JPS62185251A - Light irradiating method for optical memory disk - Google Patents

Abstract

PURPOSE:To make a spot diameter irradiated to a recording surface small in size, and to record information with a high density by setting a slit width, a diameter of a pin hole, and an interval width of a slit or a pin hole and an optical memory disk to <=2lambda, desirably <=lambda, respectively. CONSTITUTION:As for a slit which has been formed in a mask 30, its width is determined to <=2lambda against a wavelength lambda of an irradiated light, to <=lambdadesirably, and its length is determined in accordance with a track width in a disk 10. Also, a diameter LA of a pin hole PH is determined to <=2lambda, desirably <=lambda. Moreover, an interval width LB between the slit or the pin hole PH of the mask, and a recording surface of the optical memory disk 10 is held in <=2lambda, desirably <=lambda. In this regard, this interval width is held in the same degree as the width of the LB slit or the diameter LA of the pin hole PH. In this way, a spot of a laser light which is irradiated in a spot shape to the optical memory disk 10 can be converted to a small diameter easily.

Description

[Detailed description of the invention] (Technical field) The present invention relates to an optical memory disk light irradiation method.

(Prior Art) Information recording and reproducing systems using optical memory disks are well known.

FIG. 5 shows an optical memory disk 10 and an optical pickup of such a system as an explanatory diagram.

Hereinafter, with reference to FIG. 5, writing and reading information to and from the optical memory disk 10 will be briefly explained, and one problem to be solved by the present invention will also be explained.

In FIG. 5, when the semiconductor laser 12 is made to emit light, the emitted laser light is collimated by the lens 14, passes through the polarizing beam splitter 16 and the quarter-wave plate 18, and then enters the objective lens 20. The lens 20 focuses the light onto the optical memory disk 10 in the form of a spot. Therefore, while rotating the optical memory disk 10, the semiconductor laser 12 is turned on in response to an input signal.
By turning it off, information can be written to the optical memory disk 10.

The light emitted from the optical memory disk 10 is reflected by the disk, enters the objective lens, passes through the 174-wave plate 18, and enters the polarizing beam splitter 16. At this time, the light passes through the quarter-wave plate 18 twice, so that its polarization direction is perpendicular to the original direction, and is therefore reflected to the left in FIG. 5 by the polarizing beam splitter 16. This reflected light.

The light enters the light receiving element 24 via the optical system 22. The optical system 22 is an optical system for obtaining signals for controlling focusing and tracking, and various types of optical systems such as an astigmatism type and a knife type are used.

Incidentally, in the case of the astigmatism method, the optical system 22 is a combination of a converging lens and a cylindrical lens, and the light receiving element 24 is a divided light receiving element.

Well-known focusing and tracking control is performed in accordance with focusing and tracking signals.

When information has already been written on the recording surface of the optical memory disk 10, the light intensity of the light reflected by the recording surface changes depending on the written information. The information is read by converting it into an electrical signal.

The above is an overview of information writing and reading in an optical memory disk system.

Now, in such an optical memory disk system, as described above, whether writing or reading information, it is necessary to focus the irradiated laser beam onto the recording surface of the disk in the form of a sporater. And when writing information,
The size of the smallest recorded pip is about the same as the spot diameter of the focused light.

The size of the smallest pit that can be detected when reading information is also about the same as the spot diameter.

On the other hand, since the area of the recording surface of an optical memory disk is finite, in order to increase the recording density, it is necessary to reduce the spot diameter of the light irradiated onto the optical memory disk in the form of a spot.

By the way, when the laser beam is focused into a spot by an objective lens, the spora 1 at the focusing part - the diameter W
o is the wavelength λ of the laser beam and the numerical aperture NA of the objective lens
Determined by.

It is known that Wo=1.22λ/NA (1).

Therefore, in order to reduce the spot diameter Wo when using an objective lens, as is clear from equation (1), the wavelength λ may be reduced and the numerical aperture NA may be increased. However, the emission wavelength λ of semiconductor lasers that can be stably obtained at present is 780 nm;
+a is the practical minimum value of λ.

On the other hand, it is not always easy to increase the numerical aperture NA. That is, the focal length of the objective lens is λ/(NA
)” and the tolerance for optical memory disk skew and recording medium layer thickness variations.
λ/(NA)', respectively.

Since it is proportional to λ/(NA)', as the numerical aperture NA increases, the depth of focus of the objective lens becomes shallower (this means that focusing control becomes more difficult), and
Restrictions on skew and accuracy requirements for disk manufacturing become stricter.

For this reason, the current situation is to select a value near 0.45 as NA, and for λ = 780 nm, the spot diameter is 1.2 to 1.
．． In this state, a thickness of 6 μm is obtained. Therefore, the minimum recording pit size on the disk is required to be 1 μm or more.

In the case of video digital memory, the recording capacity required for 20 minutes of recording is 130 Gb, but if the diameter of the minimum recording bit can be set to 0.5 μm, the above 20
An entire minute of recording can be stored on one side of the disc. In this way, by reducing the spot diameter of the light that illuminates the optical memory disk in a spot-like manner, high-density recording becomes possible.

As mentioned above, it is extremely difficult in practice to achieve this by increasing the numerical aperture of the objective lens.

(Objective) An object of the present invention is to provide a novel optical memory disk light irradiation method that can easily reduce the diameter of a laser beam spot irradiated onto an optical memory disk.

(composition) The method of the present invention has the following characteristics.

In other words, the laser light to be irradiated onto the recording surface of the optical memory disk is irradiated onto the recording surface through a mask.The mask has a slit or pinhole formed therein, and the light is irradiated onto the recording surface through the mask. The optical memory disk is irradiated in a spot-like manner through the beam.

The width of the slit formed in the mask is determined to be 2λ or less, preferably λ or less, with respect to the wavelength λ of the irradiation light, and the length is determined according to the track width on the disk. The diameter of the pinhole is 2λ or less, preferably λ
Defined below.

Furthermore, the interval width between the slit or pinhole of the mask and the recording surface of the optical memory disk is 2λ or less,
Preferably, it is kept below 1λ.

The above-mentioned interval width is maintained to be approximately the same as the width of the slit or the diameter of the pinhole.

The present invention is due to the inventors. It is based on the following experimental discoveries.

As is well known, when light is propagated through a minute pinhole, one passing light is diffracted by the pinhole.

When the diameter of the pinhole becomes about the same as the wavelength, the diffraction effect becomes maximum, and the light that passes through the pinhole propagates as a spherical wave with the center of divergence at the position of the pinhole.

However, the light passing through a pinhole becomes a spherical wave in the so-called far-field region, which is several wavelengths away from the pinhole position, and in the near-field region immediately after the pinhole, one-passing light becomes a spherical wave. Shows properties as a plane wave.

In other words, if the diameter of the pinhole is 2λ or less relative to the wavelength of the laser beam, in the near field of approximately 2λ immediately after passing through the pinhole, the passing laser beam will proceed with a beam diameter approximately equal to the diameter of the pinhole. It was approved to do so. In particular, the diameter of the pinhole and the near field length d
When D=d, the diameter of the luminous flux in the near field after passing through the pinhole is substantially equal to the diameter of the pinhole. It is particularly good when Dαd≦λ.

Therefore, the laser beam to be irradiated onto the optical memory disk is irradiated onto the recording surface of the optical memory disk through a pinhole having a diameter of 2λ or less, preferably λ or less, relative to the wavelength λ, and the pinhole and the recording surface are The distance between the two surfaces is 2λ or less.

By maintaining the width of the slit or the diameter of the pinhole, the recording surface can be irradiated with light with a spot diameter that is substantially the same as the pinhole.

Hereinafter, description will be given based on specific examples. Incidentally, in order to avoid complexity, the same reference numerals as in FIG. 5 are used in each embodiment for parts that are unlikely to be confused.

The embodiment shown in FIG. 1 is an example in which a mask 30 having pinholes is provided between the objective lens 20 and the optical memory disk 10 in the conventional example shown in FIG.

The laser beam is directed onto the mask 30 by the objective lens 20.
Focuses into a spot. That is, as shown in Figure 2,
The focused light LO by the objective lens is focused onto the mask 30 in the form of a spot. And part of the light is a pinhole PH
The light L1 is incident on the recording surface of the optical memory disk 10 (the surface of the disk IO facing the mask 30) in the form of a spot. At this time, the spot diameter of the irradiated light on the recording surface is approximately equal to the diameter LA of the pinhole PH.

Of course, LA and LB (the interval width between the pinhole PH and the recording surface) are substantially equal to each other and each is 2λ or less.

Now, this example will be explained in detail.

First, the optical memory disk 10 was formed by vapor deposition on one side of a quartz glass substrate as a recording medium. Note that the recording medium is not limited to those listed above, and may include commonly used materials such as a total refraction thin film, an organic dye type, a silver salt type, a photoresist type, a Te type, a metal oxide type, etc. be able to.

Next, the semiconductor laser 12 has an emission wavelength of 780 nm.
nm was used.

The mask 30 was manufactured as follows.

That is, first, a thin chrome film (1000 ml thick) was formed on one side of a 1.5 mm thick low expansion glass by sputtering. Next, a photoresist is applied on this thin film, and a pinhole shape is exposed to an electron beam. The photoresist in the exposed area is removed by development, and the thin film of the claw 11 is dry etched to create pinholes. Finally, the photoresist is removed, leaving a mask with pinholes. Of course, this mask is used with the chrome thin film side facing the recording surface.

The diameter of the pinhole was 0.5 μm.

Furthermore, the distance between the pinhole of the mask 30 and the recording surface is
In order to maintain the distance at 0.5 μm±0.1 μm, the mask 3o was levitated using a method similar to the air levitation type pickup used in small Winchester disks. This eliminates the need for focusing control. Tracking control is performed using an appropriate method.

Under the above conditions, the spot diameter of the irradiated light on the recording surface was 0.5 to 0.6 μm.

In this example, pits with a diameter of 0.5μ are
It was possible to record at m pitch. This point was confirmed using a scanning electron microscope. Both writing and reading could be performed satisfactorily.

Note that the amount of light irradiated onto the recording surface depends on the diameter of the pinhole and
It is determined by the spot diameter focused on the mask by the objective lens. In the example described now, the value is about the same as the calculated value based on the ratio of the area of the spot and the area of the pinhole, that is, 10 to 17% of the amount of light focused by the objective lens.
Met. The pinhole and recording surface are very close together,
Therefore, there is little loss in the amount of light that enters the recording surface from the pinhole until it is reflected by the recording surface and passes through the pinhole again.

FIG. 3 shows another embodiment.

In this embodiment, the laser light emitted from the semiconductor laser 12 is directly irradiated onto the mask 30 without passing through an optical system such as a lens, and the light that passes through the pinhole is directed onto the recording surface of the optical memory disk 10. Irradiated in the form of a spot.

Since the light emitted from the semiconductor laser is a diverging light beam, the larger the distance between the semiconductor laser and the mask, the smaller the amount of light that enters the pinhole of the mask. Therefore, when implementing the present invention using the method shown in FIG. 3, it is necessary to place the light source of the semiconductor laser and the mask as close as possible in order to keep the loss of light amount small.

Therefore, in such an embodiment, a mask having pinholes may be provided directly on the emission mirror surface of the semiconductor laser by vapor deposition or the like. Alternatively, it is also conceivable to provide a waveguide having the same effect as a mask in front of the laser emission.

In the embodiment shown in FIG. 3, the signal detection is.

This can be done by providing a light receiving element around the pinhole at the mask position, but in addition to this,
The reflected light from the recording surface is returned to the semiconductor laser, which is the light source, and the signal from the recording surface can be detected using the self-coupling effect. The signal detection method that utilizes the self-coupling effect has been known as the 5coop method (Tokukō 5
7-58735, Japanese Patent Publication No. 59-27974).

However, in the case of the conventional optical pickup shown in FIG. 5, for example, only about 10% of the light from the semiconductor laser is incident on the recording surface due to optical loss in the path, and the signal change is 10-30% is reflected. Since the path loss is 90%, only 0.1 to 0.3% of the amount of one light emission is returned to the semiconductor laser.

With this level of returned light, signal detection using the 5-coop method is not necessarily easy.

However, when the present invention is implemented using the method shown in FIG. 3, only a few percent to several tens of percent of the light passes through the pinhole and reaches the recording surface, but almost no light is reflected by the recording surface and returns to the semiconductor laser. No loss of light intensity. Therefore, signal detection using the 5coop method is extremely easy.

Of course, if a path with less light loss is constructed, signal detection using the 5-coop method is possible even with the method of the embodiment shown in FIG.

In the above embodiments, a case was explained in which a mask having pinholes was used.

However, instead of the pinhole, a mask having slits L-SL as shown in FIG. 4 may be used with the longitudinal direction of the slits facing in the radial direction of the disk.

In this case, the width LA1 of the slit is 2λ for the light wavelength λ.
Hereinafter, it is preferably λ or less, and the length LA2 is made slightly larger than the track width. In other words, the size of the irradiation light is determined to such an extent that even if the irradiation position shifts slightly during tracking, the irradiation light will not irradiate adjacent tracks.

The length LA2 of the slit SL is determined according to the track width.

It means this.

Furthermore, although the above description has been made regarding the case of a single-reflection type optical memory disk, the present invention can of course be applied to a transmission type disk as well.

Furthermore, it goes without saying that the present invention can be applied to both writing and reading of information.

(Effects of the Invention) As described above, according to the present invention, a novel optical memory disk light irradiation method can be provided.

Since this method is configured as described above, it has the following effects.

That is, firstly, since the diameter of the spot that illuminates the recording surface can be made smaller, it is possible to increase the density of information recording. Second
Furthermore, since there is no need to reduce the size of the radial body to the focusing slot 1 by the objective lens, the design conditions for the optical system such as the objective lens can be relaxed. Furthermore, the light from the light source can be directly irradiated onto the mask, narrowed down by a pinhole or slit, and then irradiated onto the recording surface, making it possible to significantly simplify the irradiation optical system and detect signals using the 5-coop method. In this case, this can be facilitated.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing one embodiment of the present invention, and FIG.
3 is a diagram for explaining another embodiment of the present invention. FIG. 4 is a diagram for explaining a slit in a mask. FIG. 5 is a diagram for explaining the present invention. FIG. 2 is a diagram for explaining a conventional technique and its problems. 10...Optical memory disk, 12...Semiconductor laser, 30...Mask, PH...Pinhole, SL...Slit, LA...Diameter of pinhole. No. 4 [Ichika IX, LA4 Procedural Amendment October 17, 1988 Patent Application No. 28479 of 1988 2, Name of invention Optical memory disk light irradiation method 3, Person making the amendment Relationship to the case Name of patent applicant Name (674) Ricoh Co., Ltd. (and 1 other person) 4. Agent 7. Column 6 of “Detailed Description of the Invention” of the specification to be amended. Contents of the amendment (1) Line 1 of page 3 of the specification. Correct "information" to "information". (2) "Light intensity" in the 3rd line of page 4 of the same page is changed to "light intensity change"
and correct it. (3) Delete rD=J in the third line of page 9. (4) Correct "length" at the end of line 9 on page 15 to "length."

Claims (1)

[Claims] A method of irradiating an optical memory disk with light in a spot in order to write information on the optical memory disk or read information written on the optical memory disk, the method comprising: When the wavelength is λ, a slit having a width of 2λ or less and a length determined according to the track width, or
Using a mask having a pinhole with a diameter of 2λ or less, the optical memory disk is irradiated with light through the slit or pinhole of the mask, and the distance between the slit or pinhole and the recording surface of the optical memory disk is set to 2λ.
A method for irradiating light on an optical memory disk, characterized in that the width is kept at a value equal to or less than λ and approximately the same as the width of the slit or the diameter of the pinhole.