JPH02232823A - Optical pickup device - Google Patents

Abstract

PURPOSE:To obtain a control signal with reduced error, by respectively positioning optical detectors in front of the first convergent point of reflected beam and at the rear of the second convergent point, adding the quantity of detected light from the two optical detectors and detecting an error signal. CONSTITUTION:Detectors 7 and 8 are provided in positions equally deviated forward and backward from correct focal positions F1 and F2. When there is no focus error, reflected beam spots 9 and 10 of the detectors 7 and 8 obtain an equal diameter and outputs A, B, C and D are made equal. When a distance between an optical disk 5 and an objective lens 4 is small, the reflected beam is focused backward rather than the focal points F1 and F2. Then, the diameter is made smaller for the spot 10 of the detector 8 and the diameter is made larger for the spot 9 of the detector 7. When the distance between the optical disk 5 and objective lens 4 is enlarged, an opposite phenomenon is shown. Accordingly, the error signal, for which the quantity of light outputted from the detectors 7 and 8 is added, can be detected. Thus, the control signal with the error reduced, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup device suitable for use in an optical disc player such as a CD player f. [Prior Art] Conventionally, optical pickup devices perform focus control to focus a light beam onto an optical disk, and tracking control to irradiate a light beam onto a track.

This focus control signal is generated by irradiating the reflected light from the optical disc onto a photodetector that is divided into two halves in the shape of a Japanese flag, into a central part and a peripheral part, and calculating the difference in detection output between the central part and peripheral part. It can be obtained by detecting the size of this irradiation spot. In addition, the tracking control signal is generated by irradiating the reflected light onto a photodetector divided into two by a straight line corresponding to the track direction, calculating the difference between the outputs of the left and right photodetectors, and calculating the reflected light flux which is asymmetrical due to deviation from the track. It can be obtained by detecting changes in the shape of. [Problems to be Solved by the Invention] However, due to surface wobbling of the optical disk, the reflected light may irradiate a position off the center of the photodetector, or the optical pickup itself may be deformed due to temperature changes, etc., and the irradiation spot on the photodetector may be affected. If the position changes, errors will occur in the focus control signal and tracking control signal. The present invention has been made with the aim of improving these drawbacks.

[Means to solve the problem]

An optical start-up device according to the present invention includes: means for converging a light beam onto an optical disc; a first photodetector divided into two by a dividing line and disposed in front of a convergence point of a reflected light beam from the optical disc; The optical disc is divided into two parts by a dividing line, and a second photodetector is arranged behind the convergence point of the reflected light beam from the optical disc.

[For Rei]

In this way, since the photodetectors are placed in front of the first convergence point and after the second convergence point of the two reflected lights, the influence of the positional shift of the irradiation spot on one photodetector will not affect the other photodetector. As a result, unlike the influence on the photodetector, the influence due to positional deviation can be canceled.

[Embodiment] An embodiment of the optical pickup device according to the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 shows the optical system of the optical pickup device. A light beam 11 emitted from a light source 1 such as a laser passes through a beam splitter 2, passes through a collimator lens 3 and an objective lens 4, and is irradiated onto an optical disk 5. be done.

This illumination light beam 11 is reflected to the objective lens 4. It passes through the collimator lens 3, enters the beam splitter 2 again, is reflected by the beam splitter 2 to change the direction by 90 degrees, and is split into two mutually orthogonal light beams by the half mirror 6, which are then sent to the photodetector 7, 8 is irradiated. FIGS. 2A and 2B show the details of the detectors 7 and 8. The detectors 7 and 8 are composed of two-split photodiodes, and have a square outer light-receiving surface 7a. It has a structure in which circular inner light receiving surfaces 7b and 8d are provided in the center of 8C.

The light beam spot 9.10 indicated by the dotted line is the light beam 1l.
This figure shows the state in which the reflected light is irradiated onto the detector 7.8 when the beam is correctly focused on the optical disk 5. Here, the center of the beam spot 931O is made to coincide with the center of the light receiving surfaces 7b and 13d. Further, as shown in FIG. 1, the detectors 7 and 8 are placed before and after the focal positions F and F2 of the two light beams divided by the half mirror 6, respectively.

Figure 3 shows the focus error signal FE from the above-mentioned detector 6.
and a detection circuit for extracting an HF signal containing recorded information. In the figure, light receiving surfaces 7a, 7b, 8c
, 8d as A, B, C. D and output B, C
are respectively applied to the two non-inverting input terminals of the adder circuit l2, and the output A. D is applied to the two inverting input terminals of the adder circuit 12. Also, outputs A, B, C, D
are respectively applied to the non-inverting input terminal of the adder circuit l3.The outputs of the adder circuit 12.13 are respectively led out to the output terminal 14.15 as a focus error signal and an HF signal, and are added to a predetermined control or signal detection circuit. It will be done.

The operation of the above configuration will be explained in detail below.

Since the detectors 7 and 8 are located at positions that are equally shifted forward and backward from the correct focal planes F and F2 in Fig. 1, the beam spot is correctly aligned, as shown in Fig. 2 (a). When focusing on the information surface of the optical disc 5, the reflected light hitting these detectors 7.8 is 9.10 as follows:
The diameters are approximately equal. Also, in this case, outputs A and B are equal to each other, and output C. The positions of photodetectors 7 and 8 are adjusted so that D is equal to each other.

Therefore, when the distance between the optical disk 5 and the objective lens 4 becomes close, the reflected light beam is shifted to the focal plane Ft shown in FIG.
．． Focus later than Fz. Therefore, the diameter of the beam spot 10 on the photodetector 8 in FIG. As it moves further away from 7, its diameter increases. Conversely, when the optical disk 5 and the objective lens 4 move away from each other, the reflected light beam moves to the focal planes Fl and F2 shown in FIG.
Focus on something in front of you. Therefore, the beam spot 10 on the photodetector s becomes larger because its focal point moves further away from the photodetector 8, and the beam spot 9 on the photodetector 7 becomes smaller because its focal point approaches the photodetector 7. .

The light amount detection output A at each light-receiving surface shown in FIG.
B, C, and D are the adder circuit 12 of the detection circuit shown in FIG. 3, where the focus error signal FE is calculated, and FE-B-A- (D-C) ----------...
-.-.1.-(l), and the focus error signal FB can be outputted to the output terminal 14.

Now, when the beam spots 9 and IO are at the focused position as shown in FIG. 2, that is, at the position of zero error, the outputs A. Since B, C, and D are equal to each other, the focus error output FE is zero.

Next, when the focus error gradually becomes larger than zero and the focus comes to be in front of the optical disk 5, the beam spot 9 becomes smaller and the beam spot 10 becomes larger as described above. In this case, the center position of the beam spot 9.10 is the light receiving surface 7b.
, 3d. Therefore, as the focus error increases, the output B gradually becomes larger than the output A, and the output D gradually becomes smaller than the output C. Therefore, the focus error signal FE appearing at the output terminal l4 gradually increases from zero in the positive direction. do. Moreover, when the focus error gradually becomes larger than zero and the focal point is brought to the rear side of the optical disk 5, the beam spot 9 becomes larger and lO becomes smaller. Therefore, as the focus error increases, the output B gradually becomes smaller than the output A, and the output D gradually becomes larger than the output C, so the focus error signal FE appearing at the output terminal l4 gradually increases from zero in a negative direction. do. Here, as the reflected light beam moves on the detectors 7 and 8, the focus error signal obtained by the addition/subtraction circuit 12 has these output fluctuations canceled, and has very little influence on the focus error signal.

Figure 4. 5 and 6 show another embodiment of the present invention, in which the above-mentioned detectors 7 and 8 are divided by straight dividing lines 71, 81 as shown in FIG. 81, Qf
By matching the direction of the track projected on the FI devices 7 and 8, it is possible to detect a tracking error signal as well. That is, in the detector 7.8 of FIG. 4, the outer and central light receiving surfaces 7a and 7b are respectively 7a+, 7a2 and 7bt.
, 7bz, and the outer and central light receiving surfaces 8C and 8d are respectively 8C+, 8Cz and 8d. ,8
d! It is divided into two parts as shown below. These light receiving surfaces 7 a+ , 7
az * 7”+ + 7b2 and 8C+ .
The photodetection outputs of 8cz, 8d+, 8dt are A+, At
, B+, Bz, CI+ Ct. D,,D. shall be.

FIG. 5 shows this optical system, which is the same as that in FIG. 1 except that the detection H7.8 has dividing lines 71 and 812. FIG. 6 shows the focus error signal FE and tracking error signal TH. This is a detection circuit. In the figure, the non-inverting input terminal of the adder/subtracter circuit 2I has photodetection outputs A+ . A
t, D+, D! is applied to the inverting input terminal, and a photodetection output, BI. B*, C+, and C2 are added.
The non-inverting input terminal of the addition/subtraction circuit 22 has a photodetection output Ax.
,Bg,CI. Dz is applied to the inverting input terminal, and the photodetection output AI+B. ,C. ,D, is added. In the above configuration, the output FE of the adder/subtractor circuit 2l is FE" (AI + Ax) - (Bt
+ Bz ) { (C+ +Cz ) (D
+ +Dz ) 1 (2) Therefore, it becomes the same as the focus error signal FE shown in (1) 2 above, and can be used as a focus error signal.Next, the output TE of the addition/subtraction circuit 22 is TE=Az 1 B ! +C! +D! CAI 10B++CI +DI 》 −・−−11−・−・− (3) This is the total light detection output of the left half of the photodetector 7.8 and the gold light detection output of the right half. Here, as is well known, when the spot irradiated onto the optical disc 5 is located at the center of the track, the sight distribution of the reflected light spot is symmetrical with respect to the center line in the track direction on the reflected light spot. However, when the spot deviates from the track, the side of the reflected light beam that enters the half mirror 6 shown by the double arrow in FIG. 5 becomes dark, and the light quantity distribution becomes asymmetrical with respect to the center line in the track direction.
Therefore, the dividing line 17L IIN of the photodetector 17.18
! If the reflection spots 9 and 10 are arranged in the direction of the track on which they are projected, the output TE of the adder/subtractor circuit 22 can determine which side of the track of the disk 5 the irradiated light spot has deviated to and by how much, in terms of magnitude and polarity. It can be used as a tracking error signal shown in .

Now, when the reflected light beam is shifted in the direction of the double arrow as shown by arrow P in Figure 5, the reflected light spot 9 is as shown in Figure 4 (A).
, the light beam reflected by the half mirror 6 moves in the opposite direction to the side indicated by the double arrow of this light beam, as shown by the arrow Q, and the reflected light beam moves to the left (direction of arrow p). The light box 10 is shown in the right direction (arrow q) in Figure 4 (mouth).
direction). Therefore, the tracking error signal TE indicated by (3) 2 increases as the left output Ax, Bz of the photodetector 7 increases and the right output C. ,D. TE also increases, so the influence on the tracking error signal TE is extremely small. Regarding the HF signal detected to reproduce the information signal,
Output A. from each divided light receiving surface. , At...
All you have to do is add up all D2. In addition, in FIG. 4, the dividing line 7j! ,8I! In addition, there is a 7m dividing line indicated by a dotted line.
, 8m are added to divide it into four parts in a square shape, and the output king error signal of the light receiving surface in the diagonal direction can be obtained. That is, when the light spot passes through a pit, the direction of the polarity reversal between positive and negative differs depending on whether the direction of the track deviation is left or right, so the direction and degree of the tracking error can be detected. Alternatively, a light-transmissive detector may be used as the detector 7, and the detector 8 may be placed behind the focal point Fl. In this case, the half mirror 6 can be omitted.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a control signal with little error in response to positional deviations of reflected beams.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the optical system of the focus error detection device for an optical pickup according to the present invention, and Fig. 2 (
A), (opening) is a schematic diagram showing the photodetector, FIG. 3 is a circuit block diagram showing the signal detection circuit, and FIG. 4 is a schematic diagram of the photodetector showing another embodiment. FIG. 5 is a schematic diagram showing the optical system, and FIG. 6 is a circuit block diagram showing the signal detection circuit. 6...Half mirror 7.8...Detector 9.10...Beam spot

Claims (1)

[Claims] means for converging a light beam onto an optical disc; a first photodetector divided into two by a dividing line and disposed in front of a convergence point of the reflected light beam from the optical disc; and a second photodetector disposed behind the convergence point of the reflected light beam.