JPH0231330A - Optical memory device - Google Patents

Abstract

PURPOSE:To improve recording density and to increase recording capacity by providing an optical head and a signal detecting circuit to detect the information pulse of a regenerative signal, which is obtained from this optical head, as a code, to convert the regenerative signal to a digital regenerative signal and to output the signal. CONSTITUTION:The title device is provided with an optical information recording medium 1 to be formed so as to decrease incident light quantity to an optical head 2 by the diffraction of a light and to generate the information pulse in the regenerative signal outputted from the optical head 2 and the optical head 2 to project an optical beam on the optical information recording medium 1, to input a reflected light and to output the regenerative signal which includes the information pulse corresponding to the code. Further, a signal detecting circuit 3 is equipped to detect the information pulse of the regenerative signal, which is obtained from this optical head 2, as the code, to convert the regenerative signal to the digital regenerative signal and to output the signal. Accordingly, many bits of information can be included in one recording mark. Thus, the recording density can be improved in the optical information recording medium and the recording capacity can be increased.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention includes an optical information recording medium for recording information, projects a light beam onto the optical information recording medium, and reproduces information using the reflected light. The present invention relates to an optical memory device.

[Conventional technology]

This type of conventional optical memory device consists of an optical information recording medium on which information is recorded, an optical head for reading out the information recorded on the optical information recording medium, and a digital reproduction signal from the information read by the optical head. It is equipped with a signal detection circuit that obtains a signal. The optical head projects the laser beam onto the optical information recording medium, inputs the reflected light, and outputs a reproduction signal, and the signal detection circuit converts the reproduction signal into a digital reproduction signal. . The signal detection circuit has a peak position detection circuit that detects the peak position of the information pulse in the reproduced signal, or an amplitude detection circuit that detects the length and interval of the information pulse. A digital reproduction signal can be obtained from the signal.

That is, as shown in FIG. 6, recording marks shown in (b) are recorded as recording information on the optical information recording medium for digital data (a). Then, by reading this recording mark with an optical head, a reproduced signal (C) is obtained. Here, if the signal detection circuit has a peak position detection circuit, the signal detection circuit into which the above-mentioned reproduction signal (C) is input will output a digital reproduction signal (d ), while
When the signal detection circuit includes an amplitude detection circuit, the signal detection circuit obtains a digital reproduction signal (e) that becomes high level at a predetermined width with respect to a peak position in the negative direction. Digital data (f) as reproduction information is obtained from these digital reproduction signals.

[Problem to be solved by the invention]

However, the conventional configuration described above has a problem in that it is difficult to increase the recording density and recording capacity of the optical information recording medium.

That is, in the case of the above configuration, the size of the recording mark must be further reduced in order to increase the recording density of the optical information recording medium. However, the smaller the recording mark becomes, the more difficult it becomes to record it on the optical information recording medium. For example, when recording a recording mark by focusing a laser beam onto an optical information recording medium, the smaller the recording mark, the more appropriately the recording mark is formed depending on the degree of focus of the laser beam, the characteristics of the optical information recording medium, the ambient temperature, etc. This becomes difficult. This also applies when recording marks are formed by transfer, and is particularly difficult when recording marks are transferred by plastic molding. Therefore, it is difficult to increase the recording density by downsizing the recording marks, and the conventional configuration is not suitable for increasing the recording density. For convenience of explanation, the recording mark is explained as an isolated mark corresponding to one code, but the recording mark is made to correspond to multiple codes and is formed to have the same dimensions as the parts other than the recording mark. However, it is still insufficient in terms of increasing the recording density.

[Means to solve the problem]

In order to solve the above-mentioned problems, the optical memory device of the present invention records a recording mark as information, and the end of this recording mark in the direction of relative movement with the optical head is digital information consisting of two codes. The second symbol surrounded by the first symbol
When the light beam that corresponds to the code and is projected from the optical head hits the edge of the recording mark, the amount of light incident on the optical head decreases due to light diffraction, and the reproduced signal is output from the optical head. An optical information recording medium formed to generate an information pulse at The configuration includes an output optical head, and a signal detection circuit that detects the information pulse of the reproduced signal obtained from the optical head as a second code, converts the reproduced signal into a digital reproduced signal, and outputs the digital reproduced signal. .

[For production]

According to the above configuration, the recording mark of the optical information recording medium is
The end in the direction of relative movement with the optical head corresponds to the second code surrounded by the first code of digital information consisting of two codes, and the light beam projected from the optical head corresponds to the end of the recording mark. When the optical head is projected onto the optical head, the amount of light incident on the optical head is reduced due to the diffraction of the light, and an information pulse is generated in the reproduced signal output from the optical head. By forming recording marks in this manner, a large amount of information can be included in one recording mark, so that recording density can be increased. Specifically, for example, when a recording mark is formed in a convex shape toward the incident direction of the light beam, the recording mark is made to protrude slightly,
In addition, if the light beam is formed to be longer and wider than the diameter of the focused spot of the light beam, the above-mentioned information pulse is likely to occur. Furthermore, by forming the recording mark in this manner, it becomes easy to form the recording mark into an appropriate shape. Therefore, recording marks can be easily transferred even in plastic molding, for example.

On the other hand, the optical head projects a light beam onto the optical information recording medium, inputs the reflected light, and outputs a reproduced signal containing the information pulse corresponding to the second code. Then, the signal detection circuit detects the information pulse of the reproduced signal obtained from the optical head as a second code, and converts the reproduced signal into a digital reproduced signal. This allows information to be reproduced.

In order to increase the recording density using the above recording method, it is necessary to employ a modulation method in which a large number of second codes are not consecutive, such as 2-7 modulation or 1-7 modulation. If 1" is given the second code, for example, "11
This is because when "1"s are consecutive like "111", the ends of the recording marks are distorted and cannot correspond to a large number of "1s".

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

As shown in FIG. 1, the optical memory device according to the present invention includes an optical disk 1 as an optical information recording medium, an optical head 2, and a signal detection circuit 3.

The optical disc 1 described above is movable relative to the optical head 2. As shown in FIG. 2, the optical disc 1 includes:
Record mark A and record mark B as information shown in (i) are recorded on digital data (h) as digital information. The ends of these recording marks A-B in the relative movement direction with respect to the optical head 2, that is, the edge portions, are surrounded by 0, which is the first code of digital data (h) consisting of two codes, O and 1. 1 which is the second code given
It corresponds to That is, the edge portion of the recording mark corresponds to 1 surrounded by 0 and 0, and the edge portion of recording mark B corresponds to 11 surrounded by 0 and 0. Record mark A
The edge portion of the recording mark B and the edge portion of the recording mark B are formed into curved shapes with different curvatures, and the edge portion of the recording mark B has two 1
The curved portion is longer than the curved portion of recording mark A so as to correspond to this. On the other hand, a portion between the edge portions of recording marks A and B and a non-mark portion that is a portion other than recording marks A and B correspond to 0.

The recording mark A-B is formed by diffraction of the light when the laser beam as a light beam projected from the optical head 1 is irradiated onto the edge portion of the recording mark A-B. is formed so that information pulses are generated in the reproduced signal outputted from the optical head 2 by decreasing the amount of information.

For example, if the recording mark A-B is a so-called bit that protrudes in the direction of incidence of the laser beam from the optical head 2, the recording mark A -B diffraction of light occurs at the edge portion and the non-mark portion, the amount of light incident on the optical head 2 decreases, and a negative direction information pulse is generated in the output of the optical head 2.

The optical head 2 projects a laser beam onto the optical disc 1, receives the reflected light, and outputs a reproduction signal containing the above information pulse. The optical head 2 has a photodetector (not shown) that converts incident light into an electrical signal, and outputs a reproduction signal of a level corresponding to the amount of the reflected light. The diameter of the focused spot 4 of the laser beam projected by the optical head 2 may be approximately the same as the width of the recording mark A-B in order to reliably obtain information pulses, but it is preferable to set it smaller than that. preferable.

Here, FIGS. 3 to 5 show an example of the results of computer simulation regarding the reproduced signal.

FIG. 3 is an explanatory diagram showing the relationship between, for example, the recording mark C and the condensed spot 4 in a computer simulation of the reproduced signal of FIGS. 4 and 5. FIG. In the figure, a recording mark C has a length of 4 μm, a width of W, a curved edge portion of a semicircle with a radius of W/2, and a depth or height of D in the direction perpendicular to the plane of the paper. The focused spot 4 is a Gaussian beam whose radius (1/e of beam center intensity
"The radius of the doubling circle" is 0.65 μm.

The traveling direction of the focused spot 4 is the long sleeve direction of the recording mark C, and the distance between the center of the recorded mark C and the center of the focused spot 4 is shown in the upper part of the figure. The refractive index of the substrate of the optical disc 1 on which the recording marks C are formed is 1°5, the pitch between adjacent tracks in the vertical direction of the paper is 1.6 μm, the aperture ratio of the objective lens is 0.55, and the light condensing The wavelength of the laser beam forming the spot 4 is 0°78 μm.

FIG. 4 shows that the depth or height D of the recording mark C is D-0,
The simulation results are shown when the thickness is 13 μm. In the graph of the figure, the horizontal axis is the scanning direction of the condensed spot 4, and indicates the distance between the center of the recording mark C and the center of the condensed spot 4. The vertical axis indicates the intensity of the reproduction light incident on the photodetector. However, it is normalized by the amount of light when no light interference occurs. A corresponding reproduced signal is obtained at the photodetector. Then, the width W of the recording mark C (dimension twice the radius of the curved part of the edge part) is set to 0°4 μm.
, 0.6 um, 0.8 am, 1.0 μm,
1.4 um and 1.8 μm, and reproduced waveforms were simulated for these seven types. As a result, W=1.
At 4 μm and 1.8 μm, pulses were noticeable at the edge portion of recording mark C.

In addition, FIG. 5 shows that the depth or height D of the recording mark C is
The simulation results are shown when D=0.065 μm. Comparing this figure with the above-mentioned FIG. 4, the overall trend is the same as that of FIG. 4, although the signal amplitude is smaller overall.

According to the above simulation results, the information pulse can be increased when the depth or height D of the recording mark C is approximately 0.13 μm. This is the equation for maximizing the effect of diffraction: nXdX2=λ/2 where n: refractive index of the substrate d: depth or height of recording mark C λ: value obtained by the wavelength of the laser beam. , when the depth or height D of the recording mark C is 0.13 μm, the information pulse at the edge portion of the recording mark C is maximum.

In addition, the width W of the recording mark C (dimension twice the radius of the curved part of the edge part) is W = 1.8 μm and 1.4 μm.
When μm, the information pulse is noticeable, W-1,0 μm
It can be seen that even at 0.8 μm, the pulse at the edge still remains, and the level at the center of the recording mark C gradually decreases.

Furthermore, although this simulation was conducted under the conditions described above, if other conditions such as the refractive index of the glass substrate, the wavelength λ of the laser beam, or the aperture ratio of the objective lens were changed, Naturally, the optimum width, depth, or height of the recording mark C also changes accordingly.

The signal detection circuit 3 detects the information pulse of the reproduced signal inputted from the optical head 2 as a second code of 1, and converts the reproduced signal into a digital reproduced signal. That is, the signal detection circuit 3 has a peak position detection circuit that detects the peak position of the information pulse in the reproduced signal or an amplitude detection circuit that detects the length and interval of the information pulse. A digital reproduction signal can be obtained from the above reproduction signal.

In the above configuration, when the laser beam projected from the optical radar 2 enters a non-marked portion of the optical disc 1, this light is reflected almost unchanged and enters the optical radar 2. As a result, as shown in FIG. 2, the reproduction signal (j) output from the optical head 2 becomes high level.

Furthermore, when the laser beam projected from the optical head 2 is irradiated onto the machining area of the recording mark A on the optical disc 1, the reflected light from the recording mark A and the non-mark area interferes with each other.
Diffraction of light occurs. Therefore, the amount of reflected light incident on the optical head 2 decreases, and a negative direction information pulse is generated in the reproduced signal (j). This is because the diffraction effect at the edge portion is greater than at other portions.

Further, when the laser beam from the optical head 2 is irradiated between the edge portions of the recording mark, there is little diffraction of the reflected light, and the level of the reproduced signal (j) is only slightly lowered.

Next, the above reproduced signal (j) is input to the signal detection circuit 3, but if the signal detection circuit 3 is equipped with a peak position detection circuit, the negative direction peak position of the information pulse of the reproduced signal (j) A digital reproduction signal (k) having a rising edge that coincides with that of the original signal is obtained. On the other hand, when the signal detection circuit 3 includes an amplitude detection circuit, a digital reproduction signal (2) that becomes high level at a predetermined width with respect to the peak position in the negative direction of the information pulse is obtained. Since the pulse of this digital reproduction signal (k) or (2) corresponds to 1 of digital data (h), digital data (m) as reproduction information is obtained from this signal.

On the other hand, when the laser beam projected from the optical head 2 is irradiated onto the edge portion of the recording mark B on the optical disc 1,
Since the curved portion of the edge portion of the recording mark B is formed longer than the curved portion of the recording mark A, the pulse width of the information pulse generated in the reproduced signal (j) becomes wider. Therefore, when this reproduced signal (j) is input to the signal detection circuit 3 equipped with an amplitude detection circuit, the digital reproduction signal (f) obtained from the signal detection circuit 3 will be It becomes a noise level with respect to the peak position in the negative direction, and has a pulse having a width corresponding to the width of the information pulse of the reproduced signal (j).

That is, since the pulse of the digital reproduction signal C11) has a width corresponding to 11 of the digital data (h),
Digital data (m) as reproduction information is obtained from this digital reproduction signal (f).

In addition, by keeping the curvature of the edge part of the recording mark the same,
Even if the scanning speed of the optical spot of the laser beam is changed, it is possible to change the pulse length of the reproduced signal (j) as in the above example. For example, when recording pre-pits on the optical disc 1 in advance, CLV (constant l
1 near velocity) and playback using CAV (constant angular v
By doing so, the pulse length of the reproduction signal (j) at the edge portion of the recording mark can be changed between the inner and outer circumferences of the optical disc 1. That is, C.L.
When recording is performed at V, the curvature of the edge portion of the recording mark becomes the same on the inner circumferential side and the outer circumferential side of the optical disc 1. On the other hand, when this is reproduced by CAV, since the running speed is faster on the outer circumference side, the recording mark on the outer circumference side is read as having a smaller curvature.

Therefore, the width of the reproduced signal detected at the edge portion becomes longer on the inner circumferential side. Therefore, if this length is taken as one piece of information, it can be recognized as track position information (ID information). In other words, the above method captures the curvature of the edge portion of a recording mark in an analog manner.

〔Effect of the invention〕

As described above, in the optical memory device according to the present invention, a recording mark as information is recorded, and the end of this recording mark in the direction of relative movement with the optical head is the first code of digital information consisting of two codes. Corresponding to the second symbol surrounded by an optical information recording medium formed to generate an information pulse in a reproduced signal output from the optical information recording medium; and a light beam projected onto the optical information recording medium;
An optical head inputs the reflected light and outputs a reproduced signal including an information pulse corresponding to the second code, and detects the information pulse of the reproduced signal obtained from this optical head as a second code, and The configuration includes a signal detection circuit that converts a signal into a digital reproduction signal and outputs the signal.

Therefore, since a large amount of information can be included in one recording mark, it is possible to increase the recording density of the optical information recording medium, and it is possible to increase the recording capacity. Furthermore, since the recording density is not increased simply by reducing the size of the recording mark, it is possible to form the recording mark in a large size. Therefore, it is easy to form the recording mark in an appropriate shape, and the recording mark can be easily transferred even in plastic molding, for example.

[Brief explanation of the drawing]

1 to 5 show an embodiment of the present invention, in which FIG. 1 is a block diagram showing the main parts of an optical memory device, and FIG. 2 shows recording marks and signal waveforms in various parts of the optical memory device. 3 is an explanatory diagram showing the relationship between the recording mark and the focused spot in the computer simulation for the reproduced signal shown in FIGS. 4 and 5. FIG. 4 is an explanatory diagram showing the relationship between the recorded mark and the focused spot length or height 0.13
A graph showing the results of a computer simulation when the depth or height of the recording mark is set to 0.065 μm. Fig. 6 shows a conventional example. FIG. 3 is an explanatory diagram showing the relationship between recording marks and signal waveforms at various parts of the optical memory device. 1 is an optical disk (optical information recording medium), 2 is an optical head,
3 is a signal detection circuit, and 4 is a condensing spot. Digital data (a) 0010010010
0100100N) 0 Miya Miyoshi mark (b) OOO
OO0jff jm fM fM f-70? 4 Digital Re, No. 143 (@) ---j L
-Ko-j E-ji E--j E-++l
E-+++ Digital data m 00100100
100100[)O? OO＜@Ashi Tsukazu

Claims (1)

[Claims] 1. A recording mark as information is recorded, and the end of this recording mark in the direction of relative movement with the optical head is a first symbol surrounded by a first symbol of digital information consisting of two symbols. 2 code, and when the light beam projected from the optical head hits the edge of the recording mark, the amount of light incident on the optical head decreases due to light diffraction and is output from the optical head. An optical information recording medium formed to generate information pulses in a signal; and a reproduced signal containing information pulses corresponding to the above-mentioned second code by projecting a light beam onto the optical information recording medium and inputting the reflected light. and a signal detection circuit that detects the information pulse of the reproduced signal obtained from the optical head as a second code and converts the reproduced signal into a digital reproduced signal. Optical memory device.