JPH02192040A - Optical pickup device - Google Patents

Abstract

PURPOSE:To accurately detect the tilt of an optical information recording medium by detecting the displacement of the condensing position of a 0-th order reflected light by means of an objective lens with a divided light receiving element. CONSTITUTION:When a parallel light flux from a light source side is made incident on an objective lens 50, a part of the light flux is made incident on an optical information recording medium 6 as 0-th order light (j), and when it is reflected as the parallel light flux, it is made incident on the objective lens 50 as the 0-th order reflected light. Further one part of it is diffracted to be a condensed light flux 1, and condensed to the light source side focal position of the objective lens 50. When the optical information recording medium 6 has the tilt, the condensing position of the condensed light flux 1 is shifted in the direction orthogonal to the optical axis of the objective lens 50 away from the focal position. That is, at a divided light receiving element 90, the position of a spot S shifts in the direction of either one light receiving part, a tilt detecting signal is obtained from the output of the light receiving part, and the corresponding relation between the tilt detecting signal and a tilt angle theta is obtained. Thus the tilt of the optical information recording medium 6 can be accurately detected.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optical pickup device.

[Prior Art] An optical pickup device is known as a device for recording and/or reproducing information on an optical information recording medium.

In order to record and/or reproduce information properly, it is necessary to control the focusing so that the beam from the laser light source is correctly focused into a spot on the recording surface of the optical information recording medium using the objective lens, and to properly focus the light beam on the focused spot. Tracking control is required to follow the track.

FIG. 5 schematically shows only the essential parts of an example of a conventionally well-known optical pickup device.

In FIG. 5(I), a light beam from a semiconductor laser 1 as a laser light source is collimated by a coupling lens 2, and is then collimated by a polarizing beam splitter 3 and 17.
The light passes through the four-wavelength plate 4, enters the objective lens 5, and is focused by the action of the lens 5 into a spot having a diameter of approximately 1 μm on the recording surface of the optical information recording medium 6.

The reflected light from the recording surface passes through the objective lens 5 and the quarter-wave plate 4, enters the polarizing beam splitter 3 again, is reflected by the beam splitter 3, enters the condensing lens 7, and enters the polarizing beam splitter 3 again. When the light passes through the lens, it becomes a convergent light beam.

A portion of this convergent light beam is blocked by the two-split light receiving element 8 and enters the two-split light receiving element 9 .

The focus error signal is obtained from the two-split light receiving element 9 by a known knife method using the edge of the two-split light receiving element 8 as a knife, and a servo that displaces the objective lens 5 in the optical axis direction based on this focus error signal. Focusing control can be performed using the control.

On the other hand, the track error signal is obtained from the two-split light receiving element 8. As shown in FIG. 5 (II), the two-split light receiving element 8 has a light receiving surface divided into two light receiving parts A and B, and each light receiving part A
, B can obtain photoelectric conversion outputs a and b. The dividing line that separates the light receiving sections A and B corresponds to the track direction.

Now, referring to FIG. 6, tracks Tr are formed on the recording surface of the optical information recording medium 6, and the tracks are separated by track guides G.

In the state shown in FIG. 6(a), the light beam is correctly focused on the track Tr, and the light intensity distribution on the two-split light receiving element 8, that is, the far field image FFI is the light receiving part A of the two-segment light receiving element 8. , B are symmetrical with respect to the dividing line that separates them. However, when the convergence state of the light beam shifts from the track Tr to the track guide section G as shown in FIG. The interference effect with the reflected light from the track guide section G is asymmetrical with respect to the above dividing line, and the far field image F
In FI, as shown in FIG. 6(b), the light intensity increases on the side where the focused spot is shifted. Therefore, the voltage signal Va obtained by converting the outputs a and b from the light receiving sections A and B into voltage signals,
By configuring (Va-vb) as a track error signal from Vb and performing servo control to set this trunk error signal to O, 1 to racking control can be performed.

An offset of the tracking error signal due to the inclination of the optical information recording medium 6 is a cause of deterioration of the accuracy of tracking control.

That is, as shown in FIG. 7(a), there is no problem when the optical information recording medium 6 is not tilted with respect to the optical axis of the objective lens 5, but as shown in FIG. 7(b), the objective lens 5 When the normal direction of the recording surface of the optical information recording medium 6 is tilted by θ with respect to the optical axis of It is shifted by 2fθ with respect to the chief ray of the luminous flux. Here, f is the focal length of the objective lens 5. In the end, the reflected light beam is also shifted by 2fθ with respect to the two-split light receiving element 8. Then, due to this deviation, the cross-sectional areas of the light beams received by the light receiving sections A and B become different from each other, so in addition to the change in outputs a and b due to the change in the far field image due to the track deviation, the output change due to the above-mentioned change in cross-sectional area. This occurs and enters the tracking error signal as an offset component, degrading the accuracy of tracking control.

In order to correct the tracking control in consideration of the tilt of the optical information recording medium, the tilt of the optical information recording medium must be detected.

Conventional methods for detecting the tilt of an optical information recording medium include the method disclosed in Japanese Patent Application Laid-open No. 60-9018 and the method disclosed in Japanese Patent Publication No. 60-9018.
A method disclosed in Japanese Patent No. 3-22369 is known.

[Problem to be Solved by the Invention] Among the above methods, the former method requires a dedicated light source for detecting the above-mentioned tilt in the optical pickup device, which causes a problem that the cost of the optical pickup device is high. .

In addition, the latter method detects the inclination by using the DC component of the output of the light receiving element to generate a track error signal, but in addition to the information on the inclination of the optical information recording medium, the DC component also includes information about the inclination of the optical information recording medium. It is difficult to accurately detect the inclination because it also includes information on eccentric components.

The present invention was made in view of the above-mentioned circumstances, and
The objective is to provide a novel optical pickup device that has a function of easily and reliably detecting the tilt of an optical information recording medium, which causes deterioration in accuracy of tracking control.

[Means to solve the problem] The present invention will be explained below.

The optical pickup device of the present invention uses an objective lens that utilizes a diffraction phenomenon to condense a light beam from a laser light source into a spot on an optical information recording medium, and a focal point on the light source side of the objective lens. A divided light-receiving element having a plurality of light-receiving parts is arranged near the position of the divided light-receiving element, and the output from each light-receiving part of the divided light-receiving element is used to configure the tilt detection signal of the optical information recording medium. ”.

[Operation] When the light flux from a laser light source is made into a parallel light flux and is incident on an "objective lens that utilizes the diffraction phenomenon", that is, a micro Fresnel lens or a Fresnel zone lens, and is focused on the recording surface of an optical information recording medium. The light beam transmitted through the objective lens includes a so-called zero-order light component that is not affected by diffraction, and this zero-order light enters the recording surface as a parallel light beam, is reflected, and enters the objective lens. This luminous flux is called the zero-order reflected luminous flux.
When this zero-order reflected light flux re-enters the objective lens, a part of it is focused at the focal point of the objective lens on the light source side by the lens action due to the diffraction phenomenon of the objective lens.

When the optical information recording medium is tilted, the direction of the zero-order reflected light is tilted with respect to the optical axis of the objective lens, so that the focusing position of the zero-order reflected light by the objective lens is displaced. By detecting this displacement using the divided light receiving elements, the tilt of the optical information recording medium can be detected with high accuracy.

[Example code] Hereinafter, description will be given based on specific examples.

FIG. 1 schematically shows only the essential parts of one embodiment of the present invention.

To avoid complication, the same reference numerals as in Figure 5 have been used for items that are unlikely to cause confusion. Also,
Portions related to focusing control that are not directly related to the present invention are omitted from illustration.

In the embodiment, the feature of the present invention is that a micro Fresnel lens using diffraction is used as the objective lens 50, and a divided light receiving element 90 is arranged near the focal position of the objective lens 50 on the light source side. The point is that

The divided light-receiving element 90 is made as small as possible so as not to block the luminous flux to a large extent. Further, the supporting means (not shown) is also of a type that does not block the light beam as much as possible.

Now, in FIG. 1(a), when a parallel light flux from the light source side enters the objective lens 50, a part of the light flux enters the optical information recording medium 6 as a parallel light flux as zero-order light j, and the parallel light flux enters the optical information recording medium 6 as a parallel light flux. When reflected as a light beam, it becomes a 0th-order reflected light and passes through the objective lens 5.
0.

Further, due to the diffraction effect of the objective lens 50, a part of the incident light flux becomes a convergent light flux i and condenses toward the optical information recording medium 6, and when reflected on the recording surface, it returns to the objective lens 50 as a divergent light flux. incident on .

When this diverging reflected light flux passes through the objective lens 50, a part continues to diverge as zero-order light m, but the rest is diffracted and becomes return light. This returned light k is used for focusing control, tracking control, and information reproduction.

Now, when the zero-order reflected light enters the objective lens 50, a part of it is diffracted and becomes a condensed light beam 1, which is condensed at the focal position of the objective lens 50 on the light source side.

The inclination of the optical information recording medium 6 is detected using this condensed light beam 1. In FIG. 1(a), the optical information recording medium 6 is not tilted, and the focused light beam 1 is focused at the focal point of the objective lens 5o on the light source side.

However, if the optical information recording medium 6 is tilted as shown in FIG. 1(b), the convergence position of the convergent light beam l shifts from the focal position in a direction perpendicular to the optical axis of the objective lens 50. As shown in FIG. 2, the amount of deviation is 2fO, where f is the focal length of the objective lens 50 and θ is the tilt angle of the optical information recording medium 6.
It is.

The divided light-receiving element 90 is a two-part light-receiving element whose light-receiving surface is divided into light-receiving parts C and D as shown in FIG. As shown in FIG. 3(a), spot S is equally incident on the light receiving sections C and D, but if the optical information recording medium 6 is tilted, the position of the spot S will be changed as shown in FIG. 3(b). It shifts to either the light receiving part C or D. Therefore, the output c from the light receiving parts C and D
, d are obtained as voltage signals Vc and Vd as a tilt detection signal (Vc-Vd), and if the correspondence relationship between this tilt detection signal and the tilt angle θ is determined by actual measurement, the tilt detection signal yields: Since the inclination of the optical information recording medium 6 can be detected with high precision, good tracking control can be achieved by correcting the offset component of the tracking error signal according to the detection result.

In the embodiment described above, a two-divided light-receiving element is used as the divided light-receiving element, but the present invention is not limited to this, and for example, a four-divided light-receiving element 91 as shown in FIG. 4 may be used. This four-divided light receiving element 91 includes light receiving portions E and F.

A photoelectric conversion output ey f+ gy )1 can be obtained from G and H. Let the voltage signals obtained by converting this output be Ve, Vf, Vg, and Vh. By using these voltage signals, the inclination of the optical information recording medium 6 in two mutually orthogonal directions can be detected.

That is, if the state shown in FIG. 4(a) is assumed to be a state with no inclination (the spot S is equally incident on the light receiving sections E, F, G, and H), a signal of (Ve + Vf) - (Vg + Vh) will be obtained. to detect the inclination in one direction, (Ve+Vg)-(Vf+V
The inclination in the other direction can be detected using the signal h).

[Effects of the Invention] As described above, according to the present invention, a novel optical pickup device can be provided. Since this device has the above-mentioned configuration, it can easily and reliably detect the tilt of an optical information recording medium by using the light from the same light source used for information recording, reproduction, focusing control, and tracking control. Therefore, it is possible to effectively correct the offset component of the tracking error signal caused by the above-mentioned inclination and perform good tracking control.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining one embodiment of the present invention, and FIG.
3 and 3 are diagrams for explaining inclination detection of an optical information recording medium according to the above embodiment, FIG. 4 is a diagram for explaining characteristic parts of another embodiment, and FIGS. FIG. 7 is a diagram for explaining the prior art and its problems. 100. Semiconductor laser, 200. cup link lens. 306. Polarizing beam splitter, 4. ,． 1/4 wavelength plate, 50°0. Micro Fresnel lens, 600. Optical information recording medium, (S ＼ω 已υ

Claims (1)

[Claims] An objective lens that utilizes a diffraction phenomenon is used to focus the light beam from a laser light source into a spot on an optical information recording medium, and near the focal position of the objective lens on the light source side, An optical pickup characterized in that a split light receiving element having a plurality of light receiving parts is provided, and the output from each light receiving part of the split light receiving element is used to configure the tilt detection signal of the optical information recording medium. Device.