JPH0369041A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To realize a high recording density by recording at the recording pitch of 1/2 - 1/4 of a recording wavelength by the magnetic field modulation for recording and reproducing photomagnetically with the use of a light source having the wavelength of about 1/2 of a recording light source for reproducing. CONSTITUTION:A recording optical head 2 and reproducing optical head 3 are separately equipped and the information bit or domain of 1/2 - 1/4 of the wavelength of the recording light source is recorded on a photomagnetic disk 5 by a magnetic field modulation method. For the reproduction of the information, a semiconductor laser same as that of the recording light source and secondary higher harmonics generating element are used and reading is performed by the light source of 1/2 of the wavelength of the recording light source. Consequently, a recording density becomes more than two times compared with the case of recording and reproducing with the recording light source and a high density recording can be performed.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an optical recording/reproducing device that has a recording head and a reproducing head and is capable of recording/reproducing high-density information.

[Conventional technology]

In conventional recordable and reproducible optical disk devices, a high-output semiconductor laser is used as a light source for recording and reproducing, and by pulse-modulating the semiconductor laser itself and causing high-output oscillation, it is possible to record additional data containing Te etc. as the main component. Possible holes in the recording membrane (
Information is recorded by forming (pits) or magnetic domains in a perpendicularly magnetized film mainly composed of TbFe, etc., and the recorded pits, domains, etc. are read out by weakening the output of the semiconductor laser. is playing the signal.

[Problem to be solved by the invention]

The size d of pits, domains, etc. that can be stably recorded is determined by the wavelength λ of the semiconductor laser used and the numerical aperture (N, A,) of the objective lens for focusing, and is approximately half the focused spot, d=λ/2NA. Further, when reproducing continuously recorded pits or the like using the same spot, the distance between the pits is selected to be approximately the same as the spot diameter in view of amplitude deterioration of the reproduced signal. Recording of small-diameter pits is possible by lowering the recording power, but there are problems in that the recording mechanism of the recording film is unstable and it is susceptible to disturbances such as defocus. Furthermore, during reproduction, the spot diameter is larger than the pit diameter, so there is a problem in that the reproduction amplitude is significantly degraded. When considering stable recording and reproduction of optical disks in this way, it is understood that the recording density is limited by the wavelength of the semiconductor laser used. Therefore, in order to achieve high recording density, it is necessary to shorten the wavelength of the semiconductor laser, but the current situation is that there is still no short-wavelength laser capable of high-output oscillation for recording in the world. On the other hand, in rewritable magneto-optical disks, in addition to the optical modulation method that uses a semiconductor laser to oscillate pulses as described above,
There is a magnetic field modulation method in which light is used only to thermally raise the temperature of the perpendicularly magnetized film, and information is recorded by switching the magnetic field of an external magnetic coil. In this case, the size of the recording domain in the time axis direction is determined not by the wavelength of the semiconductor laser but by the switching time of the magnetic field, and currently, the size of the recording domain in the time axis direction is determined not by the wavelength of the semiconductor laser but by the switching time of the magnetic field. It has been confirmed that it is possible to record Although this method allows high-density recording, reproduction using a recording light source is also impossible in this case for the same reason as mentioned above. In this way, in the past, recording and reproduction were performed using a recording light source, and therefore, the ability to increase the density of optical discs was limited by the wavelength of the recording light source. An object of the present invention is to significantly improve the recordable and reproducible recording density of an optical disc.

[Means to solve the problem]

The above purpose has two heads, a recording head and a reproducing head, and the recording is performed by magnetic field modulation, which is 1/2 to 1/2 of the recording wavelength.
High recording density is achieved by recording at a recording pitch of 4, without using a recording light source, and using light with a wavelength approximately 1/2 that of the recording light source, and by magneto-optical reproduction. can be achieved.

[Effect]

When a head with a magnetic head capable of magnetic field modulation recording is used as a recording head, the information recording domain is determined not by the wavelength of the recording head's light source but by the magnetic field switching time of the magnetic head. 1/2 of
It is possible to record at a density of ~1/4. On the other hand, when it comes to reproducing information, it is impossible for a recording light source to read domains recorded at a density of 1/2 to 1/4 of the wavelength of the recording light source. It is read using light with a wavelength of approximately 1/2 of the wavelength of . By doing this, you can record and record with a recording light source like in the past.
The recording density can be significantly improved compared to the case of reproduction.

【Example】

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure shows the overall configuration of an optical disk device which is an embodiment of the optical recording/reproducing device of the present invention. On a base 1, a recording optical head 2 and a reproducing optical head 3 mounted on a linear actuator are installed facing each other or at positions shifted by 90 degrees. A spindle motor 4 is arranged at the center, and a magneto-optical disk 5 is attached to the spindle motor 4 and rotates at a constant speed. The recording film of the magneto-optical disk 5 is formed by vapor deposition or sputtering of rare earth-transition metals. The recording optical head 2 includes a magnetic head 2.
1 is disposed opposite to the magneto-optical disk 5 or on the optical head side, and information is recorded by magnetic field modulation that switches the direction of the current flowing through the magnetic head 21. Furthermore, the recording optical head 2 and the reproducing optical head 3 are operated by a linear actuator 22.
74, and can be positioned on the same track or on any desired track by the control circuit 6. The configuration of the recording optical head 2 will be explained in detail with reference to FIG. As the semiconductor laser 23 for recording, a high output laser with a wavelength of about 830 nm is used. The light emitted from the semiconductor laser 23 passes through the coupling lens 24
The light is focused by the polarizing prism 25.1/4 and becomes parallel light.
The light is guided to a wavelength plate 26, a galvanometer mirror 27, and a focusing lens 29 attached to a voice coil 28, and the focusing lens 29 focuses the light onto the magneto-optical disk 5 into a spot of about 1 μm. The 174 wavelength plate 26 is arranged at an angle of 45 degrees with respect to the polarization plane (P polarization) of the incident light, and the light becomes circularly polarized on the magneto-optical disk 5. The output of the semiconductor laser 23 is about 10 mW in DC on the magneto-optical disk 5 when recording information. It helps raise the temperature to record information by magnetic field modulation, and at other times it uses 1 to 2 mW to read the address information pre-recorded in uneven pits on the track in order to position the optical head to a desired track. The output is low. The light reflected by the magneto-optical disk 5 is again passed through the aperture lens 29 and the galvanometer mirror 27, 1/4
It passes through the wavelength plate 26, becomes S-polarized light, has its optical path separated by the polarizing prism 25, and enters the lens 30. Thereafter, the amount of light is divided into two by the half prism 31, and the light is divided into two by the same shape and multi-segmented photodetector 32, 33. incident on . The photodetector 32 is placed in front of the focal position of the lens 30, and the photodetector 33 is placed behind the focal position of the lens 30. An autofocus detection signal is obtained from a differential signal obtained by taking the difference between the outputs from the photodetectors 32 and 33 using a differential amplifier 34, and finely moves the voice coil 38 through an AF servo circuit 35 including a phase compensation circuit and an opening circuit. As a result, the spot narrowed down by the narrowing lens 29 is maintained at approximately 1 μmφ. In addition, a track deviation detection signal is obtained from a differential signal obtained by subtracting the difference between other outputs from the photodetectors 32 and 33 using a differential amplifier 36, and a phase compensation circuit and an open circuit are used as in the case of automatic focus control. By rotating the galvanometer mirror 27 through the included TR servo circuit 37, the spot can be accurately tracked on the track. Furthermore, by adding other outputs from the photodetectors 32 and 33 in an adder 38, an address information signal recorded in advance on the track, for example in the form of unevenness, is obtained, and the address information detection circuit 39 After digitization, the track address is detected by the demodulation circuit 40, and this value is led to the control circuit 6 and used for positioning the optical head. An external scale 41 is attached to the optical head 2 for access, and the relative movement distance can be determined from, for example, moire fringes formed by the movable scale and the fixed scale. The signal from the external scale 41 is pulsed by the external scale detection circuit 42 and guided to the control circuit 6. For access, the difference between the current address of the optical head and the target address instructed from the upper level is calculated, and that value is divided by the pitch of the external scale, and the linear actuator 22 is opened by the value obtained through the actuator operation circuit 43. Then move the optical head 2 and calculate the remaining error to the target address using the galvano mirror 2.
This will be done with a track jump based on 7. During recording, the semiconductor laser 23 emits DC-like high-power oscillation as described above, and at the same time, the information signal sent from the control circuit 6 is sent to the magnetic head 21 through the magnetic head movement circuit 44.
Information is recorded using a magnetic field modulation method by switching the direction of current flowing through the magnetic field. At this time, the size of the magnetic domain recorded on the magneto-optical disk 5 depends on the wavelength of the recording light source and the NA of the focusing lens, as in the case of conventional optical disks, such as write-once optical disks and optical modulation type magneto-optical disks. Instead, it is determined by the switching time of the magnetic field by the magnetic head 21, so 1/2 to 1/4 domains can be recorded compared to conventional optical discs. Since this size cannot be resolved by the recording semiconductor laser 23, the recording head 2 does not reproduce the recorded information. Therefore, the recording head 2 does not have a magneto-optical signal detection optical system. The configuration of the reproducing optical head 3 will be explained in detail with reference to FIG. The reproduction optical head 3 needs to reproduce 172 to 1/4 as many domains as the conventional optical disk recorded with the recording head 2, and the wavelength of the reproduction light source needs to be about 1/2 of the recording wavelength. . For this purpose, a semiconductor laser 50, which is the same as the recording light source, is used as a reproduction light source, and an optical waveguide type second high frequency generation element 51 is used as a wavelength conversion element. The light emitted from the semiconductor laser 50 is focused by a lens 52 and guided into the leading wavepath. A second harmonic wave whose phase is matched to the fundamental wave is radiated from the optical waveguide in the direction of a certain angle θ in the shape of a cone. Therefore, an optical element 53 is arranged to correct and condense the light emitted in a conical shape into parallel light. The light exiting the optical element 53 is narrowed down to a minute spot on the magneto-optical disk 5 by a polarizing prism 54 that transmits 8% of the P-polarized component (80>n50), a galvanometer mirror 55, and a focusing lens 57 attached to the voice coil 56. It will be done. The light reflected from the magneto-optical disk 5 passes through the aperture lens 5 again.
7. The light passes through a galvano mirror 55, is separated in its optical path by a polarizing prism 54, and enters a 1/2 wavelength plate 58, a lens 59, and a polarizing prism 60. The half-wave plate 58 rotates the plane of polarization incident on the polarizing prism 60 by 45 degrees.
The angle is set at 22.5 degrees with respect to the plane of polarization. By doing this, the light reflected from the magneto-optical disk 5 is divided into a P-polarized component and an S-polarized component, and enters the photodetectors 61 and 62 placed before and after the focal position of the lens 59, and is directed to the recording optical head. Similarly to 2, an autofocus detection signal, a track deviation detection signal, and an address signal are detected. Furthermore, the magneto-optical signal is detected by utilizing the Kerr effect, in which the reflection supplementary light surface rotates slightly depending on the upward and downward magnetization directions of the domains recorded in the perpendicularly magnetized film on the magneto-optical disk 5. Become. An autofocus detection signal is obtained from a differential signal obtained by subtracting the output from the photodetectors 61 and 62 using a differential amplifier 63.1 An AF servo circuit 6 including a phase compensation circuit and an a-dynamic circuit
By slightly moving the voice coil 56 through the diaphragm 4, the spot narrowed down by the diaphragm lens 57 is maintained at approximately 1 μmφ. In addition, a track deviation detection signal is obtained from a differential signal obtained by subtracting the difference between other outputs from the photodetectors 61 and 62 using a differential amplifier 65, and a phase compensation circuit and an open circuit are used as in the case of automatic focus control. By rotating the galvanometer mirror 55 through the included TR servo circuit 6, the spot can be accurately tracked on the track. Furthermore, the photodetector 6
By adding another output from 1.62 in an adder 67, an address information signal recorded in advance on the track is obtained, which is digitized by an address information detection circuit 68, and then digitized by a demodulation circuit 69. The address is detected, and this value is led to the control circuit 6 and used for positioning the optical head. Address information previously recorded on this track must be read by both the recording optical head 2 and the reproducing optical head, and is formed in the form of uneven pits. Further, the size of the pit is such that it can be read by the recording optical head 2 having a long wavelength of the light source, and the shortest pit length is equal to or greater than the wavelength of the recording light source. The output from the photodetectors 61 and 62 that obtained the address information signal is sent to the differential amplifier 7.
When the difference is taken at 0, a magneto-optical signal is obtained and guided to the control circuit 6. Similar to the recording optical head 2, an external scale 71 is attached to the reproducing optical head 3 for access, and the signal is converted into a pulse by an external scale detection circuit 72 and guided to the control circuit 6. The reproducing optical head 3 can be positioned on any track by opening the linear actuator 74 through the actuator opening circuit 73 in response to a command from a higher level. The tracking method will be explained using FIG. It is necessary to track a common track using optical heads that emit light of different wavelengths, and there are two types of tracking methods to achieve this: differential diffraction type and three-spot type. First, the case where the recording optical head 2 and the reproducing optical head 3 are of the diffraction light differential type will be explained with reference to FIG. 4(a). Guide grooves 100 are recorded in a spiral shape on the disk 5 at equal pitches, and the pitch is set so that the wavelength of the recording light source is λl,
A diaphragm lens 29 mounted on the recording optical head 2
Spot diameter dl = λ1 /N when the numerical aperture NAI is
It is almost the same as A1. The diffracted light differential type is arranged so that the track center and the dividing line of the two-split photodetector coincide with the reflected diffracted light from the optical disk 5, and the two of the two-split photodetector are
The track deviation detection signal is detected based on the difference between the two outputs, and the amplitude of the track deviation detection signal is determined by the optical depth of the guide groove 100. The track deviation detection signal is maximum when the optical depth of the guide groove is 1/8 of the wavelength of the light source, and is minimum O when it is 1/4 of the wavelength of the light source. Therefore, in this case, the optical depth of the guide groove should not be 1/4 of the wavelength for the two wavelengths, λ of the recording light source and wavelength λ2 of the reproducing light source (λ1 = 2Xλ2). It is necessary to set it to . As a first setting value, the optical depth of the guide groove 100 can be set to λl/12 (=λ2/6), and as a second setting value, the optical depth of the guide groove 100 can be set to λ1. /6 (=λ2/3). This situation is shown in FIG. Figure 5 shows λl"83'Onm (λ2=415nm),
The shape of the guide groove 100 is rectangular, and the width of the guide groove 100 is 0.4.
μm, the track pitch is 1.6 μm, and the numerical aperture of the diaphragm lens is N and A. This is the result of calculating the track deviation detection signal in the diffracted light differential type with =0.55, and - represents the polarity. By doing this, the amplitude of the tracking deviation detection signal in the recording optical head 2 and the tracking deviation detection signal in the reproducing optical head 3 can be made the same. However, in the case of the second set value, the recording optical head 2 does not track. The polarity of the deviation detection signal and the tracking deviation detection signal in the reproducing optical head 3 are different. The pitch of the guide grooves 100 is matched to the size of the narrowing spot 103 created by the recording light source, so if the narrowing spot 104 irradiated by the reproducing optical head is circular, the narrowing spot 104 will be smaller than the pitch of the guiding groove 100. is too small, a dead zone occurs in the track deviation detection signal near the center of the track. In order to prevent this, in the reproduction optical head 3, the optical element 53
Therefore, it is better to form an elliptical spot 104 as shown in the figure. Further, an address pit 102 representing address information is also recorded on the rack between the guide grooves, and its optical depth is λ, which is the same as in the case of the second set value described above.
When set to 1/6 (-λ2/3>), the amplitude of the address information signal detected by the recording optical head 2 and the reproducing optical head 3 can be made the same (Fig. 6). This was calculated using the same parameters as when calculating the detection signal.Next, Figure 4 shows the case where the recording optical head 2 is of the diffracted light differential type and the reproducing optical head 3 is of the 3-spot type.
This will be explained using b). The differential type of diffracted light in the recording optical head 2 has been described above, and its explanation will be omitted. The 3-spot type uses a diffraction grating or the like to generate 0th-order light and earthwork-order light.The 0th-order light is used as a main beam 105 and is positioned at the center of the track to read information, and the 11th-order light is used as a sub beam 106 in the guide groove 100. placed in contact with. A track deviation detection signal can be obtained by taking the difference between the outputs of the two photodetectors corresponding to the two sub-beams. The optical depth of the guide groove at this time is λ1/8 (=
λ2/4). Then, in the diffracted light differential type in the recording optical head 2, the maximum track deviation detection signal of t) is simultaneously transmitted to the reproducing optical head 3.
The maximum track deviation detection signal can also be obtained with the three-spot type. The optimum location for arranging the diffraction grating in the reproduction optical head 3 is between the optical element 53 and the polarizing prism 54. The optical depth of the address pit 102 representing address information is λl/6, which is the same as explained in FIG. 4(a).
(=λ2/3) is preferable. Although the above explanation has been made regarding the case of recording and reproducing on a single disc, it goes without saying that the same effect can be obtained when recording and reproducing a stacked multi-disc.

【Effect of the invention】

As explained above, the present invention has a recording optical head and a reproducing optical head separately, and has a wavelength of 172 to 100 nm of the wavelength of the recording light source.
Information is recorded using a magnetic field modulation method that can record /4 information pits (domains), and the information is reproduced at the wavelength of the recording light source using the same semiconductor laser and second harmonic generation element as the recording light source. This is done by realizing 172 light sources and reading the recorded information pits. By doing so, it is possible to achieve a recording density that is twice or more, and a storage capacity that is more than twice as much as when recording and reproducing is performed using a recording light source.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram showing one embodiment of the present invention, FIG. 2 is an explanatory diagram of a recording optical head in the present invention, FIG. 3 is an explanatory diagram of a reproducing optical head in the present invention, and FIG. FIGS. 5 and 6 are explanatory views of the track deviation detection method in the present invention, and are diagrams for explaining the track deviation detection operation in the present invention. 2... Optical head for recording, 3... Optical head for reproduction, 5
... magneto-optical disk, 6... control circuit, 21...
Magnetic head, 23... semiconductor laser for recording, 40.
71... External scale, 51... Optical waveguide type second harmonic generation element, 53... Optical element. m1EII+ Figure 4 Figure 5 Figure 5 (λJ0 (λl/2) → Optical depth

Claims (1)

[Claims] 1. An optical recording/reproducing device having a recording head and a reproducing head, which includes a semiconductor laser as a light source, an optical system for guiding light emitted from the semiconductor laser onto a recording medium, and a system for performing magnetic field modulation. The recording head has a recording head having a magnetic head, and further has a reproducing head having an optical system that emits reproducing light having a wavelength of about 1/2 of the wavelength of the semiconductor laser and guides the light onto the recording medium. An optical recording and reproducing device capable of recording and reproducing. 2. The optical recording/reproducing apparatus according to claim 1, wherein a light source comprising the recording semiconductor laser and an optical waveguide type second harmonic generator (SHG) is used as the reproducing head. 3. The shape of the focused spot emitted from the recording head is circular, the shape of the focused spot emitted from the reproducing head is an ellipse long in the direction perpendicular to the track, and the optical depth of the guide groove tracked by the spot is determined. 3. The optical recording/reproducing apparatus according to claim 1, wherein the wavelength of the recording light source is 1/12 or 1/6 of the wavelength of the recording light source. 4. The shape of the focused spot irradiated from the recording head is circular, the three spots are irradiated from the reproducing head separated by a diffraction grating, and the optical depth of the guide groove tracked by the spot is recorded as described above. 1/8 of the wavelength of the light source
The optical recording/reproducing apparatus according to claim 1 or 2, characterized in that: 5. The optical system according to any one of claims 1 to 4, wherein the optical depth of the uneven pits recorded in advance on the recording medium is 1/6 of the wavelength of the recording light source. Recording and reproducing device.