JPS59207033A - Error signal detector of optical head - Google Patents

Abstract

PURPOSE:To suppress the displacement of an object lens and the generation of DC offset and to enhance the detection sensitivity by dividing the light receiving face of a photodetector into three or more in the tangential direction with respect to a track and performing an operation processing on the basis of signals in the light receiving area distant from the optical axis and the light receiving area close to the optical axis. CONSTITUTION:Outputs of individual elements 31a-31f of a 6-divided optical detector 31 are denoted as (a)-(f), respectively. The first focus error signal (FE signal) (a+b+e)-(c+d+f) is obtained by sum circuits 32 and 33 and a difference circuit 34, and outputs (e) and (f) are used to obtain the second FE signal by a circuit 35. The first FE signal has a wide dynamic range but has a low detection sensitivity. The second FE signal is obtained with the quantity of light in the peripheral part of the photodetector 31. Since the variation of the quantity of light in the peripheral part is very high for the deviation of an optical disc from the in-focus position, the detection sensitivity of the second FE signal is very high. Consequently, focus servo with a wide dynamic range and a high precision is possible by both signals. Meanwhile, a radial error signal (a+b)-(b+d) is obtained by sum circuits 36 and 37 and a difference circuit 38.

Description

[Detailed description of the invention]

The present invention provides audio discs, video discs, f-
There is a focus error signal of an optical head used for signal reproduction of an optical disk such as a data disk, and a detection device for obtaining a ``fusial'' amount. An example of the configuration of an optical head optical system including a signal detection device is shown. In the figure, an optical disc 1 contains video signals, audio signals, data signals, etc. encoded in circumferential or spiral information tracks. is recorded, for example, in the form of P1~.Light J
The light from Pf 2 passes through a collimator lens 3, a polarizing prism 4, a 1/4 wavelength plate 5, and an objective lens 6. The return light that has been modulated and reflected by the edge is
Pass through the objective lens 0.1/4 wave 1 (plate) again, 1-
The light is guided by the optical prism 4 to the detection prism 7. The detection prism 7 is set so that its reflective surface 8 is approximately critical to the optical axis of the returned light. On one side of the detection prism 7, there are four strands 9a and 9b.
. When the four-split photodetector 9 consisting of 9c and 9d has a crotch of C, and the return light entering the reflective surface 8 of the detection prism 7 is parallel light, that is, with respect to the optical disc 1, the objective l nonce (5
When the light spot is in the A-cass 1 state, most of the returned light is reflected by the reflecting surface 8 and enters the four-part photodetector 9.

[This is configured. In the same figure, a 11°; l 12 represents the maximum i11+8 component of the light beam entering the reflective surface 8 of the detection prism 7 when the optical disc 1 deviates from the focused state in the direction a.
) + I, b + 2 is the irregular surface 8 of the detection prism 7 when the optical disc 1 deviates from the focused state in the b direction.
ar+, , ar2 and :)rl・, br2 represent the reflected light 831J reflected on the reflecting surface 8 atl,
bt2 each reduces the transmitted light. In such a configuration, the light intensity distribution of the return light incident on the S3 and C1 four-split photodetector 9 is as shown in FIG. Using the surface perpendicular to the plane of the paper that includes the optical axis of the returned light as a bank, the light intensity changes by the amount of light A1j or in the opposite direction, and the focusing device C (7)
Only when the light amount distribution is uniform is 4. Therefore, the detection system 9a, 9 consists of 41゛4 photodetector 9
If the rxI processing is reversed using each output of b, 9c, and 9d, the focus error (fi
You can get Q. A method for detecting such a cis-cassnizi signal has become well known from the publication of 1987-7246g, and this method will be referred to as the 1-critical angle method hereafter.
I will save up some money. Note that FIG. 1 also shows a detection circuit for detecting the −C focus error signal using the output of the quarter-811 photodetector 9. In the figure, io, i+, and i2 are sum circuits, and 13 is a sum circuit. It is a difference circuit, and each photodetecting element 9a of the quadrant photodetector 9,
Each output of 9b, 9c, and 9cl is Sl. When S21' S3 and S4 return, 85-8 La- also (Sl + S4) - (S2 To53)-37 is focused -1-La1i': '>'L S7 and -C
It is obtained from the difference circuit 13, and Sl + S4 +
An information signal is also obtained from the summation circuit 12 by setting S2 +S3 =Sz. In addition, in the configuration of the optical system shown in FIG.
Various 1 in the disk radial direction of the optical slots 1 to 1 to form the optical disk 10 and the bits forming the information 1 to the optical disk 10.
☆The light intensity distribution pattern on the exit pupil plane of the objective lens 6 according to the positional relationship is 'C' as shown in FIG. △ in the same figure shows the pin 1 where Subotsu l-111 creates information 1-rack h-5.
~112 shows the lifting platform shifted to the right, and 3) in the same figure shows the case shifted to the left. In the circle representing the light intensity distribution in each positional relationship, the hatched part is R.
In the X part, the white part represents the bright part. η, the return light reflected by the optical disc 1 (, 1, recording on the optical disk 1 (~modulated by the recorded information on the rack (], optical slot) ~ recording 1 ~ in the radial direction with respect to the hook According to the deviation, the amount of light in the far field of the recording I-hook changes. Therefore, during that far-field, the information f, the hook direction C, and the A 1j photodetector 9 is arranged in a quarter divided by 1 and 11 in the orthogonal direction, and the output of each detection element of the photodetector 9 is used to detect the radial error (No. 3 (like this)
;The method for detecting radial error names is disclosed in Japanese Patent Application Laid-Open No. 57-74.
Although it is well known as it is disclosed in detail 1 in Publication No. 837, here, for convenience of explanation, the force d1 of I will be referred to as [far field (left). ] Fig. 4 shows a conventional BLL constructed by combining two A-field sensors so as to simultaneously output focus error (+1i) and radial error signals. 11) Regarding the configuration d5 and operation of Fig. 1, Aperture 1 (described in detail in Section 1 of Publication No. 57-74837, so I will briefly explain it here. In the same figure, S5 is a four-part photodetector, which is almost the same as the optical system shown in Fig. 1. Information 1 on the optical disc 1 using an optical system (not shown) having the same configuration
- In the far field of the rack ('L-c 6°), therefore, this quadrant photodetector 9 has
As explained to Sagi by
'i? Return light with a light intensity distribution corresponding to the radial positional relationship of the light spot with respect to the knock is needed, and the light weight is determined by the detection beam of the optical system (not shown). The return light to the reflecting surface (corresponding to 7 in Fig. 1) is divided into 4 lenses from the in-focus position, as explained in Fig. 2, with the plane parallel to the fucial direction included in the optical axis as the boundary. The brightness and darkness are reversed in relation to the direction of the shift, and they are the same only when in focus.
Focus error information, which is the light amount distribution, is also included. However, the name of the photodetector 9 that detects the Iha number corresponding to the shape of the light intensity distribution is 9a, 9b, 9c.
. By using the output of 9d, it is possible to detect the focus 1 signal d5 and the tracking 1 signal separately. Since this figure mainly shows the configuration of the detection circuit, the x direction and the Y direction of the quadrant photodetector 9 correspond to the radial direction d3 of the information track and the radial direction of the σ tank 1. ) The detection of the A=- force error signal is as if the far field of the returned light (IJ is hatched in Figure 3 A, 13). It changes according to the errano 5 quotient, but the detection element 9a with the horizontal direction The ratio of the light amount does not change C', and the sum S5 of the detection element output 81.S4 of 98.9d and 9 as in the conventional example in FIG.
The sum S5 of the outputs 82° S3 of the detection elements b and 9c is obtained by each summation circuit 10.11, and the sum S and the signal of Sli are led to the difference circuit 13 to obtain the focus F-4Tr signal S.
7 is obtained from the output terminal 14. On the other hand, the radial error signal S9 is generated by a photodetecting probe 9a disposed at a diagonal position centered on the intersection of the radial direction 9C to 91. . Each output St, 83 and 82.9d. Each story S+oS++ of St is obtained by each summation circuit 1 and 16, and the sum S88 and >C812 of Sto and S++ are calculated by the summation circuit 12J>J and the difference circuit 17, respectively, and the sum is calculated. S8 is used as an information signal to take out the terminal 18. On the other hand, the rising pulse generating circuit 19 and the falling pulse are sent to the 1! 71 path 20 and 1. Goo 1 to signal S at the timing of rising d5 and falling [ILI cross 1lr)
+ 3.8 + 4 is generated. 21, 22 haso h
and each goo 1-signal SI3. This is a sampling circuit that operates normally in S14. The output SI2 of the difference circuit 17 samples the signal having the radial error information of S12 led to the sampling circuits 21 and 22 and received from the C difference circuit 17 at the timing of the L cross point of the information signal 888. Each ball 1 to circuit 23,24 sequentially covers hole 1. This hall 1 my March is converted from the skeleton 2G through the operational amplifier 25 to the fusial '2fu fM No. S9 U + m. Zunari, et al., as shown in Figure 3 A and B, Pil-1
The light hanging portion A 11 in the far field located at the end of the light spora 1 is the stone side A for the information i-rack of the light spora 1~
3 paralysis! Enter J: on the r side.
The signal of the amount of light that hits this part (1) is differentially extracted and compared by the above-mentioned Goo 1 to S+ 3.8+ 4. A radial error signal S 9 jfi is obtained. However, such a known] nihui K f't
+'jE output device a3, when carrying out fusial 1 nervo by displacing the objective 1 nons 6 in one direction X of the radial error according to Fig. 1 and sealing the radial error, as shown in Fig. If only the objective lens 6 is displaced in the radial direction The light spot moves horizontally by d5 on the arranged four-part photodetector 9. The occurrence of such lateral movement causes a DC offset to occur in the full error signal, causing the optical head to move from one direction to another.
There is a problem in that the reading light spot deviates from the center of the information i-rack. In this case, the focus error signals are output S1. The sum of S4, 9 b J'i J: and the outputs of 9C S 2 , S 3
Difference in the sum of 57 = (St +84) - (S2 +33)
Therefore, no DC offset occurs. However, as shown in FIG. 6A, when the tilt of the optical disk 1 changes from the position shown by the dotted line to the position shown by the solid line, the optical axis of the returned light shifts. A part of the light reflected from the optical disc 1 by the lens 6 is rejected. As shown by hatching in Figure 13,
A portion of the returned light incident on the quarter-v photodetector 9'' is kicked off, and furthermore, it moves laterally in the direction of the inclination of the optical disc 1. That is, when the optical disc 1 is tilted in the tangential direction, a cut occurs in the tangential direction. There are problems such as the occurrence of DC'A offset 1. It is an object of the present invention to solve the problem of the conventional equipment as described in 1.
It is an object of the present invention to provide an error signal detection device for an optical head, which suppresses the occurrence of DC off-flash, which is a serious problem, and has a high detection value of 1. The optical head error signal detection device of the present invention makes light from a light source into a minute spot using an objective lens, irradiates it onto the information 1-knock on the optical disk, and reflects the light from the optical disk. The return light that has passed through the lens is placed in the far field of the information track through a detection system in which the reflective surface forms an approximately critical angle with respect to the optical axis of the return light. into the split type photodetector.
In an error signal detection device for an optical head, which detects a focus error signal and a radial error signal from the bias of the tip distribution of the incident light, υj in three directions in the tangential direction It is divided into four parts at the border to form a large division type, and the output of each detection element in the central quarter v1 is used to detect the C radial error signal.
It is characterized in that the focus error signal is detected using at least each output of the detection elements at both ends in the full direction. Hereinafter, a detailed explanation of the present invention will be given based on the drawings. FIG. 7 is a block diagram showing an example of the configuration of the embodiment according to the present invention (only the upper error signal detection section consisting of a hexagonal split photodetector and a 71-lix processing circuit is shown). +lj in the bright device, the known critical angle γ in Fig.
In place of the 1-4-split photodetector 9, a -11 photodetector 31 is used as shown in FIG. 7, and the information on the optical disc 1 is
The optical axis of the return light from the optical disc 1 coincides with approximately the center O of the hexagonal detector 31 during the 7-hook yield. The light-receiving surface of the hexagonal split photodetector 31 is divided into three parts in a direction corresponding to the Kunsential force direction Y of the optical disc 1.
The central light-receiving surface divided into three parts is connected to a line in the tangential direction Y and radial direction X passing through the center O (
It is divided into four parts, with 191 sides on all sides. Hereinafter, the photodetecting elements forming each of the hexagonally divided light-receiving surfaces will be simply referred to as 1. As can be easily inferred from the principle of the critical angle method explained using Fig. 11, the closer to the center of the light beam incident on the hexagonal Δ]1 photodetector 31, the smaller the rate of change in the amount of light with respect to defocus, and For example, tangent direction Y
The rate of change is large around the area. Therefore, it is clear that the detection sensitivity will be increased if the focus error signal is detected using the amount of light only in the peripheral area in the tangential direction Y. Therefore, in this embodiment, in d3, 31
an element group consisting of a, 31b, 31e, and 31C
It is divided into elements 11Y consisting of elements 131d and 31f, and each output a of the element groups 31a, 31t) and 31e is
, I), e4! : In the first summation circuit 32, the latter J! Each output c, d of I'3IC, 31d, 3H
, f are respectively added in the second summation circuit 33, and these caulking outputs are led to the first difference circuit 34 and C1(a+b 10e)-
(C1d+f') and the tangency of the hexagonal split photodetector 31. / ropes 31e, 3 on both sides of the direction Y
The respective outputs e and r of 1f are led to the second sum circuit 35 (
, the second focus error signal (g5) is obtained as its output. It has the same quality as the cass error signal, and has a wide dynamic range but low sensitivity.In contrast, the 274th
-The cass error signal is sent to the hexagonal split photodetector 31! ,? I
This was obtained using the light intensity at the periphery of tJ'. The rate of change in the amount of light at the periphery is extremely large relative to the deviation from the in-focus position of the optical disc, so
The second) A-force 1:-noi signal is a signal with extremely high detection sensitivity. Therefore, for example, if you use the 1st focus l [Ra monk's name] when drawing in A-kasu 1 Pubo, and after reaching the serial book 11 human form, you can use the 2nd focus one kasu], U (in 4 If the 4D lens is switched to servo control I, the focus servo with a wide dynamic range and high precision will function.In order to obtain the first focus F(i;Qj), each sum circuit 3
31a, 3 of the hexagonal split photodetector 31 added to 2.33
The output a of each water child of 1b, 31c and 3gai,
b, c, (+ is reduced to a small value using a resistor, etc., and the output e of the cable shown as 31e and 31f is obtained,
By increasing the value of f applied to each of the summation circuits 32 and 33, it is possible to prevent the first A-cass error No. 13 with relatively high detection sensitivity without sacrificing the dynamic range. On the other hand, the radial signal is generated by the quadruplets 31a, 311), 31c, except for the quadruplets 310, 31[, which are located on both sides of the single-row photodetector 31 in the radial direction.
Using each output a, b, c, d of 31d,
The calculation process is similar to that of the conventional example shown in FIG. 4. Rinawara, Oita 81] Return light to photodetector 31 @l
Element 3 located at opposite position 11Y on the diagonal line centered on IO
The outputs a and C of the elements 1a31c are led to the third summation circuit 36, and the outputs b and d of the elements 311+ and 31d are respectively led to the fourth summation circuit 37, and are added separately, and their respective sums are The additive outputs of the circuits 36 and 37 are input to the third difference circuit 38 to obtain a radionor error signal of (a + c)" - (b + d'). In this way, the radionol error signal of 13. If necessary, if this radial error signal is processed as shown in FIG. 4 in the same manner as in the conventional Ic example, a full error signal with even higher detection accuracy can be obtained. Further, in this embodiment, the third and fourth sum circuits 3
6.37 and the addition output from the fifth summation circuit 39 of each of the cables 31e and 3H at both ends of the hexagonal photodetector 31 in the tangential h direction are led to the sixth summation circuit 40. (
To add, a + b + c + d + k (e →
-r) is configured to obtain an information signal. Furthermore, i(
is the gain constant of the fifth summation circuit 39. In addition, in this embodiment, the hexagonal photodetector 31 has a 414-component structure in which the light from the objective lens (not shown) is placed in the field of the rack.
Similar to the conventional device in which the J photodetector is placed in the Noah field, M T F (modulation tr
The effect of improving the answer (ansferfu++ction) will also be ensured. <t A3, C141 shown in A-3 in the same figure is the first fan A-cas-l 45 output 0iif terminal, 42 is the second fan A-casu signal output terminal, 43 is the Fuji Alni [-ra signal Output terminals J and 44 indicate 17S signal output terminals.
. Figure 8 shows that when an error is stopped by a single servo system using this type of error signal detection device, the higher the detection sensitivity of the error signal is, the more the servo system responds to the disturbance.
This shows that the deviation is small. That is, in the same figure,
The horizontal axis represents the amount of displacement such as the inclination of the optical disk as a disturbance, and the vertical axis represents the error signal, and the detection sensitivity is represented by diagonal lines. Now, assume that a disturbance such as a disk tilt enters the servo system, causing a DC offset. The diagonal line representing the detection sensitivity indicates that the culm detection sensitivity with a slope of Ω is high, and the higher the detection sensitivity, the greater the deviation from the scale value δ
1 is small, but when the detection sensitivity becomes low, a maximum target value deviation δ2 which is b larger than δ1 occurs. In the present invention, as is clear from the above embodiment, it is possible to detect a focus error signal with extremely high detection sensitivity in °C compared to the conventional device, so disturbances such as disk tilt can be detected by the servo system. Even if DC, I)Lt is mixed in, the deviation from the target value will be small. FIG. 9 is an explanatory diagram of another embodiment of the device of the present invention. The configuration of this embodiment (J, the previous fruit/
II! ! As an example, the hexagonal split photodetector 31 of a'3 L:j is used.
The figure below shows the same structure. I wanted to-'Cj
-, +1 Figures show a hexagonal split photodetector 5 used in this example.
Only the configuration of 1 is shown by the relative position of the return light I-C. The hexagonal split photodetector 51 of this embodiment has a long rectangular shape in the illustrated J, tangency, V, and Y times.
Similarly to Katsaki's embodiment, it is divided into two parts in the tangential direction Y, and the center part of the two parts is divided into two parts in the tangential direction Y and with the optical axis O of the returned light as the intersection point. A total of six light quantities J divided into four by a line in the serial h direction X: j S 51a, 51b, ! +10
, ! i1d, 51c, and 5H create a 14-(i).
It is arranged in a relationship to receive C light except for the luminous flux at the peripheral edge in the lateral direction X centered on the optical axis ○ of this light,
Elements 5ie on both sides of the tank's longitudinal direction Y, !
Only the luminous flux at the circumferential end in the tangential direction Y of the returned light is incident on i1f, and the four elements 5 in the central part J,
1a, 51b, ! +1c, ! iM has a configuration in which it is placed in the far field due to the incendiary light of the information hook, in that only the light beam of the medium heat part, excluding the peripheral part of the return light, is used. Oita iiri photodetector 5 configured as follows.
1 each element 5.1a, 51b, 51c, 5
Each output a, +1 of 1d, 51Q, 51f
, C, d, e, f -(, using the same processing circuit as in the previous example, fi, (a + C)7' (l
] In calculating +d>, D Cnru1~, which is less affected by the lateral movement of the cluster light, the cause of which is explained in Figures 5 and 6, was suppressed. It is possible to detect radionol error (No. B). In this example, the four elements in the center of the hexagonal J6 detector 51 are !+18, 5+13, !
The configuration of the positional relationship of the return light sub-boxes 1 to L, such as i1C and 51d, is disclosed in 7C*fffl No. 111837/1983 for the purpose of obtaining the same effect using a four-division j photodetector. Similar to the technology described above, the DC offset light of the radial error signal (1) has a structure similar to that of (13). This can be easily explained in 11.
The present invention J, W (,'?
”i)÷44! The central element 51a of j1, !
111+51c,! +1 (I = I!J) The gray light is caused by disturbances, etc. in the return light from the optical disk (the range in which the hexagonal position 11-1 to each of the above-mentioned chords changes when it moves laterally, and J, the luminous flux in the physical direction However, the radial signal detected from the bias in the previous distribution of the medium-heat part of the return light, which is less affected by disturbances, is the one in which the DC off-res 1~ is suppressed. , rv + easy.
Similarly to 'll, 15 (both sides/) elements 51e, 51 are placed in the tangential direction Y of the hexagonal light beam detector 51.
By computing C, c−f using each output of r,
The second part of the detection reaction is 8 et al.
b, 51e and 51c, 51d, 51f
By increasing the output of each group of Mizuko, and taking the spear of the output of each additional C section, the 1st] A-Sword, Sat, T, No Buddha, etc. can be completed. In addition, informatization 8 is
Example of the rabbit and 11) Add the output of the elements of the hexagonal split photodetector 5) 1 > si (buttocks). , then the return light obtained from the optical disk entering the hexagonal photodetector through the critical angle prism is λ・jJ to the optical disk of the objective lens on both sides of the tank direction.
Depending on the defocus state of Misalignment of the relative position between the information track and the objective lens, or
``!Because the light intensity of the medium flame part of the return light that is less subject to changes in light intensity due to disturbances such as 1 ml (Fujial error signal can be detected from 1ml b U) T, the detection box 1 summer The high A-cus T error signal (°1, and that) A-C Δ fret J3 and the radial error signal are detected when the D CΔ fret is depressed sufficiently. Yes, there is. (Light detection) Part 4 is configured as shown in Fig. 9) and the present invention Ril:j has a3C. In addition to the effect described above, CD0g7
It has the advantage of being able to convert Fuji Alto Sea Sign > 3 to 1-, which further reduces T-T.

[Brief explanation of drawings]

FIG.
Illustration of the known far-field method for detecting Fu-19 signals, Section 4, Criticality January (Last J3 and Far Field? 1,000,000,000 Figure 4 is an explanatory diagram of the problem fish that goes into the conventional example. Fig. 9 is an explanatory diagram of the influence of the shadow τ on the target value deviation amount of the detection 1, and Fig. 9 shows a modification of the hexagonal split photodetector used in another embodiment of the present invention. There is a diagram C of the return light system. 1... Optical disk 2... Light beam 3... Collimator lens 4... Deflection prism 5... 1/41 skin length (reverse 6...・Objective lens 7...Detection prism 8・
...Reflecting surface 9...quarter;'qJ! Detectors 9a to 9cl, :Ha to 30, 51a to 51
f-photodetection element 10.~12.15.16.32.33
．． 36.37.39.40...Summing circuit 13, 17.23.35...Difference circuit 19...Rising pulse generation circuit 20...Rising tripulse generation circuit 21.22...Sampling circuit 23 .24...Hold circuit 26.38...> is connected to dynamic amplifier 31, 1...Hexagonal split photodetector 44.42...
・1st d3 J, Higa 12] l-Cast U-i 1
:) The same output terminal J- 4 to... - NO SEAL J Noi output terminal J terminal 471.
・・111 notification im y3 output terminal 111・・light switch
-112...beep]~q,:j Applicant: Olympus Optical Industry Co., Ltd. Figure 5 Figure 6 Procedural Amendments May 12, 1981 1, Indication of Case 1982 Patent Application No. 80798 No. 2, Name of the invention Optical disk reproducing device 3, Relationship with the case of the person making the amendment Patent applicant (OA7) Olympus Optical Industry Co., Ltd. (revised) Akira ■1 Book 1, Title of the invention Optical disk reproducing device 2, Patent An optical deosk reproducing device characterized in that it obtains a claim or an information signal. playback device. The optical disc playback device according to item 1. 3. Detailed Description of the Invention The present invention relates to an optical disc reproducing device for obtaining a focus error signal, a radial error signal, and a reproduction information signal of an optical head used for reproducing signals from optical discs such as audio discs, video discs, and data discs. It is something. FIG. 1 shows an example of the configuration of an optical head optical system including this type of error signal detection device. In the figure, on an optical disc 1, video signals, audio signals, data signals, etc. encoded in circumferential or spiral information tracks are recorded, for example, in the form of bits. The light from the light source 2 passes through a collimator lens 3, a polarizing prism 4, a 1/4 wavelength plate 5, and an objective lens 6, and is spot-irradiated onto the optical disk 1, where it is modulated by the information track on the optical disk 1. The reflected return light passes through the objective lens 6.1 again.
/4 wavelength number 5 and is guided to the detection prism 7 by the polarizing prism 4. The detection prism 7 is set so that its reflective surface 8 is at almost a critical angle with respect to the optical axis of the returned light. Above the detection prism 7 are four elements 9a and 9b.
. A four-part photodetector 9 consisting of 9c and 9d is provided,
When the returned light that enters the reflective surface 8 of the detection prism 7 is parallel light, most of the returned light is reflected by the reflective surface 8 when the light spot by the objective lens 6 is in focus with respect to the optical disc 1. It is configured so that the light is incident on the four-split photodetector 9. In addition, in the same figure, ail. a12 is the maximum inclination component of the light beam hitting the non-conforming surface 8 of the detection prism 7 when the optical disc 1 deviates from the focused state in the direction a, b ++, b Indicates the maximum inclination component of the luminous flux incident on the reflective surface 8 of the detection prism 7 when the direction is shifted,
Also ar+, ar2 and 11r1. br2 redirects the reflected light to its reflecting surface 8 (at+, 1) t2
indicate transmitted light, respectively. In such a configuration, as shown in FIG. 2, when the optical disc 1 deviates from the in-focus position C in the direction a or b, the light intensity distribution of the returned light incident on the four-part photodetector 9 changes. The brightness and darkness of the light amount distribution changes in opposite directions at a point perpendicular to the plane of the paper that includes the optical axis, and only at the focal position C becomes a uniform light amount distribution. Therefore, by performing stem processing using each output of the detection elements 9a, 9b, 9c, and 9d constituting the quadrant photodetector 9, a focus error signal corresponding to the focus state can be obtained. Such a method of detecting a focus error signal is well known from Japanese Patent Laid-Open No. 7246/1983. Hereinafter, this method will be referred to as the "critical angle method." Note that FIG. 1 also shows a detection circuit for detecting a focus error signal using the output of the quadrant photodetector 9. In the figure, 10, 11, and 12 are sum circuits, 13 is a difference circuit, and each photodetector element 9a, 9b of the four-division photodetector 9,
'90.9dl/) each output s+. 82, S3, 84, 85 56=(Sl +8
4)-(S2+S3)=S7 is obtained from the difference circuit 13 as the focus error signal S7, and 8
1 +S4 +S2 +S3 =Sa as sum circuit 12
We also try to obtain information signals from In addition, in the configuration of the optical system shown in FIG. 1, the index pupil plane of the objective lens 6 corresponds to various positional relationships in the disk radial direction between the light spot in the focused state and the bits forming the information track on the optical disk 1. The light intensity distribution pattern of
As shown in Figure 3. Figure A shows the case where the spot 111 is shifted to the right side of the bit 112 constituting the information track, and Figure B shows the case where the spot 111 is shifted to the left side.
Within the circle representing the light intensity distribution in each positional relationship,
Hatched areas represent dark areas, and white areas represent bright areas. In other words, the return light reflected by the optical disc 1 is modulated by the recorded information of records 1 to 1 on the optical disc 1, and is modulated in the far field of the recording track according to the deviation of the optical spoiler 1- in the radial direction with respect to the recording track. The light intensity distribution changes. Therefore, in the far field, a four-part photodetector 9 divided into the above-mentioned information]-rack direction and a direction perpendicular thereto is arranged with the optical axis of the returned light as the center, and each of the four-part photodetector 9 is divided into two parts. A radial error signal can be detected by arithmetic processing using the output of the detection element. Such a radial error signal detection method is disclosed in detail in Japanese Patent Application Laid-Open No. 57-74837 and is well known, but for convenience of explanation, this method will be referred to as the far field method.
I will call it. FIG. 4 shows a conventional example configured to simultaneously obtain a focus error signal and a radial error signal by combining the critical angle method and the far field method. Regarding the configuration and operation of the same figure, please refer to the above-mentioned Japanese Patent Application Laid-Open No.
Since it is described in detail in Japanese Patent No. 74837, it will be briefly explained here. In the figure, a four-division photodetector 9 is provided in the 71-field of the information track of the optical disc 1 by an optical system (not shown) having almost the same configuration as the optical system shown in FIG. Therefore, as explained earlier with reference to FIGS. 3A and 3B, this four-part photodetector 9 receives return light having a light intensity distribution corresponding to the radial positional relationship of the light spot with respect to the information track on the optical disk 1. is incident, and its light intensity distribution is as follows: As explained with reference to FIG. 2, it also includes focus error information in which the brightness and darkness are reversed in relation to the direction of deviation from the in-focus position, and the light intensity distribution is the same only when in focus. Therefore, signals corresponding to the shape of the light (6) distribution are transmitted to each of the detection elements 9a, 9b, 9c of the four-part photodetector 9. By performing calculations using the output of 9d, the focus error signal, tracking error signal, and information signal can be detected separately. The figure shows the ti of the detection circuit.
The X and Y directions of the quadrant photodetector 9 correspond to the radial and tangential directions of the information track. The focus error signal is detected in the far field of the returned light.The light intensity distribution changes depending on the direction of the radial error, as shown by hatching in Figure 3A and B. 9a, 9cl bordering on X
Since the ratio of the total amount of light incident on the detection element 9b and 9c does not change,
Similarly to the conventional example shown in FIG. 1, the sum S5 of the outputs Sl and S4 of the detection elements 9a and 9d and the sum S of the outputs S2 and S3 of the detection elements 9b and 9c are calculated by the respective sum circuits 1o and ii. A focus error signal M S 7 is obtained from the output terminal 14 by introducing the sum S5 and $5 signals to the difference circuit 13. On the other hand, the radial error signal 89 is generated by the photodetecting elements 9a, 9c, and 9b, which are arranged at symmetrical positions on the diagonal line, centered on the intersection of the radial direction X and the tangential direction Y of the quadrant photodetector. 9d each output S+, S3 and S2. The respective sums S1o and S+ of S4 are obtained by each summation circuit Is, 16, and the sum S8 and difference 812 of Sho and S++ are calculated by the summation circuit 12 and the difference circuit 17, respectively, and the sum S8 is calculated as information. While taking out the signal from the 1st edition 8, the rising pulse generation circuit 19 and the falling pulse generation circuit 2
0, and a gate signal S+3.8+4 is generated at the timing of the zero crossing of rising and falling edges. 21 and 22 are the respective gate signals 813. This is a simple sampling circuit operated by S14. The output SI2 from the difference circuit 17 is connected to the sampling circuit 21.2.
The signals having the radial error information of S12 and obtained from the difference circuit 17 are lean-pulled at the timing of the zero-crossing point of the information signal S8 and are sequentially held by the hold circuits 23 and 24. This hold signal is obtained from a terminal 26 via a differential amplifier 25 as a radial error signal S9. That is, as shown in Figure 3A and B, bit 11
At the end of 2, the light intensity distribution within the field is significantly different depending on the right and left sides of the light spot information 1-rack, and the light Q corresponding to this part is
'l l/) signal is differentially extracted and compared by the gate signal SI3.8I4, so that a very accurate radial error signal S is obtained. However, in such a known error signal detection device, when performing radial servo to correct the radial error by displacing the objective lens 6 shown in FIG. 1 in one direction As shown,
When only the objective lens 6 is displaced in the radial direction The light spot on the spectroscopic M photodetector 9 moves laterally. The occurrence of such lateral movement causes a DC offset to occur in the radial error signal, and when the optical head is servo controlled, there is a problem in that the reading light spot deviates from the center of information 1 to rack. In this case, the focus error signal is the sum of the outputs St and S4 of the elements 9a and 9d arranged in the moving direction of the spot on the quadrant photodetector 9, and the outputs S2 . S: Difference in the sum of +57
= (St +S4) -, (S2 +S3), so no DC offset occurs. However, as shown in FIG. 6A, when the tilt of the optical disk 1 changes from the normal position shown by the dotted line to the direction shown by the solid line, the optical axis of the returned light is displaced and at the same time the optical disk 1 is moved away from the optical disk 1 by the objective lens 6. Some of the reflected light is kicked away. Therefore, as shown by hatching in FIG. 1B, a portion of the returned light incident on the quadrant photodetector 9 is kicked off and furthermore, it is moved laterally in the direction of the inclination of the optical disc 1. That is, if the optical disc 1 is tilted in the tangential direction, a DC offset occurs in the focus error signal, and if the optical disc 1 is tilted in the radial direction, a DC offset occurs in the radial error signal. It suppresses the occurrence of DC offset caused by the displacement of the objective lens in the radial direction, the tilt of the optical disk, etc. in the conventional device as described above, and can also be effectively used as an error signal detection device for an optical head with high detection sensitivity. KakMT'F (M odulation
It is an object of the present invention to provide an optical disc playback device that is excellent in improving the transfer function (transfer function). The optical disc playback device of the present invention uses an objective lens to make light from a light source into a minute spot and irradiates it onto an information track on an optical disc. In an optical disc reproducing apparatus, the light is input to a split-type photodetector arranged in the split-type photodetector, and an error signal such as a focus error signal, a radial error signal, and/or an information signal is obtained from the output of the split-type photodetector. With respect to the information track, the light receiving surface is divided into at least three parts in the tangential direction, and the signal of the light receiving area that is far away from the optical axis in the tangential direction, and the light receiving area near the optical axis. The error signal and/or the reproduced information signal are obtained by separately extracting the signals and processing these signals to obtain the error signal and/or the reproduced information signal. Hereinafter, the present invention will be described in detail based on the drawings. FIG. 7 is a block diagram showing an example of the configuration of an embodiment of the present invention, and shows an example in which an error signal and an information signal are obtained simultaneously by a six-part photodetector and a matrix processing circuit. In the apparatus of the present invention, in the known critical angle method shown in FIG. 1, a six-segment photodetector 31 as shown in FIG. The optical system is arranged in the far field of the information track of the optical disc 1 so that the optical axis of the return light from the optical disc 1 coincides with approximately the center 0 of the six-segment detector 31. The light-receiving surface of the six-segment photodetector 31 is divided into three parts in a direction corresponding to the tangential direction Y of the optical disc 1, and the light-receiving surface in the center of the three parts is divided into three parts in a direction corresponding to the tangential direction Y passing through the center 0 and It is divided into six parts by a line in the radial direction X into four parts. Hereinafter, the photodetecting elements forming each of the six divided light receiving surfaces will be simply referred to as "elements". As can be easily inferred from the principle of the critical angle method explained earlier in FIG. The rate of change is large in the periphery, for example in the tangential direction Y. Therefore, it is clear that the detection sensitivity will be increased if the focus error signal is detected using the amount of light only in the peripheral area in the tangential direction Y. Therefore, in this embodiment, the six-segment photodetector 3
31a bordering the line in the radial direction X passing through the center O of 1
, 31b, 31e, and 31C9
The outputs a, b, and e of the aforementioned element groups 31a, 31b, and 31e are connected to a first summation circuit 32'r, the latter element group 31c,
3id, 31? (7) Each output c, d, f is
The summation circuit 33 adds these summation outputs to the first
Leading to the difference circuit 34, (a + b + e ) - (c +
d + f) to obtain a single cassette error signal, and the respective outputs e and f of the elements 31e and 30 on both sides of the tangential direction Y of the six-segment photodetector 31 are is led to a difference circuit 35 to obtain a second focus error signal as its output. The first focus error signal obtained in this way is of the same quality as the focus error (No. g) obtained by a conventional device using a quadrant photodetector, and has a wide dynamic range but low detection sensitivity. On the other hand, the second focus mirror signal is obtained using the amount of light at the periphery of the light beam incident on the six-segment photodetector 31.The rate of change in the amount of light at the periphery is determined by the rate of change of the amount of light at the periphery. The second focus error signal is extremely sensitive to the deviation from the focus position, so it is a signal with extremely high detection sensitivity.Therefore, for example, the first focus error signal is used when the focus servo is pulled in, and continuous After the reproduction state is reached, by switching to the second focus error signal and servo-controlling the objective lens, focus servo with a wide dynamic range and high precision becomes possible.
In obtaining the first focus error signal, each sum circuit 3
31a, 3 of the six-segment photodetector 31 added to 2.33
Outputs a, b, of each element 1b, 31c and 31d,
By reducing c and d to smaller values using resistors, etc.,
By increasing the values added to the respective sum circuits 32 and 33 of the outputs e and r of the elements 1e and 3ir, the first focus error signal with relatively high detection sensitivity can be obtained without sacrificing the dynamic range. Obtainable. On the other hand, the radial error signal is transmitted from elements 31e located on both sides of the six-part photodetector 31 in the radial direction. 31 "Four chords 31a, 31b, 31c excluding
, 31d are used to obtain the outputs a, b, 'c, and d by the same arithmetic processing as in the conventional example shown in FIG. 4. That is, the element 31a is located at a symmetrical position on a diagonal line centered on the optical axis 0 of the return light to the six-segment photodetector 31. The outputs a and C of the elements 31C are sent to the third summation circuit 36, and the outputs of elements 31b and 31d are sent to the fourth summation circuit 37.
are added to each of them separately, and each summation circuit 36
．． The addition output of 37 is input to the third difference circuit 38, and (
A radial error signal of a + c ) - (b + d ) is obtained. The radial error signal obtained in this way is
Furthermore, if this radial error signal is processed in the same manner as the conventional example shown in FIG. 4, if necessary, a radial error signal with even higher pressure detection accuracy can be obtained. Further, in this embodiment, the third and fourth sum circuits 3
6.37 outputs and the addition outputs from the fifth summation circuit 39 of the elements 31e and 31f on both sides in the tangential direction of the six-segment photodetector 31 are led to the sixth summation circuit 40 and summed. '', a ten b + c ten d + k (
The configuration is such that an information signal of e+f) is obtained. Ago IX is the gain constant C of the fifth summation circuit 39. In addition, since the diffracted light from the disk becomes high-order in the far field region, it travels far away from the optical axis, so the multi-segment photodetector of this embodiment, which is separated into tangential directions, is used. , a configuration in which the signals from the light-receiving area far away from the optical axis in the tangential direction are mixed so that they are more numerous than the signals near the optical axis, that is, a + b −+−
If k of c + d 1 k (e + r) is made larger than 1 and an information signal in which a large number of e 1 f is added to a + b 10 c + d is obtained, the M king F is improved as a result. In one case where an information signal is obtained for the purpose of improving MTF, the configuration of the split type photodetector does not necessarily need to be large split type as in this embodiment, but it is necessary to use a split photodetector with three or more parts in the tangential direction. When the output signal of the detection element in the area in the tangential direction is added to the output signal of the detection element in the central area, the output signal of the former is This objective can be achieved by adding more than the output signal of the latter. In the figure, 41 is a first focus error signal output terminal, 42 is a second focus error signal output terminal, 43 is a radial error signal output terminal, and 44 is an information signal output terminal. FIG. 8 shows that when errors are automatically corrected by a nervo system using this type of error signal detection device, the higher the error signal detection sensitivity, the smaller the target value deviation of the servo system with respect to disturbance. That is, in the figure, the horizontal axis represents the amount of displacement such as the tilt of the optical disk as a disturbance, the vertical axis represents the error signal, and the detection sensitivity is represented by diagonal lines. Now, assume that a disturbance such as a disk tilt enters the servo system, causing a DC offset. The diagonal line that does not represent detection sensitivity indicates that the steeper the slope, the higher the detection sensitivity.The higher the detection sensitivity, the smaller the deviation from the target value δ1, but when the detection sensitivity is lower, the target value is larger than 61. A value deviation amount δ2 occurs. In the present invention, as is clear from the above embodiments, it is possible to detect a focus error signal with extremely high detection sensitivity compared to the conventional device, so disturbances such as disk inclination can enter the servo system and cause DC Even if an offset occurs, the deviation from the target value will be small. FIG. 9 is an explanatory diagram of another embodiment of the device of the present invention. The configuration of this embodiment is the same as that shown in FIG. 7, except that the six-segment photodetector 31 in the previous embodiment explained in FIG. 7 is modified as shown. . Therefore, in the figure, only the configuration of the six-segment photodetector 51 used in this embodiment is shown by the relative position of the returned light. The six-segment photodetector 51 of this embodiment has a rectangular shape long in the tangential direction Y as shown in the figure.
Similar to Katsaki's example, it is divided into three parts in the tangential direction Y, and the central part of the three parts is
Tangential direction Y with the optical axis 0 of the returned light as the intersection
and a total of six photodetecting elements 51a, 51b, 51c, 51d divided into four by a line in the radial direction X.
, 51e, 51. It is composed of r and d. They are arranged in a light-receiving relationship with respect to the incident light, as shown in the figure, with the exception of the light flux at the peripheral end in the radial direction Only the luminous flux at the circumferential end in the tangential direction Y of the returned light is incident on the elements 51e, 51f, and the four central elements 51a, 51b,
The light beams 510 and 51d are arranged in the far field of the objective lens of the information track so that only the light beam at the center, excluding the peripheral portion of the returned light, is incident thereon. Therefore, in this way (the grown six-segment photodetector 51
Each element 51a, 51b, '51c, 51
Each output a, b, c, d of cl, 51e, 5H,
By using e and f and calculating (a + C) - (b + d) using the same processing circuit as in the previous example, the side of the returned light, the cause of which was explained in Figures 5 and 6, can be calculated. It is possible to detect a radial error signal that is less affected by movement and has a suppressed DC offset. Zunawa also applies this embodiment to the four central elements 51a, 51b, 51c of the six-segment photodetector 51.
, 51d and the positional relationship between the return light spot L is based on the technology disclosed in Japanese Patent No. 111837/1983, which aims to obtain the same effect using a four-part photodetector. Similarly, the structure is such that the occurrence of DC offset in the radial error signal is suppressed, and its functions and effects are detailed in the same publication. To briefly explain this, the cables 51a and 51b at the center of the six-segment photodetector 51 in the device of the present invention. The return light beams incident on 51c and 51d are the radial range in which the position of the light beam entering each element changes when the light beam is returned from the optical disk and is moved laterally due to disturbance, etc., and the range in which the light beam is kicked by the objective lens. The light beams in the direction X and the tangential direction Y correspond to a portion of the light amount distribution that is equivalent to that which is substantially blocked. Therefore, it is clear that the radial error signal detected from the deviation of the light m distribution in the center of the returned light, which is less affected by such disturbances, has the DC offset suppressed. In addition, the focus error signal is generated using the respective outputs of the strands 51e and 51f on both sides in the tangential direction Y of the six-segment photodetector 51, as in the Sagi embodiment.
By calculating -f, the second focus error signal with high detection sensitivity is further generated by 51a, 51b, 51e, 51c, 5 bordering on the radial direction
By adding the outputs of each group of elements 1d and 51f and taking the difference between the added outputs,
A first focus error signal is obtained respectively. In addition,
The information signal is sent to the six-segment photodetector 51 as in the rabbit embodiment.
It can be obtained by adding the outputs of all the elements. As described above in detail, according to the apparatus of the present invention, the return light from the optical disk entering the six-segment photodetector, obtained via, for example, a critical angle prism, is reflected on both sides in the tangential direction. Depending on the differential state of the objective lens with respect to the optical disk, a focus error signal is detected by detecting the deviation of the light amount in a portion where the rate of change in the light amount is large, and the relative position of the information track on the optical disk and the objective lens is detected. The radial error signal is detected from the deviation in the light intensity at the center of the returned light, which is less likely to be affected by disturbances such as deviation of the optical disk or the tilt of the optical disk. Since the signal obtained from the light receiving area is added up so that the signal obtained from the central light receiving area near the optical axis is larger than the signal obtained from the central light receiving area near the optical axis, it is possible to obtain a focus error signal with high detection accuracy. Moreover, the focus error signal and the radial error signal can be detected with DC offset sufficiently suppressed, or an information signal can be obtained with an effect equivalent to that of improving the MTF simultaneously or independently. . Furthermore, in the device of the present invention in which the six-segment photodetector is configured as shown in FIG. 9, the light flux on both sides in the radial direction of the returned light, which is a major cause of the occurrence of DC offset, is also substantially blocked. Therefore, in addition to the above-mentioned effects, it is possible to obtain a radial error signal with further reduced DC offset. 4. Brief description of the drawings FIG. 1 is a configuration diagram showing an example of a known optical head including a focus error signal detection device, FIG. 2 is an explanatory diagram of a known critical angle method for detecting a focus error signal, FIG. 3 is an explanatory diagram of a known far field method for detecting tracking error signals, and FIG. 4 is a block diagram showing an example of a conventional error signal detection device that uses both the critical angle method and the far field method. , FIG. 5 and FIG. 6 are diagrams explaining problems in the conventional example shown in FIG. 4, FIG. 7 is a block diagram showing an example of the configuration of the embodiment of the present invention, and FIG. FIG. 9, which is an explanatory diagram of the effect of error signal detection sensitivity on the target value deviation amount, is a relational layout diagram with return light showing a modification of the six-segment photodetector used in another embodiment of the present invention. ...Optical disk 2...Light source 3...Collimator lens 4...Polarizing prism 5...1/4 wavelength plate 6...
・Objective lens 7...Detection prism 8...Reflecting surface 9...Four-division photodetector 9a to 9d, 3
1a to 31f, 51a to 51f - Photodetection elements 10 to 12.15.16.32. '33.36.37.
39.40...Summing circuit 13, 17.23.35...Difference circuit 19...Rising pulse generation circuit 20...Falling pulse generation circuit 21.22...Sampling circuit 23.24...・Hold circuit 26.38...Differential amplifier 31.51...Six-segment photodetector 41.42...First and second focus error signal output terminal 43...Radial error signal output terminal 44 ...Information signal output terminal

Claims (1)

[Claims] 1. The light from the light source is made into a minute spora 1~ by an objective lens and irradiated onto the information 1~ on the Y disk, and the return light that is reflected by the optical disk and passes through the cauterizing lens again, LJ is set so that the opposite surface is at almost a critical angle with respect to the optical axis of the returned light.Through the detection prism,
1j type photodetector placed in the I field of the information track (Z-person D'', i c kise, from the first part of the light field of the necessary light)A- Kas error 13
C1 The split type photodetector is divided into three parts in the direction of the cylinder I1 with respect to the information 1-rack. At the same time, it is further divided into two, and the 811 minutes of the medium heat C is divided into four in the tangential direction (13 and the radial direction line η perpendicular to this) with the optical axis of the returned light as the approximate intersection point. Formed into a split mold,
The output of each of the detection elements divided into four parts of the medium heat is used to detect the C radial error No. 3, and the outputs of the detection elements on both sides of the three parts divided into two are used to detect the C focus. An F-signal detection device for an optical head, characterized in that it detects an error signal.