JPS5835734A - Focusing detector and controller for optical disc reproducer - Google Patents

Abstract

PURPOSE:To detect focusing, by making a reflected light from a disc incident to two concentric photodetectors via a lens having a circular cone-shaped refraction plane. CONSTITUTION:A reflected light from a disc is made incident to a photodetector 18 having two concentric elements 18A, 18B via a lens 17 of circular cone- shaped refracted plane. At a suitable focusing state, a spot S of the reflected light appears at a boundary of the photodetectors 18A, 18B as a center. The spot appears at the inside element 18B at under-focusing and it appears at the outer elements 18A at overfocusing. A focus controlling signal is obtained by taking a difference of the output of the two photodetectors.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus state detection control device in an optical disc playback device, and in particular, it simplifies the alignment of an optical system for detecting the focus state and has high detection sensitivity. It was made so that it would become so.

Conventionally, various systems have been proposed as focus state detection control devices for optical disc playback devices, but among them, the following is proposed as one that simplifies the optical system for detecting the focus state. As shown in FIG. 1, there is a combination of a prism and a photodetector in which v photodetecting elements are arranged in one direction.

That is, the laser beam from the laser light source I is made incident on the recording surface B of the disk through the polarizing beam splitter, the collimator lens 3, the //G' wavelength plate, and the objective lens S sequentially. On the recording surface of the disk, for example, audio information is appropriately modulated and formed into a spiral recording track so that it can be optically read out by forming pits.
recorded. Then, the laser beam reflected by the recording surface 6 is made incident on the photodetector through the objective lens j, / /'I wavelength plate, collimator lens 3, polarizing beam splitter and prism 7. .

Here, as shown in FIG. 2, the prism 7 has two rectangular surfaces 7a and ? that form an obtuse angle. The refractive surfaces 7a and 7b are on the light exit side, and the ridge line 7C is arranged to perpendicularly cross the optical axis. In addition, as shown in FIG. 3, the photodetector g has two photodetecting elements gA, trB, zaC and ffD arranged on both the optical axis and the ridge line 7C in a plane perpendicular to the optical axis. They are arranged in a line in the perpendicular X direction, at the appropriate position along the optical axis, and
Place it in the correct position in the direction. And the outer element gA
and the difference signal (I A + I D) between the sum signal IA+ID of the output signals IA and ID of rD and the sum signal I B+I C of the output signals IB and Ic of the inner elements gB and tC.
(I B + I C) is extracted as a focus state detection signal. The objective lens S is moved in the optical axis direction by a current flowing through the control coil 9, and this detection signal is supplied to the control coil 9 as a focus state control signal.

In this conventional device, the recording surface 6 of the disk is
When the spot S on the photodetector S is in the proper position and just in focus, as shown in FIG. C
They appear in the form of dots at the separation zone between D and D. Therefore, in this case, the focus state detection signal (I A
+I D) (I'a+Ic) is zero, and the objective lens S maintains the same position.
- If the recording surface 6 of the disk is in a position close to the objective lens S and becomes under-focused, the third
As shown in Figure A, the spot S on the photodetector g appears in a semicircular shape on the inner elements gB and gC, respectively. Therefore, in this case, the focus state detection signal (I A+
I n) (I B + I C) becomes negative, and the objective lens star is moved in a direction away from the recording surface 6.

On the other hand, if the recording surface 6 of the disk is located far away from the objective lens 5 and overfocus occurs, see Figure 3C.
As shown in , the spot S on the photodetector g appears in a semicircular shape on the outer elements gA and D, respectively. Therefore, in this case, the focus state detection signal (IM+ID)
(IB+IC) becomes positive, and the objective lens 3 is moved in the direction closer to the recording surface B.

In this way, the prism 7 and the four photodetecting elements fA-
A photodetector g in which JrDs are arranged in one direction detects the focus state, that is, the distance of the disk to the objective lens 5, and the detection signal is sent to the control coil 9 as a control signal.
is automatically controlled so that the objective lens is always in just focus, that is, the objective lens is always at a constant distance from the disk.

However, this conventional device moves the photodetector g in the direction of the optical axis so that the spot S on the photodetector g in each focus state becomes as shown in FIGS. The photodetector g must be placed at an accurate position in the X direction, and has the drawback that strict precision is required for position adjustment of the photodetector g. In addition, there is a loss of light at the apex angle of the prism 7, but since the apex angle forms the edge 1II7C, the loss is large, and in order to reduce this loss, it is necessary to improve the finishing accuracy of the apex angle. There is also a drawback.

The present invention provides a novel focus state detection control device that eliminates these drawbacks and also improves detection sensitivity.

FIG. v shows an example of the apparatus of the present invention. In the present invention, a lens having a conical refractive surface is used instead of the above-mentioned prism 7. That is, a lens 17 having a conical refraction surface 71& is placed on the optical path from the polarizing beam splitter to the photodetector 1g, with the refraction surface /7a facing the light output side. In this case, as shown in FIG.
7 is positioned on the optical axis. Furthermore, in the present invention, as shown in FIG. 6, the photodetector/g is composed of photodetecting elements/IA and lrB in a concentric circle, and the center O of the concentric circles is above the optical axis. Place it so that it is located at

In this case, as shown in FIG. 7, the base angle of the lens 17 is set to θ
, the radius of the separation zone between the elements A and /ffB of the photodetector /g is d, then the lens /? is located very close to the optical axis. The distance l between the lens 17 and the photodetector/g is set so that the light that passes through it reaches the separation band between the elements /ffA and lzaB.
Let 1 = dcotβ. However, β is 5in (β
10 θ)=n sin θ, where n is the refractive index of the glass constituting the lens 17. And element/ffA
and /ff13 output signals IA and IB difference signal IA-
IB is extracted as a focus state detection signal, and this detection signal is supplied to the control coil 9 as a focus state control signal.

In the apparatus of the present invention, when the recording surface of the disk is at a proper position with respect to the objective lens S and is in just focus, a spot S on the photodetector ls appears as shown in FIG. 7B. appears in a ring shape in the separation zone between elements 1gA and /A'H. Therefore, in this case, the focus state detection signals IA-IB become zero, and the objective lens/shift remains at its original position.

When the recording surface 6 of the disk is in a position close to the objective lens S and becomes under-focused, the spot S on the photodetector 1g is placed on the inner element lZB, as shown in FIG. 7A. Appears in a ring. Therefore, in this case, the focus state detection signal LA-In becomes negative, and the objective lens is moved away from the recording surface 6.

On the other hand, if the recording surface 6 of the disk is located far away from the objective lens star, resulting in overfocus, see Figure 7C.
As shown in , the slot S on the photodetector 1g appears in an annular shape on the outer element /A'A.

Therefore, in this case, the focus state detection signal IA
IB is moved in the direction in which the objective lens S is brought closer to the recording surface B.

In this way, the lens 1 having a conical refractive surface /7a
A photodetector /g consisting of two concentric photodetector elements /gA and /gf3 determines the focus state, that is,
The distance of the disk to the objective lens S is detected, and the detection signal is supplied to the control coil 9 as a control signal, so that the objective lens 3 is always in just focus, that is, the objective lens 3 is always at a constant distance from the disk. automatically controlled so that

The example in Figure V is the refractive surface of a cone /? Lens 17 with a
In this case, as shown in the example shown in Fig. 3, the surface from which the return light of the polarizing beam splitter 2, that is, the light read from the disk is emitted, is provided separately from the polarizing beam splitter 2. By setting the refractive surface to /7a,
It is also possible to integrate the polarizing beam splitter 2 and the lens /l with a conical refractive surface /7a, in which case it is still possible to carry out the detection exactly as in the example of FIG.

According to the invention, the lens 1 having a conical refractive surface 17&
7 is used, and is combined with a photodetector 1 consisting of concentric photodetecting elements /gA and/, f13, so alignment of the photodetector it becomes easy.

That is, the conventional device shown in FIG. 1 uses a prism having a refractive surface consisting of two rectangular surfaces 7a and 7b, and a photodetector S in which V photodetecting elements gA-tD are arranged in one direction. Since it is a combination of
In the case of , the separation zone between the elements gA and gB and the element zones C and ll' of the spot that should appear semicircularly on the inner elements gB and the outer elements gA and gD, respectively.
In the area near the separation zone between D, not only the weak light that has passed near the center of the prism 7 but also the strong light that has passed away from the center is focused, so the amount of light is relatively large. Therefore, the position of the photodetector in the optical axis direction and the X direction is shifted, and in the case of FIG. 3A or C, the spot is on the outside of the element tH.

gl) or the inner elements gB to gc, the focus state detection signal (I A+
I n) (I B + I C) changes significantly compared to when the position is accurate, and there is a possibility that erroneous detection may be performed. Therefore, strict precision is required for position adjustment of the photodetector in the optical axis direction and the X direction.

On the other hand, in the device of the present invention, the refractive surface 1qa of the cone
In the case of FIG. 7A or C, since a light quantity hanger 17 consisting of two concentric photodetecting elements /KA and /gf3 is used, Inner element lzaB or outer element/KA
The elements /gA and / of the spots to appear annularly in respectively
The area near the separation zone between gB is the lens/? Since only the weak light that has passed near the center of
On the other hand, in the part far away from the separation zone, only the strong light that has passed away from the center of lens '/7 comes, so the amount of light increases, and in the case of Figure 7C, it is close to the separation zone. There is less on the inside, and it increases as you move toward the outside. Therefore,
The position of the photodetector/g in the optical axis direction or the XY direction is slightly shifted, and in the case of Fig. 7 A or C, the spot somewhat straddles the outer element/gA or the inner element/gH. Also, the focus state detection signal IA-IB
The position changes little compared to when the position is accurate, and there is no risk of erroneous detection. Therefore, the position adjustment of the photodetector/g in the optical axis direction and the XY direction does not need to be very precise.

Further, according to the present invention, as described above, the light intensity of the spot is small on the side closer to the separation strip, and increases as the distance from the separation strip increases, and the more the focus state deviates from just focus, the further the spot becomes from the separation strip. Since it spreads in the direction, it has the effect of significantly increasing detection sensitivity.

In addition, there is a loss of light at the apex angle of the lens 17, but since the apex angle is a point rather than a ridgeline like in a conventional prism, the loss is small. There is no need to increase accuracy.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the configuration of a conventional device, FIG. 2 is a perspective view of a prism used in this device, FIG. 3 is a diagram for explaining the operation in each focus state, and FIG. A diagram schematically showing the configuration of an example of the device of the present invention, FIG. S is a side view and a front view of a lens used in this, FIG. A diagram for explaining the operation in each focus state, and FIG. 3 shows the apparatus of the present invention. FIG. 2 is a diagram schematically showing the configuration of an example. 1 is a laser light source, 1 is a polarizing beam splitter, 13 is a collimator lens, V is a t/V wavelength plate, 1 is an objective lens, 6 is a recording surface of a disk, 1 is a lens, /? a is the refractive surface of the cone, 1g is the photodetector, /J, and /IIB
are the two concentric photodetecting elements. Figure 1 Figure 2 Figure 4 Figure 7 Figure 8 Procedural amendment 1933//70 1. Display of the case 1988 Patent Application No. 13/7 Ig 3. Person making the amendment Related Patent Applicant Address 6-7-35, Kitashinyo, Tokyo Parts Building Name C2t g) Sony Corporation Representative Kazuo Iwama 4, Agent 150 4, 6, Inventions that will increase due to amendment Number None 8. Contents of correction (1) In the specification, page 4, lines 2 to 3, "because only weak light comes" is replaced by "light, that is, the intensity is almost uniform on the lens 17". If you think about it, the circle will come out from a small area, so I corrected it to ``. (2) Same, page 1/Evening Line: ``Because only strong light comes'' is corrected to ``Because light, that is, light that comes from a large area,'' 1, (wrinkle) 2

Claims (1)

[Claims] A lens having a conical refractive surface is placed on the optical path of the reading light from the disk leading to the photodetector, and the center of the lens is located on the optical axis. The photodetecting elements are arranged so that the center of their concentric circles is located on the optical axis, and the difference signal between the output signals of the two photodetecting elements is extracted as a focus state detection signal. A focus state detection control device for an optical disc playback device that controls a focus state from the beginning.