JPH03134838A - Optical head for magneto-optical recording/reproducing - Google Patents

Abstract

PURPOSE:To obtain high-quality reproduction signals and to realize a light-weight, small-sized, thin-type head by using such a luminous flux splitting device that consists of glass and uniaxial crystal which are joined to form a joint surface, and that the normal of the joint surface is in the first plant or in the second plane which is orthogonal to the first plane and contains a third luminux flux, and further, that the optical axis of the uniaxial crystal and the first plane make an angle of 45 deg.. CONSTITUTION:The luminous flux splitting device 1 consists of crystal 2 and glass 3 adhered to form the joint surface 4. The optical axis 5 of the crystal 2 is in the Y-Z plane, making 45 deg. angle with the Y-axis. The normal 6 of the joint surface 4 is in the X-Z plane, making 45 deg. angle with the X axis. When linearly polarized light with the oscillation in the Y-axis direction enters in the splitting device, the projection component to the optical axis 5 is affected by the refractive index nE for extraordinary ray to give a luminous flux 8 which emits from the device in the positive direction of Z axis. On the other hand, the projection component to the direction perpendicular to the optical axis 5 is affected by the refractive index n0 for ordinary ray to give a luminous flux 9 which emits from the device in the negative direction of the Z-axis. By this method, reproduction signals with high quality can be obtained with a simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical head used in a magneto-optical information reproducing device that reproduces information magnetically recorded on a recording medium by utilizing the magneto-optic effect.

[Conventional technology]

BACKGROUND ART In recent years, there has been active research and development into the practical use of optical memory, which performs recording and reproduction using semiconductor laser light, as a high-density recording memory, and magneto-optical recording media, in which information can be erased and rewritten, are particularly promising. Magneto-optical recording media magnetically record information using the local temperature rise of a magnetic thin film caused by spot irradiation with laser light, and reproduce the information using the magneto-optic effect (particularly the Kerr effect). The Kerr effect here refers to a phenomenon in which the plane of polarization rotates when light is reflected by a magnetic recording medium.

Among the conventionally proposed optical heads for magneto-optical reproducing devices, the structure of an optical head using a crystal will be described as a method for reproducing information.

In the optical head 101 shown in FIG. 9, a light beam from a semiconductor laser 102 is collimated by a collimator lens 103, reflected by a beam splitter 104, and then passed through an objective lens 105 to a magneto-optical disk 106, which is a magneto-optical recording medium. imaged on top. The reflected light beam from the magneto-optical disk 106 is passed through the objective lens 105. After passing through the beam splitter 104, the beam splitter 107 separates the beam into three beams: reflected and transmitted beams. The reflected light flux is guided to a servo error detection light receiver 109 through a light receiving lens 108. The light receiver 109 generates a detection signal according to the spot shape on the detection section and sends it to the servo error signal forming section 1.
Supply to 12. A focus error signal and a tracking error signal are obtained in the servo error signal forming section 112, and based on these signals, the objective lens 105 is driven to a desired position by an actuator mechanism (not shown).

On the other hand, the luminous flux transmitted through the beam splitter 107 is 1/
The light enters the two-wavelength plate 111, and then enters the Wollaston prism 1.
] 3, the light beam is separated into three beams having orthogonal polarization components, and then guided to a photodetector 115 through a light receiving lens 114. The photodetector 115 has two detection sections corresponding to the three beams, and generates two detection output signals corresponding to changes in each polarization component and supplies them to the reproduction signal detection section 116. The reproduced signal detection section 116 mutually compares the two detection output signals, thereby detecting the magneto-optical disk 106.
The rotation of the plane of polarization (Kerr rotation) received by the light beam upon reflection on the perpendicularly magnetized film is detected, and it is possible to obtain a reproduction signal corresponding to the rotation.

Wollaston prism 11 using Figures 10 and 11.
The principle by which three luminous fluxes are separated will be explained below.

The Wollaston prism 113 consists of a crystal 120 whose optical axis 130 is parallel to the Y-axis and a crystal 1 whose optical axis 131 is parallel to the Y-axis.
21 are joined together. The incident light traveling in the X-axis direction is linearly polarized light within the xy plane. 1/2 wavelength plate 11 so that the polarization direction of this incident light is rotated by 45 degrees.
Set 1.

FIG. 11 is a sectional view of the conventional Wollaston prism 1]3 shown in FIG. When the incident light polarized in the direction of 45 degrees to the Y-axis travels from the crystal 120 to the crystal 121, the projected component to the Y-axis is affected by the extraordinary refractive index and the ordinary refractive index in order, and becomes XY. It is emitted as linearly polarized light 122 that is polarized within a plane. On the other hand, the projected component of the incident light onto the Y axis is affected by the ordinary refractive index and the extraordinary refractive index in order, and becomes XY
The light is emitted as linearly polarized light 123 that is polarized in a plane perpendicular to the plane. That is, the incident light polarized in the direction of 45° with respect to the Y axis is output as two linearly polarized lights 122° and 123 which are orthogonal to each other and have the same intensity. By the way, the polarization direction of the light beam reflected by the magneto-optical disk 106 is 1
Immediately before entering the /2 wavelength plate 111, as described above (
Due to the Kerr effect, θ3. Or -03
It is in the direction of rotation. When the polarization direction of the incident light changes periodically between the direction corresponding to θK and the direction corresponding to −θ, the intensities of the two output lights 122 and 123 have the same amplitude and change in opposite phase. becomes.

Therefore, by differentiating the outputs from the detectors corresponding to the two emitted lights, it is possible to remove light intensity fluctuations (noise) caused by foreign objects on the magneto-optical disk, for example, and improve the C/N of the reproduced signal. .

However, the above example has the following disadvantages. First, the beam splitter 107 is required to form a light beam for generating a servo signal and a light beam for generating a reproduction signal. Second, the half-wave plate 111 is required to set the polarization direction of the light beam incident on the Wollaston prism 113 to a desired direction. Thirdly, adjusting the angle setting of the 1/2 wavelength plate 111 requires a large amount of man-hours.

[Summary of the invention]

The present invention has been made in view of the drawbacks of the above-mentioned conventional examples.

An object of the present invention is to provide an optical head for a magneto-optical information reproducing device that uses a crystal element to obtain a reproduced signal of good quality and that can be easily reduced in weight, size, and thickness. It's about doing. A further object of the present invention is to provide an optical head for a magneto-optical information reproducing device that can be manufactured at low cost by reducing the number of parts.

It is an object of the present invention to provide a light source, a first beam of light directed from the light source toward a magneto-optical recording medium, and a second beam of light reflected by the magneto-optical recording medium and directed to the light source, which are separated and sent to a light receiver. a beam splitter that generates a third beam toward the opposite direction; and a beam splitter that forms a fourth beam and a fifth beam polarized in directions orthogonal to each other from the third beam to generate a reproduction signal. In the optical head, the beam separating means has a joint surface of glass and a uniaxial crystal, and the surface normal of the joint surface is within a first plane formed by the first beam and the third beam. , or within a second plane that is perpendicular to the first plane and includes the third light beam, and the optical axis of the uniaxial crystal forms an angle of 45° with the first plane. This is achieved by a characteristic optical head for a magneto-optical reproducing device.

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

[Detailed description of the invention]

First, the light beam separating means 1 suitable for the present invention will be explained using FIGS. 2 and 3. For convenience, it is assumed that an xyz coordinate system is used and the incident light beam 7 travels in the X-axis direction. The light beam separating means 1 has a structure in which a crystal 2 and a glass 3 are bonded together at a bonding surface 4 to form one body. The optical axis 5 of the crystal 2 lies within the yz plane and forms an angle of 45° with the Y axis. In addition, the surface normal 6 of the joint surface 4 is within the XZ plane,
It forms an angle of 45° to the X axis.

The ordinary refractive index of crystal 1 with respect to the wavelength of incident light is n.

1.538. A case will be described in which the extraordinary refractive index is expressed by nE=1.547 and the refractive index of the glass 2 is expressed by n=1.5425.

When linearly polarized light 7 vibrating in the Y-axis direction is incident, the optical axis 5
The projected component to is affected by the extraordinary refractive index n[ in the crystal 2. Therefore, at the junction surface 4, a light beam 8 is emitted in the direction of the Z-axis in accordance with Snell's law regarding nE and n. On the other hand, the projected component in the direction perpendicular to the optical axis 5 is the crystal 2
Among them, the ordinary refractive index n. As a result, a light beam 9 is emitted in the negative direction of the Z-axis. In the case of the above numerical example, the angle formed by the three beams 8 and 9 is 0.52°. Moreover, it is clear that the three beams are linearly polarized lights vibrating in directions orthogonal to each other.

Next, the principle of information reproduction will be explained using FIG.

In the coordinate system shown in Figure 2, Y
A case will be explained in which linearly polarized light rotated by θ from the axis is incident. Figure 4 is a schematic diagram explaining the state inside crystal 2.
The direction of the optical axis 5 of the crystal 2 is represented by the E axis, and the orthogonal coordinate axis is represented by the O axis. The incident light 7 is considered by being decomposed into two orthogonal amplitude components, a Fresnel reflection component R and a Kerr component. Let the amplitude affected by the extraordinary refractive index C and the ordinary refractive index n0 be U;
If expressed as a man, it would be shown as. Therefore, the intensity I7+ 8 of the three beams 7 and 8 generated after passing through the beam separation element 1 is as follows:
When the polarization plane of the incident light beam 7 is rotated by θ, it is expressed as , and when it is rotated by −θ3, it is expressed as .

On the other hand, for incident linearly polarized light that has been Kerr rotated by -03, if Ui, U, ; are similarly defined, it is expressed as Ui - (R+K) f(3). Therefore, the intensity of the three luminous fluxes I7. When the reproduced signal RF is obtained by calculating the difference in the electrical output from the photodetector corresponding to I8, the output is expressed as RF=I7-182KR(9) corresponding to the direction of Kerr rotation. is obtained.

However, since 1R1)IK], the item 2 was omitted.

A beam splitting means 1 according to the present invention shown in FIG. 5 is obtained by depositing a beam splitter film on the joint surface 4 of the beam separating means 1 shown in FIG. The incident light beam 7 is separated at the junction surface, and outputs as three light beams: two light beams 8 and 9 for detecting a reproduced signal and a light beam 10 for detecting a servo signal.

Obviously, the three luminous fluxes 8, 9. 10 is the same plane (X
Z plane).

P-polarized light from the beam splitter film deposited on the bonding surface 4.

The amplitude transmittance for S-polarized light is expressed as jP+tS,
The amplitude reflectance is expressed as rp and rS. At this time, the intensity of the three beams 8 and 9 for detecting the reproduced signal ■8 + I9 corresponds to the Kerr effect of ±θ3 ~ - (t82 R2 壬2t8tPRK) (10)
■ ~-(t82 R2 upper 2tstPRK) (11
), the reproduced signal RF is RF=I 8-I 9=+2t Pt SRK (
12).

On the other hand, the intensity I 10 of the light beam 10 for servo signal detection is ■+
o−(rs R)2+ (r p K)”
It is expressed as (13). Here, preferred characteristics of the beam splitter film will be explained. That is, considering that R2)R2 in equation (13), I +
o~(rsR)2(14) is obtained. At this time, if there is no absorption in the beam splitter film, t p''+r P''=j s'+r %=l
Since (15) holds true, equation (12) is RF−壬2t 8RK (16)
Therefore, it becomes possible to increase the reproduced signal component.

The above explanation is for the case where the polarization direction of the incident light beam 7 to the light beam separation means 1 is approximately within the XY plane.
When the above polarized light component is approximately within the Xz plane, RF2+2t Pt 5RK (17
) I 1O-(r P R) 2+ (r S K) 2(
18) is obtained. Therefore, in this case, RF−+2t PRK (19
) can be obtained.

As is clear from the above explanation, the beam splitter film deposited on the bonding surface 4 is such that the incident light beam 7 is approximately S with respect to the bonding surface 4.
In order to obtain a good reproduced signal, it is preferable to increase Npl when polarized light is incident, and to increase Nsl when approximately S-polarized light is incident.

FIG. 6 shows a further embodiment of the light beam separating means 1 suitable for use in the present invention. The light beam separating means 1 comprises a glass prism 3 having a parallelogram-shaped cross section and a quartz prism 2 having a right isosceles triangle shape. A surface normal 6 of the bonding surface 4 lies within the XZ plane, and a beam splitter film is applied. The optical axis of the crystal prism 2 lies within the YZ plane and is configured to form an angle of 45° with the Y axis. As can be easily understood from the figure, the three light beams 8 and 9, which are linearly polarized lights vibrating in mutually orthogonal directions for detecting the reproduced signal, and the light beam lO for detecting the servo signal are in the same direction (along the X-axis). direction), a single light receiver having three detection sections corresponding to three light beams can be used, contributing to miniaturization and cost reduction.

FIG. 7 shows a further embodiment of the light beam separating means 11 suitable for use in the present invention. The beam separating means 11 includes glass prisms 12 and 14. It consists of three prisms: a crystal prism 13. Surface normal 17 of joint surface 15. Surface normal 1 of joint surface 16
8 are both within the XZ plane. Further, the optical axis of the crystal prism 13 is located within the YZ plane and is configured to form an angle of 45° with the Y axis. Similarly to the explanation using FIG. 2, the refractive indexes of the glass prisms 12 and 14 are both equal and n=1.54.
25, and the extraordinary refractive index of the crystal prism 13 is n,
−1,547, and the ordinary refractive index is set as nO=t, sas. When the incident light beam 7 is linearly polarized light vibrating in the Y-axis direction, the projected component onto the optical axis of the crystal prism I3 is affected by the refractive index of n, nl:+n in order as the light beam advances, The components in the direction perpendicular to it are n,
nO+ It is affected by the refractive index of n. A simple calculation based on Snell's law shows that the separation angle between the two output beams 8 and 9, which are linearly polarized lights vibrating in directions orthogonal to each other, is 2 degrees, and the beam separation means shown in FIG. The opening angle is about twice that of the original one. This is advantageous when detecting intensity changes of the two light beams 8, 9 on the photoreceiver.

Also in the embodiment shown in FIG. 7, by depositing a beam splitter film on the bonding surface 15, it is possible to obtain a luminous flux for servo signal detection.

FIG. 1 shows a perspective view of an embodiment of an optical head for a magneto-optical information reproducing apparatus according to the present invention. For convenience, a coordinate system is included.

A first light beam 41 emitted from the semiconductor laser 21 in the Z-axis direction is converted into a parallel light beam by the collimator lens 22 . The first light beam 41 transmitted through the beam splitter 23 and reflected by the mirror 24 is imaged by an objective lens 25 onto a magneto-optical disk 26 which is a magneto-optical recording medium. The second light beam 42 reflected on the magneto-optical disk 26 passes through the objective lens 25° mirror 24 and is sent to the beam splitter 2.
A part of the light beam is reflected at 3 and becomes a third light beam 7 which travels in the X-axis direction. After the third light beam 7 passes through the condenser lens system 27, it enters the light beam separation means 1 explained using FIG.
A portion of the light beam is transmitted and separated by the light beam separation means 1 and becomes a fourth light beam 8 and a fifth light beam 9 for forming a reproduction signal, and a photodetector 29 on the reproduction signal photodetector 28. Reach 30. On the other hand, the servo signal detection light beam 10 reflected on the joint surface 4 of the light beam separation means 1 is received by the servo signal photodetector 31. In the figure, a diverging light beam from a semiconductor laser 21 vibrates in a direction (Y-axis direction) perpendicular to a first plane (XZ plane) formed by the first light beam 41 and the third light beam 7. It shows the state of linearly polarized light. The optical axis 5 of the crystal prism 2 of the light beam separating means 1 is Y.
It lies within the Z plane and obliquely intersects the first plane at an angle of 45°. Further, the surface normal of the joint surface 4 of the light beam separating means 1 lies within the first plane. Therefore, the third light beam 7 incident on the light beam separation means 1 is linearly polarized light vibrating approximately in the Y-axis direction, and is substantially S-polarized light incident on the joint surface 4. Fifth
For the reason explained using the figure, the beam splitter film deposited on the bonding surface 4 has, for example, (j P)2=1.
(t s )”=0.8, a polarizing beam splitter film is suitable.

In this embodiment, a 1/2 wavelength plate is not required, and the servo signal detection light beam 10, the reproduced signal detection light beam 8,
The present invention has the feature that 9 lights can be formed with a single optical element, that is, the beam separation means 1, and the number of parts and the associated man-hours for assembly and adjustment can be reduced compared to optical heads with conventional configurations. is possible.

Further, the Uniraston prism shown in the conventional example was constructed by joining two crystal prisms, but in the present invention, only one crystal prism is required for the beam separation means, and the others are glass prisms. It can also contribute to lower costs. Furthermore, among the optical elements shown in FIG. 1, the optical elements other than the objective lens 15 are arranged in the first plane (XZ plane), so the size (height) of the optical head in the Y-axis direction This allows the optical head to be made thinner and lighter. Note that when the first light beam 41 is linearly polarized light that vibrates in a direction parallel to the first plane, (tP)2=0.8. The same effect can be obtained by arranging the beam splitting means l in which a polarizing beam splitter film having a characteristic of (ts)2=1 is deposited on the bonding surface 4 as shown in the figure.

FIG. 8 shows another embodiment of the optical head according to the present invention.

The plane is orthogonal to the first plane (XY plane) formed by the first beam 41 emitted from the semiconductor laser 11 and the third beam 7 directed from the beam splitter 23 toward the receiver 28, and A surface normal to the joint surface 4 of the light beam separation means 1 exists within the second plane (xy plane) containing the light beam 7. The configuration of the beam separating means 1 is the same as the configuration explained using FIG. cross obliquely.

As a result, the three light beams 8 and 9 for forming the reproduced signal and the three light beams 10 for forming the servo signal, generated by the light beam separation means l, lie within the second plane. The optical head shown in this embodiment also provides the same effects as the optical head shown in FIG. 1.

〔Effect of the invention〕

As explained above, in the optical head for a magneto-optical signal reproducing device according to the present invention, it is possible to obtain a reproduced signal of good quality with a simple configuration, and the weight of the optical head is reduced. This makes it possible to achieve miniaturization and thinning, and also facilitates cost reduction.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the present invention, and FIGS.
The figures up to the figure are diagrams for explaining the beam separation means used in the present invention, Figure 8 is a perspective view showing another embodiment of the present invention, and Figures 9, 1O, and 11 are for explaining a conventional example. This is a diagram for 1... Luminous flux separating means 2... Crystal prism 3... Glass prism 4... Joint surface 5... Optical axis No. 10 Patent Application No. 273043 2 Name of the invention Optical spatula for magneto-optical reproducing device 1 to 3 Address name of person making the amendment 4 Residence of agent Relationship to the case Patent applicant 3-30 Shimomaruko, Ota-ku, Tokyo (100) Canon Co., Ltd. Ministry of Corporate Affairs Keiichi Yamaji 3-30 Shimomaruko, Ota-ku, Tokyo 146 January 29th 5 Specification subject to amendment 6 Contents of amendment (1) Page 5, line 4 of the specification “Linearly polarized light 122” of"
linearly polarized light 123''. (2) “Linearly polarized light 123” on page 5, line 7 of the specification is “
linearly polarized light 122''. (3) In the third line of page 10 of the specification, "Intensity T, I8 of three luminous fluxes 7 and 8" is changed to "Intensity r8, r9 of three luminous fluxes 8.9"
and correct it. (4) Correct the formula on page 10, line 5 of the specification. (5) Correct the formula on page 10, line 6 of the specification. (6) Correct the formula on page 10, line 8 of the specification. (7) Correct the formula on page 10, line 9 of the specification. (8) Page 10, line 10 of the specification: “Intensity of three luminous fluxes T7
．． IaJ is corrected to the intensity of three luminous fluxes 16.I9J. (9) Corrected to the formula % rRF=r8-1.=:1-2KRJ on page 10, line 14 of the specification.

Claims (1)

[Claims] A light source, a first beam of light directed from the light source toward a magneto-optical recording medium, and a second beam of light reflected by the magneto-optical recording medium and directed toward the light source are separated to generate a third beam of light directed toward a light receiver. In an optical head having a beam splitter and a beam separating means for forming a fourth beam and a fifth beam which are polarized in mutually orthogonal directions from the third beam in order to generate a reproduction signal, the beam separating means The means has a joint surface of glass and a uniaxial crystal, and the surface normal of the joint surface is between the first light beam and the third light beam.
or within a second plane that is orthogonal to the first plane and includes the third light beam, and the optical axis of the uniaxial crystal is within the first plane. An optical head for a magneto-optical reproducing device, characterized in that the optical head forms an angle of 45° with respect to the optical head.