JP2011076689A - Information recording and reproducing device, method of controlling gap, and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform proper gap control in accordance with tilt change. <P>SOLUTION: The device includes a light source LD projecting light LB to a disk type information recording medium 100, a solid-immersion lens 11 generating near-field light, an optical system 10 converging a part of projected light on a medium surface through the solid-state immersion lens, a signal generating means 40 for outputting an error signal in accordance with reflected light from a bottom part of the solid-state immersion lens caused by the other one part of light, a gap control means 60 for controlling gap between the medium surface and the solid-state immersion lens based on an error signal, a tilt detecting means 70 for detecting relative tilt amount of the information recording medium and the solid-state immersion lens, while calculating a limit distance in which the solid-state immersion lens and the medium surface do not come into contact with each other based on the tilt amount, and a gap changing means 60 for changing, when the limit distance exceeds the gap between the medium surface and the solid-state immersion lens controlled by the gap controlling means, the gap to the limit distance or more temporarily or continuously. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention includes, for example, a solid immersion lens (SIL), an information recording / reproducing apparatus using near-field light, a medium surface of a recording medium to be recorded / reproduced by the information recording / reproducing apparatus, and a solid immersion lens. The present invention relates to a technical field of a gap control method and a computer program for controlling a gap between them.

  In this type of apparatus, since the solid immersion lens is disposed close to the recording medium, it is important to perform appropriate gap control to avoid the solid immersion lens from colliding with the recording medium. For this reason, for example, Patent Documents and the like disclose a technique related to an optical information recording / reproducing apparatus that performs servo control using a gap error signal. Specifically, the servo control is performed by the focus error signal, and the state where the solid immersion lens is brought close to the near field region in a state where the servo is closed, that is, the solid immersion lens is brought close to the near field region. In order to change the control target value as much as possible, a technique is disclosed in which the expander lens is moved and then servo control is performed using a gap error signal.

  By the way, in the far field optical system used in the conventional recording / reproducing apparatus, the gap between the recording medium and the lens is relatively large, for example, even when the relative tilt amount between the recording medium and the lens is relatively large, There was no contact between the recording medium and the lens after the servo close. However, in the near-field optical system using near-field light, as described above, the solid immersion lens is disposed close to the recording medium, and the relative gap between the two is tens of nanometers to several hundreds of nanometers. Maintained. For this reason, even if the tilt amount between the information recording medium and the solid immersion lens is very small, the information recording medium and the solid immersion lens may come into contact after the servo close. Contact may cause scratches on the recording surface of the disk or scraping of the bottom surface of the solid immersion lens, which may render the recording / reproducing apparatus and recording medium unusable. For this reason, it is necessary to consider the influence of such tilt in the servo control for maintaining the gap.

  For example, Patent Document 1 has a configuration in which the tilt amount in the disk tangent direction of the solid immersion lens is compared with a predetermined allowable tilt amount, and the operation is stopped and the tilt amount is adjusted when the tilt amount is not allowable. It is disclosed. Patent Document 2 discloses a configuration in which the tilt amount between the solid immersion lens and the disk surface is detected by a tilt sensor, and the peak value of surface blur is detected. Patent Document 3 discloses a configuration in which a lens actuator is tilt-corrected based on capacitance detected from a plurality of capacitance terminals to prevent the lens actuator from colliding with a medium.

Special table 2009-500775 gazette JP 2006-338712 A Japanese Patent Laid-Open No. 2002-31967

  However, in the configurations of Patent Documents 1 and 3 described above, since a tilt servo mechanism for adjusting the tilt amount is employed, two axes for tilt correction in the tangential direction and the radial direction are further added to the conventional biaxial actuator. The added 4-axis actuator is required, resulting in an increase in the cost of the apparatus configuration. In the configuration of Patent Document 2, the operation during the servo close is not mentioned, and there is a possibility that the recording medium and the solid immersion lens come into contact during the servo close.

  The present invention has been made in view of, for example, the conventional problems described above, and the tilt amount varies between the information recording medium and the solid immersion lens with a relatively simple configuration without using tilt servo control. Even in this case, it is an object to provide an information recording / reproducing apparatus, a gap control method, and a computer program capable of suitable gap control without causing a collision between the information recording medium and the solid immersion lens.

  In order to solve the above problems, an information recording / reproducing apparatus of the present invention is arranged near a light source for irradiating light to a disk-shaped information recording medium and the medium surface of the information recording medium, and generates near-field light. A solid immersion lens, an optical system for condensing a part of the irradiated light on the medium surface via the solid immersion lens, and a bottom of the solid immersion lens caused by the other part of the light. Signal generating means for outputting an error signal corresponding to the reflected light of the light, gap control means for controlling the gap between the medium surface and the solid immersion lens based on the error signal, the information recording medium, and the solid immersion lens And a tilt detecting means for calculating a limit distance that is a distance at which the solid immersion lens and the medium surface do not contact each other based on the tilt amount; and the limit distance A gap changing means for changing the gap temporarily or continuously beyond the limit distance when the gap is larger than the gap between the medium surface controlled by the gap control means and the solid immersion lens. .

  In order to solve the above-mentioned problems, a gap control method according to the present invention includes a light source for irradiating light on a disk-shaped information recording medium and a medium surface of the information recording medium, which is disposed in the vicinity of the medium to generate near-field light. A solid immersion lens, an optical system for condensing a portion of the irradiated light on the medium surface via the solid immersion lens, and a bottom portion of the solid immersion lens resulting from the other portion of the light. A gap control method for an information recording / reproducing apparatus, comprising: signal generation means for outputting an error signal corresponding to reflected light; and gap control means for controlling a gap between the medium surface and the solid immersion lens based on the error signal. And detecting a relative tilt amount between the information recording medium and the solid immersion lens, and at a distance where the solid immersion lens and the medium surface do not contact each other based on the tilt amount. A tilt detection step for calculating a limit distance, and when the limit distance is larger than a gap between the medium surface controlled by the gap control means and the solid immersion lens, the gap is temporarily or continuously And a gap changing step for changing the distance to the limit distance or more.

  In order to solve the above problems, a computer program according to the present invention includes a light source for irradiating light to a disk-shaped information recording medium, and a solid that is disposed in the vicinity of the medium surface of the information recording medium and generates near-field light. An immersion lens, an optical system for condensing a portion of the irradiated light onto the medium surface via the solid immersion lens, and a reflection from the bottom of the solid immersion lens caused by the other portion of the light A signal generating means for outputting an error signal corresponding to light; a gap control means for controlling a gap between the medium surface and the solid immersion lens based on the error signal; and the information recording medium and the solid immersion lens. Tilt detecting means for detecting a relative tilt amount and calculating a limit distance that is a distance at which the solid immersion lens and the medium surface do not contact each other based on the tilt amount; A gap changing means for temporarily or continuously changing the gap to be greater than or equal to the limit distance when a field distance is larger than a gap between the medium surface controlled by the gap control means and the solid immersion lens; A computer program for controlling a computer provided in the information recording / reproducing apparatus, wherein the computer functions as at least part of the signal generating means, the gap control means, the tilt detection means, and the gap changing means.

It is a block diagram which shows the basic composition of the information recording / reproducing apparatus of a present Example. It is a block diagram which shows the basic composition which concerns on the tilt control part of a present Example. It is explanatory drawing which shows an example of the tilt between an optical disk and a solid immersion lens. It is a block diagram which shows the basic composition which concerns on the tilt control part of a present Example. It is a flowchart which shows the flow of a basic operation | movement of the gap control of a present Example. It is a graph which shows the profile of the tilt amount and gap target value which concern on gap control. It is a graph which shows the aspect of the change of RF amplitude and RF gain target value accompanying a gap change. It is a flowchart which shows the flow of the basic operation | movement of the mechanical tilt correction of a present Example. It is a graph which shows the profile of the tilt amount and gap target value concerning mechanical tilt correction.

(Embodiment of information recording / reproducing apparatus)
An information recording / reproducing apparatus according to an embodiment of the present invention includes a light source for irradiating a disc-shaped information recording medium with light, a solid immersion lens that is disposed in the vicinity of the medium surface of the information recording medium and generates near-field light. An optical system for condensing a part of the irradiated light on the surface of the medium through the solid immersion lens, and a reflected light from the bottom of the solid immersion lens due to the other part of the light. A signal generating means for outputting an error signal, a gap control means for controlling a gap between the medium surface and the solid immersion lens based on the error signal, and a relative relationship between the information recording medium and the solid immersion lens. Tilt detection means for detecting a tilt amount and calculating a limit distance that is a distance at which the solid immersion lens and the medium surface do not contact each other based on the tilt amount; and the limit distance is the gap If the medium surface controlled by control means to be larger than the gap between the solid immersion lens, and a gap changing means for changing the gap or temporarily or continuously the limit distance.

  According to the embodiment of the information recording / reproducing apparatus of the present invention, a part of light emitted from a light source that is a semiconductor laser, for example, is passed through a solid immersion lens (SIL) by an objective lens, for example, an optical disc. Is condensed on the surface of the recording medium. The solid immersion lens is disposed in proximity to the medium surface of the recording medium. Here, the term “close” refers to the gap between the information recording medium and the solid immersion lens (in other words, relative The distance) is intended to indicate that the near-field light from the solid immersion lens is small enough to be used for reading information. The gap between the information recording medium and the solid immersion lens is, for example, about several tens of nm (nanometers) or several tens of nm to about one hundred tens of nanometers or several hundreds of nanometers. It is set according to the system of a typical optical system.

  The other part of the light emitted from the light source is incident on the solid immersion lens at an angle greater than the critical angle at the bottom of the solid immersion lens, and is totally reflected at the bottom of the solid immersion lens. Here, the “bottom part of the solid immersion lens” according to the present invention refers to the side of the solid immersion lens that faces the recording medium. When the solid immersion lens is close to the medium surface in the near-field region, near-field light is transmitted through the solid immersion lens toward the recording medium due to another part of the light.

  The signal generating means includes a light receiving element and a circuit that processes a signal output from the light receiving element and generates an error signal (so-called gap error signal) for controlling the gap. Reflected light from the bottom of the lens is received through the solid immersion lens and a gap error signal is output. Here, “receiving the reflected light from the bottom of the solid immersion lens through the solid immersion lens” means “of the other part of the light incident on the solid immersion lens, This means that the light totally reflected at the bottom and received from the solid immersion lens is received.

  Therefore, typically, the light intensity of the reflected light from the bottom of the solid immersion lens is output as an error signal. In this case, the signal level is constant at a distance where all other part of the light incident on the solid immersion lens is totally reflected at the bottom of the solid immersion lens (that is, the distance where the near-field light does not pass through the solid immersion lens). As the distance closer to the medium surface than the distance, an error signal is output that changes so that the signal level related to the reflected light is reduced by the amount that the near-field light passes through the solid immersion lens. According to such an error signal, it is possible to detect a gap between the information recording medium and the solid immersion lens.

  The gap control means includes, for example, a signal comparison processing circuit, an actuator, and a controller for controlling the actuator. Based on the error signal, the gap between the information recording medium and the solid immersion lens has a predetermined gap target. For example, the position of the solid immersion lens is adjusted so as to maintain the value. Specifically, the gap control means includes a gap between the information recording medium and the solid immersion lens indicated by an error signal and a gap target value between the information recording medium and the solid immersion lens determined in advance (in other words, The solid immersion lens is moved so as to correct the calculated difference. Note that the gap control (in other words, focus control) between the information recording medium and the solid immersion lens based on the error signal is not performed when the solid immersion lens and the medium surface are close to each other in the near-field region where the near-field light is transmitted. Cannot be implemented. For this reason, outside the near-field region where the near-field light is not transmitted, focus control based on a known focus error signal may be performed.

  Furthermore, the embodiment of the information recording / reproducing apparatus of the present invention is based on the tilt detection means for detecting the relative tilt amount (in other words, the tilt angle) between the information recording medium and the solid immersion lens, and the tilt amount. Gap changing means for changing the gap controlled by the gap control means is provided.

  For example, the tilt detection means uses a tilt amount detection device such as a tilt sensor or based on the amount of surface shake between the information recording medium and the solid immersion lens, to determine the relative relationship between the information recording medium and the solid immersion lens. The amount of tilt is detected. As described above, in the information recording / reproducing apparatus using near-field light, the gap between the information recording medium and the solid immersion lens is as small as several tens of nanometers to several hundreds of nanometers. Even so, depending on the relative tilt amount generated between the information recording medium and the solid immersion lens, the edge of the bottom surface of the solid immersion lens may come into contact with the information recording medium.

  Therefore, the tilt detection means calculates a limit distance indicating a limit distance that the information recording medium and the solid immersion lens can approach without contacting, based on the detected tilt amount. Generally, the relative tilt between the information recording medium and the solid immersion lens includes a radial tilt that is a disc radial tilt in the information recording medium and a tangential tilt that is a tilt perpendicular to the radial direction. There is. Therefore, for example, the tilt detection means converts the absolute tilt amount of the radial tilt and the tilt amount of the tangential tilt into absolute values, and calculates the total tilt amount. Specifically, if the tilt amount of the radial tilt is θr and the tilt amount of the tangential tilt is θt, the total tilt amount θ is calculated by the following equation.

  Further, the limit distance dm between the information recording medium and the solid immersion lens based on the calculated total tilt amount θ is calculated from the following equation, where r is the radius of the bottom surface of the solid immersion lens.

  The gap changing means is based on a gap between the information recording medium and the solid immersion lens determined by the gap control means (that is, a predetermined gap target value) and a limit distance calculated by the tilt detecting means, Change the target gap value to be controlled. Specifically, the gap target value is compared with the limit distance. If the limit distance is larger than the gap target value, the gap target value is temporarily set so that the gap between the medium surface and the solid immersion lens is at least the limit distance or more. Change to For this reason, when the limit distance between the information recording medium and the solid immersion lens becomes larger than the predetermined gap interval due to the fluctuation of the tilt amount, the gap between the information recording medium and the solid immersion lens is appropriately adjusted. And avoid contact between the two.

  As described above, according to the embodiment of the information recording / reproducing apparatus of the present invention, it is possible to avoid contact between the information recording medium and the solid immersion lens without using a special tilt servo mechanism. . This is beneficial from the viewpoint of device configuration and cost.

  In addition, since the gap is changed by monitoring the tilt amount between the information recording medium and the solid immersion lens, for example, the gap can be controlled even during servo close for focusing, It is possible to avoid contact.

  As a result, it is possible to avoid contact between the information recording medium and the solid immersion lens even at a location where the tilt amount between the information recording medium and the solid immersion lens is relatively large.

  One aspect of the embodiment of the information recording / reproducing apparatus of the present invention further includes a tilt adjusting means for changing an angle of the solid immersion lens with respect to the information recording medium.

  According to this aspect, the relative angle between the information recording medium and the solid immersion lens can be changed by the operation of the tilt adjusting means. At this time, the tilt adjusting means may change the relative angle with respect to the information recording medium by changing the installation angle of the solid immersion lens, and the installation angle of the optical pickup on which the solid immersion lens is arranged. It may be changed. Such a tilt adjustment means is, for example, a mechanical tilt that tilts the solid immersion lens, or a mechanical tilt that changes the relative angle between the solid immersion lens and the information recording medium by tilting the optical pickup on which the solid immersion lens and the light source are arranged. Such as mechanical tilt mechanism.

  For this reason, according to the operation of the tilt adjusting means, the relative angle between the information recording medium and the solid immersion lens can be physically changed. For this reason, as will be described in detail later, the relative tilt amount between the information recording medium and the solid immersion lens can be suitably reduced, and the limit distance between the information recording medium and the solid immersion lens due to the tilt amount. Can be made smaller.

  According to another aspect of the information recording / reproducing apparatus of the present invention, the tilt detecting means is a direct current that does not change during one rotation of the information recording medium among the tilts tilted in the radial direction of the information recording medium. The component is detected, and the tilt adjusting unit changes the angle of the solid immersion lens with respect to the information recording medium so that the DC component becomes zero.

  In general, in a disc-shaped information recording medium, since the disc is warped in the radial direction, the relative tilt amount between the information recording medium and the solid immersion lens (that is, as the condensing position in the radial direction changes) , The amount of tilt in the radial direction) varies. At this time, typically, as the condensing position in the radial direction moves toward the outer peripheral side of the disk, the warpage of the disk increases, and the tilt amount tends to increase.

  On the other hand, the relative tilt amount between the information recording medium and the solid immersion lens due to the warp of the disc does not vary according to the rotation of the disc as long as it is at the same position in the radial direction, so-called direct current. It is an ingredient.

  According to this aspect, the information recording medium is operated by the operation of the tilt adjusting means so that the relative tilt amount between the information recording medium and the solid immersion lens, which is a direct current component due to the warp of the disk as described above, becomes zero. And the relative angle of the solid immersion lens is changed.

  Further, the tilt amount resulting from such warping of the disc does not vary according to the rotation angle of the disc, and varies relatively slowly during recording or reproduction with respect to the information recording medium. For this reason, relatively low-speed processing is sufficient for the control of changing the angle of the solid immersion lens with respect to the information recording medium by the tilt adjusting means.

  With this configuration, even when a mechanical tilt mechanism with a relatively low reaction speed is used, the relative tilt amount between the information recording medium and the solid immersion lens can be suitably reduced. This makes it possible to further reduce the limit distance between the information recording medium and the solid immersion lens.

  In another aspect of the embodiment of the information recording / reproducing apparatus of the present invention, the tilt detecting means is configured such that a tilt tilted in one of the tangential directions orthogonal to the radial direction of the information recording medium is a positive tilt, and the positive tilt is When the tilt tilted to the opposite side is a negative tilt, the maximum positive tilt amount and the minimum negative tilt amount during one rotation of the information recording medium are detected, and the tilt adjusting means The angle of the solid immersion lens with respect to the information recording medium is set so that an intermediate value between the maximum value of the positive tilt amount and the minimum value of the negative tilt amount during one rotation of the information recording medium becomes zero. change.

  According to this aspect, the tilt adjustment means can reduce the tilt amount in the tangential direction of the disc among the relative tilt amounts between the information recording medium and the solid immersion lens.

  The tilt in the tangential direction of the disk includes, for example, a tilt caused by a solid immersion lens with respect to the information recording medium, a scratch or unevenness on the disk surface, and the like. Since many of these tilts vary according to the rotation of the disc, in order to change the relative angle between the information recording medium and the solid immersion lens according to each tilt, processing at an extremely high speed is required. Needed and not realistic.

  On the other hand, according to the tilt adjusting means of this aspect, the maximum value of the positive tilt amount (that is, the tilt amount of the tilt in one tangential direction) and the negative tilt amount (that is, other tilt amounts) within one rotation of the disk. The angle of the solid immersion lens with respect to the information recording medium is changed so that the intermediate value of the minimum value of the tilt amount of the inclination in the tangential direction becomes zero. According to such an operation, the relative angle between the information recording medium and the solid immersion lens is set so that the absolute value of the positive tilt amount and the absolute value of the negative tilt amount within one rotation of the disk are the same. Adjusted. For this reason, when a tilt that tilts in one of the tangential directions occurs during one rotation of the disk, the amount of tilt can be reduced.

  With this configuration, even when a mechanical tilt mechanism with a relatively low reaction speed is used, the relative tilt amount between the information recording medium and the solid immersion lens can be suitably reduced. This makes it possible to further reduce the limit distance between the information recording medium and the solid immersion lens.

  Another aspect of the embodiment of the information recording / reproducing apparatus of the present invention further includes signal intensity control means for controlling the intensity of the light in a feedforward manner based on at least one of the error signal and the gap.

  According to this aspect, when the gap between the medium surface and the solid immersion lens is temporarily widened according to the limit distance resulting from the relative tilt amount between the information recording medium and the solid immersion lens, the medium surface The intensity of light emitted from the light source is controlled in a feed-forward manner so that the gain of the RF signal obtained from the above can be maintained at a constant quality.

  With this configuration, even when the gap is temporarily changed, a constant amplitude of the RF signal can be obtained, and deterioration of the error rate during data recording or reproduction can be suppressed. It becomes.

(Embodiment of Gap Control Method)
An embodiment of the gap control method of the present invention includes a light source that irradiates light to a disk-shaped information recording medium, a solid immersion lens that is disposed close to the medium surface of the information recording medium and generates near-field light, An optical system for condensing a part of the irradiated light on the medium surface via the solid immersion lens, and a reflected light from the bottom of the solid immersion lens due to the other part of the light A gap control method for an information recording / reproducing apparatus, comprising: signal generation means for outputting an error signal; and gap control means for controlling a gap between the medium surface and the solid immersion lens based on the error signal, A relative tilt amount between the recording medium and the solid immersion lens is detected, and a limit distance that is a distance at which the solid immersion lens and the medium surface do not contact each other is calculated based on the tilt amount. A tilt detecting step, and when the limit distance is larger than a gap between the medium surface controlled by the gap control means and the solid immersion lens, the gap is temporarily or continuously over the limit distance. And a gap changing step to change to.

  According to the embodiment of the gap control method of the present invention, data is stored in the information recording medium while enjoying the same effects as the various effects that can be enjoyed by the above-described embodiment of the information recording / reproducing apparatus of the present invention. In addition to recording, the data recorded on the information recording medium can be reproduced.

  Incidentally, in response to the various aspects of the embodiment of the information recording / reproducing apparatus of the present invention described above, the embodiment of the gap control method of the present invention can also adopt various aspects.

(Embodiment of computer program)
An embodiment of the computer program of the present invention includes a light source for irradiating a disk-shaped information recording medium with light, a solid immersion lens disposed near the medium surface of the information recording medium and generating near-field light, An optical system for condensing a part of the irradiated light on the surface of the medium through the solid immersion lens, and an error corresponding to reflected light from the bottom of the solid immersion lens due to the other part of the light A signal generating means for outputting a signal; a gap control means for controlling a gap between the medium surface and the solid immersion lens based on the error signal; and a relative tilt amount between the information recording medium and the solid immersion lens. Tilt detecting means for calculating a limit distance that is a distance at which the solid immersion lens and the medium surface do not contact each other based on the tilt amount; and And a gap changing means for changing the gap temporarily or continuously beyond the limit distance when the gap is larger than the gap between the medium surface and the solid immersion lens controlled by the pop control means. A computer program for controlling a computer provided in a recording / reproducing apparatus, which causes the computer to function as at least a part of the signal generation means, the gap control means, the tilt detection means, and the gap change means.

  According to the embodiment of the computer program of the present invention, if the computer program is read from a recording medium such as a ROM, a CD-ROM, a DVD-ROM, and a hard disk that stores the computer program and executed by the computer, or If the computer program is downloaded to a computer via communication means and then executed, the above-described embodiment of the information recording / reproducing apparatus of the present invention can be realized relatively easily.

  Incidentally, in response to the various aspects of the embodiment of the information recording / reproducing apparatus of the present invention described above, the embodiment of the computer program of the present invention can also adopt various aspects.

  As described above, according to the embodiment of the information recording / reproducing apparatus of the present invention, the light source, the solid immersion lens, the optical system, the signal generation unit, the gap control unit, the tilt detection unit, and the gap change unit Is provided. An embodiment of a gap control method of the present invention is a gap control method of an information recording / reproducing apparatus including a light source, a solid immersion lens, an optical system, a signal generation unit, and a gap control unit, and includes a tilt detection step, And a gap changing step. According to the embodiment of the computer program of the present invention, the computer program includes a light source, a solid immersion lens, an optical system, a signal generation unit, a gap control unit, a tilt detection unit, and a gap change unit. An embodiment of a gap control method of the present invention is a computer program for controlling a computer included in an information recording / reproducing apparatus including a light source, a solid immersion lens, an optical system, a signal generation unit, and a gap control unit. The computer is caused to function as at least a part of a signal generation unit, a gap control unit, a tilt detection unit, and a gap change unit.

  Therefore, it is possible to perform appropriate gap control according to a tilt change between the solid immersion lens and the information recording medium when data is recorded or reproduced using near-field light.

  Embodiments of the present invention will be described below with reference to the drawings.

(1) Configuration Example of Information Recording / Reproducing Device First, a basic configuration according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram schematically showing the overall configuration of the information recording / reproducing apparatus according to the embodiment. The information recording / reproducing apparatus according to the embodiment performs a so-called focusing operation of the solid immersion lens in the gap control between the solid immersion lens and the optical disk based on the return light from the solid immersion lens. As described above, the information recording / reproducing apparatus 1 according to the embodiment emits a laser beam to the optical disc 100 and receives the laser beam from the optical disc 100, a spindle motor 20, a spindle servo mechanism 30, and an error signal generator. 40, a phase compensation unit 50, a lens driving unit 60, and a tilt control unit 70.

  The optical pickup 10 is a member constituting a specific example of the light source, the solid immersion lens, and the optical system of the present invention, and includes a solid immersion lens (SIL) 11, a lens actuator 12, an objective lens 13, and a laser diode. An LD (Laser Diode) and a light receiving element PD (Photo Detector) are provided.

  When recording or reproducing data, the light LB emitted from the laser diode LD is irradiated onto the recording surface of the optical disc 100 under the control of a laser diode driver (not shown). As a result, data is recorded by forming a data pattern corresponding to the data on the recording surface of the optical disc 100, and data is reproduced by reading the data pattern on the recording surface.

  More specifically, the light LB emitted from the laser diode LD is sent through a collimator lens, a diffraction grating, a beam shaper, a non-polarizing beam splitter, a polarizing beam splitter, an expander, a quarter-wave plate, a mirror, and the like (not shown). Via the objective lens 13. A part of the light LB is condensed on the medium surface of the optical disc 100 by the objective lens 13 through the solid immersion lens 11.

  The other part of the light LB is incident on the solid immersion lens 11 at an angle equal to or greater than the critical angle at the bottom of the solid immersion lens 11, is totally reflected, becomes return light, and is emitted from the solid immersion lens 11. The return light is incident on the light receiving element PD via the objective lens 13, the mirror, the quarter-wave plate, the expander, the polarizing beam splitter, the non-polarizing beam splitter, and the condenser lens. The light receiving element PD outputs a signal corresponding to the amount of the received return light as a gap error signal to the error signal generation unit 40 via an A / D converter (not shown).

  The gap between the solid immersion lens 11 and the medium surface of the optical disc 100 is relatively small (for example, about 200 nm or less), and in the so-called near field region, the solid immersion lens 11 has an angle greater than the critical angle at the bottom of the solid immersion lens 11. Part of the incident light is emitted to the medium surface of the optical disc 100 as near-field light. The distance between the bottom surface of the solid immersion lens in the near-field region (that is, the surface of the solid immersion lens closest to the optical disc 100) and the recording surface of the optical disc 100 is referred to as a gap or gap length.

  On the other hand, in the far field state in which the gap between the bottom surface of the solid immersion lens 11 and the medium surface of the optical disc 100 is relatively large (for example, several hundred μm (micrometers)), the focus for far field position control according to the amount of return light. An error signal may be generated, and gap control (so-called known focus error control) may be performed using the focus error signal.

  The spindle motor 20 rotates and stops the optical disc 100 and operates when accessing the optical disc 100. More specifically, the spindle motor 20 is configured to rotate and stop the optical disc 100 while being turned on / off by the spindle servo mechanism 30 and controlled in rotation speed.

  The error signal generation unit 40 is a specific example of the “signal generation unit” of the present invention. In the near-field region, the error signal generation unit 40 is generated in the light receiving element PD of the optical pickup 10 and a gap error signal according to the return light amount; By comparing with a preset gap target value dt, a near field position control signal which is a specific example of the error signal of the present invention is generated. Specifically, the gap error signal is subtracted from the gap target value dt, and a near-field position control signal for instructing driving of the actuator 12 is generated so as to correct the calculated difference.

  Generally, when the gap length is about “½” or less of the light source wavelength, the near-field region is obtained. For example, when the light source is a blue-violet laser, the wavelength of the irradiated light is about 400 nm, and the gap length in the near-field region is 200 nm or less.

  As the gap length becomes shorter in the near-field region, the near-field light passes through the solid immersion lens 11 toward the optical disc 100, so that the amount of return light incident on the light receiving element PD decreases. Specifically, in the near-field region, as described above, a part of the light LB incident on the solid immersion lens 11 at an angle greater than the critical angle at the bottom of the solid immersion lens 11 is used as the near-field light as a medium of the optical disc 100. It is emitted to the surface. For this reason, the amount of return light decreases, and the signal level of the gap error signal corresponding to the amount of return light incident on the light receiving element PD also decreases.

  On the other hand, as the gap length increases as the solid immersion lens 11 and the objective lens 13 move away from the near-field region, the near-field light does not pass through the solid immersion lens 11 toward the optical disc 100 and returns through the solid immersion lens. Arrives at the light receiving element PD, the amount of return light increases and becomes constant at a certain amount of light. Specifically, in the region outside the near-field region, the light incident on the solid immersion lens 11 at an angle equal to or larger than the critical angle at the bottom of the solid immersion lens 11 is totally returned by total reflection. For this reason, the signal level of the gap error signal corresponding to the amount of return light incident on the light receiving element PD is constant.

  Therefore, the gap length can be uniquely detected by detecting the return light amount incident on the light receiving element PD. The error signal generation unit 40 uniquely detects the relative distance between the bottom surface of the solid immersion lens and the recording surface of the optical disc 100 in the near-field region based on the gap error signal corresponding to the amount of return light incident on the light receiving element PD. It is configured to be possible.

  The near field position control signal generated in the error signal generation unit 40 is input to the phase compensation unit 50. The near field position control signal phase-compensated by the phase compensation unit 50 is input to the lens driving unit 60. In response to such a near field position control signal, a driving current is generated by the lens driving unit 60, and the driving current is supplied to the actuator 12 of the solid immersion lens 11 that is a component of the optical pickup 10. The actuator 12 moves the solid immersion lens 11 in the optical axis direction according to the supplied drive current, thereby changing the gap length, which is the distance between the optical disc 100 and the bottom surface of the solid immersion lens 11.

  Such a control loop including the light receiving element PD, the error signal generation unit 40, the phase compensation unit 50, the lens driving unit 60, and the actuator 12 is a specific example of the gap control means of the present invention, and is a near field. Position control (that is, gap control) of the fixed immersion lens 11 in the region is performed. The phase compensation unit 50 functions as a control unit for performing negative feedback in the control loop.

  The lens driving unit 60 is a driver for driving the actuator 12 by supplying a driving current corresponding to the input near-field position control signal to the actuator 12. The lens driving unit 60 also receives a gap change signal from the tilt control unit 70 as will be described later, and changes the position of the solid immersion lens 11 (that is, the gap with the optical disc 100) based on the gap change signal. The drive current is supplied to the actuator 12 as described above.

  The tilt control unit 70 is a member that constitutes one specific example of the tilt detection unit and the gap change unit of the present invention, and is configured to detect the relative tilt amount between the solid immersion lens 11 and the optical disc 100. Yes. Further, the tilt control unit 70 generates a gap change signal based on the detected tilt amount and supplies the gap change signal to the lens driving unit 60. The operation of the tilt control unit 70 will be described in detail later.

  The system control unit 300 includes a CPU (Central Processing Unit), a memory, and the like, and controls the operation of each unit of the information recording / reproducing apparatus 1.

  In addition to the above-described configuration, the light receiving element PD includes a light receiving element that receives reflected light from the recording surface of the optical disc 100, and a so-called far field region in which the gap between the solid immersion lens 11 and the optical disc 100 is relatively large. A focus error signal for performing the in-focus operation may be generated and output to the error signal generation unit 40. In such a configuration, the error signal generation unit 40 performs so-called known focus servo control, which is a focusing operation based on the focus error signal, so that the solid immersion lens 11 and the optical disc 100 outside the near-field region are Adjust the gap.

(2) Configuration Example of Tilt Control Unit 70 Next, a basic configuration and operation of the tilt control unit 70 according to the present embodiment will be described with reference to FIG. FIG. 2A is a block diagram illustrating a basic configuration of the tilt control unit 70 according to the present embodiment.

  As illustrated in FIG. 2A, the tilt control unit 70 includes a surface shake acquisition unit 71, a data processing unit 72, and a gap target value setting unit 73. As shown in FIG. 1, the tilt control unit 70 is connected to the spindle servo mechanism 30, the phase compensation unit 50, and the lens driving unit 60, and inputs and outputs various data by transmitting and receiving signals.

  The surface shake acquisition unit 71 is a member constituting one specific example of the tilt detection unit of the present invention, acquires the rotation profile of the optical disc 100 from the spindle servo mechanism 30, and the surface shake of the optical disc 100 synchronized with the rotation. Get the quantity. Further, the surface shake acquisition unit 71 calculates a tilt amount between the solid immersion lens 11 and the optical disc 100 by differentiating the acquired surface shake amount and outputs the tilt amount to the data processing unit 72. The surface shake acquisition unit 71 is configured to be able to calculate the respective tilt amounts in the radial direction and the tangential direction based on the surface shake amount of the optical disc 100.

  Here, the tilt between the solid immersion lens 11 and the optical disc 100 will be described with reference to FIG. As shown in FIG. 3A, the tilt is a meaning indicating an error in angle between the bottom surface of the solid immersion lens 11 and the recording surface of the optical disc 100. As shown in FIG. 3B, such a tilt is obtained from a radial tilt θr that is an error in the radial direction of the optical disc 100 and a tangential tilt θt that is an error in the angle of the optical disc 100 in the tangential direction. It is made up.

  Such a tilt between the solid immersion lens 11 and the optical disc 100 is considered to occur when a predetermined angle is generated between the rotation axis of the optical disc 100 and the rotation axis of the spindle motor 30 that rotates the optical disc 100. It is done. Further, the warp of the optical disc 100 causes a radial tilt in the radial direction.

  Further, the radial tilt amount θr between the solid immersion lens 11 and the optical disc 100 and the maximum and minimum values of the tangential tilt amount θt typically have a certain period during one rotation of the optical disc 100. is doing. By detecting a change in the tilt amount during one rotation of the optical disc 100, for example, a tilt profile as shown in FIG. 6B is acquired.

  Returning to FIG. 2, the description will be continued. The data processing unit 72 is a member that constitutes a part of the tilt detection unit of the present invention. The data processing unit 72 is an input radial tilt amount (hereinafter referred to as a radial tilt amount θr) and a tangential tilt amount. The total tilt amount θ between the solid immersion lens 11 and the optical disc 100 is calculated based on (hereinafter referred to as a tangential tilt amount θt). Note that the tilt amount θ is calculated based on the following equation, for example.

  Further, the data processing unit 72 calculates a limit distance dm, which is a minimum gap that the solid immersion lens 11 and the optical disc 100 can approach without contacting each other, based on the calculated tilt amount θ. When the radius of the bottom surface of the solid immersion lens is r, it is calculated from the following equation.

  The calculated limit distance dm is input to the gap target value setting unit 73.

  The gap target value setting unit 73 is a part of a member constituting one specific example of the gap changing means of the present invention, and compares the limit distance dm with a preset gap target value dt. When it is larger than the gap target value dt, the limit distance dm is substituted into the gap target value dt and output to the error signal generation unit 40. The error signal generation unit 40 receives the gap target value dt and a gap error signal corresponding to the amount of return light via the A / D converter, and subtracts the gap error signal from the gap target value dt. A position control signal is generated. The near field position control signal is output to the phase compensator 50.

  The generated near field position control signal is input to the lens driving unit 60 via the phase compensation unit 50 and the D / A converter. The lens driving unit 60 supplies a driving current to the actuator 12 so as to change the gap between the solid immersion lens 11 and the optical disc 100 based on the input signal. For this reason, according to the operation of the actuator 12 based on the supplied drive current, the gap between the solid immersion lens 11 and the optical disc 100 is changed to, for example, the limit distance dm.

  Note that the tilt control unit 70 may be configured to acquire the tilt amount between the solid immersion lens 11 and the optical disc 100 by a method different from the method of acquiring the surface shake amount of the optical disc 100. For example, a tilt sensor 74 may be provided as a specific example of the tilt detection unit like the tilt control unit 70 b shown in FIG. 2B, and the tilt amount may be acquired by the operation of the tilt sensor 74.

  Further, the information recording / reproducing apparatus 1 may include a mechanical tilt actuator 14 for changing the angle of the solid immersion lens 11 with respect to the optical disc 100 or the angle of the optical pickup 10 with respect to the optical disc 100. The mechanical tilt actuator 14 is configured to realize, for example, a known lens tilt or mechanical tilt mechanism. For example, the angle of the solid immersion lens 11 with respect to the optical disc 100 is controlled under the control of the system control unit 300 or the data processing unit 72. Alternatively, the angle of the optical pickup 10 with respect to the optical disc 100 (and hence the angle of the solid immersion lens 11) is changed. FIGS. 4A and 4B are block diagrams showing configurations of the tilt control unit 70c and the tilt control unit 70d when the mechanical tilt actuator 14 is provided. The specific operation of the mechanical tilt actuator 14 will be described in detail later. In the block diagrams shown in FIGS. 4 (a) and 4 (b), the same components as those in FIGS. 2 (a) and 2 (b) are denoted by the same reference numerals and description thereof is omitted. ing.

  As described above, according to the information recording / reproducing apparatus 1 of the present embodiment, the gap control between the solid immersion lens 11 and the optical disc 100 based on the gap error signal and the gap between the solid immersion lens 11 and the optical disc 100 are performed. Gap control based on the tilt amount is performed. A detailed flow of such a gap control operation will be described below.

(3) Operation Example Next, the flow of the gap control operation according to the information recording / reproducing apparatus 1 of the present embodiment will be described with reference to FIGS. FIG. 5 is an example of a flowchart showing a flow of the gap control operation, and FIG. 6 is a graph showing a profile of the tilt amount θ and the gap target value dt related to the gap control operation. FIG. 7 is a graph showing a mode of changing the RF gain accompanying the gap change described later.

  As shown in FIG. 5, when the gap control is started, the system control unit 300 first sets the gap target initial value di and the RF gain initial value gi by referring to, for example, data stored in the memory. Set (step S101).

  Subsequently, the system control unit 300 substitutes the set gap target initial value di for the gap target value dt when the gap control is performed. Further, the set RF gain initial value gi is substituted for the RF gain gt when the gap control is performed (step S102).

  Next, the surface shake acquisition unit 71 or the tilt sensor 74 of the tilt control unit 70 acquires a tilt amount between the solid immersion lens 11 and the optical disc 100, that is, a tangential tilt amount θt and a radial tilt θr (step). S103).

  Next, it is a case where the information recording / reproducing apparatus 1 includes the mechanical tilt actuator 14 (that is, a case where the configuration of the tilt control unit is the tilt control unit 70c or the tilt control unit 70d shown in FIG. 4) (step S104). : Yes), mechanical tilt correction processing is performed (step S105). The specific operation of such mechanical tilt correction processing will be described later. Typically, the absolute values of the tangential tilt amount θt and the radial tilt θr are reduced by performing the mechanical tilt correction.

  Next, the data processor 72 of the tilt controller 70 calculates the total tilt amount θ and the limit distance dm between the solid immersion lens 11 and the optical disc 100 based on the tilt amount θ (step S106).

  Here, with reference to FIG. 6, the aspect of the data acquired by each part is demonstrated. For example, according to the operation of the surface shake acquisition unit 71, a profile of the surface shake amount of the optical disc 100 as shown in FIG. Based on the profile of the surface shake amount and the tilt amount acquired by the operation of the tilt sensor 74, a profile of the tilt amount within one rotation of the optical disc 100 as shown in FIG. 6B is created. The

  Since the total tilt amount θ calculated by the data processing unit 72 is an absolute value of the tilt amount, the tilt profile shown in the graph of FIG. c) is converted into the profile shown in FIG. Subsequently, based on the tilt profile converted to an absolute value, a profile of the limit distance dm based on the profile of the tilt amount θ as shown in FIG. 6D is generated.

  Returning to FIG. 5, the description will be continued. Subsequently, the gap target value setting unit 73 performs a comparison between the limit distance dm and the gap target value dt (step S107).

  If the limit distance dm is larger than the gap target value dt (step S107: Yes), the gap target value setting unit 73 substitutes the limit distance dm for the gap target value dt (step S108). For this reason, the error signal generation unit 40 generates a near-field position control signal by comparing the newly set gap target value dt (ie, the limit distance dm) with the gap error signal. The lens driving unit 60 then supplies the actuator 12 with a driving current corresponding to the near-field position control signal input via the phase compensation unit 50 and the DA converter. For this reason, the movement of the actuator 12 causes the solid immersion lens 11 to move so that the gap between the solid immersion lens 11 and the optical disc 100 becomes the limit distance dm.

  For example, as shown in FIG. 6E, when the set gap target value dt is 20 nm and the maximum value of the limit distance dm calculated from the tilt amount θ is 25 nm, the gap target value dt includes the limit distance. The solid immersion lens 11 is moved by the operation of the actuator 12 so that 25 nm of dm is substituted and the gap between the solid immersion lens 11 and the optical disc 100 is maintained at the limit distance of 25 nm.

  By the way, when the gap between the solid immersion lens 11 and the optical disc 100 changes, the RF signal amplitude generated in the light receiving element of the optical pickup 10 changes. The light receiving element is a light receiving element that is different from the light receiving element PD that generates a gap error signal by receiving the return light from the bottom surface of the solid immersion lens 11, and receives the reflected light from the recording surface of the optical disc 100. The light receiving element for generating the RF signal is shown. In an optical system using near-field light, generally, the larger the gap between the solid immersion lens 11 and the optical disc 100, the smaller the RF signal amplitude in the light receiving element. For this reason, by changing the gap from the gap target value dt to a larger limit distance dm, the amplitude of the obtained RF signal is reduced. FIG. 7A is an example of a graph conceptually showing the relationship between such a gap and RF amplitude.

  When the gap between the solid immersion lens 11 and the optical disc 100 changes, the system control unit 300 changes the gain of the RF signal in the light receiving element of the optical pickup 10 (step S109). Note that the mode of changing the gain of the RF signal at this time is preferably implemented in a foot forward manner, for example, depending on a gap target value dt (for example, a newly assigned limit distance dm) or a gap error signal. The RF gain gt is changed. FIG. 7B and FIG. 7C are examples of graphs conceptually showing the relationship between the gap value and the gap error signal and the set RF gain.

  As described above, according to the gap control according to the information recording / reproducing apparatus 1, the gap between the solid immersion lens 11 and the optical disc 100 is appropriately maintained without using a special tilt servo mechanism. At this time, when the limit distance dm caused by the relative tilt amount θ between the solid immersion lens 11 and the optical disc 100 is larger than the gap target value dt for gap control, the gap target value dt is the limit. The distance is changed to dm. For this reason, the contact between the solid immersion lens 11 and the optical disc 100 can be preferably avoided. As a result, it is possible to avoid contact between the information recording medium and the solid immersion lens even at a location where the tilt amount between the information recording medium and the solid immersion lens is relatively large.

  In the above-described example, the gap target value dt is continuously changed as shown in FIG. 6E by comparing the limit distance dm with the gap target value dt. Only when the limit distance dm exceeds the gap target value dt, processing for temporarily changing the gap target value dt may be performed.

  For example, in step S107, instead of the gap target value dt, the gap initial target value di and the limit distance dm are compared, and the limit distance dm is substituted into the gap target value dt based on the comparison result. A profile of the gap target value dt as shown in FIG. 6F can be obtained.

  According to this aspect, since the gap between the solid immersion lens 11 and the optical disc 100 can be kept smaller in a portion other than a portion where a relatively large tilt occurs, the RF signal amplitude can be better maintained.

(4) Mechanical Tilt Correction Processing Next, with reference to FIGS. 8 and 9, the mechanical tilt correction processing performed when the above-described mechanical tilt actuator 14 is provided will be described. FIG. 8 is an example of a flowchart showing the flow of the mechanical tilt correction process, and FIG. 9 is a graph showing a profile of the tilt amount θ and the gap target value dt related to the gap control operation when the mechanical tilt correction process is performed. is there. In this section, an aspect of the operation of the mechanical tilt correction process related to the mechanical tilt actuator 14 that changes the angle of the optical pickup 10 will be described.

  As shown in FIG. 8, when the mechanical tilt correction process is performed, it is first determined by the operation of the system control unit 300 or the like whether the mechanical tilt correction process has been performed in the previous gap control operation (step S201).

  If the mechanical tilt correction process has not been performed during the previous gap control operation (step S201: No), the predetermined amount of rotation (for example, for example, from the detection of the tilt amount in the gap control operation (step S103 in FIG. 5)). N rotations) As described above, it is determined whether the optical disk 100 is rotated (step S202). Specifically, the determination is made based on the number of rotations of the optical disc 100 detected by the spindle servo mechanism 30. When the rotation is greater than or equal to the predetermined rotation, a mechanical tilt correction process described later is performed.

  On the other hand, if the mechanical tilt correction process has been performed during the previous gap control operation (step S201: Yes), the optical disc 100 continues to have a predetermined rotation (for example, N rotations) or more from the execution of the mechanical tilt correction process. It is determined whether the rotation is performed (step S203). When the rotation is greater than or equal to the predetermined rotation, a mechanical tilt correction process described later is performed.

  Here, the predetermined N rotation is appropriately determined based on, for example, the number of rotations at which the tilt profile within the rotation of the optical disc 100 according to the execution of the mechanical tilt correction process can be appropriately acquired, the operating speed of the mechanical tilt actuator 14, and the like. May be set.

  Subsequently, the angle of the optical pickup 10 in the tangential direction is adjusted based on the acquired tangential tilt amount θt for one rotation of the optical disc 100 (step S204). Specifically, among the tilt amount θt in the tangential direction within one rotation of the optical disc 100, the maximum positive tilt amount (that is, the tilt amount of tilt in one tangential direction) and the negative tilt amount ( That is, the angle of the optical pickup 10 is changed so that the intermediate value of the minimum value of the tilt amount in the other tangential direction becomes zero.

  According to such a change in the angle of the optical pickup 10, as shown in FIG. 9D, the peak height (that is, the tangential tilt amount θt) in the tilt profile converted to an absolute value is made uniform. The For this reason, when there is a protruding peak due to tangential tilt, the amount of tilt of the peak can be reduced, and as a result, the limit distance dm can be reduced.

  Simultaneously with or before or after the mechanical tilt correction operation in the tangential direction (step S204), the radial angle of the optical pickup 10 is adjusted based on the acquired radial tilt amount θr for one rotation of the optical disc 100 (step S204). Step S205).

  For example, the radial tilt due to the warp of the optical disc 100 tends to change depending on the radial position regardless of the rotation of the optical disc 100. Since the profile of the radial tilt amount θr for one rotation of the optical disc 100 includes a tilt amount DC component caused by such warping, the overall tilt amount may increase as a result. For example, as shown in FIG. 9E, the overall radial tilt amount θr may increase due to the tilt in one radial direction caused by the warp of the optical disc 100. Therefore, the angle of the optical pickup 10 is changed so that the direct current component independent of the rotation angle of the optical disk 100 becomes zero in the radial tilt amount θr within one rotation of the optical disk 100.

  By changing the angle of the optical pickup 10 as described above, the direct current component of the radial tilt amount θt independent of the rotation angle of the optical disc 100 as shown in FIG. 9E is removed, and the radial tilt amount θr is reduced. As a result, the limit distance dm can be reduced.

  According to the mechanical tilt correction process described above, the relative tilt amount between the solid immersion lens 11 and the optical disc 100 can be reduced by using the mechanical tilt actuator 14 that operates at a relatively low speed. For this reason, it is possible to keep the limit distance dm between the solid immersion lens 11 and the optical disc 100 smaller, and as a result, the change of the gap target value dt caused by the tilt between the solid immersion lens 11 and the optical disc 100 described above is achieved. The frequency can be reduced. This leads to a reduction in processing amount and is beneficial.

  As an example of the mechanical tilt actuator 14 for performing such mechanical tilt correction processing, a mechanical tilt mechanism that changes the angle of the optical pickup 10 has been described. For example, a lens tilt change that changes the angle of the solid immersion lens 11 is described. A similar effect can be obtained even if a mechanism for this is used.

1 ... Information recording / reproducing apparatus,
10 ... Optical pickup,
11 ... Solid immersion lens,
12 ... Actuator,
20 ... Spindle motor,
30 ... Spindle servo mechanism,
40: Error signal generator,
50: Phase compensation unit,
60: Lens drive unit,
70: Tilt control unit,
100 ... optical disc,
LD ... Laser diode,
PD: light receiving element.

Claims (7)

A light source for irradiating a disc-shaped information recording medium with light;
A solid immersion lens that is disposed close to the medium surface of the information recording medium and generates near-field light;
An optical system for condensing a part of the irradiated light on the medium surface via the solid immersion lens;
A signal generating means for outputting an error signal corresponding to the reflected light from the bottom of the solid immersion lens caused by the other part of the light;
Gap control means for controlling a gap between the medium surface and the solid immersion lens based on the error signal;
Tilt detecting means for detecting a relative tilt amount between the information recording medium and the solid immersion lens and calculating a limit distance which is a distance at which the solid immersion lens and the medium surface do not contact each other based on the tilt amount. When,
When the limit distance is larger than the gap between the medium surface controlled by the gap control means and the solid immersion lens, the gap changing means changes the gap temporarily or continuously beyond the limit distance. An information recording / reproducing apparatus comprising:   The information recording / reproducing apparatus according to claim 1, further comprising a tilt adjusting unit that changes an angle of the solid immersion lens with respect to the information recording medium. The tilt detection means detects a direct current component that does not vary during one rotation of the information recording medium, among tilts tilted in the radial direction of the information recording medium,
3. The information recording / reproducing apparatus according to claim 2, wherein the tilt adjusting unit changes an angle of the solid immersion lens with respect to the information recording medium so that the DC component becomes zero. When the tilt detecting means sets the tilt tilted in one of the tangential directions orthogonal to the radial direction of the information recording medium as a positive tilt and the tilt tilted in the opposite side of the positive tilt as a negative tilt, the information Each of the maximum positive tilt amount and the minimum negative tilt amount during one rotation of the recording medium is detected,
The tilt adjusting means is configured to move the solid relative to the information recording medium so that an intermediate value between the maximum value of the positive tilt amount and the minimum value of the negative tilt amount during one rotation of the information recording medium becomes zero. 4. The information recording / reproducing apparatus according to claim 2, wherein an angle of the immersion lens is changed.   4. The information recording according to claim 1, further comprising signal intensity control means for controlling the intensity of the light in a feed-forward manner based on at least one of the error signal and the gap. 5. Playback device. A light source for irradiating light to a disc-shaped information recording medium, a solid immersion lens disposed near the medium surface of the information recording medium and generating near-field light, and a part of the irradiated light for the solid An optical system for condensing on the surface of the medium via an immersion lens, and a signal generating means for outputting an error signal corresponding to reflected light from the bottom of the solid immersion lens caused by another part of the light, A gap control method for an information recording / reproducing apparatus comprising gap control means for controlling a gap between the medium surface and the solid immersion lens based on an error signal,
A tilt detection step of detecting a relative tilt amount between the information recording medium and the solid immersion lens and calculating a limit distance that is a distance at which the solid immersion lens and the medium surface do not contact each other based on the tilt amount. When,
When the limit distance is larger than the gap between the medium surface controlled by the gap control means and the solid immersion lens, the gap changing step of changing the gap temporarily or continuously above the limit distance And a gap control method for an information recording / reproducing apparatus. A light source for irradiating light to a disc-shaped information recording medium, a solid immersion lens disposed near the medium surface of the information recording medium and generating near-field light, and a part of the irradiated light for the solid An optical system for condensing on the surface of the medium via an immersion lens, and a signal generating means for outputting an error signal corresponding to reflected light from the bottom of the solid immersion lens caused by another part of the light, Gap control means for controlling the gap between the medium surface and the solid immersion lens based on an error signal, and detecting a relative tilt amount between the information recording medium and the solid immersion lens, and based on the tilt amount Tilt detecting means for calculating a limit distance that is a distance at which the solid immersion lens and the medium surface do not contact each other, and the medium surface for which the limit distance is controlled by the gap control means; A computer program for controlling a computer provided in an information recording / reproducing apparatus comprising gap changing means for changing the gap temporarily or continuously beyond the limit distance when the gap is larger than the gap between the solid immersion lens and the solid immersion lens. Because
A computer program that causes the computer to function as at least part of the signal generation means, the gap control means, the tilt detection means, and the gap change means.

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