JP2707361B2 - Optical device for optical pickup - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used in a magneto-optical disk drive, and relates to an optical device that can be manufactured at a low cost with a simple configuration.

[Conventional technology]

FIG. 6 shows an optical device of an optical pickup for a conventional magneto-optical disk device.

The laser light output from the semiconductor laser 1 is converted into a parallel light beam by the collimator lens 2, passes through the cubic type beam splitter 3, and is condensed on the recording surface of the disk 5 by the objective lens 4 to form a minute spot. In this conventional example, since the laser beam output from the semiconductor laser 1 is configured to pass through the beam splitter 3, a linearly polarized wave emitted from the semiconductor laser 1 is used as a P-polarized wave. When used as a P-polarized wave, the polarizing film 3a of the beam splitter 3
About 80% is transmitted light and about 20% is reflected light. The return light reflected from the recording surface of the disk 5 is reflected by the polarizing film 3 a of the beam splitter 3, passes through the Wollaston prism 6, is collected by the condenser lens 7, passes through the cylindrical lens 8, and passes through the pin photodiode 9. Is received.

The Wollaston prism 6 separates the return light from the disk 5 into two lights L ₁ and L ₂ that are differentially detected, and light L ₃ that does not contribute to polarization. Each return light from L ₁ in pin photodiode 9 L ₃ is detected. By differential detecting the amount of received light L ₁ and L _2, the signal due to the Kerr rotation angle of the return light from the recording surface of the magneto-optical disc 5 is detected. The error signals such as a focus and tracking error is obtained by a central light L _3.

[Problems to be solved by the invention]

However, in the above-mentioned conventional optical device, the Wollaston prism 6 is used, but the glass material of the Wollaston prism 6 is a uniaxial crystal such as artificial quartz and is expensive. Therefore, it is difficult to configure the entire optical device at low cost.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and provides an optical pickup having a simple structure and using a low-cost optical member so as to exhibit the same function as provided with a Wollaston prism. It is intended to provide an optical device.

[Means for solving the problem]

An optical device for an optical pickup according to the present invention includes a light-collecting member that focuses detection light on a magneto-optical disk, and a light-emitting element that sends detection light to the light-collecting member. A first light-transmitting member having an inclined surface on which return light is incident at a predetermined incident angle, and an inclined surface of the light-transmitting member at the end of the traveling direction of the return light of the light-transmitting member. A second light-transmitting member having an inclined surface inclined in a direction orthogonal to the inclination direction, first and second light-receiving elements facing light-reflecting directions of the respective light-transmitting members, and the second light-transmitting element The third member which is further opposed to the end of the member in the traveling direction of the return light
Are provided.

[Action]

In the above means, 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 to an angle at which the incident angle of the return light with respect to the angle is at or near the angle of the Brewster, and the first and second light transmitting members are inclined by the inclined surfaces. The directions are orthogonal to each other. As a result, light components having different polarization plane directions are reflected by the respective inclined surfaces. First and second
In the light receiving elements of the above, light components having different directions of polarization planes reflected by the respective inclined surfaces are received, and a magneto-optical signal can be read by differentially detecting the amount of received light. In addition, by setting the inclined surfaces of the first and second light transmitting members to have the same inclination angle, light transmitted through both the first and second light transmitting members becomes a component substantially not related to polarization. By detecting with the third light receiving element, a focus error signal, a tracking error signal, and the like can be obtained.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

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

Reference numeral 1 in the figure denotes a semiconductor laser, and reference numerals 24a, 24b and 24c denote pin photodiodes. In this embodiment, the light transmission side optical axis La of the semiconductor laser 1 and the pin photodiodes 24a, 24
A polarization beam splitter 10 is arranged at a branch point between b and 24c from the light receiving side optical axis Lb. In this embodiment, a laser beam emitted from the semiconductor laser 1 is used as an S-polarized wave. That is, the direction of the plane of polarization of the laser light is the direction of the meridional plane (vertical plane direction including La). S
The polarized wave is reflected by the polarizing beam splitter 10, and about 80% is reflected and about 20% is transmitted light, and the reflected component by the polarizing beam splitter 10 is sent in the Lc direction. Reference numeral 11 denotes a galvanomirror reflector. 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 and the objective lens 13 move in the reflection direction of the reflection plate 11 as shown by the solid line and the broken line in FIG. become. The reflecting plate 11 of the galvanomirror is swung in the α direction in FIG. 1, whereby the optical axis is swung to perform tracking correction. The light component transmitted through the polarization beam splitter 10 is detected by the light receiving element 14 for monitoring. Front APC control in which the output of the semiconductor laser 1 is controlled by the detected light reception amount is employed.

A condenser lens 21 is provided on the light receiving side optical axis Lb.
The laser beam converted into a parallel light beam by the collimating lens 2 returns from the disk.
To become focused light. There are a first flat glass 22 and a second flat glass 23 at the destination of the focused light. With each flat glass 22
23 is arranged obliquely with respect to the optical axis Lb. In FIG. 1, for the sake of illustration, the first flat glass 22 is inclined with respect to the x-axis, and the second flat glass 23 is inclined with respect to the y-axis. However, in practice, as shown in FIGS. 3A and 3B, each of the flat glass plates 22 and 23 is arranged at an angle rotated 45 ° counterclockwise about the optical axis Lb from the posture of FIG. . Further, each flat glass 22 and 23 with respect to the optical axis Lb
, Ie, the angle of incidence θ with respect to each of the flat glass plates 22 and 23, is set to a value that matches or is close to the angle of the Brewster. A pin photodiode 24a as a first light receiving element is opposed to the reflection direction of the first flat glass 22. Further, a pin photodiode 24b as a second light receiving element is opposed to the reflection direction of the second flat glass 23. Furthermore, the thickness t _{1 of} the first and second flat glass is
t ₂ is different. Flat glass, each inclined 22
Astigmatism occurs in the converged light due to the difference between the plate thickness dimensions of the light receiving element and the light receiving element 23, and a focus error signal is obtained by the pin photodiode 24c as the third light receiving element.

 Next, the operation will be described.

The laser beam from the semiconductor laser 1 is applied to a collimator lens 2
Approximately 80% of the S-polarized wave is reflected by the polarizing beam splitter 10 in the Lc direction, reflected by the reflecting plate 11 of the galvanometer mirror, sent from the total reflection prism 12 to the objective lens 13, and recorded on the disk. The light is condensed on the surface to form a minute spot. The return light from the disk returns along the original path, passes through the polarization beam splitter 10, and is sent to the light receiving side optical axis Lb.

Here, in the flat glass provided in the focused light, when the incident angle θ is a Brewster angle, for example, when the refractive index of the flat glass is 1.5 and the incident angle is 56.3 °, a P-polarized wave (incident 100% of the polarization component parallel to the plane is transmitted, and 15% of the S-polarized wave (polarization component perpendicular to the plane of incidence) is reflected. This transmittance changes depending on the refractive index and the value of the above-mentioned θ. For example, if the refractive index of the flat glass is set to 1.7 and θ is set to 59 °, the flat-polarized glass transmits 100% of the P-polarized wave and 20% of the S-polarized wave. Will be reflected.

FIG. 4A shows how the two flat glass plates 22 and 23 rotated by 45 ° with respect to the xy axis reflect and transmit light to detect a magneto-optical signal. This will be described with reference to FIG. 4D. The xy-axis directions shown in these figures coincide with the xy axes in FIGS. 3A and 3B. The inclination angle θ between the first and second flat glass plates 22 and 23 is 59 ° and the refractive index is
1.7.

First, the polarization direction and amplitude of the light incident on the first flat glass 22 are represented by ▼ in FIG. 4A. ▲ ▼ is y
It can be considered separately in the components of ▲ ▼ and ▲ ▼ in the direction of ± 45 ° with respect to the axis.

The operation of the first flat glass 22 will be described. The first flat glass 22 transmits and transmits the P-polarized and S-polarized waves.
The difference in reflectance, the light intensity ▲ against ▼ as shown in Figure 4B ^{(| ▲ ▼ | 2) 20} % pin photodiode
The other light is received by 24a and transmitted through the first flat glass 22. Therefore, the light incident on the second flat glass 23 is shown in FIG. 4C. And ▲ ▼. here It is.

In the same manner in the second flat glass 23, as shown in FIG. 4D, ▲ ▼ to light intensity ^{(| ▲ ▼ | 2) 20} % of
Is reflected and received by the pin photodiode 24b, and the other light passes through the second flat glass 23. Therefore the second
The light passing through the flat glass 23 of It is. here It is.

In this way, the pin photodiodes 24a and 24b have
Each of them receives light having a polarization of ± 45 ° with respect to the x-axis, and the pin photodiode 24c receives light substantially not related to the polarization.

The Kerr rotation angle is read by differentially detecting the light receiving output of the pin photodiodes 24a and the second pin photodiodes 24b as the first light receiving elements, thereby obtaining a magneto-optical signal of the disk. Further, a focus error signal and a tracking error signal can be obtained by the pin photodiode 24c. Since the flat glasses 22 and 23 having different thickness dimensions are used, astigmatism can be generated in the converged light, and the conventional cylindrical lens 8 (see FIG. 6) 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 glass plates 22 and 23. This prism 22a and 2
Return light is incident on the respective inclined surfaces 22b and 23b of 3a at an angle of incidence θ of the angle of the Brewster or an angle near the angle. Also in this case, for example, when the refractive index of the prism is 1.5, θ is set to 56.3 °, which is the Brewster angle, or by setting the refractive index to 1.7 and θ to 59 °, similarly to the first embodiment. The Kerr rotation angle can be read by the pin photodiodes 24a and 24b, and a focus error or a tracking error can be detected by 24c.
In the embodiment shown in FIGS. 5A and 5B, since a stigmatic difference such as a flat glass cannot be produced, a cylindrical lens 8 must be provided.

Further, as a structure for generating the astigmatic difference, the first light transmitting member may be a prism 22a and the second light transmitting member may be a flat glass 23. Further, in the first and second embodiments, astigmatism may be generated by changing the refractive index of the first light transmitting members 22, 22a and the second light transmitting members 23, 23a.

In each of the light transmitting members 22, 22a, 23, and 23a, a reflection film is provided on the incident surface of the return light, and the pin photodiode 24 is provided.
The amount of received light at a and 24b may be set to be larger than that at the pin photodiode 24c.

Further, the incident angle θ of the return light can be arbitrarily selected as long as the above-mentioned action can be exerted by the three light receiving elements 24a, 24b, 24c.

〔effect〕

As described above, according to the present invention, it is not necessary to use an expensive Wollaston prism, so that an optical device for a magneto-optical disk can be configured at low cost. Further, the use of a flat glass having a different thickness can eliminate the need for a cylindrical lens.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an 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 a main part of the optical device, and FIG. 3A is a light transmitting member and a light receiving element. 3B is a side view thereof, and FIGS. 4A to 4D are 2
FIG. 5A is a plan view showing each light transmitting member and light receiving element according to the second embodiment, FIG. 5B is a side view thereof, and FIG. FIG. 3 is a front view illustrating an element configuration of the optical device. 1 ... Semiconductor laser, 2 ... Collimate lens, 9 ...
Pin photodiode, 21 …… Condenser lens, 22, 22a ……
First light transmitting member, 23, 23a... Second light transmitting member, 24a.
First light receiving element, 24b... Second light receiving element, 24c.
Light receiving element.

Claims (1)

(57) [Claims] A light-condensing member for converging the detection light on the magneto-optical disk; and a light-emitting element for transmitting the detection light to the light-condensing member. A first light-transmitting member having an inclined surface on which return light is incident at a predetermined incident angle; A second light-transmitting member having an inclined surface inclined in the direction, first and second light-receiving elements opposed in a light reflection direction by the respective light-transmitting members, and further returning light of the second light-transmitting member. An optical device for an optical pickup, comprising: a third light receiving element facing the front in the traveling direction of the optical pickup.