JP2012226813A - Objective lens and optical disc device having the same mounted thereon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in a multi-layer disc having a plurality of recording layers and a guide layer having a grooved structure layered therein that a spherical aberration occurs when the state in which a light beam that condenses on the guide layer converges and disperses changes in relation to an objective lens, resulting in a risk of deterioration in the condensation performance of the light beam that condenses on the guide layer.SOLUTION: The working distance of the objective lens is made substantially equal relative to each recording layer. As means for achieving it, the I/O characteristics of the objective lens are optimized, for example.

Description

  The present invention relates to an optical disk apparatus that reproduces information from an optical disk using a laser or records information on an optical disk, and an objective lens mounted on the optical disk apparatus.

  In recent years, in order to increase the recording capacity in the Blu-ray Disc (TM) standard optical disc, an optical disc having three or four recording layers has been developed and standardized. In the future, it is expected that an optical disc having a larger number of recording layers will be developed for the purpose of further increasing the capacity. For example, in Patent Document 1 and Non-Patent Document 1, a layer having a physical groove structure (hereinafter referred to as a guide layer) for performing tracking servo control is provided, and a land / groove structure is used for a recording / reproducing layer (recording layer). An optical disc (grooveless disc) having no recording medium is shown, and it is said that manufacture is easy even when a large number of recording layers are stacked.

JP 2010-40093 A

M. Ogasawara et.al., "16 Layers Write Once Disc with a Separated Guide Layer", ISOM2010, Th-L-07

  As one of the problems when recording and reproducing the grooveless disk as described above, the first light beam is condensed on the recording layer by the objective lens, and at the same time, the second light beam is guided using the same objective lens. It is necessary to focus on the layer.

  Here, at the time of reproduction and recording, if the working distance defined as the distance between the objective lens and the disk surface is different for each recording layer, the position of the guide layer is fixed, so that the light beam focused on the guide layer converges. The degree of divergence is set to be different for each recording layer with respect to the objective lens.

  When the convergence / divergence of the light beam incident on the objective lens changes, spherical aberration is generated accordingly, so that the condensing performance of the light beam condensed on the guide layer is deteriorated or the spherical aberration is corrected. Problems such as the need for new elements arise. Adding a new spherical aberration correction element to the light beam focused on the guide layer is disadvantageous from the viewpoint of the price, size, and complexity of the optical disc apparatus.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical disc apparatus that ensures rationalization of the apparatus and condensing performance of a light beam that is condensed on a guide layer.

  The above problems are solved by the invention described in the claims.

  According to the present invention, the rationalization of the device and the light condensing performance of the light beam condensed on the guide layer are improved.

Block configuration diagram showing one embodiment of an optical disk device Schematic diagram showing the structure of an optical disc Schematic diagram showing the processing flow of the optical disc apparatus Schematic showing the working distance of the objective lens Schematic diagram showing the optical system of an optical disk device Schematic showing the focal point of the light beam incident on the objective lens Schematic showing the I / O characteristics of the objective lens

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment of an optical disc apparatus according to the present invention. The optical disc device 101 records or reproduces information by irradiating an optical disc 102 mounted on the device with laser light, and communicates with a host 103 such as a PC (Personal Computer) through an interface such as SATA (Serial Advanced Technology Attachment). Do.

  The structure of the optical disk 102 is illustrated in FIG. The optical disc 102 has, for example, a guide layer having a track (guide groove) structure and N recording layers (N ≧ 1, N is a natural number) having no track structure. The optical disc apparatus 101 can generate laser spots on the recording layer and the guide layer by the objective lens 311.

  The optical disc apparatus 101 includes a controller 201, a signal processing unit 202, an optical pickup 203, a slider motor 204 that moves the optical pickup 203 in the radial direction of the optical disc 102, slider driving means 205 that drives the slider motor 204, Aberration correction driving means 206 for driving the spherical aberration correction element provided in the pickup 203, a spindle motor 207 for rotating the optical disk 102, and a rotation signal generation for generating a signal synchronized with the rotation of the spindle motor 207 Means 208, spindle control means 209 for generating a rotation signal for rotating the spindle motor 207, spindle drive means 210 for driving the spindle motor 207 in accordance with the rotation signal generated by the spindle control means 209, The amount of positional deviation of the laser spot focused on the recording layer and the recording layer, and the optical disc 102 A focus error signal generating unit 211 that generates a focus error signal indicating a positional deviation amount of a laser spot that is focused on the id layer and the guide layer, and a focus control unit 212 that generates a focus drive signal in accordance with the focus error signal; In addition, the actuator 312 provided in the optical pickup 203 according to the focus drive signal, the focus drive means 213 for driving the movable lens 321, and the tracking indicating the amount of positional deviation between the track on the guide layer of the optical disc 102 and the laser spot. A tracking error signal generation unit 214 that generates an error signal, a tracking control unit 215 that generates a tracking drive signal according to the tracking error signal, and a tracking drive unit 216 that drives the actuator 312 according to the tracking drive signal are provided. Yes.

  The optical pickup 203 includes two optical systems having different wavelengths such as 405 nm and 650 nm. First, the operation during reproduction of the 405 nm optical system will be described. The laser driver 301 is controlled by the controller 201 and outputs a current for driving the laser diode 302. This drive current is applied with a high frequency superimposition of several hundred MHz, for example, to suppress laser noise. The laser diode 302 emits a laser beam having a wavelength of 405 nm with a waveform corresponding to the drive current. The emitted laser light becomes parallel light by the collimator lens 303, a part of the light is reflected by the beam splitter 304, and is condensed on the power monitor 306 by the condenser lens 305. The power monitor 306 feeds back a current or voltage corresponding to the intensity of the laser light to the controller 201. As a result, the intensity of the laser beam condensed on the recording layer of the optical disc 102 is maintained at a desired value such as 2 mW. On the other hand, the laser light transmitted through the beam splitter 304 is reflected by the polarization beam splitter 307 and transmitted through the dichroic mirror 308. The dichroic mirror 308 is an optical element that reflects light of a specific wavelength and transmits light of other wavelengths. Here, it is assumed that light having a wavelength of 405 nm is transmitted and light having a wavelength of 650 nm is reflected. The laser light transmitted through the dichroic mirror 308 is controlled to converge and diverge by the movable lens 309 driven by the aberration correction driving means 206, becomes circularly polarized light by the quarter wavelength plate 310, and the optical disk 102 by the objective lens 311. Condensed on the recording layer. The position of the objective lens 311 is controlled by the actuator 312. The intensity of the laser light reflected by the optical disk 102 is modulated according to the information recorded on the optical disk 102. The light is linearly polarized by the quarter-wave plate 310, passes through the dichroic mirror 308 and the spherical aberration correction element 309, and passes through the polarization beam splitter 307. The transmitted laser light is condensed on the detector 314 by the condenser lens 313. The detector 314 detects the intensity of the laser beam and outputs a signal corresponding to the intensity to the signal processing unit 202. The signal processing unit 202 performs processing such as amplification, equalization, and decoding on the reproduction signal output from the detector 314, and outputs the decoded data to the controller 201. The controller 201 outputs data to the host 103.

  The focus error signal generation unit 211 generates a focus error signal for the recording layer from the signal output from the detector 314. The focus control unit 212 outputs a focus drive signal corresponding to the focus error signal to the focus drive unit 213 in response to a command signal from the controller 201. The focus drive unit 213 drives the actuator 312 in a direction perpendicular to the disk surface in accordance with the focus drive signal. As described above, the focus control unit 212 and the focus drive unit 213 operate, so that the focus control is performed so that the laser spot irradiated on the recording layer of the optical disc 102 is always focused on the recording layer.

  When recording, recording data is input from the host 103 to the controller 201. The controller 201 outputs a recording waveform corresponding to the input data to the laser driver 301. The laser driver 301 outputs a drive current corresponding to the recording waveform to the laser diode 302, and the laser diode 302 emits laser light with a waveform corresponding to the recording, whereby recording is performed on the recording layer of the optical disc 102.

  Next, a 650 nm optical system will be described. In this optical system, there is no difference in operation between recording and reproduction. Similar to the 405 nm optical system, the laser driver 301 drives the laser diode 315, and the laser diode 315 emits laser light having a wavelength of 650 nm. A part of the laser light passes through a collimator lens 316, a beam splitter 317, and a condenser lens 318, and the power is monitored by a power monitor 319. By feeding back the monitored power to the controller 201, the intensity of the laser light focused on the guide layer of the optical disc 102 is maintained at a desired power, such as 3 mW. The laser light that has passed through the beam splitter 317 passes through the polarization beam splitter 320, and the movable lens 321 controls the convergence and divergence. The laser light that has passed through the movable lens 321 is reflected by the dichroic mirror 308, passes through the quarter-wave plate 310, and is condensed on the guide layer of the optical disk 102 by the objective lens 311. The laser beam reflected by the optical disk 102 is reflected by the polarization beam splitter 320 and condensed on the detector 323 by the condenser lens 322.

  The tracking error signal generation unit 214 generates a tracking error signal for the guide layer of the optical disc 102 from the signal output from the detector 323. The tracking control means 215 generates a tracking drive signal corresponding to the tracking error signal in response to a command signal from the controller 201. The tracking drive means 216 drives the actuator 312 in the radial direction of the disk according to the tracking drive signal. As described above, the tracking control unit 215 and the tracking driving unit 216 operate, so that the tracking control is performed so that the laser spot irradiated on the guide layer of the optical disc 102 always follows the track on the guide layer.

  Further, the focus error signal generation unit 211 generates a focus error signal that is an error signal in the focus direction with respect to the guide layer of the optical disc 102 from the signal output from the detector 323. The focus control unit 212 generates a focus drive signal corresponding to the focus error signal in response to a command signal from the controller 201. The focus drive unit 213 drives the movable lens 321 in accordance with the focus drive signal. By driving the movable lens 321, control is performed so that the laser spot irradiated on the guide layer of the optical disc 102 is always focused on the guide layer.

  The slider driving unit 205, the aberration correction driving unit 206, and the spindle control unit 209 are also operated by a command signal from the controller 201.

  Here, the same laser driver 301 is used to drive the laser diode 302 and the laser diode 315, but each laser diode may be provided with a unique laser driver. The focus error signal generation unit 211, the focus control unit 212, and the focus drive unit 213 are also shared by the 405 nm optical system and the 650 nm optical system, but may be configured separately.

  FIG. 3 shows a processing flow of the optical disc apparatus 101 when the optical disc 102 is inserted into the optical disc apparatus 101.

  When the optical disk 102 is inserted into the optical disk apparatus 101 in S401, the optical disk apparatus 101 confirms the presence / absence of a disk and the disk type in S402. At this time, for example, the optical disc apparatus 101 can irradiate the optical disc 102 with laser light and perform recognition by reflected light.

  Next, in S403, adjustment processing for making various parameters in the optical disc apparatus 101 suitable for the inserted optical disc 102 is performed. Examples of the various parameters include adjusting the amplification factor of the amplifier included in the focus control unit 212 and the tracking control unit 215 in accordance with the reflectance of the optical disc 102.

  After performing various adjustments, the management information of the optical disc 102 is read in S404.

  When the processing proceeds to S405, the recording or reproduction is possible, and recording or reproduction can be performed in accordance with a command from the host 103.

  The timing of the adjustment process S403 is not limited to this, and a part of the adjustment process may be performed after the management information read S404.

  Next, points that characterize the present embodiment will be described. One of the features of this embodiment is that, as shown in FIG. 4, the working distance WD1 of the objective lens when recording or reproducing the first recording layer and a recording layer different from the first recording layer (for convenience, the first recording layer The working distance WD2 of the objective lens when recording or reproducing (2 recording layer) is substantially equal. This feature makes it possible to rationalize the optical disk apparatus. Hereinafter, the details will be described in order.

  In the conventional BD multilayer, which is an optical disc having a groove structure in the recording layer, the recording layer and the guide layer are not separated. Therefore, in the case of such a conventional optical disc, the problem to be solved by the present invention does not occur.

  An optical disc apparatus corresponding to an optical disc having a plurality of recording layers needs to correct a change in spherical aberration that occurs in accordance with a change in substrate thickness. In general, for the light beam focused on the recording layer, the convergence / divergence of the light beam incident on the objective lens is adjusted, and the spherical aberration is canceled by changing the object side distance of the objective lens. Spherical aberration is intentionally generated and corrected. Therefore, in general, means for changing the object side distance of the objective lens by moving the lens in the optical axis direction is provided in the optical system, which is different from the objective lens. In this embodiment, reference numeral 309 in FIG. 1 corresponds to the lens. In the optical disc apparatus, since it is necessary to focus a light beam different from the light beam focused on the recording layer on the guide layer of the optical disc 102, the focus of the light beam focused on the guide layer is adjusted. Provide a lens. In this embodiment, reference numeral 321 in FIG. 1 corresponds to the lens. Specifically, the convergence / divergence of the light beam incident on the objective lens is changed by the lens denoted by reference numeral 321, and the focus of the light beam focused on the guide layer is adjusted. Since the lens 309 and the lens 321 move in the optical axis direction, in this embodiment, for convenience, they are called movable lenses.

  FIG. 5 is a diagram focusing on optical components in the optical disc apparatus shown in FIG. In FIG. 5, reference numerals 309a and 321a indicate the position of the movable lens when recording or reproducing is performed on a predetermined recording layer (first recording layer). Reference numerals 309 and 321 indicate the positions of the predetermined recording layers. On the other hand, the position of the movable lens when recording or reproducing on another layer (second recording layer) having a different substrate thickness is shown. Here, when the movable lens moves continuously without stopping during recording and reproduction, it represents an average position. In FIG. 5, the movable direction of the movable lens 309 and the movable lens 321 is shown in one direction, but the present embodiment is not limited to this, and the first recording layer and the second recording layer are not limited to this. The movable direction changes depending on the positional relationship.

  In this embodiment, as described above, the working distance WD1 of the objective lens when recording or reproducing the first recording layer is substantially equal to the working distance WD2 of the objective lens when recording or reproducing the second recording layer. It is characterized by. Therefore, focusing on the light beam focused on the guide layer, the convergence / divergence of the light beam incident on the objective lens during recording or reproduction of the first recording layer and recording or reproduction of the second recording layer is as follows. It will be almost unchanged.

  The fact that the convergence / divergence of the light beam incident on the objective lens is not substantially changed means that the driving amount of the movable lens 321 is very small. If the working distances are completely equal, ideally Δd2 = 0. On the other hand, regarding the light beam irradiated to the recording layer, since the substrate thickness from the disk surface to the condensing point changes, in order to correct the spherical aberration caused by the difference in substrate thickness, the convergence / divergence of the light beam with respect to the objective lens is adjusted. It becomes necessary to change, and it is necessary to move the movable lens (309). In other words, more specifically, in this embodiment, the position of the movable lens when recording or reproducing on the first recording layer and the movable lens when recording or reproducing on the second recording layer are described. If the difference between the positions of Δd1 and Δd2 as shown in FIG.

Should be satisfied. Even when the working distances WD1 and WD2 are not completely equal, the difference between the working distances WD1 and WD2 is reduced by satisfying (Expression 1) that expresses (Expression 4) and (Expression 4) separately. This makes it possible to secure the light condensing performance of the light beam condensed on the guide layer.

  In the above, the first recording layer may be any of the recording layers of the optical disc 102. In other words, in this embodiment, when recording or reproducing a recording layer having a different substrate thickness, if the movable lens position when recording or reproducing another layer before that is used as a reference, the movable lens 321 is used. One feature is that the driving amount of the movable lens 309 is larger than that of the movable lens 309. As described above, in FIG. 5, the movable direction of the movable lens 309 and the movable lens 321 is shown in one direction, but the present invention is not limited to this, and the first recording layer and the second recording layer are not limited thereto. The movable direction may change depending on the positional relationship of the recording layer. One essence of this embodiment is that the positional differences Δd1 and Δd2 satisfy (Equation 4).

  In this embodiment, since the drive amount of the movable lens 321 can be reduced, the drive range of the drive mechanism for driving the movable lens can be designed to be small, which is effective in reducing the size of the apparatus. Further, since the drive amount is small, it is effective for power saving of the optical disk apparatus.

  Furthermore, this embodiment is also effective from the viewpoint of the amount of spherical aberration of the light beam condensed on the guide layer. In general, when the convergence / divergence of the light beam incident on the objective lens changes, spherical aberration occurs accordingly. However, in this embodiment, when the first and second recording layers are recorded or reproduced, the degree of convergence / divergence of the light beam condensed on the guide layer with respect to the objective lens is almost the same, so there is almost no change in spherical aberration. It is. When the degree of convergence / divergence with respect to the objective lens changes greatly, spherical aberration occurs, which may degrade the light beam condensing characteristics. From this point of view, making the working distances in the first recording layer and the second recording layer substantially the same as in the present embodiment has a great effect in terms of spherical aberration. When recording or reproducing any recording layer, it is necessary to focus the light beam on the guide layer at a predetermined position. Therefore, the above effect can be expected by applying this embodiment.

  In order to make the working distance substantially equal to the first recording layer and the second recording layer, for example, an objective lens having the following characteristics can be used.

  FIG. 6 shows a state in which a light beam is incident on the objective lens 311 at a magnification M. When the value of the magnification M changes, the image point position changes according to the lens formula shown in (Equation 5).

Here, a is the image side distance, b is the object side distance, and f is the focal length of the objective lens. The difference a−f between the image point positions when the magnification M is infinite, so-called parallel light incident state, and the magnification M = b / a is expressed as (Equation 6) using (Equation 5). Can do.

  That is, when recording or reproducing a recording layer located at a thickness that differs by δ from the substrate thickness that minimizes the amount of spherical aberration of the light beam collected in the optical disc 102 when parallel light enters the objective lens If the refractive index of the substrate is n, and δ / n, which is an air conversion distance, is equal to (Equation 6), that is, if (Equation 2) is established, the objective lens is not affected by the position of the recording layer to be recorded or reproduced. The working distance is the same. Of course, it is not necessary to strictly satisfy (Equation 2) and (Equation 6), and these may be satisfied within a range including an error.

  At this time, since a spherical aberration corresponding to the substrate thickness δ is newly generated, a spherical aberration in the opposite direction substantially equal to the amount of the spherical aberration is generated in the objective lens at a magnification M satisfying (Equation 2), for example. Then, the spherical aberration corresponding to the substrate thickness δ can be corrected. For example, when the numerical aperture of the objective lens is 0.85, assuming that the wavelength is λ, the RMS value (Root Mean Square) of the spherical aberration amount corresponding to the substrate thickness of 10 micrometers is about 0.1λ. Therefore, as shown in FIG. 7, the RMS of spherical aberration generated when the magnification of the objective lens is M with respect to the RMS value of spherical aberration generated in the objective lens when parallel light is incident on the objective lens. By using an objective lens whose value ΔW obtained by normalizing the difference from the value by the wavelength of incident light satisfies (Equation 3), the working distance is substantially reduced with respect to the first recording layer and the second recording layer. Can be equal. In (Equation 3), the unit of the focal length f is micrometer.

  In addition, one of the characteristics is that the light beam condensed on the guide layer is incident on the objective lens as substantially parallel light. By entering the light almost parallel, even if the position of the objective lens in the optical axis direction changes due to the surface shake of the optical disk 102, the convergence / divergence of the objective lens is almost unchanged, that is, the movable lens 321 is driven substantially. Without focusing on the guide layer.

  Of course, it is not necessary to strictly satisfy (Equation 3), and it may be satisfied within a range including an error.

101 Optical disk device
102 optical disc
103 hosts
201 controller
202 Signal processor
203 Optical pickup
204 Slider motor
205 Slider drive means
206 Aberration correction drive means
207 Spindle motor
208 Rotation signal generation means
209 Spindle control means
210 Spindle drive means
211 Focus error signal generator
212 Focus control means
213 Focus drive means
214 Tracking error signal generation means
215 Tracking control means
216 Tracking drive means
217 lens
218 lenses
301 Laser driver
302 Laser diode
303 collimator lens
304 Beam splitter
305 lens
306 Power monitor
307 Polarizing beam splitter
308 Dichroic Mirror
309 Movable lens
310 1/4 wave plate
311 Objective lens
312 Actuator
313 lenses
314 Detector
315 laser diode
316 collimator lens
317 beam splitter
318 lenses
319 Power monitor
320 Polarizing beam splitter
321 Movable lens
322 lenses
323 detector

Claims (7)

A first light source and a second light source;
An objective lens for condensing the first light beam emitted from the first light source and the second light beam emitted from the second light source on an optical disc;
A first movable lens that controls convergence / divergence of the first light beam incident on the objective lens;
In an optical disc apparatus comprising: a second movable lens that controls convergence / divergence of the second light beam incident on the objective lens
The optical disc includes a guide layer for performing tracking control and a plurality of recording layers,
The first light beam is focused on the recording layer;
The second light beam is focused on the guide layer;
The working distance of the objective lens when recording or reproducing the first recording layer of the optical disc and the working distance of the objective lens when recording or reproducing the second recording layer of the optical disc are approximately. An optical disk device characterized by equality. The optical disk apparatus according to claim 1, wherein
A1 is a position in the optical axis direction of the first movable lens when the first recording layer is recorded or reproduced.
The position of the second movable lens in the optical axis direction when recording or reproducing the first recording layer is B1,
A2 is a position in the optical axis direction of the first movable lens when the second recording layer is recorded or reproduced.
When the position in the optical axis direction of the second movable lens when recording or reproducing the second recording layer is B2,

An optical disc device characterized by satisfying   2. The optical disc apparatus according to claim 1, wherein the second light beam is incident on the objective lens as substantially parallel light. The optical disk apparatus according to claim 1, wherein
When the first light beam is incident on the objective lens as parallel light, a recording layer positioned at a thickness different from δ with respect to the substrate thickness that minimizes the spherical aberration amount of the first light beam is recorded or recorded. When reproducing, if the focal length of the objective lens is f and the refractive index of the substrate of the optical disk is n, the first light beam is transmitted so that the magnification M of the objective lens approximately satisfies the following equation (2). An optical disc apparatus characterized by being incident on an objective lens.

The difference between the RMS value of the spherical aberration generated when collimated light is incident on the objective lens and the RMS value of the spherical aberration generated when the magnification of the objective lens is M is specified by the wavelength of the incident light. The converted value ΔW generally satisfies Equation 3 when the focal length when the focal length of the objective lens is expressed in micrometer units is f and the refractive index of the substrate of the optical disk corresponding to the objective lens is n. Objective lens.

The optical disc apparatus according to claim 1,
The objective lens calculates a difference between an RMS value of the spherical aberration amount generated when parallel light is incident on the objective lens and an RMS value of the spherical aberration amount generated when the magnification of the objective lens is M. The value ΔW normalized by the wavelength of the incident light is f when the focal length when the focal length of the objective lens is expressed in units of micrometers and the refractive index of the substrate of the optical disc corresponding to the objective lens is n. An optical disc apparatus characterized by being an objective lens that generally satisfies Equation (3).

An optical disc apparatus comprising: a first light source that emits a first light beam; and a second light source that emits a second light beam having a wavelength longer than the wavelength of the first light beam,
An objective lens that focuses the first light beam emitted from the first light source and the second light beam emitted from the second light source on an optical disc;
A first movable lens that controls convergence / divergence of the first light beam incident on the objective lens;
A second movable lens that controls the convergence and divergence of the second light beam incident on the objective lens,
The optical disc includes a guide layer for performing tracking control and a plurality of recording layers,
The first light beam is focused on the recording layer;
The second light beam is focused on the guide layer;
A1 is a position in the optical axis direction of the first movable lens when the first recording layer is recorded or reproduced.
The position of the second movable lens in the optical axis direction when recording or reproducing the first recording layer is B1,
A2 is a position in the optical axis direction of the first movable lens when the second recording layer is recorded or reproduced.
When the position in the optical axis direction of the second movable lens when recording or reproducing the second recording layer is B2,

An optical disc device characterized by satisfying

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