HK1024087B - Optical information medium - Google Patents

Description

Optical information medium

Technical Field

The present invention relates to an optical information medium capable of recording optically reproducible information and a recording/reproducing method for recording optically readable signals, and more particularly, to an optical information medium and a recording/reproducing method for realizing a recording/reproducing system that is most suitable for a high-density recording medium on which recording/reproducing is performed by using a red laser beam having a short wavelength of 630 to 670 nm.

Background

With the recent development and practical use of short-wavelength lasers and with the standardization of the specifications of dvds (digital Versatile disc) capable of recording and reproducing at higher densities, practical use thereof has been progressing. In this DVD, a data recording area is set on at least one main surface, a pit (pit) as an information recording device is formed in the data recording area, and a reflective layer made of a metal film is formed thereon.

The DVD is specified to be a different standard because of its higher density, compared with the standard of the most popular general optical information medium cd (compact disc) at present. For example, a short-wavelength red laser beam having a wavelength of 630 to 670nm is used in an optical pickup, and an objective lens having a high aperture ratio NA of 0.6 is used. In addition, in order to cope with the warpage of the disk, a disk having a thickness of about one half of the CD, which is about 0.6mm thick, is used. In addition, in order to ensure dimensional compatibility with a CD having a disk thickness of 1.2mm, 2 disks were bonded. In the DVD specification, 1 disc is formatted according to the standard to have a maximum recording capacity of about 4.7GB, and images and sound can be recorded for 133 minutes on average.

In the standardization of the above-mentioned DVD specification, two types of optical information media for exclusive use in reproduction and optical information media capable of recording are assumed in the beginning, as in the relation between CD-ROM and CD-R or CD-RW. However, in the first standardization, only the DVD-Video for Video and DVD-ROM for computer data recording, etc. for playback exclusive use are standardized, and the standardization of recordable DVD is delayed. Under such circumstances, it is urgently required to develop a recordable high-density optical information medium having a maximum recording capacity of 4.7GB among 1 disc and a recording technique thereof.

The DVD as the high-density recording medium has a tracking pitch of 0.74 μm and a minimum pit size of 0.4 μm (0.44 μm in the case of dual-layer recording), and enables high-density recording as compared with the CD having a tracking pitch of 1.6 μm and a minimum pit size of 0.83 μm. Therefore, it can be reproduced with such a high density pitch by using the above-mentioned short-wavelength red laser having a wavelength of 630 to 670nm and using a high aperture ratio objective lens having an aperture ratio NA of 0.6.

In a recordable DVD, a recording layer made of an organic pigment or the like is provided on a substrate having a groove (groove) for tracking corresponding to the tracking pitch of 0.74 μm as described above, and recording is performed by irradiating recording light to the recording layer using an optical information medium having a reflective layer made of gold, aluminum, or the like provided thereon, to form a pit having a minimum pit size of 0.4 μm. For this reason, it is necessary to use a short-wavelength red laser having a wavelength of about 630nm to 670nm as described above, and to focus its light spot in an extremely narrow range for precise recording.

Disclosure of Invention

In view of the technical problem of recording on an optical information medium having such a high recording density, a first object of the present invention is to provide a recording method for an optical information medium capable of recording as a signal of a high-density signal that can be optically read. A second object of the present invention is to provide an optical recording medium which can perform a predetermined signal recording in the above-described high-density signal recording method, and thereby can more easily obtain a reproduced signal satisfying a predetermined specification for a high-density optical information medium, as in the above-described DVD specification.

As described above, in the DVD player for reproducing the DVD which is the currently standardized high-density recording medium, the aperture ratio NA of the objective lens of the optical pickup for irradiating the reproducing light is 0.6. The larger the aperture of the objective lens of the optical pickup, that is, the larger the aperture ratio NA of the objective lens, the more the reproduction light can be focused to a small spot on the optical information medium, and high-density reproduction can be performed.

Similarly, even when recording is performed on an optical information medium, as the aperture ratio NA of the objective lens o for irradiating recording light is larger, the recording light can be irradiated onto the optical information medium with a small spot size, and high-density recording can be performed.

However, as the NA of the objective lens increases, the deviation of the focal point or the like due to the tilt of the optical axis of the objective lens and the disk becomes more likely to occur due to the warpage of the disk or the like, and as the balance between the long and short pits formed by recording deteriorates, problems such as deterioration of the pits and the land length deviation (deterioration of pit and land) tend to occur. Therefore, in the present invention, first, the aperture ratio NA of the objective lens of the optical pickup at the time of recording is made larger than that at the time of reproduction. Secondly, in order to perform stable signal recording even under the condition of using the objective lens o having a large aperture ratio, when the inclination angle of both sides of the groove 3 for tracking is θ, the depth of the groove 3 on the transparent substrate 1 is Ds, and the depth of the recording layer 12 at the position of the groove 3 is Dr, the recording film land/groove film thickness index α represented by 1-Dr/Ds and the width of the groove 3 are appropriately set.

That is, the recording method of an optical information medium according to the present invention includes: a recording medium is provided with a translucent substrate 1 transmitting recording light, a recording layer 12 formed on the translucent substrate 1, and a reflection layer 13 formed on the recording layer 12 and reflecting reproduction light, wherein when recording a signal that can be optically read by recording light incident from the translucent substrate 1, the aperture ratio NA of an objective lens o of an optical head irradiating the recording light to the recording layer 12 is about 0.65, the aperture ratio NA of an objective lens of an optical head irradiating the recording light to the reflection layer 13 is about 0.6, and the aperture ratio of the objective lens of the optical head irradiating the recording light to the recording layer 12 is set to be larger than the aperture ratio of the objective lens of the optical head irradiating the reproduction light to the recording layer 12, thereby performing recording and reproduction, respectively.

More specifically, the aperture ratio of the objective lens o of the optical head that irradiates the recording layer 12 with the recording light is 0.65 ± 0.02 in consideration of the error, and the aperture ratio of the objective lens of the optical head that irradiates the reproducing light is 0.6 ± 0.02. The wavelength of the recording light in this case is 630 to 670nm of the same band as that of the reproduction light.

In such a recording method for an optical information medium, the aperture ratio NA of the objective lens o of the optical head at the time of recording is about 0.65, and is larger than the playback aperture ratio NA of 0.6, so that the spot diameter at the time of recording can be focused more minutely. Therefore, the recording power can be concentrated with a smaller beam diameter than before.

On the other hand, as described above, as the aperture ratio NA of the objective lens is increased, the problem of deterioration in the pit length and land length variation due to deterioration in the balance between long and short pits formed by recording, or the like, is more likely to occur, such as deviation of the focal point due to inclination of the optical axis of the objective lens and the disc due to warpage of the disc.

Therefore, the inclination angle θ of the main surface of the transparent substrate 1 with respect to the both side surfaces of the groove 3 for tracking, which is provided spirally on the side of the surface on which the recording layer 12 is formed, of the transparent substrate 1 is set to 55 to 75 °. Thus, even if the spot size NA of the objective lens o is large, the contrast due to the light interference at the pit edge portion during accurate tracking and recording can be increased, and the modulation degree of all the long and short pits can be optimized.

In order to enable accurate tracking under the condition that the aperture ratio NA of the objective lens o is 0.65. + -. 0.02 at the time of recording, and to enable recording in accordance with the DVD specification, the tilt angle is required to be 55 ℃ or more, and the larger the tilt angle, the more preferable the tilt angle is, under the condition that the thickness of the transparent substrate 1 is 0.6. + -. 0.02mm and the pitch of the tracking spiral grooves 3 is 0.74. + -. 0.01 μm on the surface side of the transparent substrate 1 on which the recording layer 12 is formed. However, if the inclination angle of the groove 3 exceeds 75 °, the mold release becomes difficult when the light-transmissive substrate 1 is injection molded, which significantly reduces the quality of the product of the light-transmissive substrate 1 and also significantly deteriorates the yield. Therefore, the inclination angle θ is set to a range not exceeding 75 °.

Further, when the depth of the groove 3 on the transparent substrate 1 is Ds and the depth of the recording layer 12 located in the groove 3 is Dr, a recording film land/groove film thickness index α represented by 1-Dr/Ds is 0.2 to 0.4. The recording film land/groove film thickness index α is 1-Dr/Ds, and is an index indicating the level of flatness (leveling) of the recording layer 12 when the recording layer 12 is formed by applying an organic pigment or the like on a light-transmitting substrate having the tracking grooves 3 by spin coating. The larger the numerical value, the better the flatness, and the larger the ratio of the groove depth of the surface of the recording layer 12 to the groove depth 3 of the surface of the transparent substrate 1.

The smaller the film thickness index α is, the better the smaller the modulation obtained at the time of reproduction after recording. In order to obtain a higher modulation factor, α must be 0.4 or less in the DVD standard under the condition that the aperture ratio NA of the objective lens o at the time of recording is 0.65 ± 0.02 and the aperture ratio NA of the objective lens o at the time of reproduction is 0.60 ± 0.02.

On the other hand, if the film thickness index α is too small, the degree of flatness is also small, and as a result, the irregularities of the reflective layer 13 become large, and the reflectance is lowered. In order to obtain a high reflectance, α is required to be not less than 0.2, with a target reflectance of 45% or more as specified for DVD.

Further, the half width of the groove 3 on the transparent substrate 1 is 1/3 to 1/2 of the pitch p of the groove 3. The half-width of the groove 3 means the width of the groove 3 at a position 1/2 of the depth Ds of the groove 3 formed on the transparent substrate 1. It has been described above that if the aperture ratio NA of the objective lens o at the time of recording is set to 0.65 ± 0.02, the spot size of the recording light can be further reduced, and if the half width of the groove 3 is made to exceed 1/2 of the pitch p (0.74 μm) of the groove 3, the effect of focusing the spot of the recording light cannot be obtained. On the other hand, if the half-value width of the groove 3 is smaller than 1/3 of the pitch p of the groove 3, a sufficient modulation degree cannot be obtained when the aperture ratio NA of the objective lens o is about 0.60 ± 0.02 and reproduction is performed.

Drawings

Fig. 1 is a half-sectional exploded perspective view showing a state before 2 substrates are bonded according to an example of an optical information medium of the present invention.

Fig. 2 is a perspective view of a portion of the optical information medium in longitudinal section.

FIG. 3 is a longitudinal sectional side view showing an important part of a recording area of the same optical information medium.

FIG. 4 is an enlarged longitudinal cross-sectional side view showing important portions of respective dimensions or angles of recording areas of the same optical information medium.

Detailed Description

Next, embodiments of the present invention will be specifically and specifically described with reference to the drawings.

Fig. 1 and 2 show an example of a write-once optical information medium having a single-sided recording/reproducing structure by bonding both sides of the medium.

The light-transmitting substrate 1 is a transparent disk-shaped substrate having a central hole 4 at the center. The translucent substrate 1 is preferably made of a transparent resin such as polycarbonate or polymethyl methacrylate (PMMA).

A clamping area (hereinafter referred to as a "clamping") area "is provided outside the central hole 4 on one surface of the translucent substrate 1, and the outer peripheral side thereof is a data recording area. A spiral tracking groove 3 is formed in a portion of the data recording area of the transparent substrate 1. The pitch of the tracking grooves 3 was set to 0.74. mu.m.

Further, a recording layer 12 is formed on the main surface of the transparent substrate 1 in the data recording region. For example, the recording layer 12 is formed by applying an organic dye or the like by a spin coating method or the like. Further, a reflective layer 13 made of a metal film of gold, aluminum, silver, copper, or the like, or an alloy film thereof is formed on the recording layer 12. A protective film 14 such as an ultraviolet curable resin is formed on the reflective layer 13.

Further, another substrate 5 is prepared in addition to the light-transmissive substrate 1. The substrate 5 is a substrate of the same size made of the same material as the transparent substrate 1, and the grooves 3, the recording layer 12, and the reflective layer 13 are not provided on the main surface thereof as in the transparent substrate 1. Of course, the other substrate 5 may be provided with the grooves 3, the recording layer 12, the reflective layer 13, and the like as in the transparent substrate 1.

Next, the 2 substrates 1 and 5 are bonded. For example, a reactive curable resin is applied as an adhesive to at least one main surface of the 2-piece substrates 1 and 5 by a method such as spin coating or screen printing, and the surfaces are opposed to each other and superimposed on each other, and the reactive curable resin is cured. Thus, the adhesive layer 11 formed by curing the reactive curing resin bonds the main surfaces of the 2 substrates 1 and 5 to each other. At this time, the surface of the transparent substrate 1 on which the recording layer 12 and the reflective layer 13 are formed is bonded.

The above example is an example in which the transparent substrate 1 having the recording layer 12 and the reflective layer 12 formed on the transparent substrate having the groove 3 and the other substrate 5 not having the recording layer 12 and the reflective layer 13 formed thereon are bonded. In this case, one-sided recording/reproduction can be performed. The other substrate 5 may be a substrate having no light transmittance, a substrate colored to maintain light resistance, or a substrate having a region on the surface thereof on which characters and patterns can be written.

On the other hand, 2 pieces of the transparent substrate 1 having the recording layer 12 and the reflective layer 13 on the transparent substrate 1 having the groove 3 may be prepared, and an optical information medium having a so-called double-sided recording/reproducing structure in which one sides of the recording layer 12 and the reflective layer 13 are bonded in a direction facing each other may be produced.

In fig. 1 and 2, reference numeral 9 denotes a projection 9 formed in an annular shape outside the data recording region on the side of the incident surface of the recording light on the front surface side of the transparent substrate 1, which prevents the recording surface from coming into contact with the surface of another optical information medium when the optical information media are stacked.

Fig. 3 is a vertical cross-sectional view of a part of a recording area where the recording layer 12 and the reflective layer 13 of the optical information medium are formed, and fig. 4 is an enlarged cross-sectional view showing the recording layer 12 and the reflective layer 13.

As shown in fig. 4, a spiral tracking groove 3 is provided on the surface of the transparent substrate 1 on which the recording layer 12 is formed, and the inclination angle θ of the incident surface of the recording light with respect to the transparent substrate 1 on both sides thereof is 55 to 75 °.

Further, when the depth of the groove 3 on the transparent substrate 1 is Ds and the depth of the groove of the recording layer 12 at the position of the groove 3 is Dr, the land/groove film thickness index α of the recording film expressed by 1-Dr/Ds is 0.2 to 0.4. The recording film land/groove film thickness index α is 1-Dr/Ds, which is an index of the flatness of the recording layer 12 when the recording layer 12 is formed by applying an organic pigment or the like on a transparent substrate having the tracking groove 3 by spin coating. The larger the numerical value, the better the flatness, and the larger the ratio of the groove depth of the surface of the recording layer 12 to the groove depth 3 of the surface of the transparent substrate 1.

The half width of the groove 3 on the transparent substrate 1 is 1/3-1/2 of the pitch p of the same groove 3. The half-width of the groove 3 means the width of the groove 3 at a position 1/2 of the depth Ds of the groove 3 formed in the transparent substrate 1.

In such an optical information medium, the aperture ratio NA of the objective lens o of the optical head is set to 0.65 ± 0.02, and the recording light beam is focused on the recording layer 12 from the side of the transparent substrate 1 to record a signal. As described above, if the aperture ratio NA of the objective lens o of the optical pickup at the time of recording is 0.65 ± 0.02, the spot size of the recording light can be further reduced by making it larger than the aperture ratio NA of the objective lens at the time of reproduction to be 0.60. Thereby, high-density recording can be performed.

Next, examples of the present invention will be described with specific numerical values.

(embodiment 1)

A polycarbonate substrate having an outer diameter of 120mm, an inner diameter of 15mm, a thickness of 0.597mm and a refractive index of 1.59, which was a light-transmitting substrate 1 having tracking grooves 3 with a half width of 0.31 μm, a depth of 140nm, an inclination angle of 65 ° at both side surfaces and a pitch of 0.74 μm on one main surface thereof, was prepared.

A solution of cyanine dye (cyclopropane dye) is spin-coated on the surface side of the light-transmitting substrate 1 having the groove 3 to form a film, thereby forming a recording layer 12.

The groove depth at the position of the groove 3 in the recording layer 12 was 105nm, and the land/groove film thickness index α of the recording film was 1-Dr/Ds was 0.25. Since the half width of the groove 3 is 0.31 μm as described above, the pitch of the groove 3 is about 42% of 0.74 μm.

Further, a reflective layer 13 is formed by sputtering gold on the recording layer 12. An ultraviolet curable resin (SD 211 manufactured by japan ink chemical industries, ltd.) was spin-coated thereon, and irradiated with ultraviolet light to cure the resin, thereby forming the protective layer 14. An adhesive made of an ultraviolet curable resin is applied on the protective layer 14, a substrate having the same material and shape as those described above except that no groove is provided is bonded, and the adhesive is irradiated with ultraviolet rays to be cured and bonded. Thereby producing an optical information medium.

The thus produced optical information medium was recorded with an EFM-Plus signal (8-16 modulation signal) at a wavelength of 635nm and a recording power of 10mW using an optical head having an aperture ratio of 0.65 of an objective lens o. The recorded optical information medium is played 10 times while repeating the loading and unloading operations using a commercially available DVD player having an optical pickup with an objective lens aperture ratio of 0.60, so that stable playback can be performed without signal reading errors. Good results were obtained for a recorded signal modulation of 64%, a maximum value of the length deviation between the pit and land of each signal of 6.0ns, a jitter of 7.5%, and a reflectance of 65%.

(embodiment 2)

An optical information medium was produced in the same manner as in example 1, except that the half-width of the tracking groove 3 on the main surface of the transparent substrate 1 was 0.28 μm, the depth was 200nm, and the inclination angle of both side surfaces was 57 °.

The groove depth at the position of the groove 3 in the recording layer 12 was 135nm, and the land/groove film thickness index α of the recording film was 1-Dr/Ds was 0.33. Since the half width of the groove 3 is 0.28 μm as described above, it is about 39% of the pitch 0.74 μm of the groove 3.

The thus produced optical information medium was recorded with an EFM-Plus signal at a wavelength of 655nm and a recording power of 12mW using an optical head having an aperture ratio of 0.66 of the objective lens o, as in the above example 1. The recorded optical information medium is played 10 times while repeating the loading and unloading operations by a commercially available DVD player having an optical pickup with an aperture ratio of 0.60, and can be stably played without causing a signal reading error. Good results were obtained with a recorded signal modulation of 75%, a maximum value of the length deviation between the pit and land of each signal of 5.0ns, a jitter of 6.7%, and a reflectance of 58%.

(embodiment 3)

An optical information medium was produced in the same manner as in example 1, except that the half-width of the tracking groove 3 on the main surface of the transparent substrate 1 was 0.35 μm, the depth was 200nm, and the inclination angle of both side surfaces was 72 °.

The groove depth at the position of the groove 3 in the recording layer 12 was 125nm, and the land/groove film thickness index α of the recording film was 1-Dr/Ds was 0.38. Since the half width of the groove 3 is 0.35 μm as described above, it is about 47% of the pitch 0.74 μm of the groove 3.

The thus-produced optical information medium was recorded with an EFM-Plus signal at a wavelength of 635nm and a recording power of 10mW using an optical head having an aperture ratio of 0.64 for the objective lens o, as in example 1. The recorded optical information medium is played 10 times while repeating the loading and unloading operations by a commercially available DVD player having an optical pickup with an aperture ratio of 0.60, and can be stably played without causing a signal reading error. Good results were obtained with a recorded signal modulation of 75%, a maximum value of the length deviation between the pit and land of each signal of 5.0ns, a jitter of 6.7%, and a reflectance of 63%.

(comparative example 1)

In comparative example 1, an optical information medium was produced which was similar to example 1 except that the inclination angle of the both side surfaces of the tracking groove 3 on the main surface of the transparent substrate 1 was 45 °.

The groove depth of the recording layer 12 at the position of the groove 3 was 95nm, and 1-Dr/Ds was 0.32. Since the half width of the groove 3 is 0.31 μm, the pitch of the groove 3 is about 42% of 0.74 μm.

The thus-produced optical information medium was recorded with an EFM-Plus signal at a wavelength of 635nm and a recording power of 10mW using an optical head having an aperture ratio of 0.65 of the objective lens o, as in example 1. The recorded optical information medium is played 10 times while repeating the loading and unloading operations using a commercially available DVD player having an optical pickup with an objective lens aperture ratio of 0.60, so that stable playback can be achieved without signal reading errors. The modulation of the recorded signal was 54%, the maximum value of the pit-land length deviation of each signal was 18.0ns, the jitter was 10.5%, and the reflectance was 60%.

(comparative example 2)

In comparative example 2, an optical information medium was produced which was similar to that of example 1 except that the half width of the tracking groove 3 on the main surface of the transparent substrate 1 was 0.41 μm and the inclination angle of both side surfaces was 45 °.

The groove depth of the recording layer 12 at the position of the groove 3 was 80nm, and 1-Dr/Ds was 0.43. Since the half width of the groove 3 is 0.41 μm, the pitch of the groove 3 is about 55% of 0.74 μm.

The thus produced optical information medium was recorded with an EFM-Plus signal at a wavelength of 655nm and a recording power of 14mW using an optical head having an aperture ratio of 0.66 of the objective lens o, as in the above example 1. The recorded optical information medium was played 10 times while repeating the loading and unloading operations using a commercially available DVD player having an optical pickup with an objective lens aperture ratio of 0.60, but the overall signal balance was poor and smooth playback was not possible even once. The modulation of the recorded signal was 54%, the maximum value of the pit-land length deviation of each signal was 20.0ns, the jitter was 16.5%, and the reflectance was 48%.

(comparative example 3)

In comparative example 3, an optical information medium was produced which was similar to that of example 1 except that the half width of the tracking groove 3 on the main surface of the transparent substrate 1 was 0.28 μm and the inclination angle of both side surfaces was 70 °.

The groove depth of the recording layer 12 at the position of the groove 3 was 115nm, and 1-Dr/Ds was 0.18. Since the half width of the groove 3 is 0.28 μm, the pitch of the groove 3 is about 37% of 0.74 μm.

The thus-produced optical information medium was recorded with an EFM-Plus signal at a wavelength of 635nm and a recording power of 10mW using an optical head having an aperture ratio of 0.64 for the objective lens o, as in example 1. The recorded optical information medium was played 10 times while repeating the loading and unloading operations using a commercially available DVD player having an optical pickup with an objective lens aperture ratio of 0.60, but the overall signal balance was poor and smooth playback was not possible even once. The modulation of the recorded signal was 63%, the maximum value of the pit-land length deviation of each signal was 19.0ns, the jitter was 14.5%, and the reflectance was 37%.

As described above, according to the present invention, when an optical head is used to optically record a signal on an optical information medium compatible with high-density recording, the optical head having an aperture ratio of 0.65 ± 0.02 is used to record the signal, which is larger than the aperture ratio of 0.60 ± 0.02 of the objective lens during reproduction, so that the recording can be performed while focusing the focus of the recording light to a small range. Further, by appropriately setting the inclination angles of both sides of the tracking groove of the light-transmissive substrate of the optical information medium, the ratio of the width of the tracking groove to the pitch, or the film thickness index of the land/groove of the recording layer, it is possible to eliminate the disadvantage that the aperture ratio of the objective lens o of the optical pickup is increased and is likely to occur. This makes it possible to obtain a reproduced signal that satisfies the specification established for a high-density optical information medium, such as the DVD specification.

Claims (3)

1. An optical information medium having a light-transmitting substrate (1) through which recording light is transmitted, a recording layer (12) formed on the light-transmitting substrate (1), and a reflective layer (13) formed on the recording layer (12) and reflecting the reproduction light, and capable of recording an optically readable signal,

the method is characterized in that:

a spiral groove (3) for tracking is provided on the side of the surface of a light-transmitting substrate (1) on which a recording layer (12) is formed, and when the depth of the groove (3) is Ds and the depth of the recording layer (12) at the position of the groove (3) is Dr, the land surface/groove thickness index alpha of the recording film expressed by 1-Dr/Ds is 0.2 to 0.4.

2. The optical information medium of claim 1, wherein:

the thickness of the light-transmitting substrate (1) is 0.6 + -0.02 mm, the light-transmitting substrate (1) has tracking spiral grooves (3) with a pitch of 0.74 + -0.01 [ mu ] m on the surface side of the light-transmitting substrate (1) on which the recording layer (12) is formed, and the inclination angle theta of the incident surface of the light-transmitting substrate (1) to the two side surfaces of the grooves (3) for recording light is 55-75 deg.

3. The optical information medium of claim 1, wherein:

a spiral groove (3) for tracking is provided on the side of the light-transmitting substrate (1) on which the recording layer (12) is formed, the depth of the groove (3) is Ds, and the half width of the groove (3) is 1/3-1/2 of the average pitch (p) of the same groove (3).