JPH07320291A - Optical disk device - Google Patents

Abstract

PURPOSE:To obtain an optical disk device in which an optimum value of reproduced laser light intensity is easily set. CONSTITUTION:The optical disk device 31 has a jitter detecting circuit 38 which detects jitter in a binarization reproduced signal c. Jitter is detected in the signal c by the circuit 38 while varying the light intensity of a laser beam using a laser ALPC circuit 41 and the light intensity, at which the jitter in the signal c becomes minimum, is used as the light intensity during the reproducing of optical disks 1 and 11. Moreover, the circuit 38 detects jitter employing the signal c and a clock signal d generated from the signal c.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for reproducing (or recording / reproducing) an optical disk for recording information at a high density, and in particular, it depends on the light intensity of laser light (or the temperature according to the light intensity). By using a layer containing a substance whose light transmittance changes, the effective spot diameter of the spot light irradiated (the actual spot diameter irradiated on the information recording part)
The present invention relates to an optical disk device for reproducing (or recording / reproducing) an optical disk that reduces the noise.

[0002]

2. Description of the Related Art In recent years, there has been an optical disk for optically recording and reproducing information, and a large storage capacity of this optical disk is under study. Since the formation of the recording mark of this optical disc depends on the temperature above a certain threshold value, it is possible to form the recording mark smaller than the light spot diameter by controlling the laser light power at the time of recording. . However, the diameter of the light spot when the laser light is narrowed down by a lens has a limit value that cannot be narrowed down to a certain value or less, and the densification of an optical disk depends on how to reduce the reproduction laser light spot. Here, the repetition wavelength (recording wavelength) of the recording mark at the reproduction limit is λ
/ (2NA) (λ is the wavelength of light, NA is the numerical aperture of the lens)
In order to identify and reproduce a recording mark having a shorter recording wavelength, it is understood that reproduction with light having a short wavelength λ or a lens having a large numerical aperture NA may be used. However, it is technically difficult to shorten the wavelength of the semiconductor laser used for reproduction, and it is not easy to incorporate a lens having a large numerical aperture NA into the optical disk device because the aberration increases with respect to the warp of the optical disk.

Therefore, as shown in FIG. 10, when the temperature rises due to the temperature rise due to light irradiation, the absorbance decreases.
By increasing the light transmittance, and increasing the absorbance again as the laser light passes and is cooled, the light transmittance is lowered and the light transmittance variable substance is provided in a layered form in the optical disc, so that information can be recorded at high density. Conventionally, a method of recording information or reproducing information recorded at high density is known. The light intensity distribution of the laser light used for information recording / reproduction usually shows a Gaussian distribution, and the temperature distribution is also a distribution close to this. When this laser light is irradiated onto the variable light transmittance material, as shown in FIG. 11 (A), the central portion A where the temperature in the irradiation spot has risen.
Only the light becomes transparent, and a so-called masking effect occurs in which the other portion B in the light spot is masked. At this time, the effective spot diameter of the laser light transmitted through the central portion A is shown in FIG.
As shown in FIG. 2, the diameter becomes smaller than the irradiation spot diameter of the irradiation laser light. By providing the light transmittance variable substance that causes the mask effect in a layered manner on the optical disc (hereinafter, this light transmittance variable substance layer is referred to as a mask layer), the light transmittance of the laser light in the spot to be irradiated can be improved. Since the light of only the high portion is transmitted and the light of the portion having low light transmittance in the irradiation spot is masked, crosstalk between adjacent tracks and intersymbol interference can be eliminated.

By the way, since the light transmittance of the mask layer changes depending on the laser light intensity (or the temperature corresponding to the light intensity), the reproduction signal error occurrence rate is set with the light intensity of the irradiated laser light as an optimum value. Need to lower. In view of this, Japanese Patent Application Laid-Open No. 5-12673 discloses a reproducing method for a high-density optical disc using a temperature-dependent mask layer, in which a laser beam is reproduced when an optical disc having optically readable recording marks is recorded. A method of setting the laser light intensity that optimizes the effective spot diameter has been proposed. The first method disclosed in the above publication is a method of optimizing the effective spot diameter of the laser light by using a guide groove crossing signal for tracking. That is, after the focus control of the objective lens of the optical head is performed and before the tracking control is performed, the reproduction laser light intensity is changed so that the groove crossing signal amplitude in the tracking error signal becomes maximum, and the groove crossing signal amplitude becomes maximum. The reproduction laser light intensity is fixed at the time when is reached, and it is set to the optimum light intensity of the reproduction laser light. This method is effective for setting the recording laser light intensity for an optical disc on which no information is recorded.

The second method is a method of optimizing the effective spot diameter of the laser light by using a reproduction signal of recorded information. That is, during reproduction, after the focus control of the objective lens of the optical head is performed and before the tracking control is performed, the reproduction laser light intensity is set so that the signal amplitude of the reproduction signal by the reflected light modulated by the recording information signal is maximized. Variable,
When the signal amplitude of the reproduction signal becomes maximum, the reproduction laser light intensity is fixed. The recorded information is analog FM
If it is a (Frequency Modulation) modulation signal, the carrier component of the FM signal is extracted by a bandpass filter, and the laser power that maximizes the amplitude of this carrier component is searched for.
According to the reproduction laser light intensity, the effective spot diameter can be optimized.

Further, in Japanese Patent Application No. 4-359176 (filed on Dec. 25, 1992), a light intensity setting track for setting the laser light intensity is provided in the optical disc,
It has been proposed to set the laser light intensity so that the reproduction signal amplitude of the recording mark on this track is maximized. Since the reproduction signal amplitude most varies depending on the change of the laser light intensity is the shortest information, that is, the recording mark of the shortest recording wavelength (hereinafter referred to as the shortest recording mark),
A large number of shortest recording marks are continuously formed on the light intensity setting track at substantially the same pitch. By setting the laser light intensity so that the reproduction signal amplitude of the shortest recording mark becomes maximum, the laser spot diameter can be optimized.

[0007]

[Problems to be Solved by the Invention]
As shown in (B), when the track pitch and the effective spot diameter do not cause intersymbol interference, the groove crossing signal amplitude in the tracking error signal becomes maximum, and stable tracking can be performed. However, as shown in FIG. 13, depending on the characteristics of the variable light transmittance material, the light intensity that maximizes the groove crossing signal amplitude does not necessarily minimize the jitter of the reproduction signal. It was clarified in an experiment conducted by the present inventor that the optimum value of is not obtained. That is, in the first method of the above-mentioned Japanese Patent Laid-Open No. 5-12673, the light intensity at which the groove crossing signal amplitude in the tracking error signal becomes maximum is the optimum value of the reproduction laser light intensity. The intensity of the light having the maximum amplitude does not always minimize the jitter of the reproduction signal, and thus there is a problem in using it for setting the intensity of the reproduction laser light.

According to the second method, the light intensity at which the information reproduction signal amplitude is maximized is the optimum value of the reproduction laser light intensity. However, as shown in FIG. 13, the shortest recording mark and the longest recording mark are used. The reproduction power that maximizes the signal amplitude depends on the relationship between the laser spot diameter and the spatial frequency band. However, since the shortest recording mark has the largest signal amplitude change depending on the laser light intensity, when the light intensity is set to maximize the signal amplitude of the shortest recording mark, the jitter of the reproduction signal is minimized. That is, FIG.
As shown in (A), when the relationship between the shortest mark length and the effective spot diameter is such that no intersymbol interference occurs when reading the adjacent recording marks, the signal amplitude of the shortest recording mark becomes maximum, and the reproduction signal The jitter is minimized, and the effective spot diameter at this time can be said to be the optimum value of the reproduction laser light intensity. However, a circuit for detecting the reproduction signal amplitude of only the shortest recording mark from a reproduction signal in which recording mark signals of arbitrary lengths are mixed has a large circuit size and becomes complicated. Is difficult to incorporate.

Therefore, a track for setting the light intensity on which the shortest recording mark is recorded may be provided as shown in Japanese Patent Application No. 4-359176, but it is necessary to provide the track for setting the light intensity on the optical disk. , It is difficult to achieve compatibility with conventional optical discs, and when the laser light intensity setting is misaligned for some reason, it is necessary to reproduce the light intensity setting track each time, and movement of the optical head, etc. However, there is a problem that it takes a long time to start the reproduction.

Therefore, the present invention has been made in view of the above-mentioned problems, and for an optical disc having a mask layer, the optical intensity setting track is not provided on the optical disc, and the circuit scale of the device is large. It is an object of the present invention to provide an optical disk device capable of setting the reproduction laser light intensity to an optimum value without doing so. The feature is that the intensity of the laser beam is set so that the magnitude of the jitter of the reproduced signal is minimized, and the jitter detection circuit for detecting the jitter is configured by a small-scale and simple circuit.

[0011]

As described above, it is actually difficult to set the optimum light intensity of the laser light by using the tracking error signal of the reproduction signal and the signal amplitude of the shortest recording mark. The person paid attention to the jitter, which is a deviation from the original signal when the recording mark read by the laser beam is a binarized reproduction signal (binarized signal). When irradiating the laser beam on the optical disc with the mask layer, if the light intensity of this laser beam is lower than the optimum value, sufficient reproduction signal amplitude cannot be obtained, jitter increases, and conversely the irradiation laser power is optimum. When the value is higher than the value, the effective irradiation spot diameter becomes large, and the jitter similarly increases due to intersymbol interference. That is, if the laser light intensity does not reach the optimum value, the jitter increases. However, the magnitude of this jitter is almost the same regardless of the recording mark length. That is, it is not necessary to see the signal amplitude of only the shortest recording mark, and moreover,
Since the reproduced signal itself is viewed, the optimum laser light intensity can be set accurately. Therefore, claim 1
The invention according to "is a light-transmitting substrate, a mask layer for reducing the spot diameter of the laser light irradiated from the light-transmitting substrate side by changing the light transmittance according to the light intensity, In an optical disc device for reproducing an optical disc on which information is recorded by a readable recording mark, a laser beam output means for outputting the laser beam and the recording mark detected by the laser beam are converted into a binary signal. Binarizing means for converting, jitter detecting means for detecting the jitter of the binarized signal output from the binarizing means, and light intensity for changing the light intensity of the laser light output from the laser light output means. At least controlling means, wherein the jitter detecting means detects the jitter of the binarized signal while changing the light intensity of the laser light by using the light intensity controlling means, and the binarized signal Jitter is intended to provide an optical disc device ", characterized in that the light intensity becomes minimum and the light intensity at the time of reproducing the optical disc.

However, the conventional jitter detecting means for detecting the jitter of the reproduced signal is complicated and expensive.
There was a problem in incorporating it in the optical disk device. Therefore, as a result of repeated studies by the present inventor, attention was paid to the binarized reproduced signal and the clock signal (PLL clock signal) extracted from the binarized reproduced signal. That is, the clock signal is extracted from the binarized reproduction signal of the optical disc in order to achieve bit synchronization between the recording mark recorded on the optical disc and the optical disc device side. It is generated by using the binarized reproduction signal and the reference clock in the device so that the information can be reproduced even if the transition point position of the binarized reproduction signal is deviated in the time axis direction. However, although this clock signal has the followability to the displacement of the transition point position of a long cycle such as the rotation fluctuation of the optical disc, it has the followability to the jitter (distortion of the signal waveform) generated by the intersymbol interference, the signal noise and the like. There is no. That is, the present inventor has paid attention to this point and found that the jitter can be easily detected by comparing the transition point positions of the clock signal and the binarized reproduction signal. Therefore, the invention according to claim 2 is that in the optical disk device according to claim 1, the jitter detecting means compares the binarized signal with a clock signal extracted from the binarized signal. An optical disc device characterized by detecting the jitter of a digitized signal.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing the structure of an optical disc used in the optical disc apparatus of the present invention. FIG. 1 (A) shows a sectional view in the track direction of a read-only optical disc, and FIG. 1 (B) shows recording. The radial sectional drawing of a possible type optical disk is shown. In the optical disc 1 shown in FIG. 1A, minute pits 2A corresponding to information are formed on a light transmissive resin substrate (hereinafter simply referred to as a substrate) 2, on which the mask layer 3, The reflective layer 4 and the protective layer 5 are sequentially stacked.
Further, in the optical disc 11 shown in FIG. 1B, a guide groove 12A is formed in a light transmissive resin substrate 12, and this substrate 12
The mask layer 3, the information recording layer 13, the reflective layer 4, and the protective layer 5 are sequentially laminated on the top.

As the light transmissive resin used as the substrates 2 and 12, those which are used as substrates for ordinary optical disks such as polycarbonate, polymethacrylic acid ester resin and epoxy resin substrates can be used.
The method of forming A and the guide groove 12A is not particularly limited, and the known method is used. The mask layer 3 is shown in FIG.
The light transmittance characteristics as shown in, for the wavelength of the light source used for optical recording and reproduction, it has absorption at light intensity below the threshold, and the absorbance decreases at light intensity above the threshold. It has the property that when the transmittance increases and the intensity becomes lower than the threshold value, the absorbance increases and returns to the original state. Various materials having the above-mentioned properties can be used as the material of the mask layer 3, and examples thereof include a thermochromic substance, a saturable absorptive substance, a phase change substance, and a photochromic substance. The reflective layer 5 is the same as a metal reflective layer generally used in optical discs, and is formed of a thin film of a metal or alloy such as gold or aluminum. The protective layer 6 provided on the reflective layer 5 is provided as necessary for the purpose of protecting the medium. The protective layer 6 can be easily formed by providing an ultraviolet curable resin by spin coating. The recording layer 13 provided on the recordable optical disk 11 is formed of a conventionally known optical recording material by a spin coating method, a vapor deposition method, a sputtering method, or the like, and is a phase change type material or a magneto-optical material. Various other types can be used.

By the way, as described above, the effective spot diameter of the irradiation laser light (see FIG. 12) depends on the light intensity. If the light intensity of the irradiation laser light is lower than the optimum value,
If a sufficient reproduction signal amplitude cannot be obtained and the jitter increases, on the contrary, if it is higher than the optimum value, the effective irradiation spot diameter becomes large, and the jitter similarly increases due to intersymbol interference. Therefore, in order to read the information recorded at high density, it is necessary to control the light intensity of the irradiation laser light on the optical disc device side to obtain the optimum effective spot diameter. In the optical disk device of the present invention, when setting the optimum laser light intensity for the optical disk, the light intensity of the irradiation laser light is controlled so as to minimize the jitter of the reproduction signal. Less than,
The optical disk device of the present invention will be described.

FIG. 2 is a schematic configuration diagram of an optical disk device according to an embodiment of the present invention. Optical disk device 31 shown in FIG.
In the figure, 32 is an optical head,
Is irradiated with the laser beam and the reflected light from the optical disk is converted into an electric signal according to the amount of the light to output a signal a. The optical head 32 includes a semiconductor laser that outputs laser light, a collimator lens that converts the laser light output from the semiconductor laser into parallel light, a condenser lens that collects the parallel laser light, and an optical disk. It is composed of a photodetector for converting the reflected light of the above into an electric signal, an actuator for focusing and tracking, etc., but the detailed structure of these optical heads 32 is not shown. Here, the photodetector (not shown) is composed of two-division or four-division photodiodes in order to generate a focus control signal and a tracking control signal. The difference signal and the addition signal of are used for focus control and tracking control. That is, the signal a is output as a light detection signal and a focus and tracking control signal. Then, the minute signal amplification circuit 3
The light detection signal b1 amplified by 3 is output to the binarization circuit 34, and the control signal b2 is output to the focus control circuit 35 and the tracking control circuit 36, respectively.

The binarization circuit 34 outputs the photodetection signal b.
2 converted from 1 to 0, 1 binary signal (digital signal)
The binarized reproduction signal c is output. The binarization circuit 34 is composed of a waveform equalizer, a data slice circuit, and the like. Further, the focus control circuit 35 and the tracking control circuit 36 perform focus control and tracking control of the laser light using the control signal b2, and the optical head according to the control signal b2 from the optical head 32. A focus / tracking actuator (not shown) in 32 is driven.

The binarized reproduction signal c of the binarization circuit 34.
Are input to the clock detection circuit 37 and the jitter detection circuit 38, respectively. The clock detection circuit 37 is a PLL
It is composed of a (Phase Locked Loop) circuit, and generates a clock signal d for bit synchronization from the binarized reproduction signal c. The clock signal d is generated so as to follow the transition point position fluctuation of the binarized reproduction signal due to the rotation fluctuation of the optical disks 1 and 11. In addition, the jitter detection circuit 38
Detects the jitter of the binarized reproduction signal c using the clock signal d output from the clock detection circuit 37 and the binarized reproduction signal c from the binarization circuit 34, and responds to the detection result. The jitter detection signal f is output. Details of the jitter detection circuit 38 will be described later. The jitter detection signal f of the jitter detection circuit 38 is input to the microcomputer 39.

The microcomputer 39 uses the jitter detection signal f of the jitter detection circuit 38 to generate a control signal g for setting the laser light intensity, and a laser ALPC (Automatic Laser Power Control) via a D / A converter 40. Output to the circuit 41. In addition, this microcomputer 39
Is a signal h output from the focus control circuit 35 and the tracking control circuit 36 according to the operating state thereof.
To monitor their operating status. Further, the microcomputer 39 is an RA for temporarily storing processing results and the like.
A storage unit 42 such as an M (Random Access Memory) is built-in or provided externally, stores the jitter detection value of the reproduction signal, and sets the optimum reproduction laser light intensity using the stored jitter detection value. A method of setting the reproduction laser light intensity by the microcomputer 39 will be described later. The laser ALPC circuit 41 controls the optical output of a semiconductor laser (not shown) in the optical head 32 based on the control signal g from the microcomputer 39. In the optical disc device 31 shown in FIG. 2, the binarized reproduction signal c from the binarization circuit 34 is output to a decoding circuit (not shown) or the like together with the black signal d and subjected to a predetermined process. Optical disc 1,11
The information will be reproduced as the information recorded in, but the details thereof will be omitted. The processing circuit of the recording system is not shown.

Next, the jitter detecting circuit 38 will be described. 3 is a diagram showing an example of the configuration of the jitter detection circuit of the optical disc device in FIG. 2, and FIG. 4 is a diagram showing an operation timing chart of the jitter detection circuit in FIG. The jitter detection circuit 38, as shown in FIG.
Delay element 5 for delaying the binary reproduction signal c by a delay time of 0.5T
1, a plurality of delay elements t having a delay time T (20 in the figure)
1-1 to t1-10, t2-1 to t2-10, EX-OR gate 5
2, AND gates 53-1 to 53-11, OR gate 54,
The low-pass filter 55, the A / D converter 56, the counter 57 that counts the number of clocks of the clock signal d, and the AN depending on the number of counts (record mark length) of this counter 57
The D gates 53-4 to 53-11 are composed of a decoder 58 which outputs a pulse signal. The jitter detection circuit 38 shown in the figure has a recording mark length recorded on an optical disc of 3T to 1 as in the case of the current compact disc (CD).
1T is shown, and the recording mark length is, for example, 2
When it is T to 11T, the pulse signal is also input from the counter 58 to the AND gate 53-3, and when the recording mark length is 3T to 10T, the number of delay elements t1 and t2 is changed. Nine each (t1-1 to t1-9, t
2-1 to t2-9), and the number of AND gates 53 is 10 (53-1 to 53-10).

Next, the operation of the jitter detecting circuit 38 will be described with reference to the timing charts shown in FIGS. 2, 3 and 4. The binarized reproduction signal c (FIG. 4B) from the binarization circuit 34 (see FIG. 2) is input to one input terminal of the EX-OR gate 52, and the other input terminal thereof. The binary reproduction signal c is output from the delay element 51 to 0.
The signal c ′ delayed by 5T is input. As a result, EX
The transition point pulse signal A1 of the binarized reproduction signal c shown in FIG. 4C is output from the OR gate 52, and the pulse signal A1 is input to one input terminal of the AND gate 53-1. become. Further, the pulse signal A1 is delayed by the delay element t1-1 for the time T to become the pulse signal A2 (FIG. 4 (D)), which is input to one input terminal of the AND gate 53-2. Similarly, the pulse signals A3 to A11 obtained by delaying the pulse signal A1 by the time T are input to the input terminals of one of the AND gates 53-3 to 53-11.

The other input terminal of the AND gate 53-1 has a D signal from the clock signal detection circuit 37 (see FIG. 2).
Clock signal d having a cycle T of 50% UTY (FIG. 4A)
Is entered. A pulse signal d2 obtained by delaying the clock signal d by a time T is input to the other input terminal of the AND gate 53-2.
And the delayed pulse signals d3 to d11 are AND gate 5
It is input to the other input terminal of 3-3 to 53-11. As described above, the clock signal d does not follow the jitter. Therefore, when the logical product of the transition point pulse of the binarized reproduction signal and the clock signal is obtained in this way, the output pulse signal is The pulse width is closer to 0.5T as the jitter of the binarized reproduction signal is smaller, and is 0 as the jitter is larger.
, And pulse signals as shown in FIGS. 4K to 4N are output, respectively.

The clock terminal C of the counter 57 is also provided.
The clock signal d is input to K, and the inverted signal of the transition point pulse signal A1 is input to the clear terminal CLK. As a result, the counter 57 keeps the clock signal d while the transition point pulse signal A1 is L (low).
As a result, the number of counts is incremented by 1, so that the mark length of the binarized reproduction signal c is counted. Then, the count number is output to the decoder 58, and the decoder 58 outputs AND gates 53-4 to 5 according to the count number.
The output signal from 3-11 is set to 0. For example, the mark length of the binarized reproduction signal c input to the jitter detection circuit 38 is 6
If it is T, in the counter 57, the transition point pulse signal A
While 1 is L (low), counting is performed from 0 to 5, and when the transition point pulse signal A1 becomes H (high),
The count value 5 is output. The decoder 56 to which the count value is input outputs an H (high) signal to the input terminals D4 to D6 of the AND gates 53-4 to 53-6, and the input terminals D7 to D7 of the AND gates 53-7 to 53-11. An L (low) signal is output to D11. As a result, AND gate 53-1
Output is made from ~ 53-6 and AND gates 53-7 ~ 5
Since there is no output from 3-11, in the OR gate 54, A
The output signals of the ND gates 53-1 to 53-6 are logically ORed.

By the way, when the logical product is obtained only by the clock signal d and the transition point pulse A1, the output is shown in FIG.
The pulse signal shown in (K) is obtained, and when this pulse signal is integrated by the low-pass filter 55, the signal amplitude which is the detection result of the jitter becomes extremely small, and the S / N of the jitter detection signal becomes low. Therefore, the jitter detection circuit 38 uses the delay element t1 that delays the transition point pulse A1 by a time of about T and the delay element t2 that delays the clock signal d, and outputs the clock signal c and the transition point pulse A1 from T to
The signal amplitude of the low-pass filter 55 is amplified by delaying every 1T up to 10T. As a result, the OR gate 5 integrated by the low pass filter 55
The output signal e of FIG. 4 (FIG. 4 (O)) is a jitter detection signal e ′ with a high S / N (FIG. 4 (P)), which is a jitter detection signal inversely proportional to the jitter of the binarized reproduction signal. . Since the microcomputer 39 handles the digital signal, it is further converted into a digital signal by the A / D converter 56 and output from the jitter detection circuit 38 as the jitter detection signal f.

When the transfer rate is low like a compact disc, that is, the cycle T of the clock signal c is about 2
In the case of a relatively long value of 30 ns, the pulse width when the logical product of the clock signal c and the transition point pulse is taken becomes long, and it becomes easy to pass through the delay element t1, so that the delay of the clock signal c as shown in FIG. Jitter detection circuit 3 with the element t2 omitted
8'may be used.

Next, the operation of the optical disk device 31 will be described with reference to the flow charts shown in FIGS.
First, when the optical discs 1 and 11 are mounted on the optical disc device 31, the microcomputer 39 rotates the spindle motor 43 (P1), sets the laser light intensity to a certain reference value PR, and sets it on the optical discs 1 and 11. Irradiate (P2). The reference value PR of the laser light intensity at this time is stored in advance in a storage means such as a ROM (Read Only Memory) not shown. This reference value PR is set smaller than the light intensity applied by the focus servo.

Next, the reflected light from the optical disks 1 and 11 is converted into an electric signal in the optical head to be a control signal b2, and the focus is controlled by using the focus control circuit 35 (P
3, P4, P5). At this time, since the irradiation laser light intensity is insufficient, the effective spot diameter is too small, and the focus servo is not pulled in due to the insufficient amount of light reflected from the disk. Therefore, the laser light is kept until the servo is pulled in while monitoring the operating state by the microcomputer 39. A certain amount of strength Δp
The focus search is performed while raising (P5) each time (P3) and the focus servo is applied. If it is confirmed in step P4 that the focus servo has been applied, then
Tracking is performed using the tracking control circuit 36 and a still state in which the same track is repeatedly reproduced is set (P6). At this time, since the effective spot diameter is small due to insufficient light intensity of the laser light, a stable tracking error signal cannot be obtained and still cannot be steered. Therefore, while monitoring the operating state, the laser power is set to a fixed amount Δ
The tracking servo is applied by increasing the value by p (P7,
P8, P9).

By the way, the reference value PR, which is the initial value of the laser light intensity, is set to be smaller than the light intensity on which focus servo or tracking servo is applied. In steps P1 to P9, jitter is not always minimized even if focus servo or tracking servo is applied. Therefore, after the servos are applied, an operation for further searching for the optimum laser light intensity is required. Here, the relationship between the reproduction laser light intensity and the amount of jitter will be described with reference to FIG. The jitter detection value Jx shown in the figure indicates the jitter detection value f of the jitter measuring circuit 38, and the larger the value, the smaller the jitter of the reproduced signal. As shown in the figure, when the irradiation laser light intensity Px is increased from the reference value PR, the jitter detection value Jx becomes larger (the actual jitter is smaller), and the irradiation laser light intensity is further increased. As it goes, a certain maximum value is taken and the jitter detection value Jx becomes smaller again. The laser light intensity at the time when the jitter detection value Jx reaches the maximum value is the light intensity at which the jitter is actually minimized, and becomes the optimum reproduction laser light intensity. However, in reality, the microcomputer 39
Since it is impossible to detect the jitter while continuously changing the laser light intensity, the laser light intensity is changed by a constant amount. Therefore, the microcomputer 3
The maximum value actually detected in 9 does not always match the maximum value.

Therefore, in the optical disk device 31 of the present embodiment, when it is confirmed in step P7 that the tracking servo has been applied and the still state has been reached, the following operation is performed to perform the optimum reproduction laser light intensity (jitter detection). We are searching for the laser light intensity that takes the maximum value. The optical discs 1 and 11 are irradiated with laser light to reproduce the information of the recorded recording marks, and the jitter of the reproduced signal is detected using the jitter detection circuit 38 (P10). The intensity setting value Px and the jitter detection value Jx are compared and stored in the RAM 42 (P11). Then, the maximum value Jmax is retrieved from the stored jitter detection values (P
12). When the light intensity is gradually increased from the tracked laser light intensity, the latest jitter detection value Jx becomes larger than the previous jitter detection value, but the latest jitter detection value Jx When it becomes smaller than the previously detected jitter detection value Jx, the immediately preceding jitter detection value Jx becomes the maximum value Jmax.

Next, the latest jitter detection value Jx is Jmax-
It is determined whether or not it is less than e (e is a certain amount) (P13). If the maximum value Jmax of the detected jitter value is not found, the process proceeds to step P14 without performing the process of step P13, and the laser light intensity is set to a fixed amount Δ.
Increase by p and return to step P10. Further, as a result of the discrimination in step 13, the jitter detection value Jx is Jx>
Similarly, when Jmax-e, the laser light intensity is increased by a fixed amount Δp (P14), and the process returns to step P10. Then, the detected jitter detection value Jx is Jx ≤ Jma
Steps P10 to P14 are repeated until x−e.

When the latest jitter detection value Jx falls below Jmax-e in step 13, the latest jitter detection value Jx is compared with the preceding jitter detection value Jx and Jma is calculated.
The laser light intensity of the jitter detection value closer to x-e is set to Pmax
(P15). When Pmax is retrieved, then RAM
From the laser light intensity Px stored in 42, the above Jmax
Is smaller than the laser light intensity
The laser light intensity Pmin that is the jitter detection value closest to the Pmax searched in (1) is searched (P16). And Pmin
Is searched for, Ppb = (Pmin + Pmax) / 2 is calculated, and this value Ppb is set as the optimum reproduction laser light intensity, and the laser light intensity is set to Ppb using the laser ALPC circuit 41 (P16). This completes the setting operation of the reproduction light intensity.

The recommended reproducing laser light intensity Po may be recorded in the optical discs 1 and 11, but the recommended reproducing laser light intensity Po is not necessarily the optimum laser light intensity for the optical disks 1 and 11. It may not always be. The above recommended reproduction laser light intensity Po is usually
As shown in FIG. 9 (A), it is set so as to be almost the same as the laser light intensity PD when the jitter detection value Jx becomes maximum. However, due to variations in manufacturing the optical discs 1 and 11 and dust or the like adhering to the condenser lens of the optical head 32, the surfaces of the optical discs 1 and 11, and the like, FIG.
In some cases, the recommended reproduction laser light intensity Po is smaller than PD, as shown in FIG. 4, or in some cases, it is larger than PD as shown in FIG. Here, the jitter detection value Jx shown in FIG.
8 shows the output signal, and the larger the value, the smaller the jitter of the reproduced signal.

Therefore, for the optical disks 1 and 11 on which the recommended reproduction laser light intensity Po is recorded, the laser light intensity around the recommended reproduction laser light intensity Po with respect to the jitter detection value Jo of the recommended reproduction laser light intensity Po. The minimum laser light intensity Pmin and the maximum laser light intensity P when the jitter detection value Jx when increasing or decreasing is such that Jx ≤ Jo-e (e is a certain value)
Obtain max and set an intermediate value as the reproduction laser light intensity. Hereinafter, a method of setting the optimum laser light intensity when the recommended reproduction laser light intensity Po is recorded on the optical disc will be described with reference to the flowchart shown in FIG.

The operation up to the still state is the same as the operation from steps P1 to P9 shown in FIG. In this still state, the recommended reproduction laser light intensity Po recorded in advance at a predetermined position (for example, the innermost circumference or the lead-in area) of the optical disks 1 and 11 is read, and the irradiation laser light intensity is set to the recommended reproduction laser light intensity. Set to strength Po (P2
1). Next, the jitter of the reproduction signal at the recommended reproduction laser light intensity Po is detected (P22), and the laser light intensity set value Po is detected.
And the jitter detection value Jo at that time are associated with each other
(P23). Next, let the laser light intensity Px be Δp
Increase (P24), detect jitter (P25),
It is determined whether or not the jitter detection value Jx is Jx≤Jo-e (P26). When the jitter detection value Jx is larger than Jo-e (Jx> Jo-e), the above steps P24-
Repeat P26 until Jx≤Jo-e. Further, the jitter detection value Jx detected in step P25 is Jx ≤
When it becomes Jo-e, the laser light intensity Px at this time is Pma
x and store it in the RAM 42 (P27). When Pmax is detected in the above step P27, next, the irradiation laser beam intensity Px is set to Po-Δp (P28), the jitter of the reproduced signal is detected (P29), and the jitter is the same as in the above step P26. It is determined whether the detected value Jx is Jx≤Jo-e (P30). When the jitter detection value Jx is larger than Jo-e (Jx> Jo-e), the irradiation laser light intensity Px is decreased by Δp (P31), and the steps P29 to P are performed.
31 is repeated until Jx≤Jo-e. The jitter detection value Jx detected in step P29 is Jx≤Jo-
When it becomes e, the laser light intensity Px at this time is set to Pmin and stored in the RAM 42 (P32).

Then, Ppb = (Pmin + Pmax) /
The calculation of 2 is performed, and this value Ppb is set as the optimum reproducing laser light intensity (P33). This completes the setting operation of the reproducing light intensity when the recommended reproducing laser light intensity Po is recorded on the optical discs 1 and 11.

As described above, the optical disk device 31 of this embodiment detects the optimum reproduction laser light intensity and reproduces the information on the optical disks 1 and 11 using the laser light having the detected light intensity.

[0037]

As described above, the optical disk device of the present invention comprises a laser beam output means for outputting a laser beam and a binarizing means for converting a recording mark detected by the laser beam into a binarized signal. , 2 output from this binarizing means
At least a jitter detecting means for detecting the jitter of the binarized signal and a light intensity control means for changing the light intensity of the laser light output from the laser light output means are provided. Since the jitter of the binarized signal is detected by the jitter detecting means while changing the light intensity, and the light intensity at which the jitter of the binarized signal is minimized is set as the light intensity for reproducing the optical disc. The laser light intensity can be set using the information recorded on the optical disc, and it is not necessary to provide a dedicated track for setting the light intensity on the optical disc, and compatibility with the conventional optical disc can be easily achieved. Further, the light intensity can be set in real time, the effective spot diameter can always be made appropriate, and the occurrence rate of the reproduction signal error can be reduced.

Further, the jitter detecting means detects the jitter of the binarized signal by comparing the binarized signal with the clock signal extracted from the binarized signal, thus reducing the circuit scale. Therefore, the cost increase of the device can be minimized.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of an optical disc used in an optical disc device of the present invention.

FIG. 2 is a schematic configuration diagram of an embodiment of an optical disk device of the present invention.

FIG. 3 is a diagram showing an example of a configuration of a jitter detection circuit in FIG.

FIG. 4 is a diagram showing an operation timing chart of the jitter detection circuit in FIG.

5 is a diagram showing another example of the configuration of the jitter detection circuit in FIG.

6 is a diagram showing an operation flowchart of the optical disc device in FIG.

FIG. 7 is a diagram for explaining the relationship between the reproduction laser light intensity Px and the jitter detection value Jx in the operation flowchart in FIG.

8 is a diagram showing another operation flowchart of the optical disc device in FIG.

9 is a diagram for explaining the relationship between the jitter detection value Jx and the reproduction laser light intensity Px in the operation flowchart in FIG.

10 is a diagram showing light transmittance characteristics of a mask layer of the optical disc in FIG.

11 is a diagram showing a relationship between a spot diameter and a recording mark when the optical disk in FIG. 1 is irradiated with laser light.

FIG. 12 is a diagram showing a light intensity distribution of an irradiation spot and an effective spot when the optical disk in FIG. 1 is irradiated with laser light.

FIG. 13 is a diagram showing a relationship between a reproduction signal amplitude characteristic and a jitter characteristic with respect to light intensity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 optical disk (reproduction-only type) 11 optical disk (recordable type) 31 optical disk device 32 optical head (laser light output means) 33 minute signal amplification circuit 34 binarization circuit (binarization means) 35 focus control circuit 36 tracking control circuit 37 Clock Signal Detection Circuit 38 Jitter Detection Circuit (Jitter Detection Means) 39 Microcomputer 41 Laser ALPC Circuit (Light Intensity Control Means) 42 RAM

Claims (2)

[Claims] 1. A mask layer on a light-transmitting substrate, which has a mask layer for reducing a spot diameter of laser light irradiated from the light-transmitting substrate side by changing a light transmittance according to light intensity, In an optical disc device for reproducing an optical disc in which information is recorded by a readable recording mark, a laser beam output means for outputting the laser beam, and the recording mark detected by the laser beam are converted into a binary signal. And a binary output from the binarizing means.
At least a jitter detection unit for detecting the jitter of the binarized signal and a light intensity control unit for changing the light intensity of the laser beam output from the laser beam output unit are provided. The jitter of the binarized signal is detected by the jitter detecting means while changing the light intensity, and the light intensity at which the jitter of the binarized signal is minimized is used as the light intensity for reproducing the optical disc. Characteristic optical disk device. 2. The optical disc device according to claim 1, wherein the jitter detecting means detects the jitter of the binarized signal by comparing the binarized signal with a clock signal extracted from the binarized signal. An optical disk device characterized in that.