JP2004335064A - Information recording device and method, and information reproducing device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To adjust a gap with high precision and to constantly stabilize the whole system by enhancing especially the DC gain for a controller even in a near-field area, in a information recording device and method, and an information reproducing device and method to record and reproduce using evanescent light. <P>SOLUTION: When recording using evanescent light is performed, if an emitting means is located in the near field to an information recording surface 2a of an optical disk 2, a laser beam is emitted to the information recording surface 2a as the near-field light. Moreover, a first control section 72 and a second control section 73 to control a SIL 63 to maintain a predetermined distance to the information recording surface 2a, according to the return light quantity of the near-field light emitted to the information recording surface 2a, are connected in parallel. When the return light quantity of the near-field light exceeds a predetermined threshold, the output in the second control section 73 is blocked. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an information recording apparatus and method for performing recording and reproduction using evanescent light, and an information reproducing apparatus and method.
[0002]
[Prior art]
In a recording / reproducing device that records or reproduces predetermined information by irradiating light to a recording medium such as an optical disk, high-density recording / reproduction exceeding the diffraction limit of light is possible by using evanescent light. A lens using SIL (Solid Immersion Lens) is widely known as a lens for emitting the evanescent light.
[0003]
In order to realize the recording and reproduction by the evanescent light, the SIL and the aspherical lens are combined and used as a second group lens so that the numerical aperture NA is 1 or more, and the distance (gap) to the information recording surface of the recording medium is reduced. ) Must be less than half the wavelength of the laser light incident on the SIL. This gap is 200 nm or less when the wavelength λ of the laser light is 400 nm, for example.
[0004]
Further, in order to perform good recording and reproduction, it is necessary to keep the gap constant. For this reason, a method has been proposed in which an actuator of an optical head equipped with an SIL is servo-controlled by a controller using a difference in the amount of return light as an error signal so that the information recording surface is followed. (For example, refer to Patent Document 1).
[0005]
[Patent Document 1]
JP 2001-76358 A
[0006]
[Problems to be solved by the invention]
When a two-axis device such as an optical head is controlled to keep this gap constant in a near-field region from the information recording surface of a disk-shaped optical recording medium, an extremely large DC gain is required for the above-described controller. Is done.
[0007]
For example, when the primary resonance frequency of the actuator of the optical head is as high as 100 Hz, the distance between the objective lens and the disk can be increased while maintaining the stability of the system even if an integrating filter or the like is separately provided. It is difficult to secure a DC gain sufficient to maintain the distance at which occurs, typically 200 nm or less.
[0008]
Further, even when a digital servo is used, the phase rotation is faster than that of an analog servo, and it is difficult to secure a sufficient DC gain due to the relationship of the sampling frequency.
[0009]
Further, even if the DC gain described above can be improved, if the actuator of the optical head is a non-linear system having a dead zone, disturbance is applied to the system, and the entire system becomes unstable. There is a problem.
[0010]
Therefore, the present invention has been devised in view of the above-described problems, and in an information recording apparatus and method for performing recording and reproduction using evanescent light, and an information reproducing apparatus and method, particularly, a DC for a controller. It is an object of the present invention to provide an information recording apparatus and method, and an information reproducing apparatus and method that can adjust a gap with high accuracy even in a near-field region and constantly stabilize the entire system by improving a gain. Aim.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventor has proposed an information recording apparatus and a method for executing a recording process using evanescent light, wherein an emitting unit is disposed in a near field with respect to an information recording surface of an optical recording medium. The laser beam is emitted to the information recording surface as near-field light, and the emitting unit is controlled to maintain a predetermined distance from the information recording surface according to the amount of return light of the near-field light emitted to the information recording surface. An information recording device which, in addition to the first control means, connects a second control means in parallel with the first control means and cuts off the output of the second control means when the return light amount of the near-field light exceeds a predetermined threshold value And a method.
[0012]
That is, the information recording apparatus to which the present invention is applied, a light source that emits laser light modulated by recording information to be recorded on the information recording surface of the optical recording medium, and condenses the laser light emitted from the light source, Emitting means for emitting the condensed laser light to the information recording surface as near-field light when disposed in the near field with respect to the information recording surface of the optical recording medium; and near-field light emitted to the information recording surface. Return light amount detection means for detecting the return light amount of the light, and at the time of recording with the near-field light, based on the return light amount of the near-field light detected by the return light amount detection means, the emission means with respect to the information recording surface. First control means for controlling the information recording surface to maintain a predetermined distance, and the emission means is connected in parallel to the first control means, and the emission means is arranged on the information recording surface in a band different from that of the first control means. Predetermined Comprising a second control means for controlling so as to keep the release, return light of the near-field light, if it exceeds a predetermined threshold, and switching means for cutting off the output of the second control means.
[0013]
In the information recording method to which the present invention is applied, a first emitting step of emitting laser light modulated by recording information to be recorded on an information recording surface of an optical recording medium, and a condensing step of condensing the emitted laser light A second emission step of emitting the condensed laser light as near-field light to the information recording surface when the unit is disposed in a near field with respect to the information recording surface of the optical recording medium; A detecting step of detecting a return light amount of the near-field light emitted to the light source, and at the time of recording using the near-field light, the light-collecting unit detects the information based on the return light amount of the near-field light detected in the detection step. A first control step of controlling to keep a predetermined distance from the recording surface; and, when the return light of the near-field light is equal to or less than a predetermined threshold, the light is emitted in a band different from that of the first control step. Means with respect to the information recording surface And a second control step of controlling to maintain the release.
[0014]
In order to solve the above-mentioned problems, the present inventor has proposed an information recording apparatus and a method for performing a reproducing process using evanescent light, wherein an emitting unit is disposed in a near field with respect to an information recording surface of an optical recording medium. The laser beam is emitted to the information recording surface as near-field light, and the emitting unit is controlled to maintain a predetermined distance from the information recording surface according to the amount of return light of the near-field light emitted to the information recording surface. An information reproducing apparatus which, in addition to the first control means, connects a second control means in parallel with the first control means and cuts off the output of the second control means when the return light amount of the near-field light exceeds a predetermined threshold value And a method.
[0015]
That is, an information reproducing apparatus to which the present invention is applied includes a light source that emits laser light for reproducing recorded information recorded on an information recording surface of an optical recording medium, and a light source that collects the laser light emitted from the light source. An emitting unit that emits the focused laser light to the information recording surface as near-field light when the optical recording medium is disposed in a near field with respect to the information recording surface of the optical recording medium; Returning light amount detecting means for detecting the returning light amount of the field light; and, at the time of recording with the near field light, the emitting means based on the returning light amount of the near field light detected by the returning light amount detecting means. A first control means for controlling a predetermined distance from the first control means, and the emission means is connected to the first control means in a different band from the first control means. Predetermined Comprising a second control means for controlling so as to keep the release, return light of the near-field light, when it exceeds the predetermined threshold, and switching means for cutting off the output of the second control means.
[0016]
Further, the information reproducing apparatus to which the present invention is applied includes a first emitting step of emitting laser light for reproducing recorded information recorded on an information recording surface of an optical recording medium, and condensing the emitted laser light. A second emitting step of emitting the collected laser light to the information recording surface as near-field light when the light-collecting unit is arranged in a near field with respect to the information recording surface of the optical recording medium; A detecting step of detecting a return light amount of the near-field light emitted to the information recording surface; and at the time of recording with the near-field light, the light-collecting unit based on the return light amount of the near-field light detected in the detection step. A first control step of controlling the distance from the information recording surface to a predetermined distance, and when the return light of the near-field light is equal to or less than a predetermined threshold, in a different band from the first control step. The emission means is predetermined with respect to the information recording surface. And a second control step of controlling to maintain the distance.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0018]
FIG. 1 shows a configuration example of an optical recording apparatus to which the information recording apparatus and method according to the present invention are applied. The optical recording device 1 shown in FIG. 1 is a recording device corresponding to a removable optical disk 2 and irradiates a spindle motor 3 for driving the optical disk 2 to rotate and a laser beam onto a signal recording surface 2a of the optical disk 2 and An optical head 4 for detecting return light from the optical disk 2 and a gap control unit 6 for generating a control signal based on the return light detected by the optical head 4.
[0019]
A disk table on which the optical disk 2 is mounted is integrally attached to the spindle motor 3. The spindle motor 3 drives the drive shaft to rotate at a constant linear velocity (CLV) or a constant angular velocity (CAV), for example, based on a spindle drive signal supplied from a system controller (not shown). As a result, the optical disk 2 mounted on the disk table is rotated.
[0020]
The optical head 4 focuses a light beam on each recording layer of the optical disk 2 that is rotated by driving the spindle motor 3, detects return light reflected on the signal recording surface of the optical disk 2, and sends the signal to the signal processing unit 5. Output. At this time, the optical head 4 is controlled so as to emit a laser beam having an optimal wavelength for the optical disk 2 depending on the type of the optical disk 2 to be rotated.
The gap control unit 6 generates a control signal based on the gap error signal GE transmitted from the optical head 4, and outputs the control signal to the optical head 4. In other words, the control signal allows the objective lens of the optical head 4 to be finely adjusted in the direction of approaching or separating from the optical disk 2.
[0021]
In the optical recording apparatus 1, the optical head 4 is moved in the radial direction of the optical disk 2 by an access mechanism (not shown), and the optical head 4 is operated so as to be positioned on a predetermined recording track of the optical disk 2. Is also good.
[0022]
Next, the optical head 4 to which the present invention is applied will be described in more detail.
[0023]
The optical head 4 includes an APC (Automatic Power Controller) 42 for controlling a driving current of the semiconductor laser, a holder 43 for supporting each semiconductor laser, and a beam arranged in an optical path of laser light emitted from the semiconductor laser. A splitter 44, a collimator lens 45 that converts the laser light transmitted through the beam splitter 44 into parallel light, a mirror 46 disposed in an optical path of the laser light that has been converted into parallel light by the collimator lens 45, and a mirror 46 A quarter-wave plate 47 on which the laser light reflected by the optical disc 2 is incident, a lens block 48 for condensing the laser light passing through the quarter-wave plate 47 on the signal recording surface 2a of the optical disc 2, A condenser lens 55 for condensing return light reflected from the signal recording surface 2a and returning, And a light receiving element 56 for light.
[0024]
A semiconductor laser 71 that emits a laser beam having a predetermined wavelength is attached to the holder 43. The semiconductor laser 71 is a light emitting device using recombination light emission of a semiconductor. The semiconductor laser 71 emits a laser beam based on the information signal supplied from the information source 58 after the driving current is controlled by the APC 42 so that the output of the laser beam becomes constant.
[0025]
The beam splitter 44 transmits the laser light emitted from the semiconductor laser 71 and guides the laser light to the optical disk 2, and reflects the return light reflected from the optical disk 2 and returns to the light receiving element 56. The divergent laser light transmitted through the beam splitter 44 is converted into a parallel light by a collimator lens 45 and passes through a 波長 wavelength plate 47. When the laser beam emitted from the semiconductor laser 71 has polarization, the beam splitter 44 uses a polarization beam splitter to prevent return light reflected from the optical disc 2 and returned from returning to the semiconductor laser 71. Can be prevented.
[0026]
The mirror 46 bends the optical path by reflecting the laser beam transmitted through the beam splitter 44. As a result, the laser light is applied substantially perpendicularly to the signal recording surface 2a of the optical disc 2 located below the optical head 4.
[0027]
The 波長 wavelength plate 47 gives a phase difference of π / 2 to the passing laser light. The linearly polarized laser light emitted from the semiconductor laser 71 passes through the quarter wavelength plate 47 and becomes circularly polarized light. The circularly polarized laser light reflected from the optical disk 2 and returned returns to linearly polarized light when passing through the quarter-wave plate 47.
[0028]
The lens block 48 is disposed in the optical path of the laser light reflected by the mirror 46, and has a function of condensing the laser light and irradiating the laser light on the signal recording surface of the optical disc 2. The lens block 48 is supported by its own biaxial actuator so as to be movable in two axial directions, that is, a direction approaching to and away from the optical disk 2 and a radial direction of the optical disk 2. Then, the lens block 48 is moved by a two-axis actuator based on a control signal generated by the return light from the optical disc 2, and focusing control is realized.
[0029]
Each laser beam condensed on the signal recording surface 2a of the optical disk 2 is reflected by the signal recording surface 2a and passes through the lens block 48 to become parallel light. The return light reflected and returned from the optical disc 2 is converged by passing through the collimator lens 45 via the quarter-wave plate 47, and is reflected by the beam splitter 44.
[0030]
Further, the light receiving element 56 reflects the beam splitter 44, receives the laser beam condensed by the condensing lens 55, performs photoelectric conversion, generates a gap error signal GE described later, and sends this to the gap control unit 6. Supply.
[0031]
Next, details of the lens block will be described in more detail. The lens block 48 is disposed in the optical path of the laser beam reflected by the mirror 46, and as shown in FIG. 2, an objective lens 62, a solid immersion lens (SIL) 63, a lens folder 64, And an actuator 65.
[0032]
The objective lens 62 is an aspheric lens having a function of condensing a laser beam and supplying the laser beam to the SIL 63. The SIL 63 is a high refractive index lens having a shape obtained by cutting out a part of a spherical lens into a plane. The SIL 63 is arranged close to the signal recording surface 2a, makes the laser beam supplied from the objective lens 62 enter from the spherical surface side, and focuses the laser light on the central portion of the surface (end surface) opposite to the spherical surface.
[0033]
In the lens block 48, as an alternative to the above-described SIL 63, a SIM (Solid Immersion Mirror) having a reflection mirror may be used.
[0034]
The lens folder 64 holds the objective lens 62 and the SIL 63 in a predetermined positional relationship. The SIL 63 is held by the lens folder 64 such that the spherical surface faces the objective lens 62 and the surface (end surface) opposite to the spherical surface faces the signal recording surface 2a of the optical disc 2.
[0035]
Thus, by disposing the SIL 63 having a high refractive index between the objective lens 62 and the signal recording surface 2a by the lens folder 64, a numerical aperture larger than the numerical aperture of only the objective lens 62 can be obtained. In general, the spot size of the laser beam emitted from the lens is inversely proportional to the numerical aperture of the lens. Therefore, the objective lens 62 and the SIL 63 can make the laser beam smaller in size.
[0036]
The two-axis actuator 65 operates the lens folder 64 in the focus direction according to a control voltage output as a control signal from the focus servo control unit 5 or the gap control unit 6.
[0037]
In the lens block 48, the evanescent light is light that has entered the end face of the SIL 63 at an angle equal to or greater than the critical angle and has oozed from the reflection boundary surface of the laser light that has been totally reflected. When the end face of the SIL 63 is in the near field (near field) described later from the signal recording face 2a of the optical disc 2, the above-described evanescent light that has oozed from the end face of the SIL 63 is applied to the signal recording face 2a. become.
[0038]
Next, the near field will be described. In general, as shown in FIG. 2, when the distance (gap) from the end face of the SIL 63 to the signal recording surface 2a of the optical disc 2 is d, as shown in FIG. 2, d ≦ λ by the wavelength λ of the laser light incident on the SIL 63. The area defined as / 2 is the near field. That is, the gap d defined by the distance between the signal recording surface 2a of the optical disk 2 and the end surface of the SIL 63 satisfies d ≦ λ / 2, and evanescent light leaks out from the end surface of the SIL 63 onto the signal recording surface 2a of the optical disk 2. The state is called a near-field state, and the state in which the gap d satisfies d> λ / 2 and the evanescent light does not seep onto the signal recording surface 2a is called the far-field state.
[0039]
By the way, in the far field state, all the laser light incident on the end face of the SIL 63 at an angle equal to or larger than the critical angle is totally reflected and returned. Therefore, as shown in FIG. 3, the return light amount in the far field state is a constant value.
[0040]
On the other hand, in the near-field state, a part of the laser light incident on the end face of the SIL 63 at an angle equal to or larger than the critical angle is, as described above, on the end face of the SIL 63, that is, the reflection interface, as a signal of the optical disc 2 as evanescent light. Bleed on the recording surface 2a. Therefore, as shown in FIG. 3, the return light amount of the laser light totally reflected is smaller than in the far field state. Further, the amount of return light in the near field state decreases depending on the distance between the end face of the SIL 63 and the disk 2.
[0041]
In the near field state, it can be classified into a linear region in which the return light amount changes linearly with respect to the gap length, and a nonlinear region in which the return light amount changes nonlinearly. Therefore, when the position of the end face of the SIL 63 is in the near-field state and belongs to the linear region, the return light amount is received by the light receiving element 56 and photoelectrically converted to generate the gap error signal GE. , The gap can be controlled to be constant. That is, if the control is performed so that the returning light amount becomes the control target value P as shown in FIG. 3, the gap d can be maintained at a constant distance.
[0042]
The configuration of the gap control unit 6 for controlling the feedback servo will be described with reference to FIG. The gap control unit 6 compares a control target voltage value for setting the gap to the control target value P with the gap error signal GE to obtain a deviation, and keeps the gap constant during recording using near-field light. A first control unit 72 for controlling, and a second control which is connected in parallel to the first control unit 72 and executes a predetermined process for a deviation obtained between the control target voltage value and the gap error signal GE. A switching unit 74 for switching the output of the second control unit 73 when the gap error signal GE exceeds the control target voltage value, an output of the first control unit 72, and a switching unit 74. And an adder 75 for adding the output to generate a control signal.
[0043]
The first control unit 72 generates a control signal Vg that is a control voltage for bringing the gap d closer to the control target value P when the SIL 63 is in the near field state. The first control unit 72 includes, for example, a phase compensation filter designed based on the frequency response, and generates a control signal Vg, which is a control voltage, from the deviation calculated by the subtractor 71.
[0044]
The second control unit 73 generates a control signal Vh that causes the SIL 63 in the lens block 48 to approach the signal recording surface 2a of the optical disc 2 to a distance in which the SIL 63 is in the near field state. By generating the control signal Vh in a band different from that of the first control unit 72, the second control unit 73 can bring the SIL 63 closer to a distance in which the SIL 63 is in a near-field state. The second control unit 73 may be configured as, for example, a low-pass filter that removes a high-frequency component in a deviation obtained between the control target voltage value and the gap error signal GE.
[0045]
The switching unit 74 determines whether or not the gap error signal GE based on the return light amount has exceeded a predetermined threshold. As a result, when the gap error signal GE exceeds the predetermined threshold, the switching unit 74 performs a switching operation to cut off the output of the control signal Vh by the second control unit 73. On the other hand, when the gap error signal GE is equal to or smaller than the predetermined threshold, the switching unit 74 performs a switching operation of transmitting the output of the control signal Vh from the second control unit 73 to the adder 75 as it is.
[0046]
That is, when the gap error signal GE exceeds the predetermined threshold, the adder 75 outputs only the control signal Vg. When the gap error signal is equal to or smaller than the predetermined threshold, the sum of the control signal Vg and the control signal Vh is output, and the DC gain can be improved.
[0047]
For example, by configuring the second control unit 73 with an LPF (cutoff frequency fc: 10 Hz) having a frequency characteristic as shown in FIG. 5, for example, the high-frequency component of the deviation output from the subtractor 71 is removed. And outputs it to the adder 75. Thus, when the primary resonance frequency of the two-axis actuator 65 is as high as 100 Hz, only the first control unit 72 can maintain a DC gain of about 60 dB as shown in FIG. By arranging the second control unit 73 composed of the LPF having the above characteristics so as to be in parallel with the first control unit 72, the DC gain in the low frequency range can be improved to 80 dB. As described above, by boosting the DC gain in the low frequency band by about 20 dB, the gap d can be controlled with high accuracy even when the SIL 63 is in the near-field state. In both cases, the cutoff frequency is about 1.7 kHz, which is not much different, so that it is possible to stabilize the gap d while maintaining the response characteristics at the time of control.
[0048]
Incidentally, in the case where the control signal from the gap control unit 6 is constituted only by the output of the control signal Vg by the first control unit 72, as shown in FIG. included. On the other hand, when the output of the control signal Vh from the second control unit 73 is also added, the fluctuation component can be eliminated as shown in FIG. Can be eliminated.
[0049]
As described above, by connecting the first control unit 72 and the second control unit 73 in parallel, the steady-state characteristics can be improved. However, for example, the position of the end face of the SIL 63 is in a near-field state, If it belongs to the region, the characteristics of the feedback servo system itself may become unstable and oscillate.
[0050]
For example, as shown in FIG. 3, the amount of return light that can be regarded as linear with respect to the gap length is d0 or less. The gap d controlled by the feedback servo described above has a relation of 0 <d <d0 <λ / 2. If the gap d is controlled in or near such a range, the feedback servo system becomes linear and stable.
[0051]
On the other hand, when a certain amount of disturbance is applied to the two-axis actuator 65 and the amount of return light becomes d0 or more, it enters a nonlinear region. In the non-linear region, if the control signal is generated by adding the outputs of the first control unit 72 and the second control unit 73 which are connected in parallel to each other, when the control signal is in the conditional stable band described below, Hunting occurs due to a limit cycle, and the control output oscillates. For this reason, the gap servo system becomes unstable, and the distance between the SIL 63 and the disk cannot be controlled to a constant distance at which evanescent light is generated, and the recording / reproducing system using near-field light breaks down.
[0052]
Here, the above-mentioned conditional stable band refers to a range of about 35 Hz to 250 Hz lower than the cutoff frequency of the system as shown in FIG. In a system having such a conditionally unstable band, that is, a conditionally stable system, even if the closed loop system is stable, it is generally unstable when the system is nonlinear.
[0053]
Therefore, in the present invention, for example, a process shown in FIG. 8 is executed in order to always stabilize the feedback servo system.
[0054]
First, in step S11, the switching unit 74 identifies the gap error signal GE based on the amount of return light. Then, the switching unit 74 determines whether the gap error signal GE exceeds a predetermined threshold T. The threshold value T is determined in advance according to the return light amount with respect to the gap length d0 indicating the boundary between the linear region and the non-linear region, as shown in FIG. 3, but is not limited to such a case. What is necessary is just to determine in advance according to the relationship of the light quantity.
[0055]
If the result of determination in step S11 is that the gap error signal GE has exceeded the threshold value T, the flow proceeds to step S13. On the other hand, when the gap error signal GE is equal to or smaller than the threshold T, the process proceeds to step S12.
[0056]
When the process proceeds to step S12, the switching unit 74 performs a switching operation of transmitting the output of the control signal Vh from the second control unit 73 to the adder 75 as it is. Thus, the sum of the control signal Vg and the control signal Vh is output from the adder 75, and the DC gain can be improved.
[0057]
When the process proceeds to step S13, the switching unit 74 performs a switching operation to cut off the output of the control signal Vh by the second control unit 73. As a result, only the control signal Vg is output from the adder 75. That is, when the gap error signal GE is in a nonlinear region exceeding the threshold value T and is in a conditionally stable band, there is a possibility that the entire feedback servo system becomes unstable and oscillates as described above. However, in the present invention, since the control signal Vg from the first control unit 72 is always output only when the control signal Vg is in the non-linear region, the system is switched from a conditionally stable system (FIG. 6A) to a stable condition. Since the system is changed to the system (FIG. 6 (2)), the system becomes unstable and does not oscillate even in the nonlinear region.
[0058]
As described above, in the optical recording device 1 to which the present invention is applied, when performing the recording process using the evanescent light, when the SIL 63 is arranged in the near field with respect to the signal recording surface 2a of the optical disc 2, the near field light Is output to the signal recording surface 2a, and the second control unit 72 controls the gap d to maintain a predetermined distance in accordance with the return light amount of the near-field light emitted to the signal recording surface. The control unit 73 is connected in parallel to this. Then, when the return light amount of the near-field light exceeds the threshold value T, a switching operation for cutting off the output of the second control unit 73 is executed.
[0059]
Thereby, in the optical recording apparatus 1 to which the present invention is applied, when the SIL 63 is in the linear region, the DC gain in the low band can be improved, and the gap d can be reduced even in the near field state. It is possible to control with high accuracy. Further, when the SIL 63 is in the non-linear region, by outputting only the control signal from the first control unit 72, the entire feedback servo system can be stabilized, and oscillation can be prevented.
[0060]
That is, in the optical recording device 1, by improving the DC gain in each control unit, the gap can be adjusted with high accuracy even in the near-field region, and the entire system can be constantly stabilized.
[0061]
Note that the present invention is not limited to the above-described embodiment, and may be applied to, for example, optical reproducing devices 8 and 9 described below.
[0062]
The configuration of the optical reproducing devices 8 and 9 will be described with reference to FIGS. In the optical reproducing devices 8 and 9, the same components as those of the above-described optical recording device 1 are denoted by the same reference numerals and description thereof is omitted.
[0063]
The optical reproducing device 8 includes a low-pass filter (LPF) 91 connected to the light receiving element 56. The LPF 91 separates and outputs the gap error signal GE obtained from the light receiving element 56 and the reproduction signal read from the signal recording surface 2a for each frequency. With the LPF 91, for example, only a reproduction signal can be extracted and transmitted to an external device.
[0064]
Further, the optical reproducing device 9 reflects a part of the laser light reflected by the beam splitter 44 and transmits the other part of the laser light, and a laser beam reflected by the polarizing beam splitter 101 by photoelectric conversion to reproduce a reproduced signal. And a second light receiving element 102 that has passed through the polarizing beam splitter 101.
[0065]
In this optical reproducing device 9, the laser light including the information read from the signal recording surface 2a is reflected by the polarization beam splitter 101, received by the first light receiving element 102, becomes a reproduction signal, and is transmitted to the outside. become. Similarly, the return light amount of the near-field light is received by the second light receiving element 103 and output to the gap control unit 6 as a gap error signal GE.
[0066]
In the optical reproducing devices 8 and 9 as well, similar to the optical recording device 1, when the SIL 63 is placed in the near field with respect to the signal recording surface 2a of the optical disc 2 when performing the reproducing process using the evanescent light. The first controller 72 that emits near-field light to the signal recording surface 2a and controls the gap d to maintain a predetermined distance in accordance with the amount of return light of the near-field light emitted to the signal recording surface In addition, a second control unit 73 is connected in parallel to this. Then, when the return light amount of the near-field light exceeds the threshold value T, a switching operation for cutting off the output of the second control unit 73 is executed.
[0067]
As a result, in the optical reproducing devices 8 and 9 to which the present invention is applied, when the SIL 63 is in the linear region, the DC gain in the low band can be improved, and even when the SIL 63 is in the near-field state. The gap d can be controlled with high accuracy. Further, when the SIL 63 is in the non-linear region, by outputting only the control signal from the first control unit 72, the entire feedback servo system can be stabilized, and oscillation can be prevented.
[0068]
That is, in the optical reproducing devices 8 and 9, by improving the DC gain in each control unit, the gap can be adjusted with high accuracy even in the near-field region, and the entire system can be constantly stabilized.
[0069]
It is needless to say that the present invention may be applied as an optical recording / reproducing apparatus in which the optical recording apparatus 1 and the optical reproducing apparatuses 8 and 9 are combined.
[0070]
【The invention's effect】
As is clear from the above description, in the information recording apparatus and method to which the present invention is applied, when performing the recording process using the evanescent light, the emitting unit is arranged in the near field with respect to the information recording surface of the optical recording medium. In this case, the laser beam is emitted to the information recording surface as near-field light, and the emitting unit is kept at a predetermined distance from the information recording surface according to the amount of return light of the near-field light emitted to the information recording surface. In addition to the first control means, the second control means is connected in parallel with the first control means, and the output of the second control means is cut off when the return light amount of the near-field light exceeds a predetermined threshold. .
[0071]
As a result, in the information recording apparatus and method to which the present invention is applied, by improving the DC gain in each control means, the gap can be adjusted with high accuracy even in the near-field region, and the entire system can be constantly stabilized. Can be.
[0072]
As is clear from the above description, in the information reproducing apparatus and method to which the present invention is applied, when performing the reproducing process using the evanescent light, the emitting unit is arranged in the near field with respect to the information recording surface of the optical recording medium. In this case, the laser beam is emitted to the information recording surface as near-field light, and the emitting unit is kept at a predetermined distance from the information recording surface according to the amount of return light of the near-field light emitted to the information recording surface. In addition to the first control means, the second control means is connected in parallel with the first control means, and the output of the second control means is cut off when the return light amount of the near-field light exceeds a predetermined threshold. .
[0073]
As a result, in the information reproducing apparatus and method to which the present invention is applied, by improving the DC gain in each control means, the gap can be adjusted with high accuracy even in the near-field region, and the entire system can be constantly stabilized. Can be.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a configuration of an optical recording apparatus to which the present invention has been applied.
FIG. 2 is a diagram for explaining a lens block provided in the optical recording device.
FIG. 3 is a diagram for explaining a relationship between a return light amount and a gap distance.
FIG. 4 is a diagram for describing a detailed configuration of a gap control unit.
FIG. 5 is a diagram illustrating frequency characteristics of a second control unit connected in parallel to the first control unit;
FIG. 6 is a diagram for describing a frequency characteristic when a second control unit is connected in parallel to the first control unit;
FIG. 7A is a diagram illustrating a state of a control voltage in a case where only a first control unit is used, and FIG. 7B is a diagram illustrating a case where a second control unit is connected in parallel; FIG. 3 is a diagram showing a state of a control voltage of FIG.
FIG. 8 is a diagram illustrating an operation of a gap control unit.
FIG. 9 is a diagram for explaining a configuration of an optical reproducing apparatus to which the present invention has been applied.
FIG. 10 is a diagram for explaining another configuration of the optical reproducing apparatus to which the present invention is applied.
[Explanation of symbols]
Reference Signs List 1 optical recording device, 2 optical disk, 3 spindle motor, 4 optical head, 5 focus servo control unit, 6 gap control unit, 8, 9 optical reproduction device, 42 APC, 43 holder, 44 beam splitter, 45 collimator lens, 46 mirror, 47 1/4 wavelength plate, 48 lens block, 55 condenser lens, 56 light receiving element

Claims (16)

A light source that emits a laser beam modulated by recording information to be recorded on an information recording surface of an optical recording medium,
The laser light emitted from the light source is condensed, and when the laser light is arranged in a near field with respect to the information recording surface of the optical recording medium, the converged laser light is emitted as the near field light to the information recording surface. Means,
Return light amount detection means for detecting the return light amount of the near-field light emitted to the information recording surface,
At the time of recording with the near-field light, a first control unit controls the emission unit to maintain a predetermined distance from the information recording surface based on the return light amount of the near-field light detected by the return light amount detection unit. Control means;
A second control unit connected in parallel to the first control unit and controlling the emission unit to keep a predetermined distance from the information recording surface in a band different from that of the first control unit;
An information recording apparatus comprising: a switching unit that shuts off an output of the second control unit when the return light amount of the near-field light exceeds a predetermined threshold. 2. The information recording apparatus according to claim 1, wherein the second control means is a low-pass filter that removes a high-frequency component in a deviation between the amount of returning near-field light and the predetermined threshold. 2. The information recording apparatus according to claim 1, wherein the switching means uses a value determined in advance according to a relationship between the return light amount and a distance between the emission means and the information recording surface, as the predetermined threshold. apparatus. 2. The information recording apparatus according to claim 1, wherein the emission unit has an SIL (Solid Immersion Lens) disposed close to the information recording surface. 2. The information recording apparatus according to claim 1, wherein the light emitting unit includes a SIM (Solid Immersion Mirror) disposed close to the information recording surface. A first emission step of emitting a laser beam modulated by recording information to be recorded on the information recording surface of the optical recording medium;
When the condensing portion for condensing the emitted laser light is disposed in a near field with respect to the information recording surface of the optical recording medium, the condensed laser light is emitted to the information recording surface as near-field light. A second emission step;
A detection step of detecting a return light amount of the near-field light emitted to the information recording surface,
At the time of recording with the near-field light, a first control section controls the light-collecting portion to maintain a predetermined distance from the information recording surface based on a return light amount of the near-field light detected in the detection step. Control process;
When the return light of the near-field light is equal to or less than a predetermined threshold, a second band is controlled to keep the predetermined distance from the information recording surface in a band different from that of the first control step. An information recording method, comprising: a control step. 7. The information recording method according to claim 6, wherein in the second control step, a high-frequency component in a deviation between the return light amount of the near-field light and the predetermined threshold value is removed. 7. The method according to claim 6, wherein in the second control step, a value determined in advance according to a relationship between the return light amount and a distance between the emission unit and the information recording surface is used as the predetermined threshold. Information recording method. A light source that emits laser light for reproducing recorded information recorded on the information recording surface of the optical recording medium,
The laser light emitted from the light source is condensed, and when the laser light is arranged in a near field with respect to the information recording surface of the optical recording medium, the converged laser light is emitted as the near field light to the information recording surface. Means,
Return light amount detection means for detecting the return light amount of the near-field light emitted to the information recording surface,
At the time of recording with the near-field light, a first control unit controls the emission unit to maintain a predetermined distance from the information recording surface based on the return light amount of the near-field light detected by the return light amount detection unit. Control means;
A second control unit connected in parallel to the first control unit and controlling the emission unit to keep a predetermined distance from the information recording surface in a band different from that of the first control unit;
An information reproducing apparatus comprising: a switching unit that cuts off an output of the second control unit when a return light amount of the near-field light exceeds the predetermined threshold. 10. The information reproducing apparatus according to claim 9, wherein the second control means is a low-pass filter that removes a high-frequency component in a deviation between the amount of return of the near-field light and the predetermined threshold. 10. The information reproducing apparatus according to claim 9, wherein the switching unit uses a value determined in advance according to a relationship between a distance between the emission unit and the information recording surface and the amount of return light as the predetermined threshold. apparatus. 10. The information reproducing apparatus according to claim 9, wherein the light emitting means has an SIL (Solid Immersion Lens) disposed close to the information recording surface. 10. The information reproducing apparatus according to claim 9, wherein the light emitting means has a SIM (Solid Immersion Mirror) disposed close to the information recording surface. A first emission step of emitting laser light for reproducing recorded information recorded on the information recording surface of the optical recording medium;
When the condensing portion for condensing the emitted laser light is disposed in a near field with respect to the information recording surface of the optical recording medium, the condensed laser light is emitted to the information recording surface as near-field light. A second emission step;
A detection step of detecting a return light amount of the near-field light emitted to the information recording surface,
At the time of recording with the near-field light, a first control section controls the light-collecting portion to maintain a predetermined distance from the information recording surface based on a return light amount of the near-field light detected in the detection step. Control process;
When the return light of the near-field light is equal to or less than a predetermined threshold, a second band is controlled to keep the predetermined distance from the information recording surface in a band different from that of the first control step. An information reproducing method comprising a control step. 15. The information reproducing method according to claim 14, wherein in the second control step, a high-frequency component in a deviation between the return light amount of the near-field light and the predetermined threshold value is removed. 15. The method according to claim 14, wherein in the second control step, a value determined in advance according to a relationship between the return light amount and a distance between the emission unit and the information recording surface is used as the predetermined threshold. Information reproduction method.

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