JPH0469838A - Optical device for optical pickup - Google Patents

Abstract

PURPOSE:To obtain a low-cost optical pickup optical device with a simple constitution by differentially detecting the reception quantities of light components, which are reflected by slopes of two light-transmissive members and are different in polarization plane direction, to obtain a photomagnetic signal. CONSTITUTION:The laser light from a laser 1 is collimated to parallel rays of a luminous flux by a collimator lens 2, and the s-polarized wave is reflected in the direction of a line Lc by a polarizing beam splitter 10 and is reflected by a reflection plate 11 of a galvanomirror and is sent from a total reflection prism 12 to an objective lens 13 and is condensed on the recording face of a disk. The return light is transmitted through the splitter 10 and is sent to a reception-side optical axis Lb. It is reflected and transmitted by two plane glass plates 22 and 33 rotated at 45 deg. to (x) and (y) axes to detect a photomagnetic signal. Light polarized at + or -45 deg. to the (x) axis are received by pinhole diodes 24a and 24b, and non-polarized light is received by a diode 24c. Two light reception outputs are differentially detected to obtain the photomagnetic signal, thereby constituting the optical device for a magneto- optical disk with a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup used in a magneto-optical disk device, and more particularly to an optical device that has a simple configuration and can be manufactured at low cost.

[Prior Art 1] FIG. 6 shows an optical device of a conventional optical pickup for a magneto-optical disk device.

The laser beam output from the semiconductor laser 1 is turned into a parallel beam by the collimating lens 2, passes through the Okovic type beam splitter 3, and is focused on the recording surface of the disk 5 by the objective lens 4, forming a minute spot. be done.

In this conventional example, since the laser beam output from the semiconductor laser 1 is configured to pass through the beam splitter 3, the linearly polarized wave emitted from the semiconductor laser 1 is
It is used as a polarized light wave. When used as P-polarized light, about 80% of the light is transmitted and about 20% is reflected by the polarizing film 3a of the beam splitter 3. disk 5
The return light reflected from the recording surface of the beam splitter 3
is reflected by the polarizing film 3a of the Wollaston prism 6.
The light passes through, is focused by a condenser lens 7, passes through a cylindrical lens 8, and is received by a bin photodiode 9.

The Oraston prism 6 divides the return light from the disk 5 into two beams that are differentially detected, a filter 7, and a beam that does not involve polarization. The bin photodiode 9 detects each return light from Ll to Ll. Ll
By differentially detecting the amount of light received by L2 and L2, a signal based on the Kerr rotation angle of the return light from the recording surface of the magneto-optical disk 5 is detected. Furthermore, error signals such as focus and tracking errors are obtained by the central light La.

[Problem to be Solved by the Invention 1] However, in the conventional optical device described above, the Oraston prism 6 is used, but the glass material of the Oraston prism 6 is a uniaxial crystal such as artificial quartz, which is expensive. It is. Therefore, it is difficult to configure the entire optical device at low cost.

The present invention solves the above-mentioned conventional problems, and provides an optical pickup that has a simple configuration and uses low-cost optical members, and can perform the same functions as an Oraston prism. The purpose of the present invention is to provide an optical device.

"Means for Solving the Problems" An optical device for an optical pickup according to the present invention is provided with a condensing member that focuses detection light on a magneto-optical disk and a light emitting element that sends detection light to the condensation member. , the path of the return light from the magneto-optical disk includes a first light-transmitting member having an inclined surface on which the return light is incident at a predetermined angle of incidence; a second light-transmitting member having an inclined surface inclined in a direction perpendicular to the direction of inclination of the inclined surface of the light-transmitting member; and first and second light-receiving members facing in the direction of light reflection by the respective light-transmitting members. The device is characterized in that a third light-receiving element facing the second light-transmitting member is provided further forward in the traveling direction of the returned light.

[Operation] In the above means, the return light from the disk passes through the first and second light-transmitting members. At this time, the inclined surface of each light-transmitting member is set at an angle such that the incident angle of the returning light thereto is at or near Brewster's angle, and the first and second
The directions of the slopes of the light-transmitting members are orthogonal to each other. As a result, light components having different directions of polarization planes are reflected by each inclined surface. The first and second light-receiving elements receive light components having different directions of polarization planes reflected by the respective inclined surfaces, and by differentially detecting the amount of the received light, a magneto-optical signal can be read. Furthermore, by setting the inclined surfaces of the first and second light-transmitting members at the same angle of inclination, the light that passes through both the first and second light-transmitting members becomes a component that does not substantially participate in polarization. By detecting with the third light receiving element, a focus error signal, a tracking error signal, etc. can be obtained.

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

FIG. 1 is a perspective view showing the element configuration of an optical device for an optical pickup according to a first embodiment of the present invention.

The reference numeral 1 in the figure is a semiconductor laser 24a.

24b and 24e are bin photodiodes. In this embodiment, a polarizing beam splitter 1 is installed at the branch point between the light transmitting optical axis La of the semiconductor laser 1 and the light receiving optical axis Lb of the bin photodiodes 24a24, b, and 24c.
0 is placed. In this embodiment, the semiconductor laser 1
Laser light emitted from the is used as S-polarized light. In other words, the direction of the polarization plane of the laser beam is the direction of the meridian plane (
(vertical plane direction including La).

About 80% of the S-polarized light wave is reflected by the polarizing beam splitter 10 and about 20% is transmitted, and the reflected component by the polarizing beam splitter 10 is sent in the Lc direction. Reference numeral 11 is a reflecting plate of a galvano mirror. A total reflection prism 12 and an objective lens 13 are provided in the pickup movable section in the direction of reflection by the reflection plate 11. Since the movable part of the pickup moves in the radial direction of the disk, the total reflection prism 12 moves as shown by solid lines and broken lines in FIG.
Then, the objective lens 13 moves in the direction of reflection of the reflection plate 11. The reflector plate 11 of the galvanometer mirror is shown as a in Fig. 1.
This causes the optical axis to swing and drag correction is performed.

Further, the light component transmitted through the polarizing beam splitter 1o is detected by a light receiving element 14 for monitoring.

Front APC control is adopted in which the output of the semiconductor laser 1 is controlled based on the detected amount of received light.

A condenser lens 21 is provided on the light receiving side optical axis Lb. The laser light that has become a parallel light beam by the collimating lens 2 returns from the disk, but this returned light is turned into a focused light by the condenser lens 2J.

The focused light is sent to a first flat glass 22 and a second flat glass 23. Each flat glass 22 and 23 has an optical axis L
4. In FIG. 1, for convenience of illustration, the first flat glass 22 is tilted with respect to the X axis,
The second flat glass 23 is arranged obliquely with respect to the y-axis. However, in reality, as shown in FIGS. 3A and 3B, each of the flat glasses 22 and 23 is arranged at an angle rotated by 45° counterclockwise around the optical axis Lb from the attitude shown in FIG. 1. . Also, the inclination angle of each flat glass 22 and 23 with respect to the optical axis 1, 1], that is, each flat glass 2
The angle of incidence θ for 2 and 23 is set to a value that matches or is close to Brewster's angle. A bin photodiode 24a, which is a first light-receiving element, faces the reflection direction of the first flat glass 22. Further, a bin photodiode 24b, which is a second light-receiving element, is opposed to the reflection direction of the second flat glass 23. Furthermore, the plate thickness dimensions tl and t2 of the first and second flat glasses are different.

Astigmatism occurs in the focused light due to the difference in thickness between the inclined flat glasses 22 and 23, and a focus error signal is obtained by the bin photodiode 24c, which is the third light receiving element.

Next, the operation will be explained.

The laser beam from the semiconductor laser is converted into a parallel beam by the collimating lens 2, and approximately 80% of the S-polarized light wave is reflected in the Le direction by the polarizing beam splitter 10, reflected by the galvanomirror reflecting plate 11, and then reflected by the total reflection prism 12. The light is then sent to the objective lens 13 and focused on the recording surface of the disk to form a minute spot. The return light from the disk returns along its original path, passes through the polarizing beam splitter 10, and is sent to the light-receiving side optical axis Lb.

Here, in the flat glass provided in the focused light, the incident angle θ
If is Prusster's angle, for example, when the refractive index of flat glass is 1.5, and the angle of incidence is 56°3, then P
100% of polarized light waves (polarized light components parallel to the plane of incidence) are transmitted,
15% of the S-polarized light wave (polarized light component perpendicular to the plane of incidence) is reflected. This transmittance changes depending on the refractive index and the value of θ. For example, if the refractive index of flat glass is 1.7 and θ is set to 59°, the flat glass will transmit 100% of the P-polarized light wave and the S-polarized light wave. 20% becomes reflective.

Therefore, how the light is reflected and reflected by the two flat glasses 22 and 23 rotated by 45 degrees with respect to the x-y axis.
How a magneto-optical signal is detected through transmission will be explained with reference to FIGS. 4A to 4D.

The x-y axis direction shown in each figure corresponds to the x-y axis in FIGS. 3A and 3B. Further, the inclination angle θ of the first and second flat glasses 22 and 23 is 59°, and the refractive index is 1.7.
It is.

First, the polarization direction and amplitude of light incident on the first flat glass 22 are represented by OA in FIG. 4A.

OA can be considered separately into OB and OC components in the ±45° direction with respect to the y-axis.

The function of the first flat glass 22 will be explained. In the first flat glass 22, due to the difference in transmittance and reflectance for the P-polarized light wave and the S-polarized light wave, 20% of the light intensity for the OB (IOB+") is received by the bin photodiode 24a, as shown in FIG. 4B. The other light passes through the first flat glass 22. Therefore, the light incident on the second flat glass 23 is OB" and OC shown in FIG. 4C. I'm here.

Similarly, in the second flat glass 23, as shown in FIG. Therefore, the light transmitted through the second flat glass 23 is OB'' and OC''.

Here, OC″″=OC-10c It is.

In this way, the bin photodiodes 24a and 24b each receive polarized light in the direction of ±45° with respect to the X axis, and the bin photodiode 24c receives light that is substantially not involved in polarization. Become.

The Kerr rotation angle is read by differentially detecting the light reception outputs of the first photodiode 24a and the second photodiode 24b, which are the first light receiving elements, and thereby the magneto-optical signal of the disk can be obtained. Further, a focus error signal, a tracking error signal, etc. can be obtained by the bin photodiode 24c. By using the flat glasses 22 and 23 with different thicknesses and J-measures, it is possible to change the astigmatism of the focused light by q゛, which makes it possible to change the astigmatism of the focused light by q゛. becomes unnecessary.

Next, FIGS. 5A and 5B show a second embodiment of the present invention.

In this embodiment, prisms 22a and 23a are used instead of the flat glasses 22 and 23. The returned light is incident on the respective inclined surfaces 22b and 23b of the prisms 22a and 23a at an incident angle θ at or near Brewster's angle. In this case, for example, if the refractive index of the prism is 1.5, θ is set to 563°, which is the Brewster's angle, or by setting θ to 59° when the refractive index is 17, it is possible to achieve the same result as in the first embodiment. Similarly, the Kerr rotation angle can be read using the bin photodiodes 24a and 24b, and focusing errors, tracking errors, etc. can be detected using the bin photodiodes 24c. In the embodiments shown in FIGS. 5A and 5B, it is necessary to interpose a cylindrical lens 8 because it is not possible to produce astigmatism as in the case of flat glass.

Further, as a structure for producing astigmatism, the first light-transmitting member may be a prism 22a, and the second light-transmitting member may be a flat glass 23. Astigmatism may be produced by changing the refractive index of the first light-transmitting member 22.22a and the second light-transmitting member 23.23a.

Also, each of the transparent members 22.22a, 2323a
In the bin photodiodes 24a, 24., a reflective film is provided on the incident surface of the returned light. The amount of light received at point b is determined by the bin photodiode 24.b. You may set more than c.

Furthermore, the incident angle θ of the returned light can be arbitrarily selected as long as it is an angle that allows the three light receiving elements 24a, 24b, and 24c to achieve the above effects.

[Effects] As described above, according to the present invention, there is no need to use an expensive Oraston prism, so it is possible to construct an optical device for a magneto-optical disk at low cost. Furthermore, by using flat glasses of different thicknesses, it is possible to eliminate the need for cylindrical lenses.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the element configuration of an optical device of an optical pickup according to a first embodiment of the present invention, FIG. 2 is a perspective view showing the main parts of the optical device, and FIG. 3A is a perspective view showing each light-transmitting member and a light-receiving element. Figure 3B is a side view, Figures 4A to 4 are
Fig. D is an explanatory diagram showing the detection effect of magneto-optical signals by two flat glasses, Fig. 5A is a plan view showing each light transmitting member and a light receiving element according to the second embodiment, Fig. 5B is a side view thereof, and Fig. 6 The figure is a front view showing the element configuration of a conventional optical device. 1... Semiconductor laser, 2... Collimator lens, 9
... Bin photodiode, 21 ... Condensing lens, 2
2.22 a--First transparent member, 23.23a--
- Second light-transmitting part; a... First light-receiving element; 24b... Second light-receiving element; 24e... Third light-receiving element.

Claims (1)

[Claims] 1. A light focusing member that focuses detection light on a magneto-optical disk;
A light emitting element that sends detection light is provided to the light condensing member, and the path of the return light from the magneto-optical disk includes a first transparent element having an inclined surface on which the return light is incident at a predetermined angle of incidence. a second light-transmitting member having an inclined surface inclined in a direction perpendicular to the direction of inclination of the inclined surface of the light-transmitting member at the end of the traveling direction of the returned light of the light-transmitting member; First and second light-receiving elements facing each other in the direction of light reflection by the light-transmitting member, and a third light-receiving element facing further ahead of the second light-transmitting member in the traveling direction of the returned light are provided. An optical device for an optical pickup characterized by