JP2004318958A - Optical head, and recording and/or reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain good track determination and track error signals without increasing the number of components or complicating the constitution of components. <P>SOLUTION: A diffraction optical element 17 separates a luminous flux emitted from a light emission means 10 into a main luminous flux to form a main spot and a pair of sub-luminous fluxes which hold the main spot to form a pair of subspots, and separates the pair of sub-luminous fluxes into a pair of half sub-luminous fluxes to form a pair of half subspots in positions shifted in a direction orthogonal to a recording track. Thus, based on optical detection signals which an optical detection means 16 receives the five separated luminous fluxes to output, good track determination and track error signals are obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical head for writing and / or reading information signals on and from an optical recording medium, and recording and / or reproducing and / or reproducing information signals on and from an optical recording medium using such an optical head. It relates to a playback device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an optical recording medium such as an optical disk or a magneto-optical disk has been proposed, and a recording and / or reproducing apparatus for recording and / or reproducing an information signal on such an optical recording medium has been proposed. In this recording and / or reproducing apparatus, optical recording media based on various systems are used. In such a recording and / or reproducing apparatus, an optical head is used to write and / or read information signals on an optical recording medium.
[0003]
The optical head has a light source such as a semiconductor laser, and is configured so that a light beam emitted from the light source is condensed on a signal recording surface of an optical recording medium by an objective lens and irradiated. The optical head writes an information signal on the signal recording surface by irradiating a light beam on the signal recording surface, and detects a reflected light beam reflected on the signal recording surface, thereby detecting the signal recording surface. It is configured to read the information signal recorded in the.
[0004]
The optical head writes and reads information signals along spirally or concentrically formed grooves or lands on a signal recording surface of an optical recording medium.
[0005]
On the other hand, in optical recording media, the density of information signals to be recorded has been increased. For example, as a so-called “ROM disk” for reproduction only, while using an optical disk having a diameter of 120 mm as in the case of a “compact disk (CD)” (trade name), the recording capacity is about 7 "DVD" (trade name) which has been doubled to 4.7 GB has been commercialized.
[0006]
Higher recording densities are also progressing in rewritable optical recording media on which information signals can be written, and so-called "DVD-RAM" has been commercialized as rewritable "DVD". This “DVD-RAM” is not a conventional method of recording an information signal only on one of a groove and a land, but recording an information signal on both a groove and a land in order to increase the density of an information signal to be recorded. The “land groove recording method” is adopted.
[0007]
[Patent Document 1]
JP-A-2002-56568 (page 3-4, FIG. 22)
[0008]
[Problems to be solved by the invention]
By the way, in the high-density rewritable disc adopting the above-mentioned “land / groove recording method”, the following problems may occur due to the fact that the widths of the land and the groove are set to be substantially equal.
[0009]
That is, when the “land recording method” in which recording is performed only on lands using an optical disk having lands wider than grooves is adopted, as shown in FIG. 23, a track error signal (TE) and return light (“ The sum signal (SUM) of the "3 spot method" when using the "3 spot method" has a relationship that the phase is shifted by (1/4) cycle when one cycle from one group to the next group is used.
[0010]
Therefore, when tracking control is performed so that the track error signal (TE) becomes 0, the state in which the track error signal (TE) becomes 0 depends on whether the light beam is irradiated on the land portion or on the groove. There are two cases, that is, the case where there is, and these two cases can be distinguished by the level of the sum signal (SUM).
[0011]
As described above, the signal for distinguishing between the case where the light beam is irradiated on the land and the case where the light beam is irradiated on the groove is a “track discrimination signal” or a “cross-track signal (CTS)”. ) ". As such a “track discrimination signal”, the level of the sum signal (SUM) is different from the case where the light beam is irradiated on the land portion and the case where the light beam is irradiated on the groove portion as in the case where the “land recording method” is adopted. 24, the AC component of the sum signal (AC-SUM) can be used as shown in FIG. 24. The AC component of the sum signal is shown in FIG. As shown, the track discrimination signal has a phase difference of 90 degrees from the track error signal.
[0012]
In the recording and / or reproducing apparatus, when the “land recording method” is adopted, even when a seek operation is performed at a high speed by using such two signals of the track error signal and the AC component of the sum signal, It is possible to accurately know in which direction and how many tracks the spot has moved with respect to the recording track, and it is possible to stably count the number of track crossings and perform the tracking servo pull-in operation.
[0013]
However, when the “land-groove method” is adopted, the land and the groove are usually set to have substantially the same width as each other in order to optimize the recording / reproducing characteristics. As a result, as shown in FIG. 25, the sum signal in the above description is substantially equal between the case where the light beam is irradiated on the land and the case where the light beam is irradiated on the groove. Cannot generate a track discrimination signal.
[0014]
As a result, it is difficult to access a predetermined recording track at one time, especially during a high-speed seek operation frequently performed in an application such as an external storage device, a commercial video recording device, an editing device, and the access time becomes longer. There was a problem.
[0015]
Further, as a format for increasing the density of information signals recorded on an optical recording medium without employing the “land-groove method”, there is a so-called “DVD + RW” or the like. Although the information signal is recorded, the AC component (AC-SUM) of the sum signal is smaller than the direct current (DC) component by the fact that the widths of the land and the group are set substantially equal to each other. Often there was only a percentage, and again had similar problems.
[0016]
In the above-described recording and / or reproducing apparatus, a push-pull signal obtained by a (differential) push-pull method is generally used as a track error signal on a writable optical recording medium.
[0017]
That is, in this writable optical recording medium, a guide groove called a groove is usually formed in the disk substrate, and based on a push-pull signal obtained from a reflected light beam reflected and diffracted by the groove, an optical head is formed. Tracking servo is performed. The portion between the grooves is generally called a land.
[0018]
The push-pull signal receives a reflected light beam reflected and diffracted by the groove by a photodetector having a light receiving surface divided into two by a dividing line corresponding to a direction parallel to the recording track, and the two divided light receiving surfaces It is obtained by taking the difference between the outputs from. When the wavelength of the light beam emitted from the light source is λ, the push-pull signal has a maximum phase depth of about λ / 8 when the phase depth of the groove is λ / 4. However, such a push-pull signal cannot be obtained.
[0019]
For this reason, in optical recording media such as CDs and MDs, a radial contrast signal obtained by a three-beam method in which the phase depth of a groove is maximum at about λ / 4 is generally used as a track error signal. Note that the radial contrast is a variation width of the total signal level of the reflected light flux when crossing the recording track in the standard state, and the light amount on the land is 11 and the light amount on the groove is 1 g. When you do
Radial Contrast = 2 | (ll-lg) | / (ll + lg)
Is represented as
[0020]
On the other hand, in a read-only optical recording medium such as a DVD-ROM, a signal obtained by a Differential Phase Detection (DPD) method or a heterodyne method is used as a track error signal. In this case, the best signal can be obtained when the phase depth of the pit recorded on the disk is about λ / 4.
[0021]
In a writable optical recording medium such as DVD + R / RW, DVD-R / RW, and DVD-RAM, the groove depth of the recording track is set to about λ / 6 to λ / 12, so that a track error is caused. As the signal, the above-described push-pull signal is generally used.
[0022]
On the other hand, in a read-only optical recording medium such as the DVD-ROM described above, the phase depth of the pits is set to around λ / 4, so that the track error signal of the DPD method or the heterodyne method is used. Detection is mandatory.
[0023]
For this reason, in the recording and / or reproducing apparatus, the tracking servo of the optical head using the push-pull signal described above cannot be performed for the read-only optical recording medium due to the difference in the phase depth. In order to reproduce the above-mentioned writable optical recording medium in a disc player of the type, special conditions are required for the recording film so that a track error signal by the DPD method can be generated from the recorded mark after recording. There was a problem.
[0024]
In the above-described optical recording medium such as a DVD-RAM, in order to increase the recording density, the recording track is formed on both the land and the group instead of the conventional method of forming the recording track on only one of the land or the group. A land-groove recording method is employed.
[0025]
However, in an optical recording medium employing such a land-groove recording method, lands and grooves are usually set to have substantially the same width as each other in order to optimize recording / reproducing characteristics. For this reason, in the recording and / or reproducing apparatus, the amount of light is substantially equal between the time when the light beam is irradiated on the land and the time when the light beam is irradiated on the groove, and whether the light beam is on the land or on the groove. (See, for example, Patent Document 1).
[0026]
In this case, it is difficult to access a predetermined recording track at one time, especially during a high-speed seek operation frequently performed in an application such as an external storage device, a commercial video recording device, an editing device, and the access time becomes longer. .
[0027]
Also, a DVD + R / RW or DVD-R / RW adopting a groove method instead of the land-groove method described above, a short wavelength light source having an emission wavelength of about 405 nm, and a high NA having a numerical aperture (NA) of about 0.85. By using an objective lens, even in a writable optical recording medium such as a new optical disk format such as a Blu-ray Disc, which achieves a higher recording density, it is difficult to determine whether the luminous flux is on a land due to a demand for high-speed access. There is a demand for discriminating whether the track is located above.
[0028]
However, if the track pitch becomes narrower in recent years and it becomes difficult to make a difference between the land and the groove, the range in which the intensity is modulated in the spot becomes narrower. The amount of light becomes almost equal between the time of irradiation and the time of irradiation.
[0029]
For this reason, even in an optical recording medium employing the groove system, a problem occurs that it is difficult to generate the above-described track determination signal. Further, when the intensity modulation becomes difficult due to the shallow groove, similarly, there arises a problem that it is difficult to generate the track discrimination signal.
[0030]
Therefore, the present invention has been proposed in view of the above-described circumstances, and is intended to provide a track that enables high-speed access to an optical recording medium without increasing the number of components or complicating the configuration of components. A discrimination signal can be detected, and a good track error signal can be detected by a method other than the differential phase difference method even for an optical recording medium in which a track error signal cannot be satisfactorily obtained by the push-pull method. An object of the present invention is to provide an optical head capable of improving overall recording and / or reproducing characteristics for optical recording media having different phase depths, and a recording and / or reproducing apparatus including such an optical head. And
[0031]
[Means for Solving the Problems]
In order to achieve this object, an optical head according to the present invention includes a light emitting unit having at least one light source for emitting a light beam, and a light condensing unit for condensing the light beam emitted from the light emitting unit on an optical recording medium. Means and an optical path, which is arranged in a light path leading to a condensing means for the light beam emitted from the light emitting means, and forms the main spot for recording and / or reproducing a signal on a recording track of the optical recording medium. A main beam and a pair of sub-beams forming a pair of sub-spots sandwiching the main spot are separated into a pair of sub-beams, and a pair of half sub-spots is shifted to a position orthogonal to the recording track. A diffractive optical element for separating into a pair of semi-sub-beams to be formed, a main light-receiving unit for receiving a main beam among reflected light beams reflected by the optical recording medium, and a pair of sub-light-receiving units for receiving a pair of sub-beams; Photodetector with It is characterized in that it comprises a means.
[0032]
As described above, in the optical head according to the present invention, the diffractive optical element converts the light beam emitted from the light emitting unit into a main light beam forming a main spot and a pair of sub-spots forming a pair of sub-spots across the main spot. And splits the pair of sub-beams into a pair of half sub-beams forming a pair of half sub-spots at positions shifted in a direction orthogonal to the recording track. A good track discrimination signal and a good track error signal can be obtained based on a photodetection signal output by the photodetector receiving the separated light flux.
[0033]
Further, the recording and / or reproducing apparatus according to the present invention comprises: a light emitting unit having at least one light source for emitting a light beam; and a condensing unit for condensing the light beam emitted from the light emitting unit on an optical recording medium. A light beam emitted from the light emitting means, which is arranged in an optical path leading to the light condensing means, and forms a main spot for forming a main spot for recording and / or reproducing a signal on a recording track of an optical recording medium. A light beam and a pair of sub-beams forming a pair of sub-spots with the main spot interposed are formed, and a pair of sub-beams are formed at positions shifted from the pair of sub-beams in directions perpendicular to the recording tracks. A diffractive optical element that separates into a pair of semi-sub beams, a main light receiving unit that receives the main beam among the reflected beams reflected by the optical recording medium, and a pair of sub light receiving units that receive the pair of sub beams. Light detection hand An optical head comprising: a signal processing unit that generates various signals based on a light detection signal received and output by the light detection unit; and a drive control of the optical head based on a signal generated by the signal processing unit. And a drive control means for performing the following.
[0034]
As described above, in the recording and / or reproducing apparatus according to the present invention, the diffractive optical element converts the light beam emitted from the light emitting means into a main light beam forming a main spot and a pair of sub spots with the main spot interposed therebetween. And a pair of sub-beams, each of which separates the pair of sub-beams into a pair of half sub-beams forming a pair of semi-sub spots at positions shifted in a direction orthogonal to the recording track. The signal processing means generates a track discrimination signal and a track error signal based on a light detection signal which is received and output by the photodetection means, and outputs the track discrimination signal and the track error signal. Thus, the drive control of the optical head can be appropriately performed by the drive control means.
[0035]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an optical head and a recording and / or reproducing apparatus to which the present invention is applied will be described in detail with reference to the drawings.
[0036]
A recording and / or reproducing apparatus to which the present invention is applied is, for example, an optical recording medium recording and reproducing apparatus for recording and reproducing an information signal on an optical disk selected from a plurality of optical disks of different types.
[0037]
Specifically, an optical recording medium recording / reproducing apparatus 101 shown in FIG. 1 includes a spindle motor 103 as a driving unit for rotating an optical disk 102 as an optical recording medium, and an optical pickup device 104 as an optical head to which the present invention is applied. And a feed motor 105 as its driving means.
[0038]
Here, the spindle motor 103 is driven and controlled by a system controller 107 also serving as a disc type discriminating unit and a servo control circuit 109, and is driven at a predetermined rotation speed.
[0039]
Further, as the optical disk 102, various types of optical disks (including so-called “magneto-optical recording”, “phase-change recording”, and “dye recording”) which are recording / reproducing disks using optical modulation recording (for example, so-called “CD”) -R / RW "," DVD-RAM "," DVD-R / RW "," DVD + RW ", etc.) or various magneto-optical recording media.
[0040]
Further, the optical disc 102 may be selectively used from at least two or more types of optical discs having different optimum recording and / or reproducing light powers on the recording layer. An optical disc in which a recording layer is divided into at least two or more recording areas different from each other, and an optical disc in which a plurality of recording layers (recording layers) are stacked via a transparent substrate can also be used.
[0041]
The optimum difference in the recording and / or reproduction light power on the recording layer is caused not only by the difference in the recording method itself on the optical disc, but also by the difference in the rotational speed of the optical disc (linear speed with respect to the optical pickup device) (so-called, N-speed disc with respect to the standard-speed disc).
[0042]
Further, as the optical disk 102, a multilayer optical disk having at least two or more recording layers having different or different optimal recording and / or reproducing light powers can be used. In this case, the optimum recording and / or reproducing light power for each recording layer is different depending on the design of the multilayer optical disc.
[0043]
The wavelength of the recording and / or reproducing light of these optical discs may be, for example, 405 nm, or about 400 nm to about 780 nm.
[0044]
The optical pickup device 104 irradiates the recording layer of the optical disc 102 with a light beam and detects the reflected light of the light beam from the recording layer. Further, the optical pickup device 104 detects various light beams as described later based on the reflected light from the recording layer of the optical disk 102, and supplies a signal corresponding to each light beam to the preamplifier unit 120.
[0045]
The output of the preamplifier 120 is sent to the signal modulator / demodulator 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 pickup device 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. By such light irradiation, recording or reproduction of a signal with respect to the optical disk 102 is performed.
[0046]
The preamplifier unit 120 is configured to generate a focus error signal, a track error signal, an RF signal, and the like based on a signal corresponding to each light beam. Depending on the type of the optical recording medium to be recorded or reproduced, predetermined processing such as demodulation and error correction based on these signals is performed by the servo control circuit 109, the signal modulation / demodulation unit, the ECC block 108, and the like. Is
[0047]
As a result, the demodulated recording signal is sent to the external computer 130 or the like via the interface 111 if the optical disk 102 is for data storage of a computer, for example. Then, the external computer 130 and the like can receive a signal recorded on the optical disc 102 as a reproduction signal.
[0048]
If the optical disc 102 is for so-called “audio / visual”, it is digital / analog converted by the D / A converter of the D / A / A / D converter 112 and supplied to the audio / visual processor 113. And this audio. The signal supplied to the visual processing unit 113 is the audio. The audio / video signal processing is performed in the visual processing unit 113 and transmitted to an external imaging / projection device via the audio / visual signal input / output unit 114.
[0049]
The optical pickup device 104 is moved by a feed motor 105 to a predetermined recording track on the optical disc 102. The control of the spindle motor 103, the control of the feed motor 105, and the control of the driving in the focusing direction and the driving in the tracking direction of the two-axis actuator holding the objective lens serving as the light condensing unit in the optical pickup device 104 are performed by servo control, respectively. This is performed by the control circuit 109.
[0050]
In addition, the servo control circuit 109 operates an optical coupling efficiency variable element disposed in the optical pickup device 104, and emits light from a laser light source such as a semiconductor laser device or the like as a light source in the optical coupling efficiency in the optical pickup device 104. The ratio between the total amount of light flux to be emitted and the amount of light condensed on the optical disk 102 is controlled to be different between the recording mode and the reproduction mode and according to the type of the optical disk 102.
[0051]
Further, the laser control unit 121 controls a laser light source in the optical pickup device 104. In particular, in this embodiment, an operation of controlling the output power of the laser light source to be different between the recording mode and the reproducing mode and according to the type of the optical disc 102 is performed.
[0052]
Further, when the optical disk 102 is selectively used from at least two or more types of optical disks having different optimum recording and / or reproducing light powers on the recording layer (different recording methods, divided recording areas, etc.). , Or any of the stacked recording layers, and those having different relative linear velocities with respect to the luminous flux), the disc type discrimination sensor 115 determines the type of the mounted optical disc 102. Is determined. As described above, as the optical disk 102, various types of optical disks using optical modulation recording or various magneto-optical recording media are conceivable, and these are optimal recording and / or reproducing optical powers on the recording layer. Also includes different ones. The disc type determination sensor 115 detects the surface reflectance of the optical disc 102 and other differences in shape and shape.
[0053]
Then, 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.
[0054]
Further, as a method of determining the type of the optical recording medium, it is conceivable to provide a detection hole of the cartridge in the optical recording medium housed in the cartridge. Also, based on information based on inventory information (Table of Contents: TOC) recorded in, for example, a premastered pit at the innermost circumference or a groove of the optical recording medium, the “disc type” or “recommended recording power” is used. And recommended reproduction power ", and setting a recording and reproduction light power suitable for recording and reproduction of the optical recording medium.
[0055]
The servo control circuit 109 serving as an optical coupling efficiency control unit controls the optical coupling efficiency of the optical pickup device 104 according to the discrimination result of the disc type discrimination sensor 115 by being controlled by the system controller 107. The control is performed according to the type of the optical disk 102.
[0056]
When an optical disk in which a recording layer is divided into at least two or more recording regions having different optimum recording and / or reproducing light powers is used as the optical disk 102, recording and / or reproduction is performed by the recording region identification means. A recording area to be detected is detected. When the 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 the recording area identification means. The servo control circuit 109, for example, detects the relative position between the optical pickup device 104 and the optical disk 102 (including the case where the position is detected based on the address signal recorded on the disk 102), thereby recording and / or reproducing. Can be determined. Then, the servo control circuit 109 controls the optical coupling efficiency in the optical pickup device 104 according to the determination result of the recording area to be recorded and / or reproduced.
[0057]
Further, 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 recorded and / or reproduced by the recording layer identification means. Is determined. The service 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 pickup device 104 and the optical disk 102. Then, the servo control circuit 109 controls the optical coupling efficiency in the optical pickup device 104 according to the determination result of the recording layer to be recorded and / or reproduced.
[0058]
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.
[0059]
As shown in FIG. 2, the optical pickup device 104 has a structure in which each optical component is individually mounted and supported in an optical block (not shown).
[0060]
Specifically, the optical pickup device 104 includes a light source unit 10 serving as a light emitting unit, and the light source unit 10 has at least one light source that emits a light beam. In this example, as shown in FIG. 3, one light source 10a is provided, and this light source 10a is supported by a holding base 10d and housed in a package 10e.
[0061]
The light beam emitted from the light source 10a is diffracted by the diffractive optical element 17, and is separated into a light beam including a zero-order light beam and ± first-order diffracted light beams.
[0062]
Of these, the zero-order light beam is emitted from the light source 10a and proceeds as it is, and becomes a main light beam that forms a main spot for recording and reproducing information signals on the optical disk 102 on a recording track. The + 1st-order diffracted light beam is equal to the light beam emitted from the first virtual light source 10b shifted from the light source 10a, and becomes the first sub light beam forming the first sub spot. The -1st-order diffracted light beam is equal to the light beam emitted from the second virtual light source 10c shifted from the light source 10a, and becomes a second sub light beam forming a second sub spot.
[0063]
Further, the first and second sub-beams are diffracted by the diffractive optical element 17 and separated into a pair of half-sub-beams forming a pair of half-sub-spots at positions shifted in a direction orthogonal to the recording track.
[0064]
As described above, in order to separate the light beam emitted from the light source 10a into five light beams, for example, the hologram optical element shown in FIG.
[0065]
This hologram optical element is formed with a hologram pattern in which the direction of the lattice is asymmetric with respect to the center boundary line. Thereby, as shown in FIG. 5, the first and second sub-spots are formed on the signal recording surface of the optical disc 102 at positions separated from each other with the main spot on the recording track therebetween. The second sub-spot forms a pair of semi-circular semi-sub spots at positions shifted in a direction orthogonal to the recording track. The distance between the centers of the pair of semi-sub spots in the direction perpendicular to the recording track is set to be Tp / 2 when the track pitch is Tp.
[0066]
The diffractive optical element 17 is rotated around the optical axis to change the positional relationship between each sub spot and the main spot on the recording track of the optical disk 102 without changing the focus position of the main spot. It is possible to change.
[0067]
Then, in the direction orthogonal to the recording track, the distance between the spot center of the main spot and the spot center of the pair of sub-spots (in this case, the distance between the center of the pair of half sub-spots and the center of the main spot) ) Are set so that when the track pitch is Tp and n is an integer of 0 or more, n · Tp / 2 (where Tp represents the track pitch and n represents an integer of 0 or more). ing.
[0068]
When n = 0, the main spot and each sub-spot are all formed on the same recording track. In this case, the sub-spot recording track is always used for a plurality of optical discs having different track pitches. Can be in the same state.
[0069]
Note that the “track pitch (Tp)” used here means that “land-groove method” is used to record information signals on both lands and groups on an optical recording medium. Distance to land "(or the distance from one group to the next).
[0070]
The diffractive optical element may impart spherical aberration having polarities opposite to each other to the pair of sub-beams.
[0071]
When writing and / or reading information signals from an optical recording medium using the optical pickup device 104, each light beam emitted from the light source unit 10 enters the polarization beam splitter prism 11 as shown in FIG. Then, since the polarized light beam splitter prism 11 is in the S-polarized state with respect to the dielectric multilayer film, substantially all of the light amount is reflected by the dielectric multilayer film and enters the quarter-wave plate 12. The luminous flux incident on the 波長 wavelength plate 12 is converted into a circularly polarized light by transmitting through the 波長 wavelength plate 12, and is transmitted through the collimator lens 13 to form a parallel luminous flux. The light enters the lens 14.
[0072]
The polarizing beam splitter prism 11 generally includes a pair of triangular prisms that are bonded to each other to form a cube, and a dielectric multilayer film formed between these triangular prisms by vapor deposition or sputtering. . In the light beam incident on the polarizing beam splitter prism 11, the P-polarized light component for the dielectric multilayer passes through the dielectric multilayer, and the S-polarized component for the dielectric multilayer is reflected by the dielectric multilayer.
[0073]
The objective lens 14 is supported by a biaxial actuator (not shown) so as to be movable in a focus direction indicated by an arrow F in FIG. 2 and a tracking direction indicated by an arrow T in FIG. Focus on the signal recording surface. At this time, the light beams emitted from the three virtual light sources 10a, 10b, 10c are collected on the signal recording surface.
[0074]
The three reflected light beams irradiated onto the signal recording surface of the optical disk 102 and reflected by the signal recording surface pass through the objective lens 14, the collimator lens 13, and the quarter-wave plate 12, and become linearly polarized. The polarization beam splitter prism 11 is reached. In the polarizing beam splitter prism 11, the reflected light flux is in a P-polarized state with respect to the dielectric multilayer film, so that substantially all of the light passes through the dielectric multilayer film and is separated from the optical path returning to the light source unit 10. Then, the light passes through the multi-lens 15 and enters the light detecting element 16 serving as light detecting means. The multi-lens 15 is a lens in which a concave surface and a cylindrical surface are combined, extends the distance to the focal point of the reflected light beam, and causes astigmatism in the reflected light beam.
[0075]
As shown in FIG. 6, the light detection element 16 includes a main light receiving unit 18 that receives a main reflected light beam from a main spot, and a first sub light receiving unit that receives a first sub reflected light beam from a first sub spot. It comprises a section 19 and a second sub-light receiving section 20 for receiving a second sub-reflected light beam from the second sub spot.
[0076]
The main light receiving section 18 has light receiving surfaces a, b, c, and d divided into four by a dividing line corresponding to a direction parallel to the recording track and a dividing line corresponding to a direction perpendicular to the recording track. The light receiving surfaces a, b, c, and d are radially arranged through a central portion. Among them, the light receiving surfaces a, c and the light receiving surfaces b, d are diagonal to each other via the central portion of the main light receiving portion 18. And are opposed to each other. The four light receiving surfaces a, b, c, and d output independent light detection signals a, b, c, and d, respectively.
[0077]
The first sub-light receiving portion 19 has a light receiving surface e, f, g, h divided into four by a dividing line corresponding to a direction parallel to the recording track and a dividing line corresponding to a direction orthogonal to the recording track, The four light receiving surfaces e, f, g, and h are radially arranged through a central portion, and the light receiving surfaces e, g and the light receiving surfaces f, h are mutually centered on the first sub light receiving portion 19. They are arranged diagonally opposite each other via the portion. Then, independent light detection signals e, f, g, and h are output from the four light receiving surfaces e, f, g, and h, respectively.
[0078]
The second sub-light receiving unit 20 has a light receiving surface i, j, k, l divided into four by a dividing line corresponding to a direction parallel to the recording track and a dividing line corresponding to a direction orthogonal to the recording track, These four light receiving surfaces i, j, k, l are radially arranged through a central portion, and among these, the light receiving surfaces i, k and the light receiving surfaces j, l are mutually centered on the second sub-light receiving portion 20. They are arranged diagonally opposite each other via the portion. Then, independent light detection signals i, j, k, l are output from these four light receiving surfaces i, j, k, l.
[0079]
The light detection signal output from the light detection element 16 is subjected to current-voltage conversion by an amplifier (not shown) formed on the semiconductor substrate of the light detection element 16, for example, and then an arithmetic circuit or each light receiving unit It is sent to an arithmetic circuit outside the photodetector connected to 18, 19, 20. In this arithmetic circuit, each signal and the like are calculated as follows.
[0080]
RF (RF signal for main spot)
= Modulated component of (a + b + c + d)
PI (pull-in signal: focus pull-in signal: sum signal of main spot)
= A + b + c + d
FCS (focus error signal (astigmatism signal for main spot))
= (A + c)-(b + d)
MPP (push-pull signal for main spot)
= {(A + d)-(b + c)}
SPP1 (push-pull signal for first sub-spot)
= {(E + h)-(f + g)}
SPP2 (push-pull signal for second sub spot)
= {(I + 1)-(j + k)}
SRC1 (radial contrast signal for first sub-spot)
= {(E + f)-(h + g)}
SRC2 (radial contrast signal for second sub spot)
= {(I + j)-(l + k)}
SAS1 (crossing calculation signal for first sub-spot)
= {(E + g)-(f + h)}
SAS2 (crossing calculation signal for the second sub spot)
= {(I + k)-(j + 1)}
SA (spherical aberration signal)
= SAS1 + SAS2 = SAS1-(-SAS2)
SPI1 (sum signal for the first sub spot)
= E + f + g + h
SPI2 (sum signal for second sub-spot)
= I + j + k + 1
By the way, in this optical pickup device, as shown in FIG. 5, the main beam among the main beam and the pair of sub-beams separated by the diffractive optical element 17 forms a main spot on a recording track of the optical disc. The first sub-beam forms a first sub-spot at a position shifted by n · Tp / 2 in one direction perpendicular to the recording track from the spot center of the main spot, and the second sub-beam is A second sub spot is formed at a position shifted from the center of the main spot by n · Tp / 2 in another direction orthogonal to the recording track. Further, the first and second sub-spots are divided into a pair of half sub-spots at a position shifted in a direction perpendicular to the recording track, the distance between the centers of the spots being Tp / 2.
[0081]
Here, in the case where the phase depth of the pit is λ / 4, as in the above-described optical recording medium for reproduction such as a DVD-ROM or the like, when each spot crosses the recording track, it is placed on each light receiving section. FIG. 7 schematically shows a change in the light intensity distribution of the formed spot.
[0082]
As shown in FIG. 7, when the main spot traverses the recording track from the on-track state, the main spot shows a change in light intensity distribution symmetrical with respect to a dividing line corresponding to a direction parallel to the recording track, and also shows a change in the recording track. The change of the light intensity distribution symmetrical with respect to the division line corresponding to the orthogonal direction is shown.
[0083]
On the other hand, when the pair of sub-spots cross the recording track from the on-track state, the pair of sub-spots show a change in light intensity distribution symmetrical with respect to a division line corresponding to a direction parallel to the recording track, whereas FIG. 9 shows an asymmetric change in light intensity distribution in which light intensity is inverted with respect to a dividing line corresponding to a direction orthogonal to the light intensity distribution.
[0084]
In this case, since the push-pull signals MPP, SPP1, and SPP2 for the main spot, the first sub-spot, and the second sub-spot are not modulated by the track, it is not possible to obtain information on a track error from these signals. .
[0085]
Therefore, for the optical recording medium in which the phase depth of the groove is λ / 4, the first sub-light receiving portion 19 and the second sub-light receiving portion receive and output the light detection signals based on the light detection signals. A track error signal is generated by the following operation.
[0086]
RCTRK (track error signal due to radial contrast)
= SRC1-SRC2
For the optical recording medium having the above-described phase depth of λ / 4, a track determination signal is generated by the following calculation based on a light detection signal received and output by the main light receiving unit 18.
[0087]
RCCTS (track discrimination signal based on radial contrast)
= Interchange (AC) component of PI
On the other hand, in the above-described optical recording medium such as a DVD-RAM, the behavior is different from the case where the phase depth is λ / 4 since the phase depth of the groove is about λ / 6 to λ / 12. . As a representative example, when the phase depth of the groove is λ / 8, the change in the light intensity distribution of the spot formed on each light receiving portion when each spot crosses the recording track is schematically shown in FIG. Show.
[0088]
As shown in FIG. 8, when the main spot crosses the recording track from the on-track state, the main spot shows a change in light intensity distribution symmetrical with respect to a dividing line corresponding to a direction orthogonal to the recording track. FIG. 9 shows an asymmetric change in light intensity distribution in which light intensity is inverted with respect to a division line corresponding to a direction parallel to a recording track.
[0089]
On the other hand, when the pair of sub-spots cross the recording track from the on-track state, the sub-spots show an asymmetrical change in the light intensity distribution across the dividing line corresponding to the direction parallel to the recording track, and also show a direction perpendicular to the recording track. 5 shows changes in the light intensity distribution that are asymmetric with respect to the dividing line corresponding to.
[0090]
In this case, since the push-pull signal MPP for the main spot described above is modulated by the recording track, it is possible to obtain information on a tracking error from this signal. Also, regarding the push-pull signals SPP1 and SPP2 for the first sub spot and the second sub spot, the distance between the spot centers of the pair of half sub spots is set to Tp / 2, so that the respective half sub spots are set to Tp / 2. Since the push-pull signals at the spot have opposite polarities and asymmetric track modulation is performed within the spot, as a result of the push-pull operation, the modulation by the recording track is reduced.
[0091]
Therefore, in the optical recording medium recording / reproducing apparatus to which the present invention is applied, a track error signal is calculated for the optical recording medium having the above-described phase depth of λ / 8 by the following operation, that is, a so-called “differential push-pull method”. However, since the track modulation of the push-pull signals SPP1 and SPP2 for the first sub-spot and the second sub-spot is small, it is possible to reduce the change in the track error signal due to the positional relationship between the main and sub-spots. Become.
[0092]
DPPTRK (Track error signal by differential push-pull method)
= MPP-K · (SPP1 + SPP2) (K is a proportional constant.)
In this case, regardless of whether the main spot is on the land or on the groove, the light intensity distribution on the light receiving surface of the main light receiving unit 18 is equal, whereas the pair of sub spots is on the land. There is a large difference between the light intensity distributions depending on whether the light is on the group or on the group, and the relationship between the land and the group is reversed depending on the direction (sign) of astigmatism.
[0093]
Therefore, with respect to the optical recording medium having the above-described phase depth of λ / 8, the first sub-light receiving portion 19 and the second sub-light receiving portion 20 are determined based on the difference in light intensity between the pair of sub-spots. Generates a track discrimination signal based on the light detection signal received and output by the following calculation.
[0094]
ASCTS (Track discrimination signal by crossing calculation)
= SAS1-SAS2
As shown in FIG. 9, the track discrimination signal (ASCTS) is shifted in phase by (1/4) from the track error signal (DPPTRK) when one cycle from one group to the next group. In a relationship.
[0095]
In this example, two spots separated by the diffractive optical element 17 are used as sub-spots for obtaining a track error signal and a track discrimination signal based on radial contrast. In order to reduce the influence of various disturbances, it is desirable to use two sub-spots as described above, but a track discrimination signal can be generated even from one sub-spot.
[0096]
As described above, according to the present invention, even with the above-described AC-SUM, that is, a recording medium having a small radial contrast, a good track determination signal can be obtained with a simple configuration.
[0097]
As for the track error signal, the first and second sub-beams are separated into a pair of half sub-beams forming a pair of half sub-spots at positions shifted in a direction orthogonal to the recording track, respectively. The first and second sub-light beams separated into a half sub-light beam are received by first and second sub-light receiving portions 19 and 20 having a light receiving surface divided by a dividing line corresponding to a direction parallel to the recording track. Accordingly, even if the first and second sub-spots are displaced in the direction orthogonal to the recording track due to the displacement of the objective lens or the tilt of the disk, the offset of the differential push-pull signal DPPTRK is generated. Can be suppressed.
[0098]
As described above, the differential push-pull signal is generated by separating the first and second sub-beams into a pair of half sub-beams forming a pair of semi-sub spots at positions shifted in a direction orthogonal to the recording track. Has a higher side spot phase shift resistance. In particular, if the distance between the spot centers of the pair of half sub-spots is Tp / 2, the offset component generated in the differential push-pull signal is canceled regardless of the positions of the first and second sub-spots, A good track error signal can be obtained.
[0099]
Therefore, according to the present invention, the control method conventionally used, such as pull-in of a tracking servo and counting of the number and direction of traversal of a recording track at the time of seeking, is described as AC-SUM, that is, a recording medium having a small radial contrast. It is possible to provide an optical pickup device and an optical recording medium recording / reproducing device which have a small number of components, a simple configuration of components, can be manufactured at low cost, and can be accessed at high speed.
[0100]
Further, according to the present invention, the present invention can be generally applied not only to the “DVD-RAM” but also to the above-described AC-SUM, that is, an optical disc of another standard using a recording medium having a small radial contrast. It is possible to provide an optical pickup device and an optical recording medium recording / reproducing device having a small number of points and a simple component configuration.
[0101]
Note that the present invention does not use a specific phenomenon that occurs with the adoption of the “land / groove method”, and therefore, either one of the land and the groove, such as “DVD + RW” or “DVD-RW”, is not used. This is also effective when an optical recording medium of a type that records information signals only in the case is used.
[0102]
Further, in the present invention, even when a push-pull signal cannot be obtained, a track error signal using a radial contrast can be obtained.
[0103]
In general, when a track error signal is obtained by using a radial contrast, a three-beam method in which a pair of sub-spots is shifted by ± ト ラ ッ ク track is generally used. Is not compatible with the differential push-pull method in which the difference is shifted by ± 1/2 track.
[0104]
On the other hand, in the present invention, it is possible to obtain the best track error signal RCTRK using the radial contrast in a state where the pair of sub-spots are shifted by ± 1/2 track. For an optical recording medium having a depth of λ / 4, a track error signal using radial contrast is detected, and for an optical recording medium having a groove phase depth close to λ / 8, a push-pull method is used. It is possible to detect the track error signal due to
[0105]
Note that the track error signal is not limited to the above-described track error signal RCTRK based on the radial contrast and the track error signal DPPTRK based on the differential push-pull method, and may be obtained by using the light receiving surfaces a, b, c, and d of the main light receiving unit 18. It can also be generated by a so-called “Differential Phase Detection (DPD) method”.
[0106]
In general, the light intensity distribution in the reflected light flux does not differ depending on whether the spot is on the land or on the group. This is also a factor that makes it difficult to generate a track discrimination signal in the optical recording medium using the land group recording method, as described above.
[0107]
On the other hand, in the present invention, the first and second sub-beams are separated into a pair of half sub-beams forming a pair of semi-sub spots at positions shifted in a direction orthogonal to the recording track, respectively. Since a large difference occurs in the light intensity distributions of the first and second sub-spots, it is possible to detect a good track discrimination signal with a simple configuration even for an optical recording medium using the land group recording method. It is possible.
[0108]
Particularly, by setting the distance between the spot centers of the pair of semi-sub spots to Tp / 2, the track discrimination signal ASCTS can be maximized together with the above-described track error signal RCTRK based on the radial contrast.
[0109]
Therefore, according to the present invention, it is possible to perform stable tracking servo with respect to the above-described various optical recording media having different phase depths, and perform a stable and high-speed seek operation of the optical pickup device. It is possible.
[0110]
Further, the above-described optical pickup device 104 may have a configuration in which a polarization hologram optical element 17a is provided instead of the diffraction optical element 17, as shown in FIG.
[0111]
In this case, the polarization hologram optical element 17a is disposed not in the space between the light source unit 10 and the polarization beam splitter prism 11, but in the optical path between the polarization beam splitter prism 11 and the quarter-wave plate 12. This is to prevent the polarization hologram optical element 17a from acting as a hologram for the light beam on the outward path toward the optical disk 101, but not to produce any optical effect on the light beam on the return path from the optical disk 101. .
[0112]
Further, in the above-described optical pickup device 104, as shown in FIG. 11, in the main light receiving portion 18 and the first and second sub light receiving portions 19 and 20 of the light detecting element 16a, only the central portion of each return light spot is used. The light receiving surface m, n, o for receiving light may be provided.
[0113]
In this case, by providing light receiving surfaces m, n, and o in each of the light receiving portions 18, 19, and 20 for receiving only the central portion of the reflected light beam, the diffracted light on the signal recording surface of the optical disc overlaps and the central portion of the reflected light beam is provided. Even when a spot moves in a state where the light intensity of the spot becomes high, it is possible to avoid a change in the focus error signal due to the spot movement.
[0114]
Also in this case, it is possible to generate a focus error signal, a track error signal, a track discrimination signal, and an RF signal by the above-described respective calculation methods.
[0115]
Further, in the above-described light detection element 16, as shown in FIG. 12, another main light receiving unit 21 for independently receiving the light beam obtained by splitting the main reflected light beam may be provided.
[0116]
In this case, the main reflected light beam branches to the second main light receiving unit 21 between the polarization beam splitter prism 11 and the multi-lens 15 as shown in FIG. 22 is provided. Then, as shown in FIG. 12, the second main light receiving section 21 has one light receiving surface s for receiving the reflected light beam from the main spot branched by the light branching element 22. The light detection signal received and output by the unit 21 is an RF signal.
[0117]
Further, the above-described diffractive optical element 17 is not limited to a hologram optical element shown in FIG. 4 described above in which a hologram pattern in which the direction of the lattice is asymmetric with respect to the center boundary is formed. As shown in FIG. 13, a hologram pattern in which the pitch of the lattice is asymmetrical about the center boundary may be formed.
[0118]
Thereby, on the signal recording surface of the optical disc 102, as shown in FIG. 14, for example, the first and second sub-beams are located at positions separated from each other with a main spot on a recording track formed by the main beam. First and second sub-spots are formed, and the first and second sub-spots are located at positions shifted in a direction orthogonal to the recording track, and a pair of semicircular shapes separated in a direction along the recording track. Is formed.
[0119]
In this case, as shown in FIG. 15, the light detecting element 16 includes a main light receiving unit 18 that receives the main reflected light beam from the main spot and a pair of half sub-spots separated from the first sub-spot. First sub-light receiving portions 19a and 19b for receiving a semi-sub light beam, and second sub-light receiving portions 20a and 20b for receiving a pair of semi-reflected light beams from the pair of semi-sub light beams separated from the second sub spot. And is configured.
[0120]
Among these, the main light receiving section 18 has light receiving surfaces a, b, c, and d divided into four by a dividing line corresponding to a direction parallel to the recording track and a dividing line corresponding to a direction perpendicular to the recording track, These four light receiving surfaces a, b, c, and d output independent light detection signals a, b, c, and d, respectively.
[0121]
The first sub-light receiving portions 19a and 19b have light receiving surfaces e and f and light receiving surfaces g and h divided by a dividing line corresponding to a direction parallel to the recording track, and these four light receiving surfaces e and f are provided. , G, and h output independent light detection signals e, f, g, and h, respectively.
[0122]
The second sub-light receiving portions 20a and 20b have a light receiving surface i, j and a light receiving surface k, l divided by a dividing line corresponding to a direction parallel to the recording track, and these four light receiving surfaces i, j , K, and l output independent light detection signals i, j, k, and l, respectively.
[0123]
Also in this case, it is possible to generate a focus error signal, a track error signal, a track discrimination signal, and an RF signal by the above-described respective calculation methods.
[0124]
Further, the above-described diffractive optical element 17 may have a hologram pattern in which the pitch and direction of the grating are alternately changed as shown in FIG.
[0125]
Thereby, on the signal recording surface of the optical disc 102, as shown in FIG. 17, for example, the first and second sub-beams are located at positions separated from each other with a main spot on a recording track formed by the main beam. First and second sub-spots are formed, and the first and second sub-spots are located at positions shifted in a direction orthogonal to the recording track, and a pair of circular spots separated from each other in a direction along the recording track. A semi-sub spot is formed.
[0126]
In this case, as shown in FIG. 18, the light detecting element 16 includes a main light receiving section 18 for receiving a main reflected light beam from a main spot and a first sub-light, as in the above-described light detecting element 16 shown in FIG. First sub-light receiving portions 19a and 19b for receiving a pair of half sub-light beams from a pair of half sub-spots separated from the spot, and a pair of half light beams from a pair of half sub-light beams separated from the second sub spot. Second sub-light receiving units 20a and 20b that receive the reflected light flux are configured.
[0127]
Also in this case, it is possible to generate a focus error signal, a track error signal, a track discrimination signal, and an RF signal by the above-described respective calculation methods.
[0128]
In addition, as shown in FIG. 19, the optical pickup device 104 to which the present invention is applied uses a hologram optical system in the optical path from the polarization beam splitter 11 to the photodetector 16 instead of the multi-lens 15 shown in FIG. A configuration in which the element 23 and the cylindrical lens 24 are arranged may be employed.
[0129]
In addition, as shown in FIG. 20, the light detection element 16 receives a first main receiving portion 25 that receives a main reflected light beam from a main spot, and receives a first sub-reflected light beam from a first sub spot. The first sub-light receiving unit 26, the second sub-light receiving unit 27 that receives the second sub-reflected light beam from the second sub-spot, and the light beam obtained by splitting the main reflected light beam from the main spot are independently processed. It is configured to include a second main light receiving unit 28 and a third main light receiving unit 29 for receiving light. The divergence of the main reflected light beam to the second main light receiving unit 28 and the third main light receiving unit 29 is performed by the hologram optical element 23 disposed between the polarization beam splitter prism 11 and the cylindrical lens 24.
[0130]
Among them, the first main light receiving section 25 is composed of two light receiving surfaces ad and bc divided into two by a dividing line corresponding to a direction parallel to the recording track, and from the two light receiving surfaces ad and bc, respectively. Independent light detection signals ad and bc are output.
[0131]
The first sub-light receiving portion 26 is composed of four light receiving surfaces e, f, g, and h divided into four by a dividing line corresponding to a direction parallel to the recording track and a dividing line corresponding to a direction perpendicular to the recording track. The four light receiving surfaces e, f, g, and h output independent light detection signals e, f, g, and h, respectively. Similarly, the second sub-light receiving unit 27 also has four light receiving surfaces i, j, k, and 4 divided by a dividing line corresponding to a direction parallel to the recording track and a dividing line corresponding to a direction perpendicular to the recording track. The four light receiving surfaces i, j, k, and l output independent light detection signals i, j, k, and l, respectively.
[0132]
On the other hand, the second main light receiving unit 28 detects a focus error signal by a so-called “Spot Size Detection (SSD) method”, so that the second main light receiving unit 28 uses a dividing line corresponding to a direction orthogonal to the recording track. It is composed of five divided light receiving surfaces n, a ', b', c ', and o, and from these five light receiving surfaces n, a', b ', c', and o, independent light detection signals n are provided. , A'b ', c', o are output. Similarly, the third main light receiving unit 29 also includes five light receiving surfaces q, f ', e', d ', and p divided into five by a dividing line corresponding to a direction orthogonal to the recording track. Independent light detection signals q, f ', e', d ', and p are output from the light receiving surfaces q, f', e ', d', and p, respectively.
[0133]
In the light detecting element 16 shown in FIG. 20, a dividing line corresponding to a direction parallel to the recording track and a dividing line corresponding to a direction perpendicular to the recording track are different from the light detecting element 16 shown in FIG. Are opposite to each other.
[0134]
The light detection signal output from the light detection element 16 is subjected to current-voltage conversion by an amplifier (not shown) formed on the semiconductor substrate of the light detection element 16, for example, and then an arithmetic circuit or each light receiving unit It is sent to an arithmetic circuit outside the photodetector connected to 25, 26, 27, 28, 29. In this arithmetic circuit, each signal and the like are calculated as follows.
[0135]
RF (RF signal for main spot)
= Modulation component of (ad + bc)
PI (pull-in signal: focus pull-in signal: sum signal of main spot)
= Ad + bc
FCS (Focus error signal by SSD method)
= {(A '+ c'-b'-no)-(d' + f'-e'-pq)}
MPP (push-pull signal for main spot)
= Ad-bc
SPP1 (push-pull signal for first sub-spot)
= {(E + h)-(f + g)}
SPP2 (push-pull signal for second sub spot)
= {(I + 1)-(j + k)}
SRC1 (radial contrast signal for first sub-spot)
= {(E + f)-(h + g)}
SRC2 (radial contrast signal for second sub spot)
= {(I + j)-(l + k)}
SAS1 (crossing calculation signal for first sub-spot)
= {(E + g)-(f + h)}
SAS2 (crossing calculation signal for the second sub spot)
= {(I + k)-(j + 1)}
SA (spherical aberration signal)
= SAS1 + SAS2 = SAS1-(-SAS2)
SPI1 (sum signal for the first sub spot)
= E + f + g + h
SPI2 (sum signal for second sub-spot)
= I + j + k + 1
Here, in the case where the phase depth of the pit is λ / 4, as in the above-described optical recording medium for reproduction such as a DVD-ROM or the like, when each spot crosses the recording track, it is placed on each light receiving section. FIG. 21 schematically shows a change in the light intensity distribution of the formed spot.
[0136]
As shown in FIG. 21, when the main spot crosses the recording track from the on-track state, the main spot shows a change in the light intensity distribution symmetrical with respect to a division line corresponding to a direction parallel to the recording track.
[0137]
On the other hand, when the pair of sub-spots cross the recording track from the on-track state, the pair of sub-spots show a change in light intensity distribution symmetrical with respect to a division line corresponding to a direction parallel to the recording track, whereas FIG. 9 shows an asymmetric change in light intensity distribution in which light intensity is inverted with respect to a dividing line corresponding to a direction orthogonal to the light intensity distribution.
[0138]
In this case, since the push-pull signals MPP, SPP1, and SPP2 for the main spot, the first sub-spot, and the second sub-spot are not modulated by the track, it is not possible to obtain information on a track error from these signals. .
[0139]
Therefore, for the optical recording medium in which the phase depth of the groove is λ / 4, the first sub-light receiving portion 19 and the second sub-light receiving portion receive and output the light detection signals based on the light detection signals. A track error signal is generated by the following operation.
[0140]
RCTRK (track error signal due to radial contrast)
= SRC1-SRC2
For the optical recording medium having the above-described phase depth of λ / 4, a track determination signal is generated by the following calculation based on a light detection signal received and output by the main light receiving unit 18.
[0141]
RCCTS (track discrimination signal based on radial contrast)
= Interchange (AC) component of PI
On the other hand, in the above-described optical recording medium such as a DVD-RAM, the behavior is different from the case where the phase depth is λ / 4 since the phase depth of the groove is about λ / 6 to λ / 12. . As a typical example, FIG. 22 schematically shows a change in light intensity distribution of a spot formed on each light receiving section when each spot crosses a recording track when the phase depth of the groove is λ / 8. Show.
[0142]
As shown in FIG. 22, when the main spot crosses the recording track from the on-track state, the main spot shows an asymmetric light intensity distribution in which the light intensity is inverted with respect to a dividing line corresponding to a direction parallel to the recording track. .
[0143]
On the other hand, when the pair of sub-spots cross the recording track from the on-track state, the sub-spots show an asymmetrical change in the light intensity distribution with a division line corresponding to a direction parallel to the recording track, and also have a division perpendicular to the recording track. FIG. 4 shows a change in light intensity distribution that is asymmetrical with respect to a dividing line.
[0144]
In this case, since the push-pull signal MPP for the main spot described above is modulated by the recording track, it is possible to obtain information on a tracking error from this signal. The push-pull signals SPP1 and SPP2 for the first sub-spot and the second sub-spot are asymmetrically modulated in the spot due to the astigmatism given. The modulation by the track is reduced.
[0145]
Therefore, in the optical recording medium recording / reproducing apparatus to which the present invention is applied, a track error signal is calculated for the optical recording medium having the above-described phase depth of λ / 8 by the following operation, that is, a so-called “differential push-pull method”. However, since the track modulation of the push-pull signals SPP1 and SPP2 for the first sub-spot and the second sub-spot is small, it is possible to reduce the change in the track error signal due to the positional relationship between the main and sub-spots. Become.
[0146]
DPPTRK (Track error signal by differential push-pull method)
= MPP-K · (SPP1 + SPP2) (K is a proportional constant.)
Note that the track error signal is not limited to the above-described track error signal RCTRK based on the radial contrast and the track error signal DPPTRK based on the differential push-pull method, and may be obtained by using the light receiving surfaces a, b, c, and d of the main light receiving unit 18. It can also be generated by a so-called “Differential Phase Detection (DPD) method”.
[0147]
In this case, regardless of whether the main spot is on the land or on the groove, the light intensity distribution on the light receiving surface of the main light receiving unit 18 is equal, whereas the pair of sub spots is on the land. There is a large difference between the light intensity distributions depending on whether the light is on the group or on the group, and the relationship between the land and the group is reversed depending on the direction (sign) of astigmatism.
[0148]
Therefore, with respect to the optical recording medium having the above-described phase depth of λ / 8, the first sub-light receiving portion 19 and the second sub-light receiving portion 20 are determined based on the difference in light intensity between the pair of sub-spots. Generates a track discrimination signal based on the light detection signal received and output by the following calculation.
[0149]
ASCTS (Track discrimination signal by crossing calculation)
= SAS1-SAS2
As shown in FIG. 9, the track discrimination signal (ASCTS) has a phase corresponding to the track error signal (DPPTRK) by (1/4) cycle when one cycle from one group to the next group is used. There is a staggered relationship.
[0150]
In this example, two spots separated by the diffractive optical element 17 are used as sub-spots for obtaining a track discrimination signal. In order to reduce the influence of various disturbances, it is desirable to use two sub-spots as described above, but a track discrimination signal can be generated even from one sub-spot.
[0151]
【The invention's effect】
As described in detail above, according to the present invention, it is possible to detect a track discrimination signal for an optical recording medium without increasing the number of components of an optical head or complicating the configuration of components. It is possible to provide an optical head and a recording / reproducing apparatus which can be provided at low cost and which can be accessed at high speed.
[0152]
Further, according to the present invention, it is possible to detect an optimum track error signal, a track discrimination signal, and the like for various optical recording media having different phase depths. In addition, by performing a stable and high-speed seek operation of the optical head, it is possible to improve the overall recording and / or reproducing characteristics for these optical recording media.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an optical recording medium recording / reproducing apparatus to which the present invention is applied.
FIG. 2 is a side view showing the configuration of the optical pickup device.
FIG. 3 is a side view illustrating a configuration of a light source unit.
FIG. 4 is a front view showing a configuration of the diffractive optical element.
FIG. 5 is a schematic diagram showing a positional relationship between a main spot and a pair of sub-spots on a signal recording surface of an optical disc.
FIG. 6 is a plan view illustrating a configuration of a photodetector.
FIG. 7 is a schematic diagram showing a change in light intensity distribution of spots formed on each light receiving section when each spot crosses a recording track when the phase depth is λ / 4.
FIG. 8 is a schematic diagram showing a change in light intensity distribution of spots formed on each light receiving section when each spot crosses a recording track when the phase depth is λ / 8.
FIG. 9 is a graph showing a relationship between a track error signal DPPTRK and a track discrimination signal ASCTS in the “land-groove recording method”.
FIG. 10 is a block diagram showing a modification of the optical pickup device.
FIG. 11 is a block diagram showing another modified example of the optical pickup device.
FIG. 12 is a front view showing a modification of the diffractive optical element.
FIG. 13 is a front view showing a modification of the diffractive optical element.
14 is a schematic diagram showing a positional relationship between a main spot and a pair of sub-spots on a signal recording surface of an optical disk when the diffractive optical element shown in FIG. 13 is used.
15 is a plan view showing another configuration of the light detecting element and a state of a spot formed on the light detecting element when the diffractive optical element shown in FIG. 13 is used.
FIG. 16 is a front view showing another modification of the diffractive optical element.
17 is a schematic diagram showing a positional relationship between a main spot and a pair of sub-spots on a signal recording surface of an optical disc when the diffractive optical element shown in FIG. 16 is used.
18 is a plan view showing another configuration of the light detection element and a state of a spot formed on the light detection element when the diffractive optical element shown in FIG. 16 is used.
FIG. 19 is a block diagram showing still another modified example of the optical pickup device.
20 is a plan view showing still another configuration of the light detecting element and a state of a spot formed on the light detecting element when the optical pickup device shown in FIG. 19 is used.
FIG. 21 is a diagram showing light of spots formed on each light receiving portion when each spot crosses a recording track when the phase depth is λ / 4 when the optical pickup device shown in FIG. 19 is used. It is a schematic diagram which shows the change of intensity distribution.
FIG. 22 is a diagram showing light of spots formed on each light receiving portion when each spot crosses a recording track when the phase depth is λ / 8 when the optical pickup device shown in FIG. 19 is used. It is a schematic diagram which shows the change of intensity distribution.
FIG. 23 is a graph showing a relationship between a track error signal and a sum signal in a conventional “land recording method”.
FIG. 24 is a graph showing a relationship between a track error signal and a track discrimination signal in a conventional “land recording method”.
FIG. 25 is a graph showing a sum signal in a conventional “land / groove recording method”.
[Explanation of symbols]
Reference Signs List 10 light source unit, 14 objective lens, 16 light detecting element, 17 diffractive optical element, 18 main light receiving unit, 19 first auxiliary light receiving unit, 20 second auxiliary light receiving unit, 101 optical recording medium recording / reproducing device, 102 optical disk, 104 optical pickup device, 107 system controller, 108 signal modulation / demodulation unit and ECC block, 109 servo control circuit

Claims (10)

A light emitting means having at least one light source for emitting a light beam; a light collecting means for condensing the light beam emitted from the light emitting means on an optical recording medium; and a light collecting means for collecting the light beam emitted from the light emitting means. A main light beam which is disposed in an optical path to an optical unit and forms a main spot for recording and / or reproducing a signal on a recording track of the optical recording medium; And a pair of sub-beams forming a pair of sub-sub-spots at positions shifted in a direction orthogonal to the recording track, respectively. A diffractive optical element for separating,
An optical head comprising: a main light receiving unit that receives the main light beam among the light beams reflected by the optical recording medium; and a light detection unit that includes a pair of sub light receiving units that receive the pair of sub light beams. In a direction perpendicular to the recording track, the distance between the spot center of the main spot and the spot center of the pair of sub spots is n · Tp / 2 (where n represents an integer of 0 or more). The optical head according to claim 1, wherein 2. The optical head according to claim 1, wherein a distance between spot centers of the pair of semi-sub spots in a direction orthogonal to the recording track is substantially Tp / 2. 2. The optical head according to claim 1, wherein the pair of sub-light receiving units have light receiving surfaces divided by dividing lines corresponding to a direction parallel to the recording track. 2. The optical head according to claim 1, wherein the pair of sub-light receiving units has a light receiving surface divided by a dividing line corresponding to a direction orthogonal to the recording track. A light emitting means having at least one light source for emitting a light beam; a light collecting means for condensing the light beam emitted from the light emitting means on an optical recording medium; and a light collecting means for collecting the light beam emitted from the light emitting means. A main light beam which is disposed in an optical path to an optical unit and forms a main spot for recording and / or reproducing a signal on a recording track of the optical recording medium; And a pair of sub-beams forming a pair of sub-sub-spots at positions shifted in a direction orthogonal to the recording track, respectively. A diffractive optical element for separating,
Among the reflected light beams reflected by the optical recording medium, an optical head including a main light receiving unit that receives the main light beam and a light detection unit having a pair of sub light receiving units that receive the pair of sub light beams,
Signal processing means for generating various signals based on the light detection signal received and output by the light detection means,
A recording and / or reproducing apparatus comprising: a drive control unit that controls driving of the optical head based on a signal generated by the signal processing unit. In the direction perpendicular to the recording track, the distance between the spot center of the main spot and the spot center of the pair of sub-spots is n · Tp / 2 (where n represents an integer of 0 or more). 7. The recording and / or reproducing apparatus according to claim 6, wherein: 7. The recording and / or reproducing apparatus according to claim 6, wherein a distance between spot centers of the pair of semi-sub spots in a direction orthogonal to the recording track is substantially Tp / 2. 7. The recording and / or reproducing apparatus according to claim 6, wherein the pair of sub-light receiving units have light receiving surfaces divided by dividing lines corresponding to a direction parallel to the recording track. 7. The recording and / or reproducing apparatus according to claim 6, wherein the pair of sub-light receiving units has a light receiving surface divided by a dividing line corresponding to a direction orthogonal to the recording track.

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