JP5191198B2 - Optical recording medium, optical recording / reproducing system - Google Patents

Optical recording medium, optical recording / reproducing system Download PDF

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JP5191198B2
JP5191198B2 JP2007253169A JP2007253169A JP5191198B2 JP 5191198 B2 JP5191198 B2 JP 5191198B2 JP 2007253169 A JP2007253169 A JP 2007253169A JP 2007253169 A JP2007253169 A JP 2007253169A JP 5191198 B2 JP5191198 B2 JP 5191198B2
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information recording
optical recording
layer
recording layer
l0
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JP2009087418A (en
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達也 加藤
浩 新開
正則 小須田
寛史 ▲高崎▼
靖博 ▲高▼木
秀樹 平田
肇 宇都宮
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Tdk株式会社
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Description

  The present invention relates to an optical recording medium having a plurality of information recording layers and an optical recording / reproducing system for recording / reproducing the optical recording medium.

  Conventionally, for viewing digital moving image contents and recording digital data, CD-DA, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-R, DVD +/- RW, DVD-RAM, etc. These optical recording media are widely used. On the other hand, the recording capacity required for this type of optical recording medium has been increasing year by year, and so-called next-generation optical discs capable of recording large-capacity movies and data have been commercialized in order to meet the demand. Yes. In the next generation type optical disc, the recording capacity is increased by shortening the wavelength of laser light used for recording and reproduction to 405 nm.

  For example, in the Blu-ray Disc (BD) standard, which is one of the next-generation DVD standards, by setting the numerical aperture of the objective lens to 0.85, recording / reproduction of 25 GB can be performed on one recording layer. I have to.

  By the way, it is expected that the capacity of moving images and data will increase further in the future. Therefore, a technology has been realized in which the information recording layer is made into two layers to achieve a total capacity of 50 GB. Further, technological development aimed at further multilayering has been carried out, and multilayering technologies aimed at a four-layer structure (100 GB), a six-layer structure (150 GB), and the like have been reported.

  On the other hand, a method for increasing the recording capacity per layer by increasing the linear recording density has been studied. In this case, assuming that the wavelength of the laser beam is λ and the numerical aperture of the objective lens is NA, if a recording mark and a space of (λ / NA) / 4 or less continue in the modulation signal, the recording mark and the space train are reproduced. There is a so-called reproduction limit in which the amplitude of the signal becomes substantially zero.

  A PRML (Partial Response Maximum Likelihood) identification method is known as a technique for solving the reproduction limit problem. In this PRML identification method, binary data recorded in an information recording layer is estimated based on an electrical analog signal detected at the time of optical recording and reproduction. In this PRML identification method, a reference class characteristic (constraint length) of PR (Partial Response) corresponding to reproduction characteristics is appropriately selected. This constraint length is the extent to which the laser beam spot that reproduces the target recording mark is affected by the recording mark adjacent to this recording mark (optical interference), that is, the state of the adjacent recording mark / space. It is determined in consideration of how much the reproduction signal output is constrained.

  For example, as described in Non-Patent Document 1, the PRML identification with a constraint length of 5 means that all 5 bits including adjacent code bits are reproduced when the code bit “1” of the target recording mark is reproduced. This means that equalization / decoding is performed on the assumption that the reproduction response waveform is expressed by the sequence “12221”.

Therefore, generally, if the constraint length is set to be large, the optical interference of a recording mark at a more distant place can be included in the calculation based on the recording mark to be reproduced. As a result, it is possible to equalize to a waveform close to the actual output waveform, and decoding with high accuracy is possible.
Toshiba Review Vol.60 No.1 p25-p28 2005

  However, the longer the constraint length, the more exponentially the computational circuit scale increases. Therefore, there is a problem that the maximum constraint length within the range where practical calculation processing results can be obtained must be selected. It was. In addition, even within the practical range, the highest constraint length is adopted, so the computation becomes enormous and new LSI designs and system changes are forced. There was a problem.

  The present invention has been made in view of the above-mentioned problems, and a plurality of layers of optical recording having sufficient margin characteristics even when the linear recording density is increased without significantly changing the current optical recording / reproducing system. It is an object to provide a medium and an optical recording / reproducing system.

  The above object can be achieved by the following means based on the earnest studies of the inventors.

(1) A recording / reproducing L1 information recording layer that is reproduced by a PRML identification method arranged on the light incident surface side , and a recording / reproducing L0 that is reproduced by a PRML identification method farthest from the light incident surface side An L1 layer reflectivity based on incident light incident on the light incident surface and reflected light emitted from the incident surface when the L1 information recording layer is irradiated with laser light. When the L0 layer reflectance based on the incident light incident on the light incident surface and the reflected light emitted from the incident surface is R0 when irradiating the L0 information recording layer with laser light, R1 And R0 is 10% or less, R0 is 2% or more, and 0.65> (R1-R0) / (R1 + R0)> 0.25.

(2) The optical recording medium according to (1), wherein the light transmittance of the L0 information recording layer is substantially zero.

(3) The optical recording medium according to (1) or (2) , wherein the recording film material of the L1 information recording layer and the L0 information recording layer is a phase change material.

(4) In any one of the above (1) to (3) , the L1 information recording layer and the L0 information recording layer are laminated at a distance within 105 μm from the light incident surface. Medium.

(5) In any one of the above (1) to (4) , the allowable wavelength λ of the laser light is 400 to 410 nm, and the allowable numerical aperture NA of the objective lens for irradiating the laser light is 0.7 to 0.00. 9. An optical recording medium, wherein

(6) The optical recording medium according to any one of (1) to (5) , wherein a minimum recording mark length recorded in the L1 information recording layer and the L0 information recording layer is 130 nm or less.

(7) In any one of the above (1) to (6) , the L1 information recording layer and the L0 information recording layer allow reproduction by a PRML identification method that is a PR equalization process with a constraint length of 4. An optical recording medium.

(8) The optical recording medium according to any one of (1) to (7) above, a laser light source that emits laser light having a wavelength λ of 400 to 410 nm, and a numerical aperture NA of 0.7 to 0.9. An objective lens for condensing the laser light and irradiating the optical recording medium; a photoelectric conversion device for receiving reflected light of the laser light and converting it into an electronic signal; and a constraint length of PR equalization processing. a 4, the optical recording and reproducing system, characterized in that it comprises, a PRML processing unit for reproducing a signal by PRML detection method, based on the electric signal.

  According to the present invention, even if the linear recording density is increased in an optical recording medium having a multilayer structure, an excellent effect that the signal quality can be improved can be obtained.

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

  FIG. 1A shows an optical recording medium 1 according to an embodiment of the present invention. This optical recording medium 1 is a disc-shaped medium having an outer shape of about 120 mm and a thickness of about 1.2 mm. 1B, the optical recording medium 1 includes a substrate 10, an L0 information recording layer 20, a spacer layer 30, an L1 information recording layer 22, a cover layer 36, a hard coat, and the like. The layers 38 are laminated in this order, and the information recording layer has a two-layer structure.

  The spacer layer 30, the cover layer 36, and the hard coat layer 38 are all light transmissive and transmit laser light incident from the outside. As a result, when the laser beam Z incident from the light incident surface 38A of the hard coat layer 38 is used, information can be recorded / reproduced with respect to the L0 to L1 information recording layers 20 and 22.

  The L1 information recording layer 22 is an information recording layer on the side close to the light incident surface 38A of the optical recording medium 1, and the L0 information recording layer 20 is the information recording layer farthest from the light incident surface 38A. The recording capacity of each information recording layer 20 and 22 is 30 GB. It is also possible to vary the recording capacity for each information recording layer.

  The substrate 10 is a disk-shaped member having a thickness of about 1.1 mm, and various materials such as glass, ceramics, and resin can be used as the material. Here, polycarbonate resin is used. In addition to the polycarbonate resin, an olefin resin, an acrylic resin, an epoxy resin, a polystyrene resin, a polyethylene resin, a polypropylene resin, a silicone resin, a fluorine resin, an ABS resin, a urethane resin, or the like can be used as the resin. Of these, polycarbonate resins and olefin resins are preferred because of their ease of processing and molding. Further, grooves, lands, pit rows, and the like are formed on the surface of the substrate 10 on the information recording layer side according to applications.

  The spacer layer 30 is laminated between the L0 information recording layer 20 and the L1 information recording layer 22 and has a function of separating them. Grooves (lands), pit rows, and the like are formed on the surface of the spacer layer 30 on the light incident surface 38A side. Various materials can be used for the spacer layer 30. However, as described above, in order to transmit the laser beam Z, it is necessary to use a light transmitting material. For example, it is also preferable to use an ultraviolet curable acrylic resin.

  In this optical recording medium 1, the thickness of the spacer layer 30 is set to 25 μm. The thickness of the hard coat layer 38 is set to 2 μm, and the thickness of the cover layer 36 is set to 73 μm. As a result, in this optical recording medium 1, both the L0 information recording layer 20 and the L1 information recording layer 22 are disposed less than 105 μm from the light incident surface 38A. In particular, the L1 information recording layer 22 is set to 80 μm or less from the light incident surface 38A.

  The L0 and L1 information recording layers 20 and 22 are layers for holding data. As a data holding form, there are a read-only type in which data is written in advance and cannot be rewritten, and a recording type in which a user can write, and a recording type is adopted here. When the data holding form is a record type, in detail, a write-once type in which data cannot be written again in an area where data has been written once, and data can be erased and written again in an area in which data has been written. Although there is a rewritable type, the rewritable type is adopted here. In the information recording layers 20 and 22, the data holding modes can be different from each other.

  When the data holding form of the L0 and L1 information recording layers 20 and 22 is a rewritable type, a phase change material is used as the material of the L0 and L1 information recording layers 20 and 22. When the heating amount and cooling rate of the phase change material are appropriately controlled using an optical recording / reproducing system described later, crystallized regions and amorphous regions are selectively created in the information recording layers 20 and 22. Recording marks are formed in the L0 and L1 information recording layers 20 and 22 by utilizing the property that the reflectances of the crystallized region and the amorphous region are different from each other. In addition, this phase change material has a property that even after a recording mark is once formed, a crystallized state and an amorphous state can be appropriately created by irradiating the laser beam Z again. As a result, recording marks are formed reversibly on the L0 and L1 information recording layers 20 and 22, and data can be erased and rerecorded.

  The groove serves as a guide track for the laser beam Z during data recording, and the information recording layers 20 and 22 on the groove are modulated by modulating the energy intensity of the laser beam Z traveling along the groove. A recording mark is formed on the surface.

  In order to irradiate the L0 information recording layer 20 with sufficient laser light Z, the L1 information recording layer 22 is required to have high light transmittance. Therefore, the L1 information recording layer 22 is made to have both the characteristics of light transmission and light reflection by reducing the film thickness. On the other hand, since the L0 information recording layer 20 is required to have a reflectance as high as possible, the light transmittance is made substantially zero by increasing the film thickness.

  Furthermore, in this embodiment, the light reflectance of the L1 information recording layer 22 is R1 (hereinafter referred to as L1 layer reflectance R1), and the light reflectance of the L0 information recording layer 20 is R0 (hereinafter referred to as L0 layer reflectance R0). In this case, 0.65> (R1-R0) / (R1 + R0)> 0.25 is set. Further, the L0 layer reflectance R0 is set to be 2% or more.

  The L1 layer reflectivity R1 is specifically determined by the incident light incident on the light incident surface 38A and the reflection emitted from the incident surface 38A when the L1 information recording layer 22 is irradiated with the laser light Z. It means the ratio of light. Similarly, the L0 layer reflectivity R0 is the ratio of incident light incident on the light incident surface 38A and reflected light emitted from the incident surface 38A when the L0 information recording layer 20 is irradiated with the laser light Z. Means.

  The above (R1−R0) / (R1 + R0) means a so-called reflectance ratio. The larger the difference between the L1 layer reflectance R1 and the L0 layer reflectance R0, the larger the reflectance ratio, and the L1 layer The smaller the difference between the reflectance R1 and the L0 layer reflectance R0, the smaller the reflectance ratio. When the reflectance ratio increases, control such as servo and gain adjustment in the RF signal processing system is required individually. For this reason, it is generally considered that a smaller reflectance ratio is preferable.

  As already described, the recording capacity of each of the information recording layers 20 and 22 is set to 30 GB. This recording capacity is determined by a combination of the size of the recording area (area) and the size of the linear recording density. However, since the recording area (area) of each information recording layer 20, 22 is limited, it is usually a line. The capacity is increased by increasing the recording density.

  The linear recording density determines whether or not the amount of data can be recorded / held during the unit distance in which the laser beam Z moves through the information recording layers 20 and 22, in other words, the recording / reproducing timing. It is determined by how much the laser beam Z moves during a unit clock (time). For example, when the relative speed between the optical recording medium 1 and the laser spot is CLV and the channel clock frequency is f, the information recording track crosses the laser spot during the clock period T (= 1 / f). The distance W is CLV / f. A smaller distance W means higher linear recording density. Therefore, in order to increase the linear recording density, it is necessary to increase the channel clock frequency (f) or decrease the linear velocity (CLV).

  As the condition values allowed by the optical recording medium 1, when the speed is 1 ×, the wavelength λ of the laser light is 400 nm to 410 nm, the numerical aperture NA of the objective lens is 0.7 to 0.9, and the linear velocity CLV is 4.24 m /. Below s, the frequency is above 66 MHz. As a result, the recording capacity is at least 29 GB or more, preferably 30 GB or more. In the case of double speed, both the linear speed and the frequency are set to double.

  Further, assuming that the modulation signal (1, 7) RLL, the minimum recording mark is a 2T mark, and the minimum space is a 2T space, the length of the minimum recording mark and the minimum space is 2W = 2CLV / f. In order to realize 29 GB or more, the minimum recording mark length is preferably 130 nm or less. According to the study by the present inventors, when the length of the recording mark becomes 1.1 × (λ / 4) / NA or less, the amplitude becomes small and the signal cannot be detected by the binary determination based on the jitter level. . For example, when the wavelength λ is 405 nm and the numerical aperture NA of the objective lens is 0.85, reproduction is not possible if the recording mark length is 131 nm or less. Therefore, in the present embodiment, reproduction is enabled by using a PRML processing device described later.

  FIG. 2 shows a configuration of an optical recording / reproducing system 100 for recording / reproducing information on / from the optical recording medium 1. The optical recording / reproducing system 100 includes a laser light source 102 that generates laser light Z used for recording and reproduction, a laser controller 104 that controls the laser light source 102, an optical mechanism 106 that guides the laser light Z to the optical recording medium 1, and laser light. Photodetection device 108 that detects reflected light of Z, PRML processing device 110 that decodes detection information of the photodetection device 108 using a PRML identification method, spindle motor 112 that rotates the optical recording medium 1, and spindle motor 112 that controls rotation A focus error (FE) is detected based on the electrical signal transmitted from the spindle driver 114 and the light detection device 108, and the lens drive coil 106B is driven and controlled in the focus direction (optical axis direction) using this focus error. Focus controller 113, photodetection device 10 A tracking error is detected based on the electric signal transmitted from the tracking controller 115, and the tracking controller 115 that drives and controls the lens driving coil 106B in the tracking direction by using the tracking error, in particular, a CPU (central processing unit) (not shown). A signal processing device 116 is provided for exchanging recorded data and reproduced data after decoding.

  The laser light source 102 is a semiconductor laser and is controlled by the laser controller 104 to generate the laser light Z. The optical mechanism 106 includes an objective lens and a polarizing beam splitter, and can appropriately focus the laser beam Z on the information recording layer. The polarizing beam splitter takes out the reflected light of the information recording layer and guides it to the light detection device 108. The light detection device 108 is a photodetector, receives the reflected light of the laser light Z, converts it into an electrical signal, and outputs it as a reproduction signal to the PRML processing device 110, the focus controller 113, and the tracking controller 115. The PRML processing device 110 decodes the reproduced signal and outputs the decoded binary identification signal to the signal processing device 116.

  Further, in this optical recording / reproducing system 100, the wavelength λ of the laser light Z is set to 400 to 410 nm in response to the demand of the optical recording medium 1. The numerical aperture NA of the objective lens 106A in the optical mechanism 106 is set to 0.7 to 0.9. Specifically, the wavelength λ of the laser beam Z is set to 405 nm, and the numerical aperture NA of the objective lens 106A is set to 0.85. The clock frequency f of this optical recording / reproducing system is set to 66 MHz, and the linear velocity LV of the optical recording medium 1 whose rotation is controlled by the spindle driver 114 is 4.24 m / s or less, preferably 4.1 m / s. s or less. In this embodiment, recording / reproduction at 1 × speed will be described. However, recording / reproduction at 2 × speed or more may be performed.

  In order to record information on the optical recording medium 1, the laser light Z is generated from the laser light source 102 with the recording power, and the L 0 and L 1 information recording layers 20 and 22 of the optical recording medium 1 are irradiated with a beam spot. On the other hand, in order to start reproducing information from the optical recording medium 1, laser light Z is generated from the laser light source 102 with a predetermined reproduction power, and this laser light Z is emitted from the L0 and L1 information recording layers 20 and 22 of the optical recording medium 1. Irradiate to and play. The laser beam Z is reflected by the L0 and L1 information recording layers 20 and 22 and taken out through the optical mechanism 106, and becomes an actual reproduction signal (hereinafter referred to as an actual signal) by the light detection device 108. In any of the optical recording and reproduction, the laser beam Z is reflected by the L0 and L1 information recording layers 20 and 22, and is converted into an electric signal by the photodetector 108.

  Next, the PRML processing apparatus 110 and the PRML (Partial Response Maximum Likelihood) identification method will be described. In the PRML identification scheme, a PR (Partial Response) reference class characteristic corresponding to the reproduction characteristic is appropriately selected. In the present embodiment, the constraint length 4 (1, 2, 2, 1) characteristic is selected as the PR reference class characteristic. The characteristic of the constraint length 4 (1, 2, 2, 1) is that the reproduction response to the code bit (channel pit) “1” constrains the adjacent 4 bits including the code bit “1” and the reproduction response. This means that the waveform can be expressed by the series “1221”. It is estimated that the reproduction response of various code bits actually recorded is formed by the convolution operation of this series “1221”. For example, the response to the code bit sequence 0010000 is 0012210. Similarly, the response to the code bit sequence 0001000 is 0001221. Therefore, the response of the code bit sequence 001000 is the convolution operation of the above two responses and becomes 0013431. The response of the code bit sequence 00111000 is 00135531. Thus, in the case of the characteristic of the constraint length 4 (1, 2, 2, 1), the response obtained by the convolution calculation is 7 levels from 0 to 6.

  The above response obtained by the PR class characteristic assumes an ideal state. In this sense, the above response is called an ideal response. Of course, since the actual response includes noise, there is a deviation from this ideal response. Accordingly, an actual response including noise and an ideal response assumed in advance are compared, and an ideal response that minimizes the difference (distance) is selected, and a decoded signal (identification signal) is selected from this ideal response. Get. This is called ML (Maximum Likelihood) identification.

In ML identification, for example, the Euclidean distance is used to calculate the difference between an ideal response and an actual response (response after equalization processing). The Euclidean distance E between the actual response sequence A (= A0, A1,..., An) and the ideal response sequence B (= B0, B1,..., Bn) is E = √ {Σ (Ai−Bi). ) 2 }. Therefore, the actual response and multiple types of ideal responses assumed in advance are compared and ranked using this Euclidean distance, and the ideal response (this is called the maximum likelihood ideal response) that gives the smallest Euclidean distance is selected. To do.

  Note that the PRML processing apparatus 110 that performs the decoding process based on this PRML identification system includes an A / D converter 110A, a PR equalizer 110B, and an ML decoder 110C, as shown in FIG. In the A / D converter 110A, the electrical analog signal detected by the light detection device 108 is converted into a digital signal to be a reproduction signal. Further, the PR equalizer 110B samples the reproduction signal in correspondence with the clock frequency from a certain reference position. The waveform level of the actual signal obtained by this sampling becomes a non-integer value because the recording mark is distorted due to the influence of the physical and chemical characteristics of the material used for the optical recording medium 1 and the recording strategy. Therefore, the PR equalizer 110B performs equalization processing so that the non-integer value voltage level approaches either level of the PR reference class characteristic to be referred to. Here, since the PR reference class has a constraint length of 4 (1, 2, 2, 1), the ideal response is distributed in 7 levels, and is necessary for equalizing the reproduction signal in the PR equalizer 110B. There are seven types (7 taps) of equalization coefficients (Tap coefficients).

  Here, a Viterbi decoder is used as the ML decoder 110C, and the identification signal is obtained by selecting the maximum likelihood ideal response from the signal equalized by the PR equalizer 110B. Specifically, the difference (Euclidean distance) between the equalized signal and all possible ideal responses is calculated, and the ideal response that minimizes this difference is selected.

  In the optical recording medium 1 and the optical recording / reproducing system 100 of the present embodiment, the reflectance ratio (R1−R0) / (R1 + R0) based on the L1 layer reflectance R1 and the L0 layer reflectance R0 is set to be larger than 0.25. As a result, the output of the L1 information recording layer 22 is increased, and the signal quality can be maintained satisfactorily. Further, since the reflectance ratio is set to be smaller than 0.65, the L0 information recording layer 20 is sufficiently irradiated with the minimum necessary laser beam Z. As a result, the recording / reproducing quality of both the L0 information recording layer 20 and the L1 information recording layer 22 is maintained in a high state.

  In this embodiment, the L0 layer reflectance of the L0 information recording layer 20 is set to 2% or more, and the light transmittance of the L0 information recording layer 20 is set to substantially zero. Therefore, the output quality of the L0 information recording layer 20 can be improved.

  In particular, in this embodiment, the L0 and L1 information recording layers 20 and 22 are made of a phase change material. In general, when a phase change material is used in the L1 information recording layer 22 where light transmission is required, the metal reflective film becomes thin, so that the effect of recrystallization is caused by insufficient cooling (heat dissipation) during recording. Easy to receive. As a result, the recording mark tends to be small or the recording mark shape is likely to be distorted. Therefore, in the present embodiment, the reflectance ratio of the L1 information recording layer 22 is increased within a range that does not adversely affect the L0 information recording layer 20 by deliberately setting the light reflectance ratio to be larger than 0.25. Specifically, the L0 information recording layer 20 has a sufficiently thick reflection film and a high cooling effect, so that a sufficient output can be secured and the distortion of the recording mark is small. Therefore, the noise during reproduction can be reduced. On the contrary, since the L1 information recording layer 22 has a thin reflection film, the cooling effect is reduced and it is affected by recrystallization. As a result, the output during reproduction tends to be small, and the noise tends to increase due to non-uniform recording marks. Therefore, in the present embodiment, the signal output is increased by increasing the reflectance of the L1 information recording layer 22, and the SNR (Signal to Noise ratio) is improved. At this time, the L0 information recording layer 20 tends to have a relatively low reflectivity. However, as described above, since the original characteristics are good, recording / reproduction that can withstand practical use is within the allowable range. Quality can be obtained. In general, if the reflectivity is too low, the influence of system noise, external noise, etc. increases rapidly. Therefore, for the L0 information recording layer 20, good reflectivity is ensured by setting the reflectivity to 2%. I can do it. As a result, it is possible to appropriately maintain the signal quality of the L0 information recording layer 20 while greatly improving the signal quality of the L1 information recording layer 22.

  Further, in the present embodiment, the L0 and L1 information recording layers 20 and 22 are stacked at a distance of 105 μm or less from the light incident surface 38A, and can be recorded / reproduced in, for example, the BD standard optical recording / reproducing system 100. Yes. Furthermore, in this optical recording medium 1, the allowable wavelength λ of the laser light Z is set to 400 to 410 nm, and the allowable numerical aperture NA of the objective lens for irradiating the laser light Z is set to 0.7 to 0.9. The recording density can be increased, and the minimum recording mark length can be 130 nm or less. As a result, the L0 and L1 information recording layers 20 and 22 can achieve a recording capacity of 29 GB or more, preferably 30 GB or more.

  In addition, since the optical recording / reproducing system 100 according to the present embodiment employs the PRML processing device 110 that is a PR system with a constraint length of 4, a highly versatile device is employed as compared with a constraint length of 5 or more. Manufacturing cost can be reduced.

  [Examples and Comparative Examples]

  The result of reproducing the optical recording medium 1 as an example of the present embodiment and the optical recording medium as a comparative example using the optical recording / reproducing system 100 will be shown. In addition, this invention is not limited to these Examples at all.

  [Execution No. 1 to No. 4 Sample media creation]

  First, the substrate 10 was manufactured by an injection molding method. A spiral groove having a track pitch of 0.32 μm was formed on the surface of the substrate 10. A polycarbonate resin was used as the material of the substrate 10 and the thickness was set to 1.1 mm and the diameter was 120 mm.

  Next, this substrate 10 was set in a sputtering apparatus, and an L0 information recording layer was formed on the surface on the side where the groove was formed. Specifically, an Ag reflective film is first formed with a film thickness of 100 nm, then a second dielectric layer made of ZnS-SiO2 (80:20) is formed with a film thickness of 15 nm, and SbTeGe (75:20: 5) is formed with a film thickness of 10 nm, a first dielectric layer of ZnS-SiO2 (80:20) is formed with a film thickness of 20 nm, and finally a heat dissipation layer of AlN is formed with a film thickness of 30 nm. Formed.

  Next, the substrate 10 on which the L0 information recording layer was formed was set in a spin coater, and an acrylic ultraviolet curable resin was dropped while rotating, and this was spin coated. Thereafter, a light transmissive stamper having a spiral groove pattern was pressed against the surface of the spin-coated resin, and the resin was cured by irradiating the resin with ultraviolet rays through the light transmissive stamper. After curing, the light transmissive stamper was peeled off to form a spacer layer having a thickness of 25 μm and having a spiral groove. This was set again in the sputtering apparatus, and an L1 information recording layer was formed on the surface of the spacer layer. Specifically, first, a third dielectric layer made of ZrO 2 —Cr 2 O 3 (50:50) is formed to a thickness of 5 nm, an AgCu reflective film is formed to a thickness of 12 nm, and then ZrO 2 —Cr 2 O 3 (50:50). 50), the second dielectric layer is formed with a film thickness of 4 nm, the recording film with SbTeGeIn (71: 10: 9: 10) is formed with a film thickness of 5 nm, and further with ZnS-SiO2 (80:20). The first dielectric layer was formed with a film thickness of 13 nm, and finally the AlN heat dissipation layer was formed with a film thickness of 45 nm. The substrate 10 on which the L1 information recording layer was formed in this manner was set in a spin coater, and an acrylic ultraviolet curable resin was dropped while rotating, and this was spin coated. Thereafter, the spin-coated resin was cured by irradiating the resin with ultraviolet rays to form a cover layer having a thickness of 73 μm.

  Next, an ultraviolet / electron beam curable hard coat agent is applied onto the cover layer by a spin coat method, and then heated in the air for 3 minutes to remove the diluting solvent inside the coating, and the uncured hard coat material layer Formed. A surface material solution was applied to the uncured hard coat material layer by a spin coat method. This surface material solution is prepared by adding perfluoropolyether diacrylate and 3-perfluorooctyl-2-hydroxypropyl acrylate to a fluorine-based solvent. Thereafter, the hard coat material layer was dried at 60 ° C. for 3 minutes, and further irradiated with an electron beam in a nitrogen stream to simultaneously cure the hard coat material layer and the surface material solution. For the electron beam irradiation, an electron beam irradiation device Curetron (manufactured by Nisshin High Voltage Co., Ltd.) was used.

  Implementation No. In the optical recording medium 1 of FIG. 1, the L1 layer reflectance R1 of the L1 information recording layer is 5.5%, and the L0 layer reflectance R0 of the L0 information recording layer is 2.8%, and the reflectance ratio (R1-R0). ) / (R1 + R0) was set to 0.33.

  In addition, by further increasing the thickness of the L1 information recording layer by the same procedure, the L1 layer reflectance R1 is 6.0%, the L0 information recording layer L0 layer reflectance R0 is 2.6%, and these reflectances. Implementation No. in which the ratio (R1-R0) / (R1 + R0) is 0.40. 2 of the optical recording medium 1 was obtained. Further, by further increasing the thickness of the L1 information recording layer by the same procedure, the L1 layer reflectance R1 is 7.4%, the L0 information recording layer L0 layer reflectance R0 is 2.4%, and these reflectances. Implementation No. in which the ratio (R1-R0) / (R1 + R0) is 0.51. 3 of the optical recording medium 1 was obtained. Further, by further increasing the thickness of the L1 information recording layer by the same procedure, the L1 layer reflectance R1 is 8.0%, the L0 information recording layer L0 layer reflectance R0 is 2.0%, and these reflectances. Implementation No. in which the ratio (R1-R0) / (R1 + R0) is 0.60. 4 of the optical recording medium 1 was obtained.

  [Evaluation of Examples]

  This implementation No. 1-No. Information was recorded at a double speed on the optical recording medium 1 of No. 4 using the optical recording / reproducing system 100. The conditions of the optical recording / reproducing system 100 at the time of recording are that the modulation signal is (1, 7) RLL, the wavelength λ of the laser light Z is 405 nm, the numerical aperture NA of the objective lens 106A is 0.85, and the clock frequency of the optical recording / reproducing system f is 132 MHz, the linear velocity LV of the optical recording medium 1 whose rotation is controlled by the spindle driver 114 is set to 8.2 m / s, the minimum recording mark length is 124 nm, and the capacities of the L0 and L1 information recording layers are 30 GB, respectively. It was made to become.

  Next, the optical recording medium 1 was reproduced at a single speed by the optical recording / reproducing system 100, and the quality was evaluated. Since the speed is 1 ×, the clock frequency f of the optical recording / reproducing system is set to 66 MHz, and the linear velocity LV of the optical recording medium 1 controlled to rotate by the spindle driver 114 is set to 4.10 m / s. The PRML processing device 110 in the optical recording / reproducing system 100 during reproduction is set to a constraint length of 4.

  BER (bit Error Rate) was used as an evaluation index of reproduction quality by the optical recording / reproducing system 100. Here, as an evaluation apparatus, a PRML evaluation unit of Pulstec Industrial Co., Ltd. was used.

  Further, the implementation No. The optical recording medium 1 of No. 3 was used, and the linear recording density at the time of information recording was changed, and reproduction was performed at 1 × speed. The change of the linear recording density is performed by changing the linear velocity CLV of the optical recording medium 1. Specifically, the linear velocity CLV is 4.92 m / s (recording capacity: 25 GB), 4.56 m / s (recording). (Capacity: 27 GB), 4.24 m / s (Recording capacity: 29 GB), 4.10 m / s (Recording capacity: 30 GB), 3.84 m / s (Recording capacity: 32 GB) .

  [Comparison No. 1 to Comparative No. 3 Create sample media]

  Next, as a comparative example, according to the same procedure as the above-mentioned example, the comparison No. 1 to Comparative No. 3 sample media were prepared and played back at 1 × speed with an optical recording / playback system having the same constraint length 4 as in the above example. In this comparison No. In the sample medium 1, the L1 information recording layer is thinned to reduce the L1 layer reflectance R1 of the L1 information recording layer to 5.0% and the L0 information recording layer L0 layer reflectance R0 to 3.0. %, And the reflectance ratio (R1-R0) / (R1 + R0) was 0.25. In addition, comparison No. In the sample medium No. 2, the L1 information recording layer is further reduced in thickness so that the L1 information recording layer has an L1 layer reflectance R1 of 4.5%, and the L0 information recording layer has an L0 layer reflectance R0 of 3. The reflectance ratio (R1-R0) / (R1 + R0) was 0.13. On the other hand, comparison No. In the sample medium 3, by increasing the thickness of the L1 information recording layer, the L1 layer reflectance R1 of the L1 information recording layer is 9.1%, and the L0 layer reflectance R0 of the L0 information recording layer is 2.0%. The reflectance ratio (R1-R0) / (R1 + R0) was 0.65.

  [Evaluation of Comparative Example]

  Information was recorded / reproduced on these comparative sample media under the condition of a recording capacity of 30 GB as in the example. In addition, comparison No. The linear recording density at the time of information recording is 4.92 m / s (recording capacity: 25 GB), 4.56 m / s (recording capacity: 27 GB), 4.24 m / s (recording capacity). : 29 GB), 4.10 m / s (recording capacity: 30 GB), and 3.84 m / s (recording capacity: 32 GB).

  [Evaluation results of Examples and Comparative Examples]

  The results of these examples and comparative examples are shown in FIGS.

As can be seen from FIG. 1 to No. In the optical recording medium 1 of No. 4, both the L0 and L1 information recording layers 20 and 22 are less than the reference value bER = 1.0 × E- 4, and it is clear that the reference quality is satisfied.

On the other hand, comparison No. 1, comparative No. In the optical recording medium of No. 2, the signal quality of the L1 information recording layer was lower than the reference value bER = 1.0 × E −4 . In addition, comparison No. In the optical recording medium of No. 3, the signal quality of the L0 information recording layer was lower than the reference value bER = 1.0 × E −4 .

  That is, if the reflectance ratio is in the range of 0.65> (R1−R0) / (R1 + R0)> 0.25, the signal quality of both the L0 information recording layer 20 and the L1 information recording 22 is reasonably improved. It became clear that they could be compatible.

Further, as shown in FIG. In the optical recording medium 3 of FIG. 3, even when the recording capacity is 30 GB, the quality of the reproduced signal is less than the reference bER = 1.0 × E −4 , and it is clear that the quality is extremely good. became. Further, even when the recording capacity exceeds 32 GB, it has become clear that a relatively good bER can be obtained although the standard is exceeded.

On the other hand, comparison No. With the optical recording medium 1 of 1, when the recording capacity was 29 GB, the result was that bER = 1.0 × E −4 as the quality standard was exceeded. In particular, in the case of 30 GB, a result that the standard was greatly exceeded was obtained.

  As described above, in the present embodiment, the distance from the light incident surface 38A to the L1 information recording layer 22 is set to 80 μm or less, more desirably 75 μm or less. However, the present invention is not limited thereto. Similarly, although the case where the distance from the light incident surface 38A to the L0 information recording layer 20 is set to 105 μm or less has been shown, the present invention is not limited thereto. In the present embodiment, the L1 information recording layer 22 is shown only when it is the recording layer closest to the light incident surface. However, the present invention is not limited to this, for example, the light incidence is higher than that of the L1 information recording layer 22. On the surface side, for example, a read-only information recording layer in which information is recorded in advance may be arranged.

  In the present embodiment, the case where the recording mark is formed on the groove has been described. However, the recording mark may be formed on the land or on both the groove and the land. Further, the data holding mode is not limited to the rewritable type, and may be a write-once type. In the write-once type, this recording mark is formed irreversibly and cannot be erased. Further, the data holding form of the L0 and L1 information recording layers 20 and 22 may be a read-only type, and a spiral pit row is formed in advance on the surface side of the substrate 10 and the spacer layer 30, thereby holding information. You may be made to do. In this case, only reflective films are formed on the L0 and L1 information recording layers 20 and 22.

  Note that the optical recording medium and the like of the present invention are not limited to the above-described embodiments, and it is needless to say that various changes can be made without departing from the gist of the present invention.

  The present invention can be widely used in an optical recording medium having a multilayer structure and an optical recording / reproducing system for reproducing the optical recording medium.

The perspective view which shows the optical recording medium based on the example of embodiment of this invention, and an expanded sectional view The block diagram which shows the system configuration | structure of the optical recording / reproducing system based on the example of embodiment of this invention The block diagram which shows the detailed structure of the PRML processing apparatus of the optical recording / reproducing system Table showing results of evaluating reproduction signal quality of optical recording media according to examples and comparative examples of the present invention Table showing results of evaluating reproduction signal quality of optical recording media according to examples and comparative examples of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical recording medium 10 ... Substrate 20 ... L0 information recording layer 22 ... L1 information recording layer 30 ... Spacer layer 36 ... Cover layer 38 ... Hard coat layer 38A ... Light incident surface 100: optical recording / reproducing system 110: PRML processing device

Claims (8)

  1. A recording / reproducing L1 information recording layer that is reproduced by a PRML identification method disposed on the light incident surface side , and a recording / reproducing L0 information recording layer that is reproduced by a PRML identification method farthest from the light incident surface side And comprising
    When irradiating the L1 information recording layer with laser light, the L1 layer reflectance based on the incident light incident on the light incident surface and the reflected light emitted from the incident surface is R1, and the L0 information recording layer When the L0 layer reflectance based on incident light incident on the light incident surface and reflected light emitted from the incident surface is R0 when irradiating laser light,
    The total of R1 and R0 is 10% or less,
    R0 is 2% or more, and
    0.65> (R1-R0) / (R1 + R0)> 0.25
    An optical recording medium characterized by
  2. 2. The optical recording medium according to claim 1 , wherein the light transmittance of the L0 information recording layer is substantially zero.
  3. 3. The optical recording medium according to claim 1 , wherein the recording film materials of the L1 information recording layer and the L0 information recording layer are phase change materials.
  4. 4. The optical recording medium according to claim 1 , wherein the L1 information recording layer and the L0 information recording layer are laminated at a distance within 105 μm from the light incident surface.
  5. 5. The laser light according to claim 1 , wherein an allowable wavelength λ of the laser light is 400 to 410 nm, and an allowable numerical aperture NA of the objective lens for irradiating the laser light is 0.7 to 0.9. An optical recording medium.
  6. 6. The optical recording medium according to claim 1 , wherein a minimum recording mark length recorded on the L1 information recording layer and the L0 information recording layer is 130 nm or less.
  7. 7. The optical recording medium according to claim 1 , wherein the L1 information recording layer and the L0 information recording layer allow reproduction by a PRML identification method that is a PR equalization process with a constraint length of 4.
  8. An optical recording medium according to any one of claims 1 to 7 ,
    A laser light source for irradiating a laser beam having a wavelength λ of 400 to 410 nm;
    An objective lens having a numerical aperture NA of 0.7 to 0.9 and condensing the laser beam to irradiate the optical recording medium;
    A photoelectric conversion device that receives the reflected light of the laser beam and converts it into an electronic signal;
    A constraint length of the PR equalization processing 4, a PRML processing unit for reproducing a signal by PRML detection method, based on the electric signal,
    An optical recording / reproducing system comprising:
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