JPH06162530A - Optical pickup device - Google Patents

Abstract

PURPOSE:To obtain an optical pickup by which an astigmatism is generated in a reflected light from a disk without using a cylindrical lens and which is miniaturized at a low cost. CONSTITUTION:Radiation light 2 radiated from a semiconductor laser 1 is converted to a parallel luminous flux through a collimator lens 3, transmitted through a beam splitter 7, and converged on a disk 5 by an objective lens 4; and the reflected light 6 from the disk 5 is separated from the radiation light 2 by the beam splitter 7, transmitted through a convex lens 8 and a concave lens 9, and converted to electric signals by an optical detector 11. The concave lens 9 is arranged abliquely in the reflected light 6; a positional adjustment mechanism 13 is attached to a holder 12 holding the concave lens 9 coincidentally with the conjugate position of the optical detector 11 and the semiconductor 1; and the astigmatismn necessary for generating focus error signals to the reflected light is generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for optically reproducing / recording information.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing the structure of a conventional optical pickup device. In FIG. 6, 1 is a semiconductor laser, 2 is radiation light emitted from the semiconductor laser 1, 3 is a collimating lens for converting this radiation 2 into parallel light flux, 4 is an objective lens, 5 is a disc, and 6 is a disc. The reflected light from 5, the beam splitter 7 separating the optical paths of the reflected light 6 and the reflected light 2, 8 a convex lens, 9 a concave lens, 10
Is a cylindrical lens, 11 is a photodetector, 12 is a holder for holding the concave lens 9 and the cylindrical lens 10,
Reference numeral 13 is a position adjusting mechanism for finely adjusting the position of the holder 12.

Next, the operation will be described. The emitted light 2 emitted from the semiconductor laser 1 is converted into a parallel light flux by the collimator lens 3, then passes through the beam splitter 7, and is condensed on the disk 5 by the objective lens 4. The disk 5 is rotated by a mechanism not shown in FIG. 6, and the light beam condensed by the objective lens 4 scans the disk 5.

The emitted light 2 focused on the disk 5 is reflected by the disk 5 and re-enters the objective lens 4,
The radiated light 2 is separated by the beam splitter 7, transmitted through the convex lens 8, the concave lens 9 and the cylindrical lens 10 and incident on the photodetector 10, where it is converted into an electric signal.

By the way, in general, the distance between the objective lens 4 and the disk 5 is not constant in the disk 5 due to the vibration from the outside or the surface contact of the disk 5 itself. However, in order to increase the storage density on the disk 5, the disk 5
The emitted light 2 needs to be accurately focused on top. That is, the disk 5 needs to be positioned exactly at the position of the image of the semiconductor laser 1 formed by the objective lens 4.

In the optical path of the reflected light 6 from the disk 5,
A convex lens 8 that collects the reflected light 6 to the photodetector 11 and a cylindrical lens 10 that applies astigmatism to the reflected light 6 are provided. Further, the photodetector 11 is the semiconductor laser 1
It is installed at a position conjugate with. When the position of the disk 5 deviates from the position of the image of the semiconductor laser 1 formed by the objective lens 4, the position of the photodetector 11 and the condensing position of the reflected light 6 deviate, and the spot shape on the photodetector 11 is changed. Changes because the astigmatism is given by the cylindrical lens 10.

A change in the spot shape of the reflected light 6 on the photodetector 11 is detected by a known method and is detected as a focus error signal, and the position of the objective lens 4 is corrected based on the focus error signal. As a result, the disk 5 is always controlled to be positioned at the position of the image of the semiconductor laser 1 formed by the objective lens 4.

In order to perform the above operation, the photodetector 11
Must be accurately located at a conjugate position with the semiconductor laser 1, and is generally provided with an adjusting mechanism for correcting an influence due to an assembly error or the like. That is, the concave lens 9 is provided between the convex lens 8 and the photodetector 11, the concave lens 9 and the cylindrical lens 10 are fixed to the holder 12, and the position of the holder 12 is adjusted by the position adjusting mechanism 13. The position is adjusted at the time of assembling the optical pickup device so that the position is conjugate with the semiconductor laser 1.

[0009]

Since the conventional optical pickup device is configured as described above, the cylindrical lens 10 is required, the configuration is complicated, the cost is low, and the small optical pickup device cannot be configured. There was a problem.

The invention set forth in claim 1 has been made to solve such a problem, and it is small in size that astigmatism can be generated and a focus error signal can be generated without a cylindrical lens. It is also intended to obtain an inexpensive optical pickup device.

It is an object of the present invention to provide an optical pickup device capable of suppressing the occurrence of coma aberration in reflected light and obtaining a stable focus error signal.

[0012]

An optical pickup device according to a first aspect of the present invention has an axially symmetric shape, is arranged to be inclined with respect to the reflected light from the disc, and has an aberration added to the reflected light. It is provided with a convex lens that makes most of it astigmatism.

In the optical pickup device according to a second aspect of the present invention, the focal length is f, and the refractive index of the constituent medium is n.
Then, the radius of curvature r on the incident side, which is reflected from the disk and enters, is approximately (Equation 2)

[0014]

[Equation 2]

A convex lens is provided.

[0016]

The convex lens according to the first aspect of the present invention is arranged in the reflected light with an inclination with respect to the reflected light, thereby imparting astigmatism to the reflected light, and the focus error signal is obtained even without the cylindrical lens. Is obtained.

The convex lens according to the second aspect of the invention is
By setting the radius of curvature r on the incident side to be approximately (Equation 1), the occurrence of coma aberration in reflected light is suppressed.

[0018]

【Example】

First Embodiment Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration explanatory diagram of the first embodiment. This Figure 1
In FIG. 6, the same parts as those of the conventional example of FIG. 6 are denoted by the same reference numerals to avoid redundant description of the configuration, and the parts different from those of FIG. As is apparent from a comparison of FIG. 1 with FIG. 6, in FIG. 1, the portions denoted by reference numerals 1 to 8 and 11 to 13 are the same as those in FIG. 6, and the concave lens 9 is different from FIG. .

That is, the concave lens 9 in FIG. 1 is used as an optical element having a lens action and having an axially symmetric shape, and a predetermined amount of the reflected light 6 is contained in the light flux of the reflected light 6 from the disk 5. It is arranged at an angle. The concave lens 9 is held by a holder 12, a position adjusting mechanism 13 is provided in the holder 12, and the position adjusting mechanism 13 can adjust the position of the concave lens 9.
With this configuration, astigmatism is given to the reflected light 6.

Next, the operation will be described. Generally, as shown in FIG.
When the light flux of is incident on the concave lens 8 as shown in FIG. 3, the converging positions of the sagittal light a in the sagittal direction and the meridional light b in the meridional direction are different, and the astigmatism c
Occurs.

In the optical pickup device according to the first embodiment of the present invention, since the astigmatism required to generate the focus error signal is arranged with the concave lens 9 inclined,
It can be obtained without the cylindrical lens 10 shown in FIG. 6, and the cylindrical lens 10 is unnecessary. Further, since the holder 12 for holding the concave lens 9 and the position adjusting mechanism 13 are provided, the conjugate point of the semiconductor laser 1 and the position of the photodetector 1 can be aligned with each other, so that the optical pickup device is inexpensive and small in size. Can be configured.

Second Embodiment Next, a second embodiment of the present invention will be described. FIG. 4 is an explanatory diagram of the configuration of the second embodiment. In the first embodiment, the concave lens 9 is arranged as an optical element with an inclination with respect to the reflected light 6, but in the second embodiment, as shown in FIG. The convex lens 8 having a symmetrical shape is arranged in the luminous flux of the reflected light 6 with an inclination, and further,
The position adjusting mechanism 1 is fixed to the holder 12 and fixed to the holder 12.
By installing 3, the astigmatism of the reflected light 6 required to obtain the focus error signal can be obtained. Further, the conjugate point of the semiconductor laser 1 and the photodetector 11 can be adjusted to coincide with each other.

In the second embodiment, not only the cylindrical lens 10 but also the concave lens 9 is unnecessary, so that a more inexpensive optical pickup device can be constructed.

Third Embodiment Next, a third embodiment of the present invention will be described. Generally, when a light beam is incident on a lens with an inclination, not only astigmatism but also coma is generated. The amount of this coma aberration can be represented by Seidel's aberration coefficient H. In a single lens,
The Seidel aberration coefficient H can be approximately represented by the following (Equation 3) when the light flux incident on the single lens is a parallel light flux.

[0025]

[Equation 3]

In this (Equation 3), h is the light ray height of the light ray incident on the lens, f is the focal length of the lens, n is the refractive index of the medium forming the lens, r is the curvature of the surface on which the parallel light flux is incident.

In the second embodiment, since the convex lens 8 is a plano-convex lens, not only astigmatism but also coma is generated. However, as shown in FIG. 5, the convex lens 8 is a biconvex lens, and By setting the curvature such that the value of (1) in the third term on the right side of (Equation 3) becomes zero, that is, the following (Equation 4), the occurrence of coma aberration in reflected light can be suppressed, An optical pickup device that can obtain a stable focus error signal can be realized.

[0028]

[Equation 4]

[0029]

Since the present invention is configured as described above, it has the following effects.

According to the first aspect of the present invention, a convex lens is arranged in the light flux of the reflected light from the disc inclining with respect to the reflected light, and the reflected light is given astigmatism, which is a major part of the aberration. By doing so, the focus error signal can be obtained without the cylindrical lens, the cylindrical lens becomes unnecessary, and the size and cost can be reduced.

Further, according to the second aspect of the present invention, by setting the radius of curvature of the convex lens to be (Equation 1), it is possible to suppress the occurrence of coma in reflected light from the disc, A stable focus error signal can be obtained.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of an optical pickup device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of an arrangement relationship of convex lenses with respect to incident light from a disc for explaining the operation of the first embodiment.

FIG. 3 is an explanatory diagram showing an astigmatism generation state when an incident light beam is obliquely incident on a concave lens for explaining the operation of the first embodiment.

FIG. 4 is a structural explanatory view of an optical pickup detection device according to a second embodiment of the present invention.

FIG. 5 is a side view showing a biconvex lens in the optical pickup detection device according to the third embodiment of the present invention.

FIG. 6 is a diagram illustrating a configuration of a conventional optical pickup device.

[Explanation of symbols]

 1 semiconductor laser 2 emitted light 3 collimating lens 4 objective lens 5 disk 6 reflected light 7 beam splitter 8 convex lens 9 concave lens 11 photodetector 12 holder 13 position adjusting mechanism

Claims (2)

[Claims] 1. A laser light source, a condenser lens system for condensing light emitted from the laser light source onto a disc, a photodetector for receiving reflected light from the disc and converting it into an electric signal, and an axis. A convex lens having a symmetrical shape and arranged in the reflected light at an angle with respect to the reflected light, in which most of the aberration added to the reflected light is astigmatism, and a position adjusting mechanism for adjusting the position of the convex lens. And an optical pickup device. 2. The reflected light incident on the convex lens is a substantially parallel light beam, and the radius of curvature r of the incident light side of the convex lens is r.
Where f is the focal length of the convex lens and n is the refractive index of the medium forming the convex lens, The optical pickup device according to claim 1, wherein