JP2636659B2 - Focusing error detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focusing error detector, and more particularly to a focusing error detector used for a compact disk (CD) and an optical disk.

[0002]

2. Description of the Related Art As shown in FIG. 2, a conventional focusing error detector includes a stop lens 11, which receives and reflects light reflected from a disk recording surface 1, a coupling lens 13, a cylindrical lens 14, and a cylindrical lens 14. Light detector 15 for detecting light from the detector and an amplifier 16 for amplifying an error
And

The light output from the light source is input to a stop lens 11 by a beam splitter 12, and the light stopped by the stop lens 11 strikes the disk recording surface 1 and is reflected. The reflected light enters the aperture lens 11 again, passes through the beam splitter 12, and enters the coupling lens 13. The light output from the coupling lens 13 enters the cylindrical lens 14. The light output from the cylindrical lens 14 is focused according to the displacement of the disk. This light is detected by a four-divided photodetector 15 and converted into an electric signal. The four photodetectors divided by the photodetector 15 are electrically connected to each other in pairs, and the output difference between the two pairs of photodetectors is amplified by the amplifier 16. Detect the focusing error.

[0004] Detection of the four light detecting elements since the photodetector 15 if in pairs on the disk recording surface 1 to focus lens 11 is normal position of the objective lens is incident on the center of true circle beam When the output is put into the error amplifier, the output becomes zero. If the disk is shifted upward or downward with respect to the focal position of the objective lens, a vertically elliptical or horizontal elliptical beam is incident on the photodetector 15, and the disk recording surface deviates from the focal position from the error amplifier 16. Is output.

[0005]

In this conventional focusing error detection, both an optical system that requires a coupling and a cylindrical lens in addition to a stop lens and a photodetector that requires four divisions have a complicated configuration. There was a problem.

[0006]

SUMMARY OF THE INVENTION A focusing error detector according to the present invention is constructed by reflecting a light beam once transmitted.
When transmitted again from the opposite side from the beginning, the polarized light
A polarizing element that differs from the first polarized light by 90 °,
Separating a part of the parallel light from the light source consisting of polarized light and
After being emitted toward the polarizing element and reflected by the reflection means
Again, there is a 90 ° difference from the first polarized light transmitted through the polarizing element.
A light beam composed of the second polarized light is converted into a parallel light beam from the light source.
The first via which is combined with the other separated one and emitted
A beam splitter and the combined first and second biases.
A birefringent lens that impinges on a target surface through light;
The light reflected by the first lens and passing through the birefringent lens again
Polarizing beam splitter that separates the polarized light into a second polarized light and a second polarized light.
And light incident from the first beam splitter.
The light is emitted toward the birefringent lens and reflected at the target surface.
The light that has passed through the birefringent lens after the
A second beam splitter that emits light toward the beam splitter
And the second beam splitter by the polarizing beam splitter.
First and second light receiving first and second polarized light, respectively
And the output difference between the first and second photodetectors.
And a differential amplifier that outputs

The object of the focusing error detector of the present invention
The surface is, for example, an optical disk recording surface.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of an embodiment of the present invention. Parallel light composed of α-wave polarized light from a light source is split into two by a beam splitter 8, one of which is reflected by a mirror 10 through a polarizing element 9 and returns to the beam splitter 8 again through the polarizing element 9. The polarized light returned to the beam splitter 8 in this way has a polarization direction of 90 ° from the polarization of the α wave by the polarization element 9.
It is a polarized β wave that has been rotated. The polarization of the β-wave and the polarization of the α-wave, which is the other one split by the beam splitter 8, are recombined from the beam splitter 8, reflected by the beam splitter 3, have optical anisotropy, and depend on the polarization direction of the incident light. The light is incident on a birefringent lens 2 composed of convex lenses having different focal lengths.

The polarized lights of α-wave and β-wave having different 90 ° polarization directions are output from the birefringent lens 2 as light having different focal lengths, and are reflected on the disk recording surface 1. The polarized lights of the α-wave and the β-wave reflected by the disk recording surface return to the refracted lens 2, become parallel light again, pass through the beam splitter 3, and enter the polarization beam splitter 4.

The polarized lights of the α-wave and the β-wave are separated by the polarization beam splitter 4 and enter the photodetectors 6 and 5, respectively. The difference between the outputs from the photodetectors 6 and 5 is determined by the amplifier 7.

The amount of light reflected from the disk recording surface 1 and passing through the birefringent lens 2 and incident on the photodetector 5 or 6 becomes maximum when the disk recording surface 1 is at the focal point of the birefringent lens 2, and from the focal point. It becomes less as it shifts. Therefore, when the disk recording surface 1 is at the focal point of the polarization of the α-wave by the birefringent lens 2, the output of the amplifier 7 also has a predetermined value of − , and changes as the disk recording surface 1 deviates from this focal point. When at the focal point of the polarization of the wave, it has a predetermined value of + .

That is, the output of the amplifier 7 is
A change in the distance between the lenses can be detected.

[0014]

As described above, the focusing error detector of the present invention has an effect that the optical system and the photodetector can be simplified by using a birefringent lens.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2A is a configuration diagram of a conventional focusing error detector, and FIG. 2B is a diagram illustrating a photodetector 15 and its peripheral circuits.

[Explanation of symbols]

 Reference Signs List 1 disc recording surface 2 birefringent lens 3 beam splitter 4 polarizing beam splitter 5 light receiving element 6 light receiving element 7 amplifier 8 beam splitter 9 polarizing element 10 mirror 11 aperture lens 12 beam splitter 13 coupling lens 14 cylindrical lens 15 photodetector 16 amplifier

Claims (2)

(57) [Claims] (1) A light beam once transmitted is reflected.
When transmitted again from the opposite side from the beginning, the polarized light
A polarizing element that differs from the first polarized light by 90 °,
Separating a part of the parallel light from the light source consisting of polarized light and
After being emitted toward the polarizing element and reflected by the reflection means
Again, there is a 90 ° difference from the first polarized light transmitted through the polarizing element.
A light beam composed of the second polarized light is converted into a parallel light beam from the light source.
The first via which is combined with the other separated one and emitted
A beam splitter, a birefringent lens that impinges on the target surface through the combined first and second polarized lights, and a light that is reflected by the target surface and passes through the birefringent lens again to the first surface.
A polarizing beam splitter that separates the polarized light into a second polarized light and a second polarized light, and the light that enters from the first beam splitter is emitted toward the birefringent lens and is reflected at the target surface.
And a second beam splitter for emitting light transmitted through the birefringent lens again to the polarizing beam splitter after the irradiation, and a first and a second light receiving the first and second polarized lights separated by the polarizing beam splitter, respectively. Second
And the output difference between the first and second photodetectors.
Focusing error detector which comprises a differential amplifier for outputting. 2. The object surface is an optical disk recording surface.
2. The focusing error detector according to 1.