JP2008310921A - Optical information recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform stable gap servo by preventing a collision with an optical disk during pulling-in of a gap servo. <P>SOLUTION: The optical information recording and reproducing device is provided with: a head part including an objective lens 10 and an SIL 11; an actuator for driving the head part in a focusing direction with respect to an optical disk 12; a circuit for detecting the focus error signal of the head part; a circuit for detecting a gap error signal indicating a gap amount between the head part and the optical disk 12; and a circuit for controlling the gap amount between the head part and the optical disk 12 by performing servo-control of the actuator on the basis of the detected gap error signal. During servo-control pulling-in of the head part is made close to the optical disk 12 while controlling the position of the actuator on the basis of the focus error signal, and then pull-in of servo control is carried out. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical information recording / reproducing apparatus, and more particularly, to an optical information recording / reproducing apparatus that performs recording / reproduction utilizing the near-field effect.

  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, the SIL disposed between the optical disk and the objective lens is brought close to a fraction of the recording wavelength (for example, 1/2) or less on the recording surface, and the NA is set to 1 or more even in the air. An attempt has been made.

  For example, they are described in detail in Non-Patent Documents 1 and 2.

  A conventional technique will be described with reference to FIGS.

  FIG. 8 is a block diagram showing a configuration of an optical pickup for near-field recording described in Non-Patent Document 1.

  A light beam emitted from the semiconductor laser 1 having a wavelength of 405 nm as a light source 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.

  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 into circularly polarized light.

  Note that a photodetector (LPC-PD) 6 for receiving the light beam reflected by the non-polarizing beam splitter (NBS) 4 and controlling the emission power of the semiconductor laser 1 is provided.

  The light beam transmitted through the quarter-wave plate enters the expander lens 9.

  The expander lens 9 is a lens for correcting spherical aberration generated in the head section described later, and is configured so 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 objective lens 10 of the head unit.

  The head portion includes an objective lens 10 and a SIL (Solid Immersion Lens) 11. The objective lens 10 and the SIL 11 are mounted on a biaxial actuator (not shown) that integrally drives the two lenses in the focus direction and the tracking direction.

  FIG. 9 is a side view showing a state where the light beam focused by the objective lens 10 is condensed on the bottom surface of the hemispherical SIL 11.

  Since the light beam is perpendicularly incident on the spherical surface of the SIL 11 and is condensed on the bottom surface through the same optical path as when there is no hemisphere, it is equivalent to the wavelength being shortened by the refractive index of the SIL 11 and the effect of reducing the light spot diameter. There is.

  That is, if the refractive index of the SIL is N and the numerical aperture of the objective lens 10 is NA, a light spot equivalent to N × NA can be obtained on the recording surface of the optical disk 12.

  For example, when an SIL of N = 2 SIL is combined with the objective lens 10 with NA = 0.7, NAeff = 1.4 is reached with the effective NA as NAeff.

  Since the thickness error of SIL11 can be tolerated about 10 μm, mass production is easy.

  Only when the distance between the bottom surface of the SIL 11 and the optical disk 12 is less than a fraction of the wavelength of 405 nm of the light source, it acts on the recording surface as evanescent light from the bottom surface of the SIL 11, and recording / reproduction with a NAeff light spot diameter is possible. The case where the light source has a wavelength of 405 nm or less is a short distance of, for example, 100 nm or less.

  In order to maintain this distance, a gap servo described later is used.

  Returning to FIG. 8, the return path optical system will be described.

  The light beam reflected by 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.

  The light beam that has passed through the expander lens 9 and the quarter-wave plate 8 and is linearly polarized in the direction orthogonal to the forward path is reflected by the PBS 7.

  Of the light beam whose polarization plane has been rotated by 45 ° by the half-wave plate (HWP) 13, the S-polarized light component is reflected by the polarization beam splitter 14 and passes through the lens 15 onto the photodetector 1 (PD 1) 16. Focused. Then, the RF output 17 that is information on the optical disk 12 is reproduced.

  Of the light beam whose polarization plane has been rotated by 45 ° by the half-wave plate (HWP) 13, the P-polarized light component passes through the polarizing beam splitter 14 and is reflected by the non-polarizing beam splitter 18. Then, the light is condensed on the two-divided photodetector 2 (PD2) 20 via the lens 19, and a tracking error 21 is output accordingly.

  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 opposite to the incident light, similarly to the light reflected from the optical disk 12 described above.

  For a light flux of NAeff ≧ 1 that causes total reflection, a phase difference δ shown by the following equation is generated between the P-polarized component and the S-polarized component, and is shifted from circularly polarized light to become elliptically polarized light.

  Therefore, when the light passes through the quarter wavelength plate 8, it includes a polarization component in the same direction as the forward path.

  This polarized component passes through the PBS 7 and is reflected by the NBS 4, and is collected on the photodetector 3 (PD 3) 27 via the lens 26.

  The light quantity of this light beam can be used as the gap error signal 28 because it monotonously decreases as the distance between the bottom surface of the SIL 11 and the optical disk 12 approaches in the near-field region.

  If the target threshold value is determined in advance, the gap servo is performed to keep the distance between the bottom surface of the SIL 11 and the optical disk 12 at a desired distance of 100 nm or less. This gap servo is detailed in Non-Patent Document 1.

  Further, since this light beam is not modulated by the recording information on the optical disc 12, a stable gap error signal can be obtained regardless of the presence or absence of the recording information.

  The overshoot during the gap servo pull-in needs to be 100 nm or less. If the overshoot exceeds 100 nm, the SIL and the optical disk collide, and the SIL 11 or the optical disk 12 is damaged.

  In order to suppress overshoot, there is a method called servo pull-in by slowing the approach speed of the SIL 11 to the optical disk 12 as much as possible during servo pull-in.

  However, if the approach speed is slow, it takes time to pull in the servo, which is not practical.

  In consideration of this point, Patent Document 1 proposes a configuration as shown in FIG.

  In FIG. 10, when pulling in the gap servo, the approach speed generation circuit 108 first outputs a drive signal for bringing the objective lens and SIL closer to the optical disc 101 to the actuator driver circuit 106. The objective lens 10 and the SIL 11 are in the pickup 102 in FIG.

  The gap error signal generated by the gap error generation circuit 104 is input to the comparator 107 in the process in which the optical disc 101 and the SIL approach each other.

  The comparator 107 outputs a low level to the switch 109 when the magnitude of the input gap error signal is equal to or greater than the predetermined value Vth, and when the magnitude is equal to or smaller than the predetermined value Vth.

  When it is detected that the output of the comparator 107 is at a high level, the distance between the optical disk and the SIL is small, and the near field state is entered, the switch 109 is turned on and the gap servo control is started.

  The output of the approach speed generation circuit 108 until the transition from the far field state to the near field state has the waveform shown in FIG.

  At the time t1 when the gap error is equal to or less than the predetermined value Vth, the output of the approach speed generation circuit 108 is set in advance to be a constant voltage.

Thus, if the approach voltage of the actuator is set to a constant voltage at the start of the gap servo pull-in, the initial speed of the SIL at the start of the servo becomes almost zero, and the gap servo can be pulled in stably.
JP 2005-209246 A “Near Field Recording ON First-Surface Write-ONce Media with NAS” .Issue of the Journal of Japan Applied Physics, Vol. 44 (2005) P. 3564-3567 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 coer

  However, the above prior art has the following difficulties.

  An approach voltage is set at which the SIL speed becomes almost zero at the start of the gap servo. When the optical disk is pulled in while being rotated by the spindle, it is difficult to make the SIL speed almost zero at the start of pulling in, considering the influence of surface fluctuation of the optical disk and the spindle.

  For example, in the case of an optical disk with a large amount of surface deflection, the near field state may be reached at a time before t1 in FIG. 11, that is, before the approach voltage becomes a constant value.

  In this case, the fact that the output of the approach speed generation circuit is not a constant voltage means that the approach speed is not substantially zero, and the gap servo is started in a state where the relative speed between the SIL having the ramp-like approach voltage and the optical disk is high.

  FIG. 12 shows how the servo is pulled in this case.

  FIG. 10 is an explanatory diagram when the gap servo control is started when the gap error signal becomes equal to or lower than a predetermined level at the time when the approach voltage is not a constant voltage but is in a ramp shape due to the influence of the surface shake of the optical disc or the spindle.

  In FIG. 12, in the upper graph, the horizontal axis represents time, and the vertical axis represents the gap amount. In the lower graph, the horizontal axis represents time, and the vertical axis represents the signal level of the actuator drive signal and the gap error signal.

  Also, the gap amount before drawing in a sine wave shape indicates that the gap amount is changed due to surface wobbling of the optical disc even if the SIL is moved at a constant speed.

  The reason why the actuator drive signal is sinusoidal after the gap servo is pulled in is that the gap servo follows the surface vibration of the optical disk.

  According to the pull-in method according to the prior art, the slope of the ramp-shaped actuator drive signal is constant until the gap error signal falls below a predetermined level depending on the influence of the surface runout.

  While continuing to approach at a constant speed, when the gap error signal falls below a predetermined level, the approach by the ramp-like function is stopped and the gap servo control is started. With this method, the gap amount immediately after pulling is less than zero.

  This indicates that the SIL and the optical disc collide. In order to avoid a collision with this processing method, it is necessary to make the approach speed sufficiently low.

  Further, the gap amount at which the gap error is equal to or less than the predetermined value Vth is as small as about 100 nm. For this reason, when an overshoot of 100 nm or more occurs, the optical disk and the SIL collide.

  SUMMARY OF THE INVENTION An object of the present invention is to prevent a collision with an optical disk when a gap servo is pulled in and to perform a stable gap servo.

  The present invention provides an optical information recording / reproducing apparatus that collects a light beam from a light source on an optical disc and collects the light beam emitted from the light source as a means for solving the above-described problems. A head portion having a lens, a SIL (Solid Immersion Lens) disposed between the objective lens and the optical disc, an actuator for driving the head portion in a focus direction with respect to the optical disc, and the head A circuit for detecting a focus error signal of a head part, a circuit for detecting a gap error signal indicating a gap amount between the head part and the optical disc, and servo-controlling the actuator based on the detected gap error signal A circuit for controlling a gap amount between the head unit and the optical disc, At the time of pulling in the servo control, pulling in the servo control is performed after the head portion is brought close to the optical disc while controlling the position of the actuator based on the focus error signal.

  According to the present invention, it is possible to control the distance between the optical disk and the SIL while performing the control by the focus error signal in a state where the SIL and the optical disk are sufficiently separated from each other. Therefore, the pull-in of control by the gap error signal can be switched after approaching slowly, and the gap servo pull-in can be performed stably and in a short time.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

[First Embodiment]
FIG. 1 is a block diagram showing the configuration of the head unit control system of the optical information recording / reproducing apparatus as the first embodiment of the present invention. In FIG. 1, blocks that perform the same functions as in the prior art are numbered the same.

  The operation of this embodiment will be described with reference to FIGS. FIG. 2 is a block diagram showing the configuration of the optical information recording / reproducing apparatus as the first embodiment of the present invention.

  The difference between the prior art and the present embodiment is a portion surrounded by a dotted line in FIG. 2 and will be described below.

  The light beam that has passed through the non-polarizing beam splitter 18 passes through the aperture 22, is shielded from the outer periphery of the light beam, and is condensed on the photodetector 4 (PD 4) 24 via the sensor lens 23.

  The output of the PD 4 is input to the focus error signal generation circuit 114 in FIG. 1, and a focus error signal is generated.

  A portion surrounded by a dotted line will be described in detail with reference to FIGS. 3 and 4. In FIG. 3, the reflected light beam from the optical disk is NA = 1.4 (NA> 1) at the periphery of the pupil diameter.

  The aperture 22 transmits a light beam with NA <1 at the center, for example, NA = 0.85, and blocks a light beam with NA> 1 at the outer periphery.

  The reason why the transmitted light beam is made about 10% smaller than NA = 1 is that when the objective lens 10 and the SIL 11 are moved in the radial direction of the optical disk due to the eccentricity of the optical disk, the light beam with NA> 1 in the outer peripheral portion is not mixed. It is.

  In order to generate the focus error signal, for example, a toric lens may be used as the sensor lens 23. The PD 4 may be generated by a known astigmatism method, for example, if the PD 4 is a quadrant sensor.

  A light beam with NA <1 or less contains a large amount of reflected light from the recording layer of the optical disk 12, and a focus error signal can be generated with high accuracy.

  Next, the focus control pull-in operation according to the present embodiment will be described in detail with reference to FIGS.

  First, when starting focus pull-in, the controller 117 drives the expander lens 9 in the pickup 102 by the expander lens drive circuit 118. At this time, the focus error signal and the gap error signal generated from the light flux of NA <1 are set to a state as shown in FIG.

  The focus error signal is focused at a position further about 1 μm away from the optical disk-SIL distance (100 nm or less in FIG. 5A) where the gap error signal level starts to decrease in the near field state.

  The focal point of the focus error signal is determined by the position of the expander lens 9 in FIG.

  Focus pull-in is performed in the state of FIG.

  First, the approach speed generation circuit 108 outputs a ramp-like drive signal and starts driving so that the objective lens 10 and the SIL 11 approach the optical disc 101.

  While continuing to approach, the comparator 114 receives the focus error signal generated from the light beam with NA <1.

  FIG. 6 is a graph showing the relationship between the output of the comparator 114 and the focus error signal.

In this embodiment, the shake in the ± around the focus error signal is 0 level, + in a direction approaching the optical disc to focus, in the direction away - so deflected, the predetermined value FE _th, the degree slightly smaller than the zero level Is set to the level of

Comparator 114 When the signal level of the input focus error signal becomes smaller than a predetermined value _{FE th,} the output is switched from Low to High.

  When the output of the comparator 112 becomes High and becomes Low again, the changed portion is near the focal point. The output of the approach speed generation circuit 108 is fixed at the current level. At the same time, the switch 116 is turned on to the phase compensation circuit 115 side. Then, the focus servo control process is started.

  As described above, the focus error signal generated from the luminous flux of NA <1 is used in a state where the position where the distance between the optical disk and the SIL is about 1 μm is the focal point of the focus error signal when the focus servo control is pulled.

  By doing so, the head portion does not collide with the optical disc when the focus control is pulled.

  When the controller 117 determines that the focus control has been successfully pulled in, the focus pull-in is finished.

  In this state, the distance between the SIL and the optical disc is controlled to be approximately 1 μm, and the optical disc is operating following the surface deflection of the optical disc.

  The distance between the SIL and the optical disk can be stably controlled by operating the expander lens 9 while the position control by the focus error signal is continued.

  Subsequently, the operation shifts from the position control by the focus error signal to the position control by the gap error.

  The controller 117 drives the expander lens 9 in the pickup 102 to the expander lens driving circuit 118 so that the focal point is in the state shown in FIG. 5B from the state shown in FIG. Let

  This amount of movement is a value determined at the time of design.

  After the drive of the expander lens 9 is completed, the controller 117 switches the switch 116 to the phase compensation circuit 105 side in order to change the condensing control to the gap servo.

  As described above, according to the present embodiment, the distance between the SIL and the optical disk can be controlled by moving the expander lens in a state where servo control is performed by a focus error generated from a light beam with NA <1. It was. Therefore, it is possible to stably control light collection on the recording layer of the optical disc.

[Second Embodiment]
FIG. 7 is a block diagram showing the configuration of the head unit control system of the optical information recording / reproducing apparatus as the second embodiment of the present invention.

  The difference from the first embodiment is that a comparator 107 is connected to the gap error generation circuit 104 and its output is connected to the controller 117.

  The process is the same as that in the first embodiment until the controller 117 determines that the focus control has been normally pulled in and the focus control pull-in is completed.

  The process until switching to the subsequent gap error control will be described in detail with reference to FIG.

  When the focus pull-in is completed, the distance between the SIL 11 and the optical disk 12 is controlled to be approximately 1 μm, and the optical disk is operating following the surface vibration of the optical disk.

  The distance between the SIL 11 and the optical disc 12 can be stably controlled by operating the expander lens 9 while the position control by the focus error signal is continued.

  Subsequently, the controller 117 starts driving the expander lens 9 to the expander lens driving circuit 118 so that the focal point is in the state of FIG. 5A from the state of FIG. 5A, that is, the focal point is in the near field region. Let

  The controller 117 monitors the output of the comparator 107 while the expander lens 9 is moving.

  The comparator 107 is connected to the gap error generation circuit 104 and compares the gap error signal with a predetermined threshold value.

  When the gap error signal falls below a predetermined threshold, the output of the comparator 107 changes from Low to High.

  At that timing, the controller 117 causes the expander lens drive circuit 118 to stop driving the expander lens 9 in the pickup 102.

  After the drive of the expander lens 9 is completed, the controller 117 switches the switch 116 to the phase compensation circuit 105 side in order to change the condensing control to the gap servo.

  In this case, the expander lens 9 can be operated with higher accuracy, and the possibility of collision between the SIL and the optical disk can be reduced.

  As described above, the distance between the SIL and the optical disc can be freely controlled in a state where the servo control is performed by the focus error generated from the light flux of NA <1, so that the optical disc can be stably collected on the recording layer. Light control became possible.

  The present invention is applicable to an optical information recording / reproducing apparatus using the near-field effect.

It is a block diagram which shows the structure of the head part control system of the optical information recording / reproducing apparatus as the 1st Embodiment of this invention. 1 is a block diagram showing a configuration of an optical information recording / reproducing apparatus as a first embodiment of the present invention. FIG. 3 is a side view showing an optical system for detecting a focus error signal in the first embodiment of the present invention. It is a top view which shows the opening 22 in the 1st Embodiment of this invention. It is a graph which shows the relationship between the gap error signal and focus error signal in the 1st Embodiment of this invention. It is a graph which shows the relationship between the output of the comparator 114, and a focus error signal. It is a block diagram which shows the structure of the head part control system of the optical information recording / reproducing apparatus as the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the conventional optical information recording / reproducing apparatus. It is a side view which shows the vicinity of SIL11 of FIG. It is a block diagram which shows the structure of the head part control system of the conventional optical information recording / reproducing apparatus. It is a timing chart at the time of the gap servo control pull-in in the conventional optical information recording / reproducing apparatus. It is a figure for demonstrating the conventional subject.

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 11 SIL
DESCRIPTION OF SYMBOLS 12, 101 Optical disk 13 1/2 wavelength plate 16, 20, 24, 27 Photo detector 17 RF output 21 Tracking error 22 Aperture 102 Pickup 103 Spindle motor 104 Gap error generation circuit 105 Phase compensation circuit 106 Actuator driver circuit 107 Comparator 108 Approach Speed generation circuit 109 Switch 110 Adder 111 Sum signal generation circuit 112 Comparator 113 Focus error generation circuit 114 Comparator 115 Phase compensation circuit 116 Switch 117 Controller 118 Expander lens drive circuit

Claims (3)

In an optical information recording / reproducing apparatus for recording / reproducing information by condensing a light beam from a light source onto an optical disc,
A head unit including an objective lens that collects a light beam emitted from the light source, and a SIL (Solid Immersion Lens) disposed between the objective lens and the optical disc;
An actuator for driving the head unit in a focusing direction with respect to the optical disc;
A circuit for detecting a focus error signal of the head unit;
A circuit for detecting a gap error signal indicating a gap amount between the head unit and the optical disc;
A circuit for controlling a gap amount between the head unit and the optical disc by servo-controlling the actuator based on the detected gap error signal, and
An optical information recording / reproducing apparatus that performs pull-in in the servo control after bringing the head portion close to the optical disc while controlling the position of the actuator based on the focus error signal at the time of pull-in of the servo control. . An expander lens is disposed on the side of the head unit on which the light beam is incident,
2. The optical information recording / reproducing apparatus according to claim 1, wherein a focal point of the focus error signal is determined by a position of the expander lens. While controlling the position of the actuator based on the focus error signal, by changing the position of the expander lens, the focus is moved closer to the optical disc,
3. The optical information recording / reproducing according to claim 2, wherein when the gap error signal becomes a predetermined threshold value or less, the position control based on the focus error signal is switched to the position control based on the gap error signal. apparatus.