JPS61214149A - Optical disk and its manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disc with pre-pits and a method for manufacturing the same.

[Conventional technology]

An optical disk is a disc-shaped glass or plastic substrate on which information signals are recorded in the form of pits (for example, depressions). 5 Information signals are recorded by detecting the arrangement of these pits by optical means. It is meant to reproduce.

That is, as shown in FIG. 7, on the recording surface of the optical disk, there is a leading edge corresponding to the rising phase and a falling phase of the limiter waveform (b) obtained by applying the limiter to the information signal (a). Pit (c) having a trailing edge is formed continuously in the circumferential direction, and by irradiating the reproduction laser beam along the pit row (track), it is possible to distinguish between parts with pits and parts without pits. The leading and trailing edges of the pit are detected using the difference in the intensity of the reflected light, and a limiter waveform is obtained from this signal to read out the information signal. To explain this process in more detail, in the part where there are no pits, as shown in FIG.
The light beam is totally reflected by the light beam, and the entire luminous flux is returned to the aperture of the final diaphragm lens 41. In addition, in the area where there are pits, as shown in FIG. 8(b), the reproducing laser beam 40 is diffracted by the pits 42 and the diffracted light beam 4 has a large reflection angle.
3, most of which are generated by the final aperture lens 41.
As a result, the amount of light that returns to the lens 41 decreases. Furthermore, a reduction in the amount of light due to the interference effect of the pits 42 is added to the light flux returning into the aperture of the lens 41. By detecting such a change in the amount of light with a detector such as a photodiode, the pit 42
Information recorded on the optical disc can be read by detecting the presence or absence of the disc and changes in its length.

The amount of reflected light at a portion with pits is related to the size of the pits. Although detailed calculations are omitted, if the refractive index of the disk is ni and the wavelength of the reproduction laser beam is λ, the pit depth d is λ/4 n x and the pit cap W is the diameter of the reproduction laser spot. At about 1/3 of 2w, the difference in the amount of light reflected by the pits becomes maximum.

By the way, such an optical disc is copied by a transfer technique from an optical disc master disc on which concavities and convexities identical to the pits to be formed on the optical disc are formed.

As a means for cutting the pits into the optical disk master, a glass or plastic substrate with a photosensitive surface formed on the surface is rotated at a constant angular speed, and a cutting head movably disposed in the radial direction of the substrate is used to cut the pits on the photosensitive surface. A method is known in which a laser beam modulated by a desired information signal is irradiated.

When pits are cut by this method, the substrate rotates at a constant angular velocity with respect to the cutting head as described above, so the relative speed between the photosensitive surface of the optical disc master and the laser spot irradiated from the cutting head is determined by the speed of the substrate. It increases in proportion to the radius from the rotation center to the irradiation center of the laser spot. The size of the pits formed on the photosensitive surface increases approximately in proportion to the irradiation time when the laser light intensity is constant. Then.

The exposure amount changes proportionally depending on the radial position of the substrate, and the pit width is large at the inner periphery of the substrate, and on the contrary, the pit width is small at the outer periphery, resulting in a change in the reproduced output signal level.

Conventionally, in order to prevent such problems, a cutting method has been adopted in which the exposure intensity of the pit portion is changed in proportion to the distance from the rotation center of the substrate to the irradiation center of the laser spot, as shown in FIG. ing. Therefore, as shown in FIG. 10, conventional optical discs have
Pit 4 where the pit width W is almost constant from the inner circumference to the outer circumference
5 is formed.

[Problems with conventional technology]

The conventional optical disc described above does not have any problems when all pit lengths are longer than the diameter of the reproduction laser spot.

However, in order to improve recording density, the pit length is becoming increasingly shorter, and it is expected that pits shorter than the reproduction laser spot diameter will be used on the inner circumference of the substrate. When reading information signals from such an optical disk, as shown in FIG. 11(a), the area occupied by the reproducing laser spot by pits whose pit length is shorter than the reproducing laser spot diameter is as shown in FIG. 11(t). As shown in
A pit whose pit length is longer than the reproduction laser spot diameter becomes smaller than the area occupied by the reproduction laser spot,
A problem arises in that the interference single diffraction efficiency of the reproduction laser beam decreases and the reproduction output signal level becomes small, making it difficult to read out information stably.

[Means for Solving the Problems J] In order to solve the above problems, the present invention includes forming pits in advance in an array corresponding to information signals in the circumferential direction.
In optical discs in which information signals are read by irradiating these pits with a reproduction laser beam, the width of pits shorter than the diameter of the reproduction laser spot is made larger than the width of pits longer than the diameter of the reproduction laser spot. It is characterized by this.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a diagram showing the relationship between pit length and pit width,
1 is a reproduction laser spot, 2 is a pit with a pit length shorter than the diameter of the reproduction laser spot l, 3 is a pit with a pit length shorter than the diameter of reproduction laser spot 1, d is a reproduction laser spot 1, Wl indicates the pit width of pit 2, and W2 indicates the pit width of pit 3.

As is clear from this figure, the pit width Wz of the pit 3 having a pit length shorter than the diameter of the reproduction laser spot 1 is the pit width Wz of the pit 2 having a pit length longer than the diameter of the reproduction laser spot 1. It is formed larger than Wx.

In this case, the area of the pit 3 having a shorter pit length than the diameter d of the reproduction laser spot l is.

When adjusted to be equal to the area of the pit 2 having a longer pit length than the diameter d of the reproduction laser spot l,
Regardless of the length of the pit, the level of the reproduced output signal is always constant, which is more preferable in terms of signal reproduction.

For example, the diameter d of the reproduction laser spot 1 is 1.6 μm.
, the pit width w1 of pit 2, which has a pit length longer than the diameter of the reproduction laser spot, is the reproduction laser spot l.
WIi is adjusted to a diameter d of 173, that is, approximately 0.5 μm, and the ratio of the area of this pit 2 to the area of the reproduction laser spot 1 is.

When the ratio is adjusted to approximately 1:0.42, even for pits 3 having a pit length shorter than the diameter d of the reproduction laser spot 1, the pit width W= is increased in inverse proportion to the pit length, and the reproduction laser spot 1 is adjusted to The area ratio of the pit 3 to the laser spot 1 is always adjusted to the above ratio.

The area of the pit can be adjusted by the exposure amount (laser light intensity x irradiation time) of the photosensitive surface when cutting the optical disc master. Also.

The length of the pit formed on the disk master is determined by the angular velocity of the disk master driven once and the radius from the rotation center of the disk master to the irradiation center of the cutting laser spot. Therefore, by rotating the master disc at an appropriate constant angular velocity, a pit array with a minimum pit length longer than the diameter of the laser spot for cutting can be created in the outer peripheral area of the master disc, and a pit array can be created in the inner peripheral area of the master disc. It is possible to form a pit array in which the minimum pit length is shorter than the diameter of the cutting laser spot.

The optical disc of the present invention can be reproduced in large numbers by a transfer technique using a disc master in which pits are formed as described above as a master model, and has a concrete structure that adjusts the length and area of the pits formed in the disc master. An example of a device and means will be explained.

FIG. 2 is a perspective view showing the overall configuration of the optical disc master cutting device, in which 10 is an optical disc master;
1 is a turntable, 12 is an Ar laser, 13 is an A-
0 Senken M instrument, 14Lj, reflector.

15 is an E-0 modulator, 16 is an information signal source applied to the E-0 modulator 15, 17° is a processing circuit for the information signal source, 18
is a reflector, and 19 is a beam expander.

20 is a He-Ne laser, 21 is a semi-transparent mirror, 22 is a beam mixing prism, 23 is a reflecting mirror, 24 is a cutting head, 25 is a focus actuator provided in the cutting head 24, and 26 is a final actuator provided in the cutting head 24. 27 is a focus control circuit that controls a focus actuator of the cutting head 24.

The Ar← laser is used for exposing the photosensitive surface coated on the optical disc master 10, and the H e -N e laser, which has a wavelength outside the photosensitive range of this photosensitive surface, is used for automatic focusing of the focus actuator 25 provided in the cutting head 24. Used for adjustment.

A-0 optical modulation@13 as shown in FIG.

For example, by applying a voltage with a frequency f to a piezoelectric material 28 such as LiNb0i, a compression wave 30 with a wavelength λ is generated in a medium 29 such as Te0z or PbMo0-, and the signal wave is diffracted using this as a diffraction grating. , modulated light 3I is obtained by amplitude modulating the ultrasonic drive voltage. Therefore, by amplitude modulating the ultrasonic driving voltage of the A-O optical modulator 13, the exposure amount of the photosensitive surface coated on the optical disc master 10 can be corrected.

The E-0 modulator 15 is as shown in FIG.

By applying a voltage to the Pockels cell 32, anisotropy is created between the main axis of the index ellipsoid of the crystal, and a phase velocity difference proportional to the electric field strength is created between the two linearly polarized waves traveling inside the crystal. The elliptically polarized light 33 emitted from the Pockels cell 32 is taken out via the analyzer 34, and
Amplitude modulated light 35 is obtained.

The beam expander 10 is a type of collimator,
The beam diameter is widened so that the beam enters the final focusing lens 17 provided in the cutting head 15 to its full aperture.

When cutting an optical disc master using such a cutting device, the turntable 11 is rotationally driven to rotate the unrecorded disc master IO at a constant angular velocity, and the photosensitive surface formed on the surface of the unrecorded disc master 10 is coated with A-0.
The exposure amount can be corrected by amplitude modulating the ultrasonic drive voltage of the optical modulator 13 or by adjusting the value of the current flowing through the Ar'' laser 12.

In this case, the value of the ultrasonic driving voltage of the A-0 optical modulator 13 or the current flowing to the Ar'' laser 12 is set in the region where the pit length of the minimum pit is greater than or equal to the diameter of the laser spot (the rectangular region in FIG. 5). is adjusted so that the photosensitive surface is exposed with an exposure intensity proportional to the distance from the rotation center of the optical disk master, as shown in FIG. In (S area in FIG. 5), as shown in FIG. 6, the photosensitive surface is exposed with an exposure amount equal to the exposure amount of the pit in the area where the pit 1-length is greater than or equal to the diameter of the laser spot for cutting. Adjusted so that

The pits formed by such cutting means are
Even if the pit length is short, the playback output signal level does not decrease, so information can be recorded in areas that were conventionally considered non-recording areas because the pit length became too short and a stable output signal could not be obtained. This makes it possible to significantly improve recording density. According to experiments, in the case of the optical disc of the present invention, it is possible to obtain a sufficiently stable output signal even from a pit with a pit length of 0.55 μm when the diameter of the reproducing laser spot is 1.6 μm, and it is possible to obtain a sufficiently stable output signal from a pit with a pit length of 0.55μ. In the case of a disc, it becomes possible to record in an area with a radius of 45 mm+ or more from the center of one rotation (conventionally, an area with a radius of 68III11 or more).

The gist of the present invention resides in that the area of the pits whose length is shorter than the diameter of the reproduction laser spot is made equal to the area occupied by the pits which are longer than the diameter of the reproduction laser spot. Therefore, the means for changing the area of the pit is not limited to the above embodiment. Further, in the above embodiment, a case where a laser spot with a diameter d of 1.6μ was used as the reproducing laser spot 1 was explained, but the gist of the present invention is not limited to this, and the diameter d is 1.6μ. It goes without saying that even a reproduction laser spot of ~1.1 μm can be implemented in exactly the same manner.

Furthermore, the present invention can be applied to all types of optical discs, such as 12-inch discs + 5.25-inch discs, video discs, and compact discs.

〔Effect of the invention〕

As explained above, according to one aspect of the present invention, the reproduced output signal level does not change depending on the pit length, and a stable signal can be read out. Furthermore, information signals can now be written in areas that were conventionally designated as non-recording # areas because the pit length was short and the reproduced output signal level was too low.

It becomes possible to improve the recording amount or to make the optical disc more compact.

[Brief explanation of drawings]

FIG. 1 is a plan view schematically showing the relationship between pit length and pit width of an optical disc according to the present invention, and FIG. 2 is a perspective view showing the overall configuration of a cutting device. 311th! I is a perspective view showing the principle of the A-0 Senken m device. Figure 4 is a perspective view showing the principle of the E-0 modulator, Figure 5 is a graph showing an example of the method for cutting an optical disk master according to the present invention, and Figure 6 is a laser for cutting in the cutting method shown in Figure 5. Move spot jll[l
A graph showing the relationship between Il (pit length) and the exposure amount of the pit, Fig. 7 is an explanatory diagram showing the phase relationship between the information signal and the pit, and Fig. 81! I is an explanatory diagram showing the signal detection principle of an optical disk, and FIG. 9 is a graph showing the relationship between the distance from the rotation center of the substrate to the cutting laser spot and the exposure intensity.
FIG. 10 is an explanatory diagram schematically showing the shape of pits formed on a conventional optical disc, No. 1113! I is an explanatory diagram illustrating a problem with a conventional optical disc. l: laser spot for reproduction, 2.3: pit. 10: Optical disc master, 11: Turntable, 12:
Ar←laser generator, 13: A-0 optical modulation excellent, 15:
E-0 modulation amount, 16: information signal source, 19: beam expander, 20: He-N@laser generator, 24:
Cutting head, 25: Focus actuator, 26: Final aperture lens. Figure 1 2.3: Pi/Nodo Figure 2 Figure 3 Figure 5 Disk flat tL Figure 6 Figure 7 Figure 8 (0) (b) Figure 9 De 4 Suge\ Angry Figure 10

Claims (1)

[Claims] 1. In an optical disc in which pits are formed in advance in an array corresponding to information signals in the circumferential direction, and information signals are read out by irradiating the pits with a reproduction laser beam, An optical disc characterized in that the width of pits shorter than the diameter of a reproduction laser spot is larger than the width of pits longer than the diameter of a reproduction laser spot. 2. The area of the pits shorter than the diameter of the reproduction laser spot is made equal to the area occupied by the pits longer than the diameter of the reproduction laser spot. The optical disc described in item 1. 3. The length of the pit corresponding to the information signal of the same wavelength is made shorter as the inner circumferential area is reached, and the length of the pit in the outer circumferential area is made longer than the diameter of the reproduction laser spot, and the inner circumferential area is made shorter. The length of the pit in the area is made shorter than the diameter of the reproduction laser spot, and the width of the pit shorter than the diameter of the reproduction laser spot is made larger than the width of the pit longer than the diameter of the reproduction laser spot. Claims 1 and 2 above characterized in that
Optical disc described in section. 4. The length of pits corresponding to information signals of the same wavelength gradually becomes shorter from the outer circumferential area to the inner cylinder area, and the pit length becomes shorter than the diameter of the reproduction laser spot in the innermost circumferential area. An optical disc master is produced with a pit pattern in which a region is formed and the pit width in this region increases in inverse proportion to the pit length. Using this optical disc master as a master, an optical disc master is created using a transfer technology. 1. A method for manufacturing an optical disc, characterized in that an optical disc replica in which an identical pit pattern is formed is produced.