WO2007080925A1

WO2007080925A1 - Optical pickup device and information processor provided with such optical pickup device

Info

Publication number: WO2007080925A1
Application number: PCT/JP2007/050245
Authority: WO
Inventors: Kouretsu Boku
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2006-01-12
Filing date: 2007-01-11
Publication date: 2007-07-19

Abstract

In an optical pickup device wherein information is recorded and reproduced by commonly using a laser light source for a plurality of kinds of recording media having different distances to recording layers, returning light noise is suppressed for any of the recording media. The optical pickup device is used for at least reading or writing data by using the common laser light source from or on a plurality of kinds of information recording media having different distances between the surface on a light incoming side and the recording layers. The optical pickup device is provided with the laser beam light source for emitting an optical beam, and an optical system for collecting the optical beam on the information recording media and detecting the reflecting light from the information recording media. In the optical pickup device, an optical path length from a laser light source emitting point to a recording layer is set so as not to be an integral multiple of the effective resonator length of the laser light source in each of the information recording media.

Description

Specification

TECHNICAL FIELD The present invention relates to an optical pickup device and an information processing device including the optical pickup device.

TECHNICAL FIELD [0001] The present invention relates to an optical pickup device and an information processing device including the optical pickup device. More specifically, the present invention is for recording information or reproducing information by emitting laser light of infrared to blue wavelength to an optical disk such as a CD, a DVD, or a high-density optical disk. The present invention relates to an optical pickup device and an optical disc device.

Background art

[0002] Data recorded on an optical disc is reproduced by irradiating a rotating optical disc with a relatively weak light beam of a constant light quantity and detecting reflected light modulated by the optical disc.

[0003] On a read-only optical disc, information by pits is recorded in a spiral shape in advance at the manufacturing stage of the optical disc. On the other hand, in a rewritable optical disc, a recording material film capable of optically recording and reproducing data Z is formed on the surface of a substrate on which tracks having spiral lands or groups are formed by a method such as vapor deposition. It is deposited. When recording data on a rewritable optical disc, the optical disc is irradiated with a light beam whose amount of light is modulated according to the data to be recorded, thereby changing the characteristics of the recording material film locally. Write.

[0004] The depth of the pits, the depth of the track, and the thickness of the recording material film are smaller than the thickness of the optical disk substrate. For this reason, the portion of the optical disc where data is recorded constitutes a two-dimensional surface and is sometimes referred to as the “recording surface” of information. In this specification, in consideration of the fact that such a recording surface also has a physical size in the depth direction, the phrase “recording layer” is used instead of the phrase “recording surface”. Will be used. An optical disc has at least one such recording layer. One recording layer force may actually include a plurality of layers such as a phase change material layer and a reflective layer.

[0005] When data is recorded on a recordable optical disk or when data recorded on such an optical disk is reproduced, the light beam is always on the target track in the recording layer. It is necessary to be in a predetermined focusing state. For this purpose, “focus control” and “tracking control” are required. “Focus control” controls the position of the objective lens in the normal direction of the recording layer (hereinafter referred to as “the depth direction of the substrate”) so that the focal position of the light beam is always located on the recording layer. That is. On the other hand, the tracking control is to control the position of the objective lens in the radial direction of the optical disc (hereinafter referred to as “disc radial direction”) so that the spot of the light beam is located on a predetermined track.

[0006] Conventionally, DVD (Digital Versatile Disc) —ROM, DVD-RAM, DVD-RW, DVD-R, DVD + RW, DVD + R, etc. have been put to practical use as high-density * large-capacity optical disks. I came. CD (Compact Disc) is still popular.

[0007] Digital versatile discs (DVDs) can record digital data at a recording density approximately six times that of compact discs (CDs), and can write large volumes of digital data such as movies and music. It is known as a possible information recording medium (optical disc).

[0008] In recent years, since the information amount of information to be recorded such as the need for recording HDTV video due to the start of terrestrial digital broadcasting has increased, an optical disk having a larger capacity has been demanded. At present, the development of a next generation optical disc such as a Blu-ray Disc (BD), which has a higher density than these optical discs and a large capacity, is being put into practical use.

In order to increase the capacity of an optical disc, it is necessary to increase the information recording density. This is generally achieved by reducing the spot diameter of the laser beam emitted to the optical disc during data writing and reading. In order to reduce the spot diameter of the laser beam, the wavelength of the laser beam may be shortened.

[0010] Since optical disks have been put into practical use, laser light has been shortened, and larger capacity optical disks have been developed. Following CDs using infrared laser light with a wavelength of 780 nm, DVDs using red laser light with a wavelength of 650 ηm and high-density optical disks using blue laser light with a wavelength of 405 nm have been developed.

These optical discs have various cross-sectional structures that differ depending on the type. For example, the physical structure of the track, the track pitch, and the depth of the recording layer (the optical incident side surface force of the optical disc is also the distance to the recording layer) are different. In this way, the physical structure is different. Several types of optical disc power In order to read or write data properly, an optical system with a numerical aperture (NA) corresponding to the type of optical disc is used to irradiate the recording layer of the optical disc with an appropriate wavelength. There is a need to.

FIG. 1 is a perspective view schematically showing an optical disc 200. For reference, FIG. 1 shows an objective lens (focusing lens) 115 and a laser beam 22 focused by the objective lens 115. The laser beam 22 is applied to the recording layer through the light incident surface of the optical disc 200, and forms a light beam spot on the recording layer.

[0013] FIGS. 2 (a), (b), and (c) schematically show cross sections of CD, DVD, and BD, respectively. Each optical disk shown in FIG. 2 has a front surface (light incident side surface) 200a and a back surface (label surface) 200b, and has at least one recording layer 214 therebetween. A label layer 218 including titles and graphics prints is provided on the back surface 200b of the optical disk. Both optical discs have a total thickness of 1.2 mm and a diameter of 12 cm. For simplicity, the concavo-convex structure such as pits and groups is not shown in the drawing, and the description of the reflective layer is also omitted.

[0014] As shown in FIG. 2 (a), the CD recording layer 214 is located at a depth of about 1.1 mm from the surface 200a force. In order to read data from the recording layer 214 of the CD, it is necessary to control near-infrared laser light (wavelength: 785 nm) so that the focal point is located on the recording layer 214. The numerical aperture (NA) of the objective lens used for focusing the laser beam is about 0.5.

[0015] As shown in FIG. 2 (b), the DVD recording layer 214 is located at a depth of about 0.6 mm from the surface 200a force. In an actual DVD, two substrates with a thickness of approximately 0.6 mm are bonded together via an adhesive layer. In the case of an optical disc having two recording layers 214, the distances from the surface 2OOa to the recording layer 214 are about 0.57 mm and about 0.63 mm, respectively, which are close to each other. Therefore, only one recording layer 2 14 is shown in the drawing regardless of the number of recording layers 214. In order to read data from the DVD recording layer 214 and write the data, it is necessary to focus the red laser beam (wavelength: 660 nm) and control the focal point to be positioned on the recording layer 214. The numerical aperture (NA) of the objective lens used for focusing the laser beam is about 0.6.

[0016] As shown in FIG. 2 (c), the BD has a thin cover layer (100 m in thickness) on the surface 200a side. The recording layer 214 is located at a depth of about 0.1 mm from the surface 200a. In order to read data from the recording layer 214 of the BD, it is necessary to control the blue (blue-violet) laser beam (wavelength: 405 nm) so that the focal point is located on the recording layer 214. The numerical aperture (NA) of the objective lens used for focusing the laser beam is 0.85.

[0017] Currently, two types of optical discs are being developed, which are broadly divided into high-density optical discs using blue laser light. In the first type of high-density optical disc, the recording layer depth is 0.1 mm, and the recording capacity per layer is increased to about 5 times the recording capacity of conventional DVD (25 GB). For example, BD falls into this type of high density optical disc

On the other hand, in the second type of high-density optical disk, as shown in FIG. 2 (b), the depth of the recording layer is 0.6 mm, which is the same as that of a conventional DVD. The recording capacity per layer has been increased to 3 times (15GB) for DVDs for read-only media and 4 times (20GB) for DVDs for rewritable media. For example, HD—DVD corresponds to this type of high density optical disc.

Focusing on the physical structure of the optical disk, the second type of high-density optical disk is similar to a DVD, so there are few changes in the conventional disk manufacturing facilities. Therefore, the second type of high density optical disk is more advantageous than the first type of high density optical disk from the viewpoint of disk manufacturing cost.

[0020] On the other hand, from the viewpoint of the recording capacity per layer, the first type of high-density optical disk is larger than the second type of high-density optical disk. Also, due to the increase in the number of recording layers, if the number of stacked layers is the same, the recording capacity difference of the first type optical disc is larger than that of the second type optical disc.

[0021] As described above, since both types have merits and demerits, it is conceivable that there is a demand to use both types according to applications. For example, the first high-density optical disk with a large recording capacity is used for long-time HDTV broadcast recording, and the second high-density optical disk with low disk manufacturing cost is used as a read-only medium for recording movie content. It may happen that you used it.

[0022] To meet such demands, from the viewpoint of manufacturing cost and downsizing of the optical disk apparatus, an optical pin having compatibility that enables recording and reproduction of information on both types of high-density optical disks. Naturally, a backup device is required.

[0023] Hereinafter, the configuration of the conventional optical pickup device will be described. FIG. 3 shows a configuration of a general optical pickup device 110. The semiconductor laser light source 111 emits a coherent light beam. The light beam is reflected by the beam splitter 112, converted into parallel light by the collimator lens 113, reflected by the mirror 114, transmitted through the objective lens 115, and condensed on the recording layer of the optical disc 100.

When reading data, the collected light beam is reflected by the recording layer of the optical disc 100, reaches the beam splitter 112 through the reverse path, passes through the beam splitter 112, and enters the photodiode 118. The photodiode 118 is a so-called photodetector and outputs an electrical signal based on the intensity of incident light. Information recorded as a change in reflectance on the recording layer is detected as a change in the amount of reflected light incident on the photodiode 118, and data is reproduced based on the electrical signal.

In the above process, a part of the reflected light may be reflected to the light source 111 without passing through the beam splitter 112. This phenomenon returns to the laser light source and causes light noise.

The return light noise is caused by the interaction between the external resonator formed by the emission surface of the semiconductor laser light source 111 and the optical disk reflection surface and the internal resonator of the semiconductor laser light source 111 itself. It is known that the return light noise increases when the optical path length from the light emitting point of the semiconductor laser light source 111 to the optical disk 100 becomes an integral multiple of the effective resonator length. Note that the effective resonator length is represented by a product nL, where L is the internal resonator length of the semiconductor laser light source 111 and n is the refractive index in the resonator.

[0027] The return light noise can be suppressed to a low level by superimposing a high-frequency current from a high-frequency oscillation circuit on the laser drive current to multimode the laser light. However, if the current to be superimposed is too large, new problems such as an increase in unnecessary radiation of the circuit occur, so there is a limit to the measures to superimpose the high-frequency current.

[0028] In order to reduce the return light noise, for example, Patent Document 1 describes light in which the optical path length from the light emitting point of the semiconductor laser light source to the optical disk is set to a value that is not an integral multiple of the effective resonator length of the semiconductor laser light source. A pickup device is disclosed. This optical pickup device is A plurality of semiconductor laser light sources with different effective resonator lengths using a common optical system are installed, and the above settings are applied to each light source. As a result, it is possible to suppress an increase in return light noise with respect to the optical path of any light source.

Patent Document 1: Japanese Patent Laid-Open No. 2001-148135

Disclosure of the invention

Problems to be solved by the invention

[0029] However, in the conventional technology, it has not been considered to provide a plurality of optical paths having different optical path lengths for one laser light source. The reason for this is that, in the past, one laser light source was designed taking into account only one optical path length. In this case, when multiple optical path lengths exist for one laser light source, it is impossible to suppress an increase in return light noise in all the optical paths.

[0030] For example, the above-mentioned two types of high-density optical discs using blue laser light having a wavelength of 405 nm have a difference in distance to the recording layer of about 0.5 mm, which is greatly different, and therefore their optical path lengths are also different. Therefore, with the conventional technology, it is difficult to suppress an increase in the return light noise when using the other high-density optical disk, but it is difficult to suppress an increase in the return light noise when using the other high-density optical disk. Such inadequate performance cannot be applied to both high-density optical disks.

[0031] An object of the present invention is to provide an optical pickup device for recording / reproducing information using a common laser light source for a plurality of types of recording media having different distances to the recording layer. Is to keep the return light noise low.

Means for solving the problem

The optical pickup device according to the present invention reads and writes data to a plurality of types of information recording media having different distances to the surface force recording layer on the light incident side using a common laser light source. Used to do at least one. The optical pickup device includes a laser light source that emits a light beam, and an optical system that collects the light beam on an information recording medium and detects reflected light from the information recording medium, and the plurality of types of information recording media For each of the above, the optical path length from the light emitting point of the laser light source to the recording layer is set to a power value that is not an integral multiple of the effective resonator length of the laser light source. [0033] The effective resonator length of the laser light source is represented by the product of the resonator length L and the refractive index n in the resonator, and among the plurality of types of information recording media, the distance to the recording layer is the shortest. The distance from one recording medium to the recording layer is the longest, and for the second information recording medium, the theoretical optical path length from the light emitting point to the recording layer of the first recording medium is L1, and from the light emitting point to the first 2 When the theoretical optical path length to the recording layer of the recording medium is L2, the surface blur amount of the first recording medium is dl, and the surface blur amount of the second recording medium is d2, m X nL <Ll -d 1 and L2 + d2 (m + 1) XnL (m: any non-negative integer) may be set to be satisfied.

[0034] The optical system includes an optical element that can be inserted into and removed from the optical path of the light beam, and the optical element is operated according to an operation performed on the first recording medium and the second recording medium. The optical path length from the light emitting point of the laser light source to the recording layer may be set on the optical path of the light beam.

[0035] The optical system has an optical element that can be inserted into and removed from the optical path of the light beam, and the optical element is arranged on the optical path of the light beam according to the distance to the recording layer, The light emission point of the laser light source The optical path length to the recording layer may be set.

[0036] The effective resonator length of the laser light source is represented by the product of the resonator length L and the refractive index n in the resonator, and the theoretical optical path length from the light emitting point to the recording layer of the recording medium is expressed as L3 And when the surface deflection amount of the recording medium is d3, m X nL + d3 <L3 (m + 1) X nL d3 (m: negative, any integer) is set to be satisfied. Well! /

[0037] The optical system includes a condensing element that condenses the light beam on a recording layer of the information recording medium, and the optical element has a numerical aperture of the condensing element according to the type of the optical disc. (NA) may be changed.

[0038] The laser light source may emit a light beam that emits light in a blue wavelength region.

[0039] Each of the plurality of types of information recording media has one or a plurality of recording layers, and the surface force has a different distance to the first recording layer, from the emission point of the laser light source. The optical path length to the first recording layer may be set to a value that is an integral multiple of the effective resonator length of the laser light source. [0040] An information processing apparatus according to the present invention is based on any one of the above-described optical pickup devices further including a light detector that detects reflected light from the information recording medium, and the detected reflected light. A signal processing circuit for generating at least one of a reproduction signal and a servo signal is provided.

The invention's effect

[0041] According to the present invention, for each of a plurality of types of information recording media, the optical path length from the light emitting point of the light source to the recording layer is set to a value that is not an integral multiple of the effective resonator length of the light source. . As a result, for any information recording medium, it is possible to avoid the peak of the return light noise of the laser beam and to suppress the deterioration of the signal characteristics.

Brief Description of Drawings

FIG. 1 is a perspective view schematically showing an optical disc 200. FIG.

FIG. 2 (a), (b), and (c) are schematic views of cross sections of CD, DVD, and BD, respectively.

FIG. 3 is a diagram showing a configuration of a general optical pickup device 110.

4 is a diagram showing the relationship between the optical path lengths L1 and L2 from the laser light source 1 to the recording layers of two types of optical discs, and the effective resonator length nL of the laser light source 1. FIG.

FIG. 5 is a diagram showing a functional block configuration of the optical disc apparatus 14 according to Embodiment 1.

[Fig. 6] (a) is a diagram showing an optical path when a light beam is focused on the recording layer of the optical disc 101 having the shortest distance to the recording layer, and (b) is an optical disc having the longest distance to the recording layer. FIG. 10 is a diagram showing an optical path when a light beam is condensed on a recording layer 102.

7 (a) and (b) are diagrams showing the relationship between the optical path length and the resonator of the laser light source in the optical pickup provided with the hologram lens 22.

FIG. 8 is a diagram showing the shape of the hologram lens 22 in view of the optical axis direction force.

FIG. 9 is a cross-sectional view of hologram lens 22 by a plane including the optical axis.

[FIG. 10] (a) and (b) are diagrams showing the relationship between the optical path length and the resonator of the laser light source in the optical pick-up provided with the intensity adjusting element 23 in addition to the first modification.

FIG. 11 is a diagram showing a configuration of an optical pickup device 23 according to Embodiment 2 having an optical path length correcting element 15. Explanation of symbols

[0043] 1 light source

2 Beam splitter

3 Collimating lens

4 Mirror

5 Objective lens

6 Actuator

7 Cylindrical lens

8 Photodiode

9 Signal processing circuit

10 Servo control circuit

11 Spinner motor

12 Traverse motor

13 Optical pickup device

14 Optical disk device

15 Optical path length correction element

100 optical disc

101 Optical disc with a short distance to the recording layer

102 Optical disc with long distance to recording layer

BEST MODE FOR CARRYING OUT THE INVENTION

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

[0045] (Embodiment 1)

First, the main features of the present invention will be described with reference to FIG.

FIG. 4 shows the relationship between the optical path lengths L1 and L2 from the laser light source 1 to the recording layers of the two types of optical disks, and the effective resonator length nL of the laser light source 1. The two types of optical discs are BD and HD—DVD, for example.

[0047] One of the main features of the present invention is that the light source power of the laser light source 1 is such that the optical path length to the recording layer of each optical disc does not become an integral multiple of the effective resonator length nL of the laser light source 1. The purpose is to adjust the optical system of the backup device.

[0048] Here,! /, "Optical path length to the recording layer of the optical disk" means an optical path length that also considers the surface blur of the optical disk, which is not limited to L1 and L2 described above. .

More specifically, the optical disc may cause surface blur when rotated due to the warp of the disc. Due to such surface blurring, the actual optical path length of the laser light source 1 to the recording layer of the optical disc varies slightly from L1 and L2. On the other hand, surface blurring of a certain amount or less is normally allowed according to the standards. In consideration of such surface blurring, the “optical path length to the recording layer of the optical disk” is determined as an amount having an allowable amount of surface blurring centering on L1 and L2 described above. Figure 4 shows the optical path length range A for BD and the optical path length range B for HD—DVD, taking into account surface blurring! When BD and HD—DVD are loaded, the position of the recording layer will fall within the ranges A and B shown.

[0050] The present embodiment is configured so that the optical path length from the light source 1 to the recording layer does not always become an integral multiple of the effective resonator length nL of the laser light source in consideration of the surface deflection of each type of optical disk. ing. Note that the effective resonator length nL is, for example, 2 to 4 mm. The difference between L1 and L2 is about 0.5mm.

Next, the configuration and operation of the optical disk device will be described with reference to FIG. 5, and further, the schematic configuration of the optical pickup device mounted on the optical disk device will be described. Thereafter, the configuration of the optical pickup device relating to the above-described features will be described in detail with reference to FIG.

The optical disc apparatus according to the present embodiment can write data to a plurality of types of optical discs using a common laser light source, or read the written data.

FIG. 5 shows a functional block configuration of the optical disc apparatus 14 according to the present embodiment. The optical disk device 14 includes an optical pickup device 13, a signal processing circuit 9, a servo control circuit 10, a spindle motor 11, and a traverse motor 12. Although FIG. 5 shows the optical disc 100, this is for convenience of explanation and is not a constituent element of the optical disc device 14. First, an outline of the operation of the optical disk device 14 will be described. The optical pickup device 13 emits a light beam to the optical disc 100 to detect the reflected light from the optical disc 100, and outputs a light amount signal corresponding to the detection position of the reflected light and the detected light amount. The signal processing circuit 9 generates a focus error (FE) signal indicating the focus state of the light beam on the optical disc 100 according to the light amount signal output from the optical pickup device 13, and the focus position of the light beam and the optical disc 100. Generates and outputs a tracking error (TE) signal that indicates the positional relationship with the track. The FE signal and TE signal are collectively called servo signals.

The servo control circuit 10 generates a plurality of types of drive signals based on these signals. The type of drive signal differs depending on the output destination. The output destination is the actuator 6 of the spindle motor 11, the traverse motor 12 and the optical pickup device 13.

The spindle motor 11 rotates the optical disc 100 at a rotational speed corresponding to the recording speed Z reproduction speed based on the drive signal. The traverse motor 12 moves the optical pickup device 13 in the radial direction of the optical disc 100 to the target recording position or reproduction position based on the drive signal.

The actuator 6 adjusts the position of the objective lens 5 based on the drive signal. Thus, the focal point of the light beam emitted to the optical disc 100 is controlled so as not to deviate from the recording layer.

[0058] In a state where the focus of the light beam is controlled so as not to deviate from the recording layer force, the signal processing circuit 9 outputs a reproduction signal based on the light amount signal. The reproduction signal indicates data written on the optical disc 100. As a result, reading of data from the optical disc 100 is realized. Also, data can be written to the optical disc 100 by making the optical power of the light beam larger than that during reproduction.

Hereinafter, the configuration of the optical pickup device 13 will be described. The optical pickup device 13 includes a light source 1, a beam splitter 2, a collimating lens 3, a mirror 4, an objective lens 5, an activator 6, a cylindrical lens 7, and a photodiode 8.

[0060] The light source 1 is a GaN-based semiconductor laser light source that emits a blue laser beam (light beam) having a wavelength of 405 nm, and is used for reading and writing data on the recording layer of the optical disc 100. Emits coherent light. Beam splitter 2 is an optical beam emitted by light source 1. Reflect the light toward the collimating lens 3. The collimating lens 3 converts the light beam emitted from the light source 1 into parallel light. The mirror 4 reflects the incident light beam and directs the reflected light beam to the optical disc 100.

The objective lens 5 focuses the light beam on the recording layer of the optical disc 100. The actuator 6 changes the position of the objective lens 5 in a direction perpendicular to the optical disc 100 or in a direction parallel to the optical disc 100 according to the level of the applied drive signal, so that the light is projected onto the recording layer of the optical disc 100. Focus the beam. The cylindrical lens 7 causes the photodiode 8 to emit light. The photodiode 8 receives the light beam reflected by the recording layer of the optical disc 100 and converts it into an electrical signal (light amount signal) according to the light amount. The photodiode 8 may include a plurality of light receiving elements. The signal processing circuit 9 that receives the light amount signal generates an FE signal and a TE signal using information on which light receiving element force is output as the light amount signal.

Next, the relationship between the optical path length during operation of the optical pickup device 13 and the resonator of the laser light source will be described with reference to FIGS. 6 (a) and 6 (b).

The optical pickup device 13 according to the present embodiment can read and write data on a plurality of types of optical discs using blue laser light having a wavelength of 405 nm. The recording layer depths of multiple types of optical discs are different from each other. Hereinafter, the configuration of the optical pickup device 13 will be described by taking the optical disc with the shortest distance to the recording layer and the optical disc with the longest distance as examples.

FIG. 6 (a) shows an optical path when a light beam is collected on the recording layer of the optical disc 101 having the shortest distance to the recording layer, and FIG. 6 (b) shows the longest distance to the recording layer. The optical path when a light beam is emitted to the recording layer of the optical disc 102 is shown. Even if there is a deviation in Fig. 6 (a) and (b), the beam splitter mirror is omitted for simplification.

The optical disk 101 is, for example, a BD whose optical incident surface force is 0.1 mm from the recording layer. In the optical disc 101, the physical structure is greatly changed from that of the conventional DVD, and a structure for minimizing the influence of the improvement in the recording density is adopted. The numerical aperture (NA) of the objective lens 5 required for the optical disk 101 is 0.85. The spot diameter of the laser beam that determines the information recording density is inversely proportional to the numerical aperture (NA) of the objective lens. Yotsu Therefore, higher density has been realized using an objective lens with a relatively large numerical aperture (NA) of 0.85. Note that the numerical aperture (NA) of the objective lens used for DVD is 0.6.

[0066] When the numerical aperture (NA) of the objective lens is increased, coma aberration generated in the optical spot increases in proportion to the cube of the numerical aperture (NA). This means that the tolerance (tilt margin) for the angle deviation between the optical disk and the optical axis of the laser beam is reduced. The coma aberration increases in proportion to the distance to the recording layer of the optical disc. Therefore, by reducing the distance by 1/6 from 0.6mm to 0.1mm of DVD, the amount of coma aberration can be reduced, and a tilt margin comparable to that of a conventional DVD can be secured.

On the other hand, the optical disk 102 is, for example, an HD-DVD whose optical incident surface force is 0.6 mm from the recording layer. The optical disk 102 is configured so that the physical structure approximates that of a conventional DVD, and the capacity is increased only by shortening the wavelength of the laser beam. The numerical aperture (NA) of the objective lens required for the optical disc 101 is at least 0.65.

However, the pickup device 13 of the present embodiment uses a common optical system for the two types of optical disks 101 and 102 having different distances to the recording layer. Therefore, the objective lens 5 having a numerical aperture (NA) of 0.85 is also used for the optical disc 102. The resolution is higher for an objective lens with a numerical aperture (NA) of 0.65 than for an objective lens with a numerical aperture (NA) of 0.65, so the latter can be achieved by applying a technique such as limiting the numerical aperture (NA) to 0.65 or equivalent. Can be used. It is also possible to use the hologram to place the focal points of 0th order light and ± 1st order light on the recording layers of the two types of optical disks 101 and 102. An example of using such a hologram will be described later with reference to FIGS.

[0069] In the following, the quantities related to the optical paths in Figs. 6 (a) and (b) are defined. 6 (a) and 6 (b), a common semiconductor laser light source 1 is used. The resonator length of this light source 1 is L, and the refractive index in the resonator is n.

In FIG. 6A, the optical path length from the light source 1 to the recording layer of the optical disc 101 is L1. In FIG. 6B, the optical path length from the light source 1 to the recording layer of the optical disk 102 is L2. These optical path lengths are assumed to be theoretical values determined when the optical discs 101 and 102 are discs in an ideal planar state in which there is no warp or the like. The optical path lengths LI and L2 are values calculated in consideration of the refractive index of each medium on the optical path. In other words, the `` optical path length '' refers to the distance that light actually feels rather than the physical distance from the laser emission point to the recording layer (the distance that is determined in consideration of the difficulty of light traveling due to the medium on the optical path). , Expressed with reference to the wavelength of light. For example, in a medium with a refractive index n, the wavelength of light is lZn, so if the physical distance of this medium is D, the optical path length is nD.

Now, it is assumed that the optical path length corresponding to the maximum surface blur amount of the optical disc 101 is dl, and the optical path length corresponding to the maximum surface blur amount of the optical disc 102 is d2. The maximum surface blur amount is, for example, the maximum surface blur amount allowed in the standard. Since the refractive index of air is 1, in the normal usage mode of the optical pickup device 13 (that is, usage in the atmosphere), the values of the optical path lengths dl and d2 described above are the maximum surface blur value. The same. In this case, for example, the value of dl is 0.3 mm, and as a result, the value of d2 is 0.3 mm as a result of tilt control described later.

First, in order to prevent the optical disk 101 from returning to the laser light source 1 and generating optical noise, it is necessary to establish the following formula 1 where m is any non-negative integer.

[0074] (Equation 1)

mX nL <Ll -dl and Ll + dl <(m + 1) X nL

[0075] Referring to Fig. 6 (a), Equation 1 specifies that ± dl range force m X nL to (m + 1) X nL is within the range from the optical path length L1! / And then.

[0076] To explain more easily with reference to FIG. 4 described above, the meaning of Equation 1 specifies that the range A does not extend over a position that is an integral multiple of the effective resonator length nL. Yes. Specifically, the first equation of Equation 1 means that the end position (LI-dl) of the range A on the light source 1 side is larger than the position p that is m times the effective resonator length nL of the light source 1. is doing. The second equation in Equation 1 indicates that the end position (LI + dl) on the opposite side of the light source 1 in range A is smaller than the position q that is (m + 1) times the effective resonator length nL of light source 1. I mean. Note that q = p + nL.

Next, in order to prevent the optical disk 102 from returning to the laser light source 1 and generating optical noise, it is necessary to establish the following formula 2 where m is an arbitrary integer.

[0078] (Number 2)

mX nL <L2-d2 and L2 + d2 (m + 1) X nL [0079] This number 2 is also interpreted in the same manner as the number 1. The value of m is the same in Equation 1 and Equation 2.

Here, the relationship between the optical path lengths L1 and L2 is examined. As described above, the optical path length L1 is defined for the optical disc 101 having the shortest distance to the recording layer, and the optical path length L2 is defined for the optical disc 102 having the longest distance to the recording layer. Therefore, it is LKL2.

[0081] Furthermore, the magnitude relationship between the optical path lengths dl and d2 is also examined. These can be regarded as the tilt margin of the optical discs 101 and 102. As described above, the optical disc 101 has the same tilt margin as a conventional DVD, and the optical disc 102 has the same distance from the light incident surface of the optical disc to the recording layer as the conventional DVD. By applying light with a large numerical aperture (NA) and short wavelengths, it is affected by aberrations, and has a tilt margin that approximates that of a conventional DVD by performing tilt control. Therefore, the optical path lengths dl and d2 can be considered to be substantially the same as described above.

[0082] According to the magnitude relationship between the optical path lengths L1 and L2 and the magnitude relation between the optical path lengths dl and d2, it can be said that (LI-dl) appearing in Equation 1 is smaller than (L2-d2) appearing in Equation 2. Therefore, if the first equation of Equation 1 is satisfied: m X nL <Ll-dl, it can be said that the Equation 1 of Equation 2 is also satisfied. In the same way, if the second equation of Equation 2: L2 + d2 <(m + 1) X nL is satisfied, the second equation of Equation 2 is also satisfied.

[0083] Summarizing the above, the following Equation 3 is obtained.

(Equation 3)

mX nL <Ll -dl and L2 + d2 (m + 1) XnL (m: any non-negative integer) [0084] If the optical path length of the optical pickup device 13 is set so as to satisfy Equation 3, In both cases of condensing and condensing on the optical disc 102, the optical path length from the laser emission point to the recording layer does not become an integral multiple of the effective resonator length nL of the laser light source. Therefore, no matter which optical disk is used, it is possible to avoid the return light noise of the laser light from becoming a peak, and to suppress the deterioration of the signal characteristics.

In the above description, the optical disk 101 having the shortest distance to the recording layer and the optical disk 102 having the longest distance have been described. If the relationship of number 3 is satisfied for these optical discs, any two of them can be loaded even when three or more types of optical discs are loaded. The relationship of number 3 is satisfied with respect to the optical disc. Therefore, the above-described effects can be obtained regardless of which optical disk is used.

Next, a first modification of the optical pickup according to the present embodiment will be described with reference to FIGS. 7 to 9, and then a second modification will be described with reference to FIG.

FIGS. 7A and 7B show the relationship between the optical path length in the optical pickup provided with the hologram lens 22 and the resonator of the laser light source. The configuration shown in FIG. 7 is different from the configuration shown in FIG. 6 in that the hologram lens 22 is provided. This difference will be described below. Figure

Constituent elements having the same functions as the constituent elements shown in FIG.

The hologram lens 22 focuses the 0th-order diffracted light (transmitted light) of the light beam on the recording layer of the optical disc 101 as shown by the solid line in FIG. 7 (a), and as shown by the solid line in FIG. 7 (b). The first-order diffracted light is focused on the recording layer of the optical disk 102.

In the hologram lens 22, a grating pattern is provided in the central area 22a including the optical axis, and no grating pattern is provided in the peripheral area 22b positioned around the central area 22a.

The light beam incident on the central region 22a is diffracted and incident on the objective lens 5 as ± first-order diffracted light. Then, the light beam is focused on the position of the recording layer of the optical disc 102.

The light beam incident on the peripheral region 22b is transmitted as it is and enters the objective lens 5 as 0th-order diffracted light. Then, the light beam is focused on the position of the recording layer of the optical disc 101.

[0092] Even if the configuration using the hologram lens 22 as shown in Figs. 7 (a) and (b) is adopted, the luminous point power of the laser light source 1 The optical path length L3 and L4 force to the recording layer of each optical disk The optical system of the optical pickup device may be adjusted so that it does not become an integral multiple of the effective resonator length nL of the laser light source 1. The definition of the optical path length is as described above. The optical path lengths L1 and L2 in Fig. 6 should be read as L3 and L4, respectively, and adjusted so that the relationship satisfying Equation 3 above is satisfied.

Hereinafter, the hologram lens 22 will be described in detail with reference to FIGS. 8 and 9.

The hologram lens 22 is formed on a transparent substrate. FIG. 8 shows the shape of the hologram lens 22 as viewed from the optical axis direction. Fig. 9 shows a hologram lens with a plane including the optical axis. 22 shows a cross section.

As shown in each figure, the lattice pattern of the central region 22a is concentric when viewed in the direction of the optical axis, and is formed only in a region having a diameter smaller than the opening determined by the objective lens 5. In addition, no lattice pattern is formed in the peripheral region 22b.

The diffraction efficiency of the + first-order diffracted light of the hologram lens 22 is less than 100%, and the 0th-order diffracted light (transmitted light) of the light beam is designed to have sufficient intensity. For example, when the lattice pattern 22a of the hologram lens 22 is formed into an uneven shape as shown in FIG. 9, the height h of the unevenness of the lattice pattern 22a is set as h λ Ζ (η-1). Where is the wavelength of the light beam, and η is the refractive index of the transparent substrate of the hologram lens.

That is, the hologram lens 22 in which the 0th-order diffracted light has sufficient intensity at any position of the hologram lens 22 is realized by making the amplitude of the phase change given to the light beam by the grating pattern smaller than 2π. can do.

At the same time, since the + first-order diffracted light and the 0th-order diffracted light have sufficient intensity, the side lobes of the condensed beam formed on the optical disc 101 or 102 can be relatively suppressed. The side lobe is an unnecessary amount of light due to high-order diffracted light or the like. Side grooves cause deterioration of recorded pit shape and playback signal.

[0099] The phase of the 0th-order diffracted light (transmitted light) by the grating pattern of the hologram lens 22 is an average value of the phase modulation amount given by the grating pattern. On the other hand, the focusing performance of the objective lens 5 can be improved by matching the phase of the light beam transmitted through the V ヽ peripheral region 22b without the grating pattern to approximately the same as the 0th-order diffracted light by the grating pattern 22a. . For example, when the grating pattern of the hologram lens 22 is a relief type, as shown in FIG. 9, the height of the surface of the peripheral region 22b without the grating pattern is adjusted to the average level of the irregularities of the grating pattern.

[0100] Note that the hologram lens 22 can be provided directly on the surface of the objective lens 5 on the light source 1 side, for example, with the force described as being provided as one optical element.

Next, a second modification of the optical pickup according to the present embodiment will be described with reference to FIG.

[0102] Figs. 10 (a) and 10 (b) show an optical pin provided with an intensity adjusting element 23 in addition to the first modification. The relationship between the optical path length in the backup and the resonator of the laser light source is shown.

[0103] The intensity adjusting element 23 is provided so that it can be inserted into and removed from the optical path by a drive mechanism (not shown), and the light transmittance is changed to keep the quantum noise of the light beam emitted from the light source 1 low. It is an optical element that changes the optical power in a state. For example, the intensity adjusting element 23 is retracted to a position that does not exist on the optical path during the recording operation with respect to the optical disk 101 or 102, and is inserted into the optical path during the reproducing operation.

[0104] The reason for providing the intensity adjusting element 23 is to realize an accurate operation regardless of whether it is a recording operation or a reproducing operation. The light emission power of the laser light source differs greatly between the recording operation and the reproduction operation. Needless to say, the light emission power during recording is greater than the light emission power during playback. However, when the emission power level of the laser light source is lowered, the laser oscillation can become unstable. This is particularly noticeable for blue laser light sources. Therefore, by inserting / removing the intensity adjusting element 23 on the optical path, it is possible to stably secure the light amount necessary for the recording operation and the reproducing operation while keeping the light emission power level of the laser light source constant.

However, the optical path length when the intensity adjusting element 23 exists on the optical path is different from the optical path length when it does not exist. For example, in the example shown in FIG. 10 (a), the optical path length L5 from the light emitting point of the laser light source 1 to the recording layer of the optical disc 101 changes depending on whether or not the intensity adjusting element 23 exists. Therefore, in any case, the optical path length from the light emitting point of the laser light source 1 to the recording layer of each optical disk is not an integral multiple of the effective resonator length nL of the laser light source 1 so that the optical system of the optical pickup device If you adjust. The same applies to the optical disk 102. The optical path lengths L3 and L4 in Fig. 7 should be read as L5 and L6, respectively. Since the optical path lengths L5 and L6 both change depending on the presence or absence of the intensity adjusting element 23, the optical path lengths L5 and L6 may be adjusted so as to satisfy the above-described equation 3 in all cases.

[Embodiment 2]

Embodiment 2 of the present invention will be described.

FIG. 11 shows a configuration of the optical pickup device 23 according to the present embodiment. The optical pickup device 23 according to the present embodiment is different from the optical pickup device 13 according to the first embodiment with respect to the optical path length. The correction element 15 is added. The optical pickup device 23 is the same as the optical pickup device 13 except for the optical path length correcting element 15. Therefore, in the following, the optical path length correction element 15 will be described in detail, and the description of other configurations and operations will be omitted.

Note that an optical disk device can be manufactured by using the optical pickup device 23 according to the present embodiment instead of the optical pickup device 13 of FIG. The configuration and operation of this optical disc apparatus have already been described with reference to FIG.

[0109] The optical path length correction element 15 is a parallel plate having a refractive index larger than 1, and can be taken in and out of the optical path of the light beam. In the present embodiment, it is arranged so as to be insertable / removable on the optical path between the mirror 4 and the actuator 6. In order to insert / remove the optical path length correction element 15, an actuator (not shown) is separately provided. This actuator moves the optical path length correction element 15 based on, for example, a drive signal from the servo control circuit 10 of FIG.

Now, it is assumed that the refractive index of the optical path length correction element 15 is n and the thickness in the optical axis direction is h. When the optical path length correcting element 15 is inserted on the optical path, the optical path length is increased by (n−l) h as compared with the case where the optical path force is also removed. This makes it possible to adjust the optical path length according to whether or not the distance to the recording layer of the optical disc is the shortest.

For example, when the optical disc 101 having the shortest distance to the recording layer is loaded, the optical path length correction element 15 is inserted into the optical path, and the optical path length is extended. On the other hand, when the optical disc 102 having the longest distance to the recording layer is loaded, the optical path length correction element 15 is removed from the optical path. If the optical path length to the recording layer of the optical disk 101 extended by the insertion of the optical path length correction element 15 is approximately equal to the optical path length to the recording layer of the optical disk 102 when the optical path length correction element 15 is not present in the optical path. Yeah!

Specifically, by setting h so that L2−Ll = (n−l) h, L 1 is set to L 1 simply by inserting the optical path length correction element 15 into the optical disc 101. + (n— 1) h = L2. As a result, mX nL + d and L2 (m + 1) X nL-d need only be satisfied.

[0113] In other words, the cavity length of the semiconductor laser light source is L, the refractive index in the cavity is n, the laser emission point force when focusing on the optical disk is L3, and the optical path length to the recording layer is L3. If the amount of runout is d3, the optical path length should be adjusted so that the following formula 4 is satisfied when focusing on any disk. [0114] (Equation 4)

mX nL + d3 <L3 <(m + 1) X nL— d3 (m: any non-negative integer)

[0115] Equation 4 is an arrangement of Equation 3 by replacing L1 and L2 with L3 and substituting dl and d2 with d3 in Equation 3.

[0116] As described above, if the optical path length of the optical pickup device 23 is set so as to satisfy the equation 4, it can be focused on the optical disc 101 or the optical disc 102. The optical path length from the laser emission point to the recording layer does not become an integral multiple of the effective resonator length nL of the laser light source. Therefore, regardless of which optical disk is used, it is possible to avoid the peak of the return light noise of the laser light and to suppress the deterioration of the signal characteristics.

Note that the optical pickup device 23 according to the present embodiment has a function of changing the aperture so that the optical path length correction element changes the numerical aperture (NA) of the objective lens in accordance with the type of the optical disk. May be.

In addition, the function of the intensity adjusting element 23 described in the second modification according to the first embodiment may be given to the optical path length correcting element 15 according to the present embodiment.

In the present embodiment, the optical path length is adjusted using the optical path length correction element 15. Instead of adjusting the optical path length, the effective resonator length nL of the laser light source may be adjusted to be variable so that the optical path length does not become an integral multiple of the effective resonator length nL of the laser light source. . For example, two curved high-reflectivity mirrors with curvature may be provided in the laser light source so as to face each other, and the number of times of laser light reflection between the two high-reflectivity mirrors may be changed. By changing the number of reflections, the resonator length can be arbitrarily extended or shortened. For example, Japanese Patent Laid-Open No. 2002-171015 discloses a laser light source having such a variable effective resonator length. Note that the optical path length correction element 15 may be omitted when the effective resonator length is variable, but the optical path length correction element 15 may be provided to finely adjust the optical path length.

[0120] In the above-described embodiment, an optical disk having a distance to the recording layer of 0.1 mm and an optical disk having a distance of 0.6 mm are taken as examples, but this is an example. The present invention can also be applied to optical disks having other distances.

[0121] Furthermore, the description has been made assuming that the number of recording layers of the optical disc is one. But record The number of layers may be one or more. When there are a plurality of recording layers, the surface force on the light incident side may be determined based on the depth to the first recording layer. In addition,

Even if one optical disk has a plurality of recording layers, it is necessary to change the light emission power of the laser light source depending on the depth of the recording layer for focusing the laser light. that time

The strength adjusting element 23 described in the second modification of the first embodiment can be used.

In the above-described embodiment, it has been described that a common laser light source is used for a plurality of types of optical disks. However, the optical pickup device may further include other laser light sources having different wavelengths. According to this configuration, it is possible to record and reproduce information on a wider variety of optical disks.

[0123] An optical disk is an example of an information recording medium, and may be a card or the like that can optically read and write data.

Industrial applicability

According to the present invention, it is possible to manufacture a highly reliable optical pickup device that suppresses deterioration of signal characteristics due to laser return light noise during recording and reproduction. Furthermore, by incorporating such an optical pickup device, an optical disc device having highly reliable recording performance and reproducing performance can also be manufactured.

Claims

The scope of the claims

[1] Surface force on the light incident side An optical pickup device for performing at least one of reading and writing of data using a common laser light source on a plurality of types of information recording media having different distances to the recording layer. And

A laser light source that emits a light beam;

An optical system that focuses the light beam on an information recording medium and detects reflected light from the information recording medium;

An optical pickup device in which the optical path length from the emission point of the laser light source to the recording layer is set to a value that does not become an integral multiple of the effective resonator length of the laser light source for each of the plurality of types of information recording media. .

[2] The effective resonator length of the laser light source is represented by the product of the resonator length L and the refractive index n in the resonator,

Among the plurality of types of information recording media, the first recording medium having the shortest distance to the recording layer and the second information recording medium having the longest distance to the recording layer,

The theoretical optical path length from the light emitting point to the recording layer of the first recording medium is L1, and the theoretical optical path length from the light emitting point to the recording layer of the second recording medium is L2, and the first recording The amount of surface blur of the medium is dl,

When the amount of surface deflection of the second recording medium is d2,

2. The optical pickup device according to claim 1, wherein mX nL <Ll −dl and L 2 + d 2 (m + 1) X nL (m: any non-negative integer) are set.

[3] The optical system includes an optical element that can be inserted into and extracted from an optical path of the light beam, and the optical element is operated according to an operation performed on the first recording medium and the second recording medium. 2. The optical pickup device according to claim 1, wherein the optical pickup device is disposed on an optical path of the light beam and sets an optical path length from a light emitting point of the laser light source to the recording layer.

[4] The optical system includes an optical element that can be inserted into and removed from the optical path of the light beam, and the optical element is disposed on the optical path of the light beam according to the distance to the recording layer. The optical pickup device according to claim 1, wherein an optical path length from a light emitting point of the laser light source to the recording layer is set.

[5] The effective resonator length of the laser light source is represented by the product of the resonator length L and the refractive index n in the resonator,

When the theoretical optical path length from the light emitting point to the recording layer of the recording medium is L3, and the amount of surface blur of the recording medium is d3,

mX nL + d3 <L3 <(m + 1) X nL— d3 (m: any non-negative integer)

Is set to be met! 5. The optical pickup device according to claim 4, wherein

[6] The optical system includes a condensing element that condenses the light beam on a recording layer of the information recording medium,

5. The optical pickup device according to claim 4, wherein the optical element changes a numerical aperture (NA) of the condensing element according to a type of the optical disk.

7. The optical pickup device according to claim 1, wherein the laser light source emits a light beam that emits light in a blue wavelength region.

[8] Each of the plurality of types of information recording media has one or more recording layers, and the distance from the surface to the first recording layer is different.

The optical pin according to claim 1, wherein an optical path length from a light emitting point of the laser light source to the first recording layer is set to a value that is not an integral multiple of an effective resonator length of the laser light source. A backup device.

[9] The optical pickup device according to any one of claims 1 to 7, further comprising a photodetector for detecting reflected light from the information recording medium, and

An information processing apparatus comprising a signal processing circuit that generates at least one of a reproduction signal and a servo signal based on the detected reflected light.