JPH03292631A - Optical multilevel recording and reproducing system - Google Patents

Abstract

PURPOSE:To reproduce recorded information with high precision by modulating a laser beam in the breadthwise direction of recording pits or recording grooves to record multilevel information and reproducing multilevel information by the light intensity pattern of reflection diffracted light due to irradiation of a reproducing beam. CONSTITUTION:The laser beam modulated with multilevel information is made incident on a recording negative as an optical disk 20 to successively form recording pits 21, which have a fixed depth and have the width made multilevel, in the track direction, thereby recording multilevel information. At the time of reading recorded information from the optical disk 20, recorded pits 21 are irradiated with a light beam to form the light intensity pattern of the reflection diffracted light, which is changed in accordance with the pit width, on a line sensor 22, and edge intervals of + or -1st-order diffracted light are detected to reproduce multilevel information. Thus, information is recorded and reproduced in multiple levels by the simple constitution, and recorded information less affected by disturbance is reproduced with high precision.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention performs high-density recording by forming multivalued recording pits on an optical recording medium such as an optical disk, and also reproduces the multivalued information. This invention relates to an optical multilevel recording and reproducing method.

[Conventional technology]

Conventionally, there has been known a recording method that enables high-density recording by multileveling the depth and width of recording pits and recording grooves of an optical recording medium.

As a means for reproducing information recorded by such a method, for example, as described in Japanese Patent Application Laid-Open No. 81-115274, when multilevel recording pits are irradiated, the shape of the recording pits is changed. There is a reproduction method that reproduces recorded information by utilizing the fact that the amount of reflected light returned to the optical head changes due to the difference.

Furthermore, as a technique for converting the width direction of a recording groove into a multi-level recording groove, as described in Japanese Patent Application Laid-Open No. 82-43839, a recording groove formed on a recording medium is formed so that its opposite edge has a multi-level recording groove. There is a recording and reproducing method in which the recording groove is displaced in the width direction so as to take a value, and the amount of this displacement is detected and reproduced using the high-frequency component of the tracking error signal.

Furthermore, as a multi-value technology regarding the arrangement position of recording pits in the array direction, the pit interval is changed using consecutive 2 pits or 3 bits, and the ±1st order of reflected diffraction light generated when a light beam is irradiated is used. A recording/reproducing method is being considered in which recorded information is reproduced by detecting the distance between peaks of light.

[Problem to be solved by the invention]

However, the recording and reproducing method that detects the amount of reflected light due to the difference in the depth and width of the recording pit described above reproduces recorded information based on the difference in the intensity level of the amount of reflected light, so the reproduction accuracy is greatly affected by external light. and S
/N, there is a very high possibility that both sensitivity will deteriorate. especially,
When the depth of recording pits, etc. is multivalued, extremely advanced technology is required because strict process control is required for the accuracy of the standby when duplicating the recording medium.

In addition, the method of displacing the recording groove in the width direction uses the error signal of the tracking servo to reproduce the recorded information, which causes a disturbance to the tracking and has the problem of reducing the performance of the tracking servo. .

Furthermore, the method of recording and reproducing using consecutive 2 pits or 3 bits requires writing pit pairs of 2 pits or 3 bits on the recording medium, so it is used for recording and reproducing compared to the case where only 1 bit is used. The system becomes more complex. Moreover, it is necessary to detect the peak of the light intensity of the reflected and diffracted light, which poses the problem of complicating the system and reducing the number of levels that can be multivalued.

The present invention has been made in view of the above-mentioned circumstances, and is an optical multi-value optical method that can perform multi-value recording and reproduction of information with a simple configuration, and can reproduce recorded information with high precision with little influence from external disturbances. The purpose is to provide a recording and playback method.

[Means and effects for solving the problem] The present invention modulates the multi-value information in the width direction of a recording pit or recording groove by using multi-value information that is multi-valued according to the information to be recorded. A reproducing beam is irradiated onto the recording pit or recording groove that is modulated in the width direction, and a light intensity pattern of reflected diffracted light generated by the irradiation of the reproducing beam is detected. The present invention is characterized in that the multivalued information is reproduced by demodulating the light intensity pattern obtained.

According to the present invention, multilevel information is recorded by applying modulation in the width direction of a recording pit or recording groove.

During reproduction, the multi-level information provided in the width direction of the recording pit or recording groove is reproduced by the light intensity pattern of reflected diffracted light generated by irradiating the recording pit or recording groove with a reproduction beam. .

〔Example〕

First, the recording and reproducing principle of the optical multilevel recording and reproducing method according to the present invention will be explained.

First, information recording is performed by making a light beam modulated by multi-value information having multi-level levels enter an optical recording medium, and recording the light beam at a constant depth and modulated in the width direction perpendicular to the track direction. Multilevel recording is performed by forming pits or recording grooves.

Reproduction of recorded information is performed using the bright and dark edge pattern of the light intensity distribution caused by the interference pattern of the 0th order light and ±1st order light of the reflected diffracted light generated when a light beam is irradiated onto a recording pit or recording groove. Replay value recording information.

An optical system as shown in FIG. 3 is conceivable as an optical system in which a light beam is incident on an optical disk in which multilevel recording grooves are formed and an interference pattern is generated by the reflected light. In this case, a laser beam emitted from a laser diode 1 is converted into parallel light by a collimator lens 2, and then made to enter a polarizing beam splitter 3. After the light transmitted through the polarizing beam splitter 3 is converted from circularly polarized light to linearly polarized light by a λ/4 plate 4, a laser beam spot is formed on the recording groove forming surface side of the optical disc 6 by an objective lens 5. Then, the reflected light from the recording groove enters the λ/4 plate 4 again, is rotated 90 degrees in a round trip, is reflected by the polarizing beam splitter 3, and is received by the optical photodetector placed on the optical path. A predetermined interference pattern is formed on the surface.

Here, as shown in FIG. 4, the recording groove W of the optical disc 1 is
It will be explained that by irradiating a light beam onto the recording groove W, an interference pattern corresponding to the width of the recording groove W is generated by the 0th-order light and the ±1st-order light of the reflected diffracted light.

As shown in FIG. 5, the incident light that enters the reflective grating 11 at a predetermined angle of incidence is reflected and diffracted by the upper surface 11m of the convex portion. At this time, the condition for the diffracted lights to strengthen each other is sinθ-5inθommλ/d-(1)m-0,±1 from the plug conditional expression.
．． ±2... Also, when the incident angle θ is 0, that is, the sixth
As shown in the figure, the incident light ν1 is applied to a reflection grating 1 with a period d.
1 at an incident angle of 0 and its reflected light ν2 is reflected at a reflection angle of θO, sinθommλ/d·(2). The following description will proceed assuming that the incident angle is O.

Next, the positions where each order of the mutually reinforcing reflected and diffracted light occurs will be explained using a reduced coordinate system based on the numerical aperture NA of the objective lens with reference to FIG.

Note that 12 shown in the figure represents the lens surface of the objective lens 5 in FIG. On this lens surface 12, a circular image is formed as zero-order diffracted light by using the collimator lens 2 as an exit pupil. This image is a circular image 13 shown in FIG. 8, the upper half of which is shown as radius hs in FIG.

Generally, the numerical aperture NA of a lens can be expressed as NA-nesinθ·(3). Note that n is 1. θ is θ shown in FIG. Furthermore, since the inclination angle θS of the spread of the 0th-order diffracted light is generally equal to θ, it can be expressed as NA−sinθ m5inθs−h s/f −(4). Next, if the position where the center of the circular image of the 1st-order diffracted light appears is point B shown in FIG. 7, then point B is a distance h from the center C of the circular image of the 0th-order diffracted light. Now, assuming that the NA of the objective lens 5 is 0.5, from equation (4),
hs-0.5f, therefore, h/hs-fsinθo10.5 f -<5)-s
in e olo, 5 (6)
becomes. This is sinθ0 when hs is 0.5.
This means that more distance is required. In addition, sin
θ0 can be determined from equation (2).

The image of the reflected diffraction light obtained in the above manner is shown in Figure 8(a).
Shown in (b) and (c). The figure (a) shows the period = 1.2 μm, the figure (b) shows the period -1.8 μm, and the figure (c
) are for periods of −2 and 5 μm, and the wavelength λ
An image calculated at -800 nm is shown. Point C in each figure is the center point B of the circular image 13 of the 0th order diffracted light.
is the center point 1 of the circular images 14a and 14b of the ±1st order diffracted light.
The dots indicate the center points of the circular images 15g and 15b of the ±2nd-order diffracted light. In this way, a brightness and darkness in the light intensity distribution caused by the interference pattern of the reflected and diffracted light that changes depending on the width of the recording groove W is formed on the light receiving surface of the optical photodetector.

FIGS. 9(a), 9(b), and 9(c) show the relationship between the groove width of the recording groove W and the light intensity distribution due to the reflected diffracted light. In addition, W1 to W3
are recording grooves with different groove widths, and W 1 < W 2
<W The width becomes thicker in the order of 3.

Further, 14a and 14b indicate edges of a circular image of ±1st-order diffracted light. As the groove width of the recording groove W changes, 0
It is shown that the light intensity pattern caused by the overlapping of the circular images of the first-order diffracted light and the ±1st-order diffracted light changes. In this way, the ±2nd-order diffracted light has almost no effect on the brightness and darkness caused by the interference of the actual image. As described above, as the width of the recording groove increases, the edges of the bright and dark boundaries of the light intensity distribution generated by the exit pupils of the ±1st-order diffracted light formed on the light receiving surface of the optical detector 7 overlap.

Furthermore, the reason why the 0th-order diffracted light and the ±1st-order diffracted light are circular is that the diameter of each diffracted light depends on the size of the exit pupil of the collimator lens 2.

In the present invention, the multi-value information of the multi-value recording groove is demodulated by detecting the change in the light intensity pattern.

Next, examples of the present invention will be described.

FIG. 1(a) shows that a light beam is incident on an optical disk 21 on which multivalued recording pits are formed in the width direction according to this embodiment, and a light intensity pattern due to the reflected diffracted light is detected by an optical detector 7. It is a figure which shows the state produced above.

In this embodiment, in order to record predetermined information on the recording master disc 20, multilevel information is generated according to the information to be recorded, and a laser beam modulated with this multilevel information is used to record the information. The recording pits 21 are incident on the master disk, and the recording pits 21 having a constant depth and multi-level pit width are sequentially formed in the track direction to record multi-level information. In this way, as shown in Figure 1 (
As in the pit row shown in b), the pit width g is changed for each recording pit 21, and multilevel recording is performed in the width direction perpendicular to the track direction.

When reading recorded information from the optical disc 20 on which such multilevel recording has been performed, the multilevel information is reproduced using, for example, an optical system shown in FIG. In this embodiment, a line sensor 22 is installed as the optical detector 7 shown in FIG. By irradiating a light beam onto the recording pit 21, which is multivalued in the pit width direction, O
The light intensity distribution is bright and dark due to the next-order light and the ±1st-order diffracted light. The line sensor 22 detects the bright and dark boundary line L.
The edge spacing of l and L2 is detected. As described above, this edge interval changes depending on the pit width p, so multi-valued information in the width direction of the recording pit is reproduced from the detected edge interval.

As described above, according to this embodiment, since multilevel information is recorded by applying modulation in the width direction of the recording pit, high-density recording is possible. In addition, a light intensity pattern of the reflected diffracted light that changes according to the multivalued pit width p is formed on the line sensor 22, and the edge spacing of the ±1st-order diffracted light is detected and held in the width direction of the recording pit. Since the multivalued information is reproduced, the influence of external disturbances can be significantly reduced compared to the conventional method of detecting the amount of reflected light, allowing for highly sensitive and highly accurate reproduction. Furthermore, the number of multilevel levels can be increased, and the recording density can be improved.

Furthermore, according to this embodiment, recording and reproduction can be performed without changing the basic configuration of a conventional optical disk system, so that it is possible to prevent the device from becoming larger.

Note that in the above embodiment, multi-value recording of three or more values is possible, but when the multi-value recording pit width p is made binary,
Two-split photodiode 23 instead of line sensor 22
can be used. If the width of the recording pit or recording groove is binarized as shown in FIGS. 9(b) and 9(c), the light intensity patterns of the reflected diffracted light will be as shown in FIGS. 2(a) and 2(b), respectively. It comes to show. Therefore, if the two-divided photodiode 23 is arranged as shown in FIGS.
Since the light intensity pattern is divided into brightness and darkness as shown in the figure, the pit width can be reproduced based on the difference in brightness and darkness. At this time, as shown in the figure, by providing a dead zone 24 in the center of the two-split photodiode 23,
Sensitivity can be improved.

〔Effect of the invention〕

As described in detail above, according to the present invention, an optical multi-value recording and reproducing method is provided which can perform multi-value recording and reproduction of information with a simple configuration and can reproduce recorded information with high accuracy with less influence from external disturbances. Can be provided.

[Brief explanation of the drawing]

FIG. 1(a) is a schematic diagram of an optical system for information reproduction according to the embodiment, FIG. 1(b) is a plan view showing a multivalued recording pit array, and FIG. 2 is a modification of the embodiment. Figure 3 is a diagram showing the configuration of the above optical system, Figure 4 is a diagram showing the state in which a light intensity distribution pattern is generated due to reflected diffraction light, and Figures 5 to 9 show the width of the recording groove and its reflected diffraction. FIG. 3 is a diagram for explaining the relationship with a light intensity pattern of light. 1...Laser diode, 2...Collimator lens, 3...Polarizing beam splitter-4...λ/4 plate,
5... Objective lens, 6... Optical disk, 7, 2o.
...Optical detector, 21... Recording pit, 22...
Line sensor, 23... 2-split photodiode, 2
4. Dead zone. Figure 1 (a) Figure (b) Figure 7 Figure 7 (a) Figure (b) 8rI! J(c) Diffracted light diagram Figure 4 Figure procedure amendment document Heisei 69/1

Claims (2)

[Claims] (1) The multi-value information is modulated in the width direction of a recording pit or recording groove by multi-value information that is multi-valued according to the information to be recorded, and the multi-value information is recorded, and the multi-value information is modulated in the width direction. A reproduction beam is irradiated onto the recorded pit or recording groove, a light intensity pattern of reflected diffracted light generated by the irradiation of the reproduction beam is detected, and the detected light intensity pattern is demodulated to generate the multi-valued signal. An optical multi-level recording and reproducing method characterized by reproducing digital information. (2) The optical multi-level recording/reproducing method according to claim 1, wherein the light intensity pattern is detected by a line sensor.