JP2685790B2 - Device consisting of optical system including polarizing element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus including an optical system including a polarizing element such as a magneto-optical head for reading information on a magneto-optical disk by utilizing a magneto-optical effect. .

[Conventional technology]

Conventionally, by recording the information by utilizing the property that the temperature of the medium is raised by the irradiation of the laser beam and the coercive force is lowered,
An erasable magneto-optical disk is known. When reproducing information on this magneto-optical disk, the Kerr effect or Faraday effect is used. That is, a minute change in the polarization state of the laser light is detected by utilizing the phenomenon that the polarization plane rotates when the laser light is reflected by the magnetized magneto-optical disk or passes through (passes through) the magneto-optical disk. The information signal is read by that. An example of a magneto-optical head for reading this information signal is shown in FIG.

In FIG. 10, 1 is a semiconductor laser (laser light source),
Reference numeral 2 is a collimator lens, 3 is a beam splitter, 4 is an objective lens, and 10 is a magneto-optical disk. Semiconductor laser 1
The laser light L emitted from is collimated by the collimator lens 2, transmitted through the beam splitter 3, focused by the objective lens 4, condensed on the magneto-optical disk 10, and reflected. The reflected light (laser light) L1 is subjected to the Kerr effect, the plane of polarization is rotated, passes through the objective lens 4 again, and is reflected by the beam splitter 3 toward the beam splitter 20.

A part of the reflected light L1 incident on the beam splitter 20 is reflected, enters a sensor lens 6 including a condenser lens and a cylindrical lens, and is condensed on a four-division photodiode (detector) 9. The comparison circuit 12 receiving the output from the four-division photodiode 9 detects the focus and tracking states, and the servo mechanism (not shown) performs focusing and tracking. On the other hand, the transmitted light of the reflected light L1 enters the polarization beam splitter 22, is transmitted or reflected, and is detected by the photodetectors 7 and 8. Here, when the polarization state of the reflected light L1 reflected on the magneto-optical disk 10 is slightly changed, the light intensity of the light directed to the photodetectors 7 and 8 is changed. Therefore, the outputs of both detectors 7 and 8 are set to the differential detector 11
Thus, the information on the magneto-optical disk 10 can be read by differential detection.

[Problems to be solved by the invention]

However, in the above-mentioned conventional technique, the reflected light L1 is separated by using the plurality of beam splitters 20 and 22 in performing the detection of the focus and tracking states and the differential detection. In addition, many expensive polarizing elements are required.

Here, in a diffraction grating having a grating pitch equal to or less than the wavelength of light, it is known that the diffraction efficiency depends on the polarization of incident light (MG Moharam et.al.Appl.Opt.23 32
14 (1984)). For example, the lattice pitch Λ is 0.5 μm
Then, when an experiment was carried out on a diffraction grating having a wavelength λ of 780 nm, as shown in FIG. 11, the diffraction efficiencies of S-polarized light and P-polarized light are significantly different. Therefore, it is conceivable that the diffraction grating is used instead of the polarization beam splitter 22 of FIG. 10, and the light L1 that has passed through the beam splitter 20 is separated by this diffraction grating to make an expensive polarizing element inexpensive.
In this method, only the diffraction grating is used instead of the polarization beam splitter, and the magneto-optical head becomes large.

The above-mentioned problem similarly occurs except when the polarizing element is used in the magneto-optical head. In other words, when viewed as a problem regarding a single polarizing element that receives laser light and emits transmitted light and diffracted light, only one transmitted light and one diffracted light can be obtained for one polarizing element. If a large number of polarizing elements are to be obtained, many polarizing elements will be required.
Further, when grasped as a subject of a polarization analyzer including a differential detector that differentially detects light from the polarization elements, again, many polarization elements are required to obtain a large amount of information.

The present invention has been made in view of the above problems, and provides a polarization analyzer that is inexpensive and can obtain a large amount of information, and a device that includes an optical system that includes a polarizing element that is effective for a magneto-optical head that can be downsized. The purpose is to do.

[Means for solving the problem]

In order to achieve the above object, the claims (1) of this application
In an apparatus including an optical system including a polarizing element, the laser light source and the first and second gratings having a short pitch which is equal to or less than the wavelength of the laser light from the laser light source are arranged on the same substrate to face each other.
A polarizing element which is provided on one surface or on one surface of the two substrates in a direction in which the grating directions intersect each other, and which receives the laser light and emits transmitted light and two diffracted light. The K vector angle formed by the two K vectors set on one surface of the substrate in a direction perpendicular to the direction of the first or second grating is set to a plane perpendicular to the optical axis of the laser light. The projected angle of projection is set to 10 ° to 20 °.

Further, in the apparatus of claim (2) of this application, the laser light source and the first and second gratings having a short pitch of the wavelength of the laser light from the laser light source or less are provided on two opposite surfaces of the same substrate or Polarization elements for polarizing the laser beam are provided on one surface of the two substrates, the polarizing elements being provided in directions in which the gratings intersect with each other and emitting the transmitted beam and the two diffracted beams in response to the laser beam. The position of the plane is a direction perpendicular to the direction of the first or second grating, and the K vector angle formed by two K vectors respectively set on one surface of the substrate is defined by the K vector angle of the laser light. The projection angle projected on a plane perpendicular to the optical axis is set to an angle having an inclination of 5 ° or less with respect to an axis line that bisects the axis line or an axis line that is rotated by 90 degrees with respect to this axis line.

[Action]

According to the invention of each of the claims of this application, the first and second gratings having a short pitch, which are equal to or less than the wavelength of the incident laser light, are provided in the polarizing element on two surfaces of the same substrate or two substrates facing each other. Since the gratings are provided on one surface in the directions intersecting with each other, the transmitted light and the two diffracted lights can be obtained from one laser light. Therefore, 1
A large amount of information can be obtained by one polarizing element, and this polarizing element has better manufacturability and is less expensive than a beam splitter.

Further, in the invention of claim (1), since the projection angle is small, the angle formed by the two diffracted lights is small. Further, in the invention of claim (2), since the position of the plane of polarization has an inclination within 5 ° with respect to an axis that bisects the projection angle or an axis that is rotated by 90 ° with respect to this axis. When the plane of polarization is rotated, the intensity of diffracted light from both gratings changes greatly.

When the above polarizing element is used in the magneto-optical head, the polarizing element emits the transmitted light and the two diffracted lights, and thus the single polarizing element serves as the conventional beam splitter and the polarizing beam splitter. Therefore, the number of partial points is reduced and the magneto-optical head is downsized.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, FIG. 7 and FIG. 8, the same or corresponding parts as those of the conventional example of FIG. 10 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 5 denotes a polarizing element, which is arranged between the beam splitter 3 and the four-division photodiode 9. In the polarizing element 5, as shown in FIG. 2, a grating 5d in the D direction is formed on one surface 5b of the substrate 5a, a grating 5e in the E direction is formed on a surface 5c opposite to the surface 5b, and the directions of the two gratings intersect each other. And the pitches Λ of the gratings 5d and 5e are set to 0.51 μm and shorter than the wavelength of the laser light (for example, 780 nm) (only the grating 5e is shown in FIG. 1). . Where
As shown in FIG. 11, by changing the depth of the lattice represented by the difference in height between the concave and convex portions of the lattice, both lattices 5d in FIG.
The diffraction efficiency of 5e can be changed.

Next, the arrangement angle of the polarizing element 5 will be described. The optical axis direction of the reflected light L1 reflected from the beam splitter 3 will be described by setting the Z axis in FIG. The X and Y axes are
It is set on the XY plane perpendicular to the Z axis.

D is the direction of the grating 5d, and both diffracted light L2, L3 and transmitted light L4
E is the line set on the surface 5b from which is emitted, E is the direction of the grating 5e,
The line set on the surface 5b, the angle ψ, is the line D in this lattice direction,
It is a three-dimensional angle formed by the E and Z axes. T is the angle between the lines D and E in the lattice direction, that is, the two lattices 5d and 5e are planes.
An intersection angle mn line formed on 5b is a center line that divides the intersection angle T into two on the surface 5b, and an angle A is an angle formed between the mn line and the Z axis. The X axis is an axis projecting the center line mn on the XY plane, and the Y axis is an axis perpendicular to the X axis.

Kd and Ke represent the K vector in the direction perpendicular to the lines D and E in the lattice direction, Tk is the K vector angle formed by the K vector Kd and Ke, and 2α is the K vector angle Tk projected onto the XY plane. The projected angles K1 and K2 are projected K vectors obtained by projecting the K vectors Kd and Ke onto the XY plane. In this embodiment, the projection angle 2α is set to 90 °. That is, the angle formed by the K vectors Kd and Ke perpendicular to the two lattices 5d and 5e on the surface 5b.
The projection angle 2α obtained by projecting Tk onto the XY plane is set to 90 °.

θ is the angle between the polarization plane P of the laser beam L1 and the X axis, and the angle θ of this polarization plane is set to 90 ° in this embodiment. Therefore, the plane of polarization P is set on the axis Y which is rotated by 90 ° with respect to the axis X which divides the projection angle 2α into two equal parts, and has an inclination of 45 ° with respect to both projection K vectors K1 and K2. There is.

Next, the characteristics of the polarizing element 5 will be described before describing the operation of the above configuration.

Now, when the angle θ of the polarization plane of the polarization plane P is 0 °,
Since the plane of polarization P makes an angle α with the projected K vectors K1 and K2, the reflected light L1 is symmetrical with respect to the K vectors K1 and K2, and the plane of polarization P is rotated from θ = 0 ° to 180 °. Since the angle between the polarization plane P of the reflected light L1 and the K vectors K1 and K2 changes, the diffracted lights L2 and L3 from both gratings 5d and 5e change.
Intensity changes. As described above, since the diffraction efficiency of the diffraction grating depends on the depth of the grating,
By setting the depth of d and 5e appropriately, both diffracted light L2, L
The intensity of 3 can be equal. FIG. 4 shows the wavelength λ of the laser light is 780 nm, the grating pitch Λ of FIG. 2 is 0.51 μm,
The depth of the grating 5d is 0.6 μm, the depth of the grating 5e is 0.55 μm, the angle A in FIG. 5 is 35.0 °, the crossing angle T is 120 °, and the projection angle 2α is 9 °.
The graph shows the result of measuring the intensity change of both diffracted lights L2 and L3 at that time by changing the angle θ of the polarization plane P from 0 ° to 180 ° by setting the angle to 0 °.

 Next, the operation of the above configuration will be described.

Laser light L emitted from semiconductor laser 1 in FIG.
After passing through the collimator lens 2, the beam splitter 3, and the objective lens 4, is condensed on the magneto-optical disk 10, and the reflected light L1 thereof is incident on the beam splitter 3 again, and is directed to the polarization element 5 to be diffracted by two diffraction elements. It is divided into lights L2 and L3 and one transmitted light L4. Here, when the portion of the magneto-optical disk 10 that has reflected the laser light L is not magnetized, as shown by the solid line in FIG. 3, the polarization plane P of the reflected light L1 is θ = 90 with respect to the X axis. The laser beam L1 is incident on the polarizing element 5 at the position of °. In this case, the angles between the projected K vectors K1 and K2 of both gratings 5d and 5e and the polarization plane P are both 90 ° -α (45
.Degree.), The diffraction intensity of both diffracted lights L2 and L3 becomes the same as shown in FIG.

On the other hand, a magneto-optical disk that reflects the laser light L of FIG.
When the portion 10 is magnetized, the Kerr effect causes the plane of polarization P of FIG. 5 to be rotated by a small angle Δ, and the angle between the plane of polarization P and the projection K vector K1 or K2 increases or decreases, respectively. Then, the reflected light L1 enters the polarizing element 5. In this case, since the angles formed by the projected K vectors K1 and K2 of both gratings 5d and 5e and the polarization plane P are different, an intensity difference L5 is generated in the diffracted light as shown in FIG. Therefore, the difference between the outputs of the photodetectors 7 and 8 is detected by the differential detector 11 shown in FIG. 1, and the information on the magneto-optical disk 10 is read.

Further, the transmitted light L4 is incident on the sensor lens 6 and condensed on the four-division photodiode 9, and the tracking state and the focus state are detected.

In the above structure, according to the present invention, as shown in FIG. 2, gratings 5d and 5e having a pitch Λ shorter than the wavelength of the laser light are provided on the opposite surfaces of the same substrate so that the directions of both gratings intersect each other. The reflected light of FIG.
Since L1 is divided into three, one polarizing element 5 serves as two conventional beam splitters. Therefore,
The number of parts is reduced and the magneto-optical head is downsized. Further, the polarization analyzer including the polarization element 5, the photodetectors 7 and 8 and the differential detector 11 or the polarization element alone has an effect that a large amount of information can be obtained at low cost.

By the way, the projection angle 2α in FIG.
Although it is set to 0 °, it may be set appropriately within the range of 0 <2α <180 °. However, the projection angle 2α appears as the phase of both diffracted lights L2 and L3, as shown in FIG.
When set to 90 °, both diffracted lights L2 and L3 fluctuate oppositely in the entire range of the polarization angle θ of 0 ° to 180 °, so that the angle θ of the polarization plane P in FIG. No
The rotation of the polarization plane P can be detected.

On the other hand, the projection angle 2α is an angle other than 90 °, for example 67
When set to °, the intensities of the diffracted lights L2 and L3 of both gratings 5d and 5e are as shown in Fig. 5, and in the shaded area S,
The intensity difference between the two diffracted lights L2 and L3 does not change, and the intensity difference L5 becomes smaller than that in the case of 2α = 90 ° in FIG.
However, when the projection angle 2α is set to about 10 ° to 20 °, both the gratings 5d and 5e are close to parallel, so that the diffracted light
Although the change in the intensity difference L5 (FIG. 5) between L2 and L3 is extremely small, the directions in which both diffracted lights L2 and L3 are emitted are close to each other. That is, the angle formed by both diffracted lights L2 and L3 becomes smaller. Therefore, for example, the magneto-optical head can be further downsized.

Further, the intensity difference L5 between the two diffracted lights L2 and L3 in FIG. 4 is obtained when the angle θ of the polarization plane P is near 0 °, 90 ° or 180 °.
It changes greatly. This phenomenon is caused by the projection angle 2α = 67 in FIG.
The same applies to the case of ° and other cases. Therefore,
The position of the polarization plane P in FIG. 3 is ± with respect to the X axis or the Y axis.
It is preferable to set the angle to have an inclination of 5 °. That is, the position of the plane of polarization P is determined by the axis X that divides the projection angle 2α into two equal parts.
Alternatively, it is preferable to set an angle having an inclination of 5 ° or less with respect to the axis Y rotated 90 ° with respect to the axis X. In particular, if the polarization plane is set at a position where the positive / negative of the intensity difference L5 in FIG. 4 is reversed, for example, θ = 86 °, θ + Δ = 94 °, etc. Can be detected. In this embodiment, the angle ψ formed by the line D of the first grating and the Z-axis on the surface 5b is the same as the angle (not shown) formed by the line E of the second grating and the Z-axis. Although set, they do not necessarily have to be the same.

Next, a method of determining the intersection angle T of the polarizing element 5 shown in FIG. 2 will be described. The crossing angle T is determined by the arrangement angles A, ψ and the projection angle 2α of the polarizing element 5 of FIG. 3 in the magneto-optical head used. Therefore, these angles A,
It is necessary to find the relationship between ψ, 2α and the intersection angle T. Sixth
In the figure, Here, β = 90 ° −T / 2, so sinT / 2 × cosA = cosψ ... The required crossing angle T can be obtained from the above equation.

The polarizing element 5 is a two-beam interference exposure method, or a photolithography method using a photomask, or an electron beam drawing method or a laser beam direct drawing method, in which a photosensitive resin such as a photoresist is applied to a substrate such as glass. It can be prepared by a method of developing a photosensitive resin after exposure by a method or the like, or a method of mechanically engraving a lattice using a ruling engine. The cross-sectional shape of both gratings 5d and 5e of the polarizing element 5 is not limited to the sinusoidal wave shape shown in FIG. 2, but may be any shape such as a rectangular wave shape or a trapezoidal wave shape.

If necessary, the polarizing element 5 is used as a matrix,
A nickel stamper (mold) may be manufactured by an electroforming method, and a replica may be manufactured using this mold by a replication method such as an injection molding method, a compression method, or a photopolymer method (2P method).

By the way, although the pitches Λ of the gratings 5d and 5e are the same in FIG. 2, they may be different from each other. Further, the curved first and second gratings 5d and 5e and the first and second gratings 5d and 5e in which the pitch Λ gradually changes, and the first and second curved and the pitch Λ in which the pitch Λ gradually changes. The polarizing element 5 having the gratings 5d and 5e may be used.

The case where the first and second lattices are formed on the opposite surfaces of the same substrate has been described in detail above. However, the first lattice is formed on the first substrate and the second lattice is formed on the second substrate. After the formation, the first and second substrates may be attached and laminated to each other, or the first and second substrates may be separated from each other. Furthermore, of course, the first and second gratings may be formed to face either the polarization beam splitter 3 or the detector 9.

FIG. 7 shows another embodiment of the present invention. A plate-type half mirror 14 is arranged between the objective lens 4 and the polarizing element 5. The polarizing element 5 in this embodiment is also the second
As shown in the figure, two grids are provided on the facing surfaces 5b and 5c of the substrate 5a.
5d and 5e are formed so as to intersect with each other (only one grating is shown in FIG. 7).

In the case of this embodiment, the laser light L emitted from the semiconductor laser 1 is reflected by the half mirror 14 and the objective lens 4
And is focused on the magneto-optical disk 10. afterwards,
The reflected light L1 passes through the objective lens 4 again, enters the polarizing element 5 from the half mirror 14, and reads the information on the magneto-optical disk 10 in the same manner as in the embodiment of FIG. And adjust the focus.
Here, since the reflected light L1 entering the half mirror 14 is convergent light, coma aberration occurs, but this coma aberration is corrected by the polarization element 5.

FIG. 8 shows another embodiment of the present invention. In this embodiment, the polarizing element 5 is integrally formed with the half mirror 14 shown in FIG. As shown in FIG. 9, the gratings 5d and 5e are formed on different substrates 5f and 5g, respectively.
f and 5g are laminated. The gratings 5d and 5e face the detector 9 and have a half mirror surface 14A on one surface of the substrate 5f on the side of the magneto-optical disk 10 on which the reflected light L1 is incident. Therefore, the magneto-optical head becomes smaller, and the number of parts becomes smaller.

The other constructions of the embodiment shown in FIGS. 7 and 8 are similar to those of the embodiment shown in FIG. 1, and the same portions or corresponding portions are designated by the same reference numerals and the description thereof will be omitted.

By the way, although the method using one beam is used in each of the above embodiments, for example, a grating (phase grating) is provided between the semiconductor laser 1 and the collimating lens 2 shown in FIG. Focusing may be performed by the four-division photodiode 9. Further, a λ / 2 plate may be provided at an arbitrary position to change the polarization direction of light.

Further, in each of the above-mentioned embodiments, the laser light reflected by the magneto-optical disk (the one utilizing the reflected light) has been described in all the embodiments, but the present invention is one in which the laser light is transmitted through the magneto-optical disk (the transmitted light). Those that use) are also applicable. That is, the Faraday effect may be used.

〔The invention's effect〕

As described above, according to the inventions of the claims of this application, in the polarizing element, the first and second gratings having a short pitch equal to or shorter than the wavelength of the incident laser light are provided on the opposite surfaces of the same substrate. Since the lattices are provided on one surface of each of the two substrates in directions intersecting with each other, 1
With one polarizing element, a large amount of information can be obtained, and the manufacturability of the polarizing element is good and the cost is low.

Further, according to the invention of claim (1), since the projection angle is small, the angle formed by both diffracted lights becomes small, and therefore the optical device can be downsized.

Further, in the invention of claim (2), the position of the polarization plane is set to an angle within 5 ° with respect to the axis that bisects the projection angle or the axis that is rotated by 90 ° with respect to this axis. As a result, the intensity of both diffracted lights changes greatly, which makes it easier to detect the rotation of the polarization plane.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a magneto-optical head showing an embodiment of the present invention, FIG. 2 is an enlarged perspective view of an embodiment of a polarizing element, and FIG.
Fig. 4 is a perspective view showing the arrangement angle of the polarizing element, Fig. 4 is a characteristic diagram of the polarizing element when the projection angle is set to 90 °, and Fig. 5 is a characteristic diagram of the polarizing element when the projection angle is 67 °. 6 is a perspective view showing a method for obtaining a crossing angle from the arrangement angle of polarizing elements, FIG. 7 is a schematic configuration diagram of a magneto-optical head showing another embodiment of the present invention, and FIG. 8 is another one of the present invention. 9 is a schematic configuration diagram of a magneto-optical head showing an embodiment, FIG. 9 is an enlarged perspective view of a polarizing element in the same embodiment, FIG. 10 is a schematic configuration view showing a conventional example, and FIG. 11 is S polarization and P in a diffraction grating. It is a characteristic view which shows the diffraction efficiency of polarized light. 1 ... Semiconductor laser (laser light source), 5 ... Polarizing element,
5a, 5f, 5g ... Substrate, 5d ... First grating, 5e ... Second grating, 9 ... Detector (quadrant photodiode), 10 ...
… Magneto-optical disk, 11… Differential detector, 14A… Half mirror surface, L… Laser light, L1… Reflected light, L2, L3…
Diffracted light, L4 ... Transmitted light, Λ ... Pitch, 2α ... Projection angle, Kd, Ke ... K vector, P ... Polarization plane, Tk ... K vector angle, X, Y ... Axis, Z ... …optical axis.

Claims (2)

(57) [Claims] 1. A laser light source and first and second gratings having a short pitch which is equal to or less than the wavelength of the laser light from the laser light source are provided on two surfaces of the same substrate facing each other or one surface of two substrates. A direction perpendicular to the direction of the first or second grating, the polarization element being provided in a direction in which the directions of the grating intersect with each other and emitting a transmitted light and two diffracted lights in response to the laser light. And the projection angle of the K vector angle formed by the two K vectors respectively set on one surface of the substrate is 10 ° to 20 ° projected onto the plane perpendicular to the optical axis of the laser beam. A device comprising an optical system including a polarizing element characterized in that 2. A laser light source and first and second gratings having a short pitch, which is equal to or less than the wavelength of the laser light from the laser light source, are provided on two surfaces of the same substrate facing each other or on one surface of the two substrates. And a polarization element that is provided in a direction in which the directions of the grating intersect with each other and that emits the transmitted light and the two diffracted light upon receiving the laser light, and the position of the polarization plane of the laser light is the first or A K vector angle, which is a direction perpendicular to the direction of the second grating and formed by two K vectors set on one surface of the substrate, is projected on a plane perpendicular to the optical axis of the laser beam. An apparatus comprising an optical system including a polarizing element, characterized in that a projection angle is set to an angle having an inclination of 5 ° or less with respect to an axis line that bisects or an axis line that is rotated by 90 degrees with respect to this axis line. .