JPH05307858A - Optical disk cassette - Google Patents

Abstract

PURPOSE:To increase the recording density of the optical disk which is housed in a cassette case and is subjected to dustproofing and to provide the optical disk cassette which has the interchangeability with the optical disk to be used without being housed in the cassette case. CONSTITUTION:The optical disk cassette provided with a transparent window 16 in the cassette case 15 housing the first optical disk 20 is so constituted that the sum of the optical path length of the transparent disk substrate 12 of the first optical disk 20 and the optical path length of the window 16 coincides with the optical path length of the transparent disk substrate formed on the second optical disk to be used without being housed in the cassette case 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a read-only type optical disc, a write-once type optical disc, a rewritable type optical disc, etc. which are housed in a cassette case.

[0002]

2. Description of the Related Art At present, so-called CDs (compact discs) and LDs (laser discs) are widely used as optical discs for irradiating laser light to reproduce audio signals and video signals. In addition to these read-only type discs for reproduction only, write-once type optical discs that can be written only once, and rewritable type discs that can be rewritten have also been developed.

Generally, these optical disks are characterized by high-density recording and relatively short access time, but because of their high density, dust, fingerprints, etc. adhere to them. It has the problem of being weak against scratches and scratches. Conventionally, there are roughly two methods for solving this problem. One of them is that a layer on which a signal of the optical disc is formed or where a signal is to be formed (hereinafter referred to as "recording layer") is covered with a relatively thick optically transparent layer, and this relatively thick Transparent layer (hereinafter,
It is called "transparent coating layer". ) Is used to irradiate light to record and / or reproduce a signal. With such a configuration, the cross-sectional area on the surface of the transparent coating layer of the light beam focused as a minute spot on the recording layer by the objective lens of the optical pickup is proportional to the square of the thickness of the transparent coating layer. Therefore, even if dust or the like adheres to the surface of the transparent coating layer, the influence thereof can be significantly reduced.

FIG. 1 is a cross-sectional view showing an example of an optical disc having such a structure, and shows the structure of the so-called CD described above. In the figure, 1 is a recording layer, 2 is a disc substrate, and 3 is a protective film provided on the opposite side of the disc substrate 2 with respect to the recording layer 1. Here, the disk substrate 2
It has a thickness (d) of 1.2 ± 0.1 mm and is made of a transparent material having a refractive index of 1.55 ± 0.1 with respect to the reading laser beam, and has a function as the above-mentioned transparent coating layer and a function for supporting the recording layer 1. ing. Then, with respect to such an optical disk 10, a laser beam is focused on the recording layer 1 by the objective lens 4 of the optical pickup arranged on the side of the disk substrate 2 and the reflected light is detected to detect a signal. Playback is performed. Here, the numerical aperture (NA) of the objective lens 4 is about 0.45 to 0.55, and the track pitch is about
1.6 μm, the shortest pit length is about 0.8 μm.

Another method is to store an optical disk in a closed cassette case, provide an optically transparent window in this cassette case, and perform recording or reproduction through this window. Is. As such a conventional technique, for example, there is an information processing device disclosed in Japanese Patent Laid-Open No. 3-185630. The schematic configuration of this information processing apparatus will be described below with reference to FIG.
It will be described with reference to FIGS. FIG. 2 shows the optical disk 10.
FIG. 11 is a plan view of a disc-in card in which the card is stored in a card-shaped case. Further, FIG. 3 is a conceptual diagram in which the optical pickup 7 and the motor 8 are shown together in a partially enlarged sectional view of FIG.
As shown in these figures, in the optical disc-in-card, the optical disc 10 is rotatably housed in a card-sized protective case 5 in a substantially sealed state. The protective case 5 is provided with a window 6 made of a transparent protective plate as a light beam incident portion, and recording or reproduction with respect to the recording layer 1 is performed through the window 6 and an optical pickup arranged outside thereof. This is done by the objective lens 4 of 7.

In FIG. 3, the recording layer 1 is formed on a transparent disk substrate 2 and is rotatably supported by a rotating shaft 9 of a motor 8 in a protective case 5. Further, the optical pickup 7 is provided below the protective case 5, and the light flux condensed by the objective lens 4 thereof passes through the window 6 provided in the protective case 5 and the disc substrate 2, and the recording layer 1 The recording or the reproduction is performed by irradiating the. As described above, according to this optical disc in-card, since the light beam incident portion is covered by the window 6 made of a transparent protective plate, dust, fingerprints, etc., are not directly attached to the recording layer 1 or the disc substrate 2. It will be less.

[0007]

The conventional techniques taken to prevent the deterioration of the signal due to the adhesion of dust or the like have been described above, but these have a certain effect as far as their purpose is concerned. It's a thing, but nothing more. That is, the problem to be solved by the present invention is to prevent dust by storing the optical disk 10 in a hermetically-sealed cassette case like the optical disk in card shown in FIG. 2 or FIG. In principle, it is possible to record or reproduce at a higher density than an optical disc that is used without being housed in a hermetically-sealed cassette case, and has higher compatibility with the optical disc shown in FIG. It is an object of the present invention to provide an optical disc cassette having the above.

Generally, it is known that the recording density of an optical disk can be increased by shortening the wavelength of the laser beam used for recording / reproducing or increasing the numerical aperture (NA) of the objective lens of the optical pickup used for recording / reproducing. Has been. The wavelength of the laser generally used at present is around 800 nm because of its easy availability. recent years,
A laser with a wavelength of about 680 nm has also been developed,
Even with such a laser, the recording density is at most 1.4 times. Further, when the NA of the objective lens is increased, the manufacturing precision of the disk becomes strict, and the current manufacturing technology limits the NA to about 0.6. That is, when recording / reproducing through the disc substrate 2 as shown in FIG.
The thickness of the disc substrate 2 is d, and the numerical aperture of the objective lens 4 is N.
Assuming A, the wavefront aberration due to the warp of the disc is d × (N
Proportional to A) ^3, the wavefront aberration due to the thickness irregularity of the disc substrate 2 is proportional to d × (NA) ^4. That is, in order to increase the NA of the objective lens 4 and increase the recording density of the optical disc, it is necessary to reduce the thickness d of the disc in order to suppress an increase in wavefront aberration. The impact will increase.

[0009]

The present invention has been made to achieve the above object, and the invention according to claim 1 is that "a first optical disk is housed in a hermetically sealed cassette case, In an optical disk cassette, which is capable of recording and / or reproducing without removing the first optical disk from the cassette case by providing an optically transparent window in the case, a transparent layer formed on the first optical disk. At the time of recording or reproducing, the sum of the optical path length in the thickness direction of the transparent layer through which the recording light or the reading light is transmitted and the optical path length in the thickness direction of the window is stored in the sealed cassette case. The transparent layer formed on the second optical disc that is used without being used, and is substantially the same as the optical path length in the thickness direction of the transparent layer through which the recording light or the reading light is transmitted during recording or reproduction. Constitution There is provided an optical disk cassette. ", Characterized in that the,

According to a second aspect of the invention, "the transparent layer formed on the second optical disk has a refractive index of 1.55 ± 0.1 with respect to the recording light or the reading light, and its thickness. Is 1.2 ± 0.1 mm. 2. The optical disk cassette according to claim 1, wherein

According to a third aspect of the present invention, "The transparent layer formed on the second optical disk has a refractive index of 1.5 ± 0.1 with respect to the recording light or the reading light, and its thickness. Is 1.2 ± 0.1 mm.
The optical disk cassette described. Is provided.

[0012]

EXAMPLE A first example of the present invention will be described below with reference to FIG. In the figure, the optical disk 20 is housed in a cassette case 15 to prevent dust from adhering and scratching. The optical disc 20 is the disc substrate 1
2, the recording layer 11 and the transparent protective film 13 are laminated, and the surface of the transparent protective film 13 has an objective lens 14 (NA = NA).
0.75) is arranged to face. The thickness d2 of this transparent protective film 13 is an extremely thin film of about 4 .mu.m to 20 .mu.m, which is almost negligible with respect to the optical path length from the objective lens 14 to the recording layer 11.

A glass window 16 having a thickness d1 of about 1.2 mm and a refractive index of about 1.55 is provided on the bottom surface of the cassette case 15, and the recording layer 1 is provided through the window 16.
Recording or reproduction for 1 is performed. Here, the shape of the window 16 has a length over a range in which a track is to be formed from the inner peripheral portion to the outer peripheral portion of the optical disc, and a width that does not kick the light beam determined by the numerical aperture of the objective lens 14. Since it is sufficient if it is sufficient and can be made very small, sufficient processing accuracy can be obtained relatively easily.

Therefore, according to this optical disk cassette, by providing the window 16, the transparent protective film 13 of the optical disk 20 may be extremely thin, and the objective lens 14 can be used.
Even if the numerical aperture is increased to NA = 0.75, the increase in wavefront aberration can be suppressed, and a higher density optical disc can be obtained. Further, since the glass thickness of the window 16 is about 1.2 mm and the refractive index thereof is about 1.55, the so-called CD shown in FIG. 1 can be reproduced by the recording / reproducing apparatus for recording / reproducing this optical disk cassette. Becomes In this case, it goes without saying that it is necessary to place a diaphragm in the optical path of the optical pickup to take measures such as reducing the NA.

Next, a second embodiment of the present invention will be described with reference to FIG. In the same figure, the optical disc 20 is housed in a cassette case 15 to prevent dust from adhering and being scratched, as in the case of the first embodiment. The optical disc 20 has a structure in which a transparent disc substrate 12, a recording layer 11, and a protective film 13 are laminated. In this embodiment, the surface of the transparent disc substrate 12 faces the objective lens 14 (NA = 0.75). It is arranged. The transparent disk substrate 12 has a thickness d2 of about 0.6 mm and a refractive index of about 1.55. The bottom surface of the cassette case 15 has a thickness d1 of about 0.6 mm.
A glass window 16 having a refractive index of about 1.55 is provided, and recording or reproduction is performed on the recording layer 11 through the window 16. The shape of the window 16 is the same as that of the first embodiment.

Therefore, according to this optical disk cassette, by providing the window 16, the transparent disk substrate 12 of the optical disk 20 may be thin, and the objective lens 14 can be used.
Even if the numerical aperture is increased to NA = 0.75, the increase in wavefront aberration can be suppressed, and a higher density optical disc can be obtained. Further, the sum of the thickness of the glass of the window 16 and the thickness of the transparent disc substrate 12 is about 1.2 mm, and both of them have a refractive index of about 1.55. Therefore, in the recording / reproducing apparatus for recording / reproducing this optical disc cassette, It becomes possible to reproduce the so-called CD shown in FIG. Incidentally, in this case, it is necessary to place a diaphragm in the optical path of the optical pickup to take measures such as reducing the NA, as in the case of the first embodiment.

As described above, in the two embodiments, the case of the optical disc cassette having the upward compatibility with the so-called read-only CD in which the thickness of the disc substrate is 1.2 ± 0.1 mm and the refractive index thereof is 1.55 ± 0.1. However, the present invention is not limited to these. The thickness of the disk substrate is 1.2 ± 0.1 mm and its refractive index is 1.5 ± 0.1
It is obvious that the present invention can also be applied to an optical disc cassette having upward compatibility with the so-called LD. Furthermore, the present invention is not only compatible with these existing optical discs, but also has two types: an optical disc that is used without being stored in a cassette case and an optical disc that is stored and used in a cassette case. It is possible to construct a new optical disk system that can be shared.

[0018]

As described above, according to the optical disk cassette of the present invention, the influence of dust and scratches can be avoided and good recording and / or reproducing can be performed, and the recording density on the optical disk can be increased. Thus, it is possible to obtain compatibility with an optical disc that is used without being housed in a cassette case.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the configuration of a conventional optical disc.

FIG. 2 is a plan view of a conventional optical disc in card.

FIG. 3 is a partially enlarged sectional view of a conventional optical disc in card.

FIG. 4 is a cross-sectional view of an optical disc cassette that is a first embodiment of the present invention.

FIG. 5 is a sectional view of an optical disc cassette according to a second embodiment of the present invention.

[Explanation of symbols]

 1 Recording Layer 2 Disk Substrate 3 Protective Film 4 Objective Lens 5 Protective Case 6 Window 7 Optical Pickup 8 Motor 9 Rotation Axis 10 Optical Disk 11 Recording Layer 12 Disk Substrate 13 Protective Film 14 Objective Lens 15 Cassette Case 16 Window 20 Optical Disk

Claims (3)

[Claims] 1. A first optical disk is housed in a hermetically sealed cassette case, and an optically transparent window is provided in the cassette case to record and / or record without removing the first optical disk from the cassette case. Alternatively, in a reproducible optical disk cassette, an optical path length in the thickness direction of the transparent layer formed on the first optical disk, through which recording light or reading light is transmitted at the time of recording or reproduction, and the window. Is a transparent layer formed on the second optical disc that is used without being housed in the hermetically-sealed cassette case, and the sum of the optical path length in the thickness direction of An optical disk cassette characterized in that the optical path length in the thickness direction of a transparent layer through which light or the read light is transmitted is substantially the same. 2. The transparent layer formed on the second optical disk has a refractive index of 1. for the recording light or the reading light.
The optical disk cassette according to claim 1, wherein the optical disk cassette has a thickness of 55 ± 0.1 and a thickness of 1.2 ± 0.1 mm. 3. The transparent layer formed on the second optical disk has a refractive index of 1. for the recording light or the reading light.
The optical disk cassette according to claim 1, wherein the optical disk cassette has a thickness of 5 ± 0.1 and a thickness of 1.2 ± 0.1 mm.