JPH0757271A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To reproduce optical information stored on an optical storage medium of an optical disk or an optical card, etc. CONSTITUTION:An objective lens is designed so that a square root mean w1 of a wave front aberration provided in a beam 70 converged on an information recording surface 4a becomes 0.07lambda or below when the thickness of the optical storage medium 4 is d1. When the thickness of the optical storage medium 4 is d2, a converged spot 7b is formed on the information recording surface 4b in the state of being defocused slightly. Although the wave front aberration provided in the whole converged spot 7b becomes larger than the wave front aberration provided in the spot 7c placing on a converged point, light quantity is concentrated to a central part relatively, and in a response characteristic at the time of reading the information recorded as a minute mark and space, the converged spot 7b becomes excellent more than the 7c.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information reproducing method for reproducing optical information stored on an optical storage medium such as an optical disk or an optical card.

[0002]

2. Description of the Related Art Optical memory technology using an optical disk having a pit-shaped pattern as a high-density and large-capacity storage medium includes digital audio disk (hereinafter referred to as DAD), video disk, document file disk, and data file disk. It has been put to practical use while expanding its applications. The mechanism of an optical information device in which recording / reproducing of information to / from an optical disk via a light beam focused on the order of microns is successfully performed with high reliability is due to the optical pickup head device, which is its optical system. ing. The basic functions of the optical pickup head device are roughly classified into a light converging property for forming a minute spot of diffraction limit, focus control and tracking control of the optical system, and pit signal detection. These are realized by a combination of various optical systems and photoelectric conversion detection methods according to the purpose and application. Taking the DAD as an example, the track pitch is 1.6 μm, the shortest pit length is 0.85 μm, and the pit width is 0.
In order to read information of 5 μm, the wavelength of the light source λ = 0.78
˜0.83 μm, NA of objective lens = 0.45 to 0.5
It is necessary to use a beam that is focused to the diffraction limit using some optics. At this time, the thickness of the substrate of the optical storage medium is 1.2 mm. By using a coherent laser light (light having a wave having a uniform phase) and a high-performance condenser lens as the light source, the spot diameter S condensed to the diffraction limit is about 1 μm. The spot diameter S is proportional to the wavelength λ of the light source and inversely proportional to NA. In order to realize a minute beam focused to the diffraction limit, the aberration of the entire focusing optical system of the optical pickup head device needs to be 0.07λ or less. It is well known that this diffraction limit condition is called the Marshall limit. Regarding the characteristics when the beam is condensed by the condensing optical system, for example, the optical disc technology pp published by Radio Technology Co., Ltd.
54-62.

In recent years, the wavelength of the light source has been shortened, for example, λ = 0.
6 to 0.7 μm, the NA of the objective lens is large, for example, N
Attempts have been made to reduce the size of the diffraction limit spot and to record / reproduce information at a higher density with A = 0.6. At this time, the quality of the signal read by the optical pickup head device is rapidly deteriorated due to the thickness error or inclination of the substrate, and therefore, attempts have been made to reduce the thickness of the substrate. The thickness of the substrate at this time is, for example, 0.6.
In mm, the thickness is half that of DAD. At this time,
The optical storage medium has a track pitch of 0.7 to 1.0 μm, a shortest pit length of 0.4 to 0.6 μm, and a pit width of 0.3 to 0.
It is possible to read information recorded at high density up to about 4 μm.

As an example of a conventional optical pickup head device, FIG. 16 shows a structure of an optical pickup head device 27 for converging a beam on the optical storage medium 4 and reading information recorded on the optical storage medium 4. The optical pickup head device 27 includes a semiconductor laser light source 1, a parallel plate 7, a finite system objective lens 17, a photodetector 51, a focus control actuator 91, and a tracking control actuator 92.

A divergent beam 70 having a linearly polarized light emitted from the semiconductor laser light source 1 is reflected by the parallel plate 7 and then transmitted through the finite system objective lens 17 onto the information recording surface 43 of the optical storage medium 4. Collected. The beam 70 reflected and diffracted by the information recording surface 43 of the optical storage medium 4 passes through the objective lens 17 again and then enters the parallel plate 7. Parallel plate 7
The beam 70 that is incident on is given an astigmatic wavefront when passing through the parallel plate 7, and then received by the photodetector 51. Using the signal output from the photodetector 51, a focus error signal, a tracking error signal, and a read signal of information recorded in the optical storage medium can be obtained. The focus error signal and the tracking error signal are supplied to the focus control actuator 91 and the tracking control actuator 92, respectively, and the focus control actuator 91 outputs the beam 70 emitted from the optical pickup head device 27 onto the optical storage medium 4. The tracking control actuator 92 scans the desired track of the optical storage medium 4 with the beam 70 emitted from the optical pickup head device 27 so that the focus position of the objective lens 17 is focused on the desired track. The position of the beam within the information recording surface 43 of the optical storage medium 4 is controlled so that

[0006]

However, an optical storage medium having a substrate thickness d of 1.2 mm, such as a DAD, and an optical storage medium having a high density information recorded substrate having a thickness d of 0.6 mm. There is no concept of reproducing the medium and one optical information device, and, up to now, an optical information device having an optical pickup head device for converging the beam to the diffraction limit for each substrate thickness. Was used to reproduce the information recorded on the optical storage medium.

If the optical information device is provided with a plurality of optical pickup head devices for converging the beams up to the diffraction limit with respect to the thickness of each substrate, the optical information device becomes large accordingly. Further, when the beam of one optical pickup head device is divided and a plurality of condensing optical systems for condensing the beams to the diffraction limit are provided for the thicknesses of the respective substrates, the condensing is performed by that amount. The light amount of the beam to be read decreases, and the SN ratio of the read signal decreases. Further, the optical pickup head device having a plurality of condensing optical systems has a complicated optical system, which causes a problem that the optical pickup head device becomes expensive.

In view of the above problems, the present invention provides information recorded on optical storage media having different substrate thicknesses.
It is an object of the present invention to provide an optical information reproducing method which enables reproduction by using an optical pickup head device having two condensing optical systems.

[0009]

In order to solve the above-mentioned problems, the present invention receives a coherent beam or a quasi-monochromatic beam emitted from a light source by a condensing optical system to form a minute spot on an optical storage medium. In the optical information reproducing method of reproducing the information recorded on the optical storage medium by receiving the beam reflected and diffracted by the optical storage medium by the photodetector after converging the beam, the beam emitted from the light source is Wavelength is λ
And the minimum and maximum optical thicknesses of the optical storage medium are d1 and d2, respectively, and the thickness of the optical storage medium is d.
When it is 1, the recording density of the information recorded on the optical storage medium in the track direction or the direction orthogonal to the track is j.
1 and j2 is the recording density of information in the track direction or in the direction orthogonal to the tracks recorded on the optical storage medium when the thickness of the optical storage medium is d2, j1
> J2, and when the thickness of the optical storage medium is d1, the root mean square of the wavefront aberration of the beam condensed on the optical storage medium by the condensing optical system is set to w1. When the thickness is d2 and w2 is the root mean square of the wavefront aberration of the beam condensed on the optical storage medium by the condensing optical system, w1 <w2 and w2> 0.07λ. The size of the beam focused on the optical storage medium having the optical thickness d1 is such that the information recorded on the optical storage medium having the optical thickness d1 can be read. To be

[0010]

In the above-described optical information reproducing method, one beam condensed by the same condensing optical system is used to record on the information recording surface of the optical storage medium with a thin substrate of the optical storage medium. When the information recording density is high, the wavefront aberration of the focused beam is smaller than that when the substrate of the optical storage medium is thick, and the information recorded on the information recording surface of the optical storage medium is reproduced. can do.

On the other hand, when the optical storage medium is thick,
Although the focused beam has a larger wavefront aberration than when the optical storage medium is thin, the recording density of the information recorded on the information recording surface of the optical storage medium is low, and the information is recorded on the optical storage medium. It is possible to reproduce the information that has been recorded.

That is, the information recorded on the optical storage medium is greatly different in the recording density of the information recorded on the optical storage medium and the optical thickness of the substrate of the optical storage medium. The optical information reproducing method can be read by using the pickup head device.

[0013]

Embodiments of the optical information reproducing method according to the present invention will be described in detail below with reference to FIGS.
It should be noted that the same numbers are assigned when the same components can be used.

(First Embodiment) As an embodiment of the present invention, an information recording surface 4a or 4b of an optical storage medium 4 is shown in FIG.
The configuration of an optical pickup head device 21 for converging a beam on the top and reading the information recorded on the information recording surface 4a or 4b of the optical storage medium 4 is shown. The optical pickup head device 21 includes a semiconductor laser light source 1, a collimator lens 2, a polarization beam splitter 3, and a quarter wavelength plate (hereinafter, λ /
4 plates) 9, an objective lens 8, a photodetector 5, a focus control actuator 91, and a tracking control actuator 92.

The semiconductor laser light source 1 has a wavelength λ = 6, for example.
A coherent beam of 80 nm is emitted. Divergence beam 7 having linearly polarized light emitted from semiconductor laser light source 1
0 becomes a parallel beam after passing through the collimator lens 2,
It is reflected by the polarization beam splitter 3. The beam reflected by the polarization beam splitter 3 passes through the λ / 4 plate 9 to become a circularly polarized beam, passes through the objective lens 8 and is focused on the information recording surface 4a or 4b of the optical storage medium 4. .
The polarization beam splitter 3 reflects 100% of a beam having the same polarization as the beam 70 emitted from the light source 1, and transmits 100% of a beam having a polarization orthogonal to the beam 70 emitted from the light source 1. It has the characteristics to Therefore, the entire beam 70 emitted from the light source 1 and directed to the optical storage medium 4 is reflected by the polarization beam splitter 3 without being transmitted. The beam 70 reflected and diffracted by the optical storage medium 4 becomes a linearly polarized beam having a 90 ° polarization direction different from the beam emitted from the light source 1 after passing through the objective lens 8 and then the λ / 4 plate 9. , Enters the polarization beam splitter 3. The beam 70 incident on the polarization beam splitter 3 is entirely transmitted and then received by the photodetector 5. The information recorded on the optical storage medium 4 is reproduced by using the signal output from the photodetector 5.

Assuming that the minimum and maximum thicknesses of the substrate of the optical storage medium 4 are d1 and d2, respectively, in the present embodiment, d1 = 0.6 mm and d2 = 1.2 mm, and the substrate of the optical storage medium 4 is set. Has a refractive index n of 1.57. The material of the substrate is polycarbonate. Digital information represented by marks or spaces is recorded on the information recording surface 4a or 4b of the optical storage medium 4. When the substrate of the optical storage medium 4 is thick (1.2 mm), the length of the shortest mark and space is 0.85 μm, the track pitch is 1.6 μm, and the substrate of the optical storage medium 4 is thin. (0.6 mm), the length of the shortest mark and space is 0.5 μm, and the track pitch is 0.75 μm.
I am trying. That is, the recording density of the information recorded on the information recording surface of the optical storage medium 4 is lower when the substrate of the optical storage medium 4 is thicker than when it is thin.

The NA of the objective lens constituting the optical pickup head device is 0.6, and when the thickness of the optical storage medium is thin (0.6 mm), the wavefront aberration of the beam focused on the optical storage medium. Root mean square w1 is 0.07
It is an aspherical lens designed to be λ or less. When the thickness of the optical storage medium is large (1.2 mm), the root mean square w2 of the wavefront aberration of the beam focused on the optical storage medium becomes 0.07λ or more. The spherical aberration is dominant in the aberration at this time.

FIG. 2 shows a state of the beam 70 focused on the information recording surfaces 4a and 4b of the optical storage medium 4. When the thickness of the optical storage medium 4 is thin (d1 = 0.6 mm), the root mean square w1 of the wavefront aberration of the beam 70 focused on the information recording surface 4a of the optical storage medium 4 is 0.07λ or less. Since the objective lens 8 is designed so that the focused spot 7a of the beam 70 formed on the information recording surface 4a is a spot narrowed to the size of the diffraction limit. The substrate of the optical storage medium 4 is thin (d1 = 0.6 m
m) sometimes the length of the shortest mark and space is 0.5
Although the information recording density is increased up to .mu.m and the track pitch is about 0.75 .mu.m, the focused spot 7a is narrowed down to the diffraction limit, and the wavelength of the light source 1 is .lamda. = 680 nm.
Since NA of the objective lens 8 is set to 0.6, the information recorded on the optical storage medium 4 can be read.

On the other hand, the optical storage medium 4 is thick (d2 =
1.2 mm), sometimes the information recording surface 4 of the optical storage medium 4
Since the root mean square w2 of the wavefront aberration of the beam 70 focused on b is 0.07λ or more, the focused spot of the beam 70 formed on the information recording surface 4b has a large diffraction limit. It is not a spot that has been narrowed down to that size.
In the embodiment of the present invention, the focused spot 7b is formed on the information recording surface 4b of the optical storage medium 4 in a slightly defocused state. At this time, the wavefront aberration of the entire focused spot 7b is due to the spot 7c located at the focusing point.
However, the light amount is relatively concentrated in the central portion, and the response characteristic when reading information recorded as minute marks and spaces is that of the focused spot 7c.
7b is better than 7b. Both spots 7b and 7c
It has a spherical aberration larger than 0.07λ and a relatively large side rope. When the substrate of the optical storage medium 4 is thick (d2 = 1.2 mm), the length of the shortest mark and space is 0.85 μm, and the track pitch is about 1.6 μm. , Wavelength of light source 1 = 680 nm, NA of objective lens 8
Is smaller than the maximum recording density that can be read as = 0.6, and the beam 70 emitted from the light source 1 is not condensed to the diffraction limit on the information recording surface 4b of the optical storage medium 4, The information recorded on the information recording surface 4b of the optical storage medium 4 can be read.

When the recording density of the information recorded on the information recording surface of the optical storage medium 4 is high, the optical thickness of the optical storage medium is thin (d1 = 0.6 mm), and When the recording density of the information recorded on the optical recording medium is low and the optical thickness of the optical storage medium is large (d2 = 1.2 mm), the focused beam has a wavefront aberration, and thus the focused beam of the focusing optical system is substantially reduced. Since the numerical aperture is small, no matter what the optical thickness of the optical storage medium,
The aberration that occurs when the optical axis is tilted is small, and the optical information reproducing method allows a large tilt of the optical axis.

FIG. 3 shows the state of the photodetector 5. The photodetector 5 includes eight light receiving units 501 to 508, and receives the beam 70 reflected and diffracted by the optical storage medium 4. Photo detector 5
The dividing line 31 which divides the light receiving portion of the optical disk is arranged so that its direction substantially coincides with the mapping of the track of the optical storage medium 4 on the beam 70.

In this embodiment, the focus error signal and the tracking error signal are obtained by the phase difference method. The methods for detecting the focus error signal and the tracking error signal by the phase difference method are well known and will not be described in detail. The focus error signal is received by the light receiving units 501, 50.
When the sum of the signals output from 3, 506 and 508 is the first signal and the sum of the signals output from the light receiving units 502, 504, 505 and 507 is the second signal, the first signal and the first signal This can be detected by comparing the timings at which the intensity of the signal 2 changes. On the other hand, the tracking error signal is
The sum of the signals output from the light receiving units 501, 502, 505, 506 is the first signal, and the light receiving units 503, 504, 5
When the sum of the signals output from 07 and 508 is the second signal, it can be detected by comparing the timings at which the intensities of the first signal and the second signal change. The focus error signal and the tracking error signal are supplied to the focus control actuator 91 and the tracking control actuator 92 of the optical pickup head device 21 shown in FIG. 1, respectively, and the focus control actuator 91 is emitted from the optical pickup head device 21. The tracking control actuator 92 adjusts the focus position of the objective lens 8 so that the focused beam 70 focuses on a desired track on the information recording surface of the optical storage medium 4.
1 so that the beam 70 emitted from the optical disc 1 scans a desired track on the information recording surface of the optical storage medium 4.
The positions of the beams in the information recording surface of are controlled respectively. The information recorded on the information recording surface of the optical storage medium 4 is obtained by the sum of the signals output from the light receiving units 501 to 508.

(Second Embodiment) As another embodiment of the present invention, a beam is focused on the information recording surface of the optical storage medium 4 in FIG. 4 and recorded on the information recording surface of the optical storage medium 4. The structure of an optical pickup head device 22 for reading information is shown. The optical storage medium 4 is similar to that of the first embodiment. The optical pickup head device 22 includes a semiconductor laser light source 1, a parallel plate 7,
Finite system objective lens 10, photodetector 51, focus control actuator 91, tracking control actuator 9
It consists of two.

A divergent beam 70 having a linearly polarized light emitted from the semiconductor laser light source 1 is reflected by the parallel plate 7 and then transmitted through the finite system objective lens 10 to form the information recording surface 4a or 4b of the optical storage medium 4. Focused on top. In the first embodiment, using the polarization beam splitter 3 and the λ / 4 plate 9, the beam 70 emitted from the light source 1 travels toward the optical storage medium 4 and the beam 70 reflected by the optical storage medium 4 is generated. Although the return path toward the photodetector 51 was completely and efficiently separated, in this embodiment, the optical system is simplified by using the parallel plate 7 and the finite system objective lens 10. The parallel plate 7 is a half mirror so that the transmittance and the reflectance are respectively 50%, and the beam 70 emitted from the light source 1 is reflected by the information recording surface 4a or 4b of the optical storage medium 4 and Although the transmission efficiency of the light incident on the detector 51 becomes poor, the polarization beam splitter and the λ / 4 plate can be omitted.
Further, the objective lens 10 is a finite system so that the collimator lens can be omitted. The beam 70 reflected and diffracted by the information recording surface 4a or 4b of the optical storage medium 4
After passing through the objective lens 10 again, enters the parallel plate 7. When the beam 70 incident on the parallel plate 7 is transmitted through the parallel plate 7, an astigmatic wavefront is given to the beam 70 and then the photodetector 5 is received.
Light is received at 1. The information recorded on the optical storage medium 4 is reproduced using the signal output from the photodetector 51.

Also in this embodiment, as in the first embodiment, the NA of the objective lens 10 constituting the optical pickup head device 22 is 0.6, and the substrate of the optical storage medium 4 is thin (d1). = 0.6 mm), the aspherical lens is designed so that the root mean square w1 of the wavefront aberration of the beam 70 focused on the information recording surface 4a of the optical storage medium 4 is 0.07λ or less. . When the substrate of the optical storage medium 4 is thick (d2 = 1.2 mm), the root mean square w2 of the wavefront aberration of the beam 70 focused on the information recording surface 4b of the optical storage medium 4 is 0. It becomes 07λ or more.
The state of the beam 70 focused on the information recording surface 4a or 4b of the optical storage medium 4 is the same as that of the beam 70 shown in FIG. 2 of the first embodiment. Also in the case of this embodiment, the substrate thickness of the optical storage medium 4 is thin (d1) as in the first embodiment.
= 0.6 mm) or thick (d2 = 1.2 mm), one focused beam 70 can be used to read the information recorded on the information recording surface 4a or 4b of the optical storage medium 4.

FIG. 5 shows the state of the photodetector 51. The photodetector 51 includes four light receiving units 509 to 512, and receives the beam 70 reflected and diffracted by the optical storage medium 4. The dividing line 32 that divides the light receiving portion of the photodetector 51 is arranged so that its direction substantially coincides with the mapping of the track of the optical storage medium 4 on the beam 70.

In this embodiment, the focus error signal is obtained by the astigmatism method and the tracking error signal is obtained by the push-pull method. A method of detecting a focus error signal by the astigmatism method is disclosed in, for example, Japanese Patent Application Laid-Open No. 50-99561, and a method of detecting a tracking error signal by the push-pull method is disclosed in, for example, Japanese Patent Application Laid-Open No. 49-60702. Detailed description is omitted. The focus error signal is the first signal when the sum of the signals output from the light receiving units 509 and 511 is the first signal and the sum of the signals output from the light receiving units 510 and 512 is the second signal. It can be detected by performing a differential operation on the second signal. on the other hand,
For the tracking error signal, the sum of the signals output from the light receiving units 509 and 512 is used as the first signal, and the light receiving units 510 and 5
When the sum of the signals output from 11 is used as the second signal,
It can be detected by performing a differential operation on the first signal and the second signal. The information recorded on the optical storage medium 4 is stored in the light receiving unit 5
It is obtained by the sum of the signals output from 09 to 512.

FIG. 6 shows the focus error signal obtained in this embodiment. The horizontal axis represents the relative distance between the objective lens 10 and the optical storage medium 4, and the vertical axis represents the intensity of the focus error signal. When the substrate of the optical storage medium 4 is thin (d1 = 0.6 mm), no offset voltage is applied so that focus control is performed at the operating point D1, and the substrate of the optical storage medium 4 is thick (d2).
= 1.2 mm), the offset voltage A is applied to the focus error signal so that focus control is performed at the operating point D2. The thickness of the substrate of the optical storage medium 4 is large (d2 = 1.2 m
m), the offset voltage A is given to the focus error signal to correct the offset generated in the focus error signal due to the difference in the thickness of the substrate of the optical storage medium 4, and the defocus state as shown in FIG. It is possible to give it to a focused spot.

(Third Embodiment) As yet another embodiment of the present invention, a beam is focused on the information recording surface of the optical storage medium 4 in FIG. 7 and recorded on the information recording surface of the optical storage medium 4. The structure of the optical pickup head device 23 for reading the recorded information is shown. The optical storage medium 4 is similar to that of the first embodiment. The optical pickup head device 23 includes a semiconductor laser light source 1, a collimator lens 2, a polarization beam splitter 3, an objective lens 8, a λ / 4 plate 9, a beam splitter 12, and a cylindrical lens 1.
3, 14, condenser lenses 15, 16, photodetectors 51a, 5
1b, a focus control actuator 91, and a tracking control actuator 92.

The beam 70 emitted from the semiconductor laser light source 1 is focused on the information recording surface 4a or 4b of the optical storage medium 4, and is reflected and diffracted by the optical storage medium 4
To the point where 0 passes through the polarization beam splitter 3,
This is exactly the same as the first embodiment. The beam 70 transmitted through the polarization beam splitter 3 enters the beam splitter 12 and is split into two beams 71 and 72. Beam 7
After the astigmatic wavefront is given by the cylindrical lens 13, 1 is condensed by the condenser lens 15 and received by the photodetector 51a. On the other hand, the beam 72 is provided with an astigmatic wavefront by the cylindrical lens 14, is then condensed by the condenser lens 16, and is received by the photodetector 51b. The photodetectors 51a and 52b are the same as the photodetector 51 shown in the second embodiment. Also in this embodiment, as in the second embodiment, the focus error signal is obtained by the astigmatism method and the tracking error signal is obtained by the push-pull method.

Also in this embodiment, as in the first embodiment, the NA of the objective lens 8 constituting the optical pickup head device 23 is 0.6, and the substrate of the optical storage medium is thin (d1 =). 0.6 mm), the aspherical lens is designed so that the root mean square w1 of the wavefront aberration of the beam 70 focused on the information recording surface 4a of the optical storage medium is 0.07λ or less. When the substrate of the optical storage medium is thick (d2 = 1.2 mm), the root mean square w2 of the wavefront aberration of the beam 70 focused on the information recording surface 4b of the optical storage medium 4 is 0.07λ. That is all. In the case of this embodiment, as in the first embodiment, when the substrate of the optical storage medium 4 is thin (d1 = 0.6 mm), it is thick (d2 = 1.
2 mm), it is possible to read the information recorded on the information recording surface 4a or 4b of the optical storage medium 4 using one converging beam 70.

FIG. 8 shows a focus error signal obtained in this embodiment. The horizontal axis represents the relative distance between the objective lens 8 and the optical storage medium 4, and the vertical axis represents the intensity of the focus error signal. The focus error signal FE1 is obtained using the signal output from the photodetector 51a, and the focus error signal FE2 is obtained using the signal output from the photodetector 51b. The condenser lenses 15 and 16 shown in FIG. 7 are arranged so that the operating points D1 and D2 are located at the zero cross points of the respective focus error signals.
The focus position of is adjusted.

In this embodiment, when the substrate of the optical storage medium 4 is thin (d1 = 0.6 mm), the focus error signal F
Focus control is performed using E1, and when the substrate of the optical storage medium 4 is thick (d2 = 1.2 mm), focus control is performed using the focus error signal FE2. By switching and using a plurality of focus error signals, the offset generated in one focus error signal due to the difference in the thickness of the substrate of the optical storage medium 4 is corrected, and the defocus state as shown in FIG. 2 is condensed. It is possible to give to the spot. When the optical system according to the present embodiment is used, an offset voltage is not added to the focus error signal, so that the focus control range can be widened and playability when disturbance occurs is improved.

In the first to third embodiments, the focus error signal is detected by the phase difference method and the astigmatism method, and the tracking error signal is detected by the phase difference method and the push-pull method. The error signal can be applied to the optical information reproducing method of the present invention without any problems, such as the spot size detection method and the Foucault method, and the tracking error signal such as the three-beam method and the wobbling method.

As for the light source, the example of the semiconductor laser light source has been described, but various other light sources such as a light source for generating a second harmonic wave by using a non-linear crystal to obtain a shorter wavelength beam can be applied. it can. Of course, there is no problem in using a hologram element as a beam splitter or an element that provides a wavefront that enables detection of a focus error signal.

The thickness of the substrate of the optical storage medium is 0.6 m.
Also, m and 1.2 mm are merely examples, and the thickness of another substrate may be used.

Various modifications can be made without departing from the spirit of the present invention. (Fourth Embodiment) As yet another embodiment of the present invention, FIG. 9 shows an optical pickup head device 24 for converging a beam on an information recording surface of an optical storage medium 4 to read information recorded on the optical storage medium. Shows the configuration of. The optical storage medium 4 is similar to that of the first embodiment. The optical pickup head device 24 includes a semiconductor laser light source 1, a collimator lens 2, a polarization beam splitter 3, an objective lens 8, a λ / 4 plate 9, a beam splitter 12, photodetectors 5 and 52, a condenser lens 16, and focus control. It includes an actuator 91 and a tracking control actuator 92.

The beam 70 emitted from the semiconductor laser light source 1 is focused on the information recording surface 4a or 4b of the optical storage medium 4 and is reflected and diffracted by the optical storage medium 4.
0 passes through the polarization beam splitter 3 and enters the beam splitter 12, and the beam 70 is divided into two beams 71, 72.
It is completely the same as the third embodiment up to the point where it is divided into. The beam 71 is received by the photodetector 5. On the other hand, the beam 72 is condensed by the condenser lens 16, and the light detector 5
The beam 72 is received by the photodetector 72 so that the beam 72 is focused on the second light receiving surface. The method of detecting the focus error signal and the tracking error signal is the same as in the first embodiment. The photodetector 52 has an aperture 60 on its light-receiving surface, and has an aperture of the same size as the beam 72 condensed by the condenser lens 16. The information recorded on the information recording surface 4a or 4b of the optical storage medium 4 is detected by the photodetector 5
It is obtained by using the signal output from 2.

The optical storage medium is thick (d2 = 1.2 m
m), the root mean square w2 of the wavefront aberration of the beam focused on the information recording surface 4b of the optical storage medium 4 is 0.
Since the beam, which is as large as 07λ or more and is focused on the information recording surface 4b of the optical storage medium 4, becomes a focused spot having a relatively large side rope, the information recording surface 4 of the optical storage medium 4 is
Crosstalk and intersymbol interference occur when reading the information recorded on b.

In this embodiment, since the beam 72 is focused on the light receiving surface of the photodetector 52, the light source 1, the optical storage medium 4, and the photodetector 52 are so-called confocal optics. The components of the crosstalk and the intersymbol interference are blocked by the aperture 60 located on the light receiving surface of the photodetector 52, and the crosstalk and the intersymbol interference included in the signal obtained from the photodetector 52. The ingredients are greatly reduced. Therefore, according to the optical information reproducing method of the present embodiment, it becomes possible to reproduce the information recorded on the information recording surface 4b of the optical storage medium 4 with extremely high reliability.

In this embodiment, an example in which the aperture 60 is arranged on the light receiving surface of the photodetector 52 has been described.
For example, a method in which the size of the light receiving portion of the photodetector is formed in advance, a non-linear transmissive film is arranged on the light receiving surface of the photodetector, or the like, the aperture of the photodetector is substantially limited. Any photodetector can be applied in place of the photodetector 52 shown in the embodiment of the present invention without any problem. In the present invention, the method of limiting the aperture of the photodetector is not restricted at all, and it becomes possible to reproduce the information recorded on the optical storage medium with high reliability.

(Fifth Embodiment) As a further embodiment of the present invention, FIG. 10 shows the configuration of an optical information device for reducing crosstalk. The signal output from the optical pickup head device 25 is input to the crosstalk reducing unit 61, the crosstalk included in the signal output from the optical pickup head device 25 is reduced, and the crosstalk from the output terminal 45 is reduced. Signal is output.

FIG. 11 shows the structure of the photodetector 53, and FIG. 12 shows the structure of the crosstalk reducing means. For example, the optical pickup head device 25 can be constructed by replacing the photodetector 53 with the photodetector 51 constituting the optical pickup head device 22 shown in FIG. Photo detector 5
The dividing line 32 of 1 is the dividing line 33 of the photodetector 53, the light receiving section 509 of the photodetector 51 is the light receiving section 517 of the photodetector 53,
At 518, the light receiving section 510 of the photodetector 51 is connected to the photodetector 53.
To the light receiving portions 519 and 520 of the
1 is the light receiving portions 513 and 514 of the photodetector 53, and the light receiving portion 512 of the photodetector 51 is the light receiving portions 515 and 5 of the photodetector 53.
16 corresponds to 16 respectively, and the focus error signal and the tracking error signal are detected as in the second embodiment.

Light receiving portions 514, 515, 5 of the photodetector 53
The sum of the signals output from 18, 519 is used as the first signal, and the sum of the signals output from the light receiving units 513, 516, 517, 520 is used as the second signal. Enter in 47. The intensity of the signal input to the input terminal 46 is adjusted by being amplified or attenuated by the gain adjusting means 80.
The adding unit 81 adds the signal applied to the input terminal 47 and the signal output from the gain adjusting unit 80 to reduce the crosstalk included in the signals input to the input terminals 46 and 47. The signal output from the adding means 81 is obtained from the output terminal 45.

In the fourth embodiment, the crosstalk is optically reduced, but in the present embodiment, the crosstalk is electrically reduced. Also in the optical information reproducing method shown in the present embodiment, it becomes possible to reproduce the information recorded on the optical storage medium with high reliability as in the fourth embodiment.

In this embodiment, an example of electrically realizing the crosstalk reducing means has been described. For example, a method of irradiating the optical storage medium with three beams and the like,
Even if the crosstalk reducing means having another structure is used, it can be applied to the optical information device of the present invention without any problem. That is, according to the present invention, the structure of the crosstalk reducing means is not restricted at all, and the information recorded on the information recording surface of the optical storage medium can be reproduced with high reliability.

(Sixth Embodiment) FIG. 13 shows the configuration of an optical information apparatus for reducing intersymbol interference, as yet another embodiment of the present invention. The signal output from the optical pickup head device 26 is input to the waveform equalizing means 62 that reduces intersymbol interference, the intersymbol interference included in the signal output from the optical pickup head device 26 is reduced, and the output terminal A signal with reduced intersymbol interference is output from 44.

The optical pickup head device 26 may be any type of optical pickup head device. For example, any of the optical pickup head devices 21 to 25 shown in the first to fifth embodiments may be used. it can.

FIG. 14 shows the structure of the waveform equalizing means 62.
The signal input to the input terminal 48 is divided into three signals. One is the same signal I1 as the signal inputted to the input terminal 48, one is the signal I2 which is given the delay time T by the delay means 82, and one is the delay time T which is given by the delay means 82 and 83 respectively. Signal I given a total delay time of 2T
It is 3. The signals I1 and I3 are supplied to the gain adjusting and adding means 84.
Then, the intensity is adjusted by adding or adding and then amplifying or attenuating. The differential operation means 85 uses the signal I
2 and the signal output from the gain adjusting and adding unit 84 are differentially calculated to reduce intersymbol interference included in the signal input to the input terminal 48. The signal output from the differential operation means 85 is obtained from the output terminal 44.

In this embodiment, intersymbol interference is electrically reduced, and this method is called a transversal filter, which is a generally well known method. Also in the optical information reproducing method shown in the present embodiment, by reducing the intersymbol interference, the information recorded on the optical storage medium can be recorded in the same manner as when the crosstalk is reduced in the fourth to fifth embodiments. It is possible to reproduce with high reliability.

In this embodiment, the example of the transversal filter which electrically realizes the waveform equalizing means has been described. For example, the photodetector of the crosstalk reducing means shown in the fifth embodiment is rotated 90 degrees. And how to achieve it,
The optical information device of the present invention can be applied without any problem even if a waveform equalizing means having another configuration such as a method of irradiating an optical storage medium with three beams is used. That is,
In the present invention, the information recorded on the information recording surface of the optical storage medium can be reproduced with extremely high reliability without any restrictions on the configuration of the waveform equalizing means.

(Seventh Embodiment) As a further embodiment of the present invention, FIG. 15 shows that both the crosstalk reducing means 61 and the waveform equalizing means 62 are used for the signal outputted from the optical pickup head device 25. 2 shows a block diagram of an optical information device. By using both the crosstalk reducing means 61 and the waveform equalizing means 62 to reduce both crosstalk and intersymbol interference, the optical information device is more highly reliable than the optical information devices shown in the fourth to sixth embodiments. It is possible to reproduce the information recorded on the information recording surface of the storage medium.

[0053]

As is apparent from the above description, according to the present invention, a coherent beam or a quasi-monochromatic beam emitted from a light source is received by a condensing optical system and converged into a minute spot on an optical storage medium. Then, in the optical information reproducing method of reproducing the information recorded on the optical storage medium by receiving the beam reflected and diffracted by the optical storage medium by the photodetector, the wavelength of the beam emitted from the light source is λ And the minimum and maximum optical thicknesses of the optical storage medium are d1 and d2, respectively, and when the thickness of the optical storage medium is d1, the track direction recorded on the optical storage medium or orthogonal to the track is recorded. The recording density of information in the direction of
When the recording density of the information recorded on the optical storage medium in the track direction or the direction orthogonal to the track is j2 when the thickness of the optical storage medium is d2, j1> j2, and the optical storage medium is Is d1, the root mean square of the wavefront aberration of the beam condensed on the optical storage medium by the condensing optical system is w1, and the thickness of the optical storage medium is d2.
At this time, when the root mean square of the wavefront aberration of the beam focused on the optical storage medium by the focusing optical system is w2,
1 <w2, w2> 0.07λ, and the size of the beam focused on the optical storage medium having the optical thickness d1 is on the optical storage medium having the optical thickness d1. By adopting an optical information reproducing method having a size capable of reading the information recorded on the optical storage medium, the recording density of the information recorded on the optical storage medium and the optical thickness of the optical storage medium are significantly different. The information recorded on the storage medium can be read using one focused beam. Therefore,
According to the optical information reproducing method of the present invention, the information recorded on the optical storage medium of different standards such as the thickness of the substrate of the optical storage medium and the recording density of information is reproduced by using the small optical pickup head device. It is possible to provide an optical information system having multiple functions.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical pickup head device showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the relationship between the optical storage medium and the focused spot showing the operation of the present invention.

FIG. 3 is a configuration diagram of a photodetector showing an embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical pickup head device showing another embodiment of the present invention.

FIG. 5 is a configuration diagram of a photodetector showing another embodiment of the present invention.

FIG. 6 is a waveform diagram showing a focus error signal showing the operation of the present invention.

FIG. 7 is a configuration diagram of an optical pickup head device showing another embodiment of the present invention.

FIG. 8 is a waveform diagram showing a focus error signal showing the operation of the present invention.

FIG. 9 is a configuration diagram of an optical pickup head device showing another embodiment of the present invention.

FIG. 10 is a block diagram showing the configuration of an optical information device showing another embodiment of the present invention.

FIG. 11 is a configuration diagram of a photodetector showing another embodiment of the present invention.

FIG. 12 is a circuit diagram showing a configuration of crosstalk reducing means showing another embodiment of the present invention.

FIG. 13 is a block diagram showing the configuration of an optical information device showing another embodiment of the present invention.

FIG. 14 is a circuit diagram showing the configuration of a waveform equalizing means showing another embodiment of the present invention.

FIG. 15 is a block diagram showing the configuration of an optical information device showing another embodiment of the present invention.

FIG. 16 is a configuration diagram of a conventional optical pickup head device.

[Explanation of symbols]

 1 Semiconductor Laser Light Source 2 Collimating Lens 3 Polarizing Beam Splitter 4 Optical Storage Medium 4a Information Recording Surface 4b Information Recording Surface 5 Photodetector 7 Parallel Plate 7a Focused Spot 7b Focused Spot 7c Focused Spot 8 Objective Lens 9 1/4 Wavelength Plate 10 Finite Objective Lens 12 Beam Splitter 13 Cylindrical Lens 14 Cylindrical Lens 15 Condenser Lens 16 Condenser Lens 17 Objective Lens 21 Optical Pickup Head Device 22 Optical Pickup Head Device 23 Optical Pickup Head Device 24 Optical Pickup Head Device 25 Optical Pickup Head Device 26 Optical pickup head device 27 Optical pickup head device 31 Divided line 32 Divided line 33 Divided line 43 Information recording surface 44 Output terminal 45 Output terminal 46 Input terminal 47 Input terminal 48 Input terminal 51 Photodetector 5 a photodetector 51b photodetector 52 photodetector 53 photodetector 60 aperture 61 crosstalk reducing means 62 waveform equalizing means 70 beam 71 beam 72 beam 80 gain adjusting means 81 adding means 82 delaying means 83 delaying means 84 gain adjusting Addition unit 85 Differential calculation unit 91 Focus control actuator 92 Tracking control actuator 501 Photodetector 502 Photodetector 503 Photodetector 504 Photodetector 505 Photodetector 506 Photodetector 507 Photodetector 508 Photodetector 509 Photodetector 510 Photodetector 511 Photodetector 512 Photodetector 513 Photodetector 514 Photodetector 515 Photodetector 516 Photodetector 517 Photodetector 518 Photodetector 519 Photodetector 520 Photodetector A Offset voltage d Thickness of substrate of optical storage medium d1 Light Thickness of substrate of storage medium d2 Thickness of substrate of optical storage medium D1 Operating point D2 Operating point FE1 Focus error signal FE2 Focus error signal I1 signal I2 signal I3 signal

Front page continued (72) Inventor Sadao Mizuno 1006 Kadoma, Kadoma-shi, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A coherent beam or a quasi-monochromatic beam emitted from a light source is received by a converging optical system, converged into a minute spot on an optical storage medium, and then a beam reflected and diffracted by the optical storage medium is converted into a beam. In an optical information reproducing method of reproducing information recorded on the optical storage medium by a photodetector, a wavelength of a beam emitted from the light source is λ, and an optical thickness of the optical storage medium is respectively set. d1 or d2, and when the thickness of the optical storage medium is d1, the recording density of information recorded on the optical storage medium in the track direction or in the direction orthogonal to the track is j1, and the thickness of the optical storage medium. Is d2, where j2 is the recording density of information recorded on the optical storage medium in the track direction or in the direction orthogonal to the track, j1> j2,
When the thickness of the optical storage medium is d1, the root 2 of the wavefront aberration of the beam condensed on the optical storage medium by the condensing optical system 2
If the root mean square of the wavefront aberration of the beam condensed on the optical storage medium by the condensing optical system is w2 when the root mean square is w1 and the thickness of the optical storage medium is d2, then w1 < w
2 and an optical information reproducing method in which w2> 0.07λ. 2. A signal obtained from a photodetector is input to a waveform equalizing means or a crosstalk reducing means to reduce inter-symbol interference or crosstalk from an adjacent track to reduce information recorded on an optical storage medium. The optical information reproducing method according to claim 1, wherein the optical information is reproduced. 3. The optical information reproducing method according to claim 1, wherein the light source, the optical storage medium, and the photodetector are arranged so as to form a confocal optical system, and the information recorded on the optical storage medium is reproduced. 4. The focus position of the condensing optical system is controlled by using the focus error signal having different thicknesses d1 and d2 or the focus error signal having different operating points, thereby controlling the focus position on the optical storage medium. The optical information reproducing method according to claim 1, wherein the recorded information is reproduced.