JP2004334962A - Optical head, and optical recording medium recording/reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To expose a regular position of a light receiving element with a light spot irrespective of optical recording media by carrying out tracking using three-spot method to a laser light source corresponding to a plurality of wavelengths. <P>SOLUTION: The optical head optics 1 is provided with diffraction areas 12b, 12a differing in grid spacing and grid angle from each other, and a diffraction-grating 12 with which the diffraction region 12a is arranged on both sides of the diffraction region 12b at two symmetrical positions between these two diffraction regions is arranged between a semiconductor laser component 11 and an objective lens 15. Especially, when the grid spacing and grid angle of the diffraction region 12a are expressed by P<SB>1</SB>, θ<SB>1</SB>, those of the diffraction region 12b are expressed by P<SB>2</SB>, θ<SB>2</SB>, and the wavelengths used are expressed by λ<SB>1</SB>, λ<SB>2</SB>, a grid pitch is set satisfying P<SB>2</SB>/P<SB>1</SB>=ε*λ<SB>2</SB>/λ<SB>1</SB>(0.9≤ε≤1.1) considering various errors such as dimensional tolerances. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical head and an optical recording medium recording / reproducing apparatus, and more particularly, to an optical head and an optical recording medium that use a same optical system to handle light beams of a plurality of wavelengths prepared for recording and reproducing a plurality of optical recording media. The present invention relates to a recording / reproducing device.
[0002]
[Prior art]
2. Description of the Related Art In recent years, optical recording media such as optical discs are capable of recording large-capacity information signals, and are increasingly used as recording media for various data types such as audio data, video data, and computer data.
[0003]
As the optical disk, various types of recording / reproducing disks using optical modulation recording, optical disks including so-called “magneto-optical recording”, “phase change recording”, and “dye recording”, and more specifically, “CD-R / RW” , "DVD-RAM", "DVD-R / RW", "DVD + RW", etc., and the types have been diversified with the increase in storage capacity.
[0004]
Therefore, two laser light sources (laser diode: LD) for CD (780 nm band) and DVD (650 nm band) having different recording / reproducing wavelengths are used, and both standards can be read and written. Recording and playback devices have also been developed.
[0005]
By the way, a tracking servo method for an optical disk includes a well-known technique of a push-pull signal of a main beam and a push-pull signal of a sub-beam irradiated on an optical recording medium so as to be 180 ° out of phase with respect to the push-pull signal. (Differential Push Pull method) for generating a tracking error signal by differential of the two, and a three spot method for generating a tracking error signal by an intensity difference between two sub-beams. In an optical pickup equipped with laser light sources corresponding to the wavelength bands of CD and CD as separate packages, a diffraction grating having a grating interval corresponding to each wavelength is prepared for each laser light and the laser light is separated. In either case of the DPP method or the three-spot method, The positions of the in spot and the side spot can be optimized according to each recording medium.
[0006]
On the other hand, using a two-wavelength laser light source (two-wavelength LD) in which two laser light sources corresponding to the respective wavelength bands of DVD and CD are arranged adjacently and integrated into one package, an optical disc having a different track pitch is used. For example, a method of applying a tracking servo is disclosed (for example, see Patent Document 1).
[0007]
[Patent Document 1]
JP 2001-250250 A
[Problems to be solved by the invention]
However, in an optical pickup using a two-wavelength laser light source (two-wavelength LD), laser beams having different wavelengths read information on an optical disk via the same optical component or write information on the optical disk. You will be in.
[0009]
In this case, if a diffraction grating as disclosed in Patent Document 1 is used, the push-pull signal by the sub-beam does not appear, so that the push-pull signal of the main beam can be detected and the tracking error by the DPP method using the DC light amount of the sub-beam. A signal can be generated. However, since the push-pull signal cannot be detected by the sub-beam, the intensity of the two sub-beams does not change with respect to the track shift of the optical recording medium, and the tracking error signal cannot be generated by the three-spot method.
[0010]
As described above, in the optical system using the two-wavelength LD, laser beams having different wavelengths pass through the same optical component. Therefore, when the diffraction grating disclosed in Patent Document 1 is used, the tracking error can only be obtained by the DPP method. Although signals cannot be generated, there is still a high demand for performing tracking servo using the three-spot method.
[0011]
There are also a method of combining a diffraction grating having wavelength selectivity, a method of combining a quarter-wave plate having wavelength selectivity and a polarization grating, in order to perform tracking by the DPP method for DVD and the three spot method for CD. . However, in the former, even if a zero-order light efficiency of 100% is obtained in scalar diffraction efficiency, the zero-order light efficiency is reduced to about 90% in an actually manufactured device. Further, the latter has a problem that the cost of the device is high and the extinction ratio of polarized light is not high, so that the risk of generating unnecessary light is high.
[0012]
Furthermore, since the wavelength bands of light to be used are different between CD and DVD, if the same diffraction grating is used for both wavelengths, the distance between the main spot and the side spot on the light receiving element will be different. Thus, in order to detect a push-pull signal in both a CD and a DVD, it is necessary to provide a dividing line of the light receiving element at a position irradiated with each spot.
[0013]
Therefore, the present invention has been proposed in view of such a conventional situation, and a tracking error signal is generated by three spots using a laser light source corresponding to a plurality of wavelengths. It is an object of the present invention to provide an optical head for providing a light spot at a fixed position and an optical recording medium recording / reproducing apparatus.
[0014]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, an optical head according to the present invention differs in an optical head that generates a tracking error signal by three spots formed on an optical recording medium according to at least two types of optical recording media. A laser light source in which two light sources for emitting light beams of wavelengths are arranged adjacent to each other, and a light source having at least a first diffraction region and a second region arranged symmetrically to the first diffraction region. Diffractive optical means for diffracting light beams of different wavelengths according to the emitted optical recording medium, and 0-order diffracted light and ± 1st-order diffracted light for each light beam different according to the optical recording medium obtained by the diffractive optical means And an error detecting means for generating a tracking error signal from the intensity of the diffracted light detected by the light detecting means.
[0015]
Here, the light detecting means detects the 0th-order diffracted light and the ± 1st-order diffracted light of the light beam having the first wavelength for the first optical recording medium and obtained in the first diffraction area at the fixed position. At the same time, the 0th-order diffracted light and ± 1st-order diffracted light of the light beam having the second wavelength for the second optical recording medium obtained in the second diffraction region are detected.
[0016]
As the diffractive optical means, a diffraction grating is used, and the diffraction grating interval is made different between the first diffraction region and the second diffraction region. In particular, when the diffraction grating interval of the first diffraction region is P ₁ , the diffraction grating interval of the second diffraction region is P ₂ , the first wavelength is λ ₁ , and the second wavelength is λ ₂ , P ₂ It is preferable to select a lattice spacing that satisfies / P ₁ = ε * λ ₂ / λ ₁ (0.9 ≦ ε ≦ 1.1).
[0017]
Further, it is preferable to change the grating angle of the diffraction grating between the first diffraction region and the second diffraction region of the diffraction grating used as the diffraction optical means. At least one of the first diffraction area and the second diffraction area of the diffractive optical means may have wavelength selectivity.
[0018]
In order to achieve the above-mentioned object, an optical recording medium recording / reproducing apparatus according to the present invention irradiates an optical recording medium with a light beam and generates a tracking error signal generated by three spots formed on the optical recording medium. In a recording / reproducing apparatus for an optical recording medium that performs a tracking operation by using a light source that emits light beams having different wavelengths according to at least two types of optical recording media, the light source is arranged symmetrically at least in the first diffraction area and the first diffraction area. Diffractive optical means having a second region to be diffracted and diffracting a light beam from a light source, light detecting means for detecting zero-order diffracted light and ± first-order diffracted light obtained by the diffractive optical means, and light detection Error detecting means for generating a tracking error signal from the intensity of the diffracted light detected by the means, and control for controlling the recording / reproducing operation based on the tracking error detected by the error detecting means. Characterized in that it comprises a stage.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
In an optical head shown as a specific example of the present invention, a grating (diffractive optical means) arranged in an optical system includes a first diffraction area and a second area symmetrically arranged with respect to the first diffraction area. With this configuration, a tracking error signal can be generated by a three-spot method in an optical head that uses a single optical system to handle light beams of a plurality of wavelengths prepared for recording and reproducing a plurality of optical recording media. Optical head.
[0020]
Hereinafter, specific examples of an optical head and an optical recording medium recording / reproducing apparatus according to the present invention will be described in detail with reference to the drawings. The specific examples described below is a preferred embodiment because technically preferable various limitations of the present invention is attached, in the following description, unless there are descriptions to limit the present invention, It is not limited to these embodiments. Hereinafter, the optical recording medium will be described as an optical disk.
[0021]
First, FIG. 1 shows an optical disk recording / reproducing apparatus 101 to which an optical head according to the present invention is applied. Optical disk recording and reproduction apparatus 101 includes a spindle motor 103 of the optical disc 102 is an optical recording medium as a driving means for rotating operation, the optical head 104 according to the present invention, and a feed motor 105 as driving means.
[0022]
The optical disk 102 is an optical disk including various types of recording / reproducing disks using optical modulation recording, such as so-called “magneto-optical recording”, “phase change recording”, and “dye recording”, and more specifically, “CD-R / RW”. "," DVD-RAM "," DVD-R / RW "," DVD + RW ", etc., or various magneto-optical recording media. Also, as the optical disc 102, an optical disc in which the recording layer is divided into at least two or more recording areas having different optimum recording and / or reproducing light powers on the recording layer, and a plurality of recording layers are laminated via a transparent substrate. Even an optical disk can be used.
[0023]
The optimum difference in the recording and / or reproducing light power on the recording layer is caused not only by the difference in the recording method itself in the optical disc, but also by the difference in the rotation speed of the optical disc (linear speed with respect to the optical head 104) (so-called N-speed disc with respect to the standard speed disc).
[0024]
Further, as the optical disk 102, a recording medium having different optimum recording and / or reproducing light power or a multilayer optical disk having at least two or more recording layers can be used. In this case, by way of the design of the multilayer optical disk, a difference occurs in the optimum recording and / or reproducing light power for each recording layer.
[0025]
The optical disk used in this specific example is a CD (optical disk 102a) using laser light in the 780 nm band as recording / reproducing light, and a DVD (optical disk 102b) using laser light in the 650 nm band as recording / reproducing light.
[0026]
The drive of the spindle motor 103 is controlled by a system controller 107 and a servo control circuit 109 also as disc type discriminating means according to the disc type, and is driven at a predetermined rotation speed for each disc.
[0027]
The optical head 104 irradiates the recording layer of the optical disc 102 with a light beam, and detects the light beam reflected by the recording layer. Further, the optical head 104, based on the reflected light from the recording layer of the optical disc 102, and detects various light beams, which will be described later, supplies a signal corresponding to the light beam to a preamplifier section 102. The optical system of the optical head 104 will be described in detail with reference to FIG.
[0028]
The output of the preamplifier unit 102 is sent to the signal conversion / demodulation unit and the ECC block 108. The signal modulation / demodulation unit and the ECC block 108 modulate and demodulate a signal and add an ECC (error correction code). The optical head 104 irradiates the recording layer of the rotating optical disc 102 with light in accordance with a command from the signal modulation / demodulation unit and the ECC block 108 to record or reproduce a signal on or from the optical disc 102.
[0029]
The preamplifier unit 120 is configured to generate a focus error signal, a tracking error signal, an RF signal, and the like based on a signal corresponding to each light beam. The servo control circuit 109, the signal modulation / demodulation unit, the ECC block 108, and the like perform predetermined processing such as demodulation and error correction based on these signals according to the type of optical recording medium to be recorded or reproduced. Is
[0030]
The demodulated recording signal is sent to an external computer 130 or the like via the interface 111 if the optical disk 102 is for data storage of a computer, for example. The external computer 130 or the like can receive a signal recorded on the optical disc 102 as a reproduction signal.
[0031]
If the optical disk 102 is a so-called “audio-visual” disk, the digital-to-analog conversion is performed by the D / A conversion unit of the D / A / A / D converter 112 and supplied to the audio-visual processing unit 113. The signal supplied to the audiovisual processing unit 113 is subjected to audio / video signal processing in the audiovisual processing unit 113, and is transmitted to an external imaging and projection device via the audiovisual signal input / output unit 114.
[0032]
The optical head 104 is moved by a feed motor 105 to a predetermined recording track on the optical disk 102. The servo control circuit 109 controls the spindle motor 103, the feed motor 105, and the driving in the focusing direction and the driving direction in the tracking direction of the two-axis actuator that holds the objective lens serving as the light focusing unit in the optical head 104. Done.
[0033]
The servo control circuit 109 operates an optical coupling efficiency variable element disposed in the optical head 104, and controls the optical coupling efficiency in the optical head 104, that is, the total amount of light flux emitted from a laser light source such as a semiconductor laser device and the optical disc 102. Control is performed so that the ratio with the amount of light condensed upward changes in the recording mode, the reproduction mode, or according to the type of the optical disc 102.
[0034]
The laser controller 121 controls the laser light source of the optical head 104. In particular, in this specific example, control is performed to make the output power of the laser light source different between the recording mode and the reproduction mode, or according to the type of the optical disc 102.
[0035]
In the laser control unit 121, when the optical disc 102 is selectively used from at least two or more kinds of optical discs having different optimum recording and / or reproducing light powers on the recording layer (recording methods different from each other, The disc type discrimination sensor 115 determines the type of the optical disc 102 by using any of the divided recording areas, the stacked recording layers, and those having different relative linear velocities with respect to the light flux. Determine. As the optical disk 102, there are various types of optical disks using optical modulation recording or various magneto-optical recording media as described above, and among them, recording with different recording and / or reproducing light powers optimal on the recording layer. Medium is also included. The disc type determination sensor 115 can detect the surface reflectivity of the optical disc 102 and other differences in shape and shape.
[0036]
The system controller 107 determines the type of the optical disk 102 based on the detection result sent from the disk type determination sensor 115. As a method of determining the type of the optical recording medium, there is a method of providing a detection hole in the cartridge if the optical recording medium is of a type accommodated in a cartridge.
[0037]
Further, as another example, based on information based on inventory information (Table Of Contents; TOC) recorded in pre-mastered pits or grooves at the innermost circumference of the optical recording medium, “disc type” or “recommended recording power” is used. And a recommended reproduction power ”, and a recording and reproduction light power suitable for recording and reproduction of the optical recording medium is set.
[0038]
A servo control circuit 109 serving as an optical coupling efficiency control unit is controlled by the system controller 107 to control the optical coupling efficiency of the optical head 104 according to the discrimination result of the disc type discrimination sensor 115.
[0039]
When the optical disc 102 is an optical disc in which the recording layer is divided into at least two or more recording areas having different optimum recording and / or reproducing light powers, the recording area to be recorded and / or reproduced is detected by the recording area identification means. I do.
[0040]
When a plurality of recording areas are concentrically divided according to the distance from the center of the optical disc 102, the servo control circuit 109 can be used as recording area identification means. The servo control circuit 109 uses recording and / or reproduction by, for example, detecting a relative position between the optical head 104 and the optical disk 102 (including a case where the position is detected based on an address signal recorded on the disk 102). Can be determined. Then, the servo control circuit 109 controls the optical coupling efficiency in the optical head 104 according to the determination result of the recording area using the recording and / or the reproduction.
[0041]
When the optical disc 102 is a multilayer optical disc having at least two or more recording layers having different optimum recording and / or reproducing light powers, the recording layer to be used for recording and / or reproduction is determined by the recording layer identification means. The servo control circuit 109 can be used as the recording layer identification means. The servo control circuit 109 can detect a recording layer on which recording and / or reproduction is to be performed, for example, by detecting a relative position between the optical head 104 and the optical disk 102. The servo control circuit 109 controls the optical coupling efficiency of the optical head 104 according to the result of discriminating the recording layer that uses recording and / or reproduction.
[0042]
The information on the type, recording area, and recording layer of these optical discs can also be determined by reading inventory information such as so-called TOC recorded on each optical disc.
[0043]
Next, FIG. 2 shows an optical system 1 of an optical head 104 of an optical disk recording / reproducing apparatus shown as a specific example of the present invention. The optical head optical system 1 includes a semiconductor laser element 11 for irradiating a laser beam of a 780 nm band for CD and a laser beam of a 650 nm band for DVD as a forward optical system, a diffraction grating 12, and a polarizing beam splitter 13. And a collimator lens 14 for converting incident light into a parallel light beam, and an objective lens 15, and irradiates a laser beam emitted from a light source onto the surface of the optical disk 102 (optical disk 102a or 102b). A reflection mirror 16 for changing the direction of the optical axis may be provided in the middle of the optical path. The optical head shown as this specific example employs a three-beam method as a tracking method. Therefore, although not shown, the laser light emitted from the semiconductor laser element 11 as a laser light source is split into three beams by a diffraction grating (grating) or the like. Here, the diffraction grating 12 may be located between the collimator lens 14 and the objective lens 15 as shown in FIG.
[0044]
Further, the optical head optical system 1 has, as a return optical system, a converging lens 17 for condensing the reflected laser light that has passed through the polarization beam splitter 13, a cylindrical lens 18, and a photodetector 19; The reflected laser light reflected by the board 102b is detected by the photodetector 19.
[0045]
Subsequently, the diffraction grating 12 used in this example will be described in detail with reference to FIG.
[0046]
The diffraction grating 12 includes a diffraction region 12b and a diffraction region 12a whose grating intervals and grating angles are different from each other. Of the two regions, two diffraction regions 12a are arranged at symmetrical positions across the diffraction region 12b. ing.
[0047]
In this specific example, the diffraction area 12a is used to diffract laser light for a DVD (optical disc 102a) using a 650 nm band as recording / reproducing light, and the diffraction area 12b is a CD using a 780 nm band as recording / reproducing light. It is used to diffract the laser light for (optical disc 102b). Hereinafter, the grating interval (grating pitch) of the diffraction region 12a is represented by P ₁ and the grating angle is θ ₁ , the grating interval (grating pitch) of the diffraction region 12b is represented by P ₂ , and the grating angle is represented by θ ₂ . These values of each grating interval and each grating angle are parameters determined according to the laser light wavelength to be used.
[0048]
FIGS. 5 and 6 show the effective range of the laser beam diffracted in each region of the diffraction grating 12. 5, the grating pitch CD laser beam resulting diffracted in the diffraction region 12a of the P ₁ and the DVD laser beam 0-order diffracted light of the diffraction area 12a, the focal spot diameter of the objective lens of ± 1-order diffracted light described ing.
[0049]
On the other hand, FIG. 6 shows the focal light diameter of the 0th-order diffracted light and ± 1st-order diffracted light on the objective lens corresponding to the grating pitch P1 of the diffraction region 12b. The diffraction angle due to the grating pitch P1 is proportional to the wavelength.
[0050]
Here, the spot D ₀ indicates the spot of the 0th-order diffracted light of the DVD laser light, the spot D ₊₁ and the spot D _-1 indicate the spot of the ± 1st-order diffracted light of the DVD laser light, and the spot C ₀ indicates the CD. The spots of the 0th-order diffracted light of the laser light for CD are shown, and the spots C _{+ 1} and C- ₁ are the spots of the ± first-order diffracted light of the laser light for CD.
[0051]
The light beam diameter (beam spot) of the light beam irradiated on the optical disc on the diffraction grating is determined by the outer diameter of the objective lens 15, and its position is determined by the longer the wavelength, the longer the diffraction angle if the grating pitch of the diffraction grating 12 is constant. Is big. In the CD (780 nm band) and the DVD (650 nm band), since the wavelength used for CD is long, the spot position of the diffracted light of the laser light for CD must be shifted away from the diffracted light of the laser light for DVD. become.
[0052]
5 and 6 show that a diffraction spot is formed on the diffraction grating 12, but actually, for the sake of explanation, the light beam (spot position) immediately after passing through the diffraction grating is diffracted. This is shown in association with each area of the lattice.
[0053]
Here, the manner in which the laser light passing through the diffraction grating 12 is diffracted and the diffracted light shifts between the CD laser light and the DVD laser light is schematically shown. FIGS. 7 and 8 show, for the sake of explanation, an essential part of the optical system shown in FIG. FIG. 7 shows how laser light emitted from the semiconductor laser element 11 is diffracted in the region 12a, and FIG. 8 shows how laser light is diffracted in the region 12b.
[0054]
Laser light emitted from the semiconductor laser element 11 is diffracted by the diffraction grating 12 to generate 0th-order diffracted light and ± 1st-order diffracted light. At this time, diffraction spots are generated at different positions depending on the incident wavelength.
[0055]
By diffracting two laser beams emitted from the semiconductor laser element 11 using the diffraction grating 12 having a plurality of regions having different lattice intervals and lattice angles, a main beam generated from each laser beam is obtained. And the focus position of the side beam can be separated.
[0056]
FIGS. 9A and 9B show spot lights detected by the photodetector 19 in the optical head optical system 1 using the diffraction grating 12. The light detector 19 includes light receiving elements 191, 192, and 193, and detects reflected light on the optical disc of the diffracted light spot of the main beam and the side beam diffracted by the diffraction grating 12 by the light receiving elements. In FIG. 9, the spot is a spot where the diffraction area 12a is used for DVD and the diffraction area 12b is used for CD. The light receiving element 191 has light receiving areas 191a to 191d, the light receiving element 192 has light receiving areas 192a and 192b, and the light receiving element 193 has areas 193a and 193b.
[0057]
In this specific example, the spot on the light receiving element is detected by being rotated by 90 ° to detect a focus error by the astigmatism method. In other words, the spots shown in FIGS. 9A and 9B are such that the spot aC- ₁ is the reflected light of the -1st-order diffracted light of the CD laser light applied to the diffraction area 12a on the optical disc, and the spot aD- ₁ is the spot aD- _1. This is the reflected light of the minus first-order diffracted light of the DVD laser light applied to the diffraction area 12a on the optical disk. Thus, the reflected light on the optical disk is rotated by 90 ° and received by the light receiving area 192. The spot aD _{+ 1} reflects the + 1st-order diffracted light of the DVD laser light irradiated on the diffraction area 12a on the optical disc, and the spot aC _{+ 1} reflects the + 1st-order diffracted light of the CD laser light irradiated on the diffraction area 12a on the optical disc. Light.
[0058]
In addition, a spot bC- ₁ shown in FIG. 9B is a reflected light of the -1st-order diffracted light of the CD laser light applied to the diffraction area 12b on the optical disc, and a spot bD- ₁ is applied to the diffraction area 12b. This is reflected light of the -1st-order diffracted light of the DVD laser light on the optical disk. Further, the spot _{bD + 1} is the reflected light in the +1 disc order diffracted light of the DVD laser beam irradiated to the diffraction area 12b, spot _{bC + 1} is the CD laser beam irradiated to the diffraction area 12b +1 order diffracted light This is reflected light from the optical disk.
[0059]
In this way, tracking can be performed on both CD and DVD optical disks by the same light receiving element and in the same pattern.
[0060]
Subsequently, for each light-receiving element provided at a fixed position as described above, determination of the optimum lattice spacing and lattice angle for irradiating the diffracted light of both the laser light for CD and the DVD to the appropriate position. The method will be described. If the position of the side spot is different between the CD and the DVD, it is necessary to separately provide the dividing line for the CD spot and the DVD spot. Therefore, the grating interval between the diffraction regions 12a and 12b is selected so that the side spot positions of the CD and DVD coincide on the light receiving element.
[0061]
The grating interval (grating pitch) of the diffraction region 12a is P ₁ , the grating angle is θ ₁ , the grating interval (grating pitch) of the diffraction region 12b is P ₂ , the grating angle is θ _2, and the used wavelength of the optical disk used is Assuming λ ₁ and λ ₂ , the condition at that time is expressed by the following equation.
[0062]
P ₂ / P ₁ = λ ₂ / λ ₁
[0063]
By designing the grating pitch so as to satisfy the above condition, the side spot positions on the light receiving element can be matched. However, in practice, the condition that satisfies the above equation is a theoretical value, and when various errors such as dimensional tolerance are considered, the following equation is obtained.
[0064]
P ₂ / P ₁ = ε * λ ₂ / λ ₁ (0.9 ≦ ε ≦ 1.1)
[0065]
Thereby, as shown in FIG. 9, the spot position on the light receiving element can be substantially matched between when the laser light for CD is used and when the laser light for DVD is used.
[0066]
By using the two regions of the divided diffraction grating in correspondence with the CD side and the DVD side by utilizing the difference in the wavelength band of the CD / DVD, recording and reproduction can be performed with this optical head. The irradiation position for irradiating the side spot on the fixed light receiving element can be easily optimized in accordance with a suitable optical disc.
[0067]
However, even though the DVD laser beam uses the diffraction region 12a, the DVD laser beam is also diffracted in the diffraction region 12b at the central portion of the main beam, and a diffraction laser beam is generated. Similarly, the main beam is diffracted by the diffraction region 12a, and a diffracted laser beam is generated at the same time. Diffracted light generated in a diffraction area not used by each of these discs slightly affects the tracking error signal, and is therefore preferably suppressed as much as possible.
[0068]
Therefore, in this specific example, the influence of unnecessary light is suppressed by giving wavelength selectivity to optically select another wavelength in each region. As an example, the phase depth of the grating in the diffraction region 12a is set to a depth at which ± 1st-order diffracted light does not occur in the CD wavelength band (780 nm). The phase depth of the grating of the diffraction region 12b is set to a depth at which ± 1st-order diffracted light is not generated in the DVD wavelength band (650 nm). Thereby, the influence of unnecessary light of other light beams can be suppressed.
[0069]
Further, DVD has three different disc standards such as ± R / RW and −RAM, and ± R / RW and −RAM have different track pitches. As described above, the push-pull is detected by significantly deteriorating the MTF of the ± 1st-order diffracted light so that the present invention can be widely applied to an optical disk using the recording / reproducing laser beam of the same wavelength band but having a different track pitch. There is also a method in which the push-pull of the zero-order diffracted light is detected so that the DC offset due to the lens shift is canceled by the DC offset of the ± first-order diffracted light.
[0070]
Also, for three different types of DVDs, there is a method of significantly deteriorating the MTF (Modulation Transfer Function) of the ± 1st-order diffracted light spot diffracted in the area 12a.
[0071]
As the method, for example, as shown in FIG. 10 (a), constituting a combination of a region 12a, and two additional grating patterns 12a ₁ formed of a diffraction grating pattern of the grating pattern 12a _2. As shown in FIG. 10B, the concave portions 121 and the convex portions 122 are alternately arranged in the lattice patterns 12a ₁ and 12a ₂ , and the concave portions 121 and the convex portions 122 are further arranged between adjacent lattice patterns. They are arranged adjacently. As a result, the MTF of the ± 1st-order diffracted light spot to be diffracted is significantly deteriorated, and the influence of unnecessary light is suppressed.
[0072]
As described above, according to the optical head optical system 1, the performance of an optical head in which two types of laser light sources (two-wavelength laser light sources) for irradiating two types of laser beams corresponding to the use bands of two optical disks are configured as one package. Can be used without impairment, and a beam splitter or the like for combining two wavelengths can be omitted, and the number of parts can be reduced. Further, since the tracking error signal of CD and DVD can be detected by the same light receiving element, the size of the optical head itself can be greatly reduced as compared with the conventional two-wavelength laser.
[0073]
Further, it is possible to provide an optical head for both CD and DVD optical discs, which enables tracking by a three-spot method using a two-wavelength laser. Further, it is possible to provide an optical head that outputs a tracking servo signal using the DPP method for DVD and the three spot method for CD.
[0074]
It should be noted that the present invention is not limited to only the above-described embodiment, and it is needless to say that various changes can be made without departing from the gist of the present invention.
[0075]
【The invention's effect】
As described in detail above, the optical head according to the present invention is an optical head including a light source that emits light beams of different wavelengths according to at least two types of optical recording media, and includes a first diffraction region and the first diffraction region. A plurality of wavelengths corresponding to a plurality of wavelengths is provided by providing at least a second region symmetrically disposed in the first diffraction region and diffractive optical means for diffracting light beams of different wavelengths according to the optical recording medium emitted from the light source. It is possible to generate a tracking error signal using the three-spot method with respect to the laser light source, and to provide a light spot at a fixed position of the light receiving element regardless of the optical recording medium. As a result, the beam splitter and the light receiving element can be omitted, the number of components can be reduced, and the overall size can be significantly reduced as compared with the conventional product.
[0076]
Further, according to the recording / reproducing apparatus for an optical recording medium according to the present invention, it is possible to generate a tracking error signal using a three-spot method for a laser light source corresponding to a plurality of wavelengths. A light spot can be given at a predetermined position.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating an optical disc recording / reproducing apparatus shown as a specific example of the present invention.
FIG. 2 is a configuration diagram illustrating an optical system of an optical head of the optical disc recording / reproducing apparatus.
FIG. 3 is a configuration diagram illustrating a diffraction grating of the optical head.
FIG. 4 is a diagram illustrating an optical path of a light beam diffracted by the diffraction grating.
FIG. 5 is a schematic diagram illustrating spots of a diffracted light beam diffracted by a region 12a of the diffraction grating.
FIG. 6 is a schematic diagram illustrating spots of a diffracted light beam diffracted by the diffraction grating region 12b.
FIG. 7 is an enlarged view showing a main part of the optical system shown in FIG. 3 and the vicinity of the optical disk in an enlarged manner.
FIG. 8 is an enlarged view showing a main part of the optical system shown in FIG.
FIG. 9 is a diagram illustrating spot light that is diffracted by the diffraction grating, reflected by an optical disk, and detected by a photodetector.
FIG. 10 is a diagram illustrating another specific example of the diffraction grating.
[Explanation of symbols]
Reference Signs List 1 optical head optical system, 11 semiconductor laser element, 12 diffraction grating, 13 polarization beam splitter, 14 collimator lens, 15 objective lens, 16 reflection mirror, 17 focusing lens, 18 cylindrical lens, 19 photodetector, 102a, 102b optical disk

Claims (7)

In an optical head that generates a tracking error signal from three spots formed on an optical recording medium,
A laser light source in which two light sources that emit light beams having different wavelengths according to at least two types of optical recording media are arranged adjacent to each other;
Diffractive optical means having at least a first diffraction area and a second area symmetrically arranged with respect to the first diffraction area, and diffracting a light beam having a different wavelength according to an optical recording medium emitted from the light source. When,
Light detecting means for detecting 0th-order diffracted light and ± 1st-order diffracted light for each light beam different according to the optical recording medium obtained by the diffractive optical means,
An optical head comprising: an error detection unit that generates a tracking error signal from the intensity of the diffracted light detected by the light detection unit. The light detecting means detects the 0th-order diffracted light and the ± 1st-order diffracted light of the light beam having the first wavelength for the first optical recording medium and obtained in the first diffraction area at the fixed position. And detecting the 0th-order diffracted light and the ± 1st-order diffracted light of the light beam having the second wavelength for the second optical recording medium obtained in the second diffraction area. Optical head as described. 2. The optical head according to claim 1, wherein said diffraction optical means is a diffraction grating, and said first diffraction region and said second diffraction region have different diffraction grating intervals. The diffractive optical means sets a diffraction grating interval of the first diffraction region to P ₁ , sets a diffraction grating interval of the second diffraction region to P ₂ , sets the first wavelength to λ ₁ , and sets the second wavelength to when the λ _2,
P ₂ / P ₁ = ε * λ ₂ / λ ₁ (0.9 ≦ ε ≦ 1.1)
4. The optical head according to claim 3, wherein 2. The optical head according to claim 1, wherein the diffractive optical means is a diffraction grating, and the first diffraction region and the second diffraction region have different diffraction grating angles. 2. The optical head according to claim 1, wherein at least one of the first diffraction area and the second diffraction area of the diffractive optical means has wavelength selectivity. An optical recording medium recording / reproducing apparatus that irradiates an optical recording medium with a light beam and performs a tracking operation based on a tracking error signal generated by three spots formed on the optical recording medium,
A light source that emits light beams of different wavelengths according to at least two types of optical recording media;
Diffractive optical means for diffracting a light beam from the light source, the diffractive optical means having at least a first diffraction area and a second area symmetrically arranged with respect to the first diffraction area;
Light detection means for detecting the 0th-order diffraction light and ± 1st-order diffraction light obtained by the diffraction optical means,
Error detection means for generating a tracking error signal from the diffracted light intensity detected by the light detection means,
An optical recording medium recording / reproducing apparatus, comprising: control means for controlling a recording / reproducing operation based on the tracking error detected by the error detecting means.

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