JPH04289533A - Plane plate like information recording carrier and its recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain an optical disk which has less crosstalk between adjacent tracks and has a structure of high productivity and to record and reproduce the optical disk with respect to the optical disk as the large-capacity and high- density information recording medium used in a computer system or the like. CONSTITUTION:Tracking guides 2 like recessed or projecting stripes are concentrically or spirally formed on a substrate 1 like a plane plate, and a recording layer 3 is provided on them. Information is optically recorded as an information signal 4 on edges 5 and 6 on boundaries of tracking guides 2 on the recording layer 3 by a laser beam. Since directions of steps of edges 5 and 6 are difference, information is recorded with less crosstalk and a high density by the interference of diffracted light when adjacent edges 5 and 6 are irradiated with the laser beam to record and reproduce information.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat information recording carrier, such as an optical disk capable of recording high-density information, which is utilized as a storage section of a computer system, and a recording/reproducing apparatus thereof.

0002

2. Description of the Related Art In recent years, improvements have been made in recording and reproducing devices that use optical disks as information storage units in computer systems. In particular, there is a strong demand for high-density recording on optical discs for miniaturization. When performing high-density recording on this optical disk, the recording spot can only be narrowed down to the physical diffraction limit, which is limited by the wavelength of the recording laser beam and the numerical aperture (hereinafter referred to as NA) of the recording lens. There is a limit to density. Conventionally, in order to improve the recording density, lenses with a recording laser wavelength as short as possible or lenses with a large NA have been used. Also, attempts have been made to use the principle of super-resolution to reduce the size of the zero-order portion of the Airy disk of the focused spot. FIG. 10 shows a conventional embodiment. The shape of the spot formed on the focal plane by the recording focusing lens 36 shown in FIG. If it is made larger than the area, a spot with an intensity distribution as shown in FIG. 10(b) will be obtained. The width (spot diameter) of the zero-order light intensity distribution 40 (Airy disk) with the light shield 37 can be made smaller than the intensity distribution 38 without it. However, the distribution of the primary light is different from the intensity distribution 39 when there is no shielding object 37.
The strength increases as shown in 1. As a result, the recording density can be improved by the smaller Airy disk diameter, but 1
As the optical intensity increases, crosstalk to adjacent tracks increases. Further, FIG. 11 shows another conventional example. This method, proposed in Japanese Patent Application Laid-Open No. 57-105828, involves forming the guide grooves on an optical disk into a V-shape and using the slopes of each groove as a recording area to increase the recording density. One method for forming continuous V-shaped grooves is to mechanically carve grooves on a metal plate. However, this method requires a metal disk with high precision and high machinability, and it is difficult to record track addresses and the like.

0003

SUMMARY OF THE INVENTION In order to improve the recording density, it is necessary to reduce the recording spot size or the recording track pitch. However, in the conventional method, when trying to increase the recording density, crosstalk occurs and there are problems in productivity. In the present invention, the recording laser wavelength is made shorter than before,
To provide a flat information recording carrier capable of recording and reproducing information signals with a smaller recording track pitch than before without increasing the NA of a recording lens and suppressing crosstalk to a practical level, and a recording and reproducing device thereof. It is.

0004

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an information recording carrier in which information is optically recorded on a flat substrate, in which a tracking guide has a concave or convex structure and has a concentric or spiral shape. It is a flat information recording carrier that optically stores information in a recording layer formed thereon, particularly in an area including the boundary of a tracking guide.

[0005] The present invention also includes a recording/reproducing means for generating a beam of light for recording and reproducing information on the recording layer in an area including the boundary of the tracking guide, and a recording/reproducing means for irradiating this beam of light onto the boundary of the tracking guide, that is, the edge portion of the tracking guide. This recording and reproducing apparatus has a guiding means for guiding the flat information recording carrier, and records and reproduces optical information on the flat information recording carrier.

[0006]

[Operation] Generally, during recording, the recording layer has a recording gamma characteristic (the rise of the change in the recording material with respect to the recording power), and recording does not start unless light of a predetermined intensity is input. have. Therefore, by using a recording spot of a light beam with an intensity distribution close to a Gaussian distribution on the optical disk surface, it is possible to write according to the gamma characteristics of the recording layer with a part of the intensity distribution, so that the resolution is higher than the recording spot size. Recording pits can be formed as optical records. However, when reading signals from the surface of an optical disc, recorded information is reproduced by diffracted light from a region irradiated with a spot of a light beam for reproduction according to its intensity distribution. Therefore, although minute pits can be recorded, if they are reproduced using a reproduction spot using a light beam having the same intensity distribution as recording, large crosstalk will occur. Therefore, the present invention uses a spot with the same intensity distribution as the conventional one for recording and reproduction, irradiates the boundary of the tracking guide on the optical disk surface with a light beam, and by recording and reproduction, the reflected diffracted light is used to distinguish between the information reproduction track and the adjacent track. By creating intensity distributions in spatially different directions between the two, crosstalk is significantly reduced.

In other words, when light is incident on a reflective surface having a concavo-convex structure on the order of the wavelength of light or a light-transmitting object having a phase structure, the reflected light or transmitted light is diffracted and transmitted due to the structure.
cause interference. In particular, when a light spot crosses a stepped portion such as a boundary portion of a tracking guide, diffraction occurs in various directions depending on the shape and height of the step. By appropriately selecting the height of this step, the diffraction direction can be adjusted relative to the direction of the incident light beam depending on the direction of the step relative to the direction of travel of the light spot caused by the light beam, that is, when the step is a positive step or when it is a negative step. They swing in opposite directions. The diffraction directions can be set to different directions by making the areas having the positive level difference and the negative level difference adjacent to each other as recording areas. Therefore, since the steps are in opposite directions at the boundaries on both sides of the tracking guide, even if the distance between adjacent tracks is reduced by placing photodetectors in each diffraction direction,
High-quality signal recording and playback with little crosstalk can be performed.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a flat information recording carrier according to an embodiment of the present invention. Tracking guide 2, which is a so-called guide groove
Information signals 4 are placed on a flat substrate 1 in which land portions, which are isolation zones provided between adjacent tracking guides 2, have approximately equal widths. This shows the state of the part of the optical disc in which the information is recorded on the recording layer 3. The reproduced signal information obtained by irradiating a light beam to reproduce this information signal 4 appears as a change in the intensity of diffracted light when the recording layer 3 is of a phase change type or a perforated type, and in the case of a magneto-optical film. appears as a rotation of the plane of polarization.

When the edges 5 and 6 of the tracking guide 2 are irradiated with focused laser light, the edges 5 and 6 diffract and interfere with each other, and the far-field distribution is first determined. Figure 2 shows the near field (on the disk surface) coordinate system (x, y
) and the far field (lens surface) coordinate system (x,
y). The amplitude reflectance at x=x0, y=0 is r
(x, x0), then r(x, x0)=u(x-x0)exp[ikG(
x)]...(1) When G(x)=2h |
x|≦a/2 When G(x)=0 |x|>
It can be expressed as a/2. However, u(x) is the amplitude distribution of the spot on the disk surface, h is the groove depth, a is the groove width, k = 2π
/λ represents.

The amplitude of the far-field diffracted light in the θ direction is

[
0011

[Math 1]

It can be expressed as: Here, if the focal length of the recording/reproducing lens is f and the numerical aperture is NA, then X=f・sinθ, and (Equation 1) is

[0013]

[Math 2]

[0014] However, a1=(-x0-a/2
)kNA,a2=(-x0+a/2)kNA, and the intensity distribution is the square of the absolute value of (Equation 2), |R(x/f,x0
)｜2. Figure 3 shows the calculation results. When there is a spot on the right edge 6, the far field distribution is as shown in A in Figure 3(b), and when there is a spot on the left edge 5, the far field distribution is as shown in B in Figure 3(b). Become. It can be seen that the amount of change in the intensity distribution with respect to the incident optical axis is maximum when the optical groove depth is λ/8 in the case of a rectangular groove. By placing two photodetectors at the positions where the intensity of the diffracted light is maximum when the spot traces the right edge 6 and the left edge 5, information from each part can be sufficiently separated and detected. can do. Figure 3(c) shows photodetectors (A1) and (A2).
is for edge 6, and photodetectors (B1) and (B2) are for edge 5.
This is an example of how it is arranged for use. This reproduced signal information appears as a change in the intensity of diffracted light when the recording layer is of a phase change type or a perforation type, and as a rotation of the plane of polarization when it is a magneto-optical film. When a laser cutting machine records grooves on a glass master coated with photoresist, the edges of the grooves are not perfectly rectangular but always have an inclination. In the case of an inclined groove, the depth of the groove is apparently shallower than in the case of a rectangular groove. Therefore, it is desirable to increase the groove depth slightly as the slope of the groove edge increases.

[0015] Also, for the recording layer, it is better to have a sloped groove edge than a sharp groove edge to improve environmental resistance and
This is desirable from the viewpoint of repeated recording and erasing characteristics. 1
There are two edges for each groove in a book, and in order to track both edges, for example, as shown in Figure 4.
As shown in , it is necessary to jump the spot to the adjacent edge every round. By doing so, it is possible to trace all edges within the disk surface. In order to be able to trace all edges without jumping to the adjacent edge every turn, the photoresist master is traced every turn, as shown in Figure 5(a), where the diagonal lines are concave stripes and the blank areas are convex stripes. At the time of manufacturing, the polarity of the grooves, that is, the tracking guide 2 may be changed from concave to convex. To achieve this, by repeatedly turning the cutting laser beam on and off each time the master disk rotates, it is possible to obtain a spiral edge with a different polarity for the information recording/reproducing recording beam each time the disk rotates. A discontinuous portion 8 occurs at the polarity change portion. FIG. 5(b) shows an enlarged view of the polarity switching section. The spot 9, which was following the left edge 5 of the groove, passes through the discontinuous portion 8, which is the polarity switching section of the tracking guide 2, and then follows the right edge 6 of the groove.

FIG. 6 shows an embodiment of an optical disk recording and reproducing apparatus which is an embodiment of the flat information recording carrier of the present invention. The components include a beam splitter 22 into which the laser beam 11 from a laser generating means (not shown) is input, and a flat substrate 1 of the optical disk into which the laser beam 12 transmitted through the beam splitter 22 is input. A lens 7 focuses the beam of the laser beam 13 and irradiates it as a spot on the track 23 for recording and reproducing the aforementioned optical information, and the diffracted light reflected by the optical information recorded on the track 23 passes through the lens 7 to a beam splitter. photodetectors 18, 19, 20, 21 into which the laser beam 14 is input as diffracted light containing reproduced information after being reflected by 22; and a differential amplifier 24 which receives the outputs of the photodetectors 18, 19, 20, 21 as input. , 25, summing amplifiers 27, 28, and a polarity changeover switch 26 for selecting and outputting the outputs of these amplifiers. The related operations of its components will be explained.

The laser beam 11 passes through a beam splitter 22,
The light passes through a recording/reproducing lens 7 and is focused on a track 23 on which a recording layer 3 is formed. The light beam reflected by the recording layer 3 is transmitted to photodetectors 18 and 19 arranged on the far field surface.
, 20, 21. It has already been explained with reference to FIG. 3 that the light intensity distribution in the far field changes greatly depending on which of the edges 5 and 6 of the tracking guide 2 the light spot is located. Therefore, for example, to track the right edge 5, the photodetectors 18 and 19 are used for the aperture of the reproduction lens, and to track the left edge 6, the output signals of the photodetectors 20 and 21 are used. . A tracking signal can be obtained by connecting the outputs from the photodetectors 18 and 19 to a subtractor 24 and the output signals from the photodetectors 20 and 21 to a subtractor 25. Depending on which side of the edge of the tracking guide 2 is to be followed, the polarity is switched using a tracking polarity changeover switch 26. Also R
The F signal is obtained by adding the photodetector outputs using adders 27 and 28. This is also switched by the polarity changeover switch 26 depending on which edge is to be followed.

Next, the tracking detector and tracking polarity switching will be explained. As already mentioned, as shown in FIG. 3, when the optical depth of the groove is about λ/8, the polarization of the diffracted light from the left and right edges of the groove becomes the largest. As shown in Fig. 7, the far-field distribution of the reflected and diffracted light from the optical disk is the result of the interference of the 0th-order light (15), +1st-order light (16), and -1st-order light (17), which are reflected on the reproduction lens surface. Photodetectors 18, 19, 20, 21 on top
The relationship with the position of is shown in the figure. Depending on whether the right edge or the left edge of the groove of the tracking guide 21 is followed, the 0th-order and +1st-order overlap becomes brighter, or the 0th-order and -1st-order overlap becomes brighter. For example, in order to track the right edge 5 of the groove, tracking detectors 18 and 19 are arranged with respect to the aperture of the reproduction lens, and in order to track the left edge 6, tracking detectors 20 and 21 are arranged. . As shown in FIG. 6, the output from the tracking detector is connected to differential amplifiers 24 and 25, and a polarity changeover switch 26 switches the tracking polarity at the discontinuous portion 8 in FIG. 5 every revolution of the disk. The switching signal of the polarity changeover switch 26 is obtained by a rotation synchronization signal that is output every revolution of the disk. The RF signal is detected by the detector 18
, 19 or the detectors 20 and 21. If the width of the groove of the tracking guide 2 and the width of the land portion, which is the isolation zone between the remaining adjacent tracking guides 2, are set to approximately 1:1, the track pitch can be minimized. Recording track pitch from 1μm to 0.8
Even when the crosstalk is reduced to μm, it is possible to reduce the crosstalk to about -25 dB or less, which is necessary for reproducing data information.

Next, a means for forming a wide groove having a width of about 1 μm or more will be described. Either increase the peak power of the focused spot with a normal Gaussian distribution and form a wide groove around the base of the intensity distribution, or make the focus of the focused spot worse and widen the base of the Gaussian distribution to form a wide groove. There are methods. However, in these methods, the photoresist is irradiated with a laser beam that extends beyond the exposed area, causing so-called fog, which causes film thinning of the photoresist in areas that should not be exposed. As shown in FIG. 8(a), when the condensed spot is a normal Gaussian beam 29, the influence on adjacent areas is very large. By combining a plurality of focused spots as in the method of the present invention, a trapezoidal intensity distribution 30 can be obtained. An example for combining a plurality of spots is shown in FIG. 8(b). If two beams perpendicular to each other are incident on the polarizing beam splitter 31, the recording lens 32
A combined intensity distribution of 30 spots is obtained on the focal plane of . The shape of the intensity distribution is determined by the angle θ between the two beams.
It can be controlled by changing the By using a trapezoidal spot with a narrow base, a high-quality wide groove with little fogging can be formed. The two beams may be combined either spatially or temporally.

[0020] In order to identify the recording track, it is necessary to record the track address. An example of the recording method will be described. When performing wide groove recording by irradiating two beams, as shown in FIG. 9(a), one beam is turned off and the other beam is turned on and off to create a pit 33 corresponding to the address information. can be formed. FIG. 9B shows how address information 34 is recorded when one beam remains on and the other beam is turned on and off. The above is a case where individual addresses are given to the right and left edges of the groove. If the right edge of the groove is set as an even number address and the left side edge is set as an odd number address, one set can be represented by one representative address 35, as shown in FIG. 9(c). If the tracking polarity is positive for the representative address, the representative address +
It becomes address 1, and if it is negative, it becomes the same address as the representative address, and the addresses corresponding to the left and right groove edges can be read.

According to the present invention, it is possible to record and reproduce optical information on the recording layer of adjacent edges of the tracking guide 2. Therefore, by arranging a plurality of photodetectors, recording and reproduction can be performed from adjacent edges. Can be done at the same time. Also, even if the step direction of the edge changes midway, the 2
By configuring one set of photodetectors, all adjacent edge information can be detected.

Generally, in order to form a tracking guide, a so-called guide groove, on an optical disk, a light-sensitive photoresist is coated on a glass master using a spinner, prebaked, and then argon laser or He-Cd laser light is focused. exposure and recording. A guide groove is then formed through a development process. From there, a metal stamper is made and a duplicate disk is made from resin such as polycarbonate or PMMA. A recording layer is formed thereon. This recording layer uses not only thermomagnetic recording materials, but also materials that change reflectance or transmittance due to deformation or melting and evaporation, phase change type, perforated type, dye materials, etc. to record and reproduce information. It goes without saying that the same effect can be obtained by deleting the data.

[0023]

[Effects of the Invention] As described above, by using the edge portion of the tracking guide as the information recording area,
Compared to conventional recording methods, it is possible to significantly improve recording density while keeping crosstalk low. The guide groove can be easily formed using a photoresist master. The high-density optical disk of the present invention can be applied not only to thermomagnetic recording materials but also to phase change type, perforated type, and dye materials.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of an optical disc according to an embodiment of the present invention.

[Figure 2] A state diagram showing the irradiation of a light beam onto the optical disk surface in the same embodiment.

FIG. 3 (a) is a state diagram showing light flux irradiation in different step directions in the same embodiment; (b) is a graph showing far-field intensity distribution of diffracted light due to the light flux in the same embodiment; (c) is a graph showing the far-field intensity distribution of diffracted light by the light flux in the same embodiment; Front view showing the arrangement of photodetectors in

[Figure 4
] Conceptual diagram showing the shape of the tracking guide on the optical disc of the same example

FIG. 5(a) is a top view showing the shape of the tracking guide on the optical disk of the same example; FIG. 5(b) is a top view showing an enlarged portion of the discontinuous portion of the tracking guide on the optical disk of the same example;

FIG. 6 is a block diagram of the main parts of a recording and reproducing device that records and reproduces information on an optical disc according to an embodiment of the present invention.

FIG. 7 is a top view showing the arrangement of photodetectors in the same example.

[Figure 8
] (a) is a state diagram showing the relationship between the guide groove of the optical disk and the intensity distribution of the exposure light beam according to an embodiment of the present invention (b)
is a conceptual diagram (c) showing exposure using multiple beams in the same embodiment.
is a graph showing the intensity distribution of the exposure beam in the same example.

[Figure 9
]A state diagram showing the information recording state of the recording layer of the optical disc according to an embodiment of the present invention.

[Figure 10] (a) is a state diagram showing the state of the light flux to the conventional optical disk; (b) is a graph showing the intensity distribution due to the conventional light flux;

[Fig. 11] Partial cross-sectional view showing the state of information recording on the conventional optical disc.

[Explanation of symbols]

1. Flat substrate 2 Tracking guide 3 Recording layer 4 Information signal 5,6 Edge

Claims (9)

[Claims] 1. A flat substrate in which optical information is stored; a tracking guide having a continuous or discontinuous spiral or concentric concave or convex structure formed on the flat substrate; and a tracking guide formed on the flat substrate. a recording layer for storing information formed of a single layer or a plurality of layers formed on a surface having the tracking guide; A flat information recording carrier on which optical information is recorded. 2. The flat information recording carrier according to claim 1, wherein the concave or convex structure is inverted to a convex or concave structure at the discontinuous portion of the tracking guide. Claim 3: The level difference in the concave or convex structure of the tracking guide is 1/9 of the wavelength of light when recording and reproducing optical information.
3. The flat information recording carrier according to claim 1 or 2, which has a particle size of 1/6. 4. Planar information according to claim 1, wherein the optical information recorded on the recording layer is recorded on the recording layer in an area approximately half the width of the tracking guide. record carrier. 5. The flat information recording carrier according to claim 1, wherein the width of the tracking guide and the width of the isolation zone provided between adjacent tracking guides are approximately equal. . 6. A recording and reproducing means for recording and reproducing information by focusing a light beam for recording and reproducing on the recording layer of the flat information recording carrier according to claim 1; A recording/reproducing device comprising a guide means for guiding a recording medium to a boundary portion of a tracking guide, and configured to record and reproduce information in an area of the recording layer centered on the boundary of the tracking guide. 7. The recording and reproducing device according to claim 6, wherein the recording and reproducing means includes a plurality of photodetectors, each of which performs recording and reproducing of portions on different boundary lines of the tracking guide. 8. The recording/reproducing means is provided with two sets of photodetectors each including two photodetectors, and the two sets of photodetectors are arranged in the far field of diffracted light by a light beam for recording/reproducing. 7. The recording and reproducing apparatus according to claim 6, wherein the recording and reproducing apparatus performs recording and reproducing on two adjacent boundary lines of the tracking guides of the recording layer. 9. Among a set of two photodetectors, one photodetector reproduces information from the recording layer on the tracking guide having a concave or convex structure according to claim 2, and the other photodetector 9. A recording and reproducing apparatus according to claim 8, wherein the device is adapted to reproduce information from a recording layer on a tracking guide having a convex or concave structure according to claim 2.