JP2013222492A - Reproduction device and reproduction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a reproduction technique by which signal reproduction can be executed with an excellent SNR even when a reflectance difference between a formed part and a non-formed part of a recording mark is low.SOLUTION: For example, p-polarized light and s-polarized light are radiated on a recording layer of an optical recording medium so that respective radiation spots have a preceding-succeeding relationship, the p-polarized light and the s-polarized light having passed via the recording layer are overlapped, and the overlapped light is received via a polarizing plate. When, for example, one of the p-polarized light and s-polarized light is positioned on a mark, and the other is positioned at a non-formed part of the mark, an optical path difference (phase difference) is generated between the p-polarized light and the s-polarized light, so that a polarization direction of the overlapped light varies. On the other hand, when both of the p-polarized light and the s-polarized light are positioned on the formed part or the non-formed part of the mark, the polarization direction does not vary. Such variation in the polarization direction is detected as change in reception light amount by the polarizing plate so as to enable signal reproduction.

Description

  The present technology relates to a reproducing apparatus and a method for reproducing an optical recording medium.

JP 2008-135144 A JP 2008-176902 A

  As an optical recording medium on which signals are recorded / reproduced by light irradiation, for example, an optical disc recording medium (hereinafter referred to as an optical disc) such as a CD (Compact Disc), a DVD (Digital Versatile Disc), or a BD (Blu-ray Disc: registered trademark). Is also popular.

  As an optical disk to be used for the next generation, such as CDs, DVDs, and BDs, the present applicant previously described a so-called bulk recording type optical disk as described in Patent Document 1 and Patent Document 2 above. Has proposed.

  Here, the bulk recording refers to, for example, a sequential focal position with respect to an optical recording medium (referred to as a bulk type recording medium 100) having at least a cover layer 101 and a bulk layer (recording layer) 102 as shown in FIG. This is a technique for increasing the recording capacity by performing multi-layer recording in the bulk layer 102 by irradiating laser light instead.

  The bulk layer 102 does not have an explicit multilayer structure in the sense that, for example, a plurality of reflective films are formed. That is, the bulk layer 102 is not provided with a reflective film and a guide groove for each recording layer as provided in a normal multilayer disc.

Regarding the bulk recording as described above, Patent Document 1 discloses a recording technique called a so-called micro-hologram method.
In the micro-hologram method, a so-called hologram recording material is used as a recording material for the bulk layer 102. As a hologram recording material, for example, a photopolymerization type photopolymer or the like is widely known.

The micro hologram method is roughly classified into a positive micro hologram method and a negative micro hologram method.
The positive micro-hologram method is a method in which two opposed light beams (light beam A and light beam B) are collected at the same position to form fine interference fringes (holograms), which are used as recording marks.
The negative type micro-hologram method is a method opposite to the positive type micro-hologram method, in which interference fringes formed in advance are erased by laser light irradiation, and the erased portion is used as a recording mark. Specifically, in the negative microhologram method, an initialization process for forming interference fringes on the bulk layer 102 is performed in advance before performing the recording operation. That is, the parallel light beams C and D are irradiated oppositely to form the interference fringes on the entire bulk layer 102. Then, after the interference fringes are formed in advance by the initialization process as described above, information recording is performed by forming erase marks. Specifically, information recording with an erasure mark is performed by irradiating a laser beam in accordance with information to be recorded in a state in which an arbitrary layer position is in focus.

The present applicant has also proposed a recording method for forming voids (holes, voids) as recording marks as disclosed in Patent Document 2, for example, as a bulk recording method different from the micro-hologram method. .
The void recording method is a method of recording holes in the bulk layer 102 by irradiating the bulk layer 102 made of a recording material such as a photopolymerization type photopolymer with a laser beam at a relatively high power. is there. As described in Patent Document 2, the hole portion formed in this manner is a portion having a refractive index different from that of the other portion in the bulk layer 102, and the light reflectance is increased at the boundary portion. become. Therefore, the hole portion functions as a recording mark, thereby realizing information recording by forming the hole mark.

Since such a void recording method does not form a hologram, it is only necessary to perform light irradiation from one side for recording. That is, there is no need to form a recording mark by condensing two light beams at the same position as in the case of the positive micro-hologram method.
Further, in comparison with the negative type micro hologram method, there is an advantage that the initialization process can be made unnecessary.
Note that Patent Document 2 shows an example in which pre-cure light irradiation is performed before performing void recording, but void recording is possible even if such pre-cure light irradiation is omitted.

  However, in the bulk recording method as described above, since a reflective film is not formed for each recording layer, the amount of reflected light of the recording mark is very small. For this reason, it is difficult to improve the SNR (signal to noise ratio) during signal reproduction, and it is difficult to reduce the error rate.

  The present technology has been made in view of such a problem, and realizes a reproduction method capable of performing signal reproduction with good SNR even when the difference in reflectance between a recording mark forming portion and a non-forming portion is low. Is the subject.

In order to solve the above problems, the present technology proposes the following configuration as a playback device.
That is, the reproducing apparatus of the present technology optically records the first light and the second light whose polarization directions are substantially orthogonal to each other so that the respective irradiation spots have a leading and trailing relationship. A light irradiation unit for irradiating the recording layer of the medium is provided.
In addition, a correction optical system that superimposes the first light and the second light via the recording layer is provided.
In addition, a polarizing plate is provided on which the superimposed light of the first light and the second light obtained by the correction optical system is incident.
In addition, a light receiving unit that receives the superimposed light via the polarizing plate is provided.
In addition, a reproduction unit that performs signal reproduction based on a light reception signal by the light reception unit is provided.

In the above configuration, when both the first light (for example, P-polarized light) and the second light (for example, S-polarized light) are located in the mark non-formation portion in the recording layer, the first light and the second light There is no difference in the optical path length (phase) of light. At this time, the superposed light of the first light and the second light has a predetermined polarization direction (45 ° polarization). For example, the optical reference axis of the polarizing plate is adjusted so as to selectively transmit light having such a predetermined polarization direction. In this case, as described above, the received light signal level becomes maximum when both the first light and the second light are in the mark non-formed portion.
On the other hand, for example, in a state where one of the first light and the second light is positioned on the mark and the other is positioned on the mark non-formation portion, the optical path difference between the first light and the second light ( Phase difference) occurs, and the polarization direction of the superimposed light changes from the predetermined polarization direction. For this reason, for example, under the setting of the polarizing plate described above, the amount of transmitted light of the superimposed light of the first light and the second light is reduced, and the light reception signal level is lowered.
Using the change in the received light signal level according to the presence or absence of such a mark, the reproducing unit can perform signal reproduction.
Since this is a reproduction method that uses a change in the polarization state of the light applied to the recording layer, signal reproduction can be performed with good SNR even when the difference in reflectance between the mark formation part and the non-formation part is low.

  As described above, according to the present technology, signal reproduction can be performed with good SNR even when the difference in reflectance between the recording mark forming portion and the non-forming portion is low.

1 is a cross-sectional structure diagram of an optical recording medium targeted in an embodiment. It is explanatory drawing about the position control method at the time of recording / reproduction | regeneration. It is a figure for demonstrating mainly the structure of the optical system with which the reproducing | regenerating apparatus of embodiment is provided. It is a figure for demonstrating the internal structure of the whole reproducing | regenerating apparatus of embodiment. It is the figure which extracted and showed the structure of the principal part which concerns on the reproduction | regenerating method of embodiment among the optical systems shown in FIG. It is explanatory drawing about the basic principle of the reproducing | regenerating method of embodiment. It is the figure which illustrated the relationship between the mark size and the spot size of P polarization and S polarization. It is explanatory drawing about the relationship between the mark row | line | column formed in the recording layer by mark position recording, and the amplitude of a read signal, and a specific code | symbol determination method. It is explanatory drawing about the structure for implement | achieving the reproducing | regenerating technique as embodiment. 1 is a cross-sectional structure diagram of a reflective optical recording medium. It is a figure showing an example of composition of an optical pick-up corresponding to a reflection type optical recording medium. It is explanatory drawing about the distance between the spots of P polarized light and S polarized light. It is explanatory drawing about a bulk recording system.

Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described.
The description will be made in the following order.

<1. Example of Optical Recording Medium Targeted in Embodiment>
<2. About position control method>
<3. Configuration of Playback Device of Embodiment>
<4. Reproduction method of embodiment>
<5. Modification>

<1. Example of Optical Recording Medium Targeted in Embodiment>

FIG. 1 shows a cross-sectional structure diagram of an optical recording medium targeted by the reproducing apparatus of the embodiment.
The optical recording medium targeted in the embodiment is a so-called bulk recording type optical recording medium, and is hereinafter referred to as a bulk type recording medium 1.
The optical recording medium is a general term for recording media on which a recording signal is reproduced by light irradiation.

The bulk type recording medium 1 is a disc-shaped optical recording medium.
The bulk type recording medium 1 is irradiated with laser light in a state where it is rotationally driven by a reproducing apparatus to be described later to perform mark recording (information recording) and reproduction.

As shown in FIG. 1, a cover type 2, a selective reflection film 3, an intermediate layer 4, and a bulk layer 5 are formed in order from the upper layer side on the bulk type recording medium 1.
Here, the “upper layer side” in this specification refers to the upper layer side when a surface on which a laser beam from a reproducing apparatus side of an embodiment described later is incident is an upper surface.

  In this specification, the term “depth direction” is used, and this “depth direction” is a direction (that is, reproduction direction) that coincides with the vertical direction (vertical direction) according to the definition of “upper layer side”. The direction parallel to the incident direction of the laser beam from the apparatus side: the focus direction).

In the bulk type recording medium 1, the cover layer 2 is made of a resin such as polycarbonate or acrylic, and a position guide for guiding the recording / reproducing position is formed on the lower surface side as shown in the drawing. Yes.
In this case, the position guide is formed by a continuous groove (groove) or a guide groove as a pit row. The guide groove is formed in a spiral shape, for example.
For example, when the guide groove is formed of a pit row, position information (absolute position information: for example, rotation angle information and radius position information, hereinafter also referred to as address information) is recorded by a combination of the pit and land lengths. Alternatively, when the guide groove is a groove, the groove is periodically meandered (wobbled) to record position information based on the meandering period information.
The cover layer 2 is generated by injection molding using a stamper in which such guide grooves (uneven shape) are formed.

In addition, a selective reflection film 3 is formed on the lower surface side of the cover layer 2 in which the guide grooves as described above are formed.
A bulk layer 5 is formed on the lower layer side of the selective reflection film 3 via an intermediate layer 4 (adhesive layer).
The intermediate layer 4 is made of, for example, a UV curable resin or a thermoplastic resin, and a material for forming the intermediate layer 4 such as the UV curable resin is applied to the surface of the cover layer 2 on which the selective reflection film 3 is formed. The state in which the bulk layer 5 is formed (adhered) via the intermediate layer 4 on the lower layer side of the selective reflection film 3 by performing the curing process while the material as the bulk layer 5 is pressed against the surface. can get.

Here, as can be understood from the description of FIG. 13, in the bulk recording method, the bulk layer 5 as the recording layer has an explicit multilayer structure in the sense that, for example, a plurality of reflective films are formed. I do not have. That is, the bulk layer 5 is not provided with a reflective film and a guide groove for each recording layer as provided in a normal multilayer disk.
For this reason, when the mark is not recorded, the servo by the laser beam irradiated to the recording layer cannot be applied.

Therefore, in practice, for the bulk type recording medium 1, the reference reflecting surface (reference surface Ref) having the guide groove as described above is provided outside the bulk layer 5.
In addition, as will be described later with reference to FIG. 2, the bulk type recording medium 1 is also irradiated with a laser beam (hereinafter referred to as recording) that is to be irradiated on the bulk layer 5 for mark recording and reproduction. And a reference surface laser beam to be irradiated on the reference surface Ref as a position control laser beam.
As shown in FIG. 2, the recording layer laser light and the reference surface laser light are irradiated onto the bulk type recording medium 1 through a common objective lens.

At this time, the laser light for the reference surface is reflected by the reference surface Ref, and position control based on the return light is to be performed. On the other hand, the recording layer laser light reaches the bulk layer 5 formed on the lower layer side of the reference surface Ref and should be used for recording and reproducing marks.
For this reason, in the bulk recording method, a laser beam having a wavelength band different from that of the recording layer laser beam is used as the reference surface laser beam, and as a reflection film for forming a reflection surface as the reference surface Ref, As described above, the selective reflection film 3 is provided. Specifically, the selective reflection film 3 is a reflection film having a wavelength selectivity that reflects light in the same wavelength band as the laser light for the reference surface and transmits light having other wavelengths.

Here, the material (recording material) of the bulk layer 5 is optimally suited depending on the bulk recording method employed, such as the positive micro-hologram method, negative micro-hologram method, and void recording method described above. May be adopted.
Note that the mark recording method related to the optical recording medium targeted by the present technology is not particularly limited, and any method may be adopted in the category of the bulk recording method.
As an example, the following description will be continued on the assumption that a void recording method is adopted in this example. As understood from the above description, the void recording method is a method of forming an empty packet as a mark, and the mark in this case has a refractive index different from that of other portions. In other words, a refractive index modulation mark is formed.

<2. About position control method>

FIG. 2 is an explanatory diagram of a position control method during mark recording / reproduction with respect to the bulk recording medium 1.
First, when performing multilayer recording on the bulk layer 5 on which no guide groove or reflective film is formed, it is determined in advance which position the layer position for recording the mark in the depth direction in the bulk layer 5 is set as. It will be set. In the figure, as the layer positions (mark formation layer positions: also expressed as information recording layer positions) in the bulk layer 5, the first information recording layer position L1 to the fifth information recording layer position L5, a total of five positions. The case where the information recording layer position L is set is illustrated. As shown in the figure, the first information recording layer position L1 is set as a position separated from the selective reflection film 3 (reference surface Ref) where the guide groove is formed by the first offset of-L1 in the focus direction (depth direction). Is done. In addition, the second information recording layer position L2, the third information recording layer position L3, the fourth information recording layer position L4, and the fifth information recording layer position L5 are respectively the second offset of-L2 from the reference plane Ref and the third information recording layer position L5. The positions are set apart by an offset of-L3, a fourth offset of-L4, and a fifth offset of-L5.

  Note that the number of information recording layer positions L should not be limited to five.

At the time of recording in which the mark is not yet formed, focus servo and tracking servo cannot be performed based on the recording layer laser beam. Accordingly, the focus servo control and tracking servo control of the objective lens during recording are based on the reflected light of the reference surface laser light as the position control light, and the irradiation spot position of the reference surface laser light on the reference surface Ref. This is achieved by controlling the position of the objective lens so as to follow the guide groove.
As described above, since the reference surface laser beam and the recording layer laser beam are irradiated through the common objective lens, the recording layer laser beam can be similarly subjected to position control.

  However, the recording layer laser light needs to reach the bulk layer 5 formed below the selective reflection film 3 for mark recording. For this reason, the optical system in this case is provided with a focus mechanism for adjusting the focusing position of the recording layer laser beam independently from the focus mechanism of the objective lens (in this example, This applies to the focus mechanism 17 shown in FIG.

  By setting the in-focus position of the recording layer laser beam to the position offset by the offset of-L from the reference plane Ref by such a focus mechanism, the mark can be recorded at the required information recording layer position L. It can be carried out.

Further, during reproduction of the bulk layer 5 on which mark recording has been performed, light that has undergone modulation of the already recorded mark row is obtained, so that focus servo and tracking servo using recording layer laser light can be performed.
Therefore, at the time of reproduction, tracking servo control of the objective lens is performed using a light reception signal for the recording layer laser light.
Here, focus servo control at the time of reproduction is performed based on the light reception signal of the recording layer laser beam. In this case, the focus servo can be controlled by either the objective lens or the focus mechanism described above. Can be realized.
However, in this example, in order to enable reading of address information on the reference surface Ref by the reference surface laser light at the time of reproduction, the focus servo for the recording layer laser light at the time of reproduction uses the above-described focus mechanism. It shall be executed by controlling.

<3. Configuration of Playback Device of Embodiment>

Next, the configuration of a playback device as an embodiment according to the present technology will be described with reference to FIGS. 3 and 4.
Here, the reproducing apparatus of the embodiment has a recording function as well as a reproducing function for the bulk type recording medium 1. In this sense, hereinafter, the reproducing apparatus according to the embodiment is referred to as a recording / reproducing apparatus 10.

  FIG. 3 is a diagram for mainly explaining the configuration of the optical system provided in the recording / reproducing apparatus 10. Specifically, the internal configuration of the optical pickup OP provided in the recording / reproducing apparatus 10 is mainly shown.

In FIG. 3, the bulk type recording medium 1 loaded in the recording / reproducing apparatus 10 is set so that its center hole is clamped at a predetermined position in the recording / reproducing apparatus 10, and a spindle motor (SPM) 40 in the figure. It is held in a state in which it can be driven by rotation.
In this example, it is assumed that the CLV method (constant linear velocity method) is adopted as the rotational driving method of the bulk type recording medium 1.
The optical pickup OP irradiates recording layer laser light and reference surface laser light onto the bulk type recording medium 1 that is rotationally driven by the spindle motor 40.

In the optical pickup OP, a recording layer laser 11 serving as a light source of the recording layer laser light and a reference surface laser 34 serving as a light source of the reference surface laser light are provided.
Here, as described above, the recording layer laser light and the reference surface laser light use light having different wavelength bands. In this example, the recording layer laser light has a wavelength of about 405 nm (so-called blue-violet laser light), and the reference surface laser light has a wavelength of about 650 nm (red laser light).

In the optical pickup OP, an objective lens 19 serving as a common output end of the recording layer laser light and the reference surface laser light to the bulk type recording medium 1 is provided.
Further, the optical pickup OP in this case employs a so-called transmission type configuration that receives the recording layer laser light transmitted through the bulk type recording medium 1, and an objective lens that forms a pair with the objective lens 19 as shown in the figure. 21 is provided at a position opposite to the objective lens 19 through the bulk type recording medium 1.
As shown in the drawing, the recording layer laser light by the divergent light after being focused on the required information recording layer position L in the bulk layer 5 is incident on the objective lens 21 through the objective lens 19.
The optical pickup OP is provided with a reproducing light receiving unit 30 and a servo light receiving unit 33 as light receiving units for receiving the recording layer laser light incident on the objective lens 21 as described above.
The optical pickup OP is also provided with a reference surface light receiving portion 39 for receiving the reflected light from the reference surface Ref of the reference surface laser light.

First, the configuration of the recording layer laser light irradiation / light receiving system will be described.
The polarization direction of the recording layer laser light emitted from the recording layer laser 11 is adjusted by the half-wave plate 12.
In the case of this example, the mounting angle of the half-wave plate 12 is adjusted (that is, the optical reference axis is adjusted) so that the recording layer laser light is 45 ° polarized.

The recording layer laser light via the half-wave plate 12 is incident on a PBS (polarized beam splitter) 13.
The PBS 13 is configured such that its selective reflection surface transmits P-polarized light and reflects S-polarized light. Accordingly, the recording layer laser light incident on the PBS 13 is split into P-polarized light and S-polarized light as a result of transmission of the P-polarized component and reflection of the S-polarized component.
The P-polarized light transmitted through the PBS 13 is incident on one surface side of the selective reflection surface of the PBS 16 as shown in the figure.

The S-polarized light reflected by the PBS 13 is incident on the other surface side of the selective reflection surface of the PBS 16 via the mirror 14 and the mirror 15 in the drawing.
At this time, the arrangement positions and arrangement angles of the mirror 14 and the mirror 15 are adjusted so as to cause a predetermined shift between the optical axes of the S-polarized light and the P-polarized light output from the PBS 16. The relationship between the P-polarized irradiation spot position and the S-polarized irradiation spot position realized by adjusting the optical axes of the mirror 14 and the mirror 15 will be described later.

  The PBS 16 is configured to transmit P-polarized light and reflect S-polarized light on its selective reflection surface. Since the optical axis on the S polarization side is adjusted by the mirrors 14 and 15 as described above, the P polarized light and the S polarized light are emitted from the PBS 16 with the optical axes shifted as shown in the figure.

P-polarized light and S-polarized light emitted from the PBS 16 enter the focus mechanism 17.
In the focus mechanism 17, for example, a fixed lens is disposed on the side close to the light source (the recording layer laser 11) and a movable lens is disposed on the side close to the objective lens 19, and the movable lens is driven to the light source side or the objective lens 19 side. Thus, the focusing position of the recording layer laser light (P-polarized light and S-polarized light) can be adjusted.
Specifically, depending on the focus mechanism 17, the collimation state of the recording layer laser light incident on the objective lens 19 (the transition state of convergent light / parallel light / divergent light) is changed. The focal position can be adjusted independently.

P-polarized light and S-polarized light that have passed through the focus mechanism 17 are incident on the dichroic mirror 18.
The dichroic mirror 18 is configured such that its selective reflection surface transmits light in the same wavelength band as the recording layer laser light, and reflects light of other wavelengths. Therefore, the P-polarized light and S-polarized light incident as described above are transmitted through the dichroic mirror 18.

  The P-polarized light and S-polarized light transmitted through the dichroic mirror 18 are passed through the objective lens 19 as shown in the figure, and are respectively placed at different positions (different positions in the in-plane direction) on the bulk type recording medium 1 (bulk layer 5). Focus. For confirmation, since P-polarized light and S-polarized light are irradiated through the same focus mechanism 17 and objective lens 19, the focus position (focus position in the focus direction) is the same.

Here, the objective lens 19 is held by the first lens actuator 20 so as to be displaceable at least in the radial direction (tracking direction) and the focus direction of the bulk type recording medium 1.
The first lens actuator 20 is provided with a focus coil and a tracking coil, and a drive signal (a focus drive signal FD and a tracking drive signal TD, which will be described later) is given to each of the first lens actuator 20 so that the objective lens 19 is moved in the focus direction and the tracking direction. Displace each.

As described above, the recording layer laser light after focusing in the bulk layer 5 enters the objective lens 21.
The objective lens 21 is held by a second lens actuator 22 so as to be displaceable at least in the tracking direction and the focus direction. Similar to the first lens actuator 20, the second lens actuator 22 is provided with a focus coil and a tracking coil, and a drive signal (a focus drive signal FD ′ and a tracking drive signal TD ′, which will be described later) is given to each. Thus, the objective lens 21 is displaced in the focus direction and the tracking direction, respectively.

P-polarized light and S-polarized light that have passed through the objective lens 21 enter the PBS 23.
The PBS 23 is configured to transmit P-polarized light and reflect S-polarized light. The P-polarized light transmitted through the PBS 23 is incident on one surface side of the selective reflection surface of the PBS 26.

S-polarized light reflected by the PBS 23 enters the other surface side of the selective reflection surface of the PBS 26 via the mirror 24 and the mirror 25.
In this case, the arrangement positions and the arrangement angles of the mirror 24 and the mirror 25 are adjusted so as to correct the deviation between the optical axes of the P-polarized light and the S-polarized light output from the PBS 26. Specifically, the spot positions of the P-polarized light and the S-polarized light are adjusted to overlap on the light receiving surfaces of the reproducing light receiving unit 30 and the servo light receiving unit 33.

  The PBS 26 transmits P-polarized light and reflects S-polarized light. By such selective reflection by the PBS 26, the P-polarized light and the S-polarized light are emitted from the PBS 26.

The superposed light of P-polarized light and S-polarized light emitted from the PBS 26 enters a BS (non-polarized beam splitter) 27 and is split by a predetermined spectral ratio (for example, 1: 1).
As shown in the figure, one light split by the BS 27 is guided to the light receiving optical system on the reproducing light receiving unit 30 side, and the other light is guided to the light receiving optical system on the servo light receiving unit 33 side.

Specifically, in the optical system on the reproducing light receiving unit 30 side, one light split by the BS 27 is condensed on the light receiving surface of the reproducing light receiving unit 30 via the polarizing plate 28 and the condenser lens 29. .
Here, the light reception signal by the reproduction light receiving unit 30 is expressed as a light reception signal DT-rd.

In the optical system on the servo light receiving unit 33 side, the other light split by the BS 27 is reflected by the mirror 31 so that its optical axis is bent by approximately 90 °, and then passes through the cylindrical lens 32. The light is condensed on the light receiving surface of the servo light receiving unit 33.
In this case, the servo light receiving unit 33 is composed of a plurality of light receiving elements, in which the light receiving region is divided into a plurality (for example, four) in order to correspond to the servo system based on the astigmatism method.
Hereinafter, light reception signals obtained by the plurality of light receiving elements obtained by the servo light receiving unit 33 are collectively referred to as a light reception signal DT-sv.

  Subsequently, in the optical system for the reference surface laser light, the reference surface laser light emitted from the reference surface laser 34 enters the PBS 35 as shown in the figure. The PBS 35 is configured to transmit the reference surface laser light (outgoing light) incident from the reference surface laser 34 side in this way.

The reference surface laser light transmitted through the PBS 35 enters the dichroic mirror 18 through the quarter-wave plate 36.
As described above, the dichroic mirror 18 is configured to transmit light in the same wavelength band as that of the recording layer laser light and reflect light of other wavelengths, so that the reference surface laser light is dichroic. Reflected by the mirror 18, the bulk type recording medium 1 (reference surface Ref) is irradiated through the objective lens 19 as shown in the figure.

In addition, the reflected light (reflected light from the reference surface Ref) obtained in response to the irradiation of the reference surface laser beam on the bulk type recording medium 1 in this way is transmitted by the rear dichroic mirror 18 via the objective lens 19. The light is reflected and enters the PBS 35 through the quarter-wave plate 36.
In this way, the reflected light (return light) of the laser light for reference surface incident from the bulk type recording medium 1 side is forwarded by the action of the quarter wavelength plate 36 and the action at the time of reflection on the bulk type recording medium 1. The polarization direction differs from that of light by 90 °. Therefore, the reflected light of the reference surface laser light as the return light is reflected by the PBS 35.

The reflected light of the reference surface laser light reflected by the PBS 35 is reflected by the mirror 37 so that its optical axis is bent by 90 °, and then received by the reference surface light receiving unit 39 via the cylindrical lens 38. Condensed on the surface.
Here, the reference surface light receiving unit 39 is also provided with a plurality of light receiving elements (for example, four) so as to correspond to the servo system based on the astigmatism method. Hereinafter, the plurality of light receiving elements as the reference surface light receiving unit 39 are provided. The light reception signals obtained in the above are collectively referred to as a light reception signal DT-ref.

  Here, although description by illustration is omitted, the recording / reproducing apparatus 10 is actually provided with a slide drive unit that slides the entire optical pickup OP described above in the tracking direction, and the optical pickup OP by the slide drive unit is provided. By driving this, the irradiation position of the laser beam can be displaced over a wide range.

FIG. 4 shows the overall internal configuration of the recording / reproducing apparatus 10.
4, the internal configuration of the optical pickup OP is the recording layer laser 11, the reference surface laser 34, the first lens actuator 20, the second lens actuator 22, and the focus mechanism 17 in the configuration shown in FIG. Only extracted and shown.

In FIG. 4, a recording processing unit 41 is provided for processing data to be recorded on the bulk layer 5 (recording data in the figure).
For example, the recording processing unit 41 performs actual recording on the bulk layer 5 by adding an error correction code, interleaving processing, predetermined recording modulation encoding, and address information addition to the input recording data. A recording modulation data string which is a binary data string of “0” and “1” is obtained.

  Here, as described later, in this example, mark position recording is performed on the bulk layer 5 instead of mark edge recording. Therefore, the recording modulation encoding performed by the recording processing unit 41 corresponds to mark position recording.

  For confirmation, the mark position recording referred to here refers to a recording method in which channel data “0” and “1” are simply determined based on whether or not a mark is formed. More specifically, when a mark is formed on a portion where a mark is to be formed on the mark row when a mark of a monotone shape in which marks having a predetermined length are arranged at a predetermined cycle is used as a reference, for example, If the channel data is “1” and the mark is not formed in the portion where the mark is to be formed, the channel data is “0”, for example.

At the time of recording, the light emission drive unit 42 generates a laser drive signal D1 based on the modulated data sequence input from the recording processing unit 41, and drives the recording layer laser 11 to emit light with a recording power by the laser drive signal D1.
Further, at the time of reproduction, the light emission drive unit 42 generates a laser drive signal D1 for causing the recording layer laser 11 to emit light continuously with reproduction power based on an instruction from a controller 55 which will be described later, and the recording layer based on the laser drive signal D1. The laser 11 is driven to emit light.

  In addition, the light emission drive unit 43 generates a laser drive signal D2 for causing the reference surface laser 34 to emit light continuously with reproduction power based on an instruction from the controller 55, and the reference surface laser 34 is based on the laser drive signal D2. Is driven to emit light.

The light reception signal DT-rd obtained by the reproduction light receiving unit 30 shown in FIG. 3 is input to the I / V conversion amplifier 44.
The I / V conversion amplifier 44 converts the received light signal DT-rd into a voltage signal and outputs the result to the reproduction processing unit 45 as a signal SR.

The reproduction processing unit 45 performs predetermined reproduction processing on the signal SR, thereby obtaining reproduction data obtained by restoring (reproducing) the above-described recording data.
The specific contents of the reproduction process and the internal configuration of the reproduction processing unit 45 will be described later.

The signal generator 46 receives the light reception signal DT-ref from the reference surface light receiver 39 shown in FIG.
The signal generation unit 46 performs I / V conversion of light reception signals from the plurality of light receiving elements as the light reception signal DT-ref, and generates various necessary signals by matrix calculation processing based on the result.
Specifically, a focus error signal FE-ref for focus servo control (a signal representing a focus error of the reference surface laser beam with respect to the reference surface Ref), and a tracking error signal TE-ref for tracking servo control (reference A signal representing a position error in the radial direction of the irradiation spot of the reference surface laser beam with respect to the position guide on the surface Ref is generated.
The signal generation unit 46 generates a position information detection signal Dps as a signal for detecting the position information recorded on the reference plane Ref. As the position information detection signal Dps, a sum signal is generated when the guide groove is formed of a pit row, and a push-pull signal is generated when the guide groove is formed of a wobbling groove.

  The position information detection signal Dps generated by the signal generation unit 46 is supplied to the address detection unit 47. The address detection unit 47 detects position information (referred to as address information ADR) recorded on the reference surface Ref based on the position information detection signal Dps. The detected address information ADR is supplied to the controller 55.

The focus error signal FE-ref and the tracking error signal TE-ref generated by the signal generator 46 are supplied to the reference surface servo circuit 48.
In response to an instruction from the controller 55, the reference surface servo circuit 48 generates a focus servo signal FS-ref (for causing the focus position of the reference surface laser light to follow the reference surface Ref based on the focus error signal FE-ref. Signal) and a tracking servo signal TS-ref (a signal for causing the irradiation spot of the laser light for the reference surface to follow the position guide on the reference surface Ref) based on the tracking error signal TE-ref. .

  The reference surface servo circuit 48 also performs execution control of a track jump operation for turning off the tracking servo and jumping the irradiation spot of the reference surface laser beam to another track in accordance with an instruction from the controller 55.

The focus servo signal FS-ref obtained by the reference surface servo circuit 48 is supplied to the driver 51.
A tracking servo signal TS-ref (a jump pulse, a brake pulse, etc. at the time of the track jump) is supplied to the switch SW1.

  The driver 51 generates a focus drive signal FD based on the focus servo signal FS-ref input from the reference surface servo circuit 48, and drives the focus coil of the first lens actuator 20 by the focus drive signal FD. Thereby, the objective lens 19 is driven so that the focal position of the laser light for reference surface follows the reference surface Ref.

In this case, the focus drive signal FD generated by the driver 51 is input to the inverting circuit 52. The focus drive signal FD (denoted as focus drive signal FD ′) whose polarity is inverted by the inversion circuit 52 is supplied to the second lens actuator 22, whereby the focus coil of the second lens actuator 22 is focused on the focus drive signal FD ′. It will be driven by.
As a result, the objective lens 21 shown in FIG. 3 is driven in conjunction with the driving of the objective lens 19 in the focus direction, and as a result, the emitted light of the objective lens 21 (the emitted light toward the light receiving unit) is It is intended to maintain a parallel light state.

  In the case of this example, the focus control of the objective lens based on the reflected light of the reference surface laser light is executed corresponding to both recording and reproduction.

Further, the light generation signal DT-sv from the servo light receiving unit 33 shown in FIG.
The signal generator 49 performs I / V conversion on the received light signal from each light receiving element as the received light signal DT-sv, and based on the result, a focus error signal FE-sv (for recording layer) for focus servo control. Generates a focus error for the laser beam mark row) and a tracking error signal TE-sv for tracking servo control (a signal representing the radial position error of the recording layer laser beam irradiation spot with respect to the mark row) To do.
These focus error signal FE-sv and tracking error signal TE-sv are supplied to the recording layer servo circuit 50.

  The recording layer servo circuit 50 generates a focus servo signal FS-sv and a tracking servo signal TS-sv based on the focus error signal FE-sv and the tracking error signal TE-sv in response to an instruction from the controller 55. To do. The focus servo signal FS-sv is a signal for causing the focus position of the recording layer laser light to follow the information recording layer position (mark formation layer position) Ln to be reproduced (cancel the focus error). The tracking servo signal TS-sv is a signal for causing the spot position of the recording layer laser light to follow the mark row (cancelling the tracking error).

  The recording layer servo circuit 50 also performs execution control of a track jump operation for turning off the tracking servo and jumping the irradiation spot of the recording layer laser beam to another mark row in accordance with an instruction from the controller 55.

The tracking servo signal TS-sv generated by the recording layer servo circuit 50 (which becomes a jump pulse, a brake pulse or the like at the time of the track jump) is supplied to the switch SW1 described above.
Further, the focus servo signal FS-sv is supplied to the switch SW2.

Here, as understood from the above description, the tracking servo control for the objective lens 19 should be performed based on the reference surface laser light during recording and should be performed based on the recording layer laser light during reproduction. Become.
The switch SW1 is provided in order to realize such tracking servo switching during recording / reproduction.

Based on an instruction from the controller 55, the switch SW1 selects the output signal of the reference surface servo circuit 48 in response to recording, and selects the output signal from the recording layer servo circuit 50 in response to reproduction. To be done.
The selection output of the switch SW1 is supplied to the driver 51.

The driver 51 generates a tracking drive signal TD based on the signal selected and output by the switch SW1, and drives the tracking coil of the first lens actuator 20 based on the tracking drive signal TD.
As a result, tracking servo control of the objective lens 19 is realized based on the tracking servo signal TS-ref output from the reference surface servo circuit 48 for recording, and the recording layer servo circuit 50 is used for reproduction. Tracking servo control of the objective lens 19 based on the output tracking servo signal TS-sv is realized.

In this case, the tracking drive signal TD generated by the driver 51 is input to the inverting circuit 53. The tracking drive signal TD (denoted as tracking drive signal TD ′) whose polarity has been inverted by the inversion circuit 53 is supplied to the second lens actuator 22, whereby the tracking coil of the second lens actuator 22 is fed into the tracking drive signal TD ′. It will be driven by.
As a result, the objective lens 21 shown in FIG. 3 is driven in conjunction with the driving of the objective lens 19 in the tracking direction. As a result, the light emitted from the objective lens 19 (the recording layer via the bulk layer 5) is driven. Therefore, it is possible to prevent the occurrence of a situation in which signal reproduction and servo control cannot be performed properly.

Here, the focus servo signal FS-sv from the above-described recording layer servo circuit 50 and the offset of-L from the controller 55 are input to the switch SW2.
As can be understood from the above description, the focus control of the recording layer laser beam by the focus mechanism 17 is performed by applying the offset of-L as shown in FIG. This should be performed based on the focus servo signal FS-sv. The switch SW2 is provided for such focus control switching.

Specifically, the switch SW2 selects the offset of-L output from the controller 55 in response to recording based on an instruction from the controller 55, and the recording layer servo circuit 50 in response to playback. The focus servo signal FS-sv from is selected.
The selection output of the switch SW2 is supplied to the driver 54.

  The driver 54 generates a focus drive signal FD-sv based on the output signal of the switch SW2, and drives the focus mechanism 17 with the focus drive signal FD-sv. This realizes focus control based on the offset of-L at the time of recording, that is, focus control to match the focus position of the recording layer laser beam with the information recording layer position Ln to be recorded, and at the time of reproduction, the focus servo signal Focus servo control based on FS-sv (that is, focus control for causing the focus position of the recording layer laser beam to follow the information recording layer position Ln to be reproduced) is realized.

The controller 55 is constituted by a microcomputer including a memory (storage device) such as a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), for example, and a program stored in the ROM or the like, for example. The overall control of the recording / reproducing apparatus 10 is performed by executing the processing according to the above.
For example, the controller 55 controls (sets) the focus position of the recording layer laser light during recording based on the value of the offset of-L set in advance corresponding to each layer position L as described above. Specifically, the output of the offset of-L to the switch SW2 and the switching control of the switch SW2 are executed.

  Further, the controller 55 issues an instruction to the reference surface servo circuit 48, the recording layer servo circuit 55, and the switch SW1, so that the tracking servo is performed by a method corresponding to each case of recording / reproducing with respect to the bulk type recording medium 1. Control is performed so that is executed.

The controller 55 also performs a seek operation control (movement control to the recording / reproduction start position) based on the address information ADR detected by the address detection unit 47.
Here, at the time of seek, since the movement on the reference plane Ref is performed, the output signal of the reference plane servo circuit 48 is selected by the switch SW1.
The focus servo control of the objective lens 19 at the time of seek is performed based on the focus servo signal FS-ref generated by the reference surface servo circuit 48.

<4. Reproduction method of embodiment>

Subsequently, a reproduction method as an embodiment realized by the recording / reproducing apparatus 10 described above will be described.
FIG. 5 shows the configuration of the main part related to the reproduction method of the embodiment extracted from the optical system shown in FIG.
As described above, the recording layer laser light is incident on the half-wave plate 12. In the case of this example, the laser light for the recording layer is 45 ° polarized light through the half-wave plate 12.

The recording layer laser light having 45 ° polarization is split into P-polarized light and S-polarized light by the PBS 13, and then enters the objective lens 19 with the optical axis being shifted by the mirror 14, the mirror 15, and the PBS 16.
P-polarized light and S-polarized light through the objective lens 19 are condensed at different positions on the information recording layer position Ln to be reproduced in the bulk type recording medium 1.

The P-polarized light and S-polarized light after focusing on the information recording layer position Ln to be reproduced are converted into parallel light through the objective lens 21. The P-polarized light and S-polarized light that have passed through the objective lens 21 are incident on a correction optical system including the PBS 23, the mirror 24, the mirror 25, and the PBS 26. By this correction optical system, the superimposed light of P-polarized light and S-polarized light can be obtained as described above.
The superimposed light of the P-polarized light and the S-polarized light is received by the reproducing light receiving unit 30 via the polarizing plate 28.

  In the case of this example, the optical reference axis of the polarizing plate 28 is adjusted so as to selectively transmit 45 ° polarized light. In other words, the transmittance is maximum with respect to 45 ° polarized light, and the transmittance is minimized with respect to polarized light (135 ° polarized light) whose polarization direction is shifted by 90 ° from 45 ° polarized light.

Here, the polarization direction of the superposed light of P-polarized light and S-polarized light obtained by the correction optical system changes from 45 ° according to the passage of the mark portion formed in the bulk layer 5.
Hereinafter, this point will be described with reference to FIG.

FIG. 6 is an explanatory diagram of the basic principle of the reproduction method according to the embodiment.
In FIG. 6, with the rotation of the bulk type recording medium 1, the P-polarized light and S-polarized light pass through the mark M formed on the bulk layer 5 (left side in the figure), and the P-polarized light and S-polarized light at that time The phase state (center in the figure) and the relationship between the polarization direction of the superposed light of P-polarized light and S-polarized light and the amount of received light (right side in the figure) are shown.
Specifically, in FIG. 6A, both P-polarized light and S-polarized light are in the non-formation portion (space portion) of the mark M, in FIG. 6B, only P-polarized light is in the formation portion of the mark M, and in FIG. A state in which both S-polarized light is in the mark M forming portion is shown.

First, as a premise, in the reproducing method of the present embodiment, P-polarized light and S-polarized light are irradiated so that their irradiation spots have a relationship between a preceding spot and a subsequent spot. Specifically, in this example, the optical axis adjustment by the PBS 13, the mirror 14, the mirror 15, and the PBS 16 is performed so that the P-polarized irradiation spot becomes the preceding spot and the S-polarized irradiation spot becomes the subsequent spot.
Here, “preceding” and “following” mean the relationship on the same track, and the positions of both spots in the tracking direction are the same.

As can be seen with reference to FIGS. 6A and 6C, when both beams are in the mark M forming part or non-forming part, the optical path lengths of P-polarized light and S-polarized light (optical path length to the polarizing plate 28) are as follows. They coincide and there is no phase difference between P-polarized light and S-polarized light.
In these states, the superimposed light of P-polarized light and S-polarized light incident on the polarizing plate 28 does not change from the polarization direction after passing through the half-wave plate 12, and therefore remains 45 ° polarized light. .
As a result, in the state of FIG. 6A and FIG.

On the other hand, when only one of P-polarized light and S-polarized light is in the mark M forming portion as shown in FIG. 6B, the refractive index of the mark M forming portion is different from that of the mark M non-forming portion. The optical path length difference corresponding to the difference in the refractive index is generated between the P-polarized light and the S-polarized light (Δ in the figure). That is, due to this, a phase difference occurs between the P-polarized light and the S-polarized light.
In the drawing, it is assumed that the phase difference generated in the state where only one of the P-polarized light and the S-polarized light is in the mark M forming portion is 180 °.
Therefore, in this case, the polarization direction of the superimposed light of P-polarized light and S-polarized light is 135 ° as shown in the figure, and as a result, the amount of light transmitted through the polarizing plate 28 is minimized and the amount of light received by the reproducing light receiving unit 30 is also minimum. It becomes.

  As described above, in the reproduction method of the present embodiment, signal reproduction is performed by using the change in the amount of received light caused by the phase difference generated between the P-polarized light and the S-polarized light as the mark M passes.

Here, the manner of changing the amount of received light described in FIG. 6 is based on the premise that the spot sizes of P-polarized light and S-polarized light are very small with respect to the mark size.
In this case, the signal SR obtained based on the light reception signal DT-rd of the reproduction light receiving unit 30 has a maximum amplitude when both the P-polarized light and the S-polarized light are in the non-formed portion of the mark M, and the P-polarized light is the mark M The amplitude is minimized while the S-polarized light is still in the non-formed portion of the mark M, and the minimum value is maintained while the P-polarized light is on the mark M and the S-polarized light is in the non-formed portion of the mark. To do.
Then, when the S-polarized light also reaches the mark M, the amplitude returns to the maximum again, and thereafter the maximum value is maintained when the P-polarized light and the S-polarized light are on the mark M, and the P-polarized light is at the rear edge of the mark M. The amplitude is again minimized when the S-polarized light is still on the mark M. Thereafter, when both the P-polarized light and the S-polarized light are in a state where the mark M is not formed, the amplitude returns to the maximum value.

  As described above, in the present embodiment, a waveform whose amplitude decreases corresponding to the edge portion of the mark M can be obtained as the signal SR. In this case, for example, by detecting the time length between the edges of the signal SR, it is possible to properly reproduce the signal recorded with the mark edge.

However, in practice, the beam spot size is set to have a certain size with respect to the mark size.
For example, in the case of BD, for the shortest mark length L = 0.15 μm, the spot size S_p is

S_p = 0.82λ / NA = 0.39 μm

About the size is set.

FIG. 7 shows the relationship between the size of the mark M and the size of the P-polarized and S-polarized spot Sp when the mark M having the shortest mark length L is formed in a monotone shape with the interval L.
Here, as shown in the figure, the P-polarized spot Sp is expressed as “Sp-P”, and the S-polarized spot Sp is expressed as “Sp-S”.

As can be seen with reference to FIG. 7, according to the relationship between the mark M and the size of the spot Sp that can be actually assumed, as shown in FIG. 6B, only one of the P-polarized light and the S-polarized light is marked. It can be seen that a state in which only the other side is located on M and only the other side is located only in the non-formed portion of the mark M cannot be obtained (in the section where the shortest marks are continuous in this way).
Considering this point, it can be seen that it is difficult to simply reproduce the signal recorded with the mark edge by the edge detection of the signal SR as described above.

Therefore, in this example, a case where mark position recording is employed instead of mark edge recording is illustrated.
Specifically, in this case, the mark position recording is based on the monotone signal of the mark M with the shortest mark length L (alternate arrangement of the mark M and the space with the length L in both cases), and the code “0” depending on whether or not the mark M is formed. It is assumed that “1” is expressed. More specifically, in this example, for each position spaced by the length L, a “code recording position” is set as a position where the mark M by the length L is to be formed. If M is formed, the code “1” is represented, and if M is not formed, the code “0” is represented.

Under this premise, in the present embodiment, the interval D between the P-polarized spot Sp-P and the S-polarized spot Sp-S is set to at least the shortest mark length L or less.
Here, as shown in FIG. 7, the spot interval D means the distance in the linear direction (track longitudinal direction) between the center of the P-polarized spot Sp-P and the center of the S-polarized spot Sp-S. It is.
In this example, the interval D is set to 0.10 μm with respect to the shortest mark length L = 0.15 μm.

FIG. 8A illustrates the relationship between the mark row formed in the bulk layer 5 by mark position recording and the amplitude of the signal SR.
Specifically, FIG. 8A shows the relationship between the mark string and the amplitude of the signal SR when the code “1001011101” is recorded at the mark position. In the figure, the solid line represents the waveform of the signal SR, and the broken line represents the on / off of the mark.
In the drawing, the relationship between the signal SR and the mark row when the center position of the P-polarized spot Sp-P, which is the preceding spot, is used as a reference is shown.

According to the basic principle described with reference to FIG. 6, when the size of the spot Sp is somewhat larger than the mark size as illustrated in FIG. Thus, the amplitude of the signal SR changes according to the difference between the area occupied by the mark and the area occupied by the mark in the spot Sp-S.
As a result, the waveform of the signal SR as shown is obtained for the recording state of the code “1001011101”.

According to FIG. 8A, it can be seen that two peaks are obtained for one mark in the signal SR.
Therefore, by performing peak detection for the signal SR, it is possible to detect the presence of a mark (ie, code “1”) based on the result.

The detection of the code “0” (that is, no mark) is performed by utilizing the point that the interval of the “code recording position” as the position where the mark is to be formed is known in mark position recording.
Specifically, in mark position recording, the interval of “code recording position” is information known in the standard (in this example, the interval for each length L).
As described above, by performing peak detection on the signal SR, the position of the code “1” can be specified. Therefore, the interval between the detection positions of the code “1” is between the code recording positions known as described above. The number of codes “0” existing between the codes “1” can be specified depending on how long the length is in relation to the interval of “1”. For example, if the length of the interval between the detection positions of the code “1” is about three times the length of the interval between the known code recording positions, the detection position of the code “1” Since it can be estimated that there are two code recording positions between them, the number of codes “0” between the detected positions of code “1” in that case can be determined to be two.

FIG. 8B is an explanatory diagram of a specific code determination method. In FIG. 8B, as the waveform of the signal SR, the waveform obtained in the recording state of “1001011101” is shown as in FIG. 8A.
First, in this example, a threshold value th as shown in the figure is set for the signal SR for the above-described peak detection.
The threshold value th may be set to a value in the vicinity of the middle between the maximum value and the minimum value of the signal SR obtained in accordance with the passage of the mark M formed / non-formed portion as shown in FIG. 8A.
A position where the amplitude value of the signal SR exceeds the threshold th (is smaller than the threshold th) is detected as a peak position.

  Here, as described above, two peak positions are detected per mark. In the present embodiment, only one of the two peak positions detected per mark is detected in this embodiment. Is detected as an effective peak position. For example, in this example, only the peak position on the front side on the time axis is detected as the effective peak position.

Further, in the code determination method of this example, in order to realize the code determination using the “interval between code recording positions” described above, a time length corresponding to the “interval between code recording positions” is obtained (hereinafter, this Such a time length between code recording positions is expressed as a time length Tr).
The time length Tr between the code recording positions can be obtained, for example, based on the known value of the interval between the code recording positions and the linear velocity information. Specifically, the time length Tr between the code recording positions is obtained by dividing the value of the interval between the code recording positions by the value of the linear velocity.

In this example, the detection of the effective peak position as described above is performed, and the time length between the detected effective peaks (hereinafter referred to as the time length Tp-p) is obtained as described above. The number of codes “0” between the codes “1” is determined according to how many times the time length Tr between the recording positions corresponds.
Specifically, if the time length Tp-p is near n times the time length Tr, the number of codes “0” between the codes “1” determined by detecting the effective peak position is “n−1”. Is determined.

  In this example, a margin m of less than 0.5 is provided for the number n. Specifically, for example, if the time length Tp-p is greater than 1.5 times the time length Tr and less than 2.5 times, the number of codes “0” between the codes “1” is set to “1”. If the time length Tp-p is in the range of n ± m times the time length Tr, the number of codes “0” between the codes “1” is determined as “n−1”. And

  For example, the code recorded in the mark position can be properly determined by the above-described method.

  FIG. 9 is an explanatory diagram of a configuration for realizing the reproduction technique according to the embodiment described above. Specifically, FIG. 9 shows the internal configuration of the reproduction processing unit 45 shown in FIG.

As shown in FIG. 9, a peak detection unit 60, a code determination unit 61, and a demodulation unit 62 are provided in the reproduction processing unit 45.
The signal SR shown in FIG. 4 is input to the peak detector 60 in the reproduction processor 45.
The peak detection unit 60 detects the peak of the signal SR based on the threshold value th. Specifically, in this example, a portion that is smaller than the threshold th is detected as the peak of the signal SR.

The code determination unit 61 determines the codes “0” and “1” based on the peak detection result by the peak detection unit 60 and the input linear velocity information Ir. Specifically, in this example, the codes “0” and “1” are determined by the code determination method based on the time length Tp-p between the effective peak positions and the time length Tr between the code recording positions described above.
That is, the time length Tp-p between the effective peak positions (in this example, the front peak position) among the peak positions detected by the peak detector 60 is sequentially measured, and the value of the time length Tp-p is determined as The value is divided by the value of the time length Tr obtained from the input linear velocity information Ir and the value of the interval between known code recording positions. Then, the number of the code “0” between the codes “1” is determined according to the value obtained by the division. Specifically, according to the value obtained by the division, if the time length Tp-p is in the range of n ± m times the time length Tr, the number of codes “0” between the codes “1” is calculated. It is determined as “n−1”.
In this way, the recorded codes “0” and “1” can be properly determined.
The linear velocity information Ir is obtained from the rotational velocity information of the spindle motor 40 and the current reproduction radius position information, and is input from the controller 55, for example. For the linear velocity information Ir, for example, a fixed value defined in the standard may be used.

The demodulator 62 performs a predetermined demodulation process on the code string (reproduced code string) obtained based on the code determination result by the code determination unit 61 as described above, so that the recording data described in FIG. Get the playback data restored.
Specifically, the demodulator 62 in this case performs predetermined demodulation processing such as decoding of a recording modulation code, deinterleaving processing, and error correction processing on the playback code string to obtain the playback data.

  As described above, in the present embodiment, the bulk layer 5 is irradiated with P-polarized light and S-polarized light so as to form a leading / following spot, and superposed light of these P-polarized light and S-polarized light. Is received through the polarizing plate 28. Under this configuration, signal reproduction is performed by using the change in the polarization direction of the superimposed light that occurs according to the formation state of the mark M on the bulk layer 5.

Since the reproduction method as such an embodiment is a reproduction method that uses a change in the polarization state of the light irradiated to the recording layer, the difference in reflectance between the mark M forming part and the non-forming part is low. Even in this case, signal reproduction can be performed with good SNR.

<5. Modification>

The embodiments according to the present technology have been described above. However, the present technology should not be limited to the specific examples described above.
For example, in the description so far, the case where the optical recording medium to be reproduced is a bulk type recording medium having a bulk-shaped recording layer, but the present technology is not a bulk-shaped recording layer. The present invention can also be suitably applied to an optical recording medium (referred to as multilayer recording medium 65) provided with a recording layer having a multilayer structure in which a plurality of recording films are formed as shown in FIG.

10, the multilayer recording medium 65 is the same as the bulk type recording medium 1 shown in FIG. 1 in that the cover layer 2, the selective reflection film 3, and the intermediate layer 4 are formed in order from the upper layer side. In this case, instead of the bulk layer 5, a recording layer having a layer structure in which the semitransparent recording film 66 and the intermediate layer 4 are repeatedly laminated a predetermined number of times as shown in the figure is laminated. As shown in the figure, the translucent recording film 66 formed in the lowermost layer is laminated on a substrate 67. Note that a total reflection recording film can be used as the recording film formed in the lowermost layer.
It should be noted that the translucent recording film 66 is not formed with a position guide accompanying the formation of grooves or pit rows. That is, also in this multilayer recording medium 65, the position guide is formed only for one layer position as the reference plane Ref.

  In such a recording layer of the multilayer recording medium 65, a translucent recording film 66 that functions as a reflecting film is formed. Therefore, P-polarized light and S-polarized light are reflected on the apparatus side as reflected light from the translucent recording film 66. It should be returned.

FIG. 11 is a diagram exemplifying a configuration of an optical pickup OP ′ for performing reproduction corresponding to the reflective multilayer recording medium 65 as described above.
In FIG. 11, parts that are the same as the parts that have already been described so far are denoted by the same reference numerals and description thereof is omitted.

As can be seen from comparison with FIG. 3, the optical pickup OP ′ in this case includes an objective lens 21 and a second lens actuator 22 for entering the light transmitted through the optical recording medium, as compared with the optical pickup OP. Is omitted, and the BS 70 is inserted between the focus mechanism 17 and the PBS 16.
In this case, the P-polarized light and S-polarized light reflected by the translucent recording film 66 are converted into parallel light through the objective lens 19 and then passed through the dichroic mirror 18 and the focus mechanism 17 as shown in the figure. , Enters the BS 70.
The BS 70 reflects a part of each of the P-polarized light and the S-polarized light thus obtained as reflected light.

  After the P-polarized light and S-polarized light reflected by the BS 70 are superimposed through the same correction optical system (PBS 23, mirror 24, mirror 25, PBS 26) as that provided in the optical pickup OP shown in FIG. , BS 27 and the light receiving optical system for reproduction (polarizing plate 28, condensing lens 29, light receiving light receiving unit 30) and servo light receiving optical system (mirror 31, cylindrical lens 32, servo light receiving unit 33). And led to.

Here, if the configuration of the optical pickup OP ′ corresponding to such a reflection type optical recording medium is used, the objective lens 21 and the second lens actuator 22 can be omitted, and the objective lens 21 is interlocked with the objective lens 19. There is an advantage that the configuration for position control can also be omitted.
Further, in such a reflection type configuration, the reflected light from the translucent recording film 66 can be obtained even when the mark M is in an unrecorded state. Based on the reflected light.

  In the optical recording medium shown in FIGS. 10 and 1, the reference surface Ref is provided on the upper layer side of the recording layer. However, the reference surface Ref may be provided on the lower layer side of the recording layer. it can.

  In the description so far, the polarization direction of the light emitted from the light source is adjusted by the half-wave plate 12 so that 45 ° polarized light is input to the PBS 13 that separates the P-polarized light and the S-polarized light. However, this allows the spectral ratio in the PBS 13 to be 1: 1. However, the half-wave plate 12 can be omitted when 45 ° polarized light is obtained without using the half-wave plate 12 or when the spectral ratio is not required to be 1: 1. .

  In the above description, the example in which the optical reference axis of the polarizing plate 28 is adjusted so that the amount of transmitted light is maximized when 45 ° polarized light is incident is described. However, the method for adjusting the optical reference axis is limited to this. For example, the amount of transmitted light may be maximized when 135 ° polarized light is incident. For example, a difference in the amount of received light may be caused by another adjustment method.

  In the description so far, the case where the space is the code “0” and the mark M is the code “1” is illustrated, but these relations may be reversed.

In addition, the specific determination methods of the symbols “0” and “1” should not be limited to those exemplified above.
For example, in the above description, the time length Tr is obtained from the linear velocity information Ir. However, the time length Tr may be obtained based on the clock after generating a clock corresponding to the mark formation period. it can.
Alternatively, when such a clock is generated, the timing of the code recording position is estimated based on the clock, and the number of codes “0” as the number of code recording positions between the effective peak positions can be obtained. .

Further, in the description so far, the case where the distance D between spots of P-polarized light and S-polarized light is set to 0.10 μm is exemplified. However, the distance D between spots is obtained by the reproduction method as the above-described embodiment. In realization, it may be at least the shortest mark length L or less.
Here, in the present technology, the P-polarized light and the S-polarized light are irradiated so as to form the preceding / following spots. Therefore, as shown in FIG. A shift such as “d” (shift in the line direction) always occurs.
If such a shift d is slight, a phase difference can be generated between the P-polarized light and the S-polarized light at the edge portion of the mark M as shown in FIGS. 12B and 12C, and an amplitude change corresponding to the phase difference can be obtained. be able to.

  However, if the deviation d is excessive, the amplitude change according to the formation state of the mark M is taken into consideration when the relationship between the actual mark size and the spot size as shown in FIG. Therefore, there is a possibility that the code “0” or “1” cannot be properly obtained from the viewpoint that the determination can be made.

Therefore, the condition “the shortest mark length L or less” is imposed on the inter-spot distance D as described above.
Under such conditions, for example, when mark position recording as described above is assumed, it is possible to perform the determination of the codes “0” and “1” by a relatively simple method (peak detection).

For confirmation, the above-mentioned condition of the inter-spot distance D indicates an indispensable condition in terms of changing the polarization direction of the superimposed light of P-polarized light and S-polarized light according to the formation state of the mark. Not a thing.
Here, the point that “the polarization direction of the superimposed light of P-polarized light and S-polarized light changes according to the formation state of the mark” is a basic prerequisite for the establishment of the reproduction method of the present technology. In order to satisfy the preconditions, the distance D between spots may be small. In other words, it is sufficient if the P-polarized light and the S-polarized light are irradiated so as to have a preceding / following spot relationship.

In the above description, P-polarized light and S-polarized light are used as the first light and the second light. However, the first light and the second light are not limited to P-polarized light and S-polarized light. Light in which the polarization directions are orthogonal can be used.
Here, according to the basic principle described with reference to FIG. 6, even if the polarization directions of the first light and the second light are not completely orthogonal, a change in amplitude corresponding to the formation state of the mark M is detected. It is understood that is possible. Therefore, in the present technology, as the first light and the second light, not only when the polarization directions thereof are completely orthogonal, it is sufficient if they are approximately orthogonal.

  Further, in the above description, the case where the reproduction method of the present technology is applied to the reproduction method for the signal recorded with the mark position is exemplified, but the present technology is also suitable as a reproduction method for the signal recorded with the mark edge. Applicable.

  In the above description, the case where the present technology is applied to the optical recording medium in which the reference surface Ref is provided on the upper layer side of the recording layer (the recording layer of the mark M) is illustrated. However, the present invention can also be suitably applied to an optical recording medium provided on the lower layer side of the recording layer.

  In the description so far, the case where the present technology is applied to a recording / reproducing apparatus capable of recording along with the reproduction of the optical recording medium (recording layer) has been exemplified. However, the present technology relates to the optical recording medium (recording layer). The present invention can also be suitably applied to a reproduction-only device (reproduction device) in which the recording function is omitted.

In addition, the present technology can also employ the following configuration.
(1)
Irradiate the recording layer of the optical recording medium with the first light and the second light whose polarization directions are substantially orthogonal to each other so that the respective irradiation spots have a preceding and following relationship. A light irradiation unit;
A correction optical system for superimposing the first light and the second light via the recording layer;
A polarizing plate on which superimposed light of the first light and the second light obtained by the correction optical system is incident;
A light receiving portion for receiving the superimposed light via the polarizing plate;
A reproducing unit that performs signal reproduction based on a light reception signal from the light receiving unit.
(2)
The light irradiation part is
The reproducing apparatus according to (1), wherein the light emitted from the common light source is separated into P-polarized light and S-polarized light using a polarization beam splitter to obtain the first light and the second light.
(3)
The light irradiation part is
The irradiation spot is formed so that the relationship between the preceding and following can be obtained by shifting the optical axis of at least one of the first light and the second light,
The correction optical system is
The reproducing apparatus according to any one of (1) and (2), wherein the optical axes of the first light and the second light passing through the recording layer are made to coincide with each other.
(4)
The reproducing apparatus according to any one of (1) to (3), wherein an interval between the irradiation spot of the first light and the irradiation spot of the second light is set to be equal to or shorter than a shortest mark length in the recording layer.
(5)
In the recording layer, the mark is recorded in position,
The playback unit
The reproduction apparatus according to any one of (1) to (4), wherein signal reproduction is performed based on a result of detecting a pattern of the presence / absence of the mark from the light reception signal.
(6)
The playback unit
The reproduction apparatus according to (5), wherein the signal reproduction is performed by determining the presence or absence of the mark based on a result of performing peak detection on the light reception signal.
(7)
The recording layer is a bulk recording layer, and a refractive index modulation mark is formed on the recording layer.
The correction optical system is
The reproducing apparatus according to any one of (1) to (6), wherein the first light and the second light transmitted through the recording layer are incident and superimposed.
(8)
The recording layer has a reflective film,
The correction optical system is
The reproducing apparatus according to any one of (1) to (6), wherein the first light and the second light reflected by the reflective film of the recording layer are incident and superimposed.

  1 Bulk type recording medium, 2 cover layer, 3 selective reflection film, Ref reference plane, 4 intermediate layer, 5 bulk layer, L information recording layer position (mark formation layer position), OP, OP 'optical pickup, 11 for recording layer Laser, 12 1/2 wavelength plate, 13, 16, 23, 26, 35 PBS (polarization beam splitter), 14, 15, 24, 25, 31, 37 mirror, 17 focus mechanism, 18 dichroic mirror, 19, 21 objective Lens, 20 First lens actuator, 22 Second lens actuator, 27,70 BS (Non-polarizing beam splitter), 28 Polarizing plate, 29 Condensing lens, 30 Receiving light receiving part, 32,38 Cylindrical lens, 33 Light receiving for servo 34, laser for reference plane, 36 1/4 wavelength plate, 39 light receiving section for reference plane, 40 SPM (spindle motor), 4 I / V conversion amplifier, 45 playback processing unit, 55 controller, 60 a peak detection unit, 61 sign determination unit, 62 demodulating unit, 65 multilayer recording medium, 66 a semi-transparent recording film, 67 substrate

Claims (9)

Irradiate the recording layer of the optical recording medium with the first light and the second light whose polarization directions are substantially orthogonal to each other so that the respective irradiation spots have a preceding and following relationship. A light irradiation unit;
A correction optical system for superimposing the first light and the second light via the recording layer;
A polarizing plate on which the superimposed light of the first light and the second light obtained by the correction optical system is incident;
A light receiving portion for receiving the superimposed light via the polarizing plate;
A reproducing unit that performs signal reproduction based on a light reception signal from the light receiving unit. The light irradiation part is
The reproducing apparatus according to claim 1, wherein the first light and the second light are obtained by separating light emitted from a common light source into P-polarized light and S-polarized light using a polarization beam splitter. The light irradiation part is
The irradiation spot is formed so that the relationship between the preceding and following can be obtained by shifting the optical axis of at least one of the first light and the second light,
The correction optical system is
The reproducing apparatus according to claim 1, wherein the optical axes of the first light and the second light that pass through the recording layer are made to coincide with each other. The reproducing apparatus according to claim 1, wherein an interval between the irradiation spot of the first light and the irradiation spot of the second light is set to be equal to or shorter than a shortest mark length in the recording layer. In the recording layer, the mark is recorded in position,
The playback unit
The reproduction apparatus according to claim 1, wherein signal reproduction is performed based on a result of detecting a pattern of presence / absence of the mark from the light reception signal. The playback unit
The reproducing apparatus according to claim 5, wherein the signal reproduction is performed by determining the presence or absence of the mark based on a result of performing peak detection on the light reception signal. The recording layer is a bulk recording layer, and a refractive index modulation mark is formed on the recording layer.
The correction optical system is
The reproducing apparatus according to claim 1, wherein the first light and the second light transmitted through the recording layer are incident and overlapped. The recording layer has a reflective film,
The correction optical system is
The reproducing apparatus according to claim 1, wherein the first light and the second light reflected by the reflective film of the recording layer are incident and overlapped. Irradiate the recording layer of the optical recording medium with the first light and the second light whose polarization directions are substantially orthogonal to each other so that the respective irradiation spots have a preceding and following relationship. Light irradiation procedure;
A correction procedure for superimposing the first light and the second light through the recording layer;
A light receiving procedure for receiving the superimposed light of the first light and the second light obtained by the correction procedure via a polarizing plate;
A reproduction procedure for performing signal reproduction based on a light reception signal obtained by the light reception procedure.