JP2003217145A - Optical head and optical information recording and reproducing apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head for preventing destruction of recording data by a side beam and realizing a stable tracking servo in the case of adopting a DPP (Differential Push-Pull) method for a system employing a short wavelength laser light source and a high NA (Numerical Aperture) objective lens as a tracking error detection system and an optical information recording and reproducing apparatus with the optical head mounted on it. <P>SOLUTION: The purpose above can be attained by changing a luminous quantity ratio of a main beam to a side beam between recording and reproduction of information. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for recording or reproducing information on an information recording medium such as an optical disc.

[0002]

2. Description of the Related Art An optical disk apparatus is an information recording / reproducing apparatus characterized by non-contact, large capacity, high-speed access, low cost, etc., and by making use of these characteristics, it is used as a recording / reproducing apparatus for digital audio signals or in a computer. It is used as an external storage device. Although the performance of optical disk devices is being improved with the expansion of application fields, it is essential to improve various performances of optical heads. Above all,
Improvement of recording density and recording capacity has become an important issue.

In order to improve the recording density of the optical disk device, it is effective to shorten the wavelength of the light source and increase the numerical aperture (NA) of the objective lens. For example, the Conference Digest of 2000 Optical Dat
a Storage) p.15 The optical disk device described in the presentation number MA-1 is based on the above idea and is used as a light source.
It has been reported that a recording capacity of 20 GB or more is possible on one side of an optical disc having a diameter of 120 mm by using a GaN semiconductor laser (wavelength of about 400 nm) and a two-lens objective lens of NA 0.85. In the same report, as a structure of an optical disk which is an information recording medium, a so-called land / groove structure is adopted, which records information on and between the grooves formed on the optical disk, as in the current recording type DVD.

On the other hand, with the aim of further improving the recording density, the proceedings of the 2001 lecture of Optical Data Storage Topical Meeting (Technical Digest of
Optical Data Storage Topical Meeting 2001) p.13
9 In the lecture number TuD-3, a so-called in-groove structure is proposed in which information is recorded in a groove formed on an optical disc. Further, in the proposal, it is reported that the track error signal obtained from the optical disc having the in-groove structure is significantly lower than that of the optical disc having the conventional land-groove structure.

For a low level track error signal,
As a track error signal detection method for realizing stable tracking servo, a so-called differential push-pull method (DPP method) is used.
Is effective, and the same method is adopted in the above two reports.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
As described in JP-A-272303, a light beam emitted from a laser light source is divided into a main beam and a side beam and irradiated onto an optical disc, and a track error signal generated from the side beam and the main beam are generated. This is a method of generating a final track error signal from the difference between the generated track error signals. This method
In tracking servo for an optical disc having a groove structure, even if the objective lens position shifts following the eccentricity of the optical disc, the track error signal is less likely to cause an offset, and is currently used in CD-R, etc. Is generally used in the optical disc devices of the above.

Since the diameter of the light spot focused on the optical disk is proportional to the wavelength and inversely proportional to the NA of the objective lens,
Wavelength 650nm / NA used in current DVD
In contrast to the 0.6 system, the 400 nm / NA 0.85 system has a light spot diameter of 1/2 or less. If the power of the light spot is the same, the power density of the irradiated light spot reaches about 5.3 times. Therefore, the current recording type D
The light spot power at the time of reproducing information in VD is about 1 mW, whereas in a system using a short wavelength laser light source and a high NA objective lens, from the viewpoint of preventing the destruction of recorded data, The light spot power (reproduction power) is suppressed to about 0.3 mW.

On the other hand, in the current optical disk device employing the DPP method, the main beam and the side beam are formed separately by the diffraction grating, but the light quantity ratio of the main beam and the side beam is 5 in DVD. : 1
To 10: 1 and CD-R 12: 1 to 15: 1 are typical values. These values are determined because the re-light spot power (recording power) for recording information on the various optical discs is required to be about 5 to 15 times the reproducing power.

It has been reported at present that the recording power in a system using a short wavelength laser light source and a high NA objective lens is required to be about 5 mW to 6 mW. Therefore, in order to prevent the light power of the beam at the time of recording information from exceeding the reproduction power of the main beam at the time of reproducing information, the light quantity ratio of the main beam to the side beam should be 15: 1 to 20 :.
Must be set to 1. However, with such a light amount ratio, the light amount of the side spot during information reproduction becomes extremely small from 0.02 mW to 0.015 mW, which makes it difficult to realize stable tracking servo. There is.

That is, when the DPP method is adopted as the track error signal detecting method in the method using the short wavelength laser light source and the high NA objective lens, the recording data is prevented from being destroyed by the third beam at the time of information recording, and stable tracking servo is performed. There was a problem that it was difficult to achieve both of them.

An object of the present invention is to solve the above-mentioned problems, and when the DPP method is adopted as a track error signal detection method in a system using a short wavelength laser light source and a high NA objective lens, the recorded data is destroyed by side beams. It is an object of the present invention to provide an optical head capable of preventing the above and realizing stable tracking servo, and an optical information recording / reproducing apparatus equipped with the same optical head.

[0012]

The above object can be achieved by changing the light quantity ratio of the main beam and the side beam during recording and reproduction of information.

Alternatively, a laser light source and a light beam emitted from the laser light source are condensed on an optical information recording medium,
A condensing optical system for forming a plurality of light spots including a light spot having a first light intensity and a light spot having a second light intensity; and a light detecting means for detecting reflected light from the optical information recording medium, The above object can be achieved by an optical head having means for changing the light intensity difference between the light spot having the first light intensity and the light spot having the second light intensity during recording and reproduction.

Generally, it is possible to form a diffraction grating by a liquid crystal element. A plurality of diffraction gratings set to different separation ratios are formed by a liquid crystal element, and the light quantity ratio of the main beam and the side beam is set to, for example, 20: 1 when recording information,
During reproduction, the diffraction grating may be selectively switched so as to be 5: 1. As a result, even when the DPP method is used as the track error signal detection method in a system using a short wavelength laser light source and a high NA objective lens, it is possible to prevent the recorded data from being destroyed by the side beam and to realize stable tracking servo. It is possible to provide a simple optical head and an optical information recording / reproducing apparatus equipped with the same optical head.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a rotating optical information recording medium (hereinafter referred to as “optical disc”), which has a recording layer 102 and a protective layer 103 on a disc-shaped transparent substrate 101. In this embodiment, a single-plate optical disk is shown as shown in the figure, but the structure of the optical disk 1 may be different from this embodiment, such as a laminated type or a structure having a plurality of recording films.

The light emitted from the laser light source 2 is converted into a parallel light flux by the collimator lens 3 and converted into a light flux having a substantially circular emission intensity distribution by the beam intensity shaping optical system 4. After that, the light beam passes through the DPP light beam separation element 5 and the polarization beam splitter 6. Further, the optical axis direction is bent by approximately 90 degrees by the rising mirror 7, the light passes through the wave plate 8, and the objective lens 9 narrows down the spot 1 on the disk 1. The wave plate 8 is a quarter wave plate,
The emitted light becomes substantially circularly polarized light.

The wave plate 8 and the objective lens 9 follow the vertical deflection of the disc 1 so that the focal point is always on the recording layer 102, and an information recording track (not shown) formed on the disc 1 is provided. It is mounted on the actuator 11 and driven integrally so that the narrowed spot 10 is always arranged on a desired track following the eccentricity. A part of the light that has entered the polarization beam splitter 6 is reflected and enters the monitor photodetector 12. The output of the monitor light detector 12 is used to control the light emission output of the laser light source 2.

In this embodiment, the wave plate 8 is mounted on the actuator 11 and is driven integrally with the objective lens 9. However, the wave plate 8 is arranged between the polarization beam splitter 6 and the rising mirror 7. Good. Also, the objective lens 9
It may be arranged between the raising mirror 7 and the objective lens 9 instead of being integrally driven with.

Further, although the beam shaping optical system 4 is used in the present embodiment, this is not an essential constituent element of the present invention, and it is not necessary to use it. Further, although the light flux from the collimator lens 3 to the objective lens 9 is bent by the rising mirror 7, it may be configured to go straight.

The reflected light (substantially circularly polarized light) from the disk 1 again becomes linearly polarized light after passing through the objective lens 9 and the wave plate 8. However, since the light passes through the quarter-wave plate twice, the polarization direction of the linearly polarized light on the return path is orthogonal to the polarization direction on the outward path and is reflected by the polarization beam splitter 6. Then, the beam splitter 13 guides the light beam to the optical system 14 for detecting the light spot control signals such as the focus error and the track error, and the lens 1
5, the information signal recorded on the disk 1 by the light detector 16 is split into a light beam for detecting and reproducing.

The above-mentioned various optical systems and optical components are mounted in a casing to form an optical head 17, and can be moved in the radial direction of the disk 1 by a moving mechanism 18 such as a linear motor or a step motor. ing. The optical output of the semiconductor laser light source 1 is controlled by the laser light source drive circuit 19. The DPP light beam separation element 5 is controlled by the light beam separation element control circuit 20. Further, the entire optical head is controlled by the control circuit 21.

FIG. 2 shows an example of the DPP light beam separation element 5. The DPP light beam separation element 5 has a grating A50 formed by a liquid crystal element on both surfaces of a substrate member 501 which is transparent to the wavelength used.
2 and a grating B503 are formed, and a voltage is selectively applied to one liquid crystal element by the beam splitting element control circuit 20 to switch between the two gratings at the time of recording and reproducing information. Up to now, the optical power of the main beam during reproduction has been reported to be 0.3 mW. At the time of recording information, if the optical power I0 of the main beam required for recording is 6 mW, the grating A502 is operated to operate the main beam (I0) and the side beams (I + 1, I) as shown in FIG. -1) Separated light quantity ratio is 20: 1
In this case, the optical power of the side beams (I + 1, I-1) is 0.3 mW, which does not exceed the light amount of the main beam at the time of reproduction, so that the side beam does not cause data destruction.
On the other hand, when reproducing information, if the separated light amount ratio remains 20: 1, the light amount of the side beam becomes 0.015 mW,
It is difficult to perform stable tracking servo.
Therefore, at the time of reproducing information, the grating B503 is operated as shown in FIG. 2B to switch the separated light amount ratio of the main beam (I0) and the side beams (I + 1, I-1) to 5: 1. . As a result, if the main beam light quantity at the time of reproducing information is 0.3 mW, the side beam light quantity is 0.0
Since 6 mW is obtained, more stable tracking servo can be realized.

In the above description, an example of a diffraction grating using a liquid crystal element as the DPP light beam separation element 5 has been shown, but two diffraction gratings may be mechanically switched. The same effect can be obtained by using a so-called A / O modulator or E / O modulator using an acousto-optic crystal for separating the main beam and the sub beam.

Next, a second embodiment of the present invention will be described with reference to FIG. The number of each component is the same as that of FIG. In the present embodiment, as the configuration of the optical head 17, the polarization beam splitter 6 is arranged between the collimator lens 3 and the laser light source 2, and the light spot control signal detection and the recording information signal detection are performed by one detection optical system 22. Is characterized by. The DPP light beam separation element 5 is arranged between the laser light source 2 and the polarization beam splitter 6. As a result, the number of parts of the optical head 17 can be reduced and the optical head 17 can be downsized.
Note that in FIG. 3, the various drive circuits and control circuits shown in FIG. 1 are omitted. Further, the wave plate 8 may be arranged between the collimator lens 3 and the rising mirror 7, and the rising mirror 7 is not driven integrally with the objective lens 9.
It may be arranged between the lens and the objective lens 9.

FIG. 4 shows a perspective view of an optical information recording / reproducing apparatus 200 according to a third embodiment of the present invention. In this embodiment, the optical head 17 described in the first or second embodiment of the present invention is moved in the radial direction of the optical disc 1 by the optical head moving mechanism 18.

As described in the first and second embodiments, the optical head 17 includes the laser light source 2, the collimating lens 3, the beam intensity shaping optical system 4, the DPP beam splitting element 5, the polarization beam splitter 6, Start-up mirror 7,
A wave plate 8, an objective lens 9, an actuator 11, a monitor photodetector 12, a beam splitter 13, a light spot control signal detection optical system 14, a lens 15, a photodetector 16 and the like are mounted. The optical disc 1 is inserted into a shutter 23 that can be opened and closed and a cartridge 24 having a dustproof function,
It is inserted into the device through the opening 25 of the device 200 and is rotated by the spindle motor 26. The entire device is covered with a dustproof case 27. As the optical head moving mechanism 18, any of various types such as a gear, a screw screw, a step motor, and a linear motor may be used. Further, although the case where the cartridge 24 is used as the optical disc 1 has been described, the cartridge 24 may not be used. Further, although a mechanism for inserting the optical disk 1 is not shown, various conventionally known methods such as a method of placing the optical disk 1 on a tray and inserting the optical disk 1 or a method of automatically or manually inserting the optical disk 1 or the cartridge 24 itself. Can be used.

The flow of various signals in the optical information recording / reproducing apparatus 200 will be described with reference to FIG. Optical head 1
The various detection signals detected in 7 are the servo signal generation circuit 2101 and the information signal recording / reproducing circuit 2 in the control circuit 21.
Sent to 102. In the servo signal generation circuit 2101,
A light spot control signal such as a focus error signal or a track error signal is generated from these detection signals, and the actuator 11 (illustrated in FIG. 1) in the optical head 17 is driven through the actuator drive circuit 2103 based on the generated light spot control signal. The position control of the objective lens 9 (shown in FIG. 1) is performed.

In the information signal recording / reproducing circuit 2102, during reproduction, the information signal recorded on the optical disk 1 is reproduced from the detection signal and output through the reproduction signal output terminal. On the other hand, at the time of recording, the recording signal input through the recording signal input terminal is subjected to recording processing by the information signal recording / reproducing circuit 2102 and then recorded on the optical disc 1 by the optical head 17.

Some of the signals obtained by the servo signal generation circuit 2101 and the information signal reproduction circuit 2102 are sent to the device control section 2104. The device controller 2104 controls the optical information recording / reproducing device 20 based on the various signals.
0 Controls overall operation.

The device control unit 2104 includes an access control circuit 2105 and a spindle motor drive circuit 210.
6. A laser light source drive circuit 19 and a light beam separation element control circuit 20 are connected to the optical head 17 for access position (radial direction of the disk 1) position control, spindle motor 26 rotation control, and information recording and reproduction. The corresponding laser light source emission output control and drive control of the light beam separation element are performed.

The configuration of the optical information recording / reproducing apparatus and the flow of various signals have been described above with reference to FIG. 5, but the configuration is not limited to that of FIG. For example, the servo signal generation circuit 2101, the information signal reproduction circuit 2102, the actuator drive circuit 2103, the device control unit 2104, the access control circuit 2105, the spindle motor drive circuit 2
Although the process of 106 is performed in the control circuit 21 in FIG. 5, it does not necessarily have to be performed in the control circuit 21, and any one of the above processes may be performed outside the control circuit 21. It may be processed.

[0033]

As described above, according to the present invention, when the DPP method is adopted as the track error signal detecting method in the system using the short wavelength laser light source and the high NA objective lens, the side beam is used at the time of recording information. It is possible to provide an optical head capable of preventing the destruction of recorded data due to the above, and capable of realizing stable tracking servo, and an optical information recording / reproducing apparatus equipped with the optical head.

[Brief description of drawings]

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

FIG. 2 is a diagram showing the operation of the light beam separation element in the first embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of an optical head that is a second embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of an optical information recording / reproducing apparatus which is a third embodiment of the present invention.

FIG. 5 is a diagram for explaining the flow of various signals in the optical information recording / reproducing apparatus which is the third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical information recording medium (optical disk), 101 ... Substrate, 102 ... Recording layer, 103 ... Protective film, 2 ... Laser light source, 3 ... Collimating lens, 4 ... Beam shaping optical system, 5
... DPP light beam separation element 501 ... substrate member 502 ...
Grating A, 503 ... Grating B, 6 ... Polarizing beam splitter,
7 ... Stand-up mirror, 8 ... Wave plate, 9 ... Objective lens, 1
0 ... Narrowing spot, 11 ... Actuator, 12 ... Monitor photodetector, 13 ... Beam splitter, 14 ... Light spot control signal detection optical system, 15 ... Lens, 16 ... Photodetector, 1
Reference numeral 7 ... Optical head, 18 ... Optical head moving mechanism, 19 ... Laser light source drive circuit, 20 ... Luminous flux separation element control circuit, 21 ... Control circuit, 2101 ... Servo signal generation circuit, 2102 ... Information signal reproduction circuit, 2103 ... Actuator drive circuit,
2104 ... Device control section, 2105 ... Access control circuit,
2106 ... Spindle motor drive circuit, 22 ... Signal detection optical system, 200 ... Optical information recording / reproducing device, 23 ... Shutter, 24 ... Cartridge, 25 ... Opening section, 26 ... Spindle motor, 27 ... Dustproof case.

Continued front page    F-term (reference) 5D090 AA01 CC01 CC04 FF02 FF09                       KK03                 5D118 AA13 AA28 BA01 CD03 DA35                 5D119 AA28 AA31 BA01 EA02 HA44                 5D789 AA28 AA31 BA01 EA02 HA44

Claims (6)

[Claims] 1. A laser light source, and a plurality of light spots having a first light intensity and a second light intensity, which are condensed on an optical information recording medium by a light beam emitted from the laser light source. Condensing optical system for forming a light spot, light detecting means for detecting reflected light from the optical information recording medium, light spot of the first light intensity and light spot of the second light intensity. An optical head having means for changing the intensity difference during recording and during reproduction. 2. A laser light source, an objective lens for condensing a light beam emitted from the laser light source on an optical information recording medium, and a reflected light from the optical information recording medium is detected to detect the optical information recording medium. Means for detecting the information signal recorded on the optical information recording medium and the light spot control signal of the light spot condensed on the optical information recording medium, and means for forming a plurality of light spots on the optical information recording medium. And an optical head having means for changing a light intensity difference between the plurality of light spots at the time of recording and reproducing information on the optical information recording medium. 3. A light intensity difference between the plurality of light spots when recording information on the optical information recording medium is a light intensity between the plurality of light spots when reproducing information from the optical information recording medium. 3. The optical head according to claim 1, wherein the optical head is larger than the difference. 4. The optical head according to claim 1, wherein the means for changing the light intensity difference between the plurality of light spots is a liquid crystal diffraction element. 5. The optical head according to claim 1, wherein the means for changing the light intensity difference between the plurality of light spots is a plurality of diffraction grating switching means. 6. A rotating means for rotating an information recording medium, an optical head according to any one of claims 1 to 5 for writing information to or reading information from the information recording medium, and the optical head for the information. Optical head moving means for moving the recording medium in the radial direction, information recording medium mounting means for mounting the information recording medium on the rotating means, and writing or reading of information on the information recording medium by the optical head. An information signal recording / reproducing processing means for reproducing or recording a signal to be output, a servo signal generating means for generating a light spot control signal including a focus error signal or a track error signal from the signal read by the optical head, It has a rotation means, the optical head moving means, the information recording medium mounting means, the information signal recording / reproducing processing means, and device control means for controlling the servo signal generating means. Optical information recording / reproducing apparatus, wherein a plurality of light spots are formed on the information recording medium, and a light intensity difference between the plurality of light spots is changed during recording and during reproduction. Playback device.