JP2012208991A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium having high recording/reproducing quality.SOLUTION: The optical recording medium comprises: a servo layer 18 having irregularities or grooves for tracking control; and a recording/reproducing layer 14 having no irregularities for tracking control. The medium records or reproduces information by irradiating the recording/reproducing layer 14 with a beam 170 for recording/reproducing of a second wavelength shorter than a first wavelength while performing tracking control by irradiating the servo layer 18 with a beam 270 for tracking of the first wavelength. The reflectance of the servo layer 18 when irradiated with light of the second wavelength passing through the recording/reproducing layer 14 is made smaller than the reflectance of the servo layer 18 when irradiated with light of the first wavelength passing through the recording/reproducing layer 14.

Description

  The present invention relates to an optical recording medium having a plurality of recording / reproducing layers.

  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, Optical recording media such as Blu-ray Disc (BD) are widely used. Among them, BD, which is one of the next-generation DVD standards, has a wavelength of laser light used for recording and reproduction as short as 405 nm, and a numerical aperture of the objective lens is set to 0.85. On the optical recording medium side corresponding to the BD standard, tracks are formed at a pitch of 0.32 μm. In this way, recording / reproducing of 25 GB or more is possible with respect to one recording / reproducing layer of the optical recording medium.

  By the way, the capacity of moving images and data is expected to increase more and more in the future. Therefore, a method for increasing the capacity of the optical recording medium by increasing the number of recording / reproducing layers in the optical recording medium has been studied. In the BD standard optical recording medium, a technique for realizing a super-large capacity of 200 GB by providing six to eight recording / reproducing layers has been reported (see Non-Patent Documents 1 and 2).

  On the other hand, when the recording / reproducing layer is multilayered in the optical recording medium, if the recording / reproducing layer is formed with irregularities for tracking control such as grooves / lands, the medium configuration becomes complicated, and work such as eccentricity adjustment is performed. There is concern that it will be difficult. Further, each time a recording / reproducing layer is provided, a stamper as a mother die for forming irregularities is required, and the more layers are used, the more times the stamper is used and the higher the manufacturing cost.

  Therefore, in recent years, in an optical recording medium, a servo layer having irregularities and grooves and a recording / reproducing layer not having irregularities and grooves are provided separately, and tracking signals are obtained from the servo layer using a beam dedicated to tracking control. Techniques have been proposed for recording information on a recording / reproducing layer with a recording / reproducing beam (see Patent Documents 1 and 2).

  For the purpose of simultaneous reading of two layers, a technique of alternately laminating a recording layer having unevenness and grooves and a recording layer not having unevenness and grooves has also been proposed (see Patent Document 3).

JP 2008-97693 A JP 2008-97694 A International Publication WO2008 / 099708

I. Ichimura et. Al., Appl. Opt, 45, 1974-1803 (2006) K. Mishima et.al., Proc. Of SPIE, 6282, 62820I (2006)

  In the case of the techniques disclosed in Patent Documents 1 to 3, for example, when a dedicated recording / reproducing beam leaks from a desired recording / reproducing layer, the leaked light is reflected by the servo layer to cause crosstalk. there were. In particular, when the number of recording / reproducing layers is increased, the reflectivity of each recording / reproducing layer has to be lowered, resulting in an increase in the amount of leakage of a recording / reproducing dedicated beam.

  The present invention has been made in view of the above problems, and an object of the present invention is to improve signal quality at the time of recording / reproducing in an optical recording medium having a servo layer and a recording / reproducing layer.

  The above-mentioned object is achieved by the following means by the inventors' extensive research.

  That is, the present invention that achieves the above object includes a servo layer having irregularities or grooves for tracking control, and a recording / reproducing layer that is laminated in advance or formed later and has no irregularities for tracking control. In addition, while performing tracking control by irradiating the servo layer with a tracking beam having the first wavelength, the recording / reproducing layer is irradiated with a recording / reproducing beam having a second wavelength shorter than the first wavelength. Is an optical recording medium on which recording or reproduction is performed, and the reflectance of the servo layer when the servo layer is irradiated with light of the first wavelength of the tracking beam through the recording / reproduction layer; In comparison, the servo layer has a low reflectance when the servo layer is irradiated with the second wavelength light of the recording / reproducing beam through the recording / reproducing layer, Which is a recording medium.

  The optical recording medium that achieves the above object is characterized in that the servo layer is transmitted through the recording / reproducing layer as compared with the amount of light reflected from the recording / reproducing layer when the recording / reproducing layer is irradiated with the recording / reproducing beam. On the other hand, the amount of reflected light from the servo layer when the recording / reproducing beam is irradiated is 5 times or less.

  The optical recording medium that achieves the above object is characterized in that the servo layer is transmitted through the recording / reproducing layer as compared with the amount of light reflected from the recording / reproducing layer when the recording / reproducing layer is irradiated with the recording / reproducing beam. On the other hand, the amount of reflected light from the servo layer when the recording / reproducing beam is irradiated is small.

  The optical recording medium that achieves the above object is characterized in that an interlayer distance between the recording / reproducing layer and the servo layer is 10 μm to 200 μm.

  The optical recording medium that achieves the above object has a reflectivity of 40% to 95% when the servo layer is irradiated with the tracking beam through the recording / reproducing layer, The servo layer has a reflectivity of 60% or less when the servo layer is irradiated with the recording / reproducing beam through the recording / reproducing layer.

  The servo layer of the optical recording medium that achieves the object includes a reflective film containing metal as a main component, and an auxiliary film that is disposed in contact with the reflective film and has a refractive index different from that of the reflective film. Features.

  The servo layer of the optical recording medium that achieves the above object includes two or more reflective films and three or more auxiliary films.

  The optical recording medium that achieves the above object includes a filter layer in which a dye is dispersed or combined between the servo layer and the recording / reproducing layer, and the filter layer includes the first tracking beam. The absorbance at a wavelength is low, and the absorbance at the second wavelength of the recording / reproducing beam is high.

  The optical recording medium that achieves the above-mentioned object is preliminarily laminated on the opposite side of the servo layer from the first recording / reproducing layer when the recording / reproducing layer is the first recording / reproducing layer, or afterwards. A second recording / reproducing layer that is formed and does not have irregularities for tracking control, wherein the second recording / reproducing layer records information while performing tracking control using the servo layer. .

  The servo layer of the optical recording medium that achieves the above object is formed directly on the first recording / reproducing layer side of the substrate, and the second recording / reproducing layer is formed on the opposite side of the substrate from the servo layer. It is characterized by that.

  The substrate of the optical recording medium that achieves the object is characterized by being made of a light transmissive material.

  The first recording / reproducing layer and the second recording / reproducing layer of the optical recording medium that achieves the above-mentioned object are previously laminated or formed afterwards in a symmetrical position with respect to the center in the thickness direction of the substrate. It is characterized by.

  The optical recording medium that achieves the above object is characterized in that the substrate has a thickness of 10 μm to 600 μm.

  According to the present invention, in an optical recording medium having a servo layer and a recording / reproducing layer, signal quality at the time of recording / reproducing can be improved.

1 is a block diagram showing an internal configuration of an optical recording medium according to a first embodiment of the present invention and an optical pickup that realizes the optical recording / reproducing. FIG. It is sectional drawing which shows the laminated structure of the same optical recording medium. (A) is sectional drawing which expands and shows the recording procedure of the optical recording / reproducing method with respect to the optical recording medium, (B) is sectional drawing which expands and shows a reproducing procedure. (A) is sectional drawing which shows the laminated structure of the optical recording medium based on 2nd Embodiment, (B) is sectional drawing which expands and shows the recording / reproducing procedure with respect to the optical recording medium. (A) is sectional drawing which shows the other example of the laminated structure of the optical recording medium which concerns on 2nd Embodiment, (B) is sectional drawing which expands and shows the recording / reproducing procedure with respect to the optical recording medium. It is sectional drawing which shows the laminated structure of the optical recording medium which concerns on 3rd Embodiment. It is a figure which shows the whole structure of the optical pick-up which implement | achieves the same optical recording / reproducing. FIG. 3 is a cross-sectional view illustrating a partially enlarged laminated structure of an optical recording medium in an example. It is a table | surface which shows the evaluation result of an Example and a comparative example. It is a figure which shows the output waveform of the reproduction signal of an Example and a comparative example. It is sectional drawing which shows the other structural example of the optical recording medium which concerns on 1st Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows a configuration of an optical recording medium 10 according to the first embodiment of the present invention and a pickup 90 used for recording / reproducing of the optical recording medium 10.

  As shown in FIG. 2, the optical pickup 90 includes a recording / reproducing optical system 100 and a tracking optical system 200. The recording / reproducing optical system 100 is an optical system that performs recording / reproduction with respect to the recording / reproducing layer group 14 of the optical recording medium 10. The tracking optical system 200 is an optical system that performs tracking control using the servo layer 18 when recording information in the recording / reproducing layer group 14 using the recording / reproducing optical system 100.

  The divergent recording / reproducing beam 170 emitted from the light source 101 of the recording / reproducing optical system 100 passes through the collimating lens 153 provided with the spherical aberration correcting means 193 and enters the polarization beam splitter 152. The beam 170 has a blue wavelength of 380 to 450 nm (here, 405 nm). The beam 170 incident on the polarization beam splitter 152 passes through the polarization beam splitter 152 and is further converted into circularly polarized light by transmission through the quarter-wave plate 154, and then enters the beam splitter 260 of the tracking optical system 200. Incident. The beam splitter 260 is set to have a high transmittance and a low reflectance. Specifically, the ratio of the transmittance to the reflectance is set to 10 times or more. Accordingly, the beam 170 passes through the beam splitter 260 and is converted into a convergent beam by the objective lens 156. The beam 170 is focused on either the recording / reproducing layer group 14 or the servo layer 18 to be recorded / reproduced, which is formed inside the optical recording medium 10.

  The aperture of the objective lens 156 is limited by the aperture 155, and the numerical aperture NA is 0.70 to 0.90 (here, 0.85). For example, the beam 170 reflected by the recording / reproducing layer group 14 passes through the objective lens 156, the beam splitter 260, and the quarter-wave plate 154, is converted into linearly polarized light that is 90 degrees different from the forward path, and then polarized. Reflected by the beam splitter 152.

  The beam 170 reflected by the polarization beam splitter 152 passes through the condenser lens 159 and is converted into convergent light, and enters the photodetector 132 through the cylindrical lens 157. Astigmatism is imparted to the beam 170 when passing through the cylindrical lens 157.

  The photodetector 132 has four light receiving units (not shown), and outputs a current signal corresponding to the amount of light received. From these current signals, a focus error (hereinafter referred to as FE) signal by an astigmatism method, a tracking error (hereinafter referred to as TE) signal by a push-pull method limited at the time of reproduction, and reproduction of information recorded on the optical recording medium 10 A signal or the like is generated. The FE signal and the TE signal are amplified and phase compensated to a desired level, and then fed back to the actuators 191 and 192 for focus control and tracking control. The tracking control by the recording / reproducing optical system 100 is used only during reproduction.

  A divergent tracking control beam 270 emitted from the light source 201 of the tracking optical system 200 and having a red wavelength of 630 to 680 nm (here, 650 nm) is transmitted through a collimating lens 253 provided with spherical aberration correcting means 293. , And enters the polarization beam splitter 252. The beam 270 incident on the polarization beam splitter 252 is transmitted through the polarization beam splitter 252, further transmitted through the quarter-wave plate 254, converted into circularly polarized light, and then reflected by the beam splitter 260. The beam 270 is further converted into a convergent beam by the objective lens 156 and condensed on the servo layer 18 formed inside the optical recording medium 10. The beam 270 reflected by the servo layer 18 passes through the objective lens 156, is reflected by the beam splitter 260, is converted into linearly polarized light that is 90 degrees different from the forward path in the quarter-wave plate 254, and then is polarized beam splitter. Further reflected at 252. The beam 270 reflected by the polarization beam splitter 252 passes through the condensing lens 259 and is converted into convergent light, and enters the photodetector 232 via the cylindrical lens 257. Astigmatism is given to the beam 270 when passing through the cylindrical lens 257.

  The photodetector 232 has four light receiving units (not shown) and outputs a current signal corresponding to the amount of light received. From these current signals, a tracking error (TE) signal is generated by the push-pull method. When information is also recorded on the servo layer 18, a reproduction signal may be generated from this current signal. On the photodetector 232 side, it is not necessary to generate a focus error (FE) signal. Of course, a focus error (FE) signal may be generated.

  As already described, the beam splitter 260 is set to have a high transmittance and a low reflectance. Accordingly, part of the return light emitted from the light source 101 of the recording / reproducing optical system 100 and reflected by any of the recording / reproducing layer groups 14 is reflected by the beam splitter 260 and proceeds to the tracking optical system 200 side. Conversely, most of the return light emitted from the light source 201 of the tracking optical system 200 and reflected by the servo layer 18 may pass through the beam splitter 260 and travel toward the recording / reproducing optical system 100 side. In the recording / reproducing optical system 100 and the tracking optical system 200, the recording / reproducing optical system 100 and the tracking optical system 200 have different focal points in the optical recording medium 10 even when both return lights are mixed. Because of the position, the spread angles of the beams 170 and 270 are different. Therefore, the influence of mixing is removed by extracting only one of the beams 170 and 270 using a slit or aperture having a fixed shape (not shown) and then entering the light detectors 132 and 232. Of course, the beams 170 and 270 may be separated by a filter having wavelength dependency.

  In particular, the difference between the focal position of the beam 170 in the optical recording medium 10 in the recording / reproducing optical system 100 and the focal position in the optical recording medium 10 of the beam 270 of the tracking optical system 200 is always within a certain range. By doing so, the above-mentioned slits and apertures can be made simple, so that the beam can be more easily separated. In order to stabilize the difference in focal length, it can be said that the closer the focal position of the recording / reproducing beam 170 and the focal position of the servo beam 270 is, the smaller the error is.

  When information is recorded on the recording / reproducing layer group 14 by the recording / reproducing optical system 100, the TE signal of the tracking optical system 200 is amplified and phase compensated to a desired level, and then fed back to the actuators 191 and 192. It is supplied and tracking control is performed. As a result, the recording / reproducing optical system 100 records information on the recording / reproducing layer group 14 based on the tracking control of the tracking optical system 200. In this embodiment, when information recorded on the recording / reproducing layer group 14 is reproduced, the recording / reproducing optical system 100 independently performs tracking control using the recording marks on the recording / reproducing layer group 14. ing. On the other hand, it is of course possible to perform reproduction while using the tracking control of the tracking optical system 200.

  FIG. 2 shows an enlarged cross-sectional structure of the optical recording medium 10 of the present embodiment.

  The optical recording medium 10 has a disk shape with an outer diameter of about 120 mm and a thickness of about 1.2 mm. The optical recording medium 10 includes a cover layer 11, a recording / reproducing layer group 14, an intermediate layer group 16, a buffer layer 17, a servo layer 18, and a support substrate 12 from the light incident surface 10A side.

  Here, the recording / reproducing layer group 14 includes first to sixth recording / reproducing layers 14A to 14F, and has a structure capable of recording information on each of them. The first to sixth recording / reproducing layers 14 </ b> A to 14 </ b> F have a planar structure that does not have unevenness and grooves for tracking control, and a recording beam 170 with high energy is emitted from the first optical system 100. As a result, a recording mark is formed. The types of the recording / reproducing layer group 14 include a write-once recording / reproducing layer in which information can be additionally written but cannot be rewritten, and a rewritable recording / reproducing layer in which information can be rewritten.

  The support substrate 12 is a disk-shaped substrate having a thickness of about 1.0 mm and a diameter of 120 mm to ensure the thickness required for the optical recording medium (about 1.2 mm). The light incident surface of the support substrate 12 A servo layer 18 is formed on the surface on the 10A side. Specifically, on the light incident surface 10A side of the support substrate 12, lands 18A and grooves 18B are formed in a spiral shape from the vicinity of the center toward the outer edge. The land 18A and the groove 18B become irregularities (grooves) for tracking control, and the beam 270 of the second optical system 200 is guided.

  Note that various materials can be used as the material of the support substrate 12, and for example, glass, ceramics, and resins can be used. Of these, a resin is preferred from the viewpoint of ease of molding. Examples of the resin include polycarbonate resin, olefin resin, acrylic resin, epoxy resin, polystyrene resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, and urethane resin. Among these, polycarbonate resin and olefin resin are particularly preferable from the viewpoint of processability.

  The servo layer 18 is configured by forming a reflective layer on the tracking control unevenness (groove and land) of the support substrate 12. Compared with the amount of reflected light when the recording / reproducing layer 170 is irradiated with the recording / reproducing beam 170, the amount of reflected light when the servo layer 18 is temporarily irradiated with the recording / reproducing beam 170 is 5 times or less. Is set to In this way, even when the recording / reproducing layer group 14 is irradiated with the recording / reproducing beam 170, even if the beam 170 leaks to the servo layer 18 side, the amount of reflected light from the servo layer 18 is reflected on the servo layer 18. Is attenuated, the influence of crosstalk can be made extremely small.

  Furthermore, in the present embodiment, the reflectance of the servo layer 18 when the servo layer 18 is temporarily irradiated with the recording / reproducing beam 170 is set smaller than the reflectance when the servo beam 18 is irradiated with the tracking beam 270. Has been. In other words, the servo layer 18 has a wavelength dependency characteristic such that the reflectance increases when irradiated with the red beam 270 having a long wavelength and decreases when irradiated with the blue beam 170 having a short wavelength. Have.

  Specifically, when the servo layer 18 is irradiated with the tracking beam 270, the reflectance of the servo layer 18 is 40% to 95%, and the servo layer 18 is temporarily irradiated with the recording / reproducing beam 170. The servo layer 18 is set to have a reflectance of 60% or less.

  As a configuration example of the servo layer 18 having such optical characteristics, a reflection film (metal film) containing at least one of Ag, Al, Au, and Cu as a main component and an auxiliary layer laminated adjacent to the reflection film Provide a membrane. By making the refractive index and thickness of the reflective film and the auxiliary film different, the reflectance of the long wavelength (red wavelength) beam 270 can be increased, and the reflectance of the short wavelength (blue wavelength) beam 170 can be decreased. The servo layer 18 preferably has a structure of three or more layers by laminating one or more reflective films serving as metal films and further laminating two or more auxiliary films. At this time, the reflective film is laminated on the support substrate 12 side, and the auxiliary film is laminated thereon. For example, a three-layer structure in which an Ag reflection film, an Si auxiliary film, and a ZnS—SiO 2 auxiliary film are sequentially stacked from the support substrate 12 side is also possible.

  Furthermore, the servo layer 18 preferably has a structure of five or more layers by laminating two or more reflective films and three or more auxiliary films. At this time, at least one auxiliary film is interposed between the first reflective film and the second reflective film. For example, a five-layer structure in which an Ag reflection film, a ZnS—SiO 2 auxiliary film, a Cu reflection film, a Si auxiliary film, and a ZnS—SiO 2 auxiliary film are sequentially laminated from the support substrate 12 side is preferable. With this five-layer structure, information can be recorded also on the servo layer 18. In the present embodiment, the servo layer 18 having the five-layer structure exemplified here is employed.

  According to the servo layer 18, the reflectance of the long wavelength beam 270 can be increased, and the reflectance of the short wavelength beam 170 can be decreased.

  Here, the pitch P1 between adjacent lands 18A or grooves 18B in the servo layer 18 is set to be less than 0.74 μm. Specifically, the pitch P1 is desirably set in the range of 0.6 μm to 0.7 μm, and more preferably set in the vicinity of 0.64 μm. On the other hand, the track pitch P2 of the recording mark is set to half (1/2) of the pitch P1 of the land 18A and the groove 18B. That is, the track pitch P2 between the recording marks is set to be less than 0.37 μm, desirably set in the range of 0.26 μm to 0.35 μm, and more preferably set in the vicinity of 0.32 μm. As a result, the track pitch P2 between the recording marks is about 0.32 μm which is compatible with the BD standard.

  The pitch P1 (around 0.64 μm) between the lands 18A / grooves 18B of the servo layer 18 is large enough to allow sufficient tracking with the beam 270 in the relatively long red wavelength region. In the present embodiment, tracking is performed using both the land 18A and the groove 18B. As a result, with respect to the pitch P1 of the servo layer 18, the track pitch P2 of the recording mark is about 0.32 μm, which is a half thereof. Thus, by performing tracking control using the land 18A and the groove 18B, the track pitch P2 of the recording marks in the recording / reproducing layer group 14 can be reduced without reducing the pitch P2 of the servo layer 18.

  The buffer layer 17 is made of a light-transmitting acrylic ultraviolet curable resin. The thickness of the buffer layer 17 is preferably set to 10 μm to 200 μm. If the thickness of the buffer layer 17 is 10 μm or less, the servo layer 18 and the recording / reproducing layer group 14 are too close to each other, which tends to adversely affect each other. On the other hand, when the thickness of the buffer layer 17 is 200 μm or more, the uniformity of the thickness tends to deteriorate in the step of forming the buffer layer 17. Here, it is set to 30 μm.

  Each of the first to sixth recording / reproducing layers 14A to 14F stacked on the light incident surface 10A side of the buffer layer 17 has a three-layer structure in which dielectric films are stacked on both outer sides of the write-once recording film ( (Not shown). It should be noted that the first to sixth recording / reproducing layers 14A to 14F are optimized in terms of light reflectance, absorptivity, transmittance and the like for the beam 170 in the blue wavelength region (short wavelength) in the first optical system 100. Yes.

  In addition to the basic function of protecting the write-once recording film, the dielectric film of each recording / reproducing layer also plays a role of expanding the difference in optical characteristics before and after the formation of the recording mark.

  When the beam 170 is irradiated, if the energy absorbed by the dielectric film is large, the recording sensitivity tends to be lowered. Therefore, in order to prevent this, it is preferable to select a material having a low absorption coefficient (k) in the wavelength region of 380 nm to 450 nm (particularly 405 nm) as the material of these dielectric films. In the present embodiment, TiO 2 is used as the material for the dielectric film.

  The write-once recording film sandwiched between the dielectric films is a film on which an irreversible recording mark is formed, and the reflectance with respect to the beam 170 is greatly different between the portion where the recording mark is formed and the other portion (blank region). . As a result, data can be recorded / reproduced.

  The write-once recording film is formed mainly of a material containing Bi and O. This write-once recording film functions as an inorganic reaction film, and the reflectance is greatly different due to a chemical or physical change caused by the heat of laser light. Specific materials include Bi-O as the main component, or Bi-MO (where M is Mg, Ca, Y, Dy, Ce, Tb, Ti, Zr, V, Nb, Ta). , Mo, W, Mn, Fe, Zn, Al, In, Si, Ge, Sn, Sb, Li, Na, K, Sr, Ba, Sc, La, Nd, Sm, Gd, Ho, Cr, Co, Ni And at least one element selected from Cu, Ga, and Pb). In this embodiment, Bi—Ge—O is used as the material of the write-once recording film.

  Although the case where the write-once recording film is employed in the first to sixth recording / reproducing layers 14A to 14F is shown here, it is also possible to employ a phase change recording film capable of repetitive recording. In this case, the phase change recording film preferably contains SbTeGe as a main component.

  The intermediate layer group 16 has first to fifth intermediate layers 16A to 16E in order from the side far from the light incident surface 10A, and is laminated between the first to sixth recording / reproducing layers 14A to 14F. Each of the intermediate layers 16A to 16E is made of an acrylic or epoxy ultraviolet curable resin. The film thicknesses of the intermediate layers 16A to 16E are preferably set to 20 μm or less in order to increase the number of stacked layers. The first intermediate layer 16A is 16 μm, the second intermediate layer 16B is 12 μm, and the third intermediate layer 16C is 16 μm, the fourth intermediate layer 16D is 12 μm, and the fifth intermediate layer 16E is 16 μm. That is, intermediate layers having two kinds of film thicknesses (16 μm and 12 μm) are alternately stacked. As a result, as the interlayer distance between the first to sixth recording / reproducing layers 14A to 14F, the first distance (16 μm) and the second distance (12 μm) different from the first distance are alternately set in order from the light incident surface side. Will be. The difference between the first distance and the second distance is set to 4 μm. In this way, interlayer crosstalk is reduced. Of course, all the intermediate layer groups 16 may have the same film thickness.

  The cover layer 11 is made of a light-transmitting acrylic ultraviolet curable resin, like the intermediate layer group 16, and has a thickness of 38 μm.

  As a result of the optical recording medium 10 being configured as described above, the servo layer 18 is located at a distance of 0.140 mm (140 μm) from the light incident surface 10 </ b> A. The first recording / reproducing layer 14A farthest from the incident surface 10A is located at a distance of 0.11 mm (110 μm) from the light incident surface 10A, and the second recording / reproducing layer 14B is 94 μm from the light incident surface 10A, and the third recording layer. The reproducing layer 14C is 82 μm from the light incident surface 10A, the fourth recording / reproducing layer 14D is 66 μm from the light incident surface 10A, the fifth recording / reproducing layer 14E is 54 μm from the light incident surface 10A, and the sixth closest to the light incident surface 10A. The recording / reproducing layer 14F is located at a distance of 38 μm from the light incident surface 10A. The overall thickness of the recording / reproducing layer group 14 (distance between the first recording / reproducing layer 14A to the sixth recording / reproducing layer 14F) is 72 μm.

  In the optical recording medium 10 of the present embodiment, the servo layer 18 is disposed at a position farther from the light incident surface 10A than the recording / reproducing layer group 14. In this way, it can be reduced that the tracking land 18A and the groove 18B adversely affect the recording / reproducing beam 170 irradiated to the recording / reproducing layer group 14.

  Next, a method for manufacturing the optical recording medium 10 of this embodiment will be described.

  First, the support substrate 12 on which grooves and lands are formed is manufactured by injection molding of polycarbonate resin using a metal stamper. By using an injection molding die, the support substrate 12 is provided with a recording condition including recording / reproducing layer group 14 address information, recording / reproducing power, and the like, and the position or interlayer distance of the recording / reproducing layers 14A to 14F. Basic information to be held in advance is preformatted. Specifically, basic information is preformed using the wobble of the land 18A or the groove 18B. The production of the support substrate 12 is not limited to the injection molding method, and may be produced by the 2P method or other methods.

  Thereafter, the servo layer 18 is formed on the surface of the land 18 </ b> A or the groove 18 </ b> B on the support substrate 12. The servo layer 18 is formed by laminating a reflective film and an auxiliary film using a sputtering method or a vapor phase growth method.

  Next, the buffer layer 17 is formed on the servo layer 18. The buffer layer 17 is formed, for example, by coating an ultraviolet curable resin whose viscosity is adjusted by a spin coating method or the like, and irradiating and curing the ultraviolet ray. In addition, it can also form by sticking the light transmissive sheet | seat which consists of light transmissive resin on the servo layer 18 using an adhesive agent, an adhesive, etc. instead of an ultraviolet curable resin. If necessary, when forming grooves or pits necessary for recording on the buffer layer 17, a light-transmitting resin stamper is bonded to the spin-coated ultraviolet curable resin by the 2P method. In this state, grooves and pits can be formed by curing by irradiating with ultraviolet rays.

  Next, the first recording / reproducing layer 14A is formed. Specifically, a dielectric film, a write-once recording film, and a dielectric film are formed in this order using a vapor phase growth method. Among these, it is preferable to use a sputtering method. Thereafter, the first intermediate layer 16A is formed on the first recording / reproducing layer 14A. The first intermediate layer 16A is formed, for example, by coating an ultraviolet curable resin whose viscosity is adjusted by a spin coating method or the like, and then irradiating the ultraviolet curable resin with ultraviolet rays and curing. By repeating this procedure, the second recording / reproducing layer 14B, the second intermediate layer 16B,.

  When the sixth recording / reproducing layer 14F is completed, the cover layer 11 is formed thereon, and the optical recording medium 10 is completed. The cover layer 11 is formed, for example, by coating a viscosity-adjusted acrylic or epoxy ultraviolet curable resin by a spin coating method or the like and irradiating it with ultraviolet rays to cure. In addition, although the said manufacturing method was demonstrated in this embodiment, this invention is not specifically limited to the said manufacturing method, Other manufacturing techniques can also be employ | adopted.

  Next, a recording / reproducing method using the optical recording medium 10 of the first embodiment and its operation using the optical pickup 90 will be described with reference to FIG.

  <Recording to recording / reproducing layer group>

  For example, when information is recorded on the first recording / reproducing layer 14 </ b> A adjacent to the servo layer 18, first, tracking is performed by irradiating the servo layer 18 with the beam 270 in the red wavelength region of the second optical system 200. Specifically, as shown in FIG. 3A, tracking is performed by alternately irradiating the spot of the beam 270 to both the groove 18B and the land 18A in the servo layer 18. Simultaneously with this operation, the recording / reproducing beam 170 in the blue wavelength region of the first optical system 100 is irradiated to the first recording / reproducing layer 14A.

  As a result, information is recorded on the first recording / reproducing layer 14A along the groove 18B or land 18A while tracking the groove 18B and land 18A. At this time, a part of the recording / reproducing beam 170 irradiated to the first recording / reproducing layer 14A passes through the first recording / reproducing layer 14A and reaches the servo layer 18. However, as described above, the amount of reflected light when the recording / reproducing beam 170 is irradiated onto the servo layer 18 is five times that of the amount of reflected light when the recording / reproducing layer 170 is irradiated with the recording / reproducing beam 170. It is set to be as follows. Therefore, even if the beam 170 leaking from the first recording / reproducing layer 14A is reflected by the servo layer 18, the amount of reflected light is greatly attenuated. As a result, adverse effects on the recording marks formed on the first recording / reproducing layer 14A can be suppressed. Further, the servo layer 18 sufficiently reflects the tracking beam 270 while suppressing the reflection of the recording / reproducing beam 170. Specifically, in the servo layer 18, the reflectance of the tracking beam 270 is maintained as high as 40% to 95%. On the other hand, the reflectance of the recording / reproducing beam 170 is suppressed to 60% or less. As a result, stable tracking control is realized.

  The servo layer 18 has basic specifications relating to the optical recording medium 10 and information relating to the number of stacked information recording layer groups 14 recorded in advance in recording pits and BCA (burst cutting area), and tracking control is started. Always read before. The basic information regarding the optical recording medium includes rules regarding the position of the servo layer 18, the positions of the first to sixth recording / reproducing layers 14A to 14F, and the interlayer distance of the recording / reproducing layer group.

  After the necessary information has been recorded on the first recording / reproducing layer 14A, the current additional recording information (address information on recording, content information, etc.) is recorded on the first recording / reproducing layer 14A. Thereafter, when resuming the recording of information on the first recording / reproducing layer 14A, first, the management information recorded on the first recording / reproducing layer 14A is reproduced to confirm the position where the previous recording is completed, Recording continues from that position. In this way, information can be recorded in all the data areas of the first recording / reproducing layer 14A to the sixth recording / reproducing layer 14F.

  <Reproduction of recording / reproducing layer group>

  For example, when reproducing information recorded on the first recording / reproducing layer 14A adjacent to the servo layer 18, first, the servo layer 18 is irradiated with the beam 270 in the red wavelength region of the second optical system 200 for tracking. . Specifically, as shown in FIG. 3B, tracking is performed by irradiating a spot of a beam 270 to the groove 18B and the land 18A in the servo layer 18. Simultaneously with this operation, the recording / reproducing beam 170 in the blue wavelength region of the first optical system 100 is irradiated to the first recording / reproducing layer 14A.

  As a result, the information recorded in the first recording / reproducing layer 14A is reproduced along the groove 18B or land 18A while tracking the groove 18B and land 18A. At this time, a part of the recording / reproducing beam 170 irradiated to the first recording / reproducing layer 14A passes through the first recording / reproducing layer 14A and reaches the servo layer 18. However, as already described, the amount of reflected light when the beam 170 is temporarily irradiated to the servo layer 18 is 5 times or less compared to the amount of reflected light when the recording / reproducing layer group 14 is irradiated with the beam 170. Is set. Therefore, even if the beam 170 leaked from the first recording / reproducing layer 14A is reflected by the servo layer 18, the amount of reflected light is greatly attenuated, so that crosstalk with the reproduction signal can be greatly suppressed. Further, the servo layer 18 sufficiently reflects the tracking beam 270 while suppressing the reflection of the recording / reproducing beam 170. Specifically, in the servo layer 18, while the reflectance of the tracking beam 270 is maintained as high as 40% to 95%, the reflectance of the recording / reproducing beam 170 is suppressed to 60% or less. As a result, even if a part of the recording / reproducing beam 170 leaks to the servo layer 18, the quality of the tracking signal does not deteriorate. In this way, the information recorded in the data area of the first recording / reproducing layer 14A to the sixth recording / reproducing layer 14F is reproduced.

  As described above, according to the optical recording medium 10 of this embodiment, the servo layer 18 is temporarily irradiated with the recording / reproducing beam 170 as compared with the reflectance when the recording / reproducing layer group 14 is irradiated with the recording / reproducing beam 170. In this case, the reflectance of the servo layer 18 is set to be small. As a result, when the recording / reproducing layer group 14 is irradiated with the recording / reproducing beam 170, even if a part of the recording / reproducing layer 170 leaks to the back servo layer 18, the reflected light amount of the servo layer 18 becomes small, which adversely affects the recording / reproducing operation. Can be avoided.

  In the present embodiment, the amount of reflected light when the recording / reproducing beam 170 is temporarily irradiated onto the servo layer 18 is five times that of the amount of reflected light when the recording / reproducing layer group 14 is irradiated with the recording / reproducing beam 170. Since the recording / reproducing beam 170 irradiated to the recording / reproducing layer group 14 leaks out to the back servo layer 18, the servo layer 18 is almost absorbed or transmitted. .

  On the other hand, in this optical recording medium 10, the recording / reproducing layer group 14 is transmitted through the recording / reproducing layer group 14 and compared with the reflectance when the servo beam 18 is irradiated with the tracking beam 270. The reflectance when the recording / reproducing beam 170 is temporarily irradiated onto the layer 18 is set to be small. If the servo layer 18 is employed, the tracking beam 270 is sufficiently reflected while suppressing the reflection of the recording / reproducing beam 170, so that it is possible to prevent deterioration of the quality of the tracking signal.

  In particular, in the present embodiment, as described above, since the optical characteristics of the servo layer 18 are changed depending on the wavelength, a reflective film (metal film) containing a metal material as a main component, the reflective film, the refractive index, and the film It has a structure in which auxiliary films having different thicknesses are stacked. By doing in this way, the reflected light intensity of the specific wavelength (here blue wavelength) which is not required at the time of tracking can be optically reduced.

  Furthermore, as a result of configuring the optical recording medium 10 as described above, the distance between the recording / reproducing layer group 14 and the servo layer 18 can be reduced to 10 μm to 200 μm, and the number of the recording / reproducing layer group 14 can be increased. It becomes possible.

  Next, an optical recording medium 310 according to the second embodiment of the present invention will be described with reference to FIGS. In addition, regarding this optical recording medium 310, the same or similar parts as those of the optical recording medium 10 of the first embodiment are made to coincide with the last two digits of the reference numerals in the drawings and description, and the description of individual members is omitted. The explanation will focus on the different points.

  The optical recording medium 310 includes a cover layer 311, a recording / reproducing layer group 314, an intermediate layer group 316, a buffer layer 317, a servo layer 318, and a support substrate 312 from the light incident surface 310A side.

  The servo layer 318 includes a single-layer metal film containing at least one of Ag, Al, Au, and Cu as a main component. Therefore, no auxiliary membrane is provided.

  The buffer layer 317 is provided between the servo layer 318 and the recording / reproducing layer group 314 and is made of a material in which a dye is kneaded or uniformly dissolved in the light transmitting resin. Specifically, the buffer layer 317 is made of a material having a low absorbance at the first wavelength (here, 650 nm) of the tracking beam 170 and a high absorbance at the second wavelength (here, 405 nm) of the recording / reproducing beam 270. It functions as a filter layer having dependency characteristics. Here, as the material, a material in which a general dye having a yellow chromophore or auxiliary color group such as azo, diazo, azomethine is dispersed or bonded to a transparent resin is used.

  According to the optical recording medium 310, even if the recording / reproducing beam 170 irradiated to the recording / reproducing layer group 314 leaks out to the servo layer 318 side, the leaking light reaches the servo layer 318 before reaching the servo layer 318. Absorbed in. Even if the leaked light is reflected by the servo layer 318, the reflected light is again absorbed by the buffer layer 317.

  Further, the optical recording medium 310 is set so that the reflectance when the recording / reproducing beam 170 is irradiated becomes smaller than the reflectance when the servo layer 318 is irradiated with the tracking beam 270. The This is because the recording / reproducing beam 170 is absorbed by the buffer layer 317 before reaching the servo layer 318.

  As a result, the present optical recording medium 310 can improve the quality of both the reproduction signal and the tracking signal. In the present optical recording medium 310, the buffer layer 317 is disposed on the back side of the recording / reproducing layer group 314. In this way, external light such as ultraviolet rays that cause bleaching of the dye material is absorbed by the recording / reproducing layer group 314 on the near side, and thus hardly reaches the buffer layer 317. Therefore, long-term stability of the buffer layer 317 can be ensured, and deterioration of the optical recording medium 310 over time can be suppressed. In particular, when an organic dye is employed, the structure of the optical recording medium 310 is preferable because the influence of ultraviolet rays is large.

  In the present embodiment, the buffer layer 317 is illustrated using a material having wavelength-dependent characteristics such that the absorption rate or transmittance varies depending on the wavelength band. For example, the buffer layer 317 is illustrated in FIGS. 5A and 5B. As described above, the filter layer 317B is disposed separately from the buffer layer 317, and a wavelength-dependent characteristic is added to the filter layer 317B by kneading the dye into the light transmitting resin of the filter layer 317B. good.

  Next, with reference to FIG. 6, an optical recording medium 410 according to a third embodiment of the invention will be described. Regarding the optical recording medium 410, the same or similar parts as those of the optical recording medium 410 of the first embodiment are matched with the last two digits of the reference numerals in the drawings and description, and the description of individual members is omitted. The explanation will focus on the different points.

  The optical recording medium 410 includes a first cover layer 411, a first recording / reproducing layer group 414, a first intermediate layer group 416, a first buffer layer 417, a servo layer 418, a support substrate 412, a first substrate, in order from the first surface 410A side. 2 buffer layer 437, second recording / reproducing layer group 434 and second intermediate layer group 436, second cover layer 431, and second surface 430A. That is, as compared with the optical recording medium 10 of the first embodiment, this optical recording medium 410 has the second buffer layer 437, the second recording / reproducing layer group 434, and the second surface 430A side with respect to the support substrate 412 as well. The difference is that the second intermediate layer group 436 and the second cover layer 431 are provided.

  Here, the thickness of the support substrate 412 is set to 900 μm, and on the first surface 410A side, lands 418A and grooves 418B are formed in a spiral shape from the vicinity of the center toward the outer edge.

  The servo layer 418 includes a single-layer metal film that contains at least one of Ag, Al, Au, and Cu as a main component. Therefore, no auxiliary membrane is provided. The pitch P1 between the lands 418A or the grooves 418B of the servo layer 418 is set in the vicinity of 0.64 μm. On the other hand, the track pitch P2 of the recording mark is set to half (1/2) of the pitch P1 of the land 418A and the groove 418B. That is, the track pitch P2 between the recording marks is set in the vicinity of 0.32 μm. As a result, the track pitch P2 between the recording marks is about 0.32 μm which is compatible with the BD standard.

  In this embodiment, tracking is performed using both the land 418A and the groove 418B. As a result, with respect to the pitch P1 of the servo layer 418, the track pitch P2 of the recording mark is about 0.32 μm, which is a half thereof.

  The first buffer layer 417 has a thickness of 30 to 40 μm and is made of a material in which a pigment is kneaded or uniformly dissolved and concentrated in a light transmissive resin and dispersed or bonded. The Specifically, the first buffer layer 417 is made of a material having a low absorbance at the first wavelength (here, 650 nm) serving as a tracking beam and a high absorbance at the second wavelength (here, 405 nm) serving as a recording / reproducing beam. The Here, a material obtained by dispersing or binding a general dye having a chromophore or auxiliary color group such as azo, diazo, and azomethine in a transparent resin is used.

  The first cover layer 411 is made of a light-transmitting acrylic ultraviolet curable resin and has a thickness of 40 μm.

  The second buffer layer 437 has a film thickness of 20 to 40 μm and is made of a material obtained by kneading or uniformly dissolving a dye with respect to the light transmissive resin. Specifically, the second buffer layer 437 is made of a material having a low absorbance at the first wavelength (here, 650 nm) serving as a tracking beam and a high absorbance at the second wavelength (here, 405 nm) serving as a recording / reproducing beam. The Here, a material obtained by dispersing or binding a general dye having a chromophore or auxiliary color group such as azo, diazo, and azomethine in a transparent resin is used.

  The second recording / reproducing layer group 434 (L0 to L5 recording / reproducing layers 434A to 434F) and the second intermediate layer group 436 laminated on the second surface 430A side of the second buffer layer 437 are the first recording / reproducing layer group 414. The second intermediate layer group 416 has almost the same structure.

  The second cover layer 431 is made of a light-transmitting acrylic ultraviolet curable resin and has a thickness of 40 μm.

  As a result of the configuration described above, the boundary (servo layer 418) between the support substrate 412 and the first buffer layer 417 in the optical recording medium 410 is located at a distance of about 150 μm from the first surface 410A. In the first recording / reproducing layer group 414, the L0 recording / reproducing layer 414A farthest from the first surface 410A is located at a distance of 112 μm from the first surface 410A, and the L1 recording / reproducing layer 414B is the first surface 410A. To 96 μm, the L2 recording / reproducing layer 414C from the first surface 410A to 84 μm, the L3 recording / reproducing layer 414D from the first surface 410A to 68 μm, the L4 recording / reproducing layer 414E from the first surface 410A to 56 μm, and the most on the first surface 410A The near L5 recording / reproducing layer 414F is located at a distance of 40 μm from the first surface 410A. The overall thickness of the first recording / reproducing layer group 414 (distance between the L0 recording / reproducing layers 414A to L5 recording / reproducing layer 414F) is 72 μm.

  In the second recording / reproducing layer group 434, the L0 recording / reproducing layer 434A farthest from the second surface 430A is located at a distance of 112 μm from the second surface 430A, and the L1 recording / reproducing layer 434B is the second surface 430A. To 96 μm, the L2 recording / reproducing layer 434C from the second surface 430A to 84 μm, the L3 recording / reproducing layer 434D from the second surface 430A to 68 μm, the L4 recording / reproducing layer 434E from the second surface 430A to 56 μm, and the second surface 430A The near L5 recording / reproducing layer 434F is located at a distance of 40 μm from the second surface 430A. The overall thickness of the second recording / reproducing layer group 434 (the distance between the L0 recording / reproducing layers 434A to L5 recording / reproducing layer 434F) is 72 μm.

  The optical recording medium 410 has a symmetrical structure in the thickness direction, except that the servo layer 418 is disposed asymmetrically. As a result, internal stress generated during the production of the optical recording medium 410 is generated symmetrically in the thickness direction, so that warpage and deformation can be reduced. In particular, even when the support substrate 412 is thinned to 600 μm or less, for example, 100 μm, it is possible to suppress warping and deformation of the optical recording medium 410.

  FIG. 7 shows the configuration of the first and second optical pickups 90A and 90B used for recording and reproduction of the optical recording medium 410 of the third embodiment. The first optical pickup 90A irradiates a beam from the one first surface 410A side of the optical recording medium 410. The second optical pickup 90B irradiates a beam from the other second surface 430A side of the optical recording medium 410. Since the internal configuration of the first and second optical pickups 90A and 90B is substantially the same as that of the optical pickup 90 shown in the first embodiment, the first optical pickup 90A side is designated by the reference numerals in the drawing or text. A is added to the end, and the second optical pickup 90B side adds B to the end of the reference numeral in the drawing or text, thereby omitting illustration and description thereof.

  The first optical pickup 90A includes a recording / reproducing optical system 100A and a tracking optical system 200A. The recording / reproducing optical system 100A is an optical system that performs recording / reproduction by irradiating the first recording / reproducing layer group 414 of the optical recording medium 410 with the recording / reproducing beam 170A. The tracking optical system 200A performs tracking control by irradiating the servo layer 418 with the tracking beam 270A when recording information on the first recording / reproducing layer group 414 using the recording / reproducing optical system 100A. It becomes an optical system.

  The second optical pickup 90B includes a recording / reproducing optical system 100B and a tracking optical system 200B. The recording / reproducing optical system 100B is an optical system that performs recording / reproducing by irradiating the second recording / reproducing layer group 434 of the optical recording medium 410 with the recording / reproducing beam 170B. The tracking optical system 200A performs tracking control by irradiating the servo layer 418 with the tracking beam 270B when recording information on the first recording / reproducing layer group 414 using the recording / reproducing optical system 100A. It becomes an optical system.

  Next, a method for recording and reproducing information on the optical recording medium 410 using the first and second optical pickups 90A and 90B will be described.

  <Recording / reproducing of the first recording / reproducing layer group>

  For example, when recording / reproducing information on the L0 recording / reproducing layer 414A of the first recording / reproducing layer group 414, first, the servo layer 18 is irradiated with the tracking beam 270A in the red wavelength region of the first optical pickup 90A. Perform tracking. Specifically, as shown in FIG. 6, tracking is performed by irradiating the groove 418 </ b> B and the land 418 </ b> A in the servo layer 418 with a spot of the tracking beam 270 </ b> A. Simultaneously with this operation, the L0 recording / reproducing layer 414A is irradiated with the recording / reproducing beam 170A in the blue wavelength region of the first optical pickup 90A, thereby recording or reproducing the L0 recording / reproducing layer 414A.

  At this time, even if the recording / reproducing beam 170A irradiated to the first recording / reproducing layer group 414 leaks to the servo layer 418 side, the leaked light is absorbed by the first buffer layer 417 before reaching the servo layer 418. Is done. Even if the leaked light is reflected by the servo layer 418, the reflected light is again absorbed by the first buffer layer 417. On the other hand, the first buffer layer 417 actively transmits the tracking beam 270A having a red wavelength, thereby increasing the amount of the tracking signal. As a result, stable tracking control is realized.

  <Recording / Reproducing of Second Recording / Reproducing Layer Group>

  When recording information in the L0 recording / reproducing layer 434A of the second recording / reproducing layer group 434, first, the tracking beam 270B in the red wavelength region of the second optical pickup 90B is transmitted to the servo layer 418 while passing through the support substrate 412. Irradiate and track. Specifically, as shown in FIG. 6, tracking is performed by irradiating a spot of a tracking beam 270B to lands 18A and grooves 418B in the servo layer 418. Simultaneously with this operation, the L0 recording / reproducing layer 434A is irradiated with the recording / reproducing beam 170B in the blue wavelength region of the second optical pickup 90B, thereby recording or reproducing the L0 recording / reproducing layer 434A.

  At this time, even if the recording / reproducing beam 170B irradiated to the second recording / reproducing layer group 434 leaks to the servo layer 418 side, the leaked light is absorbed by the second buffer layer 437 before reaching the servo layer 418. Is done. Even if the leaked light is reflected by the servo layer 418, the reflected light is again absorbed by the second buffer layer 437. On the other hand, the second buffer layer 437 actively transmits the tracking beam 270B having a red wavelength, thereby increasing the amount of the tracking signal. As a result, stable tracking control is realized.

  Note that it is possible to simultaneously record or reproduce the first recording / reproducing layer group 414 and the second recording / reproducing layer group 416. This doubles the recording or playback transfer rate.

  As described above, according to the optical recording medium 410 of the third embodiment, the servo layer 418 is formed only on one surface of the support substrate 412, and the first recording / reproducing layer group 414 and the second recording layer 414 are formed on both surfaces of the support substrate 412. A recording / reproducing layer group 434 is arranged. As a result, since the internal stress when forming the first and second recording / reproducing layer groups 414 and 434 is dispersed on both sides of the support substrate 412, warping and deformation of the optical recording medium 410 can be suppressed. By dispersing the internal stress in this way, the warp of the optical recording medium 410 is suppressed even when the thickness of the support substrate 12 is set within a range of 10 μm to 1000 μm, preferably within a range of 10 μm to 600 μm. It becomes possible.

  At this time, if an unevenness for tracking is formed on both sides of the support substrate 412, the manufacturing process itself of the support substrate 412 becomes complicated, and the accuracy of the support substrate 412 is likely to deteriorate. Therefore, in this embodiment, the unevenness for tracking is formed on one side of the support substrate 412, and the production of the support substrate 412 is simplified to improve accuracy. Since the servo layer 418 is shared by the first and second recording / reproducing layer groups 414 and 434 on both sides, the recording and reproducing layers of the first and second recording / reproducing layer groups 414 and 434 There is no need to form irregularities for tracking. As a result, the shape accuracy of the optical recording medium 410 can be further improved. Since the first recording / reproducing layer group 414 and the second recording / reproducing layer group 434 are arranged on both sides of the support substrate 412, the recording capacity can be increased.

  Further, in the optical recording medium 410, the reflectance of the servo layer 418 when irradiated with the tracking red wavelength beams 270A and 270B is the reflectance when the servo layer 418 is irradiated with the recording and reproducing beams 170A and 170B. It is set larger than In order to realize this specifically, a material is used for the first and second buffer layers 417 and 437 that has a larger light absorption as the beam wavelength is shorter. In this case, even if the recording / reproducing beams 170A and 170B having a blue wavelength are incident on the servo layer 18 side, they are absorbed by the first and second buffer layers 417 and 437. The amount of leakage light that reaches and the amount of reflected light reflected from the servo layer 418 can be attenuated. On the other hand, since the tracking beams 270A and 270B having a red wavelength can be actively transmitted through the first and second buffer layers 417 and 437, the amount of reflected light from the servo layer 418 can be increased. As a result, the crosstalk between the recording / reproducing beams 170A and 170B and the tracking beams 270A and 270B is reduced, and the quality of the reproduced signal can be improved, and at the same time, stable tracking control is realized.

  In addition, as shown here, the reflectivity when the servo layer 418 is irradiated with the recording / reproducing beams 170A and 170B is reduced. As a result, the thicknesses of the first and second buffer layers 417 and 437 are reduced. This leads to the thinning. In this embodiment, specifically, it becomes possible to make it preferably 200 μm or less, desirably 100 μm or less, and more desirably 50 μm or less. Thus, if the thickness of the first and second buffer layers 417 and 437 can be reduced, the film thickness error when forming the first and second buffer layers 417 and 437 can be reduced accordingly. At the same time, since the thickness of the support substrate 412 can be increased, warpage during the production of the optical recording medium 410 can be further reduced.

  Furthermore, in this optical recording medium 410, the thicknesses of the first buffer layer 417 and the second buffer layer 437 are set to be substantially the same. As a result, warpage of the support substrate 412 during the formation process of the first and second buffer layers 417 and 437 can be suppressed. This means that the support substrate 412 can be made thin or made of a material having low rigidity, and the number of layers of the first recording / reproducing layer group 414 and the second recording / reproducing layer group 434 can be increased by that amount. It becomes possible.

  Further, the first recording / reproducing layer group 414 and the second recording / reproducing layer group 434 of the optical recording medium 410 are laminated at symmetrical positions in the thickness direction with the center of the support substrate 412 as a reference. Accordingly, the internal stress generated in the first and second recording / reproducing layer groups 414 and 434 is also symmetric, so that the warp of the optical recording medium 410 can be suppressed.

  When manufacturing the optical recording medium 410 of the third embodiment, the first buffer layer 417 and the second buffer layer 437, the first recording / reproducing layer group 414, the second recording / reproducing layer group 434, and the first intermediate layer are used. It is preferable to form the group 416 and the second intermediate layer group 436 simultaneously on both sides. As a result, the internal stress generated during UV curing acts evenly on both sides of the support substrate 412, so that the warp of the optical recording medium 410 can be further reduced.

  In the present embodiment, the first and second buffer layers 417 and 437 are given different light absorption characteristics between the red wavelength and the blue wavelength. As a result, the reflectance of the servo layer 418 is changed to the tracking beam. However, the present invention is not limited to this. For example, the reflection film itself formed on the servo layer 418 may be provided with wavelength dependent characteristics such that the reflectance varies depending on the wavelength. In addition to the first and second buffer layers 417 and 437, a filter layer having wavelength dependent characteristics of light transmittance and absorptance may be separately formed, and wavelength dependent characteristics are imparted to the substrate material. You may let them.

  For the purpose of simply confirming the characteristics of the optical recording medium 10 of the first embodiment, the optical recording medium is actually created and used for an optical disk standard in the optical disk industry having a function as a general spectrometer. Evaluation was performed using a measuring machine ETA-optic (manufactured by Steag, Germany). Specifically, for the servo layer of this optical recording medium, the reflectance of the recording / reproducing laser diode near the wavelength of 405 nm and the reflectance of the tracking laser diode near the wavelength of 650 nm were measured. As a result, the reflectivity of the blue wavelength (405 nm) is 9%, and the reflectivity of the red wavelength (650 nm) is 52%. Reflection of the servo layer when the servo layer is irradiated with light of the recording / reproducing beam wavelength. It was confirmed that the rate was smaller than when the light having the wavelength of the tracking beam was irradiated.

  Furthermore, in order to confirm the reflectivity of the servo layer in more detail, a calculation disk that does not form each metal film and auxiliary film of the servo layer (becomes a transparent servo layer) is created separately, and the reflectivity is similarly set. evaluated. By taking the difference in reflectance between this calculation disk and the above-mentioned ordinary optical recording medium, the reflectance characteristics unique to the servo layer can be analyzed. In the measurement of reflectance with this calculation disk, the blue wavelength (405 nm) was 14%, and the red wavelength (650 nm) was 32%. Furthermore, when calculating the optical difference between a normal optical recording medium and a calculation disk (this is not a simple subtraction, but an optical difference assuming various situations), the difference from the servo layer is calculated. The unique reflectance components were 1% or less at the blue wavelength and about 20% at the red wavelength. That is, regarding the reflection from the servo layer in an actual optical recording medium, it was confirmed that the reflectance of the wavelength of the recording / reproducing beam was significantly smaller than the reflectance of the wavelength of the tracking beam.

  Next, in order to perform verification in a state closer to actual signal processing characteristics, the recording / reproducing layer group 14 of the optical recording medium 10 shown in the first embodiment is used as the optical recording medium according to Examples 1 and 2. A single layer was produced. That is, the optical recording medium 10 includes a cover layer 11, a recording / reproducing layer 14, a buffer layer 17, a servo layer 18, and a support substrate 12, as shown in FIG.

  The servo layer 18 of Example 1 employs a five-layer structure film in which an Ag reflection film, a ZnS-SiO2 auxiliary film, a Cu reflection film, a Si reflection film, and a ZnS-SiO2 auxiliary film are stacked. The total film thickness was 119 nm. The total thickness of the Ag reflection film and the Cu reflection film was 91 nm. In Example 1, the thickness of the buffer layer 17 was 30 μm. In Example 2, the total thickness of the Ag reflection film and the Cu reflection film in the servo layer 18 was similarly 91 nm, while the thicknesses of the other auxiliary films were changed. The thickness of the buffer layer 17 was also changed to 40 μm.

  In addition, an optical recording medium according to Example 3 was manufactured in which the number of recording / reproducing layer groups 14 of the optical recording medium 310 shown in the second embodiment was a single layer. The servo layer 18 of Example 3 employs a single layer metal film of an Ag alloy having a thickness of 80 nm, and the buffer layer 17 has a general chromophore having a yellow chromophore or auxiliary color group such as an azo skeleton. Was mixed with the transparent acrylic resin material. This material has a low absorbance at the first wavelength (here, 650 nm) of the tracking beam 170 and a high absorbance at the second wavelength (here, 405 nm) of the recording / reproducing beam 270.

  In all of Examples 1 to 3, the recording / reproducing layer 14 was formed using Bi—Ge—O as a material. Further, in order to evaluate the reproduction signal of the recording / reproducing layer 14, a land 19A and a groove 19B for signal quality evaluation are formed in the recording / reproducing layer 14, and the quality of the tracking signal using the land 19A and the groove 19B is determined. A technique for indirectly evaluating the quality of the playback signal was adopted.

  On the other hand, as the optical recording media of Comparative Examples 1 to 3, optical recording media in which the servo layer 18 is a metal single layer film without the light absorbing function added to the buffer layer 17 were manufactured. The servo layer 18 of Comparative Example 1 is an Ag alloy metal film having a thickness of 80 nm, the Servo Layer 18 of Comparative Example 2 is an Ag alloy metal film having a thickness of 20 nm, and the Servo layer 18 of Comparative Example 3 is 10 nm in thickness. It was set as the metal film of Ag alloy.

  As an evaluation method for each optical recording medium, a recording / reproducing beam 170 having a blue wavelength is irradiated onto the recording / reproducing layer 14, and reflected light including a tracking signal of the land 19A or the groove 19B is detected by voltage fluctuation by the photodetector 132. Whether or not tracking control is possible and the amount of noise in the tracking signal were determined. If the land 19A or the groove 19B can be tracked by the tracking signal included in the reflected light of the recording / reproducing layer 14, it can be estimated that the quality of the reproducing signal of the recording / reproducing layer 14 is good. Similarly, if the noise included in the tracking signal is small, it can be estimated that the quality of the reproduction signal is good. A part of the blue wavelength recording / reproducing beam 170 irradiated to the recording / reproducing layer 14 leaks to the servo layer 18 side, and if this leaked light is strongly reflected by the servo layer 18, the noise included in the tracking signal increases. To do.

  For reference, the amount of reflected light when the recording / reproducing beam 170 is applied to the recording / reproducing layer 14 and the amount of reflected light when the recording / reproducing beam 170 is directly applied to the servo layer 18 are confirmed, and the magnification of both is evaluated. did. Further, the servo layer 18 is irradiated with a recording / reproducing beam 170 having a blue wavelength (405 nm) and a tracking beam 270 having a red wavelength (650 nm), and the reflectivity of each is confirmed.・ Evaluated in three low grades. The evaluation apparatus used was a pulse tech industrial optical disk inspection device ODU1000 which is a standard inspection device in the optical disk industry.

  The above evaluation results are shown in FIG. In Example 1, the amount of reflected light when the servo layer 18 is irradiated with the recording / reproducing beam 170 is 74.0 mV, the amount of reflected light when the recording / reproducing beam 170 is irradiated on the recording / reproducing layer 14 is 84.5 mV, The ratio of the reflected light amount of the servo layer 18 to the reflected light amount of the recording / reproducing layer 14 was 0.9 times. Furthermore, tracking using this reflected light (tracking signal) was good, and there was little noise contained in this tracking signal. The reflectance when the servo layer 18 is irradiated with the recording / reproducing beam 170 of blue wavelength (405 nm) is low, and the reflectance when the tracking beam 270 of red wavelength (650 nm) is irradiated is high. became.

  In Example 2, the amount of reflected light when the servo layer 18 is irradiated with the recording / reproducing beam 170 is 112.0 mV, and the amount of reflected light when the recording / reproducing beam 170 is irradiated on the recording / reproducing layer 14 is 160.0 mV. The ratio of the reflected light amount of the servo layer 18 to the reflected light amount of the recording / reproducing layer 14 was 0.7 times. Furthermore, tracking using this reflected light (tracking signal) was good, and the noise contained in this tracking signal was very small. The reflectance when the servo layer 18 is irradiated with the recording / reproducing beam 170 of blue wavelength (405 nm) is low, and the reflectance when the tracking beam 270 of red wavelength (650 nm) is irradiated is high. became.

  In Example 3, the amount of reflected light when the servo layer 18 is irradiated with the recording / reproducing beam 170 is 740.0 mV, the amount of reflected light when the recording / reproducing beam 170 is irradiated on the recording / reproducing layer 14 is 160.5 mV, The ratio of the reflected light amount of the servo layer 18 to the reflected light amount of the recording / reproducing layer 14 was 4.5 times. Furthermore, tracking using this reflected light (tracking signal) was good, and there was little noise contained in this tracking signal. The reflectance when the servo layer 18 is irradiated with the recording / reproducing beam 170 of blue wavelength (405 nm) is low, and the reflectance when the tracking beam 270 of red wavelength (650 nm) is irradiated is high. became. From Example 3, it can be seen that if the ratio of the reflected light amount of the servo layer 18 to the reflected light amount of the recording / reproducing layer 14 is 5 times or less, the signal quality can be maintained satisfactorily. Also, from Examples 1 and 2, it can be seen that if this ratio is 1 or less, it can be maintained very well.

  In Comparative Example 1, the amount of reflected light when the servo layer 18 is irradiated with the recording / reproducing beam 170 is 5000.0 mV, the amount of reflected light when the recording / reproducing beam 170 is irradiated on the recording / reproducing layer 14 is 216.0 mV, The ratio of the reflected light amount of the servo layer 18 to the reflected light amount of the recording / reproducing layer 14 was 23.1 times. Furthermore, tracking using this reflected light (tracking signal) is impossible, and the noise contained in this tracking signal is extremely large. The reflectance when the servo layer 18 is irradiated with the recording / reproducing beam 170 of blue wavelength (405 nm) is high, and the reflectance when the tracking beam 270 of red wavelength (650 nm) is irradiated is also high. became.

  In Comparative Example 2, the amount of reflected light when the recording / reproducing beam 170 is applied to the servo layer 18 is 1615.0 mV, and the amount of reflected light when the recording / reproducing beam 170 is applied to the recording / reproducing layer 14 is 216.0 mV. The ratio of the reflected light amount of the servo layer 18 to the reflected light amount of the recording / reproducing layer 14 was 19.7 times. Furthermore, the tracking using the reflected light (tracking signal) is in a bad state, and the noise included in the tracking signal is extremely large. Note that the reflectance when the servo layer 18 is irradiated with the recording / reproducing beam 170 of the blue wavelength (405 nm) is moderate, and the reflectance when the tracking beam 270 of the red wavelength (650 nm) is irradiated is also. It became moderate.

  In Comparative Example 3, the amount of reflected light when the recording / reproducing beam 170 is applied to the servo layer 18 is 930.0 mV, the amount of reflected light when the recording / reproducing beam 170 is applied to the recording / reproducing layer 14 is 174.5 mV, The ratio of the reflected light amount of the servo layer 18 to the reflected light amount of the recording / reproducing layer 14 was 5.3 times. Furthermore, although tracking using this reflected light (tracking signal) was possible, the noise contained in this tracking signal was extremely large. The reflectivity when the servo layer 18 is irradiated with the recording / reproducing beam 170 of blue wavelength (405 nm) is extremely low, but the reflectivity when the tracking beam 270 of red wavelength (650 nm) is irradiated. Has also become low. That is, when Example 3 and Comparative Example 3 are compared, if the ratio of the reflected light amount of the servo layer 18 to the reflected light amount of the recording / reproducing layer 14 exceeds 5 times, the signal characteristics deteriorate as in Comparative Example 3 and 5 times. It can be seen that the signal characteristics are good as in Example 3 below.

  Note that the signal waveform shown in the lower part of the screen output in FIG. 10A is the tracking signal of the first embodiment, and it can be seen that the signal quality is very small with few noise components. On the other hand, the signal waveform shown in the lower part of the screen output in FIG. 10B is the tracking signal of Comparative Example 1, and it can be seen that there are many noise components and the signal quality is poor.

  In all of the above embodiments, the recording and reproducing layers are shown only when a recording film is formed in advance, but the present invention is not limited to this. For example, like the optical recording medium 510 shown in FIG. 11, the entire place that can be a future recording / reproducing layer group can be a bulk layer 513 having a predetermined thickness. When the recording beam 170 is irradiated onto the bulk layer 513, only the focal portion of the beam spot changes its state, and a recording mark is formed. That is, the optical recording medium in the present invention is not limited to the recording / reproducing layer on which the beam is irradiated in advance, but a recording mark is formed at any time in a planar region, and the recording / reproducing layer group is formed as an aggregate of the recording marks. This includes the case where the multi-layer structure 514 is formed afterwards. By adopting the structure of the bulk layer 513 in the optical recording medium 510, the position of the recording / reproducing layer can be freely set within the range of the bulk layer 513. A similar bulk structure can also be adopted in the optical recording medium 410 shown in the third embodiment.

  In this embodiment, the tracking beam wavelength is shown in the red band and the recording / reproducing beam wavelength is shown in the blue band. However, the present invention is not limited to this, and beams in other wavelength regions are used. It may be adopted.

In the present embodiment, the case where two types of interlayer distances (16 μm, 12 μm) are alternately set in the recording / reproducing layer group has been shown. However, the present invention is not limited to this, and three or more types of interlayer distances are combined. May be. Of course, all may be set to the same film thickness.

  The optical recording medium and the like of the present invention can be applied to various optical recording media having a servo layer and a recording / reproducing layer.

10, 310, 410, 510 Optical recording medium 11, 311 Cover layer 12, 312 Support substrate 14, 314 Recording / reproducing layer group 16, 316 Intermediate layer group 17, 317 Buffer layer 18, 318 Servo layer 412 Support substrate 414 First recording Reproduction layer group 416 First intermediate layer group 417 First buffer layer 418 Servo layer 431 Second cover layer 434 Second recording / reproduction layer group 436 Second intermediate layer group 437 Second buffer layer 90 Optical pickup 90A First optical pickup 90B First 2-light pickup

Claims (13)

A servo layer having irregularities or grooves for tracking control, and a recording / reproducing layer that is laminated in advance or formed afterwards and has no irregularities for tracking control, and the servo layer has a first wavelength tracking. An optical recording medium on which information is recorded or reproduced by irradiating the recording / reproducing layer with a recording / reproducing beam having a second wavelength shorter than the first wavelength while performing tracking control by irradiating the recording beam. And
Compared with the reflectance of the servo layer when the servo layer is irradiated with light of the first wavelength of the tracking beam through the recording / reproducing layer, the recording / reproducing layer is transmitted and the servo layer is transmitted. An optical recording medium characterized in that a reflectance of the servo layer when the servo layer is irradiated with light of the second wavelength of the recording / reproducing beam is small. Compared with the amount of reflected light from the recording / reproducing layer when the recording / reproducing layer is irradiated with the recording / reproducing layer, the recording / reproducing layer is transmitted and the servo layer is irradiated with the recording / reproducing beam. The amount of reflected light from the servo layer at the time is 5 times or less,
The optical recording medium according to claim 1. Compared with the amount of reflected light from the recording / reproducing layer when the recording / reproducing layer is irradiated with the recording / reproducing layer, the recording / reproducing layer is transmitted and the servo layer is irradiated with the recording / reproducing beam. The amount of reflected light from the servo layer at the time is small,
The optical recording medium according to claim 1 or 2. The interlayer distance between the recording / reproducing layer and the servo layer is 10 μm to 200 μm,
The optical recording medium according to claim 1. The reflectance of the servo layer when passing through the recording / reproducing layer and irradiating the tracking beam to the servo layer is 40% to 95%, and is transmitted through the recording / reproducing layer to the servo layer. On the other hand, the reflectivity of the servo layer when the recording / reproducing beam is temporarily irradiated is 60% or less,
The optical recording medium according to claim 1. The servo layer includes a reflective film containing a metal as a main component, and an auxiliary film disposed in contact with the reflective film and having a refractive index different from that of the reflective film.
The optical recording medium according to claim 1. The servo layer has two or more reflective films and three or more auxiliary films.
The optical recording medium according to claim 6. A filter layer in which a dye is dispersed or combined is provided between the servo layer and the recording / reproducing layer,
The filter layer has a low absorbance at the first wavelength of the tracking beam and a high absorbance at the second wavelength of the recording / reproducing beam,
The optical recording medium according to claim 1. When the recording / reproducing layer is the first recording / reproducing layer,
On the opposite side of the servo layer from the first recording / reproducing layer, the servo layer further includes a second recording / reproducing layer that is laminated in advance or is formed afterwards and has no unevenness for tracking control,
In the second recording / reproducing layer, information is recorded while performing tracking control using the servo layer,
The optical recording medium according to claim 1. The servo layer is formed directly on the first recording / reproducing layer side of the substrate,
The second recording / reproducing layer is formed on a side of the substrate opposite to the servo layer,
The optical recording medium according to claim 9. The substrate is made of a light transmissive material,
The optical recording medium according to claim 10. The first recording / reproducing layer and the second recording / reproducing layer may be laminated in advance or formed afterwards at positions symmetrical with respect to the center in the thickness direction of the substrate,
The optical recording medium according to claim 9. The thickness of the substrate is 10 μm to 600 μm,
The optical recording medium according to claim 9.