JPH03183040A - Optical disk - Google Patents

Abstract

PURPOSE:To use a ready-made objective lens even when using any constituting material for an optical disk by specifying the sum of respective optical path lengths = (thickness)X(refractive index) for a supporting substrate, recording medium and protecting film to a prescribed wavelength. CONSTITUTION:A sum n1d1+n2d2+n3d3 of the respective optical path lengths calculated from thickness d1, d1 and d1 and refractive indexes n2, n2 and n2 of a supporting base 1, a recording medium 2 and a protecting film 3 is made 1.87+ or -0.28mm. As the fundamental configuration of the read only optical disk, the optical path is only the substrate and the optical path length is 1.87+ or -0.28mm. Therefore, by controlling the sum of the optical path lengths of the supporting base, the recording medium and the protecting film so as to be equal with this optical path length, the ready-made objective lens can be used even when using any constituting material for the optical disk.

Description

[Detailed Description of the Invention] [Summary] The purpose of the present invention is to make it possible to focus an incident light beam on an optical disc even when using a supporting substrate, a recording medium, a protective film, etc. that have a thickness and refractive index different from conventional ones. It has a support substrate, a recording medium, and a protective film, and the support substrate has a thickness of d1 mm, a refractive index of n for light with a wavelength of X nm, and optical path lengths of light emission n and x. d
, and the recording medium has a thickness dz
mm, and the refractive index for light with a wavelength of X nm is n2
and has an optical path length of light emission ntXd2, and the protective film has a thickness of d3mm and a wavelength of Xn
The refractive index for the light of m is 03, and the optical path length of the emitted light is n
5Xdi, and the thicknesses d+, d2, and ds of the supporting substrate, recording medium, and protective film are as follows: n+dt +nzd2+n5ds =1.87±0.2
The configuration is such that the relationship 8mm m is satisfied.

[Industrial application field]

The present invention relates to optical discs, and particularly to optical discs that are made mutually compatible by controlling the thickness and refractive index of constituent materials.

2. Description of the Related Art In recent years, optical discs have made remarkable progress and are beginning to be widely used in applications ranging from information processing to consumer use.

Because the amount of information that can be stored is extremely large, for example, in the field of information processing, it is used as a large-capacity file memory, or as a color image or high-quality sound, as seen in LD (laser disc) and CD (compact disc). This is because it is possible to digitize vast amounts of analog information, such as music, and to pack it into bit information that is resistant to noise.

Optical disks can be broadly classified into, for example, read-only types, write-once types, and rewritable types, each of which is put into practical use using unique optical principles.

Among these, read-only optical discs have been put into practical use based on the specifications proposed by Philips, and range from music discs, which are commonly called CDs and are widely used, to CD-ROMs, which are used particularly in the information processing field. (R
It has been widely developed up to 100% memory (ead only memory).

On the other hand, write-once and rewritable optical discs are being standardized in each country.

It is expected mainly in the field of information processing, and it is desired to further increase the storage capacity.

[Conventional technology]

As mentioned above, there are three types of optical discs, but read-only CDs were first developed for consumer use and are the most advanced with unified standards. And the CD
Playback devices have become widespread, and discs are being produced in large quantities, surpassing conventional records.

FIG. 2 is a sectional view of the structure of a read-only optical disc.

In the figure, 1 is a support substrate, 3 is a protective film, 4 is light, and 5
6 is an objective lens, 6 is a reflective film, and is a cross-sectional view taken in the radial direction.

In the case of a read-only optical disc, a group 11 corresponding to the stylus groove of a record is formed on the surface of a support substrate 1 made of, for example, a transparent acrylic resin plate, with a width of, for example, 1.6 mm.
It is provided in μm.

Along this group 11, unit bits divided into eight parts, each having a unit length from 3 times to 11 times, are provided in a concavo-convex shape with a depth of, for example, 0.07 μm.

This unevenness is provided by replicating it with a mold called a stamper, just like on a record, for example.

And, for example, AI! The entire surface of the support substrate 1, including the groups 11, is covered with a reflective film 6 made of a vapor-deposited film or the like.

What corresponds to the recording medium is, so to speak, this group 11.
These are the unevenness provided on the surface and the reflective film 6 covering the unevenness.

The light 4 is, for example, a laser beam emitted from a semiconductor laser, is narrowed down by an objective lens 5 so as to be focused on the surface of the reflective film 6, and is incident through the support substrate l.

Then, when reflecting in group 11, 8
The light is modulated into bits and returned to a photodetector (not shown), and the light 4
The strength of is converted corresponding to, for example, the information l and 0.

As described above, the read-only optical disc has a simple structure, and the support substrate l may be made of glass or plastic as long as it is transparent. And now PM
Plastic plates such as MA (polymethyl methacrylate) and polycarbonate are used.

The constituent materials of these supporting substrates 1 have a refractive index of 71.5 with respect to light used for reading, for example, a 780 nm laser beam.

Optical systems, especially objective lenses, designed with an optical path length commensurate with this refractive index are mass-produced together with optical disc playback devices.

On the other hand, in the case of a write-once optical disc, additional writing is made possible by, for example, perforating a thin film recording medium with a laser beam or causing a phase transition in the material of the recording medium.

Furthermore, in the case of a rewritable optical disk, a magnetic thin film is used as a recording medium. Rewriting is possible using principles such as extinction and reversal of magnetization that occur when this recording medium is heated above its Curie temperature.

Writing to and reading from this rewritable optical disk involves irradiation of light (heat) and application of a magnetic field, and there are two methods: a light modulation method and a magnetic field modulation method.

Figure 3 is a cross-sectional view of the structure of an optical disk in which light passes through a support substrate.
FIG. 4 is another structural sectional view of FIG. 3.

In the figure, l is a supporting substrate, 2 is a recording medium, 3 is a protective film, 4 is a light, and 6 is a reflective film.

In FIG. 3, the support substrate l is transparent and the light 4 is reflected back from the surface of the recording medium 2. In FIG.

Therefore, the recording medium 2 and the protective film 3 do not need to be transparent, and the optical path length in the optical disk of the incident light and the reflected light 4 is determined by the thickness dl of the support substrate l through which the light 4 passes and the refraction. It is determined only by the rate n1, which is n+dt.

Optical discs with this configuration include, for example, a write-once type and a rewritable type using an optical modulation method.

In FIG. 4, both the support substrate 1 and the recording medium 2 are transparent, and the protective film 3 does not need to be transparent. Then, the light 4 passes through the support substrate 1 and the recording medium 2, is reflected on the back surface of the recording medium 2, and returns.

Therefore, the reflective film 6 is provided on the back surface of the recording medium 2.

In this configuration, the one-way optical path length of the incident light 4 or the reflected light 4 within the optical disk is determined by the respective thicknesses d+, dt of the support substrate l and the recording medium 2, and the respective refractive indexes n+, nz. The sum of the optical path lengths determined by is ntdt+nt(L).

Optical discs with this configuration include, for example, a write-once type and a rewritable type using an optical modulation method.If the recording medium 2 is configured with a reflective film 6 provided on a support substrate l having unevenness, it is read-only. CDs, etc.

The supporting substrate 1 is transparent, and the light 4 is transmitted to the supporting substrate 1.
In the case of an optical disk configured to allow the light to enter through the light, glass or plastic with a refractive index of '-'1.5 is often used.

FIG. 5 is a cross-sectional view of the structure of an optical disk in which no light passes through the support substrate, and FIG. 6 is a cross-sectional view of another structure of FIG. 5.

In the figure, l is a supporting substrate, 2 is a recording medium, 3 is a protective film, 4 is a light, and 6 is a reflective film.

Since the light 4 does not pass through the support substrate 1, it may be transparent or opaque.

In FIG. 5, light 4 enters through a transparent protective film 3 provided on the recording medium 2, is reflected from the surface of the recording medium 2, and returns.

Therefore, the one-way optical path length of the incident light 4 and the reflected light 4 is n5ds from the thickness d of the protective film 3 and the refractive index n3.

Optical disks with this configuration include, for example, a write-once type and a rewritable type using a magnetic field modulation method.

In FIG. 6, light 4 enters through the transparent protective film 3 provided on the recording medium 2 and the recording medium 2, and is reflected by the reflective film 6 provided on the back surface of the recording medium 2. Go back.

Therefore, the optical path lengths of the incident light 4 and the reflected light 4 are the sum of the optical path length of the recording medium 2 and the optical path length of the protective film 3, which is ntd2+n5ds.

Optical disks with this configuration include, for example, a write-once type and a rewritable type using a magnetic field modulation method.

For all of these four types of optical discs, in order to increase the recording density, increase capacity, and improve read quality, the irradiating light, that is, the mainly used laser beam, is reduced to a narrow beam of 1 μmφ. The key is to focus the image on the recording medium 2.

Then, in order to narrow down this laser beam, a ready-made,
In particular, it would be truly advantageous if an objective lens commonly used in CDs could be used.

[Problem to be solved by the invention]

As mentioned above, in order to increase the density and capacity of write-once and rewritable optical discs, the group width and bit length are reduced to, for example, 1 μm, and along with this, the group width and bit length are reduced to, for example, 1 μm. The laser beam incident on the optical disk also needs to be narrowed down.

On the other hand, in order to further increase the recording density or improve the read quality, it often happens that it is desired to replace the conventional supporting substrate material such as glass or plastic with another material.

Furthermore, efforts are being made to develop new recording media and new protective films suitable for these recording media.

However, if the constituent material of the support substrate is changed or a new recording medium or protective film is used, the refractive index of the substrate may change.
Added to this is the thickness and refractive index of the recording medium and protective film, making the optical path length different from that of conventional optical discs.

Therefore, if a conventionally used objective lens, for example a widely used read-only CD objective lens, is used, there is a problem in that the laser beam cannot be narrowed down to a small spot of, for example, 1 μmφ.

On the other hand, designing a new dedicated objective lens has the problem of not being compatible with commonly used objective lenses, both from an economic point of view.

Therefore, the present invention enables the use of a support substrate with a refractive index different from that of glass or plastic whose refractive index is 1.5, and a recording medium or protective film with a thickness and refractive index different from conventional ones. , the objective is to provide an optical disc that can focus an incident light beam.

[Means to solve the problem]

The problem described above includes a support substrate, a recording medium, and a protective film, and the support substrate has a thickness of dlmm, a refractive index of nl for light with a wavelength of Xnm, and a light emitting The recording medium has a thickness of dzmm and a refractive index of 02 for light with a wavelength of X nm, and has an optical path length of emission n2Xdz, The film has a thickness of damm, a refractive index of n for light with a wavelength of Xnm, and an optical path length of emitted light of n5Xd.
3, and the thicknesses d11d2 and d3 of the supporting substrate, recording medium, and protective film are as follows: n+d+ +nzd2+n5d3=1.87±0.28
This is achieved by an optical disc configured so that the relationship of mm is satisfied.

[For production]

As mentioned above, there are three types of optical discs, and read-only CDs are the first with unified standards. The objective lens commonly used in the optical system of this CD can be used.

In other words, in the basic configuration of read-only optical discs such as CDs, the only optical path for incident light and reflection and return is the support substrate, and currently, a practical laser beam with a wavelength of 780 nm or 830 nm is The tolerance range for the refractive index is 1.2±0.1mm, and the tolerance range for the refractive index is 1.5.
When passing through a transparent supporting substrate such as glass or plastic with a size of 5±0゜, the optical path length is (1,2±0.1).
Focusing on the fact that The sum of the respective optical path lengths d n x n n is set to be 1.87±0.28 mm.

Therefore, if the thickness d and refractive index n are respectively dl and nl for the support substrate, (L and nt for the recording medium, and d1 and n3 for the protective film, then n+d+ +n2dx +n5ds = 1.87
±0.28mm・−・−1111・■ ■The formula holds. If the light passes through only the support substrate and is reflected on the surface of the recording medium, then d2=0 and d3=0, so nod,=1.87
±0.28mm m --- ■If it passes through the supporting substrate and the recording medium and is reflected on the back surface of the recording medium, d
, = 0, so n+d+ +nzdz = 1.87±0
．． 28mm m---■If the supporting substrate is opaque and light passes through the protective film and the recording medium and is reflected on the back surface of the recording medium, d1=0, so nzdz +n5CI+ =1.87±0. 28mm
−−−−−■, the relationships of the formulas ■, ■, and ■ hold true, respectively.

If the supporting substrate, recording medium, and protective film are controlled so as to satisfy this relationship, it is possible to use the conventional objective lens, regardless of the constituent material used for the optical disk. In some cases, the optical system itself can also be applied.

Here, the thickness dl of the support substrate is, for example, about 1 m. However, the thickness d2 of the recording medium is, for example, 11
The thickness d of the protective film is often a value such as 10 μm, for example.

Therefore, in the present invention, what can be most effectively controlled is the thickness d of the support substrate.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the present invention.

In the figure, ■ is a support substrate, 2 is a recording medium, 3 is a protective film, 4 is a light, 5 is an objective lens, and 6 is a reflective film.

As the support substrate l, a GGG (Gadolinium Gallium Garnet, Gd-Ga Garnet) substrate with a diameter of 3 inches is used.

The recording medium 2 is placed on the supporting substrate 1 made of GGG.
A Bi-substituted garnet film with a thickness of 200 nm is provided by sputtering.

Further, A4' is deposited on top of this recording medium 2 to form a reflective film 6.

In this configuration, the incident light 4 passes through the support substrate l and the recording medium 2, is reflected by the reflective film 6, and returns.

In order to protect the reflective film 6, a UV-curable acrylic resin film with a thickness of 10 μm is provided as the protective film 3. However, this protective film 3 is not directly involved in the transmission of light 4.

The light 4 has a wavelength 514 that is highly transparent to the supporting substrate l.
A n'm Ar laser is used, and the refractive indexes of the support substrate l and the recording medium 2 with respect to this light 4 are 1.98 and 2.8, respectively.

The objective lens 5 is an aspherical lens designed for use with existing CDs.

The performance of this objective lens 5 is such that a beam of light with a wavelength of 780 nm is transmitted through a supporting substrate having a thickness of 1.2±0.1 mm and a refractive index of 1.
．． 55±0.1, optical path length 1.87±0.28mm
Since the intensity of the beam-shaped light 4 is generally distributed in a Gaussian distribution, the design is such that the half-width at which the intensity is halved is narrowed down to 1 μm.

The present invention will be evaluated by varying the thickness of the GGG serving as the support substrate 1.

When the thickness of the support substrate l is 0.5 mm, the beam half width of the light 4 focused on the surface of the reflective film 6 by the objective lens 5 is 1.3 μm. At 0.9mm, the beam half width of light 4 is 1.0μ
It was m.

In other words, formula (2), n+d+ +ntdt =1.87±0.28m
In m, n+=1.98 and nz=2.8.

However, since d t = 0.0002 mm, the second term can be ignored.

Therefore, it was confirmed that there was good correspondence with d l = 1.87/1.98 #0.94 mm.

The constituent materials and thickness of the support substrate, recording medium, protective film, etc.
Various modifications are possible depending on the method of writing and reading the optical disc, and all materials can be used except for materials whose refractive index differs drastically depending on the wavelength of light.

〔Effect of the invention〕

According to the present invention, even if constituent materials with different refractive indexes are used for various optical discs on which writing and reading are performed using various methods, the thickness of each constituent material can be controlled.
The sum of the optical path lengths of each constituent material is 1.87±0.28
Make it m m.

This makes it possible to sufficiently focus the light beam by using the objective lens that is often used in read-only CDs.

Therefore, the present invention greatly contributes to improving efficiency in the development of optical discs, which are expected to develop in the direction of higher density and higher quality in the future.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a cross-sectional view of the structure of a read-only optical disk, FIG. 3 is a cross-sectional view of the structure of an optical disk in which light passes through a support substrate, and FIG. FIG. 5 is another cross-sectional view of the structure of an optical disk in which no light passes through the support substrate. FIG. 6 is a cross-sectional view of another structure of FIG. 5. In the figure, l is a support substrate, 3 is a protective film, and 5 is an objective lens. 2 is a recording medium, 4 is light, 6 is a reflective film, 3 is a cross-sectional view of the field, resistant to molded light, and a cross-sectional view of the tape showing the features of the present invention. Hitsu ＼ [Drawing light Tizuku's tank port axis valve face concave 3rd figure pigeon 3 figure's ``) visiting one lecture figure 4 female ♂ and 4 pegs Σ consort' Optical disc nozumi 5
Myokuncan Design 5 B Figure 5 has a relation to Hamenzu Man et al.

Claims (1)

[Claims] 1) A supporting substrate (1), a recording medium (2), and a protective film (3).
), the support substrate (1) has a thickness of d_1 mm, a refractive index of n_1 for light (4) with a wavelength of X nm, and an optical path length of the light (4) of n_1×d_1. The recording medium (2) has a thickness of d_2 mm, a refractive index of n_2 for the light (4) with a wavelength of X nm, and an optical path length of the light (4) of n_2×d_2. The protective film (3) has a thickness of d_3 mm, a refractive index of n_3 for the light (4) with a wavelength of X nm, and an optical path length of the light (4) of n_3×d_3. The thicknesses d_1, d_2, and d_3 of the supporting substrate (1), the recording medium (2), and the protective film (3) are n_1, respectively.
d_1+n_2d_2+n_3d_3=1.87±0.
An optical disc characterized in that a relationship of 28 mm is satisfied. 2) The optical disc according to claim 1, wherein the light (4) is a laser light having a wavelength of 780 nm or 830 nm.