JPH05166237A - Magneto-optical head device - Google Patents

Abstract

PURPOSE:To simultaneously satisfy two conditions of the simple constitution of an electric circuit and the prevention of the deterioration of regenerative C/N in a magneto-optical head device using a diffraction element for detecting an error signal or an information signal. CONSTITUTION:A reflected beam from a disk 5 is separated to three beams of zero-order light and + or -1st-order diffracted light by a polarization property simple grating 34 having polarization dependency in diffraction efficiency and further, respective light beams are separated to three beams of the zero-order light and the + or -1st-order diffracted light by a nonpolarization hologram 35 having no polarization dependency in the diffraction efficiency. The error signal is detected by using a part of beams separated by the nonpolarization hologram 35 between the zero-order light of the polarization property simple grating 34. On the other hand, the information signal is detected from the difference between the remaining light beam separated by the nonpolarization hologram 35 among the zero-order light of the polarization property simple grating 34 and the + or -1st diffracted light of the polarization property simple grating 34.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical head device for recording, reproducing or erasing information on a magneto-optical disk.

[0002]

2. Description of the Related Art Recently, a structure using a diffraction element for detecting an error signal and an information signal has been proposed for the purpose of reducing the size and cost of a magneto-optical head device.

FIG. 9 shows a configuration example of a conventional magneto-optical head device using a diffraction element (see, for example, Japanese Patent Laid-Open No. 3-29137). The light emitted from the semiconductor laser 1 of the light source is converted into parallel light by the collimator lens 2, transmitted through the beam splitter 3, and then focused by the objective lens 4 on the disk 5 which is a magneto-optical recording medium. The reflected light from the disk 5 is converted into parallel light again by the objective lens 4 and then reflected by the beam splitter 3 to be separated outside the condensing optical system. This light is converted into convergent light by the lens 6, and then enters the polarization hologram 7 which is a diffraction element. The transmitted light (0th order light) and the ± 1st order diffracted lights from the polarization hologram 7 are received by the common photodetector 8. The polarization hologram 7 is divided into four regions 9 to 12 having different lattice directions, as shown in FIG. The direction of the optical axis 13 of the substrate is set to about 45 ° with respect to the polarization direction of incident light.

FIG. 11 shows a sectional shape of the polarization hologram 7. On a lithium niobate substrate 14 having birefringence, a two-layer diffraction grating composed of a proton exchange region 15 and a phase compensation film 16 is formed. As the phase compensation film 16, for example, Nb ₂ O ₅ is used. The phase difference between the line portion and the space portion of the diffraction grating is set to 0 for the polarization component (ordinary ray) perpendicular to the optical axis 13 and π for the polarization component (extraordinary ray) parallel to the optical axis 13. ing. Therefore, all the ordinary components of the incident light are transmitted without being diffracted, and all the extraordinary components are diffracted without being transmitted.

FIG. 12 shows the structure of the photodetector 8 and the photodetector 8.
The shape of the upper light spots 17-25 is shown. (A) shows that the disc 5 is too close to the objective lens 4, (b) shows that the disc 5 is correctly positioned at the focal point of the objective lens 4,
(C) shows the case where the disk 5 is too far from the objective lens 4. The photodetector 8 has eight light receiving parts 26.
It is divided into ~ 33. The light spot 17 is the 0th order light (ordinary light component) of the polarization hologram 7 and is received by the light receiving unit 26. The light spots 18 to 21 are polarized holograms 7.
+ 1st order diffracted light (extraordinary light component), and the diffracted light in regions 9 to 12 are light spots 18, 19, 20, 21 respectively.
It corresponds to. In (b) of the figure, the light spot 18 is on the dividing line of the light receiving portions 27 and 28, and the light spot 19 is the light receiving portion 2.
It is condensed on each of the dividing lines of 9 and 30. Further, the light spot 20 is the light receiving portion 31, and the light spot 21 is the light receiving portion 32.
Are received respectively. The light spots 22 to 25 are the −1st order diffracted light (extraordinary light component) of the polarization hologram 7,
The diffracted lights in the regions 9 to 12 are the light spots 23 and 2 respectively.
It corresponds to 2, 25, 24. All four light spots are received by the light receiving unit 33.

Outputs from the light receiving portions 26 to 33 are respectively V
When expressed by (26) to V (33), the focus error signal is (V (27) + V (3
0))-(V (28) + V (29)). Further, the track error signal can be obtained from V (31) -V (32) by the push-pull method principle. On the other hand, the information signal is V (26) − (V (27) +, which is the difference between the 0th-order light and the ± 1st-order diffracted lights, due to the principle of the differential detection method.
V (28) + V (29) + V (30) + V (31) + V
(32) + V (33)) or V (26) −V (33) which is the difference between the 0th order light and the −1st order diffracted light.

[0007]

The transmittance of the ordinary light component in the polarization hologram 7 is theoretically 100%, and the ± 1st order diffraction efficiency of the extraordinary light component is theoretically 40.5%. On the other hand, in the differential detection method, in order to suppress the in-phase noise caused by the variation in the intensity of the semiconductor laser and the variation in the reflectance of the disk, it is necessary that the amounts of the ordinary light component and the extraordinary light component used for detecting the information signal are substantially equal.

In the system in which the information signal is obtained from the difference between the 0th order light and the ± 1st order diffracted lights, the light quantity ratio between the ordinary light component and the extraordinary light component is 10
It is slightly unbalanced at 0:81, but in-phase noise can be suppressed considerably. However, in this method, the + 1st order diffracted light is used for both the error signal detection and the information signal detection, so that it is necessary to separate two types of signals on the electric circuit, which complicates the structure of the electric circuit.

In the method in which the information signal is obtained from the difference between the 0th-order light and the -1st-order diffracted light, separate lights are used for error signal detection and information signal detection, so that it is not necessary to separate two types of signals on an electric circuit. .. However, in this method, the light quantity ratio between the ordinary light component and the extraordinary light component is 100: 40.5, which is a considerable unbalance, and in this state, in-phase noise cannot be sufficiently suppressed. It is possible to make the light amount ratio 1: 1 by shifting the angle formed by the direction of the optical axis 13 of the polarization hologram 7 and the polarization direction of the incident light from 45 °, but with this, the carrier level is lowered this time. Therefore, in any case, as a result, the reproduction C / N decreases.

As described above, the conventional magneto-optical head device has a problem that the two conditions that the electric circuit has a simple structure and the reproduction C / N does not decrease cannot be satisfied at the same time.

An object of the present invention is to provide a magneto-optical head device which can solve the above-mentioned conventional problems and satisfy two conditions at the same time.

[0012]

A first magneto-optical head device of the present invention comprises a light source, a condensing optical system for condensing light emitted from the light source on a magneto-optical recording medium, and the magneto-optical recording. Separation means for separating the reflected light from the medium to the outside of the condensing optical system, a diffraction element for diffracting the light separated by the separation means, and a photodetector for receiving the transmitted light and the diffracted light from the diffraction element. In a magneto-optical head device having at least: a first diffraction element in which a diffraction grating having polarization dependence on diffraction efficiency is formed on a substrate having birefringence, and the diffraction element is on an isotropic substrate. In addition, it is characterized in that the second diffraction element is formed with a second diffraction element in which a diffraction grating having no polarization dependence on the diffraction efficiency is formed.

A second magneto-optical head device of the present invention comprises a light source, a condensing optical system for condensing light emitted from the light source onto a magneto-optical recording medium, and reflected light from the magneto-optical recording medium. A magneto-optical head having at least a separating means for separating the light from the condensing optical system, a diffractive element for diffracting the light separated by the separating means, and a photodetector for receiving the transmitted light and the diffracted light from the diffractive element. In the device, in the diffraction element, a first diffraction grating having polarization dependency on diffraction efficiency is formed on one surface of a substrate having birefringence, and the other surface of the substrate has diffraction efficiency. It is characterized in that a second diffraction grating having no polarization dependency is formed.

[0014]

In the magneto-optical head device of the present invention, the reflected light from the magneto-optical recording medium is the 0th-order light (ordinary component) and ± 1 by the first diffraction grating having the polarization dependence of the diffraction efficiency.
The second diffracted light (extraordinary light component) is separated into three, and the second diffraction grating, which does not have polarization dependence on the diffraction efficiency, further separates each into three light of 0th order light and ± 1st order diffracted light. The error signal is detected using, for example, a part of the 0th-order light of the first diffraction grating, which is separated by the second diffraction grating. On the other hand, the information signal is detected, for example, from the difference between the 0th order light of the first diffraction grating and the remaining light separated by the second diffraction grating, and the ± 1st order diffracted light of the first diffraction grating.

With such a structure, it is not necessary to separate the error signal and the information signal on the electric circuit, and the structure of the electric circuit is simplified. Further, by setting the diffraction efficiency of the second diffraction grating so that the light amounts of the ordinary light component and the extraordinary light component used for information signal detection are substantially equal, it is possible to suppress common mode noise without lowering the carrier level. Play C
There is no decrease in / N.

[0016]

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

FIG. 1 shows the configuration of an embodiment of the first magneto-optical head device of the present invention. The structure until the reflected light from the disk 5 is converted into the convergent light by the lens 6 is the same as that of the conventional example shown in FIG. The light converted into the convergent light by the lens 6 enters the polarizing simple grating 34, which is the first diffractive element having the polarization dependence of the diffraction efficiency, and is separated into the 0th-order light and the ± 1st-order diffracted lights. These lights are incident on the non-polarization hologram 35 which is the second diffractive element having no polarization dependency on the diffraction efficiency, and are further separated into 0th-order light and ± 1st-order diffracted lights. These lights are received by the common photodetector 36.

As shown in FIG. 2, the polarizing simple grating 34 has a single area on the entire surface. The direction of the optical axis 13 of the substrate is about 45 ° with respect to the polarization direction of the incident light.
Is set to.

FIG. 3 shows a sectional shape of the polarizing simple grating 34. On the lithium niobate substrate 14 having birefringence,
A two-layer diffraction grating including the proton exchange region 15 and the phase compensation film 16 is formed. As the phase compensation film 16, for example, Nb ₂ O ₅ is used. The phase difference between the line portion and the space portion of the diffraction grating is set to 0 for the polarization component (ordinary ray) perpendicular to the optical axis 13 and π for the polarization component (extraordinary ray) parallel to the optical axis 13. ing. Therefore, all the ordinary components of the incident light are transmitted without being diffracted, and all the extraordinary components are diffracted without being transmitted.

As shown in FIG. 4, the non-polarization hologram 35 is divided into four regions 9 to 12 having different lattice directions. Similar to the polarization hologram 7 shown in FIG. 10, (a) is a structure in which the whole is divided into two regions 9 and 10, and eyeball-shaped regions 11 and 12 are added thereto, and (b) is two in total. It is a configuration in which it is divided into four areas 9 to 12 evenly by the diagonal line.

FIG. 5 shows the cross-sectional shape of the non-polarization hologram 35. A diffraction grating made of a dielectric film 38 is formed on an isotropic glass substrate 37. As the dielectric film 38, for example, SiO ₂ is used. The phase difference between the line portion and the space portion of the diffraction grating can be freely set by changing the thickness of the dielectric film 38. Incident light is separated into transmitted light and diffracted light according to the diffraction efficiency determined by the phase difference, regardless of the polarization direction.

FIG. 6 shows the structure of the photodetector 36 and the photodetector 3.
6 shows the arrangement of light spots 39-65 on No. 6. This figure shows the case where the disk 5 is correctly positioned at the focal point of the objective lens 4. The photodetector 36 includes 14 light receiving units 66.
It is divided into ~ 79.

The light spot 39 is the 0th order light (ordinary component) of the polarizing simple grating 34 and the 0th order light of the non-polarization hologram 35, and is received by the light receiving section 66. Light spot 40-4
Reference numeral 3 denotes the 0th-order light (ordinary light component) of the polarizing simple grating 34 and the + 1st-order diffracted light of the non-polarization hologram 35.
The diffracted light at 2 is the light spot 40, 41, 42,
It corresponds to 43. The light spot 40 is the light receiving portion 67, 6
The light spot 41 is focused on the dividing line of 8 and on the dividing line of the light receiving units 69 and 70. The light spot 42 is received by the light receiving portion 71, and the light spot 43 is received by the light receiving portion 72. The light spots 44 to 47 are the polarization simple grating 3
No. 4 zero-order light (ordinary component) and non-polarization hologram 35 −
The first-order diffracted light, and the diffracted lights in the regions 9 to 12 correspond to the light spots 45, 44, 47, and 46, respectively. Four
All one light spots are received by the light receiving unit 73.

The light spot 48 is the + 1st order diffracted light (extraordinary light component) of the polarizing simple grating 34 and the non-polarization hologram 35.
And is received by the light receiving section 74. The light spots 49 to 52 are the + 1st order diffracted light (extraordinary light component) of the polarizing simple grating 34 and the + 1st order diffracted light of the non-polarization hologram 35, and the diffracted lights in the regions 9 to 12 are the light spots 4 respectively.
It corresponds to 9, 50, 51 and 52. All four light spots are received by the light receiving unit 75. Light spots 53-5
Reference numeral 6 denotes the + 1st-order diffracted light (extraordinary light component) of the polarizing simple grating 34 and the -1st-order diffracted light of the non-polarization hologram 35,
The diffracted lights in the regions 9 to 12 are the light spots 54 and 5 respectively.
It corresponds to 3,56,55. All four light spots are received by the light receiving unit 76.

The light spot 57 is the −1st order diffracted light (extraordinary light component) of the polarizing simple grating 34 and the non-polarization hologram 35.
Is the 0th order light and is received by the light receiving unit 77. The light spots 58 to 61 are the −1st order diffracted light (extraordinary light component) of the polarizing simple grating 34 and the + 1st order diffracted light of the non-polarization hologram 35, and the diffracted light in the regions 9 to 12 is the light spot 5 respectively.
It corresponds to 8, 59, 60, 61. All four light spots are received by the light receiving unit 78. Light spots 62-6
Reference numeral 5 denotes the -1st-order diffracted light (abnormal light component) of the polarizing simple grating 34 and the -1st-order diffracted light of the non-polarization hologram 35,
The diffracted lights in the regions 9 to 12 are light spots 63 and 6 respectively.
It corresponds to 2,65,64. All four light spots are received by the light receiving unit 79.

Outputs from the light receiving units 66 to 79 are respectively set to V
When expressed by (66) to V (79), the focus error signal is (V (67) + V (7
0))-(V (68) + V (69)). Further, the track error signal can be obtained from V (71) -V (72) by the push-pull method principle. On the other hand, according to the principle of the differential detection method, the information signal is 0 of the non-polarization hologram 35 in the 0th order light of the polarization simple grating 34.
Addition of the 2nd-order light and the -1st-order diffracted light, and the polarizing simple grating 3
This is the difference between the 0th-order light of the non-polarization hologram 35 and the ± 1st-order diffracted light of the ± 1st-order diffracted light of 4 (V (66)).
+ V (73))-(V (74) + V (75) + V (7
6) + V (77) + V (78) + V (79)). In this case, the light receiving units 66 and 73, the light receiving unit 7
It is also possible to integrate 4 to 76 and the light receiving portions 77 to 79, respectively.

In this embodiment, the transmittance of the ordinary light component in the polarizing simple grating 34 is theoretically 100%, and the ± 1st order diffraction efficiency of the extraordinary light component is theoretically 40.5%. Here, when the phase difference between the line portion and the space portion of the non-polarization hologram 35 is set to 81.9 °, for example, the transmittance is theoretically 57.0%, and the ± 1st-order diffraction efficiencies are theoretically 17.4%, respectively. %. Therefore, of the 0th-order light (ordinary light component) of the polarizing simple grating 34, the efficiency of the sum of the 0th-order light and the -1st-order diffracted light of the non-polarization hologram 35, and the ± 1st-order diffracted light (extraordinary light) Among the components, the efficiency of both the 0th-order light and the ± 1st-order diffracted lights of the non-polarization hologram 35 is 74.4%. In this way, by making the light amounts of the ordinary light component and the extraordinary light component used for detecting the information signal equal, it is possible to suppress the in-phase noise without lowering the carrier level, so that the reproduction C / N does not decrease.

Further, in the method of this embodiment, since separate light is used for error signal detection and information signal detection, it is not necessary to separate two types of signals on the electric circuit, and the construction of the electric circuit is simplified. ..

In FIG. 1, the lens 6, the polarizing simple grating 34, and the non-polarization hologram 35 are arranged in this order between the beam splitter 3 and the photodetector 36. The simple grating 34 and the non-polarization hologram 35 may be arranged in any order. It is also possible to integrate two or more elements of the beam splitter 3, the lens 6, the polarization simple grating 34, and the non-polarization hologram 35 by adhesion.

FIG. 7 shows the configuration of an embodiment of the second magneto-optical head device of the present invention. The structure until the reflected light from the disk 5 is converted into the convergent light by the lens 6 is the same as that of the conventional example shown in FIG. In this embodiment, as the diffractive element, an element in which a polarizing simple grating surface 80 is formed on the entrance side of the substrate and a non-polarization hologram surface 81 is formed on the exit side of the substrate is used. The light converted into the convergent light by the lens 6 is separated into the 0th-order light and the ± 1st-order diffracted lights at the polarizing simple grating surface 80 which is the first diffraction grating having the polarization dependence of the diffraction efficiency. These lights are further separated into 0th-order light and ± 1st-order diffracted lights on the non-polarization hologram surface 81 which is the second diffraction grating having no polarization dependence on the diffraction efficiency. These lights are received by the common photodetector 36.

Similar to the polarizing simple grating 34 shown in FIG. 2, the polarizing simple grating surface 80 is entirely composed of a single region. The direction of the optical axis 13 of the substrate is set to about 45 ° with respect to the polarization direction of incident light.

The non-polarization hologram surface 81 is divided into four regions 9 to 12 having different lattice directions, like the non-polarization hologram 35 shown in FIG. (A) is wholly divided into regions 9 and 10, and eyeball-shaped regions 11 and 12 are divided into two regions.
(B) is a configuration in which the whole is equally divided into four regions 9 to 12 by two diagonal lines.

FIG. 8 shows the sectional shape of the diffractive element used in this embodiment. Lithium niobate substrate having birefringence 1
On the incident side of No. 4, a polarizing simple grating plane 80 which is a two-layer diffraction grating composed of the proton exchange region 15 and the phase compensation film 16 is formed. As the phase compensation film 16, for example, Nb ₂ O ₅ is used. The phase difference between the line portion and the space portion of the diffraction grating is set to 0 for the polarization component (ordinary ray) perpendicular to the optical axis 13 and π for the polarization component (extraordinary ray) parallel to the optical axis 13. ing. Therefore, all the ordinary components of the incident light are transmitted without being diffracted, and all the extraordinary components are diffracted without being transmitted. On the other hand, a non-polarization hologram surface 81 which is a diffraction grating made of a dielectric film 82 is formed on the exit side of the lithium niobate substrate 14 having birefringence. As the dielectric film 82, for example, Nb ₂ O ₅ is used. The phase difference between the line part and the space part of the diffraction grating is
It can be freely set by changing the thickness of the dielectric film 82. Incident light is separated into transmitted light and diffracted light according to the diffraction efficiency determined by the phase difference, regardless of the polarization direction.

The configuration of the photodetector 36 and the arrangement of the light spots on the photodetector 36 are as shown in FIG. 6 as in the first embodiment of the magneto-optical head device of the present invention.
The description is omitted. The method of detecting the focus error signal, the track error signal, and the information signal is also the same as in the first embodiment of the magneto-optical head device of the present invention, and therefore its explanation is omitted.

Also in this embodiment, as in the first magneto-optical head device of the present invention, by making the light amounts of the ordinary light component and the extraordinary light component used for detecting the information signal equal,
Since the common-mode noise can be suppressed without lowering the carrier level, the reproduction C / N does not decrease. Further, since different lights are used for error signal detection and information signal detection, it is not necessary to separate the two types of signals on the electric circuit, and the structure of the electric circuit is simplified.

FIG. 7 shows a diffractive element in which a polarizing simple grating surface 80 is formed on the incident side of the substrate and an unpolarized hologram surface 81 is formed on the emitting side of the substrate. The order of 80 and the non-polarization hologram surface 81 may be reversed. Furthermore, the order of the lens 6 and the diffraction element may be reversed. It is also possible to integrate two or more of the beam splitter 3, the lens 6, and the diffractive element by bonding.

[0037]

As described above, in the magneto-optical head device of the present invention, it is not necessary to separate the error signal and the information signal on the electric circuit, and the electric circuit configuration is simplified.
Further, by making the light amounts of the ordinary light component and the extraordinary light component used for the information signal detection equal, it is possible to suppress the in-phase noise without lowering the carrier level, so that the reproduction C / N does not decrease. That is, according to the present invention, it is possible to obtain a magneto-optical head device capable of simultaneously satisfying the above two conditions, which cannot be realized by the conventional magneto-optical head device.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a configuration of a polarizing simple grating used in an embodiment of a first magneto-optical head device of the present invention and a direction of an optical axis of a substrate.

FIG. 3 is a diagram showing a cross-sectional shape of a polarizing simple grating used in an embodiment of the first magneto-optical head device of the present invention.

FIG. 4 is a diagram showing a configuration of a non-polarization hologram used in an embodiment of the first magneto-optical head device of the present invention.

FIG. 5 is a diagram showing a cross-sectional shape of a non-polarization hologram used in an embodiment of the first magneto-optical head device of the present invention.

FIG. 6 is a diagram showing a configuration of a photodetector used in an embodiment of the first and second magneto-optical head devices of the present invention and an arrangement of light spots on the photodetector.

FIG. 7 is a diagram showing a configuration of an embodiment of a second magneto-optical head device of the present invention.

FIG. 8 is a diagram showing a cross-sectional shape of a diffraction element used in an example of the second magneto-optical head device of the present invention.

FIG. 9 is a diagram showing a configuration example of a conventional magneto-optical head device.

FIG. 10 is a diagram showing a configuration of a polarization hologram used in a conventional magneto-optical head device and a direction of an optical axis of a substrate.

FIG. 11 is a diagram showing a cross-sectional shape of a polarization hologram used in a conventional magneto-optical head device.

FIG. 12 is a diagram showing a configuration of a photodetector used in a conventional magneto-optical head device and a shape of a light spot on the photodetector.

[Explanation of symbols]

 1 Semiconductor Laser 2 Collimator Lens 3 Beam Splitter 4 Objective Lens 5 Disk 6 Lens 7 Polarizing Hologram 8 Photodetector 9-12 Region 13 Optical Axis 14 Lithium Niobate Substrate 15 Proton Exchange Region 16 Phase Compensation Film 17-25 Light Spot 26 ˜33 Light receiving part 34 Polarizing simple grating 35 Non-polarizing hologram 36 Photodetector 37 Glass substrate 38 Dielectric film 39 to 65 Light spot 66 to 79 Light receiving part 80 Polarizing simple grating surface 81 Non-polarizing hologram surface 82 Dielectric film

Claims (2)

[Claims] 1. A light source, a condensing optical system for condensing light emitted from the light source onto a magneto-optical recording medium, and a separation for separating reflected light from the magneto-optical recording medium outside the condensing optical system. Means, a diffractive element for diffracting the light separated by the separating means, and a photodetector for receiving transmitted light and diffracted light from the diffractive element, wherein the diffractive element is a birefringent element. The first diffractive element has a diffraction grating having polarization dependence on diffraction efficiency, and a diffraction grating having no polarization dependence on diffraction efficiency is formed on an isotropic substrate. And a second diffractive element, which is a magneto-optical head device. 2. A light source, a condensing optical system that condenses light emitted from the light source onto a magneto-optical recording medium, and a separation that separates reflected light from the magneto-optical recording medium outside the condensing optical system. Means, a diffractive element for diffracting the light separated by the separating means, and a photodetector for receiving transmitted light and diffracted light from the diffractive element, wherein the diffractive element is a birefringent element. A first diffraction grating having a polarization dependence on the diffraction efficiency is formed on one surface of the substrate having an optical property, and a second diffraction grating having no polarization dependence on the diffraction efficiency is formed on the other surface of the substrate. A magneto-optical head device having a structure in which a grating is formed.