JPS6149730B2 - - Google Patents

Description

[Detailed description of the invention] Disc-shaped information recording medium (information recording medium disc...
It is well known that research and development is being actively conducted on technology for recording various information signals at high density using discs (hereinafter sometimes simply referred to as disks) and reproducing them. The applicant company has also been conducting research on the development and practical application of high-density recording and reproducing methods using various types of disks, and has so far published the results of its research through numerous patent applications. It's clear.

Now, when trying to record information signals on a master disc at a high recording density, the typical recording method conventionally used is to use a minute laser beam modulated by the information signal. The conventional method used to project a small spot of an electron beam modulated by an information signal onto a beam-sensitive material layer (for example, a photoresist layer) of a disk master. Since recording means using an electron beam requires the use of expensive equipment, recording means using an inexpensive laser beam is used except when the rotation speed of the disk is set low. There are many things.

By the way, the recording trace of the information signal to be recorded on the disc is determined by the existence of many factors such as the information reading ability of the reproducing element used to read the information signal from the recording trace. For this purpose, the beam spot projected when recording information signals onto the master disc has a cross-sectional shape that is wider than the length of the recording trace in the extending direction. It was sometimes made into a roughly rectangular shape, with the width of the trace being larger.

FIG. 1 shows an example in which the recording of an information signal on a master disk is modulated by the information signal, and the cross-sectional shape and dimension of the recording trace in the width direction is approximately larger than the length of the recording trace in the extending direction. 1 is a block diagram showing a schematic configuration of an optical recording device that performs optical recording by projection of a rectangular laser beam spot, and in FIG. 1, reference numeral 1 denotes a turntable; 1 is rotated by a motor M at a predetermined rotational speed and is laterally transferred by a transfer mechanism (not shown). On the turntable 1, a disk master D is fixed, which is made by depositing a photoresist layer on a substrate with a flat surface (for example, a glass plate), and the photoresist layer formed on the master D is fixed. Recording is performed by projecting a laser beam spot modulated by an information signal and having a predetermined cross-sectional shape.

That is, in FIG. 1, 2 is a laser light source, and a laser beam emitted from this laser light source 2 is supplied to a light amount adjustment modulator 4 via a reflecting mirror 3. In this step, the laser beam drift is removed, laser noise is removed, and the light amount is controlled in the radial direction of the disk master (for the optical modulator 4 for adjusting the light amount, see Japanese Patent Laid-Open No. 52-76003). good)
After that, the information signal is applied to the optical modulator 5 and modulated by the information signal supplied to the terminal 6.

The laser beam modulated by the information signal in the optical modulator 5 is applied to the optical system 8 via the reflecting mirror 7, and after the cross-sectional shape of the beam is transformed in the optical system 8 as required, the laser beam is modulated by the information signal. , is applied to the imaging lens 10 via the reflecting mirror 9, and is modulated by the information signal to the photoresist layer of the disk D by the imaging lens 10, and
A laser beam spot having a predetermined cross-sectional shape is projected.

In FIG. 1 described above, the optical system 8 that deforms the cross-sectional shape of the laser beam as required is:
Lens 8a and cylindrical lenses 8b, 8c, 8e
and a light shielding member 8d having a slit S. Its operation is shown in the plan view shown in Fig. 2a and the side view (portion of the slit S) shown in Fig. 2b. The laser beam having a circular cross-sectional shape incident on the optical system 8 from the reflecting mirror 7 passes through the lens 8a and the cylindrical lens 8b. , 8c, etc., the laser light beam is formed into a flat cross-sectional shape such that the longitudinal direction of the cross section coincides with the longitudinal direction of the slit S, and the light shielding member 8
It is projected onto the slit S at point d.

The light shielding member 8d has two sides Su of the slit S,
The laser beam is blocked by the part Sd, and the slit S
Only what passes through is applied to the imaging lens 10 via the cylindrical lens 8e and the reflecting mirror 9.

Then, the imaging lens 10 focuses the laser beam given thereto and has a flat cross-sectional shape, and projects a spot having a substantially rectangular cross-sectional shape onto the disk master D. The spot having a substantially rectangular cross-sectional shape has long sides α and α in the flat cross section of the incident light applied to the imaging lens 10, and short sides α′ and α′ of the spot having a substantially rectangular shape. In addition, the incident light applied to the imaging lens 10 is imaged so that the short sides β and β of the flat cross section become the long sides β′ and β′ of a substantially rectangular spot. It is.

The length of the short side α' of the approximately rectangular laser beam spot imaged on the disk master D by the imaging lens 10 described above is the numerical aperture of the imaging lens 10 (NA ) and the wavelength of the laser beam used, and the numerical aperture of the imaging lens 10 is determined by A large one is used. Furthermore, the length of the long side β' of the substantially rectangular laser beam spot mentioned above is the slit width S _t of the slit S.
, the focal length f _8e of the cylindrical lens 8e, and the focal length f ₁₀ of the imaging lens are expressed by the following equation.

β'=S _t ×f ₁₀ /f _8e ...(1) However, in reality, the long side β' of the above spot
The length becomes a value slightly larger than the length shown by the above equation (1) due to the diffraction of the lens.

A disk with a diameter of about 30 cm and rotating at 900 revolutions per minute,
If you want to record an information signal for one hour with the innermost recording trace located approximately 15 cm from the outer circumference of the disk, the interval between recording traces will be approximately 1.5 μm, but a recording device such as the one shown in Figure 1 When recording an information signal using a laser beam with a wavelength of 4579 Å and an imaging lens 10 with a numerical aperture of 0.9, α' is approximately 0.6 μm on the master disk.
A substantially rectangular laser beam spot with β' of about 1.5 μm can be projected. It goes without saying that the size of the laser beam spot can be adjusted appropriately depending on the interval between recording marks.

Now, the intensity distribution of the light passing through the slit S in the optical system described above is caused by the diffraction of the light by the slit S.
direction) as shown in FIG. 3a. S ₀ , S ₁ , S ₂ , and S ₃ in the figure are zero-order diffraction light and 1st-order diffraction light, respectively.
It shows the second-order diffracted light, the second-order diffracted light, and the third-order diffracted light.

The dotted line shown in FIG. 3a indicates the numerical aperture of the imaging lens 10 in the recording apparatus shown in FIG.
0.9, and the numerical aperture of the cylindrical lens is the imaging lens 1.
This shows the range in which the diffracted light from the slit S passes through the imaging lens 10 when the numerical aperture is sufficiently larger than the numerical aperture of 0.

FIG. 3B shows a case where a laser beam showing the intensity distribution as shown in FIG. , is a longitudinal cross-sectional side view of the bits formed on the master disc D of the disk after the development process, and in this figure 3b {the same applies to each figure b of figures 4 to 6 to be described later}, the horizontal axis represents the recording trace. The width direction and the vertical axis are the depth direction, and
The vertical axis direction in the drawings is illustrated in a state in which the dimensions are enlarged compared to the horizontal axis direction to facilitate illustration and explanation.

In addition, FIG. 4a shows that among a large number of diffracted lights of different orders generated by the slit S in the width direction of the slit S, only the zero-order diffracted light S ₀ and the first-order diffracted light S ₁ pass through the imaging lens 10. FIG. 4B is a curve diagram showing the distribution of light intensity when projected onto the master D of the disk, and FIG. 4B is a curve diagram showing the distribution of light intensity as shown in FIG. 4A. Therefore, the vertical side view of the bits formed on the master disk D of the disk, and FIG. Only the second order diffracted light S ₀ passes through the imaging lens 1
FIG. 5B is a curve diagram showing the distribution of light intensity when the laser beam is projected onto the master disk D of the disk through 0, and FIG. 5B is a curve diagram showing the distribution of light intensity as shown in FIG. FIG. 3 is a longitudinal sectional side view of a pit formed in a master disk D by a beam.

Looking at figures a and b in Figs. 3 to 5, the change in depth of the pit formed in the master D of the disk is as follows:
This is roughly similar to the change in intensity of light incident on the imaging lens 10.

The presence of unevenness on the bottom surface of the pit as shown in Figure 3b and Figure 4b is not only undesirable in appearance, but also when a contact type reproducing element is used as the reproducing element. In addition, there is an undesirable tendency that the life of the contacts (such as the reproducing needle) in the reproducing element is shortened and the disk is easily damaged. Shape is the fifth
If something like the one shown in FIG. b is used, a problem arises in that the width of the recording trace varies greatly depending on the variation in the intensity of the light used for recording.

Furthermore, if the pit has a cross-sectional shape as shown in FIG. 5b, there is a drawback that the information signal cannot be detected sufficiently when a contact type reproducing element is used.

In this way, if the cross-sectional shape of the pit formed on the disk when information signals are optically recorded is as shown in each of Figures 3 to 5, Various problems have arisen, and improvements have been desired.

The present invention modulates a laser beam from a light source with an information signal, passes it through a slit to form a laser beam whose cross section is approximately rectangular, and projects this beam onto an information recording medium via an imaging lens. In the optical recording method for recording information signals on the information recording medium, a slit for regulating the cross-sectional shape of the laser beam is interposed in the optical path from the light source to the incident side of the imaging lens, and the slit and the imaging lens In between, a means for changing the intensity ratio of the diffracted light generated by the slit is provided, so that the intensity _S1a of the first-order diffracted light generated by the slit and the intensity S1a of the first-order diffracted light after passing through the imaging lens are ₁ b is the ratio S ₁ b / S ₁ a of the intensity S ₀ a of the zero-order diffracted light generated at the slit and the intensity S ₀ b of the zero-order diffracted light after passing through the imaging lens _. S ₀ a
The present invention provides an optical recording method in which the above-mentioned problems are solved by flattening the peak portion of the beam projected onto the recording medium by adjusting the beam to be smaller than the following. , the specific contents will be clarified with reference to the attached drawings.

FIG. 6 is a perspective view showing the configuration of essential parts of an embodiment of an optical recording device to which the optical recording method of the present invention is applied to the optical recording device shown in FIG. 1 described above. In FIG. 6, components similar to those shown in FIG. 1 are given the same drawing symbols as those used in FIG. 1.

In FIG. 6, there is a light shielding member 8 in the optical system 8 in the optical path between the reflecting mirror 9 and the imaging lens 10.
A light shielding plate 11 provided with a slit SL having a longitudinal direction parallel to the longitudinal direction of the slit S provided in d.
is installed.

The slit provided in the light shielding plate 11 described above
Among the many diffracted lights of different orders generated by the slit S in the light shielding member 8d in the optical system 8, SL exists in all of the zero-order diffracted light and on both sides of the zero-order diffracted light mentioned above. The laser light beam emitted from the slit SL is made to enter the imaging lens 10 by passing only a part of the first-order diffracted light.

Figure 7a is a diagram showing the intensity distribution of the diffracted light that has passed through the slit SL.
The dotted lines indicated by SL ₁ and SL ₂ correspond to the longitudinal edges SL ₁ and SL ₂ of the slit SL,
Further, XX in the figure indicates the XX direction in FIG. 6.

When the laser light beam showing the intensity distribution of light as shown in FIG. 7a that has passed through the slit SL is focused by the imaging lens 10 and exposes the positive photoresist layer on the master D of the disk. After the development process, bits are formed in the photoresist layer on the disk master D, the longitudinal cross-sectional shape of which is shown in FIG. 7b.

When reducing the amount of the first-order diffracted light from the slit S by inserting the slit SL into the optical path, if the amount of the first-order diffracted light is reduced too much by the slit SL, the above-mentioned problem will occur. The situation approaches the state shown in FIGS. 5a and 5b, which causes a problem.

Therefore, the rate of decrease in the amount of first-order diffracted light when trying to reduce the amount of first-order diffracted light by the slit SL depends on the state of the distribution of the light incident on the slit S, but for example, It should be around 30%.

In the above example, the slit SL provided on the light shielding plate 11 was placed in the optical path just before the imaging lens 10 as a means for changing the intensity ratio of the diffracted light, but a density filter was used instead of the slit SL. The first-order diffracted light may be reduced by a predetermined amount by using it as a means for changing the intensity ratio of the diffracted light.

As in the method of the present invention, by means of changing the intensity ratio of the diffracted light, the intensity ratio of the first-order diffracted light S ₁ b/
S ₁ a (where, S ₁ a is the intensity of the first-order diffracted light generated by the slit for regulating the cross-sectional shape of the laser beam, and S ₁ b
is the intensity of the first-order diffracted light that passed through the imaging lens 10)
is the intensity ratio of zero-order diffracted light S ₀ b / S ₀ a (however, S ₀ a
is the intensity of the zero-order diffracted light generated by the slit for regulating the cross-sectional shape of the laser beam, and S ₀ b is the intensity of the imaging lens 10.
Since the intensity of the zero-order diffracted light that has passed through the pit is made to be smaller than the intensity of the zero-order diffracted light that has passed through the pit, the cross-sectional shape of the bit formed on the disk is smaller than the bottom of the cross-sectional shape of the pit, as shown in Figure 7b. is formed into a flat trapezoidal shape, and in the conventional example, as shown in Figures 3 to 5, the bottom surface of the pit has unevenness, In addition, the method of the present invention eliminates the conventional drawbacks, since the bottom part does not have a flat part and does not become cone-shaped. That is, if the cross-sectional shape of the pit formed on the disk is trapezoidal in the width direction of the recording trace as shown in FIG. When information signals are reproduced using a contact-type reproduction element, there is less wear on the contacts of the reproduction element and damage to the disk, and even when the guide groove and information signal are recorded simultaneously during recording. This allows for good recording.

In the explanation so far, only one part of the 0th-order diffracted light and the 1st-order diffracted light of the diffracted light from the slit S passes through the recording lens, so that the cross-sectional shape of the pit can always be reproduced in a good condition. Although we have described using a trapezoidal shape like this, it is well known that aberrations are unavoidable in lenses due to various factors at each stage of design, manufacturing, and use. Therefore, when recording is performed without applying the present invention, the shape of the recorded pit deteriorates due to the aberration of the lens used, and the cross-sectional shape of the pit in the width direction also changes variously as the lens is replaced. things happen. However, when recording is performed by applying the method of the present invention, only the center portion of the lens is used due to the presence of the slit, so deterioration of the cross-sectional shape of the bit due to the presence of lens aberration can be effectively prevented. It can be done.

As is clear from the above detailed explanation, when information signals are recorded by applying the optical recording method of the present invention, all of the conventional problems mentioned above can be satisfactorily solved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of an optical recording device, FIG. 2a is a plan view of the optical system 8 and subsequent parts of the device shown in FIG. a in Figures to Figures 5 and 7;
In Figure B, each Figure A is a curve diagram showing the change in the light intensity of the diffracted light, each Figure B is a longitudinal cross-sectional side view of the pit in the width direction of the recording trace, and Figure 6 is a curve diagram showing the change in the light intensity of the diffracted light. 1 is a block diagram of an optical recording device; FIG. 1... Turntable, 2... Laser light source,
3, 7, 9...Reflector, 4, 5...Light modulator, 8
...Optical system, 8a...Lens, 8b, 8c, 8e
... Cylindrical lens, 8d... Light shielding member, 10...
Imaging lens, 11... light shielding plate, SL... slit.

Claims (1)

[Claims] 1. A laser beam from a light source is modulated by an information signal, passed through a slit to form a laser beam whose cross section is approximately rectangular, and this beam is transmitted to an information recording medium via an imaging lens. In an optical recording method in which information signals are recorded on the information recording medium by projection, a slit for regulating the cross-sectional shape of the laser beam is interposed in the optical path from the light source to the incident side of the imaging lens. A means for changing the intensity ratio of the diffracted light generated by the slit is provided between the imaging lens, and the intensity ratio of the first-order diffracted light _S1a generated by the slit and the first-order diffracted light after passing through the imaging lens is _{The ratio} of _{the intensity S 1 b of} 1. An optical recording method characterized in that the peak portion of a beam projected onto a recording medium is flattened by adjusting the beam to be smaller than ₀ b/S ₀ a. 2. The optical recording method according to claim 1, wherein a slit is used as a means for changing the intensity ratio of diffracted light. 3 Claim 1 in which a density filter is used as a means for changing the intensity ratio of diffracted light
Optical recording method described in section.