JPS61284837A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To always execute stably an adjustment of a focus by adjusting a distance to an information storage medium of an optical means by a difference signal of outputs of two sets of opposed photodetecting parts. CONSTITUTION:The second photodetecting parts 40C, 40E of a photodetector 40 are connected to an adder 42, and the second photodetecting parts 40B, 40D are connected to an adder 44. Also, these adders 42, 44 are connected to a differential amplifier 46, this differential amplifier 46 is connected to a lens driving circuit and a focus detection is executed by the processing circuits. Also, the first photodetecting part 40A, 40B are connected to a differential amplifier 52 and an adder 54, respectively, and a tracking detection and an information reproduction are executed. That is to say, a distance to an information storage medium 14 of an objective lens 12 is detected by detecting by the differential amplifier 46 a difference between a signal added output signals of the photodetecting parts 40C, 40E by the adder 42, and a signal added output signals of the photodetecting part 40D, 40F by the adder 44.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention provides an optical information processing device that automatically focuses a light beam so that an information storage medium on which information is recorded is always irradiated with a focused light beam. This invention relates to an automatic focus adjustment device that adjusts the focus.

[Technical background of the invention and its problems]

In an optical information processing device that uses focused light to read information from an information storage medium or write new information to an information storage medium, the convergence point of the focused light is always on the recording layer of the information storage medium or on the light reflection layer. It must match the layer position. Therefore, this device includes an automatic focus adjustment device that automatically adjusts the focus.

By the way, as a method for automatically adjusting the focus, information detection and focus position detection are performed using a single light beam.
For example, Special Publication No. 53-39123 (Automatic focus adjustment device)
is proposed. This method is an automatic focusing method using an astigmatism optical system, and uses a cylindrical lens with unidirectional lens action. It is detected as follows.

This basic principle will be explained below with reference to what is shown in FIGS. 3 to 5.

As shown in FIG. 3, the light beam L that enters and passes through the beam sinter lO from the direction A is focused by the objective lens 12, then reflected by the information storage medium 14, and returns to the objective lens 10.
After passing through the beam splitter 2, the beam is reflected by the beam splitter 10 and directed toward the condenser lens 16. The light beam L focused by the condenser lens 16 is collected by the cylindrical lens 18 and irradiated onto the photodetector 20. Here, the cylindrical lens 18 has a curvature in the horizontal direction and a vertical curvature as shown in FIG. If parallel light is incident on a lens that has no curvature in any direction, the vertical light beam L that has no curvature will pass through the lens as is, but the horizontal light beam L that has curvature will pass through this lens. Focal length f =
Focus on OB.

Therefore, if the condensing lens 16 is placed in front of this cylindrical lens 18, the condensing point in the vertical direction and the condensing point in the lateral direction are different. The way the light beam L is focused at this focusing point is that it becomes elongated horizontally at the focusing point in the vertical direction, becomes elongated vertically at the focusing point in the horizontal force direction, and becomes circular at the intermediate point. On the outside, it becomes an ellipse that expands vertically or horizontally.

Therefore, when the objective lens 12 is in a focused state with respect to the information storage medium 14, a position K where the light beam L is focused circularly
For example, by arranging a photodetector 20 having four light receiving sections and detecting the convergence shape of the light beam L on this photodetector 20, the focus state of the objective lens 12 with respect to the information storage medium 14 can be determined. and adjust the distance of the objective lens 12.

That is, on this photodetector 20, the convergence shape of the light beam L changes as shown in FIG. 5 depending on the focus state of the objective lens 12 with respect to the information storage medium 14. In FIG. 5, four times are when the objective lens 12 is too close to the information storage medium 14, (B) is when the objective lens 12 is in focus with respect to the information storage medium 14, and (C)
) The figure shows the time when the objective lens 12 does not reach the information storage medium 14. Therefore, the difference between the sum output value of the light receiving parts A and C of this photodetector 20 and the sum output value of B and D is The focus state of the objective lens 12 with respect to the information storage medium 14 is detected.

However, in this method, the light beam irradiated onto the information storage medium 14 is formed on a recording trunk or a recording trunk by a pre-group array formed in advance in a spiral or concentric shape on the information storage medium 14. When the light crosses the bit, the brightness distribution of the light due to diffraction causes one turn of the diffracted light to be irradiated onto the photodetector 20 as shown in FIG.

Therefore, in this automatic focusing method, in addition to the convergence shape of the light beam, it is also affected by the imbalance of just over 1 light distribution, so the light beam L has a circular light distribution shape on the photodetector 20. In other words, even when the objective lens 12 is in focus with fN@storage medium 14, it is detected that it is not in focus, and the objective lens 12 is moved up and down with respect to the information storage medium 14. [Objective of the Invention] The present invention has been made based on the above-mentioned circumstances, and it is an object of the present invention to eliminate the influence of the recording trunk on the information storage medium and the diffracted light due to the focus, and to always stably adjust the focus. The object of the present invention is to provide an automatic focus adjustment device that can perform the following functions.

[Summary of the invention]

The present invention accomplishes two of the above objects! i! In order to achieve this, in the automatic focus A adjustment device using the astigmatism method, the photodetector that detects the light beam from the information storage medium has a convergence shape of the original beam irradiated to this photodetector at the time of focusing. A first light receiving section having substantially the same shape and at least four second light receiving sections provided around the circumference of the light receiving section and arranged symmetrically with respect to an axis substantially orthogonal to each other, The distance between the optical means and the information storage medium is adjusted by a difference signal between the outputs of two sets of light receiving sections facing each other with respect to the orthogonal axes of the light receiving sections.

[Embodiments of the invention]

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

In FIG. 2, a light beam L generated from a semiconductor laser beam 30 as a light source is converted into a parallel light beam by a collimator lens 32,
It passes through the wave plate 36 and the objective lens 12 as an optical means.
The information is converged into a recording trunk on the information storage medium 14 by .

↑The light beam L reflected from the R information storage medium 14 passes through the objective lens 12 and the 1/4 wavelength plate 36 and is returned to the polarization beam splinter 34. The light beam L is a quarter wavelength plate 36
By reciprocating, the plane of polarization is rotated by 90 degrees compared to when it passes through the polarization beam splinter 34, so this time it is reflected without passing through the polarization beam splinter 34.
The light 1 norm L that has passed through the cylindrical lens 18 is sent to the photodetector 40 which detects the light receiving part as shown in FIG.
irradiated on top.

This photodetector 40 has an objective lens 12 and an information storage medium 14.
This photodetector 40KJ'! l
Light receiving sections 40A and 40B are obtained by dividing a first light receiving section having substantially the same shape as the focused shape of the emitted light beam L, and these light receiving sections 40A.

four second light receiving sections 40C and 40D provided around the light receiving section 40B and arranged symmetrically with respect to mutually orthogonal axes;
It consists of 40E and 40F.

Moreover, each light receiving section 40A of this photodetector 40.

40B, 40C, 40D, 40B, and 40F are each connected to an adder or a differential amplifier, and focus detection, tracking detection, and information reproduction are performed. Second light receiving section 40C of photodetector 4o, 40Elt71111X
The second light receiving sections 40B and 40D connected to the adder 42 are connected to the adder 44.
2.44 is connected to the differential amplifier 46, and this differential amplifier 4
6 is connected to a lens drive circuit, and focus detection is performed by these processing circuits. In addition, the first light receiving portions 40A, 4
0B are connected to a differential amplifier 52 and an adder 54, respectively, for tracking detection and information reproduction.

That is, in the photodetector 40 having the light receiving section as described above, the output signals of the light receiving sections 40C and 40E are added to the adder 4.
The objective lens 1
In other words, when the objective lens 12 is in focus with respect to the information storage medium 14, the light receiving parts 40C, 4 of the photodetector 4o
0D, 40E, and 40PK are the source beams L and A from the information storage medium 14. Therefore, when the output signal obtained by the photodetector 40 is calculated as described above, at the time of focus,
I can't get any signal. Furthermore, when the objective lens 12 is out of focus with respect to the information storage medium 14, the information storage medium 14
Due to the change in the focusing shape of the light beam L from the photodetector 40
A light beam L is irradiated onto one of the light receiving sections 40C, 40D, 40E, and 40F that is symmetrical about the orthogonal axis. Therefore, when the output signal obtained by the photodetector 40 is calculated as in the above method, either a positive or negative signal will be obtained when the focus is out of focus. Therefore, the detection signal from the differential amplifier 46 is sent to the lens drive circuit 48, and the lens drive circuit 48 sends a signal to the voice coil 50 as necessary to move the objective lens 12 up and down in the optical axis direction. By moving, the distance of the objective lens 12 with respect to the information storage medium 14 is controlled,
It is possible to automatically focus on the t# information storage medium 14.

In addition, as in this embodiment, the information storage medium 14 is
If the light-receiving section of the photodetector 40, which has substantially the same shape as the convergence shape of the light beam L from the I get a signal. Therefore, by sending this tracking signal to a tracking processing circuit (not shown), tracking correction can be performed.In addition, by adding the output signals of the light receiving sections 40A and 40B using an adder 54, an information reproduction signal is obtained. This signal is sent to a signal processing circuit (not shown) and processed.

In this embodiment, the light receiving section of the photodetector 40 that detects the focus state is divided into four parts, but the light receiving part is not necessarily limited to this, and the light receiving part is divided into four parts, and the light receiving part is divided into four parts. It suffices if it is placed in In addition, although the light-receiving section having substantially the same shape as the convergence shape of the original beam L at the time of focusing has been described as being divided into two, this is not limited to this, and the light-receiving section may be divided into four, eight, etc. However, for example, if tracking correction is performed using another optical system, the division may not be necessary.

It goes without saying that the present invention can be modified in other ways without departing from the gist of the invention.

〔Effect of the invention〕

As explained above, according to the invention, when the optical means for irradiating the information storage medium with the light beam from the light source is focused on the information storage medium, the photodetector is not irradiated with the light beam from the information storage medium. Since the focus state of the optical means with respect to the fW reporting medium is detected using the light receiving section, stable focus detection is always performed without erroneous focus detection due to the influence of diffracted light, and the optical means The distance to the information storage medium can be adjusted.

[Brief explanation of the drawing]

FIG. M1 is a block diagram of a photodetector and circuit showing an embodiment of the present invention, FIG. 2 is a schematic block diagram of an information recording and reproducing apparatus of the present invention,
Figure 3 is a schematic configuration diagram showing the focus detection optical system;
The figure is a perspective view of a cylindrical lens and an explanatory diagram of a light advancing point, and FIG.
FIG. 6 is an explanatory diagram showing the influence of diffracted light on a photodetector. 12... Objective lens, 14... Information storage medium, 16
... Condensing lens, 18... Cylindrical lens,
30... Light source, 40... Photodetector, 42.44...
- Adder, 46... Differential amplifier, 48... Lens drive circuit. Agent Patent Attorney Noriyuki Chika (and 1 other person) Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] In an automatic focusing device that irradiates a light beam from a light source onto an information storage medium using optical means and detects the reflected light or transmitted light using an astigmatism method, the reflected light or transmitted light from the information storage medium is detected. a first light-receiving portion having substantially the same shape as a convergence shape of a light beam irradiated to the photodetector when the optical means is in a focused state with respect to the information storage medium; at least four second light-receiving parts arranged symmetrically with respect to an axis provided around the part and substantially orthogonal to each other, and two sets of light-receiving parts facing each other with respect to the orthogonal axis of the second light-receiving parts. An automatic focus adjustment device, characterized in that the distance of the optical means with respect to the information storage medium is adjusted by a difference signal of the outputs of.