JPH04209320A - Information reproducing device - Google Patents

Abstract

PURPOSE:To separate a regenerated signal from noise and to reproduce practical multilevel recording information by setting the modulation degree of the regenerating signal whose level is the lowest to be >=5%. CONSTITUTION:The output of a recording signal processor 10 corresponds with multilevel information recorded on a recording medium 20. Then, the signal valve of reproduced waveform fetched through a regenerated signal processor 40 at the rise or fall timing of a demodulation clock. Thus, the regenerating signal (multilevel information bit) is obtained almost without time lag from a recording pulse. When the information bit is reproduced from the reproduced signal waveform, the size of the regenerated signal from a non-recording part is set to be (a) and the size of the regenerated signal of the recording mark of the information whose level is the lowest is set to be (b). Besides, the modulation degree (c) is set to be the absolute valve of (a-b)/(a). The signal is detected so as to make the modulation degree (c)>5% and the multilevel information is reproduced. By such constitution, the signal whose level is the lowest is sufficiently seperated from a noise level and the multilevel recording information is faithfully rerpoduced.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to information reproduction in which multi-value information is reproduced by irradiating a light beam onto an information recording medium on which multi-value information is recorded. Regarding equipment.

(Prior Art) Currently, with the development of information and communication technology, there is a strong demand for larger capacity, higher processing speed, smaller size, lower cost, etc. of auxiliary storage devices for storing information. Optical disk devices meet these demands and have become popular as auxiliary storage devices for computers.

In an optical disc device, information to be recorded is converted into binary information consisting of "0" and "1", and the binary information is recorded on the recording layer of the optical disc in accordance with this information. When using a phase change type optical disc, for example, an amorphous recording region formed by irradiation with a light beam corresponds to a "1", and a crystalline non-recording region corresponds to a "0". It records binary information. However, the optical discs currently in use can only write binary information corresponding to the presence or absence of recording in one recording area (hereinafter referred to as a recording mark), so the recording spot determined by the diffraction limit of light cannot be written. There is a certain limit to the recording density depending on the size. For the future, recording devices capable of higher density and higher speed processing are desired.

In response to such demands, an information recording apparatus that can practically achieve high-density recording has been disclosed in Japanese Patent Laid-Open No. 2-14427. The recording device disclosed here is
a signal processing means for converting an input information signal into a signal of three or more stages; a light beam output means for outputting a light beam whose energy is modulated in multiple stages according to the processed signal of three or more stages; and an optical system that condenses and irradiates the information recording medium with a beam, and records multi-stage information in different states on the beam irradiated portion of the information recording medium. moreover,
This publication describes an information recording medium 1 in which a recording portion having multiple levels of information recording levels is formed! - a destination beam output means for outputting a light beam; an optical system for focusing the light beam on the information recording medium; An information reproducing apparatus is disclosed that includes a reproduction signal processing means for creating a reproduction signal and reproduces multi-stage information recorded as described above. By using these devices, it is possible to record and reproduce multivalued information on one recording mark.
It is expected that future optical disk devices will be able to handle higher density and faster processing.

(Problem to be Solved by the Invention) However, in such a multilevel recording method, the state of the recorded mark is different for each recording level, so the magnitude of the multilevel reproduction signal at the recorded mark when reproducing recorded information is This becomes a problem. Therefore, in order to reproduce multilevel recorded information, different reproduction signal processing is required from that in conventional binary recording.

This invention was made in view of such circumstances, and
It is an object of the present invention to provide a reproducing device that can practically reproduce multi-level recorded information.

[Configuration of the Invention (Means for Solving the Problems) An information reproducing apparatus according to the present invention is an information reproducing apparatus that reproduces information recorded on an information recording medium by multilevel recording, and has multiple recording levels. a light beam output means for outputting a light beam to an information recording medium having a recording portion on which information is recorded; an optical system for focusing the light beam outputted by the light beam output means on the information recording medium; and a reproduction signal processing means for generating a predetermined reproduction signal by detecting the multi-level optical characteristics of the recording area obtained by irradiation with the beam, and adjusting the magnitude of the reproduction signal from the non-recorded area by Let the magnitude of the reproduced signal of the lowest level among the recorded parts be , and the modulation degree C of this lowest level reproduced signal be (
When expressed as the absolute value of a-b)/a, this modulation degree C
The reproduced signal processing means detects the signal and reproduces the information such that the ratio is 5% or more.

(Function) In the reproduction of multilevel recorded information, the reproduction signal is changed in multiple stages, so detecting the lowest level signal becomes a problem.If this signal is small, it becomes difficult to separate it from the noise level. By setting the degree of modulation of the reproduced signal to 5% or more, this signal can be separated from the noise level, and practical reproduction of multilevel recorded information can be realized.

(Example) An embodiment of the present invention will be described below.

FIG. 1 is a schematic configuration diagram showing an information recording/reproducing apparatus incorporating an information reproducing apparatus according to the present invention.

The recording signal processing device 10 converts an information signal inputted to a control circuit (not shown) into a multi-value signal, and outputs this multi-value processed signal to the semiconductor device 11. The semiconductor laser 11 irradiates a recording laser beam with energy or wavelength corresponding to the signal level of the processed signal output from the recording signal processing device 10. Here, in order to change the energy of the beam in multiple stages according to the signal level, it is necessary to change the intensity or pulse width of the light beam, or both, or to change the wavelength of the light beam. Bye. By irradiating the recording layer of the information recording medium (optical disk) 20 with a laser beam with energy or wavelength corresponding to the signal level through the optical system 30, the energy or wavelength of the laser beam is applied to the irradiated portion of the beam. A corresponding state change occurs, a recording mark is formed, and multi-value information is recorded.

In addition, when reproducing multivalued information recorded in this way, the information recording medium 2 is
A reproducing laser beam with a constant wavelength and low energy so that no state change occurs in the irradiated portion of 0 is output. The reproduction laser beam output from the semiconductor laser 11 is irradiated onto the information recording medium 20 via the optical system 30 , and its reflected light is guided to the photoelectric conversion element 12 via the optical system 30 . Photoelectric conversion element] 2 converts the received laser beam into an electrical signal. The information signal converted into an electrical signal is guided to a reproduction signal processing device 40 via a processing circuit 4, and a reproduction signal corresponding to the multi-level information is outputted from the reproduction signal processing device 40 to a control circuit.

Note that when the information recording medium 20 is a rewritable type such as a phase change type, for example, the information recording medium 20 is irradiated with an erasing laser beam of lower intensity than during recording.
Information can be erased by changing the phase of this portion to the state before recording. Moreover, this information recording medium 20
If it is of a type that allows overriding, overriding can be performed by irradiating the erasing level laser beam with a recording laser pulse modulated according to the multilevel information or a superimposed laser beam.

- In the optical system 30, the diverging laser beam output from the semiconductor laser 11 is converted into a parallel beam by the collimator lens 3 and guided to the beam splitter 32. The beam reflected by the beam splitter 32 is condensed and irradiated onto the information recording medium 20 by a condensing lens 36 . During reproduction, a portion of the laser beam irradiated onto the information recording medium 20 is further reflected, and the reflected light travels straight through the beam splitter 32 and is guided to the half mirror 33. Here, the beam that has passed straight through the half mirror 33 is guided to the photoelectric conversion element 13 via the lens 35.

On the other hand, the light reflected by the half mirror 33 is guided to the photoelectric conversion element 12 via the lens 34.

The signal output from the photoelectric conversion element 12 is outputted to the reproduction signal processing device 40 via the processing circuit 14 as described above, and is also guided to the tracking control device 19 via the amplifier circuit 6, where the beam is This is used as correction data to optimize the irradiation position. In addition, photoelectric conversion element 1
The signal output from 3 is guided to the focusing control device 18 via the processing circuit 15 and the amplifier circuit 17.
Used as data for focus control.

Next, the recording signal processing device]0 will be specifically explained.

In this embodiment, it is assumed that four-value recording is performed on the information recording medium 20. FIG. 2 is a block diagram showing a schematic configuration of the recording signal processing device. As shown in FIG. 2, the recording signal processing device 10 includes a quaternization circuit 10]
, a modulation circuit 102 , and a semiconductor laser drive circuit 10
3. Input data (information signal) is input in a binarized state, that is, as a binary signal, and this signal is first converted into information in units of 4 bits, that is, 4-valued data, in a 4-value conversion circuit 10. Ru. This quaternary data is converted into a signal of one of four signal levels of "0", "1", r2J, and r3J by the modulation circuit 102, and is applied as a voltage to the semiconductor laser drive circuit 103. As a result, the intensity of the light beam and the like are modulated in four stages according to the recording signal.

Next, the reproduced signal processing device 40 will be specifically explained.

FIG. 3 is a block diagram showing a schematic configuration of the reproduced signal processing device 40. As shown in FIG. As described above, the reproduction signal processing device 40 receives the electrical signal from the processing circuit 14 and outputs a reproduction signal corresponding to the information recorded on the information recording medium 20.

As shown in FIG. 3, this reproduction signal processing device 40 also includes a low-pass filter (LPF) 401 that removes high frequency components of the electrical signal input from the processing circuit 14, and a low-pass filter (LPF) 401 that removes high frequency components of the electrical signal input from the processing circuit 14, and It includes a clock generation circuit 402 that generates a demodulated clock corresponding to the recording pulse, and a reproduced signal generation circuit 403 that detects the signal level of the electrical signal in synchronization with the demodulated clock obtained by the clock generation circuit 402. .

An example of signal processing in the reproduced signal processing device 40 will be described below with reference to FIGS. 4(a) to 4(f).

FIG. 4(a) is a diagram conceptually showing a state in which four-value recording has been performed on the recording portion of the information recording medium 20. In the figure, the shaded areas are recording marks. Moreover, FIG. 4(b) is a diagram showing the output pulses (recording pulses) of the recording signal processing device 10 when forming recording marks as shown in FIG. This corresponds to multivalued information recorded in 20. Note that, as described above, when using a heat mode optical disk, the larger the signal level of the recording pulse, the larger the area of the recording mark. Therefore, if the recording power is high, the recorded mark will be large, and conversely, if the recording power is low, the recorded mark will be small.

FIG. 4(C) shows an example of a demodulated clock generated by the clock circuit 402 in correspondence with the recording pulse shown in FIG. 4(b). Further, FIG. 4(d) shows that the signal photoelectrically converted by the photoelectric conversion element 12 is taken into the reproduced signal processing device 40 via the processing circuit 14 during reproduction of multivalued information, and
It shows a signal waveform (reproduced waveform) when high frequency components are removed by the LPF 401. At this time, the reproduced signal waveform' has multiple levels corresponding to the area size of the corresponding recording mark (that is, according to the recording power of multiple levels). When the demodulated clock shown in (C) and the reproduced waveform shown in (d) are manually input to the reproduced signal generation circuit 403, and the signal value of the reproduced waveform is taken in at the rising or falling timing of the demodulated clock, A reproduced signal (multilevel information bit) as shown in FIG. 4(e) can be obtained.

It can be seen that the reproduced signal thus obtained has almost no time lag from the recording pulse shown in (b), and the recorded information is faithfully reproduced.

When reproducing information bits from the above-mentioned reproduced signal waveform corresponding to multilevel recorded information, in the present invention, the magnitude of the reproduced signal from the non-recorded part is a, and the reproduction of the recording mark where the lowest level information is recorded is Let the signal be b, and the modulation degree C in this case is
When is the absolute value of (a-b)/a, this modulation degree C
Signal detection is performed so that the difference is 5% or more, and multi-level information is reproduced.

In this case, the modulation degree C is set to the absolute value of (a-b)/a because the magnitude of the reproduced signal of the recorded mark may be larger or smaller than the magnitude of the reproduced signal of the unrecorded area. This is taken into consideration.

In multilevel recording, information is recorded so that the recording mark can have multiple signal levels. Therefore, in the multilevel recorded recording mark, the degree of modulation of the reproduced signal differs depending on the multilevel level. In multilevel recording, the magnitude of the reproduced signal is changed in multiple stages, so it becomes a problem to detect the lowest level signal. That is, when the signal level is small, it becomes difficult to separate noise and signal level. Therefore, in the present invention, the modulation degree of the lowest level reproduction signal in the recording mark is set to 5% or more. That is, when reproducing a multi-level recording track, multi-level information is reproduced using a reproduction signal whose lowest level modulation degree is 5% or more. In this way, the reason why the modulation degree of the lowest level signal is set to 5% or more is that a signal with a modulation degree smaller than 5% may not be separated from the noise level and will be considered as a non-recorded part. . On the other hand, if the modulation degree is 5% or more, the lowest level signal can be sufficiently separated from the noise level, and multilevel recorded information can be faithfully reproduced.

Next, the information recording medium 20 will be explained in detail. Note that a phase change type optical disc will be explained here as an example. FIG. 5 is a sectional view showing the layer structure of this optical disc. As shown in FIG. 5, the disc is composed of an optical disc substrate 1, a protective layer 2, a recording layer 3, a protective layer 4, a reflective layer 5, and a protective layer 6. Note that it is also possible to omit all or part of the protective layers 2, 4.6 and the reflective layer 5 depending on the application.

The optical disk substrate 1 is made of a transparent material that does not change much over time, such as acrylic resin such as polymethyl methacrylate, polycarbonate resin, epoxy resin, styrene resin, or glass. Further, continuous grooves, sample servo marks, preformat marks, etc. are formed on this optical disk substrate 1 according to the recording format.

The recording layer 3 is made of a material whose state changes when irradiated with a light beam. Examples of such materials include GeTe-based, TeSe-based, Ge5bSe-based,
Chalcogenide-based amorphous semiconductor materials such as TeOx-based, InSe-based, Ge5bTe-based, InSb-based, Ge
Compound semiconductor materials such as Sb-based and In5bTe-based materials are available.

This recording layer 3 can be formed by a vacuum deposition method, a sputtering method, or the like. Further, the thickness of the recording layer 3 is preferably in the range of several nanometers to several micrometers for practical purposes.

The protective layer 2 and the protective layer 4 are provided to protect the recording layer 3, and are formed so as to sandwich the above-mentioned recording layer 3 between them. With these protective layers 2 and 4,
For example, it is possible to prevent inconveniences such as scattering or holes in the recording layer 3 due to laser beam irradiation.

The material for forming the first protective layer 2 and the second protective layer 4 is, for example, SiO2, 5lo1ApN, Al1
203, Z r02, TiO2, T a 203
, Z n S % S z s, Ge, or the like is suitable, and can be formed by, for example, a vacuum evaporation method, a sputtering method, or the like. In addition, the film thickness of the protective layer 2.4 is practically
Preferably, it is several nm to several μm.

The reflective layer 5 has the function of enhancing changes in the characteristics of reflected light due to changes in the optical characteristics of the recording layer 3 and cooling the recording layer 3 by rapidly diffusing heat from the recording layer 3 . This cooling effect can facilitate override. The material for forming the reflective layer 5 is, for example, Au.

AI%Cu, Ni-Cr alloy, or the like is suitable, and can be formed by, for example, a vacuum evaporation method, a sputtering method, or the like. In addition, the film thickness of the reflective layer 5 is several nanometers in practice.
- It is preferably several μm.

The protective layer 6 is provided to prevent scratches, dents, etc. during handling of the optical disc.

Further, as a forming material, an ultraviolet curable resin or the like is usually used. For example, the ultraviolet curable resin is applied to the surface of the reflective layer 5 by a spin code method and then cured by irradiation with ultraviolet rays.

The thickness of this protective layer 6 is practically suitable in the range of several μm to several hundred μm.

When recording multivalued information on such an optical disc, it is effective to control the cooling rate of the recording layer 3 during recording to adjust the shape of the recording mark.

This cooling rate is controlled by the protective layer 2, the recording layer 3, and the protective layer 4.
This can be achieved by appropriately selecting the constituent material and film thickness of the reflective layer 5. For example, in order to increase the cooling rate of the recording layer 3, it is necessary to reduce the thickness of the recording layer 3, increase the thickness of the reflective layer 5, and use a material with high thermal conductivity as the forming material. It is effective to use a material with high thermal conductivity as the material for the protective layer 2.4.

Furthermore, when recording multilevel information on an optical disk, it is also effective to devise a profile of the output pulse of the semiconductor laser 11 during recording.

In addition to the single-sided recording optical discs mentioned above,
It is also possible to configure the optical disc so that double-sided recording is possible. A double-sided recording optical disc can be obtained, for example, by laminating two optical discs described above with the substrate 1 facing outside.

As described above, although the present embodiment has been described with reference to the case of reproducing multilevel information recorded on a phase change type optical disc, the information reproducing apparatus of the present invention is not limited to such a case.
A similar effect can be obtained when reproducing multivalued information recorded on an optical disc made of an organic material, a shape-changing material, a perforated material, or a composite material thereof.

[Effects of the Invention] According to the present invention, it is possible to provide an information reproducing device that can practically reproduce multivalued information.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an information recording/reproducing apparatus incorporating an information reproducing apparatus according to the present invention, and FIG.
FIG. 3 is a block diagram showing a schematic configuration of a recorded signal processing device of the information recording/reproducing device. FIG. 4 explains signal processing of the reproduced signal processing device. FIG. 5 is a sectional view showing an example of an information recording medium used in the present invention. 10; recording signal processing device, 11-semiconductor laser, 20;
Information recording medium, 30; optical system, 40: reproduction signal processing device, 401. Low pass filter (LPF), 402;
Clock generation circuit, 403° reproduction signal generation circuit. Applicant's representative Patent attorney Takehiko Suzue Figure 1 ¥ 2 Processing circuit Poor clock reproduction signal (multiple information and nodes) Figure 3 Figure 4, 20 / Figure 5

Claims (1)

[Claims] (1) An information reproducing device that reproduces information recorded on an information recording medium by multilevel recording, which outputs a light beam to the information recording medium that has a recording part in which information with multiple recording levels is recorded. a beam output means, an optical system that focuses the light beam outputted by the light beam output means on the information recording medium, and a predetermined optical system that detects multi-level optical characteristics of the recording area obtained by irradiation with the light beam. a reproduction signal processing means for producing a reproduction signal of When the degree of modulation c of the level reproduction signal is expressed as the absolute value of (a-b)/a, the reproduction signal processing means performs signal detection and outputs information so that the degree of modulation c becomes 5% or more. An information reproducing device characterized by reproducing information.