JPH0748268B2 - Optical pickup device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for reading or writing information on an information recording medium such as a digital audio disc or a video disc.

[Conventional technology]

Conventionally, this type of device has been shown in FIG.
FIG. 3 is a layout view of optical parts showing a conventional optical pickup device, 1 is a light emitting source such as a semiconductor laser, 2 is a half mirror as an optical separator having a reflection and transmission action, and 3 is the half mirror 2. An objective lens 4 for converging the reflected light beam, 4 is an optical disk which is an optical information recording medium, and 5 is a four-division photodetector for detecting data on the optical disk 4.

The y-axis indicates the data column direction in the data reading section of the optical disc 4, and the x-axis indicates the optical disc outer peripheral direction at right angles to the y-axis.

Further, the light emitting source 1 is located in the u-axis direction forming an angle of (45 ° −θ). The division line direction of the 4-division photodetector 5 is in the directions of the s axis and the t axis, and forms an angle of 45 ° with the u axis in the direction of the position of the light emitting source 1.

Further, the objective lens 3 can be moved in the x-axis direction and the z-axis direction so that follow-up reproduction is possible even when the surface wobbling or eccentricity of the optical disc 4 occurs.

The light flux emitted from the light emitting source 1 is reflected by the half mirror 2, and subsequently enters the objective lens 3, and is converged by the objective lens 3 to form an image on the optical disc 4. The reflected light flux on the optical disk 4 becomes diffused light and enters the objective lens 3 again, and is converged from the objective lens 3 and exits and enters the half mirror 2.

In the half mirror 2, a part of the light flux is transmitted and enters the four-division photodetector 5. The light flux that passes through the half mirror 2 is
Since the half mirror 2 gives astigmatism to the u-axis direction, it does not form an image at the same point, but if the 4-division photodetector 5 is arranged at an appropriate position, the 4-division photodetector 5 The minimum circle of confusion 6 can be obtained with.

In the optical pickup device configured as described above, when the optical disc 4 moves in the z-axis direction, defocus occurs on the optical disc 4, the light beam reflected by the optical disc 4 passes through the half mirror 2, and then the four-division photo detector. 5 does not become the circle of least confusion 6 but becomes an ellipse as shown in FIG.

By setting the focus error signal F · E = (A + C) − (B + D), F · E> 0 when the optical disc 4 moves away from the objective lens 3 and F · E <0 when the optical disc 4 approaches, so that the focus shift occurs. Can be detected, and by further amplifying this focus error signal and driving the objective lens 3 so that F · E = 0, the optical disc 4 is always focused.

[Problems to be Solved by the Invention]

Generally, when the objective lens 3 moves along the x-axis so as to follow the eccentricity of the optical disc 4, the minimum circle of confusion 6 on the four-division photodetector 5 is displaced by a small amount. As shown in FIG. 5, when the astigmatism direction u-axis and the moving direction x-axis of the objective lens 3 form an angle of (45 ° −θ), the displacement direction is between the u-axis and (45 ° −θ). Move on an angled t'axis.

However, the dividing line of the 4-split photodetector 5 is the u-axis and 45
Since it is in the direction of the s and t axes formed by °, the objective lens 3 is + x
When operated along the axis, the received light power of the four-division photodetector 5 is C>D> A≈B, and FE = (A + C)-(B
+ D)> 0 and a focus error signal is generated, and the objective lens 3 operates in the z-axis direction so that FE = 0.

However, since the optical disc 4 is not displaced in the z-axis direction, a focus shift occurs.

That is, when the objective lens 3 moves in the x-axis direction, a pseudo focus error signal is generated, and as a result, a focus shift occurs.

The present invention has been made in order to solve the above-mentioned problems, and even if the objective lens 3 operates in the x-axis direction, the focus error signal does not change and an optical defocus can be prevented. The purpose is to obtain a pickup device.

[Means for solving problems]

In the optical pickup device according to the present invention, when the u-axis in the direction in which astigmatism is generated forms an angle of (45 ° -θ) with the x-axis in which the objective lens moves, the direction of the dividing line of the 4-division photodetector The s ′ and t ′ axes are arranged so as to form an angle of (45 ° + θ) or (45 ° −θ) with the u-axis in the direction in which astigmatism is generated.

[Action]

In the optical pickup device according to the present invention, when the objective lens moves in the x-axis direction, the t'-axis forming (45 ° -θ) with the u-axis, which is the direction in which the beam produces astigmatism, on the four-division photodetector. However, since the dividing line direction of the 4-division photodetector is also the u axis and the t'axis in the direction of (45 ° -θ) and the s'axis orthogonal to it, no focus error signal is generated. No
Therefore, no focus shift occurs.

〔Example〕

 An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, 1 is a light emitting source such as a semiconductor laser, 2 is a half mirror as an optical separator having a reflection and transmission action, 3 is an objective lens for converging the light beam reflected by the half mirror 2, and 4 is an optical lens. Optical disks 5 which are information recording media are 4-division photodetectors for detecting data on the optical disk 4.

The y-axis is the data reading unit on the optical disc 4,
The data column direction is shown, the x axis is orthogonal to the y axis, and the outer peripheral direction of the optical disc 4 is shown.

Further, the light emitting source 1 is located in the u-axis direction forming an angle of (45 ° -θ) with the x-axis. The division line directions of the 4-division photodetector 5 are in the directions of the s'axis and the t'axis, and the u-axis in the direction of the position of the light emitting source 1 forms an angle of (45 ° + θ) and (45 ° -θ), respectively. In addition, θ shows the range of −45 ° ≦ θ ≦ 45 °, and the angle θ
Regarding the sign of S, when the S axis is seen from the disk 4, S
A plus value indicates a counterclockwise direction and a minus value indicates a time direction with respect to the axis. .

Next, the operation will be described.

The light flux emitted from the light emitting source 1 is reflected by the half mirror 2,
It is converged by the objective lens 3 and forms an image on the optical disc 4.

The light flux reflected by the optical disk 4 is re-incident on the objective lens 3, transmitted through the half mirror 2, and incident on the four-division photodetector 5.

The angle between the u-axis in the incident direction of the light emitting source 1 and the astigmatism direction and the x-axis which is the moving direction of the objective lens 3 is (45 ° −
At θ), when the light beam emitted from the light emitting source on the u-axis moves on the x-axis along with the movement of the objective lens 3, among the light beams reflected from the optical disc 4, the light beam transmitted through the half mirror 2 is , Its optical characteristics, that is, the component (sagittal surface) orthogonal to the inclined surface (meridional surface) of the half mirror 2 is inverted with respect to the u axis. As a result, the axis of movement of this light beam becomes an axis symmetrical with the x axis about the u axis, that is, the t'axis.

Therefore, with the movement of the objective lens 3, the beam on the four-division photodetector 5 moves along the t ′ axis forming an angle of (45 ° −θ) with the u axis.

By the way, the dividing line direction of the four-division photodetector 5 is the t'axis forming an angle of (45 ° -θ) with the u axis and the s'axis forming an angle of (45 ° + θ).

Therefore, when the objective lens 3 moves on the x-axis as shown in FIG. 2, the focus error signal becomes D = C> A = B when the objective lens 3 moves in the + x-axis direction, and FE = 0,
When the objective lens 3 moves in the -x-axis direction, A = B> C =
D, and F · E = 0.

That is, even if the objective lens 3 is displaced on the x-axis, the focus error signal always shows FE = 0, and no focus shift occurs.

In addition, although the astigmatism generation optical system by the half mirror 2 is used in the above-mentioned embodiment, the same effect can be obtained by the astigmatism method using a prism or a cylindrical lens.

〔The invention's effect〕

As described above, according to the present invention, the minute displacement of the beam on the four-division photodetector due to the movement of the objective lens and the division line direction are matched, so that the focus error signal is always F · E = 0.
Therefore, since a pseudo signal is not generated, there is an effect that a highly accurate device can be obtained.

[Brief description of drawings]

FIG. 1 is an optical layout diagram showing an optical pickup device according to an embodiment of the present invention, FIG. 2 is a diagram showing beam displacement on a four-division photodetector according to the present invention, and FIG. 3 is a conventional optical pickup device. FIG. 4 is a diagram showing the optical arrangement and the focus error signal on the 4-division photodetector when the distance between the objective lens and the optical disc is changed. FIG. 5 is a conventional 4-division photodetector. It is a figure which shows the displacement of the beam above. Reference numeral 1 is a light source, 2 is a half mirror (light separator), 3 is an objective lens, 4 is an optical disk, and 5 is a 4-split photodetector. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A light beam from a light source is separated by a light separator, and is made incident on a disk through an objective lens operable in a direction perpendicular to the optical axis direction, and reflected light from this disk is again objective. In an optical pickup device that generates astigmatism through a lens and the light separator and makes it incident on a four-division photodetector, the optical pickup device is perpendicular to the optical axis of the objective lens and parallel to the radial direction of the disc. When the moving direction of the moving objective lens and the astigmatism generation direction form an angle of (45 ° −θ), one of the dividing lines of the four-division photodetector is An optical pickup device, characterized in that an angle of (45 ° + θ) is formed with the astigmatism generation direction, and the other direction is substantially perpendicular to the direction.