holder 4. it can.

Optical Disk Drive FIG. 3 is a schematic block diagram showing an optical disk drive as an example of an optical system positioning apparatus according to the present invention. In the optical disk drive 100, the optical head 1 of FIG. 1 is attached to an optical pickup. The optical disk drive device 100 is installed in, for example, a recording / reproducing device that records or reproduces information by irradiating the optical disk 51 with laser light from a semiconductor laser via an optical system.

The optical disk drive 100 includes an optical head 1
, An optical pickup 12, a spindle motor 11,
A voltage controlled oscillator (VCO) 13, a reference voltage controlled oscillator (RVCO) 14, a comparing circuit 15, phase compensating circuits 16 and 20, amplifying circuits 17, 18, 21 and a tracking matrix circuit 19; Processing unit (CPU)
22, a semiconductor laser drive circuit 25, a motor drive circuit 26, and a detection circuit 27. The semiconductor laser drive circuit 25 includes an automatic power control (APC) circuit 23.
And an intensity modulation circuit 24.

The optical disk drive 100 includes an optical head 1
Then, the optical disk 51 is irradiated with laser light having a wavelength of 640 nm using the optical pickup 12 to record or reproduce information. The optical disk 51 mounted on the optical disk drive 100 is rotated at a constant rotation speed by the spindle motor 11. This optical disk 51 has a C
AV (Constant Angular Velocity)
Information is recorded according to the method.

The signal processing system for the focus servo is configured as follows. VCO (Voltage Controlle
The d oscillator 13 has an LC oscillation circuit having an inductor inside and a capacitor outside. One electrode of the external capacitor is a conductive film 6 formed on the flat surface of the solid immersion lens 3 of the optical head 1, and the other electrode is a reflective film or a recording film of the optical disk 51. And the capacitance Cg according to the distance h between the flat surface and the optical disk 51. This V
The oscillation frequency f of the CO 13 is expressed by the following equation using the capacitance Cg of the external capacitor, the stray capacitance Cf of the circuit, and the inductance L of the internal inductor.

[0050]

F = 1 / [2π × ｛L × (Cg + Cf)｝ ^1/2 ]

The air gap A, the interval h, and the capacitance C
FIG. 4 shows the correspondence between g and the oscillation frequency f. Here, as an example, the inductance L was set to 100 μH, and the stray capacitance Cf was set to 5 pF. That is, the air gap A
Are 0 nm, 50 nm, 100 nm, 200 nm, 10 μ
In the case of m, the oscillation frequency f can be calculated from the above equation by about 4.45 MHz, about 4.48 MHz, and about 4.51 MHz, respectively.
z, about 4.57 MHz and about 6.34 MHz.

A voltage controlled oscillator (RVCO: Reference Vo)
ltage Controlled Oscillator) 14 generates a reference signal. The frequency fr of the reference signal is, for example, 4.48 MHz.
z, which is equal to the oscillation frequency of the VCO 13 when the air gap A is 50 nm. In addition, RVCO
Reference numeral 14 includes, for example, a varactor diode. The frequency fr of the reference signal can be set by controlling the voltage applied to the varactor diode from the CPU 22.

The comparison circuit 15 is supplied with the output signal of the frequency f from the VCO 13 and the output signal of the frequency fr from the RVCO 14. The comparison circuit 15 includes a VCO 13
Is compared with the frequency and phase of the output signal of the RVCO 14, and a signal (error signal) corresponding to the difference between the frequency and phase of the output signal is generated.

The phase compensation circuit 16 is supplied with the output signal of the comparison circuit 15, generates a compensation signal in which the output signal of the comparison circuit 15 is compensated (phase compensation and / or frequency compensation), and supplies it to the amplification circuit 17. . The amplification circuit 17 amplifies the compensation signal and supplies the compensation signal to the focusing actuator of the electromagnetic actuator 5 as a control signal for adjusting the air gap A.

The focusing actuator comprises:
The lens holder 4 based on the control signal from the amplifier circuit 17
Is moved in the focus direction, the air gap A is set to be within the region where the near field is formed, and the air gap A is kept within the region. Thus, the air gap A is maintained at 0 <A ≦ 100 nm and A ≒ 50.
The distance h is adjusted to 2.05 μm, and the focus servo is realized.

A central processing unit (CPU: Central Processi)
The ng Unit) 22 is a controller that controls the entire optical disc driving device 100, and is constituted by, for example, a one-chip microcomputer (one-chip microcomputer). The CPU 22 is supplied with the output signal of the comparison circuit 15 and detects based on the output signal of the comparison circuit 15 that the air gap A is maintained in the near-field region (the region where the near-field is formed). Then, a start signal ST is generated, and the start signal ST is supplied to the motor drive circuit 26. Also, CP
U22 is the spindle motor 11 or the optical disc 51
A signal indicating the number of rotations or the rotation speed is supplied. The tracking servo and the focus servo are performed under the control of the CPU 22.

CPU 22, VCO 13, RVCO 1
4, the comparison circuit 15, the phase compensation circuit 16, and the amplification circuit 17 form a control circuit 28. The control circuit 28 determines that the air gap A is in a near-field region (for example, 0 <A ≦ 500 nm, preferably 0 <A ≦ 200 n).
m, more preferably 0 <A ≦ 100 nm). By setting the air gap A within the near-field region, the optical disk 5
The beam intensity at the center of the beam spot on the recording surface of No. 1 can be maintained at, for example, 50% or more (preferably 60% or more) with respect to the case where the air gap A is 0 nm. , It is possible to obtain a beam intensity of about 80%.

The motor drive circuit 26 supplies power to the spindle motor 11 to rotate it at a constant rotation speed. For example, rotation control may be performed by PWM (Pulse Width Modulation) control or the like. This motor drive circuit 26
Is, when the start signal ST is supplied from the CPU 22,
The rotation of the spindle motor 11 is started. A turntable (not shown) is mounted on the rotation shaft of the spindle motor 11, and the optical disk 51 on the turntable rotates with the rotation of the spindle motor 11.

FIG. 5 is a diagram showing a configuration example of the optical pickup 12. The optical pickup 12 includes a semiconductor laser 31
, A collimator lens 32, a diffraction grating 33, and a half
Wave plate 34, polarizing beam splitter 35, quarter wave plate 36, condenser lenses 37 and 39, photodetectors 38 and
40, an objective lens 2 and a solid immersion lens 3. This optical pickup 12 has an optical head 1
The optical head 1 has an optical system 10 comprising an objective lens 2 and a solid immersion lens 3.
Having.

The semiconductor laser 31 is an example of a light source that emits coherent light and a light emitting element. The semiconductor laser 31 has a linearly polarized laser beam LB having a wavelength of 640 nm.
Is generated, and this laser beam LB is
Feed to 2. The collimator lens 32 converts the laser beam LB from the semiconductor laser 31 into parallel light,
Supply 3

The diffraction grating 33 separates the laser beam LB from the collimator lens 32 into a main beam (0th-order diffracted light) and a sub-beam (first-order diffracted light), and separates the main beam and the sub-beam into a half-wave plate. 34. 1/2 wave plate 3
Reference numeral 4 rotates the polarization planes of the main beam and the sub-beam from the diffraction grating 33 and supplies the rotated beam to the polarization beam splitter 35.

The polarizing beam splitter 35 passes most of the incident laser beam from the half-wave plate 34 and
The laser beam is supplied to the 波長 wavelength plate 36, and a part of the incident laser beam is reflected and supplied to the condenser lens 39.

The condensing lens 39 converges the reflected laser beam from the polarizing beam splitter 35 and supplies it to the photodetector 40. The photodetector 40 photoelectrically converts the laser beam from the condenser lens 39 and generates a signal SP corresponding to the intensity of the laser beam. The photodetector 40 is used for monitoring the emission intensity of the semiconductor laser 31 or for monitoring the beam intensity on the recording surface (recording film) of the optical disk 51. The amount of the laser beam incident on the photodetector 40 can be adjusted by rotating the half-wave plate 34.

The quarter-wave plate 36 rotates the plane of polarization of the laser beam passing through the polarizing beam splitter 35 into circularly polarized light, and supplies the circularly polarized laser beam to the objective lens 2 of the optical head 1. The objective lens 2 includes a 波長 wavelength plate 36
Is converged and supplied to the solid immersion lens 3. Solid immersion lens 3
Converges the laser beam from the objective lens 3 and passes it through the central portion 3a, and supplies this passing laser beam to the signal recording surface of the optical disk 51.

The laser beam reflected on the signal recording surface (recording film) of the optical disk 51 is supplied to the 波長 wavelength plate 36 via the solid immersion lens 3 and the objective lens 2. The 波長 wavelength plate 36 rotates the plane of polarization of the laser beam from the objective lens 2 to be linearly polarized, and supplies this linearly polarized laser beam to the polarization beam splitter 35. The polarization plane of the incident laser beam supplied from the polarization beam splitter 35 to the quarter wavelength plate 36 is
The plane of polarization of the reflected laser beam supplied from the four-wavelength plate 36 to the polarization beam splitter 35 is orthogonal.

The polarization beam splitter 35 reflects the laser beam from the 波長 wavelength plate 36 and supplies the laser beam to the condenser lens 37. The condenser lens 37 is used for the polarization beam splitter 3.
The reflected laser beam from 5 is converged and supplied to the photodetector 38. The photodetector 38 photoelectrically converts the laser beam from the condenser lens 37 to generate signals SA to SH. This photodetector 38 is used for detecting the tracking error signal TE and the reproduced RF signal.

As shown in FIG. 6, the photodetector 38 has a first light receiving portion 381 for receiving a main beam at the center thereof, and a sub-beam receiving portion on both sides of the first light receiving portion 381. Second light receiving unit 382 and third light receiving unit 383 are disposed. The first light receiving unit 381 includes four light receiving units 3
It is equally divided into 8A to 38D. Second light receiving unit 382
Are equally divided into two light receiving sections 38E and 38F.
The third light receiving unit 383 is equally divided into two light receiving units 38G and 38H. The light detector 38 may be formed by a light receiving element in which a light receiving portion is divided into eight.

The output signals SA to SH of the respective light receiving sections 38A to 38H of the photodetector 38 are amplified by an amplifier circuit (head amplifier) 18 in FIG. 3 and are tracked by a tracking matrix circuit (tracking error detection circuit) 19 and a detection circuit. 27. The tracking matrix circuit 19 calculates the following equation based on the amplified output signals SA to SH, and generates a tracking error signal TE using a differential push-pull method. Note that k in the equation is a constant.

[0069]

## EQU6 ## TE = (SA + SD)-(SB + SC) + k × {(SE-SF) + (SG-SH)}

The phase compensation circuit 20 is supplied with the tracking error signal TE, generates a compensation signal obtained by phase-compensating the tracking error signal TE, and supplies the compensation signal to the amplifier circuit 21. The amplification circuit 21 amplifies the compensation signal and supplies it to the tracking actuator of the electromagnetic actuator 5 as a control signal. The tracking actuator moves the lens holder 4 in the radial direction (or the tracking direction) of the optical disk 51 based on a control signal from the amplifier circuit 21. As a result, tracking servo is realized.

The detection circuit (information detection circuit) 27 outputs the output signal SA amplified by the amplification circuit (head amplifier) 18.
To SD, the following equation is calculated to obtain the reproduced RF signal R
Generate F. Then, the recording information So of the optical disk 51 is reproduced by performing demodulation and the like based on the reproduced RF signal.

[0072]

## EQU7 ## RF = SA + SB + SC + SD ...

The semiconductor laser drive circuit 25 has an intensity modulation circuit 24 and an APC circuit 23, and
Drive the semiconductor laser 31 inside. Intensity modulation circuit 24
Supplies information Si to be recorded on the optical disk 51 from a memory or an external device or the like, and generates a modulation control signal SM in accordance with the input information Si.

An APC (Automatic Power Control) circuit 23 is supplied with the output signal SP of the monitoring photodetector 40 in the optical pickup 12 and the modulation control signal SM. When recording information, the APC circuit 23 modulates the drive voltage or drive current of the semiconductor laser 31 based on the modulation control signal SM to modulate the intensity of the laser beam LB, and also controls the output signal SP of the photodetector 40. Thus, the emission intensity of the semiconductor laser 31 is kept within the first set range R1, and the laser light output of the semiconductor laser 31 is adjusted. On the other hand, when reproducing information, the APC circuit
, The light emission intensity of the semiconductor laser 31 is kept within the second set range R2 (<R1) based on the output signal SP, and the laser light output of the semiconductor laser 31 is adjusted.

[0075] Operation Example Figure 7 and Figure 8 of the optical disk drive is a schematic flow diagram illustrating the operation of the optical disk drive 100. First, in step S1, the CPU 22 detects a focus servo start command. For example, when the operator performs a recording or reproducing switch operation on the recording / reproducing device provided with the optical disk drive device 100, the start command is supplied to the CPU 22. Note that the air gap A at this time is an initial setting value outside the near-field region.

Next, in step S2, the CPU 22
The oscillation frequency fr of the RVCO 14 is set to about 6.34 MHz, and the target value of the air gap A is set to an intermediate target value of 10%.
Set to μm. Then, the drive of the electromagnetic actuator 5 is started, and the pull-in (focus pull-in) of the solid immersion lens 3 (and the optical system 10) is started.
The oscillation frequency fr = 6.34 MHz is equal to the oscillation frequency f of the VCO 13 when the air gap A = 10 μm, as shown in FIG.

In step S3, the CPU 22 determines whether or not the pull-in operation for setting the air gap A to 10 μm or substantially 10 μm is completed based on the output signal of the comparison circuit 15. If the retraction has not been completed, wait until it is completed. When the retraction is completed, the air gap A is maintained at the intermediate target value (10 μm) or substantially at the intermediate target value, and the process proceeds to step S4.

In step S4, the CPU 22 determines whether the RVC
The oscillation frequency fr of O14 is set to 4.48 MHz, and the target value of the air gap A is set to 50 nm which is the final target value. Then, the solid immersion lens 3 (and the optical system 10) is further retracted (focus retracted) by the electromagnetic actuator 5. Oscillation frequency fr =
4.48 MHz is equal to the oscillation frequency f of the VCO 13 when the air gap A = 50 nm as shown in FIG. The oscillation frequency fr of the VCO 13 may be made to follow by dividing the oscillation frequency fr gradually from 6.34 MHz to 4.48 MHz in a plurality of stages,
Thereby, the air gap A can be gradually reduced.

In step S5, the CPU 22 determines whether or not the pull-in operation (focus pull-in operation) for setting the air gap A to 50 nm or substantially 50 nm has been completed.
The determination is made based on the output signal of the comparison circuit 15. If the retraction has not been completed, wait until it is completed. When the retraction is completed, the process proceeds to step S6. At this time, the air gap A is maintained at the final target value (50 nm) or substantially at the final target value, and is maintained in the near-field region.

At step S 6, the CPU 22 generates a start signal ST and supplies it to the motor drive circuit 26. In step S7, the motor drive circuit 26 starts power supply to the spindle motor 11 based on the start signal ST, and starts rotation of the optical disk 51.

In step S8, the CPU 22 determines whether or not the rotation speed (disk rotation speed) V of the optical disk 51 is a predetermined constant rotation speed Vc (> 0). If the disk rotation speed V is not the constant rotation speed Vc, the CPU 22 controls the rotation of the spindle motor 11 via the motor drive circuit 26 to set the rotation speed to the constant rotation speed Vc. If the disk rotation speed V is the constant rotation speed Vc, the process proceeds to step S9.

At step S9, the CPU 22 supplies a power-on signal to the APC circuit 23 in the semiconductor laser drive circuit 25. The APC circuit 23 turns on the semiconductor laser 31 based on the power-on signal and outputs the laser beam LB
Output.

While the optical disk 51 is stopped, the semiconductor laser 3
When 1 is turned on, the solid immersion lens 3
When a laser beam is applied to a specific portion of the optical disk 51 for a long time at the time of pull-in (at the time of focus pull-in), the temperature of the irradiated portion may be high, and the characteristics of the irradiated portion may change. On the other hand, as shown in the present embodiment, by turning on the semiconductor laser 31 after the rotation of the optical disk 51, a specific portion of the optical disk 51 is irradiated with the laser beam for a long time when the solid immersion lens 3 is retracted, so that the irradiated portion has a high temperature. Can be prevented.

As described above, according to the optical disk drive 100, the solid immersion lens 3
Can be used to obtain a numerical aperture exceeding 1, and to control the air gap A to a predetermined value (for example, about 50 nm) in the near-field region based on the capacitance Cg with high accuracy. Can be. The numerical aperture of the optical system 10 is
For example, it may be larger than 1 and 3 or less, and may be larger than 1 and 2.5 or less. Since the conductive film 6 is formed on the bottom surface of the solid immersion lens 3, the gap between the conductive film 6 and the optical disk 51 can be reduced to increase the capacitance Cg, and the focus servo can be performed with higher precision. It is.

The control circuit 28 controls the air gap A
However, since the electromagnetic actuator 5 is controlled so as to be shortened in a multi-step manner from outside the near-field region to inside the region, the air gap A can be gradually shortened to prevent the optical system 10 from contacting the optical disk 51. It is possible, and in the event of a contact, the impact can be reduced.

This control circuit 28 sets the air gap A
The air gap A is stepped by controlling the electric actuator 5 so that the initial target value outside the near-field region is set to the intermediate target value and temporarily maintained, and the intermediate target value is brought closer to the final target value within the near-field region. In addition to the above, the overshoot can be reduced when the overshoot occurs, and the impact can be suppressed to a small extent in the event of a contact. A plurality of intermediate target values are set between an initial set value outside the near-field region and a final target value within the near-field region, and the air gap A is set by sequentially passing through the plurality of intermediate target values. May gradually approach the final target value. For example, the capacitance C
g is substantially formed (for example, about 10 μm
To about 100 μm), a plurality of the intermediate target values may be set.

Further, according to the optical disk drive 100, the optical disk 51 can be stopped when the optical system 10 is pulled to a close distance in the near-field region. In this way, if the optical system 10 and the optical disk 51 come into contact with each other, the contact area and the impact are reduced.
1 can be made smaller than when it is rotating.

In the above embodiment, the optical system 10 is formed by the objective lens 2 and the solid immersion lens 3, and the optical system 10 having a numerical aperture of about 1.5 is provided in the optical head 1. However, the optical head 1 may be provided with an optical system including a single optical element in which the objective lens 2 and the solid immersion lens 3 are integrated. Such single optical elements include, for example, Chul Woo Lee, Kun
Ho Cho, Chong Sam Chung, Jang Hoon Yoo, Yong Hoon
Lee, "Feasibility study on near field optical memo
ry using a catadioptric optical system, "Digest of
Optical Data Storage, pp.137-139, Aspen, CO. (199
The reflection type light condensing element disclosed in 8) may be used. Further, as the optical element having the function of the objective lens 2 and the optical element having the function of the solid immersion lens, three or more optical elements may be provided in the optical head 1, and the hologram element may be provided in the optical head 1. .

In this embodiment, the phase-change optical disk 51 is used as an example of the optical recording medium, but a magneto-optical disk may be used. Further, even when a passive optical head using a flying slider is used, the capacitance C
From g, the flying height corresponding to the air gap A can be detected and the flying height can be optimized.

The radius of the opposing surface of the solid immersion lens 3 (or the optical system 10) on which the conductive film 6 is formed is smaller than the width from the inner edge of the recording surface of the optical disk 51 to the innermost track. It is preferable to use a positive value and a positive value smaller than the width from the outer edge of the recording surface of the optical disc 51 to the outermost track. By doing so, the laser beam LB is applied to the innermost track.
When the laser beam LB is focused on the outermost track, the entire bottom surface of the solid immersion lens 3 can be opposed to the recording surface, and the capacitance Cg varies depending on the focusing position. Can be reduced.

In the present embodiment, the optical disk drive 100 has been described as an example of an optical system positioning device. The optical system positioning apparatus according to the present embodiment has an optical system in which the coherence of the light source is high and the working distance of the optical system (or the objective lens) is short, that is, interference fringes are likely to occur. Useful in equipment. In such an optical device, an error is likely to occur in focus control by an optical method due to intensity distribution due to optical interference. In the optical disc drive device 100, focus control using an output signal (electric signal) of an LC oscillation circuit is performed. The error can be reduced.

The optical disk drive device 100 may be applied to various light irradiation devices for irradiating light, in addition to the recording / reproducing device, for example, to a processing device, an exposure device, an inspection device, and the like. For example, when inspecting a sample such as a metal and a semiconductor wafer using an optical inspection apparatus, it is possible to perform focus control based on the capacitance between the optical system 10 and the sample. Of course, an optical recording medium may be used as a sample. When it is necessary to quickly inspect the entire region of a sample as in a semiconductor wafer inspection apparatus, focus control is performed based on the capacitance between the optical system 10 and the sample, thereby enabling the movable stage and the sample to be inspected. The position of the optical system can be corrected according to the inclination, and the time required for the inspection can be reduced.

The above embodiment is an exemplification of the present invention, and the present invention is not limited to the above embodiment.

[0094]

According to the positioning apparatus and the positioning method of the optical system according to the present invention, the air gap is shortened in multiple steps from outside the near-field region to the inside thereof, so that the contact between the optical system and the optical recording medium is prevented. It is possible to improve the reliability and durability of the optical system and the optical recording medium.

For example, the air gap is temporarily set to an intermediate target value from an initial setting value outside the near-field region, and is maintained once, and the air gap is gradually brought close to the final target value in the near-field region from the intermediate target value. In addition to the above, the overshoot can be reduced when the overshoot occurs, and the impact can be suppressed to a small extent in the event of a contact.

In the recording / reproducing apparatus according to the present invention, the air gap is shortened from outside the near-field region to the inside of the region in multiple steps, so that contact between the optical system and the optical recording medium can be prevented. It is possible to improve the reliability and durability of the optical recording medium and the reliability of recorded information and reproduced information.

For example, the air gap is temporarily set to an intermediate target value from an initial setting value outside the near-field region and is maintained once, and the air gap is gradually increased by approaching the final target value within the near-field region from the intermediate target value. It is possible to reduce the amount of overshoot when an overshoot occurs, and to reduce the impact in the event of contact with the optical system and optical recording. It is possible to improve the reliability and durability of the medium and the reliability of recorded information and reproduced information.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration example of an optical head.

FIG. 2 is a diagram illustrating a configuration example of a solid immersion lens.

FIG. 3 is a schematic block diagram showing an optical disk drive as an example of an optical system positioning apparatus according to the present invention.

FIG. 4 shows an air gap A, an interval h, and a capacitance Cg.
FIG. 5 is a diagram illustrating an example of correspondence between the oscillation frequency f and the oscillation frequency f.

FIG. 5 is a diagram illustrating a configuration example of an optical pickup.

FIG. 6 is a diagram showing an example of the arrangement of a light receiving section of the photodetector 38.

FIG. 7 is a schematic flowchart showing the operation of an optical disk drive as an example of the optical system positioning apparatus according to the present invention.

FIG. 8 is a schematic flowchart showing the operation of the optical disk drive as an example of the optical system positioning device according to the present invention, following FIG. 7;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical head, 2 ... Objective lens, 3 ... Solid immersion lens (SIL), 3a ... Central part, 3b ... Peripheral part,
4 lens holder, 5 electromagnetic actuator (actuator), 6 conductive film, 7 solder, 10 optical system, 11
... Spindle motor (motor), 12 ... Optical pickup, 13 ... Voltage controlled oscillator (VCO), 14 ... Voltage controlled oscillator (RVCO), 15 ... Comparing circuit, 16,20 ... Phase compensation circuit, 17,21 ... Amplifying circuit, 18 Amplification circuit (head amplifier), 19 Tracking matrix circuit, 22 Central processing unit (CPU), 23 Automatic power control circuit (APC circuit), 24 Intensity modulation circuit, 25 Semiconductor laser drive circuit, 26 Motor drive circuit, 27 detection circuit, 28 control circuit, 31 semiconductor laser (light source), 32 collimator lens, 33 diffraction grating, 34 half-wave plate, 35 polarization beam splitter, 36 1 / 4 wavelength plates, 37, 39 ... condenser lens, 3
8, 40: photodetector, 38A to 38H: light receiving section, 51:
Optical disk (optical recording medium), 100 ... optical disk drive (optical system positioning device), 381-383 ... first
To the third light receiving portion, D, φ: diameter, h: interval, LB: laser beam (laser light), r: radius.

Claims (14)

[Claims] An optical system that forms a near field with the optical recording medium and irradiates the optical recording medium with a convergent light; and sets the optical system in a focus direction orthogonal to a recording surface of the optical recording medium. The actuator to be moved, and the distance between the optical system and the optical recording medium is shortened in a multi-step manner from outside the region where the near field is formed to within the region,
A control circuit for controlling the actuator so as to maintain the actuator in the region. 2. The control circuit sets the distance to an intermediate target value from an initial set value outside the area and temporarily maintains the intermediate target value or substantially the intermediate target value. 2. The positioning device for an optical system according to claim 1, wherein the actuator is controlled so as to approach a final target value in the area. 3. The first optical system comprising an objective lens for converging light and a solid immersion lens for converging light passing through the objective lens and irradiating the optical recording medium. The positioning device for an optical system according to claim 1, further comprising a second optical system in which an objective lens and the solid immersion lens are integrated. 4. The optical recording medium is an optical disk, and the solid immersion lens has a central portion protruding from a surface facing the optical disk, a peripheral portion thereof is flat, and a peripheral portion thereof is provided. A conductive film is formed, the light passing through the objective lens is converged and passed through the central portion, and the control circuit controls the actuator based on a capacitance between the conductive film and the optical disk. The positioning device for an optical system according to claim 3, wherein the distance is adjusted. 5. The numerical aperture of the optical system is greater than 1 and 3
The region where the near field is formed is such that the optical system and the optical recording medium are in a non-contact state and the distance is 500 nm.
The positioning device for an optical system according to claim 1, wherein: 6. A method for positioning an optical system for controlling a distance from an optical system that forms a near field with the optical recording medium and irradiates convergent light to the optical recording medium to the optical recording medium, comprising: An optical system comprising: a step of shortening the distance between the optical system and the optical recording medium from outside the region where the near field is formed to a region in multiple stages; and a step of maintaining the distance within the region. How to position the system. 7. The multi-step shortening step includes: changing the distance from an initial value outside the region to an intermediate target value, and maintaining the distance at the intermediate target value or substantially at the intermediate target value; 7. A method for positioning an optical system according to claim 6, further comprising: changing a distance from the intermediate target value to a final target value in the area. 8. The numerical aperture of the optical system is greater than 1 and 3
The region where the near field is formed is such that the optical system and the optical recording medium are in a non-contact state and the distance is 500 nm.
7. The positioning method for an optical system according to claim 6, wherein the area is the following area. 9. An optical system that forms a near field between a light source and an optical recording medium, converges light from the light source and irradiates the optical recording medium, and a recording surface of the optical recording medium. An actuator for moving the optical system in the orthogonal focus direction, shortening the distance between the optical system and the optical recording medium in multiple steps from outside the area where the near field is formed to an area,
A control circuit for controlling the actuator so as to be maintained in the area; a motor for rotating the optical recording medium when recording and reproducing information; and recording when recording information. A recording / reproducing apparatus comprising: an intensity modulation circuit for modulating the intensity of light from the light source according to information; and a detection circuit for detecting recorded information from light reflected by the optical recording medium when reproducing information. 10. The control circuit sets the distance to an intermediate target value from an initial set value outside the area and temporarily maintains the intermediate target value or substantially the intermediate target value. The recording / reproducing apparatus according to claim 9, wherein the actuator is controlled so as to approach a final target value in the area. 11. A first optical system comprising: an objective lens for converging light from the light source; and a solid immersion lens for converging light passing through the objective lens and irradiating the optical recording medium. Or a second one in which the objective lens and the solid immersion lens are integrated.
The recording / reproducing apparatus according to claim 10, further comprising an optical system. 12. The optical recording medium is an optical disk, and the solid immersion lens has a central portion protruding from a surface facing the optical disk, a peripheral portion thereof is flat, and a peripheral portion thereof is provided. A conductive film is formed, the light passing through the objective lens is converged and passed through the central portion, and the control circuit controls the actuator based on a capacitance between the conductive film and the optical disk. The recording / reproducing apparatus according to claim 11, wherein the distance is adjusted. 13. The motor according to claim 1, wherein the motor rotates the optical recording medium after the distance is maintained within the area.
0. The recording / reproducing apparatus according to 0. 14. The numerical aperture of the optical system is greater than 1 and 3 or less, and the area where the near field is formed is in a state where the optical system and the optical recording medium are not in contact with each other and the distance Is 500 nm
The recording / reproducing apparatus according to claim 10, wherein the recording / reproducing apparatus is the following area.