JPH02108247A - Optical pickup device - Google Patents

Abstract

PURPOSE:To cancel astigmatism and to correctly read information on an information recording carrier by providing a laser light source and a converging lens so that the astigmatism directions can intersect orthogonally with each other. CONSTITUTION:An emitting luminous flux 2 from the laser light source 1 forms a spot 5 through a beam splitter (BS) 6 and a converging lens 3 on the information recording carrier 4. The reflecting light is retrograded, reflected by BS 6 and made incident on a photodetector 7. An astigmatism direction 9 of a light source 1 and an astigmatism direction 10 of a convergence lens 3 are allowed to intersect orthogonally, with each other, the astigmatism quantity of both is made equal and then, the whole optical type astigmatism is cancelled and a satisfactory spot is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention focuses the emitted light beam from a laser light source onto an information recording carrier using a condensing lens system, and refocuses the reflected light beam from this information recording carrier. The present invention relates to an optical pickup device that optically performs recording and reproduction by focusing light onto a photodetector using an optical lens system.

[Prior Art] FIG. 3 is a perspective view showing a schematic configuration of a conventional optical pickup device. In the figure, (1) shows a laser light source made of a semiconductor laser, and (2) shows the light emitted from the laser light source (1). The luminous flux (3) is the output luminous flux (2) that is transferred to the information recording carrier (4).
A condensing lens condenses the light above, (5) is a condensing spot of the emitted light beam (2), and (6) is a reflected light beam reflected by the information recording carrier (4) and condensed by the condensing lens (3). (8
) and the output beam (2), a beam splitter (7
) is a photodetector that converts the focused reflected light beam (8) into an electrical signal.

In the above configuration, the emitted light beam (2) emitted from the laser light source (1) is passed through the condensing lens (3) to the information recording carrier (4).
) to form a focused spot (5).

The light beam focused on the focused spot (5) is modulated and reflected by the information recorded on the information record carrier (4),
The light is focused by the condenser lens (3) and sent to the beam splitter (
6) and enters the photodetector (7). The intensity of the reflected light beam (8) incident on the photodetector (7) changes depending on the information recorded on the information recording carrier (4), and the change in the intensity of the reflected light beam (8) is detected by the photodetector (7). The strength of the electrical signal is changed and used as an audio, video signal, or digital data by a circuit not shown here.

In addition, information corresponding to the deviation of the focused spot (5) from a predetermined track on the information recording carrier (4) and the defocus is also included in the reflected light beam (8), and this information is detected by the photodetector (7). In response to the detected information, the entire optical pickup device is moved to the information recording carrier (
4) be moved against.

By the way, since information is recorded at an extremely high density on the information recording carrier (4), in order to pick up this information with high precision, the focused spot (5) needs to be a perfect circle with a diameter as small as possible. be.

However, it is well known that the emitted light beam (2) has astigmatism because the oscillation light of the laser light source (1) made of a semiconductor laser is not axially symmetrical. Further, the condensing lens (3) also has astigmatism, with its condensing power varying depending on the lens axis direction.

[Problems to be Solved by the Invention] Since the conventional optical pickup device is configured as described above, the focused spot deteriorates due to astigmatism of the laser light source and the focusing lens, and it is inevitable that the focused spot will become a perfect circle with the minimum diameter. Therefore, there was a problem that the information on the information recording carrier could not be read out correctly and with high precision.

This invention was made to solve the above-mentioned problems, and provides an optical pickup device that can correctly read information on an information recording carrier even when using a laser light source with astigmatism or a condensing lens. The purpose is to obtain.

[Means for Solving the Problems] An optical pickup device according to the present invention includes five laser light sources and five condenser lens systems arranged such that their astigmatism directions are orthogonal to each other.

[Function] In the optical pickup device according to the present invention, the astigmatism directions of the condensing lens and the laser light source are orthogonal and are shifted by 90 degrees, so the astigmatism is canceled out and a good focused spot can be obtained. Thereby, the information on the information record carrier can be read correctly.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a perspective view showing a schematic configuration of an embodiment of the present invention.
The figure is an operation explanatory diagram showing the exit pupil plane of this embodiment. In the figure, (1) is a laser light source 5 (2) is an emitted light flux, (
3) is a condensing lens, (4) is an information recording carrier, (5) is a condensing spot, (6) is a beam splitter, (7) is a photodetector, (8) is a reflected light beam, and (9) is a laser. The astigmatism direction of the light source (1) (the direction in which the focused spot becomes elongated), (i
o) is the astigmatism direction of the condenser lens (3), (11) is
exit pupil, which is the image of the aperture seen through the condensing lens (3);
(12) is a point on the exit pupil plane. Note that the laser light source (1) and the condenser lens (3) are arranged so that their astigmatism directions (9) and (lO) can be determined in advance by their configuration and measurement, and their directions are orthogonal to each other. It is set up.

The operation of this embodiment as an optical pickup is similar to that of the conventional example shown in FIG. 3, so its explanation will be omitted, and its astigmatism will be explained with reference to FIG.

Now, as shown in Fig. 2, set the polar coordinates with the origin at the center of the exit pupil (11), and set a point P (r,
0 ) If the delay of the wavefront at (12) is W(r, θ), then α is the astigmatism direction (9) and W(r, θ)=Wcos(2(θ−α)) ”(1
). Here, W indicates the amount of astigmatism.

The amount of astigmatism of the condensing lens (4) is Wo, and the astigmatism direction (
9) is α0, the amount of astigmatism of the laser light source (1) is Wb, and the astigmatism direction (10) is α2, then the condenser lens (4)
From equation (1), the wavefront W□(r, θ) of the luminous flux emitted is Wl(r, θ)=W, cos(2(θ-cz, ))+W
Lcos(2(O-αg)) = W, (cos"(θ-a,)-sin"(θ-
α, ))+WL, (Cog” (θ−a,) −si
n” (θ−α2))・−・(2).By the way,
cos” (θ+”t)=si from α□=α2±π/2
n”(θ+α2)sin” (0+α□)=cos”(
θ + α2) ... (3), so the astigmatism of the entire optical system is W, (r, θ) = (W, WL) ((
CO1122(θ+α, ))-sin” (2(0-α
2))] = (W, -WL)cos(2(θ+α11))-
---(4), the condenser lens (3) and the laser light source (
1) is the difference in the amount of astigmatism. Therefore, the amount of astigmatism of this optical pickup is reduced, and a good focused spot (
5) is obtained, and the information in (4) on the information record carrier can be read out correctly.

In addition, in the above embodiment, the astigmatism directions of the condenser lens (3) and the laser light source (1) were only made perpendicular to each other, but in addition, the astigmatism directions of the condenser lens (3) and the laser light source (1) If the amounts are made equal, the astigmatism of the light emitted from the condenser lens (3) will be completely eliminated, and an even better condensed spot can be obtained.

[Effects of the Invention] As described above, according to the present invention, the laser light source and the condensing lens system are arranged so that their astigmatism directions are orthogonal to each other, so that the astigmatism of the condensing lens and the laser light source is This has the effect that aberrations cancel each other out, a good focused spot is obtained, and an optical pickup device that can correctly read information on an information recording carrier can be obtained at a low cost.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a schematic configuration of an embodiment of the present invention;
Figure 2 is an operation explanatory diagram showing the exit pupil plane of this embodiment;
The figure is a perspective view showing a schematic configuration of a conventional optical pickup device. In the figure, (1) is a laser light source, (2) is an emitted light flux,
(3) is a condensing lens, (4) is an information recording carrier, (5) is a condensing spot, (6) is a beam splitter, (7) is a photodetector, (8) is a reflected light beam, and (9) is The astigmatism direction of the laser light source, and (10) is the astigmatism direction of the condenser lens. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] In an optical pickup device comprising a laser light source and a condensing lens system that focuses the emitted light beam from the laser light source onto an information recording carrier and focuses the reflected light beam from the information recording carrier onto a photodetector. . An optical pickup device, characterized in that the laser light source and the condensing lens system are arranged such that their astigmatism directions are orthogonal to each other.