KR100232048B1 - Optical disc having thin substrate - Google Patents

Abstract

An object of the present invention is to provide an optical disk having a large recording capacity and that can be loaded into an optical disk recording and reproducing apparatus made of a conventional cartridge standard. The optical disk is an information carrier for accumulating information on a track 32 by laser light irradiation. The first disc substrate 30 having the film 35 formed thereon, and the second disc substrate 3 having the information carrier film 36 for accumulating information on the track 33 by laser light irradiation, are formed on the information carrier film side. Of the first and second disk substrates having a thickness of 0.6 mm, wherein the first and second disk substrates are formed by adhering the adhesive layer 37 and integrally molded to record and reproduce a signal by injecting a laser beam. It has an outer thickness of less than mm.

Description

Optical discs with thin disc materials

1 is a block diagram of an essential part of an optical disc recording and reproducing apparatus using the optical disc of the embodiment of the present invention.

2 (a) is a structural diagram of a conventional single light emitting disc having a recording surface on one side.

2 (b) is a structural diagram of a double-sided recording / reproducing double-sided optical disc having two recording surfaces, which is an embodiment of the present invention.

3 is a graph showing the relationship between the peak intensity of the light beam focused on the recording layer by the aperture lens and the NA of the aperture lens, with the substrate thickness of the disc as a parameter.

* Explanation of symbols for main parts of the drawings

2: optical disc 26: double-sided optical disc

29: protective layer 30, 31: base material

32,33 Track 35,36 Recorded thin film

37: adhesive layer

The present invention relates to an optical disk having a thin substrate.

Optical discs have attracted attention as high-density recyclable media, and international standardization work is in progress. A draft proposal DP10090 for a 90mm rewritable optical disc cartridge was created in January 1990 by the International Standard Organization (ISO).

This standard covers 86 mm diameter optical discs, and one layer of magneto-optical recording surface is formed on a 1.2-mm-thick polycarbonate substrate, the capacity of which is 128 MB single-sided disc.

The single-sided structure is aimed at the purpose of enabling overwriting by magnetic field modulation, providing a thin and convenient cartridge, and further, thinning the drive.

However, there has been a problem that since the disk is single-sided, the capacity per disc is small and the capacity of the optical disk cannot be utilized.

In order to solve this problem, a double-sided structure can be considered. However, if both surfaces are simply doubled, the thickness is doubled as compared with the conventional disk. The doubling of the disk thickness also increases with the thickness of the cartridge in which the disk is inserted, which makes it impossible to load even a conventional recording and reproducing apparatus made for an optical disk of the conventional standard.

As another solution, it is conceivable to increase the recording density. For that purpose, it is necessary to use a high numerical aperture NA (Numerical Aperture = h / f, h: effective image height of the lens, f: focal length) as the aperture lens. However, the thickness of the base material of the disc becomes the obstacle. That is, there is a limit to using a lens with high NA by the thickness of the base material.

It is a first object of the present invention to provide an optical disc with a large recording capacity suitable for use in an optical disc recording and reproducing apparatus.

A second object of the present invention is to provide a double-sided optical disc which can be loaded into an optical disc recording and reproducing apparatus made of a conventional cartridge standard.

The optical disk of the present invention is a recording thin film which reversibly or irreversibly changes between a first and second disk substrate having a thickness of 0.6 mm and a plurality of states detectable by irradiation of laser light formed on the first and second disk substrates. And the ones on which the recording thin films of the first and second disk substrates are formed are brought into close contact with each other to be molded integrally.

Hereinafter, an optical disc recording and reproducing apparatus using an optical disc of an embodiment of the present invention will be described with reference to the drawings.

1, reference numeral 1 denotes a cartridge for accommodating the optical disc 2, 2 an optical disc for recording and reproducing a signal, 8 a recording surface for forming a track for recording and reproducing a signal, and 23 a cartridge. This is an identification hole for identifying the disk base material thickness (1).

Denoted at 6 is a fixed optical portion for emitting the collimated light 16, at 7 a movable optical portion for pinching the collimated light 16 at a track of the recording surface 8 of the optical disc 2, and at 9 a semiconductor. A laser, 10 is a collimated lens for shaping the exit light of the laser 9 into parallel light, and 11 is a photo director 14 without substantially returning the reflected light from the optical disc 2 to the laser 9. A polarization beam splitter for reflecting the signal toward (), (12) is a λ / 4 plate, (13) is a cylindrical lens for generating astigmatism, and (14) receives reflected light from the optical disk (2) A photo director for detecting a signal or a reproduction signal, (15) is a moving vehicle for focusing or tracking the collimated lens (10), (16) collimated light, (17) a complete reflection mirror, (18) collie Aperture lens for focusing the mate light 16 on the recording surface 8 of the optical disc 2, 19 is a parallel flat plate, 20 is a parallel flat plate 19 exchange A nine. (3) is an identification hole detecting element for discriminating the thickness of the substrate of the optical disk (2) housed from the identification hole (23) formed in the cartridge (1), (4) is a motor for rotating the optical disk (2), ( 5) is a rotating shaft for fixing the optical disk (2) to rotate by the motor (4), 21 is a linear motor for transferring the movable optical unit 7 to the target track, 22 is a guide for the movable optical unit (7) The rails 24 denote identification signals of the optical disc 2.

The optical disc recording and reproducing apparatus configured as described above will be described below.

In FIG. 1, the optical head is divided into the fixed optical section 6 and the movable optical section 7, and the movable optical section 7 is mounted on the linear motor 21 in the radial direction of the rotating optical disk 2. It is conveyed along the rail 22 to the target track.

The collimated light 16 of the laser 9 condensed by the collimated lens 10 is reflected by the full reflecting mirror 17, so that the aperture lens 18 is approximately perpendicular to the recording surface 8 of the optical disc 2. Condensed into. Reflected light from the optical disc 2 is generally completely reflected by the polarization beam splitter 11 under the action of the λ / 4 plate 12, and enters the photo director 14 via the cylindrical lens 13. The photo director 14 detects the focus error signal by the astigmatism of the cylindrical lens 13 and the tracking error signal by the perfield pushple method. The focus shift of the aperture lens 18 caused by the surface shake of the optical disc 2 is brought into focus by driving the collimated lens 10 by the operator 14.

When the laser 9 is intensity-modulated to the recording power level by the data signal, data is recorded in the corresponding track.

In Fig. 2, the conventional single-plate disk 25 and the double-sided optical disk 26 of the present invention have the same disk outline thickness t.

In Fig. 2 (a), reference numeral 27 denotes a substrate made of a transparent resin such as polycarbonate having a thickness t1, and reference numeral 28 denotes a track formed with guide grooves or the like formed on the recording surface, and as a recording thin film 34, magneto-optical recording. A thin film or phase change recording thin film is formed. Reference numeral 29 denotes a protective layer made of an ultraviolet curable resin or the like.

In FIG. 2 (b), (30) and (31) are the base materials of thickness t2 which consist of transparent resin, such as polycarbonate, and glass, similar to the base material 27. FIG. Reference numerals 32 and 33 are recording surfaces, and phase change recording thin films are formed as recording thin films 35 and 36 on tracks provided with guide grooves. These recording surfaces 32 and 33 are bonded to each other by the adhesive layer 37. t3 is the thickness of the parallel flat plate 19.

Substrate thickness is t = 1.4 mm, t1 = 1.2 mm, t2 = 0.6 mm, for example.

In the case where the recording film of the single plate disk 25 of FIG. 2 (a) is a magneto-optical thin film, the intensity modulation of the tightening force of 1 占 퐉 or less is performed by the aperture lens 18 on the track 28 having the same magnetization direction by the erase operation in advance. The irradiated laser light is irradiated from the substrate 27 side, the irradiated pit is heated up above the Curie temperature, and the magnetization is inverted by the bias magnetic field to record. The reading is performed by detecting a state in which the polarization of the reflected light of the irradiated laser light is changed by the car effect in the magnetization direction of the pit of the track 28.

On the other hand, in the double-sided optical disk 26 of FIG. 2 (b), when the recording film is a phase change medium, the laser beam is directed from the substrate 30 side or the substrate 31 side to the tracks 32 and 33 of the recording surface. Phase change recording is performed to generate a reversible phase change phenomenon in a crystalline state and an amorphous state or an amorphous state and another amorphous state in accordance with the irradiation conditions of the laser beam, and the reproduction is irradiated to the track with a weak laser beam. By changing the intensity of the reflected light. That is, the laser light is modulated to three levels of recording power, erasing power, and reproducing power, and the portion irradiated with recording power on the recording film is heated above the melting point, and then quenched to become an amorphous state so that a signal is recorded. The portion irradiated with elimination power is heated to a temperature below the melting point above the crystallization temperature and is brought to a crystalline state (ie, erased). In this manner, in phase change recording, so-called direct overwrite is possible in the track 32 or the track 33 in which new signals are simultaneously recorded while erasing the still recorded signals.

In addition, since the above overwrite operation is performed by the conventional magneto-optical disk 25, there is a magnetic field modulation recording for irradiating laser light of a constant intensity while modulating the bias magnetic field as a signal. The magneto-optical disk 25 of FIG. 2 (a) is composed of a substrate having a thickness of 1.2 mu m with a protective layer 29 having a thickness of 0.2 mu m or less and a track on which a magneto-optical medium is formed so as to enable magnetic field modulation recording. It is contemplated that the magnetic head can be disposed on the protective layer 29 side.

However, in the magnetic field modulation recording, in the double-sided disc 26 bonded with a relatively thick substrate as shown in FIG. 2 (b), the recording frequency characteristic is poor due to the expansion of the magnetic beam, and the magnetic head modulation power is increased from the attenuation of the magnetic field strength. It is difficult to use.

The aperture lens 18 of the optical disc recording / reproducing apparatus of FIG. 1 assumes an optical disc of the substrate thickness t1, and generates a large aberration at the substrate thickness t2 of the double-sided optical disc 26. Then, the parallel flat plate 19 is inserted, and the difference of the optical path crystal (= refractive index x thickness) by a base material thickness is correct | amended. In consideration of the refractive index of the substrate, the thickness t3 of the parallel plate 27 is (n1 t1-n2 t2) / n3. Here, n1, n2, n3 are the refractive indices of the substrates 27, 30, 31 and the parallel flat plate 19, respectively. For example, when n1, n2, n3 is the same value (for example, 1.5), and t1 = 1.2 mm and t2 = 0.6 mm, t3 is 0.6 mm.

In the above description, a configuration in which one parallel flat plate is provided for two types of optical discs has been described. In general, for m types of optical discs, the parallel flat plate depends on the type of thickness of the substrate of the optical disc to be mounted. Plural sheets are installed.

The thickness of the base material of each optical disk is t1, t2,... … tm, the refractive index of each optical disk is n1, n2,... … , nm, the thickness and refractive index of the parallel plate T1, T2, ... , Tm: N1, N2,... , Nm,

n1t1 + N1T1 = n2t2 + N2T2 =... … nmtm + TmNm = T1, T2,... , Tm: N1, N2,... Nm is selected.

The parallel flat plate may not be m types for m types of optical discs. For example, in the example of FIG. 2 (b), it becomes m-1 type by making the reference | standard into which the parallel plate is not inserted like T1 = 0, T2 = t3, and N2 = n3. Further, by combining a plurality of parallel flat plates, it is possible to configure a smaller type depending on the type of the thickness of the base material of the optical disc. For example, when the relationship of N1T1 + N2T2 = TmNm is established, it can be substituted by two parallel flat plates.

Next, the operation of the optical head when the single plate disk 25 and the double-sided optical disk 26 in FIG. 2 (a) are loaded into the optical disk recording / reproducing apparatus in FIG. 1 will be described below.

When the cartridge 1 is mounted on the rotary shaft 5 of the motor 4, the identification hole detecting element 3 detects the identification hole 23 of the cartridge 1, and the substrate thickness of the mounted optical disc 2 is adjusted. The displayed identification signal 24 is output. The control CPU (not shown) instructs the exchange mechanism 20 to detach the parallel flat plate 19 from the identification signal 24 to the exit surface of the aperture lens 18 at the beginning.

That is, when the loaded optical disc 2 is the single-plate disc 25 (substrate thickness t1 = 1.2 mm), the parallel flat plate 19 is not mounted. When the loaded optical disc 2 is a double-sided optical disc 26, a parallel flat plate 19 is mounted. The collimated light 16 of the laser 9 condensed by the collimated lens 10 is reflected by the fully reflecting mirror 17, so that the aperture lens 18 is approximately perpendicular to the recording surface 8 of the optical disc 2. It is focused and focused. Also, if the substrate thickness is different, the distance between the graph reference plane for fixing the optical disk to the motor rotation table and the recording thin films 34 and 35 and 36 changes, but this is due to the action of the operator driving the aperture lens 18. Is corrected by

As described above, by correcting the difference in the substrate thickness of the optical disc 2 with the parallel flat plate 19, a good condensation result with little aberration can be obtained.

As described above, according to the present embodiment, an optical disk having a different substrate thickness can be recorded and reproduced by one optical disk recording / reproducing apparatus, and a double-sided optical disk can be handled by a cartridge having the same thickness as that of a single-plate disk. At this time, the optical disc recording capacity can be doubled, and an optical disc recording and reproducing apparatus having compatibility with a single-plate optical disc and a double-sided optical disc can be enabled.

Next, an embodiment of an optical disc that is optimal for use in the above optical disc recording and reproducing apparatus will be described.

Surface of the optical recording recording density D is, the light wavelength to the λ, the numerical aperture of the lens aperture NA is given by the Dα (NA / λ) ^2. The shorter wavelength of optical wavelength lambda must wait for the advancement of semiconductor laser technology. At present, the development of semiconductor lasers of 630 mm to 670 mm is rushing, but the crystalline material that enables lasers with wavelengths of less than this still does not endure practical use, and it is realistic to raise the NA of the aperture lens.

However, in a disc structure in which a light beam is irradiated to a recording layer through a disc substrate to record and reproduce a signal, the NA of the aperture lens is limited from the thickness of the disc base material and coma and astigmatism caused by the disc tilt.

The problem of disc skew in optical discs is less than 0.5 °, and the degree of astigmatism is small and coma is dominant. This coma aberration lowers the intensity peak value of the light beam, that is, the recording laser peak power, and hinders good signal recording. In addition, during reproduction, crosstalk increases and C / N of the signal decreases.

For example, in order to suppress the decrease of the light beam intensity peak value to several percent or less, the current situation is to use a lens having a disc tilt of 0.3 degrees or less and an NA of 0.5 to 0.55 or less in a 1.2 mm substrate.

3 is a graph obtained by calculating the light beam intensity peak values for the substrate thickness t = 1.2 mm, 0.6 mm, and 0.3 mm of the disk at the disc tilt of 0.2 ° and the wavelength of 780 nm.

At t = 1.2 mm, the light beam intensity peak value drops to about 99% at NA = 0.5, and at NA = 0.85 the intensity peak value drops to about 56%.

In order to suppress the light beam intensity peak value to about 99% or less of the fall of NA = 0.5, the substrate thickness t = 0.6 mm or less must be used for NA = 0.6. In addition, in order to make NA = 0.75, the substrate thickness t = 0.3 mm or less.

On the other hand, the thickness of the substrate is preferably 0.6 mm or more from the viewpoint of the transferability from the master disc of the replicator manufacturing process, the mechanical strength of the replicator, and, if thick, the influence of dust is small as described above.

Therefore, in order to use a lens having a high aperture performance of not less than 0,6 and to maintain sufficient strength, the disc substrate is preferably 0,6 mm.

The influence of dust on the thickness of the substrate becomes remarkable as the thickness of the substrate becomes thin. This is because the irradiation area of the laser light on the substrate surface is lowered, and this influence is PW, Bogels: “System coding parameters, mechanics and electro-mechanics of the reflective video disc player”, IEEE Trans.on Cnsumer electronics p309-317 (Nov., 1976) (see Fig. 19).

According to the above paper, there is no signal degradation at a thickness of 0.6 mm or more for a large dust of about 75 µm, and no signal degradation up to about 0.3 µm for a small dust of about 20 µm. Considering that the optical disc is contained in the cartridge, relatively small dust may be used, and even a substrate of about 0.3 mm can be used as a replaceable medium.

In the case of thin substrates, the influence on the signal amplitude due to the adhesion of dust is larger than that of conventional thick substrates. Thus, as a recording thin film, it is 20 to 20 times more than the magneto-optical material that detects signals with rotation of a polarized plane of about 0.2 °. Phase change materials that detect signals with a 30% change in reflectance are preferred.

In the international standardization of a 90 mm optical disc cartridge, the base material thickness is prescribed | regulated to 1.4 mm or less, and the thickness of the cartridge which accommodates a disc is 6 mm. In standardization, the single disk structure is 128MB on one side. However, when a double-sided optical disc structure having the above-described substrate thickness of 0.6 mm or less is used, a double-capacity optical disc compatible with a single plate disc can be realized by using a cartridge having the same 6 mm thickness.

In addition, the NA of the aperture lens can be increased by thinning the disk substrate. For example, when Na = 0.6, the capacity per optical disc becomes (0.6 / 0.5) ² x 2 = 2.9 times, and the capacity is 368 MB. do.

As described above, according to the present embodiment, a double-sided optical disc capable of about three times the capacity of the disc recording capacity can be obtained by using a cartridge having the same thickness as the single-plate disc.

In addition, the fixed optical system 6 in which the beam splitter 11 and the λ / 4 plate 12 are arranged in the optical paths of the collimated lens 10 and the laser 9 is displayed. The optical system which arrange | positions the lens 10 and injects the collimated light 16 into the beam splitter 11 and (lambda) / 4 plate 12 may be sufficient.

In addition, the above-mentioned embodiment is only the minimum component which is necessary for description of this invention, and it is well-known for making an optical disc recording / reproducing apparatus, such as a servo, a modulation / modulation signal process, and an error correction circuit, for example. Needless to say, the means are used as needed.

Claims (4)

An information layer made of a phase change material capable of recording and reproducing information, and having first and second disc substrates having a thickness of approximately 0.6 mm, and sandwiching the information layer between the first disc substrate and the second disc substrate. An optical disk formed by adhering the first and second disk substrates to each other, wherein an optical thickness of the optical disk is 1.4 mm or less. An information layer, and the first and second disc substrates having a thickness of approximately 0.6 mm, wherein the first and second disc substrates are sandwiched between the first disc substrate and the second disc substrate. An optical disc formed by bonding, wherein an external thickness of the optical disc is 1.4 mm or less. An optical disc according to claim 1, wherein a signal is recorded or reproduced by irradiating a laser beam to said information layer using a lens having a numerical aperture (NA) of 0.6 or more. The optical disc according to claim 2, wherein a signal is recorded or reproduced by irradiating a laser beam to said information layer using a lens having a numerical aperture (NA) of 0.6 or more.