JPH0778348A - Detecting method for focus deviation and information processing device using it - Google Patents

Abstract

PURPOSE:To obtain a new detecting method for focus deviation, an optical disk device consisting of an optical system which realize the detecting method, and an information processing device incorporating it. CONSTITUTION:When focus deviation of an optical disk device is detected, the quantity of focus deviation is obtained from a time difference of diffracted light beams of high order among reproduced signals of a pit, since diffracted light beams emitted from a peripheral part of an object lens 50 is diffracted light beam of high order, an optical detector 70 is provided at a position where only diffracted light beams from peripheral part of the object lens 50 is received. Focus deviation is obtained using the detected value, and an optical system is constituted so that an optical head is controlled to correct the deviation. Thereby, a detector 70 having high accuracy can be realized, while an optical system can be simplified, and small size and light weight for an optical disk device can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a reflected light from an optical disc by two photodetectors, and detects the amount of defocus from the time difference between the waveforms of the two optical detectors. The present invention relates to an optical disc device using the same, and an information processing device.

[0002]

2. Description of the Related Art When reproducing or recording / erasing information on an optical disk, focusing and tracking control are performed by moving a light spot focused by an objective lens of an optical head so as to follow the surface deviation and eccentricity of the optical disk. Therefore, the optical head needs a detection optical system for detecting the focus shift amount and the tracking shift amount. Therefore, simplification of these detection optical systems is effective in reducing the size, weight and cost of the optical head and the optical disk device.

As a method for detecting a focus shift of an optical disk, there is an optical disk technology supervised by Morio Onoe (Radio Technology Co., Ltd.) p.
As described in Nos. 80 to 85, the knife edge method, the astigmatism method, etc. are conventionally used. In addition, JP-A-60-13
There is a method called the phase difference method, such as the one described in the publication No. 330 and the publication No. 2-64921. A feature of the phase difference method is that it does not require a precisely adjusted detection optical system such as the knife edge method or the astigmatism method.

[0004]

Since the phase difference method simplifies the detection optical system, the optical disc apparatus can be downsized and the cost can be reduced. Here, the detection principle of the phase difference method is shown in FIG.
Will be explained. Of the reflected light from the optical disk, the light that has passed through the objective lens is received by a photodetector divided into two sensors, F and B. FIG. 2 shows the positional relationship between the focused spot and the pits on the optical disk and the shape of the beam on the photodetector at that time. The optical depth of the pit is λ
Is set to λ / 4. When the focused spot is at the position of just focus on the recording surface of the optical disc, the shape of the spot on the detector is symmetrical left and right and up and down regardless of the positional relationship between the spot and the pit, and the outputs from the sensor F and the sensor B are It will be of equal size. When the objective lens comes close to the optical disc and defocuses, if the spot hits the tip of the pit, the sensor B will be diffracted by the pit.
The amount of light incident on is reduced. When the spot has just come to the center of the pit, the same amount of light enters the sensors F and B. Further, when the spot advances and reaches the rear end of the pit, the amount of light incident on the sensor F decreases. Conversely, when the distance between the objective lens and the optical disk becomes large and defocusing occurs, if the spot hits the tip of the pit, the amount of light incident on the sensor F decreases. When the spot advances and the spot hits the edge of the pit, the amount of light incident on the sensor B decreases this time. Considering the time change of the output of each detector, the waveforms of the outputs of the sensor F and the sensor B are the same when the focus is just. When the objective lens and the optical disk are close to each other, the output of the sensor B first decreases and then the output of the sensor F decreases. When the objective lens is far from the optical disk, the output of the sensor F first decreases, and then the output of the sensor B decreases. As described above, the two sensor output waveforms are temporally different depending on the defocus direction, and thus the defocus amount, that is, the focus shift amount can be detected by measuring the time difference.

However, according to the phase difference method, when the pits formed on the optical disk are uneven, an offset occurs in the focus shift detection amount when the optical depth of the unevenness deviates from λ / 4. There was a problem. Therefore, in Japanese Unexamined Patent Publication (Kokai) No. 2-64921, 4
By sequentially arranging the two photodetectors, the phase difference between the outputs of the two photodetectors placed outside and the phase difference between the outputs of the two photodetectors placed inside can be adjusted with an appropriate gain ratio. The offset of the focus shift detection amount is reduced by adding or subtracting. However, this method is just a method of reducing the offset, and there is a problem that the offset occurs when the reflectance of the optical disk medium or the output of the reproduction light of the optical head changes.

In view of the above problems, the present invention provides a focus shift detection method that does not generate an offset even when the pit depth deviates from λ / 4, and a compact and low-cost optical disc device and information processing device using the same. Is provided.

[0007]

In order to solve the above-mentioned problems, the present invention provides a focus shift signal from high-order diffracted light diffracted out of an aperture of an objective lens among reflected light from an optical disk. It's something I got to get.

That is, it is known that the high-order diffracted light of the light reflected by the optical disc comes out around the aperture of the objective lens, and the high-order diffracted light is respectively directed to the center of the lens. Detected by the photo detector provided on the target,
By utilizing the fact that there is a temporal shift when the peak one has a focus shift, the shift amount is detected and the optical head is controlled so as not to slip.

[0009]

According to the present invention, the high-order diffracted light of the reproduced signal from the pits of the optical disk is arranged in the track direction.
It is possible to detect the amount of defocus by using the fact that the peak positions of the reproduced waveforms of the two photodetectors are deviated with time due to defocus. This makes it possible to provide a focus shift detection method that does not cause an offset even when the pit depth deviates from λ / 4. This can simplify the configuration of the detection optical system. Further, by applying the present invention, small size, light weight,
It is possible to realize a low-cost optical disc device and an information processing device equipped with the same.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

First, the principle of the present invention will be briefly described before describing specific embodiments.

FIG. 3 is a schematic diagram showing the light diffracted by the pit. Numerical values in parentheses represent diffraction orders in the direction along the track and the direction perpendicular thereto. (0,0) represents 0th-order diffracted light, that is, light that is specularly reflected, and is transmitted through the aperture of the objective lens. High-order diffracted light other than the 0th order is reflected from the disc at a certain angle, so that only part of the diffracted light passes through the aperture of the objective lens. For the handling of the light diffracted by the pits, see, for example, Japan Society of Applied Physics, Optical Communication Society, Optical Disc System (Asakura Shoten) p. 45-50. When the Fourier coefficient of the diffracted light is R (m, n), this is R (0,0) = 1 + (αexp [iφ] -1) A (0,0) R (m, n) = (αexp [iφ] -1) Excluding A (m, n) m = n = 0 It can be expressed as (1). Here, m and n are the diffraction orders in the direction along the track and the direction perpendicular thereto, α is the amplitude reflectance of the pit, φ is the phase change due to reflection at the pit portion, and A (m, n) is the pit. Is a term depending on the shape of. φ is expressed as φ = 4πd / λ (2) using the wavelength λ of light and the optical depth d of the pit. From equation (1), it can be seen that the Fourier coefficients R (m, n) other than R (0,0) have the same phase.

In the conventional phase difference method, the light transmitted through the aperture of the objective lens is received by a two-divided photodetector to obtain the focus shift amount. FIG. 4 shows a reproduction waveform of a signal obtained at the time of just focusing calculated by this method. As calculation conditions, the wavelength of the light source is 830 nm, the numerical aperture of the objective lens is 0.52, and the shape of the pit is 0.6 μm.
As an ellipse having a length of 0.68 μm, the light intensity distribution on the photodetector was calculated by the Fourier transform method using the Fraun-Hofer diffraction theory. In the figure, x represents the distance between the center of the pit and the center of the focused spot, which can be converted into time by dividing this by the linear velocity of the rotation of the optical disk. As can be seen, when the pit depth is λ / 4, the two sensor outputs match. However, when the pit depth is λ / 8, the sensor outputs do not match. Since the phase difference method detects a time shift of the sensor output and converts it into a focus shift amount, a focus detection offset occurs when the pit depth deviates from λ / 4 as in the example shown here. This is because the 0th-order diffracted light and the high-order diffracted light have different phases. When the pit depth is λ / 4, φ = π from equation (2), the Fourier coefficient becomes a real number, the two sensor outputs match, and no offset occurs. In the past, since the photodetector received a combination of 0th-order diffracted light and high-order diffracted light, the pit depth was λ
It was not possible to prevent the occurrence of offset when deviated from / 4.

In the present invention, only the high-order diffracted light other than the 0th order is detected so that the phases of the diffracted light are equal to each other so that the offset is not generated.

FIG. 5 shows an example of the result of calculation of a reproduced waveform when high-order diffracted light is received by two detectors F and B arranged in the track direction. Since the 0th-order diffracted light is not detected, the reproduced waveform of the pit is convex upward. FIG. 5A is a reproduction waveform at the time of just focus, in which the pit depth is λ /
In both cases of 4 and λ / 8, the output waveforms of the detectors F and B coincide with each other and no offset occurs. FIG. 5B shows a reproduction waveform when the defocus is 4 μm. The output waveforms of the detectors F and B are such that the peak positions are deviated by δt.
The peak shift amount δt does not depend on the pit depth and is λ / 4.
The same value is obtained in both case and λ / 8. Therefore, the detection sensitivity of the focus shift amount can be kept constant.
Focusing control can be performed by moving the position of the objective lens or the like so that δt becomes zero.

FIG. 1 shows an embodiment of the configuration of an optical system of an optical head suitable for the present invention. This optical head uses a so-called finite optical system that allows diffused light from a light source to enter an objective lens without acting on other lenses.

The beam emitted from the semiconductor laser 20 is
The direction is changed by the half mirror 35, and the objective lens 50 is transmitted through the central opening of the donut-shaped optical path separating glass plate 62.
And is focused on the optical disc 300. At this time, the central opening of the optical path separating glass plate acts as the opening of the objective lens. The optical disc is rotating in the direction of 380. Of the light reflected by the optical disc 300, the light including the 0th-order diffracted light is transmitted through the objective lens 50 and the half mirror 35 and received by the sensor C73. Higher-order diffracted light of the light reflected from the optical disc 300 passes through the peripheral portion of the objective lens 50, is refracted by the optical path separating glass 62, and is detected by the sensor F71 and the sensor B72. Where sensor F,
C and B are arranged in the direction along the track of the optical disc, and form one photodetector 70. In the arrangement shown in the figure, the sensor F detects information on the front side in time, and the sensor B detects information on the rear side in time. With this configuration, high-order diffracted light that does not include the 0th-order light reflected from the optical disc can be detected by the two sensors, so that focus shift detection can be realized by the above-described detection principle. By applying servo control to this and moving the position of the objective lens so that the focus shift is always zero, it is possible to reproduce information from the optical disk or record information on the optical disk using the present optical head. it can. At this time, the information recorded on the optical disc can be read by the sensor C. In this method, the sensors F, B, C having a sufficiently large detection area for the light spots on the sensors may be used to detect the total amount of light, and fine position adjustment of the detector is not necessary. Therefore, assembling adjustment of the optical head can be simplified as compared with the conventional astigmatism method, knife edge method, and the like.

In this embodiment, the sample servo method is adopted as the tracking deviation detection method. In the sample servo method, ± 1 / from the track center of the optical disk
The amount of tracking deviation is detected from the intensity difference between the reproduction signals of a pair of wobble pits formed by shifting by 4 track pitches. For this reason, the optical system for detecting the tracking deviation is not required, and the configuration of the optical head can be simplified. The focus shift signal can be obtained from the reproduction signal of the clock pit or wobble pit of the servo marks of the sample servo.

As another tracking deviation detecting method, there is a continuous servo method using diffracted light from a continuous groove. If a detector for detecting diffracted light from the continuous groove is provided in the embodiment of FIG. 1, it is easy to adapt to the continuous servo system. At this time, since the light reflected by the groove is diffracted in the direction perpendicular to the track, the focus shift amount can be detected without affecting the outputs of the sensors F and B arranged in the direction along the track.

In the above optical head, when the objective lens is moved to perform focus / tracking alignment control, the objective lens and the optical path separating glass plate are mounted on a drive mechanism such as a two-dimensional actuator and moved simultaneously. Good.

Further, in this embodiment, the case where the finite image forming system objective lens is used is shown, but the infinite image forming system in which the emitted light of the laser is once converted into parallel light by using the collimator lens and then condensed by the objective lens. It is also easy to use for an optical head.
In that case, it is desirable to use a lens to guide the reflected light to the photodetector.

FIG. 6 shows the result of calculation of the focus shift signal obtained from the optical head of FIG. As can be seen from the figure, there is a one-to-one correspondence between the amount of focus shift and the amount of positional shift of the peaks of the output waveforms of the sensors F and B, and it can be seen that focusing control can be performed using this characteristic.

In the results of FIG. 6, the focus shift amount and the peak position shift amount are not in a perfect proportional relationship, and the change rate of the peak position shift, that is, the detection sensitivity is small in a region where the focus shift amount is about ± 2 μm or less. You can see that it has become. It is desirable that the detection sensitivity is constant when focusing control is performed. The following is a method for improving the decrease in the focus shift detection sensitivity near the zero point.

FIG. 7 shows the output waveforms of the sensors F and B when there is a focus shift. In the above examples, the shift of the peak positions of the two is used, but here the output difference between the two is integrated to determine the area of the hatched region in the figure as the differential integrated value.

FIG. 8 shows the calculation of the differential outputs of the sensor F and the sensor B. Due to the focus shift, the outputs of the sensor F and the sensor B are shifted. Therefore, the differential output is always zero when the focus shift is zero, and has an s-shaped characteristic depending on the magnitude of the focus shift. A value obtained by sampling the value at the point of x = 0 by temporally integrating this waveform can be obtained as the differential integrated value.

FIG. 9 shows an example of the result of calculating the relationship between the focus shift amount and the differential integral value. The focus error signal obtained by this method changes depending on the size of the pits on the disc. Here, the focus error signal obtained for pit lengths from 1T to 4T is shown in the figure, assuming that the pit width is constant at 0.6 μm and the length is 0.68 μm as 1T. The characteristics shown in the figure are very similar to the focus shift detection characteristics of the conventional astigmatism method and knife edge method, and are generally called s-shaped curves. It can be seen that the focus shift amount and the differential integral value have a substantially proportional relationship in the vicinity of the zero point, and the detection sensitivity is improved by being kept constant. Further, the detection sensitivity (inclination near the zero point) is almost constant regardless of the size of the pit. It can be seen that the detection range increases as the pit length increases from 1T to 4T. In this method, the pit length is preferably in the range of about 1T to 10T in order to make the detection sensitivity and the detection range appropriate.

In the defocus detection method of the present invention, the reproduction waveform changes when the light beam passes directly above the pit (on-track state) and when it passes between the pits (off-track state). . FIG. 10 shows changes in the focus shift detection characteristic depending on the light beam passage position. The calculation conditions are as follows: the wavelength of the light source is 830 nm, the numerical aperture of the objective lens is 0.52, and the shape of the pit is 0.6 μm.
It is assumed that the pits are arranged at equal intervals in the radial direction of the optical disc, with an ellipse of m, a length of 0.68 μm, a linear velocity of rotation of the optical disc of 7.5 m / s, and a track pitch of 1.5 μm. The figure shows the time difference between the peaks of the reproduced waveforms in the on-track state and in the state of off-tracking by 1/2 track pitch. As can be seen from the figure, the time difference between the reproduced waveforms is almost the same in the on-track state and the 1/2 off-track state in the range where the focus shift is ± 15 μm. This is because the pits are arranged at equal intervals in the radial direction of the optical disc, so when the amount of defocus increases and the size of the light spot increases, multiple pits are reproduced at the same time, and the reproduction signal is transmitted to the beam passing position. This is because they are almost the same without depending on each other. In order to eliminate the fluctuation of the focus shift detection characteristic due to off-track, a groove may be formed in the radial direction of the optical disc and the focus shift amount may be detected from the reproduction signal. At this time, since the light beam crosses the same groove regardless of the off-track amount, the reproduced signal does not change.

FIG. 11 shows the same examination as in FIG. 10 for the differential integral value. It can be seen that, like the time difference between the peak positions, the change in the focus shift detection amount depending on the light beam passage position is small.

Now, let us consider the difference between the time difference detection and the differential integration detection in the focus shift detection range. Figure 1
0, ± 10 μm in the case of time difference detection from the results of FIG.
Although the focus shift amount can be detected almost linearly in the above wide range, the range in which the focus shift detection can be performed linearly becomes narrow in the case of the differential integration detection, which is ± 5 under the condition of FIG.
It can be seen that it is about μm. On the other hand, the linearity near the zero point is better in the differential integration detection than in the time difference detection. Therefore, in an optical disc device having two detection methods, first, when the focus is pulled into the optical disc, the time difference detection with a wide detection range is used, and subsequently, when the focus control becomes stable within ± 2 μm, High-performance focusing control can be realized by switching to differential integration detection with excellent linearity.

FIG. 12 shows another embodiment of the optical system of the optical head suitable for the present invention. This optical head is improved so as to improve the light utilization efficiency of the optical head of the embodiment of FIG. In this embodiment, since the optical isolator consisting of PBS and λ / 4 plate is used, there is no light loss due to the half mirror of the embodiment of FIG. The linearly polarized beam emitted from the semiconductor laser 20 is reflected by the PBS 30, passes through the opening of the optical path separating glass plate 62, becomes circularly polarized by the λ / 4 plate, enters the objective lens 50, and is incident on the optical disc 300. Collected. The light reflected by the optical disk 300 passes through the objective lens 50, becomes a linearly polarized light having a 90 ° polarization direction different from that of the light source by the λ / 4 plate, passes through the PBS 30, and is received by the photodetector 70. Here, the PBS 36 is also formed on the optical path separating glass plate 62, which acts as an opening for reflecting the emitted light from the semiconductor laser and transmits the reflected light from the disk to the sensors F and B. The focus deviation amount is detected.

In the present optical head, when the objective lens is moved to perform focus / tracking alignment control,
The objective lens, the optical path separating glass plate, and the λ / 4 plate may be mounted on a driving mechanism such as a two-dimensional actuator and moved simultaneously.

FIG. 13 shows one embodiment of an optical head suitable for the present invention. In this embodiment, the high-order diffracted light of the light reflected by the optical disk is detected by the sensors F and B arranged outside the aperture of the objective lens. Therefore, no means for switching the aperture of the objective lens such as a glass plate for separating the optical path is used. The principle of defocus detection is the same as that of the optical head embodiment described above. In this embodiment, the light emitted from the semiconductor laser 20 is guided to the objective lens 50 by using the half mirror 35, and the reflected light from the optical disc 300 is guided to the sensor C. As described in the above embodiment, the optical utilization efficiency can be improved by using the optical isolator.

FIG. 14 shows an embodiment of an optical head in the case where the entire optical system of the optical head is moved to perform focus / tracking adjustment. This optical head for light uses a finite optical system, and integrally drives an optical head movable part 16 including a semiconductor laser 20, a half mirror 35, an objective lens 50, sensors F71, B72, and C73 by a two-dimensional actuator 100. It is a method to do. The operation of this optical head is the same as that described in FIG. With this configuration, the objective lens 50
Is sufficient considering only the axial focusing performance, and it is possible to use a small and thin objective lens as compared with one in which only the objective lens is driven by a two-dimensional actuator.

FIG. 15 shows another embodiment of the configuration of the optical system of the optical head suitable for the present invention. In this embodiment, as compared with the embodiment of FIG. 1, the photodetector is arranged in a plane parallel to the optical disk to reduce the thickness of the optical head. This optical head also uses a finite optical system that allows the diffused light from the light source to enter the objective lens without acting on other lenses. In this configuration, the PBS and the startup mirror are separated, and the photodetector can be arranged in the same plane as other optical components, so that the optical system can be made thinner. The operation of this optical head is similar to that described with reference to FIG. 12, for example.

In this embodiment, the case where a finite image forming system objective lens is used is shown. However, an infinite image forming system optical head which uses a collimator lens to collimate laser emission light once and then condense it with the objective lens. It is also easy to use. In that case, it is desirable to use a lens to guide the reflected light to the photodetector.

FIG. 16 shows an embodiment showing the structure of a detection circuit for measuring the time difference between the peak positions of the reproduced waveform as a method for detecting the focus shift. To detect the peak position of the reproduced waveform, the waveform may be differentiated to detect the zero-cross position. The signals respectively detected by the sensor F71 and the sensor B72 are amplified by the preamplifiers 205 and 206, differentiated by the differentiators 210 and 211, and input to the zero cross detectors 220 and 221. The zero-cross detectors 220 and 221 generate a logical pulse having a rising edge at the zero-cross position of the input waveform. The pulses having these time-shifted edges are input to the clock counter 230. The clock counter 230 has a built-in reference clock of a crystal oscillator, and measures the time interval between the rising edge of the logical pulse from the sensor F and the rising edge of the logical pulse from the sensor B as the count number of the reference clock. The preceding case can be output as positive with a sign. This value corresponds to the focus shift amount. According to this method, since the peak position of the reproduced waveform is detected and the time difference is measured, it can be applied even if there is a difference in the amount of light received by the sensor F and the sensor B. In the conventional focus shift detection method, the focus shift amount is detected from the difference in the light receiving amount of the sensor. Therefore, the position of the sensor is adjusted with an accuracy of 10 μm or less so that the light receiving amount of each sensor becomes an appropriate value. It had to be fixed to the optical head. In this method, the time difference of the reproduced waveform is measured instead of the difference in the light amount between the sensors, so there is no need to make adjustments so that the received light amounts are exactly the same, and the adjustment of the detection system of the optical head can be greatly simplified. it can.

Since the focus control band of the optical disk is about 2 to 3 KHz, a sampling cycle of defocus of 100 KHz or less is sufficient. Since the reproduction time of one pit is about 100 ns, this method can perform sampling at a maximum of about 10 MHz. Therefore,
The focus shift detection circuit does not always need to operate. For example, the focus shift should be synchronized with the focus shift sampling cycle of the sample servo, and the focus shift amount should be sampled only from the preformatted pits that are pre-formatted to be operable. You can Further, it is possible to add a function of judging whether the reproduced pit is defective or missing, and judging whether the defocus amount is a normal value or the like.

FIG. 17 is an embodiment showing the structure of the detection circuit when the differential integration method is used as the method of measuring the focus shift. The signals respectively detected by the sensor F71 and the sensor B72 become differential outputs by the differential amplifier 207 and are integrated by the integrator 250, and the A / D converter (AD
C) Input into 260. The differential outputs are simultaneously input to the zero-cross detector 222, the zero-cross point of the waveform, that is, the point of x = 0 in FIG. 8 is detected and the timing command is sent to the ADC 260. The ADC 260 converts the output of the integrator 250 from an analog output into a digital value according to the fetched timing sent, and outputs a value corresponding to the focus shift amount.

In this embodiment, the ADC fetch timing is determined at the zero-cross position of the differential output, but the ADC fetch timing may be specified at the position where the sum of the sensor F and the sensor B is minimum, or they may be specified. It may be a combination of.

Further, in this method, since the integration circuit is used, if there is an offset in the circuit element, it may be added by the integration operation, and a focus detection offset may occur in the circuit. As described above, the sampling of this method can be performed up to about 10 MHz, whereas the sampling frequency required for focus control of the optical disk is 100 KHz or less. Therefore, it is desirable to provide a correction unit that makes the output of the integrator zero during the period in which the focus shift amount is not sampled.

In the present invention, the focus deviation can be detected without offset regardless of the depth of the pit, so that the optical disk medium is a read-only compact disk that has already been commercialized, a rewritable 3.5 inch or It can also be used for 5.25-inch magneto-optical disks and 12-inch write-once optical disks. Since these optical disc media are well known, a 2.5 inch overwritable phase change type optical disc medium will be described below.

FIG. 18 is an embodiment showing the format of an optical disk medium suitable for the present invention. As shown in FIG. 18A, the optical disc medium 300 has spiral tracks.
Format information such as 350 and track address 351 and servo marks 360 for focus and tracking servo are formed as irregularities on the substrate. FIG.
(B) schematically shows an example of the track configuration of an optical disk of the sample servo format. Servo marks 360 and a data area 37 are provided on the track 350.
0, 371, 372 are alternately arranged, and a segment 375 is composed of the servo mark and the data area. About 1000 segments are formed per track. Servo marks 360 are wobble pits 361 and 362 for tracking servo, clock pits 363 for synchronization signals, and mirror portion 3 in which pits are not formed.
It is composed of 64. In the normal sample servo system, a system clock is generated from the reproduction signal of the clock pit 363, the wobble pits 361 and 362 are read separately, and the track shift amount is detected from the output difference.

When the focus error detection method of the present invention is applied to the optical disk medium of the sample servo format, the reproduced waveform of the clock pit or wobble pit in the servo mark may be used. Further, a pit or groove for focus deviation detection may be newly formed in the mirror portion which has been conventionally used for detecting the focus deviation amount.

The format of the optical disk 300 shown here is compatible with the CAV (Constant Angular Velocity) method, but the CLV (Constant Linear Velocity) method and the MCAV (Modulated Constant Angular Velocity) method are used.
Method and MCLV (Modulated Constant Linear Velocit)
y) It is easy to adapt the system.

FIG. 19 shows an embodiment showing the structure of an optical disk medium having a diameter of 64 mm (about 2.5 inches). Optical disc 3
00 is built in the protective case 310, the laser beam is slid on the slidable protective cover 330 attached to the protective case 310 to open the optical path, and is irradiated through the opening 335, and the information recording surface 301 is irradiated with laser light. It A magnetic chuck 320 for bonding to a spindle motor is attached to the optical disc 300.
Glass, polycarbonate, and PMMA with a thickness of 0.6 mm were used for the substrate of the optical disk. By reducing the thickness of the optical disc substrate from 1.2 mm to 0.6 mm for conventional compact discs and magneto-optical discs with a diameter of 90 mm, it becomes possible to use an objective lens with a small focal length, and a thin optical head. ， It has become possible to reduce the weight. Also, by reducing the diameter of the optical disk medium to 64 mm,
The amount of surface wobbling of the medium was reduced and the case thickness was reduced to 3.5 mm. Since the optical head can be miniaturized by the present invention,
For optical disc media, the thickness of the disc substrate is 1.2mm
It is also applicable to ultra-small optical discs with diameters of 20 mm or less in the range from 0.1 mm to 0.1 mm. In addition, the focus shift detection method of the present invention can be applied to a conventional compact disc or a diameter 9
It can also be used as a medium such as a magneto-optical disk of 0 mm or more.

As a recording material for the information recording surface of the optical disk medium, in addition to the ROM type which is used in a compact disk or the like and which is previously formed in a concave-convex shape on a substrate, a write-once type used for a document file and A rewritable material using a variable optical recording material or a magneto-optical recording material can be used.

The protective case is not limited to the structure in which the beam is incident through the opening, but may be the system in which the beam is incident through the transparent case. When the beam is incident through the case, it is necessary to match the thickness of the substrate and the thickness of the case so that the thickness becomes a predetermined value. For example, when using an objective lens designed to correspond to a substrate thickness of 0.8 mm, if the transparent portion of the case has a thickness of 0.3 mm, the actual optical disc substrate has a thickness of 0.5 mm. do it. The thickness of the optical disk substrate is preferably thin in order to make the case thin, and is preferably 1.2 mm to 0.1 mm.

FIG. 20 shows an embodiment of the film structure of a phase change type optical disk medium suitable for the present invention. This optical disk medium comprises SiN, AlN, Zn having a refractive index of about 2 on a transparent substrate 400 such as glass, polycarbonate and PMMA.
First interference film 410 of transparent dielectric such as S, InSbTe
System, AgInSbTe system, GeSbTe system, InSb
System, SbTe system, GeTe system, etc. rewritable phase change type recording film 420, transparent second dielectric interference film 430 similar to the first interference film, metal reflection film 440 such as Au, Al, SiO
₂ or a protective film 450 made of UV resin or the like is sequentially formed. This optical disk medium can rewrite new information on the previous information only by irradiating the laser beam.

As the recording material, a write-once type optical recording material medium which can be written only once using a thin film of Te-based, cyanine-based, or naphthalocyanine-based organic dye can be used. Furthermore, TbFeCo system, GdFeC
It can also be applied to a magneto-optical disk using a magneto-optical recording material such as an o type. In that case, the detection optical system may be changed so as to detect the Kerr rotation angle of the reflected light by making the beam irradiating the optical disk into linearly polarized light.

Next, an embodiment of the optical disk device of the present invention will be described.

FIG. 21 is a system configuration showing up to the data processing unit of the optical disk device. In the figure, the medium and the drive unit are composed of an optical disk 300, an optical head 10, a spindle motor 900, and a course actuator 700. The drive control system 600 controls the drive unit and performs signal processing. The drive control system 600 sends an operation command to each control system of a spindle control system 611, a focus control system 612, a tracking control system 613, and a course actuator control system 614. Further, the drive control system 600, when recording data on the optical disk 300, uses the optical head 1
The recording signal 660 modulated to 0 is sent. The focus shift detection method of the present invention comprises an optical system in the optical head 10 and a focus shift detection system 650 including a circuit for reading the optical system. The drive control system 600 detects the focus shift amount and the track shift amount from the focus shift detection system 650 and the track shift detection system 651, respectively. The system control system 605 sends an operation command to the drive control system 600, receives a reproduction signal from the optical disc, and performs error correction or the like. Further, the system control system 605 also controls the interface when connecting to an external computer or the like. The spindle control system 611 controls the number of rotations of the spindle motor 900, and the number of rotations control includes CAV control, CLV control, MCAV control, MCLV control, etc., which should be appropriately selected according to the optical disc format. You can

FIG. 22 shows an embodiment in which the optical disk device of the present invention is used as an external memory of a personal computer. The data processing section of the personal computer is the Procese unit 18
20 and a semiconductor main memory 1840, and a keyboard 1850 and a display 1810 are connected via a system bus 1860. The feature of this embodiment is that the optical disk device 800 of the present invention is further connected via an interface 1830. In point. The optical disc medium 300 has an outer diameter of 64 mm (about 2.5 inches) and a capacity of 1
It has a large capacity of over 00MB, which enables large-scale data processing similar to a workstation even though it is a personal computer. Since the optical disc medium 300 can be attached to and detached from the optical disc device 800, only the processed data can be stored in the optical disc medium and can be easily carried.

FIG. 23 shows an embodiment in which the optical disk device of the present invention is built in a notebook computer. The notebook computer 1800 includes a liquid crystal display 1810 and a keyboard 1850 and incorporates the optical disk device 800 of the present invention. Optical disk medium 30
When 0 is set in the optical disc device 800, the recorded information can be reproduced by the notebook computer and the edited result can be stored in the optical disc medium 300.

[0054]

According to the present invention, the reproduction signal from the information pit of the optical disk is detected by the two photodetectors, and the peak positions of the waveforms of the two photodetectors are deviated with time due to the defocusing, so that the focusing is performed. The amount of deviation can be detected. According to the present invention, the detection optical system of the optical head can be simplified and the accuracy required for position adjustment of the photodetector can be relaxed, so that the optical head can be made smaller and lighter.

By using this optical head, it is possible to realize a small-sized, lightweight, low-cost optical disk device and an information processing device equipped with the same.

[Brief description of drawings]

FIG. 1 shows an example of an optical head suitable for the present invention.

FIG. 2 is a schematic diagram illustrating the principle of focus shift detection using a phase difference method.

FIG. 3 is a schematic diagram showing reflected light from an optical disc.

FIG. 4 is a diagram showing a reproduction signal of a pit of an optical disc.

FIG. 5 is a diagram showing a reproduction signal according to the focus shift detection method of the present invention.

FIG. 6 is a diagram showing characteristics of focus shift detection according to the present invention.

FIG. 7 is a diagram showing a concept of a differential integration method.

FIG. 8 is a diagram showing a waveform of a differential output.

FIG. 9 is a diagram showing a focus shift detection characteristic by a differential integration method.

FIG. 10 is a diagram showing a focus shift detection characteristic by a time difference method.

FIG. 11 is a diagram showing a focus shift detection characteristic by a differential integration method.

FIG. 12 shows an example of an optical head suitable for the present invention.

FIG. 13 shows an example of an optical head suitable for the present invention.

FIG. 14 shows an example of an optical head suitable for the present invention.

FIG. 15 shows an example of an optical head suitable for the present invention.

FIG. 16 is a block diagram showing one configuration of a focus shift detection circuit.

FIG. 17 is a block diagram showing another configuration of a focus shift detection circuit.

FIG. 18 is a schematic diagram showing a format of an optical disc suitable for the present invention.

FIG. 19 shows an example of an optical disc medium suitable for the present invention.

FIG. 20 shows an example of an optical disk medium suitable for the present invention.

FIG. 21 shows an embodiment of the optical disk device of the present invention.

FIG. 22 is an embodiment when the optical disk device of the present invention is connected to an information processing device.

FIG. 23 is an embodiment of a notebook type information processing device equipped with the optical disk device of the present invention.

[Explanation of symbols]

10 ... Optical head, 20 ... Semiconductor laser, 50 ... Objective lens, 70 ... Photodetector, 650 ... Defocus detection system,
800 ... Optical disk device.

Claims (6)

[Claims] 1. An optical system in which laser light emitted from a light source is condensed by an objective lens to form a minute light spot on an information track of an optical disk medium, and reflected light from the optical disk medium is received by a photodetector. A method for detecting a focus shift of an optical disc device having a system for recording or reproducing information on the optical disc medium, wherein a diffraction order in a direction along the information track of the light diffracted by the optical disc medium is + 1st order or more. Of the light of the first photodetector, and the light of which the diffraction order is -1st order or less is
Of the pit-shaped or strip-shaped information recording marks that are detected and photoelectrically converted into the first and second reproduction signals and are formed on the optical disc medium with a change in phase or reflectance. A focus shift detection method characterized by detecting a time shift between the first and second reproduction signals obtained from at least one and converting it into a focus shift amount. 2. An optical system in which laser light emitted from a light source is condensed by an objective lens to form a minute light spot on an information track of an optical disc medium, and reflected light from the optical disc medium is received by a photodetector. A method for detecting a focus shift of an optical disc apparatus having a system for recording or reproducing information on the optical disc medium, wherein a high-order diffracted light diffracted out of the aperture of the objective lens is reflected light from the optical disc. , A phase or reflection formed on the optical disc medium by receiving light by the first and second photodetectors arranged in the direction along the information track and photoelectrically converting into first and second reproduction signals, respectively. The focus is detected by detecting a time shift between the first and second reproduction signals obtained from at least one of the pit-shaped or band-shaped information recording marks accompanied by the rate change. Focus deviation detecting method characterized by converting the shift amount. 3. An optical system in which a laser beam emitted from a light source is condensed by an objective lens to form a minute light spot on an information track of an optical disc medium, and reflected light from the optical disc medium is received by a photodetector. A method for detecting a focus shift of an optical disc apparatus having a system for recording or reproducing information on the optical disc medium, wherein a high-order diffracted light diffracted out of the aperture of the objective lens is reflected light from the optical disc. , A phase formed on the optical disc medium, which is received by first and second photodetectors arranged in a direction along the information track and photoelectrically converted into first and second reproduction signals, respectively. The difference between the first and second reproduction signals obtained from at least one of the pit-shaped or band-shaped information recording marks accompanied by reflectance changes is calculated and integrated temporally to obtain the difference. An integration amount is obtained, and the differential integration amount is detected at the time when the center of the light spot and the center of the information recording mark match in the track direction, and is converted to a focus deviation amount. Method. 4. An optical disc medium having a light source, an objective lens for condensing laser light emitted from the light source, an information track on which the condensed light is irradiated by the objective lens, and reflected light from the optical disc medium. In an optical disc device including an optical system having a photodetector for receiving light, a deviation amount detecting unit for detecting high-order diffracted light at a position outside the opening of the objective lens at a target position in the lens center, Control means having a computing means for calculating a focus shift amount using the output of the detection means, and information detection means for detecting light diffracted into the aperture of the objective lens among reflected light from the optical disc. An optical disc device comprising: 5. The optical disk device according to claim 4, wherein the shift amount detecting means includes an optical path separating means and an optical sensor for detecting light. 6. An optical disk medium having a light source, an objective lens for condensing a laser beam emitted from the light source, an information track on which the condensed light is irradiated by the objective lens, and an outside of an opening of the objective lens. Of the displacement amount detecting means for detecting higher-order diffracted light at a target position in the center of the lens, and information detection for detecting light diffracted in the aperture of the objective lens among reflected light from the optical disc. Means and the output of the shift amount detecting means, information is reproduced from the output of the calculating means and the information detecting means for calculating the focus shift amount, and the light source, the optical disc medium, the objective lens and the like are driven and controlled. It has a control means, an input means for the user to input information from the outside to the processor, and an output means for outputting the information processed by the processor to the user. Broadcast processing apparatus.