JPH03108129A - Focusing error signal detecting method - Google Patents

Abstract

PURPOSE:To reduce the crosstalk of a focusing error signal and a tracking error signal by computing the difference of the sum of the output of partition photodetectors being positioned at both ends of each of two partition detectors with an arithmetic means, and outputting it as the focusing error signal. CONSTITUTION:Assuming the values of the output signals of the partition photodetectors 25A-25C as A-C and that of the partition photodetectors 26A-26C as A'-C', a differential amplifier 31 outputs the focusing error signal with a value FES=(A+C)-(A'+C') in equation (2). Meanwhile, an adder 30 outputs the total sum (A+B+C+A'+B'+C') of the output signals as a reproducing information signal. Since a spot is made incident on only the partition photodetectors 25B, 26B in the center when focusing is obtained, the focusing error signal in equation (2) shows zero, and also, next equation SUM=(A+ C)+(A'+C') goes to zero when the focusing is obtained, which prevents the tracking error signal mixed (servo crosstalk) to the focusing error signal when the focusing is obtained.

Description

[Detailed Description of the Invention] [Summary] This method relates to a detection method for detecting a focus error signal, which is a displacement on the optical axis of an optical disc, and is aimed at reducing zero stalk between the focus error signal and the track error signal. The reflected light passes through a condensing lens and is split into two by a beam splitter,
One reflected light enters a first divided photodetector located before the focal point of the condensing lens, and the other reflected light enters a second divided photodetector located after the focal point of the condensing lens. and detecting a focus error signal that is a displacement on the optical axis of the optical disc based on each output signal of the first and second split photodetectors. Each of the two divided photodetectors is composed of at least three divided light receiving elements divided into strips, and the two divided light receiving elements T located at both ends of the first divided photodetector are calculated by the calculation means. The difference between the sum of outputs of T and the sum of outputs of two divided light receiving elements T located at both ends of the second divided photodetector is calculated and extracted as a detection focus error signal.

[Industrial application field]

The present invention relates to a track error signal detection method, and more particularly to a detection method for detecting a focus error signal, which is a displacement on the optical axis of an optical disc.

Optical disks are expected to expand in the field of application as external storage devices for information processing systems due to their Hitoyoshi mother nature and medium interchangeability, and have recently undergone a generation shift from the conventional write-once type to the self-replaceable type. Replacement is rapidly progressing.

In such an optical disc apparatus that records and reproduces information on an optical disc, the track error signal and focus error signal are detected simultaneously as changes in the beam light incident on the photodetector, so two error signals are inevitably generated. There is crosstalk (hereinafter referred to as servotalk).

Reducing this Rivo crosstalk is an important issue that determines the 4n reliability of the optical disc vitv1.

[Conventional technology]

FIG. 4 shows a configuration diagram of an example of an optical disk device.

In the figure, the emitted diverging light from a semiconductor laser 11 as a light source is made into parallel light by a collimating lens 12, and then enters an objective lens 15 via a beam spring 9139 reflecting mirror 14, thereby causing a microscopic beam to be projected onto an optical disk 16. Irradiated as a spot.

At this time, the objective lens 15 detects surface runout of the optical disk 16,
It is necessary to always irradiate a spot on a predetermined track by following the eccentric component, and for this purpose the device is equipped with an actuator (f not shown) that allows the spot to move independently in the focus and track directions. .

The spot on the optical disk 16 travels backward along the same optical path as the incident light, enters the beam splitter 13 and is reflected there, further passes through the condenser lens 17 and enters the beam splitter 18, where it is reflected. Some of it is transmitted and the rest is reflected. The light beam reflected by the beam splitter 18 is incident on a photodetector 19 and photoelectrically converted, and the light beam transmitted through the beam splitter 18 is incident on a photodetector 20.
is incident on the battery and is converted into a charge.

The output detection signals of the photodetectors 19 and 20 are added by an adder 21 and subtracted by differential amplifiers 22 and 23, respectively. An information signal from the optical disk 16 is taken out by an adder 21, and a focus error signal and a track error signal are taken out from differential amplifiers 22 and 23, respectively.

Among the above-mentioned track error signals and focus error signals, there are many documents that have already explained in detail the principle of detecting the track error signal, and since it is not directly related to the present invention, the explanation will be omitted here.

On the other hand, the principle of detecting the focus error signal will be explained in detail since it is directly related to the present invention. Conventionally used focus error signal detection methods include the following.

■ Spot size detection (880) method ■ Astigmatism method ■ Critical angle method ■ Knife T-Tsuji method ■ Fuco method All of these methods have their advantages and disadvantages. Therefore, the complementary SSD method, which is an improved version of the SSD method (2), has recently been attracting attention for its excellent performance.

The principle of this complementary SSD method will be explained with reference to FIGS. 5 and 6. In FIG. 5, the reflected light from the optical disc, which is converted into focused light by the condensing lens 17, is
The beam is split into two by the beam splitter 18 and is incident on a first three-split photodetector 19 placed in front of the focal point of the condenser lens 17 and a second three-split photodetector 20 placed after the focal point. Ru.

Here, as shown in the figure, the three divided light receiving elements of the three divided photodetector 19.20 are 19A to 19G, 20A to
It is assumed to be 20C.

In this state, when the optical disc is in focus (just in focus), both spots on the light receiving surfaces of the photodetectors 19 and 20 are circular with approximately the same diameter, as shown in FIG. 6(B). On the other hand, when the optical disc is located far from the focal point, a small diameter spot is formed only on the divided light receiving element 19B of the photodetector 19, as shown in FIG. A large-diameter spot is formed over substantially the entire area of the light-receiving surface. On the other hand, when the optical disc is located closer to the focal point, a large-diameter spot is formed over almost the entire light-receiving surface of the photodetector 19, as shown in FIG. 6(C). The photodetector 20 includes the divided light receiving element 2.
A small diameter spot is formed only at 0B.

Therefore, according to this complementary ssD method, the focus error signal FES is 19A.

19B, 19C (7) Each output signal value is A, B, 0°2
0A, 20B and 20C as A', 8' and C'
If it is expressed as FES = (A+C+8') - (8+A'10'
) (1), and from the sum of the rain detection signals of the divided light receiving elements 19A and 190 (2OA and 20C) on both sides of the photodetector 19.20, the detection signal of the middle divided light receiving element 19B (20B) is obtained. Light detection F! ! :it 9°20 each output value (this is (A+C-8).

(denoted as A'+C'-8')) and subtract these.

(F!jI problem to be solved by the invention) In the case of an optical disk device, the distance between the objective lens 15, which participates in signal reproduction, and the optical disk 16 is about 1 sI, and the problem of head collision, which is a problem in magnetic disk devices, is Anxiety is significantly reduced.

However, since the recording density is one order of magnitude higher than that of a magnetic disk device, it is necessary to precisely control the focus of a minute spot of less than 1 μm focused by the objective lens 15 with submicron precision by following the surface runout and eccentricity of the optical disk 16. For this purpose, it is essential to generate a focus 1 color signal that is stable and has good signal to noise.

However, since the tracking error signal and the focus 1 error signal are generated simultaneously by the photodetector, servo crosstalk inevitably exists. According to the above-mentioned complementary SSD method, since the reflected light from the optical disk is divided and completed, there is a possibility that this servo crosstalk can be reduced.

However, in this complementary SSD method, complementary SSD is only possible when the spot sizes on both the light receiving surfaces of the two photodetectors 19 and 20 match exactly at the time of focusing, but the aberration of the condenser lens 17, Due to the accuracy of the photodetectors 19 and 20 in the Z-axis direction, the spot shapes on the light receiving surfaces of the photodetectors 19 and 20 actually differ, so it is extremely difficult to adjust the relative positions of the photodetectors 19 and 20. However, in the past, the photodetector 19.2 was used when the focus was focused.
The focus error signal is detected by increasing the total amount of incident light on the split light receiving element in the middle of 0, whereas the track error signal is obtained at and around the focused point, so the servo cross is detected at the focused point. There is a problem that it is easy to receive a talk award.

The present invention has been made in view of the above points, and an object of the present invention is to provide a focus error signal detection method that can reduce crosstalk between a focus error signal and a track error signal.

[Means to solve the problem]

FIG. 1 shows a diagram explaining the principle of the present invention. In the same figure, the same components as those in FIG. 4 are given the same symbols and their explanations will be omitted. In FIG. 1, the first divided photodetector 25 is a photodetector located in front of the focal point of the condensing lens 17, and includes at least three divided light receiving elements 7-25Δ, 25 divided into strips.
Consists of B and 25C. In addition, the second split photodetector 26
is a photodetector located after the focal point of the condensing lens 17,
At least three divided light receiving elements f26 divided into strips
Consisting of A, 26B and 26G.

The present invention is characterized by a calculation means 27 that calculates the Yamada power signals of these two divided photodetectors 25 and 26 and outputs a detection focus error signal. The difference between the sum of the outputs of the elements 25A and 25G and the sum of the outputs of the divided light receiving elements 26A and 26G located at both ends is calculated and taken out as a focus error signal.

[Effect]

The light focused by the condensing lens 17 (reflected light from the optical disc) is divided into parts v1 by the beam splitter 18 and enters the first and second split photodetectors 25 and 26, respectively. In this state, the two divided photodetectors 25 and 26 are arranged so that the spot is incident only on the negative medium divided light receiving elements 25B and 26B. Therefore,
The light incident on the divided light receiving elements 25A and 25G and 26A and 26G at both ends is theoretically zero when in focus.

On the other hand, when the optical disk moves away from or approaches the focal point, the spot shape of one of the first and second photodetectors 25 and 26 becomes larger depending on the h direction, and
The other spot shape becomes smaller.

Therefore, from the above-mentioned driver 27, a focus error signal is taken out which is basically a gap when the optical disc is in focus, and whose polarity is different when the optical disc is near (=j) and when it is far away.

That is, in the present invention, two divided photodetectors 25 and 26 are used.
Even if the accuracy of the position adjustment is the same as before, the split light receiving element 25 is used to obtain a focus error signal when the focus is focused.
A and 250. Furthermore, the sum total between the incident lights 26A and 26G can be minimized.

(Embodiment) Fig. 2 shows a configuration diagram of an embodiment of the essential parts of an optical disk device to which the method of the present invention is applied.In the figure, the same components as in Fig. 1 are denoted by the same symbols. be.

The configuration of the optical disk device to which the method of the present invention is applied is roughly the same as the optical disk device shown in FIG. 4, except that the photodetectors 19, 20, . The adder 21 and differential amplifier 23 are used for split light detection as shown in FIG. 25, 26. addition 5
30 and tF difference 1111 [The difference is that it is replaced with 31.

In FIG. 2, the differential amplifier 31 constitutes the arithmetic means 27, and the divided light receiving element? 25A.

If the values of the output signals of 25B and 25C are respectively A, B and C, and the values of the output signals of the split light receiving elements 26A, 26B and 26C are respectively A', B' and C', then the differential The amplifier 31 is FES=(A+C)-(A'
+C') Outputs a focus error signal with a value represented by (2).

On the other hand, the adder 30 connects all the divided light receiving elements 25A to 25.
(A+B10)-F (A'+8'+C'), which is the sum of the output signals of G and 26A to 26C, is extracted as a reproduction information signal.

As mentioned above, when the focus is focused, the spot is in principle split into the center of the photodetector. Since the separate light receiving elements 25 and 26 are arranged so that the light is incident only on 25B and 26B, 0
The focus error signal expressed by the formula is a pyro when the focus is focused, and changes with respect to the disk position as shown by the solid line ■ in FIG.

In addition, the following formula, SUM-(A+C)+ (A'+C') (
The sum signal SUM represented by 3) is as shown by the broken line ■ in FIG. As can be seen from Figure 3, the in-focus point (third
(indicated by O in the figure), the rim signal SUM becomes pyro. This means that the divided light receiving elements 25A, 25C, 26A used for detecting the focus error signal FES
The sum of the amounts of incident light of 26C and 26C indicates that there is a gap when the focus is focused. Therefore, it can be seen that the tracking error signal is not mixed into the focus error signal when the focus is focused, and servo crosstalk does not occur when the focus is focused.

Due to an adjustment error in the relative positional relationship between the two divided photodetectors 25 and 26, the divided light receiving element 25A.

Even if a part of the spot hits one or more of 25G, 26A, and 26C at the focused point, the total amount of incident light at the focused point will always be the minimum, significantly reducing servo crosstalk compared to conventional methods. can do.

Although it is expected that a discontinuous point will occur in the focus error signal in the focused state, there will be no problem as long as this range is within the depth of focus of the objective lens.

Although not directly related to the present invention, in order to detect a track error signal, divided light receiving elements 25B and 26B are used.
At least one of them may be further divided into upper and lower halves.

Since the total amount of incident light can be minimized especially at the focused point (to a gap in the original drum), servo crosstalk at the focused point can be significantly reduced compared to conventional methods, making it possible to use rewritable optical disk devices to which the 3-beam method cannot be applied. There is one type that has features such as being particularly effective when applied to the neck and the like.

[Brief explanation of drawings]

Figure 1 shows the origin of the present invention! l! 2 is a configuration diagram of an embodiment of the main part of an optical disc device to which the method of the present invention is applied, FIG. 3 is a diagram showing a focus error signal and a rim signal, and FIG. 4 is a diagram of an optical disc device. An example configuration diagram, FIG. 5 is an explanatory diagram of the complementary SSD method, and FIG. 6 is an explanatory diagram of the main part of FIG. 5. (Effect of the invention)
In the figure, as described above, according to the present invention, the focuser 17 is a condensing lens, the split light receiving element 18 is a beam splitter, and 25 is a split light receiving element for detecting a blur signal.
26 is a first divided photodetector, 27 is a calculation means, and 25A to 25C, 26A to 260Lt are divided light receiving elements.

Claims (1)

[Claims] The reflected light from the optical disk passes through a condensing lens (17) and is split into two by a beam splitter (18), one of which is split into two by a beam splitter (18). The other reflected light enters a second divided photodetector (26) located after the focal point of the condenser lens (17), 2 split photodetectors (
In the focus error signal detection method of detecting a focus error signal that is a displacement on the optical axis of the optical disc based on each output signal of 25, 26), the first and second divided photodetectors (25, 26) are divided into at least three divided light receiving elements (
25A, 25B, 25C: 26A, 26B, 26C), and two divided light receiving elements (25A, 25C) located at both ends of the first divided photodetector (25) are determined by the calculation means (27). and the sum of the outputs of the two divided light receiving elements (26A) located at both ends of the second divided photodetector (26).
, 26C) and the sum of the outputs thereof is calculated and extracted as a detected focus error signal.