JP2008234691A - Optical information recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information recording and reproducing device in which a gap servo can be pulled in stably by evading a risk of collision of SIL and an optical disk caused by external vibration, attitude difference, or the like during pull-in of the gap servo. <P>SOLUTION: The device is provided with a converging optical system 50 composed of an objective lens 10 and SIL 11, an actuator driving the converging optical system in the vertical direction and in the tracking direction for an optical disk surface, a displacement detecting circuit 105 detecting a displacement signal in the tracking direction of the converging optical system, a gap error detecting circuit 103 detecting a gap error signal, a gap servo circuit 110 performing gap servo based on the gap error signal, and a position servo circuit 112 servo-controlling the actuator in the tracking direction during pull-in of the gap servo. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical information recording / reproducing apparatus that records or reproduces information on an optical disk using a solid immersion lens (hereinafter abbreviated as SIL), and more particularly to a stabilization technique at the time of pulling in a gap servo.

  In order to improve the recording density of the optical disc, it is required to shorten the wavelength of light used for recording and reproduction, increase the numerical aperture (NA) of the objective lens, and reduce the light spot diameter on the optical disc recording surface. . Conventionally, there has been an attempt to construct a so-called SIL by bringing the front lens of the objective lens close to a fraction of the recording wavelength (for example, ½) or less on the recording surface, and to set NA to 1 or more even in the air. It has been made. They are described in detail in, for example, Non-Patent Document 1 and Non-Patent Document 2.

  The prior art will be described with reference to FIGS. The configuration of the near-field recording optical pickup of Non-Patent Document 1 will be described with reference to FIG. A light beam emitted from the semiconductor laser 1 having a wavelength of 405 nm is converted into a parallel light beam by the collimator lens 2 and is incident on the beam shaping prism 3 to form an isotropic light amount distribution.

  Further, the light beam that has passed through the non-polarizing beam splitter (NBS) 4 and transmitted through the polarizing beam splitter (PBS) 7 passes through the quarter-wave plate (QWP) 8 and is converted from linearly polarized light to circularly polarized light. A light detector (LPC-PD) 6 for receiving the light beam reflected by the non-polarizing beam splitter (NBS) 4 through the lens 5 and controlling the emission power of the semiconductor laser 1 is provided.

  The light beam that has passed through the quarter-wave plate (QWP) 8 enters the expander lens 9. The expander lens 9 is a lens for correcting spherical aberration generated in the objective lens or SIL, and is configured such that the distance between the two lenses can be controlled in accordance with the spherical aberration.

  The light beam from the expander lens 9 enters the rear lens 10 of the objective lens. The objective lens is composed of a rear lens 10 and a SIL (front lens) 11, which are mounted on a biaxial actuator (not shown) that integrally drives the two lenses in the focus direction and the tracking direction. In the present specification, the rear lens is called the objective lens 10 and the front lens is called SIL11.

  FIG. 12 shows how the light beam focused by the objective lens 10 is condensed on the bottom surface of the SIL 11 of the hemispherical lens. The light beam is incident on the spherical surface of the hemispherical lens perpendicularly, and is condensed on the bottom surface through the same optical path as when there is no hemispherical lens. There is an effect to.

  That is, assuming that the refractive index of the hemispherical lens is N and the numerical aperture of the objective lens 10 is NA, a light spot equivalent to N × NA is obtained on the recording surface of the optical disk 12. For example, if the SIL of the hemispherical lens of N = 2 is combined with the objective lens 10 of NA = 0.7, NAeff = 1.4 is reached with the effective NA as NAeff. Since the thickness error of the hemispherical lens 11 can be allowed to be about 10 μm, mass production is easy.

  Only when the distance between the bottom surface of the SIL and the optical disk 12 is a short distance of a fraction of the wavelength of the light source 405 nm, for example, 100 nm or less, the recording surface acts as evanescent light from the bottom surface of the SIL, and recording with the NAeff light spot diameter And playback is possible. In order to maintain this distance, a gap servo described later is used.

  Returning to FIG. 11, the return optical system will be described. The light beam reflected from the optical disk 12 becomes reverse circularly polarized light, enters the SIL 11 and the objective lens 10 and is converted again into a parallel light beam. This parallel light beam passes through the expander lens 9 and the quarter wave plate (QWP) 8 and is linearly polarized in a direction orthogonal to the forward path. This light beam is reflected by a polarization beam splitter (PBS) 7.

  This reflected light beam is rotated by 45 ° on the plane of polarization by a half-wave plate (HWP) 13, and the S-polarized component of the light beam is reflected by a polarizing beam splitter (PBS) 14 and passes through a lens 15 to be a photodetector. The light is condensed on (PD1) 16. An RF output 17 that is information on the optical disk 12 is obtained from the light reception signal of the photodetector (PD1) 16.

  In addition, the P-polarized component of the light beam whose polarization plane is rotated by 45 ° by the half-wave plate (HWP) 13 passes through the polarization beam splitter (PBS) 14 and is reflected by the non-polarization beam splitter (NBS) 18. . Further, the light is condensed on the two-divided photodetector (PD 2) 20 via the lens 19. A tracking error signal 21 is obtained from the light reception signal of the two-part photodetector (PD2) 20 by a known detection method.

  On the other hand, among the light beams reflected by the bottom surface of the SIL 11, a light beam of NAeff <1 that does not totally reflect is reflected as circularly polarized light that is reverse to the incident, similarly to the light reflected from the optical disk 12. For a beam of NAeff ≧ 1 that causes total reflection, a phase difference δ expressed by the following equation is generated between the P-polarized component and the S-polarized component, and becomes elliptically polarized light that deviates from circularly polarized light.

tan (δ / 2)
= Cos θi × √ (N ² × sin ² θi−1) / (N × sin ² θi) (1) Therefore, when passing through the quarter wave plate (QWP) 8, the polarization component in the same direction as the forward path is included. It will be. This polarization component passes through the polarization beam splitter (PBS) 7, is reflected by the non-polarization beam splitter (NBS) 4, and is condensed on the photodetector (PD 3) 27 via the lens 26. Since the amount of the light beam monotonously decreases as the distance between the bottom surface of the SIL and the optical disk approaches in the near-field region, it can be used as the gap error signal 28.

  If the target threshold value is determined in advance, the distance between the bottom surface of the SIL and the optical disk can be kept at a desired distance of 100 nm or less by performing gap servo. The gap servo is detailed in the paper of Non-Patent Document 1 described above. Since this light beam is not modulated by the recording information on the optical disk 12, a stable gap error signal can be obtained regardless of the presence or absence of the recording information.

  The overshoot at the time of pulling in the gap servo needs to be 100 nm or less. If the overshoot exceeds 100 nm, the SIL and the optical disk collide, and the SIL and the optical disk are damaged.

  The pull-in of the gap servo is disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-209246 (Patent Document 1). FIG. 13 shows the apparatus configuration of the publication. FIG. 14 shows a timing chart at the time of gap servo pull-in. When pulling in the gap servo, the approach speed generation circuit 208 outputs a drive signal for bringing the objective lens and SIL in the pickup 202 including the optical system as shown in FIGS. Output to.

  The gap error signal generated by the gap error generation circuit 204 is input to the comparator 207 in the process in which the optical disc 201 and the SIL approach each other. As shown in FIG. 14, the comparator 207 outputs a low level to the switch 209 if the magnitude of the input gap error signal is greater than or equal to a predetermined value Vth, and if it is less than or equal to the predetermined value Vth.

  When it is detected that the output of the comparator 207 is at a high level, that is, the gap error signal is equal to or smaller than the predetermined value Vth, the distance between the optical disk and the SIL is reduced, and the near field state is entered, the switch 209 is turned on and the gap servo is started. Further, the output of the approach speed generation circuit 208 until the transition from the far field state to the near field state has a waveform shown in FIG.

It is set in advance so that the output of the approach speed generation circuit 208 becomes a constant voltage at the time t1 when the gap error is equal to or less than the predetermined value Vth. In this way, if the approach voltage of the actuator is set to be a constant voltage at the start of the gap servo pull-in, the initial speed of the SIL at the servo start becomes almost zero, and the gap servo can be pulled in stably.
Japan Journal NA1 Applied Physics Vol. 44 (2005) P. 3564-3567, “Near Field Recording on First-Surface Write-Once Media with Iol. Optical Data Storage 2004, Proceedings of SPIE 5380 (2004) "Near Field read-out of first-surface disk with NA-1.9 and a proposal for a co- er for the coer JP 2005-209246 A

  As described above, the gap length at which the gap error is less than or equal to the predetermined value Vth when the gap servo is pulled in is as small as about 100 nm. Therefore, if the tracking direction is not controlled during gap servo pull-in, the operation becomes unstable due to vibration. Further, depending on the posture of the apparatus, the end surface of the SIL may be tilted with respect to the optical disk surface due to the weight of the SIL, and may collide.

  Furthermore, depending on the structure of the actuator, the SIL may move in the tracking direction due to the occurrence of external vibration or a posture difference, and the SIL may tilt and tilt may occur in a situation where it is positioned at the end of the movable range in the tracking direction. . When the gap servo pull-in operation is performed in such a state, the SIL collides with the optical disk, and the recorded data may be damaged depending on the situation.

  An object of the present invention is to avoid the risk of collision between an SIL and an optical disk, which is generated due to external vibration or a posture difference at the time of gap servo pull-in, and is capable of stably pulling in the gap servo. Is to provide.

  The present invention relates to a condensing optical system that condenses a light beam from a light source and includes an objective lens and a SIL disposed between the objective lens and the optical disc, and the condensing optical system in a direction perpendicular to the optical disc surface. And an actuator that drives in the tracking direction, a displacement detection circuit that detects a displacement signal that indicates the displacement in the tracking direction of the condensing optical system, and a gap error detection circuit that detects a gap error signal that indicates the amount of space between the SIL and the optical disk A gap servo circuit that controls the distance between the condensing optical system and the optical disk by servo-controlling the actuator in the vertical direction based on the detected gap error signal, and an actuator based on the displacement signal when the gap servo is pulled in And a position servo circuit for servo-controlling in the tracking direction.

  According to the present invention, by performing position control in the tracking direction when pulling in the gap servo, collision between the SIL and the optical disk can be avoided even if external vibration or the like occurs, and stable pull-in can be realized.

  Next, the best mode for carrying out the invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a first embodiment of an optical information recording / reproducing apparatus according to the present invention. An optical information recording / reproducing apparatus according to the present invention condenses a light beam from a light source (semiconductor laser) on an optical disk to record or reproduce information. In FIG. 1, a circuit necessary for recording information on the optical disc, a circuit necessary for reproducing recorded information, a circuit for performing focus servo, and other circuits and mechanisms are omitted.

  In the figure, 100 is an optical pickup including the optical system shown in FIG. 2, and 101 is a spindle motor that rotationally drives the optical disk 102. In the optical pickup 100, a light collecting unit including a objective lens 10 and a solid immersion lens (SIL) 11 disposed between the objective lens 10 and the optical disk 102, which collects a light beam from a light source (semiconductor laser). It has an optical system. In FIG. 1, the condensing optical system is shown as a head 50.

  In addition, a gap error detection circuit 103 that detects a gap error signal indicating an interval amount between the SIL and the optical disc 102 is provided. The gap error detection circuit 103 detects a gap error signal based on the reflected light from the SIL end face received by the photodetector (PD3) 27 in the optical pickup of FIG.

  Reference numeral 110 denotes a gap servo signal processing unit that performs gap servo to control the distance between the condensing optical system (head) 50 and the optical disk based on the detected gap error signal. Reference numeral 106 denotes a head drive actuator driver circuit for driving a head drive actuator 52 that drives the condensing optical system in a direction perpendicular to the optical disk surface.

  Thus, the present invention includes a gap servo circuit that controls the distance between the condensing optical system and the optical disk by servo-controlling the actuator 52 in the direction perpendicular to the optical disk surface based on the detected gap error signal. .

  A tracking error detection circuit 104 detects a tracking error signal from the signal of the photodetector (PD2) 20 in FIG. Reference numeral 111 denotes a tracking servo signal processing unit for performing tracking servo.

  A lens position signal detection circuit 105 generates a lens position signal from the output of the photodetector (PD3) 27 in FIG. Reference numeral 112 denotes a signal processing unit that performs lens position servo based on the detected lens position signal.

  Here, the lens position signal is a signal indicating the displacement in the tracking direction of the condensing optical system. The lens position signal is obtained by adjusting the attitude of the tracking actuator 51 and the position of the photodetector 27 so that the optical axis of the condensing optical system (head) 50 coincides with the optical axis of the parallel light beam incident thereon. Is set to zero when

  As described above, the present invention includes the displacement detection circuit (lens position signal detection circuit 105) that detects the displacement signal indicating the displacement in the tracking direction of the condensing optical system. Further, a position servo circuit (lens position signal processing unit or the like) that servo-controls the tracking actuator 51 in the tracking direction based on a displacement signal (lens position signal) when the gap servo is pulled in is provided.

  Reference numeral 107 denotes a switch SW (switch). Reference numeral 108 denotes a head drive actuator driver circuit for driving the tracking actuator 51 that drives the condensing optical system (head) 50 in the tracking direction.

  The displacement detection circuit (lens position signal detection circuit 105) is a displacement signal (lens position signal) based on the detection signal of the photodetector (PD3) 27 that detects the return light reflected from the end surface facing the SIL optical disk. ) Is detected.

  FIG. 2 shows the configuration of the optical system of this embodiment. In the figure, the same parts as those in FIG. The feature of this embodiment is that the tracking actuator 51 is servo-controlled in the tracking direction based on the lens position signal (displacement signal) during the gap servo pull-in.

  That is, the tracking actuator 51 is driven based on the lens position signal obtained from the output of the photodetector (PD3) 27, which is a gap sensor, when the gap servo is pulled. Specifically, the position of the condensing optical system (head) 50 is held at a position where the lens position signal becomes a predetermined value (preferably zero).

  The lens position servo processing unit 112 in FIG. 1 is a position servo circuit that performs servo control of the head drive actuator 52 in the tracking direction based on a displacement signal (lens position signal) when the gap servo is drawn.

  Here, FIG. 2 shows the tracking actuator 51 and the head drive actuator 52 as described above in addition to the optical system such as the semiconductor laser, each lens, each polarization beam splitter, or each photodetector. These components constitute the optical pickup 100 of FIG.

  In FIG. 2, the condensing optical system composed of the objective lens 10 and the SIL 11 is shown as the head 50 as described above. The head driving actuator 52 drives the condensing optical system (head) 50 in the direction perpendicular to the optical disk surface, and the tracking actuator 51 drives the condensing optical system (head) 50 in the tracking direction.

  That is, the present invention includes an actuator that drives the condensing optical system in a direction perpendicular to the surface of the optical disc and in a tracking direction. As described in the prior art, the condensing optical system may be mounted on a biaxial actuator that integrally drives two lenses in the focus direction and the tracking direction.

  The detection signal of the photodetector (PD3) 27 will be described with reference to FIG. FIG. 3A schematically shows a light amount distribution in the pupil, and FIG. 3B schematically shows a relationship between the optical disk-SIL distance and the gap error signal. In FIG. 3A, the reflected light beam from the optical disk is NA = 1.4 (NA> 1) at the periphery of the pupil diameter.

  The ring portion with NA> 1 contains a lot of reflected light from the bottom surface of the SIL, and as shown in FIG. 3B, the amount of reflected light is large when the distance between the optical disk and the SIL is wide. Further, when the SIL is brought closer to the optical disc, the near-field region starts from around 100 nm, and the reflected light from the bottom surface of the SIL decreases monotonously as the optical disc approaches.

  FIG. 4 is a circuit diagram showing a gap error detection circuit 103 and a lens position signal detection circuit 105 that generate a gap error signal and a lens position signal from the output signal of the photodetector (PD3) 27 in FIG. The photodetector (PD3) 27 is a two-divided photodetector that is divided into two in the tracking direction.

  Here, as shown in FIG. 4, the divided regions of the photodetector (PD3) 27, which is a gap sensor, are A and B. As a gap error signal supplied to the gap servo that controls the distance between the optical disk and the SIL, a sum signal obtained by adding the signals of the areas A and B by the addition 41 as shown in FIG. 4 is used.

Gap error signal = A + B
Further, the lens position signal supplied to the lens position servo for controlling the condensing optical system (head) 50 in FIG. 2 to a predetermined position in the movable range in the tracking direction includes signals of the areas A and B as shown in FIG. The difference signal obtained by subtracting the signal by the subtractor 42 is used.

Lens position signal = BA
Here, when the optical axis of the condensing optical system (head) 50 is shifted as shown in FIG. 7B from the state where the optical axis of the condensing optical system (head) 50 coincides with the optical axis of the incident incident light as shown in FIG. The light distribution shifts left and right with respect to the sensor center. Therefore, the lens position can be detected by using the difference between the region A and the region B.

  5 (a) and 5 (b) schematically show the relationship between the lens position and the lens position error signal. The relationship between the lens position and the lens position error signal is proportional. By detecting the value of the lens position signal, the amount by which the condensing optical system is shifted to the left and right with respect to the optical axis of the incident parallel light beam is calculated. Can do.

  Note that the distribution of reflected light indicated by a broken line on the gap sensor (PD3) 27 in FIG. 5A indicates a state in which the luminous flux coincides with the center of the sensor. The distribution of the reflected light indicated by the solid line on the gap sensor (PD3) 27 in FIG. 5B shows a state in which the luminous flux is shifted with respect to the sensor center.

  Next, a gap servo pull-in method according to the present invention will be described with reference to the flowchart of FIG. 6 and the timing chart of FIG. In step 1 of FIG. 6, the gap servo pull-in operation is started. In this state, as shown in FIG. 8, the gap between the optical disk and the SIL is not less than a predetermined amount, so that the level of the gap error signal is substantially constant. The SW 107 in FIG. 1 is connected to the lens position servo signal processing unit 112.

  Next, in step 2, lens position servo is started. That is, as shown in FIG. 8, lens position servo is started in (1). In the lens position servo, the lens position signal is detected by the lens position signal detection circuit 105 of FIG. 1, and the tracking actuator 51 is driven and controlled by the lens position servo signal processing unit 112 so that the lens position signal becomes a predetermined value (preferably zero). To do. At this time (when the lens position signal is zero), the optical axis of the condensing optical system (head) 50 and the optical axis of the parallel light beam incident thereon are kept in agreement during the gap servo pull-in operation.

  Next, in step 3, the condensing optical system (head) 50 is brought close to the optical disk. That is, as shown in (2) of FIG. 8, the head drive actuator 52 is driven in a direction in which the condensing optical system (head) 50 approaches the optical disc from a predetermined position. During the approach, the gap servo signal processor 110 monitors the gap error signal.

  If it is detected in step 4 that the gap error signal is equal to or smaller than the predetermined value Th1 ((3) in FIG. 8), the lens position servo is stopped in step 5 ((4) in FIG. 8).

  Next, as shown in FIG. 8, when the gap error signal reaches a predetermined value Th2, a gap servo is started in step 6 to keep the distance between the optical disk and SIL constant within a predetermined range ((6 in FIG. 8). )). When the distance between the optical disk and the SIL is maintained within a predetermined range of the near-field region, the tracking error signal can be detected from the output of the photodetector (PD2) 20 in FIG.

  The photodetector (PD2) 20 is divided into two in the tracking direction, and a tracking error signal is generated by detecting a difference signal of each region by the tracking error detection circuit 104. SW 107 in FIG. 1 is connected to the tracking servo signal processing unit 111 side at the same timing as when tracking servo is started. Thereafter, the tracking actuator 51 is controlled based on the tracking error signal from the tracking error detection circuit 104 to perform tracking servo of the condensing optical system ((6) in FIG. 8).

  Although the lens position servo is stopped when the gap error signal becomes equal to or smaller than the predetermined value, the lens position servo can be stopped simultaneously with the gap servo start or after the gap servo start.

  In the present embodiment, when it is detected that the distance between the condensing optical system and the optical disk is equal to or smaller than a preset value when the gap servo is pulled in, the servo control by the position servo circuit is stopped. Then, the gap servo is started, and the tracking servo of the condensing optical system is started based on the tracking error signal detected from the reflected light beam of the optical disk by the tracking error detection circuit 104.

  As described above, in this embodiment, by performing lens position servo at the time of gap servo pull-in, the gap servo can be pulled in with the lens position held at a predetermined position. For this reason, even if vibration, a posture difference, or the like occurs as described above, it is possible to prevent the SIL and the optical disc from colliding with each other, and it is possible to perform stable gap servo pull-in.

(Second Embodiment)
In the second embodiment, a photodetector (PD3) 27 that is a gap sensor is divided into six regions as shown in FIG. Other configurations and operations are the same as those in the first embodiment. The generation method of the gap error signal is the same as that of the first embodiment, but the lens position signal is generated by the following method.

  That is, the lens position signal detection circuit 105 adds the signals of the regions A and C of the gap sensor PD3 by the adder 43 and adds the signals of the regions D and F by the adder 44 as shown in FIG. Further, the lens position signal is detected by taking the difference between the addition signals by the subtractor 42. The lens position signal is obtained by the following equation.

Lens position signal = (A + C) − (D + F)
Here, as shown in FIG. 9, when the condensing optical system (head) 50 shifts in the tracking direction, the reflected light moves to the left and right according to the shift amount (the reflected light indicated by the solid line from the reflected light indicated by the broken line of PD3). ).

  In this case, among the divided areas of the photodetector (PD3) 27, which is a gap sensor, the sensor outputs of the areas B and E do not change before and after the movement, whereas the areas A, C, and D In addition, the sensor output in the region F varies greatly. Therefore, to detect the tracking direction shift amount of the condensing optical system (head) 50, it is effective to use only the upper and lower four regions (A, C, D, F) of the gap sensor PD3. The gap error signal is obtained by taking a difference between the signals of the regions B and E of the gap sensor PD3 by the subtractor 41. Except for the lens position signal detection method, the second embodiment is the same as the first embodiment.

  As described above, in this embodiment, when lens position servo is performed, a lens position signal is generated using only a region having a high sensitivity to the tracking direction shift in the sensor divided region. Therefore, it is possible to perform control with higher accuracy, and it is possible to perform more stable pull-in of the gap servo.

(Third embodiment)
In the third embodiment, a sensor for detecting the shift amount in the tracking direction of the condensing optical system (head) 50 is mounted separately from the gap sensor PD3. The rest is the same as in the first embodiment. FIG. 10 shows the configuration.

  In FIG. 10, a light emitting element 60 is mounted on a condensing optical system (head) 62 including an SIL and an objective lens. A two-divided sensor 61 is attached to the pickup chassis 63. When the condensing optical system (head) 62 moves in the tracking direction, the light irradiated on the two-divided sensor 61 also moves.

  FIG. 10A shows a state in which light from the light emitting element 60 is irradiated to the center of the two-divided sensor 61 (the centers of the regions A and B). FIG. 10B shows a state in which light from the light emitting element 60 is shifted to the region B side on the two-divided sensor 61.

  Therefore, a lens position signal can be obtained from the difference signal between the outputs of the area A and area B of the two-divided sensor 61. In this embodiment, since the lens position signal is detected by another sensor, the lens position can always be stably detected without depending on the fluctuation of the gap sensor output due to the gap servo pull-in.

  Thus, in this embodiment, the displacement detection circuit (lens position signal detection circuit 105) detects the displacement signal (lens position signal) based on the sensor output that detects the relative position of the condensing optical system in the tracking direction.

  In FIG. 10, the light emitting element 60 is mounted on the condensing optical system (head) 62 and moved integrally. However, even if the split sensor is mounted on the head and the light emitting element 60 is fixed to the pickup chassis 63. good. In addition, although an optical sensor including a light emitting element and a sensor is used, a known position detection unit such as a magnetic sensor may be used.

  When performing lens position servo as described above, by using a dedicated sensor for lens position detection, lens position detection can be performed stably, and more stable gap servo pull-in can be performed.

1 is a block diagram showing a first embodiment of an optical information recording / reproducing apparatus according to the present invention. It is a block diagram which shows the optical pick-up of 1st Embodiment. It is a figure explaining the relationship between the detection signal of gap sensor PD3 of 1st Embodiment, the distance between optical disk-SIL, and a gap error signal. FIG. 3 is a circuit diagram illustrating a gap error generation circuit and a lens position signal generation circuit according to the first embodiment. It is a figure explaining the relationship between the lens position of 1st Embodiment, and a lens position error. It is a flowchart which shows the gap servo pull-in operation | movement of 1st Embodiment. It is a figure explaining the production | generation principle of the lens position signal of 1st Embodiment. It is a timing chart which shows gap servo pull-in operation of a 1st embodiment. It is a circuit diagram which shows the production | generation circuit of the gap error signal and lens position signal of 2nd Embodiment. It is a figure explaining the lens position error generation method of 3rd Embodiment. It is a block diagram which shows the conventional optical pickup for near field recording. It is a figure explaining hemisphere SIL. It is a block diagram which shows the conventional optical information recording / reproducing apparatus using SIL. It is a timing chart which shows the conventional gap servo pull-in operation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimator lens 3 Beam shaping prism 4, 18 Non-polarization beam splitter (NBS)
5, 15, 19, 23, 26 Lens 6 LPC-PD
7, 14 Polarizing beam splitter 8 1/4 wavelength plate 9 Expander lens 10 Objective lens (rear lens)
11 SIL (tip lens)
12, 101 Optical disc (recording medium)
13 1/2 wavelength plate 16, 20, 24, 27 Photo detector 17 RF output 21 Tracking error 28 Gap error 31 Lens position error 50 Condensing optical system (head)
51 Tracking Actuator 52 Head Drive Actuator 100 Optical Pickup 101 Spindle Motor 103 Gap Error Detection Circuit 104 Tracking Error Detection Circuit 105 Lens Position Signal Detection Circuit 106 Head Drive Actuator Driver Circuit 107 SW
108 tracking actuator driver circuit 110 gap servo signal processing unit 111 tracking servo signal processing unit 112 lens position servo signal processing unit

Claims (4)

In an optical information recording / reproducing apparatus for condensing a light beam from a light source on an optical disk and recording or reproducing information,
A condensing optical system that condenses the luminous flux from the light source and includes an objective lens and a solid immersion lens (SIL) disposed between the objective lens and the optical disc;
An actuator for driving the condensing optical system in a direction perpendicular to the surface of the optical disc and in a tracking direction;
A displacement detection circuit for detecting a displacement signal indicating displacement in the tracking direction of the condensing optical system;
A gap error detection circuit for detecting a gap error signal indicating an interval amount between the SIL and the optical disc;
A gap servo circuit that controls the distance between the condensing optical system and the optical disc by servo-controlling the actuator in the vertical direction based on the detected gap error signal;
An optical information recording / reproducing apparatus comprising: a position servo circuit that servo-controls the actuator in the tracking direction based on the displacement signal when the gap servo is retracted. The said displacement detection circuit detects the said displacement signal based on the detection signal of the photodetector which detects the return light reflected from the end surface facing the said optical disk of said SIL. Optical information recording / reproducing apparatus. The optical information recording / reproducing apparatus according to claim 1, wherein the displacement detection circuit detects the displacement signal based on a sensor output that detects a relative position of the condensing optical system in a tracking direction. When it is detected that the gap between the condensing optical system and the optical disk is equal to or smaller than a preset value when the gap servo is pulled in, the gap servo is started after the servo control by the position servo circuit is stopped. The tracking servo of the condensing optical system is started based on a tracking error signal detected from a reflected light beam of the optical disk by a tracking error detection circuit. The optical information recording / reproducing apparatus described.