JPS61230633A - Focus position detecting device - Google Patents

Abstract

PURPOSE:To obtain a focus position detecting signal which has reduced effects of the position shift of the detection light and the track data signal, by extracting the differential signal of the detected light quantity of a two-split photodetector after the signal passed through a beam splitter having the dependence of incident angle and then extracting only the angle change of the detection light. CONSTITUTION:A beam splitter 30 having no change of the output light intensity to the change of an incident angle is set between a beam splitter 20 whose output light quantity has the dependence of incident angle and a stop-down lens 17. At the same time, a photodetector 31 having the same form as a photodetector 21 is set so that the distance from the lens 17 is equal to the distance between the lens 17 and the detector 21. Then the differential output of the detector 31 is obtained by a subtractor 32, and the differential output is obtained by subtractor 33 to a subtractor 22. Thus a detecting signal 28 obtains the difference of detector outputs between the plus and minus sides of the incident angle of the detection light after subtracting the light intensity of the same areas of both detectors 21 and 31. Thus it is possible to extract only the change of light quantity on the detector 21 due to the change of the focus point.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a focus position detection method in an optical disc device such as a video disc device, an audio disc device, or a digital optical disc device.

[Background of the invention]

Conventionally, various methods have been proposed as focus position detection devices, but when used in optical disk devices, errors in detecting the focus position occur due to the influence of data signals and track signals recorded on the reflective surface of the optical disk. It is desirable to have a lens that is hard to use, and it is also necessary to have a lens that does not cause detection errors in the focal position even when the light flux of the detection light shifts or tilts due to positional deviation of optical components due to temperature changes or changes over time.

For example, the November 21, 1985 issue of Nikkei Electronics, page 202, describes the use of a knife. In this method, the knife is inserted at the imaging point of the detection light, so if the direction of the light flux of the detection light deviates,
The relative relationship with the knife affects the detection error. Also, Japanese Patent Application Laid-Open No. 59-77657 or Utility Model Application No. 59-77657
As described in Publication No. 74526, in the method of comparing the light intensity of the detection light at the center and the periphery, the change in light intensity due to data signals and track signals is different between the center and the periphery, so the focus position detection signal is It is easy to cause errors. Such a focus position detection error causes defocusing, which causes deterioration of information recording or reproducing performance.

[Object of the invention] 1. .

It is an object of the present invention to prevent focal position detection errors from occurring due to beam deviation of the detection light, and at the same time to prevent detection errors from occurring due to data signals and track signals on the reflective surface of the optical disk. The object of the present invention is to provide a detection device.

[Summary of the invention]

In order to achieve the above object, the present invention is characterized in that the detection light is separated into two, and only one of the light beams is passed through a beam splitter that has incidence angle dependence.
By detecting the light intensity with two two-split photodetectors of the same shape whose central part is masked and extracting a differential signal, light beam deviation and changes in light intensity due to data signals and track signals are canceled out, resulting in a pure The reason is that only the focal position shift is extracted as a change in light amount.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1(α) is an example of a conventional detection device. The light beam emitted from the 1,1 light source 12 is turned into parallel light by the collimator lens 15 , and is focused by the objective lens 15 to be focused on the reflective surface 1 of the optical disk 16 . disk 16
The light beam reflected from the lens 15 and the beam splitter 1
4, the light passes through the focusing lens 17 and is focused, and then reaches the photodetector 5 as spread light. 1st
Figure Cb) is a schematic diagram for explaining only the function of the detection device.

When the focal point is at the desired focal position IK, the light beam is refracted by the lens 5 as shown by the solid line, forms a focal image at the position of the front flame 4' of the shielding element 4, and reaches the detectors 5α and 5b. 6 in FIG. 2(6) shows the original pattern (light-receiving image) on the surfaces of the detectors 5a and 5b.

When the focal position is II (from desired position 1, lens 5
When shifted away from , the ray becomes a broken line F.

As shown in (, after the image is formed at a position close to the lens 5 by the shielding element tip 4#, the light beam heading toward the detector 5α is blocked by the shielding element 4, and only the light beam heading toward the detector 5b is received by the detector. FIG. 2(') Ill shows the optical pattern 6 on the detectors 5α and 5b in such a state. Also, FIG. 2(C) shows that the pain point position is closer to the lens 5 than the desired position 1. The light pattern 6rz on the detector surface is shown in a direction-shifted state.

The solid line 8 in FIG.
It shows the difference V between the outputs of a and 5h. In this device, when the focal point is at the desired position 1, the tip 4t of the shielding element 4 is
Since a focal image is formed at , high precision is required for the insertion position of the shielding element 4 so that the light beam ti is scattered and the same amount of light is received by the detectors 5a and 5h. When the direction of the light flux changes due to temperature changes, etc., the focal image of the light beam moves 5, which means that the insertion position of the shielding element 4 changes relatively, resulting in an imbalance in the amount of light received by the detectors 5a and 5b. This causes a detection error. If the amount of shielding by the shielding element 4 becomes large (if this happens, a distortion as shown by the broken line 9 will occur in the curve of the output difference (2) between the detectors 5a and 5h).

FIG. 4 shows an example of another detection device employed in the present invention.

When the focal point is at the desired position 1, the light beam reaches the refractive member 10α, 10h at the lens 3, as shown by the solid line 2. 6 in FIG. 5(b) indicates a light pattern on the surface of the photodetectors 10α, 10b, and in this case, the photodetector 10=, 1
The output of 0A is equal. Desired position 1 such that the reflective surface is 1-
When the light ray shifts further away from lens 5, it becomes straight line 2.
As shown in □, the light pattern 6I on the photodetector 10a becomes smaller as shown in Fig. 5(a).
The output of the photodetector 10α is thicker than the output of the photodetector.
In this case, the output of the photodetector becomes smaller at 10α than at IOb.

In this way, a focus position detection signal is obtained.

FIG. 6 shows a case where first-order diffracted lights 11α and 116 from the track position detection grooves are generated in the original pattern 6. Since the light intensity of 11α and 11b changes when the truck passes, the outputs of photodetectors +oa and +ob are as shown in Figure 7 (α) and (b).
). The amount of change B, C, 1° is the amount by which the intensity changes of the first-order diffraction sources 11α and 11b do not cancel each other out, and the values are the values for the photodetector 10a.

It varies depending on the position of original pattern 6 on +OA, and
The values are different for 107Z and IO+6. Therefore, Fig. 7 (C
), C-8 becomes loud as an error signal, causing a focus detection error. It is clear that such a detection error also occurs when the original spot passes through a data writing section on the original disk surface, and has been a major problem with conventional focus position detection devices.

FIG. 8 is a block diagram of a focal position detection device showing one embodiment of the present invention, and the basic principle of the present invention will be explained based on this. Although the path from the light emitting source 12 to the focusing lens 17 is the same as the configuration shown in FIG. 1, a beam splitter 20 is used in the present invention. The beam splitter 20 is specially processed, and as shown in FIG. 9(α), the amount of emitted light is dependent on the angle of incidence. Figure 9 (b
), the parallel light beam emitted from the light source 25 is passed through the beam splitter 20, and the front bridge thereof is passed through the beam splitter 20.

When reading the light intensity at positions 26A, 26B, and 26C with a light intensity measuring device, if the incident light intensity of the beam splitter 20 is Aj, the transmitted source light intensity is B, and the refracted light intensity is C, depending on the value of the incident angle θ, ( B/A) and (CIA)
The value of changes as shown in FIG. 9 (α).

In FIG. 8, a light beam passing through the beam splitter 20 as described above is received by a photodetector 21.

The photodetector 21 is divided into two parts by a mask section 21-2, and outputs α and b are outputted from 21-1 and 21-5, respectively.

live. When the light beam is approximately at the center of the photodetector 21,
The light-receiving surface 21-1 receives only light rays with an incident angle θ<0, and the light-receiving surface 21-5 receives only light rays with an incident angle θ>0. Therefore, α<b, and a differential output is generated in the subtracter 22.

When the focal position changes, the narrowing angle of the emitted light from the diaphragm lens 17 changes, so the output of the subtracter 21 changes to a value corresponding to the focal position. Focus position is disk 16
Let K be the output of the subtracter 22 when the voltage is in a state of coincidence on the recording film, and keep the constant voltage generator 24 constant.

The focus position detection signal 27 can be obtained by generating a voltage and taking the differential output between the subtracter 22 and the constant voltage generator 24 in the subtracter 25.

However, if the position of the optical component shifts due to a change in temperature, for example, if the position of the softened lens 17 shifts, the entire position of the light beam irradiating the photodetector 21 will shift, and the The outputs α and b change, which tends to cause detection errors. .

FIG. 10 shows another embodiment of the present invention. 1 shows an improved focus position detection device; In the configuration shown in Figure 8.

In addition, a beam splitter 50 and a photodetector 51 are newly arranged. The beam splitter 50 has normal performance, i.e.
A photodetector 51 and a photodetector 21 are used in which the output light intensity hardly changes with respect to a change in the incident angle, and the photodetector 51c and the photodetector 21 are used in the same shape as the photodetector 21,
They are arranged so that the distances from the diaphragm lens 17 are equal. After taking the differential output of the photodetector 51 with the subtracter 52,
A subtracter 55 takes a differential output from the subtracter 22. Since the detection signal 28 is ((α-h)-(α-c)-K), it can be rewritten as (((L-(L)-(b-0)-K),
After subtracting the light intensities of the same light portions of the photodetectors 21 and 51, the difference between the photodetector outputs on the middle side and one side of the detected light incident angle is calculated. This means that all unbalanced light intensity changes such as light beam movement, track signals, and data signal changes are canceled, and only the light intensity changes on the photodetector 21 due to focal position changes are canceled. can be taken out.

Note that the constant voltage generator 24 and the subtracter 25 perform this as follows.

Can be omitted. That is, as shown in FIG. 1, the original pattern on the detectors 21 and 51 is biased,
Each photodetector 21 and 51 when at the desired focal position
The subtracter outputs 22 and 52 may be adjusted so that they become zero.

〔Effect of the invention〕

As described above, according to the present invention, detection light is separated into two directions, only one side of the light is made to pass through a beam splitter that is incident angle dependent, and the difference between the same portions of each separated detection light is taken. Therefore, only the angular change of the detected light can be extracted. Therefore, it is possible to obtain a focal position detection signal that is less affected by positional deviation of the detection light, track signal, or deniter signal.

Further, by devising the shape of the photodetector, it is also possible to simultaneously detect the one-track position detection signal.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are diagrams for explaining the configuration of a conventional focus position detection device, and FIG. 2 shows the above configuration. FIG. 5 is an explanatory diagram of the detection signal; FIG. 4 is an explanatory diagram of the operation of another conventional focal position detection method; FIG. 5 is a diagram of the light pattern on the detection surface; Figures 6 to 7 are diagrams for explaining the influence of diffracted light, Figure 8 is a configuration diagram of a detection device for explaining the present invention in detail, and Figure 9 is a diagram of the beam splitter employed in the present invention. FIG. 10 is a diagram for explaining the characteristics, FIG. 10 is a configuration diagram for explaining an embodiment of the detection device according to the present invention, and FIG. 11 is a diagram showing another embodiment of the detector quantity-force circuit. l111... Reflective surface, 2... Light beam, 5... Lens, 4... Shielding element, 5, 10... Photodetector, 6... Light pattern, 7...
...Dark line, 11...First order diffraction source, 15...Objective lens, 16...Optical disk, 17...Focusing lens, 2
0...Beam splitter having incident angle dependence, 21
．． 51... Photodetector, 22.25, 52.55...
Subtraction function, 50...normal beam splitter. 12"

Claims (1)

[Claims] 1. In a focal position detection device that detects the relative position between a point where a light beam is focused by a lens or the like and a reflective surface that reflects the light beam in the vicinity of the focused point, a beam splitter having angular dependence in relation to the emitted light flux;
1. A focal position detection device comprising a photodetector divided into at least two parts, the beam splitter being disposed between the lens etc. and the photodetector. 2. A second beam splitter having a constant beam separation performance regardless of the incident angle is arranged between the beam splitter and the lens etc. to separate the light beam, and the light beam is placed on the separated light beam. The focal position detection device according to claim 1, further comprising a second photodetector having the same shape as the detector.