JPS6232528B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an optical system for reproducing information signals using light emitted from a light source, focused on a signal surface of a recording medium by a condensing lens, and reflected on the signal surface of the recording medium. In an information signal reproducing device, even if the optical axis of the light reflected from the signal surface of the recording medium is tilted or the intensity distribution of the light is biased, focus errors can be detected well, and tracking error signals can also be detected. The purpose of this invention is to provide an optical information signal reproducing device with excellent performance.

In an optical information signal reproducing device, when reading an information signal from the signal surface of a recording medium, it is necessary to project a spot of light with a minute diameter onto the signal surface of the recording medium. Since the surface is not a perfect plane, in order to ensure that the signal surface of the recording medium is always in the focused position of the condenser lens,
The condenser lens is displaced and driven by so-called focus control.

Conventionally, as a focus error detection method for the focus control described above, (1) as shown in FIG. Place 3 and
A focus error signal is generated from the differential amplifier 4 depending on the state of astigmatism that occurs on the photodetector 1 due to convergence or divergence of the reflected light beam when the recording medium (disc) deviates from the focal position of the condenser lens. The so-called astigmatism method is used to obtain
(2) As shown in Fig. 2, the reflected light beam from the disk is projected onto a prism 5 having a reflective surface with a critical angle,
The difference in reflectance that occurs on both sides of the optical axis due to convergence or divergence of the reflected light beam from the disk is extracted by the output signals from the two parts of the photodetector 6, and a focus error signal is obtained from the differential amplifier 4. (3) As shown in FIG. 3, the reflected light beam from the disk is divided into two by a Fresnel compound prism 7 and sent to two sets of two-split photodetectors 8. and applying the output signal of the two-split photodetector 8 corresponding to the polarization of the projected light on the two sets of two-split detectors 8 to the differential amplifier 4,
A method using a so-called Fresnel compound prism in which a focus error signal is obtained from a differential amplifier 4 is known.

However, in the method (1) using the astigmatism method described above, the optical axis of the reflected light beam shifts on the photodetector due to the inclination of the disk surface, and the optical spot for signal reading also shifts. There is a disadvantage in that if the signal is shifted from the center of the recording trace on the disk, the distribution of the intensity of the reflected light will be biased, resulting in a false focus error signal. This method has the disadvantage that a false focus error signal is generated due to movement and inclination of the optical axis of the reflected light beam.Furthermore, in the method (3) using Fresnel's double prism, the light in the true focus state is Since the light spot on the detector is extremely small, it is difficult to place the light spot on the dividing line on the photodetector, and this also causes a sharp transition in the focus error signal, making it difficult to control the focus near the true focus state. The drawback was that it was difficult.

The disadvantage of the above method (3) is that the photodetector 8
is shifted from the conjugate point so that a semicircular light beam as shown in FIG. 4 is given to the photodetector 8, and the area of the semicircle is 2 i.e. S ₁
This can be solved by adjusting the light intensity of S2 and _S2 to be equal, but this adjustment is difficult unless a level adjuster is installed before the differential amplifier.
In addition, even in the above solution, there are many problems that exist in design and manufacturing, such as the position of the dividing line in the photodetector to equalize the light intensity for S ₁ and S ₂ , and the determination of sensitivity determined by the distance from the conjugate point. cannot escape from the difficulty of

The present invention provides an optical information signal reproducing device that does not have the problems of the various conventional methods described above. The contents will be explained in detail.

FIG. 5 is a block diagram of an embodiment of the optical information signal reproducing device of the present invention, and in FIG. 1, 11 is a light source, and as the light source 11, for example, a semiconductor laser light source is used. . Divergent light (diffused light) emitted from the semiconductor laser light source 11
is made into parallel light by the collimation lens 12 and then applied to the polarizing prism 13.

14 is a λ/4 plate, and this polarizing prism 13
The λ/4 plate 14 is provided to separate incident light and reflected light, and the incident light and reflected light are linearly polarized lights that are direct to each other.

15 is a condensing lens, and this condensing lens 1
5 projects a light spot of minute diameter onto the signal surface of the disk 16. The tiny spot of light projected onto the signal surface of the disk 16 is reflected by the signal surface of the disk 16 and is then reflected by the condenser lens 15 and the λ/4 plate 14.
The reflected light is applied to the polarizing prism 13 through the polarizing prism 13, and is laterally reflected by the polarizing prism 13, but the reflected light is intensity-modulated by diffraction and interference caused by the unevenness recorded on the signal surface of the disk 16. It is in good condition.

17, the signal surface of the disk 16 is the condenser lens 1
5, the disc 16 is in focus position.
A device that can split the reflected light beam from the signal surface of In FIG. 5, it is assumed that the optical system 17 is composed of two cylindrical lenses CL ₁ and CL ₂ that are joined at the optical axis position of the reflected light beam. As shown, the two cylindrical lenses CL ₁ ,
The CL ₂ 's are arranged on both sides of the optical axis of the reflected light beam so that their respective cylindrical axes (cylindrical axes of a cylinder having a cylindrical surface corresponding to the cylindrical surface of the cylindrical lens) are parallel to each other.

The above-described optical system 17 to be provided in the optical path of the reflected light beam up to the photodetector 18 may have a configuration other than that shown in FIG. It is also possible to use configurations whose cross-sectional shapes are shown in FIGS. 9 through 9.

FIG. 6 shows two cylindrical lenses CL ₁ and CL ₂ in the optical system 17 having the configuration shown in FIG.
6 is a cross-sectional view of an optical system 17 formed into a composite configuration by combining only the end portions of the lens. In FIG. 6, the portion indicated by the dotted line is an unused portion of the original two cylindrical lenses, and is shown for reference. It is something.

Further, FIG. 7 shows a configuration in which the two cylindrical surfaces of the optical system 17 having a cross-sectional shape as shown in FIG. The cross-sectional shape of an optical system 17 whose shape has been modified to become an optical system that performs an action is shown. By the way, since the optical system 17 having the cross-sectional shape shown in FIG. 7 has a cross-sectional shape that is a combination of one cylindrical lens and a Fresnel biprism, it has the same function as the optical system 17 shown in FIG. The optical system includes one optical system 17 as shown in FIG.
It can also be realized by a combination of two cylindrical lenses CL and one Fresnel compound prism FP.

The optical system whose cross section is shown in FIG. 9 is constructed by combining the Fresnel biprism FP in the optical system 17 shown in FIG. 8 with the left and right wedge portions swapped, and a cylindrical lens CL. This is the optical system 17. Since the optical system 17 shown in FIG. 9 does not have much difference in wall thickness, it is suitable for manufacturing by injection molding of plastic, for example, and provides an optical system with the required functions at a low cost. It has the characteristic of being able to

The optical system 17 shown in FIG. 5 mentioned above
are two parallel lines whose axis of symmetry is the optical axis of the reflected light.
Two cylindrical lenses are arranged on both sides of the optical axis of the reflected light, with individual cylindrical axes located at the intersection of two planes and a plane perpendicular to the optical axis. In addition, the optical system 17 shown in FIGS. 7 and 9 is constructed so that the cylindrical surfaces of two cylindrical lenses whose centers are separated with their cylinder axes parallel to each other are made into a common cylindrical surface. Each of these optical systems 17 is shown in FIG. Optical system 1
Similarly to 7, when the signal surface of the disk is in the focus position of the condenser lens, the beam of reflected light from the signal surface of the disk is divided into two, and each of the two divided beams is divided into two. It has a function of condensing light separately and forming a parallel linear image on the photodetector 18.

The photodetector 18 detects each of the two straight line images formed by the optical system 17,
It is composed of a plurality of light-receiving elements divided by two dividing lines that are inclined and intersect with each other. Shows a plan view of something.

The photodetector 18 shown in FIG. 10a is composed of three light receiving elements PE ₁ , PE ₂ , PE ₀ divided by two parallel dividing lines l ₁ , l ₂ . Also,
The photodetector 18 shown in FIG. 10b has two parallel dividing lines l ₁ and l ₂ and a separate dividing line l ₃ provided between the two dividing lines l ₁ and l ₂ . divided into 4
It is composed of photodetecting elements PE ₁ to _{PE 4} . Fifth
The photodetector 18 used in the optical information signal reproducing device shown in the figure is of the configuration shown in FIG. 10b. As will become clear from the description below, the photodetector 18 having the configuration shown in FIG.
A focus error signal is generated based on the output signals from PE ₀ to PE ₂ , and the photodetector ₁₈ having the configuration shown in FIG. Based on the output signal from ₄ , a focus error signal and a tracking error signal are generated.

That is, when the photodetector ₁₈ having _the configuration shown _{in FIG} . The output from the sandwiched photodetector PE ₀ ,
A focus error signal is generated by the signal of the difference between the output of the sum of the output from the photodetector PE ₁ outside the dividing line l ₁ and the output from the photodetector PE ₂ outside the dividing line _l 2. In addition, when the photodetector 18 having the configuration shown in FIG. 10b is used, in its four light receiving elements PE ₁ to PE ₄ ,
The sum of the outputs of the light receiving elements sandwiched by the dividing line l ₁ and the dividing line l ₂ , that is, the light receiving element PE ₃ and the light receiving element PE ₄ , and the output of the light receiving element PE ₁ outside the dividing line l ₁ . A focus error signal is obtained based on the signal of the difference between the output sum and the output sum of the light receiving element PE ₂ outside the line _{l 2 ,} and the focus error signal is obtained based on the signal of the difference between the output sum and the output sum of the light receiving element PE ₂ outside the line l 2. A tracking error signal is obtained based on the signal of the difference between the sum of the outputs of the light receiving elements _{PE 3 and} the sum of the outputs of the light receiving elements on both sides of the dividing line _l2 , that is, the light receiving elements PE ₂ and PE 4.

In FIG. 5, 19 to 21 are computing units, and the computing unit 19 outputs the sum of the outputs from the four light receiving elements PE ₁ to _{PE 4} in the photodetector 18 to the output terminal 22 as a reproduction signal of the information signal. The arithmetic unit 20 also performs the function of outputting
Of the outputs from the photodetecting elements PE ₁ to _{PE 4} , the sum of the outputs of the photodetecting elements PE ₁ and PE ₂ , and the output of the photodetecting elements PE 1 to PE 4
A signal representing the difference between the output sum of PE ₃ and the light receiving element PE ₄ is generated and outputted to the output terminal 9 as a focus error signal.
Among the outputs from the four light receiving elements PE ₁ to _{PE 4} , the difference between the sum of outputs of light receiving elements PE ₂ and PE ₄ and the sum of outputs of light receiving elements PE ₁ and PE ₃ A signal is generated and outputted to the output terminal 10 as a tracking error signal.

In the optical information signal reproducing device having the configuration shown in FIG. 5, a tracking error signal can also be obtained by using the photodetector 18 having the configuration shown in FIG. 10b. However, when the tracking error signal is also obtained based on the output from the photodetector 18, when the disk 16 is in the focused position of the condensing lens 15, the photodetector 18 Parallel imaged 2
It is necessary to install the above-mentioned optical system so that a straight line image of the book is generated in a plane parallel to a plane perpendicular to the signal surface of the disk 16, including the direction of extension of the recording trace on the signal surface of the disk 16. be done.

Now, in the optical information signal reproducing device of the present invention, when the disk 16 is at the focused position of the condensing lens 15, the reflected light from the signal surface of the disk 16 passes through the condensing lens 15 and becomes parallel. When it is given to the optical system 17, the optical system 17 splits the reflected light beam into two and focuses each of the divided light beams individually only in the direction perpendicular to the cylinder axis. Thus, two straight line images parallel to the cylindrical axis of the cylindrical lens in the optical system 17 are formed on the photodetector 18, but in the optical information signal reproducing apparatus of the present invention, the two parallel straight images are The optical system 17 and the light beam are arranged so that the straight line image of the book and the two parallel dividing lines l ₁ and l ₂ in the photodetector 18 intersect with each other at an angle. The arrangement mode relative to the detector 18 is set.

FIG. 11 shows a state in which reflected light from the signal surface of the disk 16 forms an image on the photodetector 18 in the optical information signal reproducing apparatus of the present invention when the disk 16 is at the focal position of the condensing lens 15. This is a plan view for explanation, and in the figure, f ₁ is the focal length of the condensing lens 15, and f ₂ is the focal length of the optical system 17 (optical system 1
7), Lf is the distance between the back focal point of the condensing lens 15 and the front focal point of the optical system, and the lower part in FIG. Straight line images that are inclined and intersect with the dividing line _L1 and the dividing line _L2 are illustrated and explained. The intersection points of the straight line image on the photodetector 18 and the dividing lines l ₁ , l ₂ are O ₁ , O ₂ , and each straight line image is connected to each dividing line l ₁ , so that ₁ = ₁ = ₂ = ₂ . l ₂
When the light-receiving elements PE ₁ and PE ₃ of the photodetector 18 intersect with each other, the amounts of light received by the light-receiving elements PE ₂ and PE ₄ become equal. , therefore, the computing unit 20
The focus error signal sent from the output terminal 9 to the output terminal 9 becomes zero. That is, when the disk 16 is at the focused position of the condensing lens 15, the focus error signal becomes 0, and a signal indicating the focused state is obtained.

In FIG. 5, the cross-sectional shape of the light beam is shown in the light path, but the cross-sectional shapes of the light beam before and after the photodetector 18 are circular on opposite sides as shown in the figure. .

When the signal surface of the disk 16 moves further away from the focal position of the condenser lens 15, the reflected light from the signal surface of the disk 16 passes through the condenser lens 15, and the light emitted from the condenser lens 15 becomes convergent light. , the light condensing position by the optical system 17 is in front of the photodetector 18 (a position close to the optical system 17), and the distribution of light on the photodetector 18 at this time is such that the parallel light is
It is clear from FIG. 11 that the state is biased toward the optical axis side compared to the state given in FIG.

Figures 12a to 12c show the straight line image formed on the photodetector 18 by the cylindrical lens CL ₁ in the optical system 17 in Figure 5 in the YYZ rectangular coordinate system.
This is an XY plan view when the photodetector 18 is viewed from the back side when aligned with the axis, and as described above, when the disk 16 moves away from the focusing position of the condenser lens 15, light is detected by the optical system 17. The light projected onto the element 18 illuminates a semi-elliptical area in the positive direction of the X-axis, as shown by A in FIG. 12A and B in FIG. 12B.

In the above case, the width of the semi-ellipse is d, the major axis of the semi-ellipse is _D1 , the focus error δ on the side where the disk 16 moves away from the focusing position of the condensing lens 15, and the focal length of the condensing lens 15. When f ₁ is set, the above-mentioned d and D ₁ in the case of f ₁ >>δ are shown by the following equations (1) to (3), respectively.

D ₁ ≒ D ₀ = {where, D ₀ is the pupil diameter of the condenser lens 15, f ₂ is the focal length of the cylindrical lens, r is the offset distance of the cylindrical lens (the 11th
), Lf is the distance on the optical axis between the focal point of the condenser lens 15 and the focal point of the cylindrical lens (FIG. 11)} As is clear from the above equation, the focus error of the photodetector 18 due to the focus error δ is The width d of the semi-ellipse on the plane changes relatively with respect to the focus error δ. Incidentally, C in Fig. 12c indicates disk 16.
For reference, the area irradiated with light on the photodetector 18 is shown when the image approaches the focal position of the condenser lens 15.

In FIGS. 12 a to 12 c, l ₁ is a dividing line, and the outputs from light receiving element PE ₁ and light receiving element PE ₃ are as follows:
When the light irradiation area on the photodetector 18 is as shown by A in FIGS.
It approximately corresponds to the areas Sa and Sb.

It is clear that as the width X of the light irradiation area on the photodetector 18 increases, the area Sb increases and the area Sa decreases. Therefore, the focus error signal is expressed as (Sa - Sb). is output, which is proportional to the focus error δ.

As can be seen from Figures 12a to 12c, the dividing line l ₁
The smaller the angle between
-Sb) is large, that is, the focus error detection sensitivity is high, so the angle between the dividing line _l1 and the Y axis can be set to a favorable value in terms of design.

A state in which the dividing line l ₁ and the Y axis coincide, that is,
If it is done in the same way as the conventional example described above,
If δ≠0, Sa or Sb becomes 0, so the focus error signal suddenly changes after δ=0,
As mentioned above, the servo loop of the focus control system becomes extremely unstable and is not practical, but in the present invention, the dividing line _l1 and the straight line image at the time of focusing are relatively Since they are arranged to intersect with an inclination to , the drawbacks of the conventional example do not occur. Also, like conventional equipment,
When a spherical lens is used instead of a cylindrical lens, a point image is formed at the 0 point of the photodetector 18 during focusing, but in this case, the point image is formed due to the inclination of the signal surface of the disk, etc. When moves from 0 point, Sa=
The relationship that should be Sb collapses, and the focus operation becomes unstable. Furthermore, since the dividing line l ₁ actually has a finite thickness, the above-mentioned point image may fall within the dividing line l ₁ , and in that case, both Sa and Sb will be indefinite. As a result, the focus servo loop will not operate correctly.

By the way, in the optical information signal reproducing apparatus of the present invention, as is clear from FIG.
When the signal plane of the disk 16 is at the focused position of the condensing lens 15, two straight line images are formed on the photodetector 18. optical lens 1
Even if the optical axis of the reflected light beam from the signal surface of the disk 16 moves at an angle with respect to the optical axis of the disk 16, the two straight line images move in the same direction and by the same distance, resulting in a false focus error signal. will not occur.

Also, since the disk 16 is at a position other than the focus position of the condensing lens 15, the irradiation area of the reflected light on the photodetector 18 has a light distribution as shown in A and C in FIGS. 12a to 12c. Even if it is biased by the focus error δ, the area irradiated by each reflected light for each dividing line moves in the same direction and the same distance, so no false focus error signal is generated, as in the case of the in-focus state. .

As mentioned above, by setting =≈D ₀ , it goes without saying that the allowable distance for movement of the image in the Y-axis direction is large.

In the optical information signal reproducing device shown in FIG.
The cylindrical axes of the cylindrical lenses CL ₁ and CL ₂ in the optical system 17 are in a plane parallel to a plane perpendicular to the disk, including the direction of extension of the recording trace on the signal surface of the disk 16, and the dividing line of the light beam is also as described above. Since it is contained within the plane, if the spot of light on the signal surface of the disk 16 by the condensing lens 15 deviates from the center of the recording trace, the two light beams split into the left and right by the optical system 17 will have different intensities. It makes a difference. Therefore, when the arithmetic unit 21 generates an output proportional to the difference in intensity between the two divided luminous fluxes, the tracking error signal is output from the arithmetic unit 21 to the output terminal 1 as described above.
0 will be sent.

As is clear from the above detailed explanation, in the optical information signal reproducing device of the present invention, a straight line is imaged on the photodetector when the signal surface of the disk is at the focused position of the condenser lens. The length of the image can be made sufficiently long, and since the straight line image mentioned above intersects at an angle with respect to the dividing line in the photodetector, the dynamic range of focus error detection can be appropriately adjusted. It can be set to any value.

Furthermore, even when the two linear images described above or the irradiation area generated on the photodetector due to disk inclination or tracking error move, the two straight images,
Alternatively, since the movements of the irradiation area are complementary, even if a focus error signal occurs, it is canceled out. Furthermore, as described above, since the range in which the two straight images or two irradiation areas can intersect with the dividing line is large, false focus error signals do not occur over a wide complementary compensation range.

Further, in the optical information signal reproducing apparatus of the present invention, a tracking error signal is generated by detecting the deviation due to diffraction of the reflected light from the signal reading spot, thereby making it possible to easily perform tracking control.

Therefore, in the device of the present invention, the optical system can be easily assembled and adjusted, and it can be highly reliable with little effect on distortion of the structure on which the optical system is mounted, and the optical system can be easily designed. It has the characteristics of being easy and having a high degree of freedom in design.

[Brief explanation of the drawing]

Figures 1 to 3 are block diagrams of conventional devices;
FIG. 4 is a diagram for explaining a solution to the drawbacks of the device shown in FIG. 3, FIG. 5 is a block diagram of an embodiment of the optical information signal reproducing device of the present invention, and FIGS. 6 to 9
10A and 10B are plan views of different embodiments of the photodetector, FIG. 11 is a plan view for explaining the operation of the device of the present invention, and FIG. Figures 12a to 12c are explanatory diagrams of imaging and illumination areas in the photodetecting element. 11...Light source, 12...Collimating lens, 1
3...Polarizing prism, 14...λ/4 plate, 15...
...Condensing lens, 16...Disk, 17...Optical system, 18...Photodetector, _l1 to _l3 ...Dividing line, CL,
CL ₁ , CL ₂ ... Cylindrical lens, FP ... Fresnel double prism.

Claims (1)

[Scope of Claims] 1. An optical information signal reproducing device that reproduces an information signal using light emitted from a light source, focused on a signal surface of a recording medium by a condensing lens, and reflected on the signal surface of the recording medium. The signal surface of the recording medium is provided in the optical path between the photodetector and the condensing lens, which is provided after the reflected light from the signal surface of the recording medium passes through the condensing lens. is in the focusing position of the condensing lens, the luminous flux of the reflected light from the signal surface of the recording medium is divided into two, and each of the two divided luminous fluxes is focused separately. An optical system configured to form parallel straight-line images on the photodetector is provided, and
The photodetector is composed of a plurality of light-receiving elements divided by two dividing lines that intersect with each other at an angle with respect to each of the two straight-line images imaged thereon. Furthermore, the output from the light-receiving element on the inside of the photodetector sandwiched by the two dividing lines, and the output from the light-receiving element outside of the two dividing lines. An optical information signal reproducing device which obtains a signal representing the difference between the sum and the sum, and drives and controls a condensing lens based on the signal so that a light spot on a signal surface of a recording medium has a minimum diameter. 2. The optical information signal reproducing device according to claim 1, wherein the two dividing lines in the photodetector are parallel. 3 The optical system to be installed in the optical path of the reflected light between the condenser lens and the photodetector consists of two planes parallel to each other with the optical axis of the reflected light as the axis of symmetry, and a plane perpendicular to the optical axis. The optical information signal according to claim 1, which uses two cylindrical lenses arranged on both sides of the optical axis of reflected light, each having their own cylindrical axis at the intersection line. playback device. 4. As an optical system to be installed in the optical path of the reflected light between the condenser lens and the photodetector, two cylindrical lenses whose cylinder axes are parallel and whose centers are separated have a common cylindrical surface. Optical information according to claim 1, which uses a composite cylindrical lens integrally molded so that the joining line of the composite cylindrical lens is arranged on the optical axis of reflected light. Signal regenerator. 5. An optical information signal reproducing device that reproduces an information signal using light emitted from a light source, focused on a signal surface of a recording medium by a condensing lens, and reflected on the signal surface of the recording medium, which reproduces the above-mentioned recording. The signal surface of the recording medium passes through the condenser lens during the optical path between the photodetector and the condenser lens, which is provided after the reflected light from the signal surface of the medium passes through the condenser lens. At the in-focus position, the beam of reflected light from the signal surface of the recording medium is divided into two, each of the two divided beams is focused separately, and the beam of light reflected from the signal surface of the recording medium is focused. An optical system is provided that is configured to form linear images parallel to each other in two planes parallel to a plane perpendicular to the signal plane of the recording medium, including the direction of extension of the recording trace in the recording medium. The detector is individually tilted and intersected with respect to each of the two straight line images imaged on it.
It is composed of a plurality of light-receiving elements having a book dividing line and another dividing line provided between the two dividing lines described above, and furthermore, A signal of the difference between the sum of outputs from the two light-receiving elements on the inside sandwiched by the two dividing lines and the sum of outputs from the two light-receiving elements outside the two dividing lines. On the basis of the,
The condenser lens is driven and controlled so that the light spot on the signal surface of the recording medium has a minimum diameter, and the output of the light receiving elements on both sides of each of the two dividing lines in the photodetector is controlled. Based on the difference signal between the sums, the condenser lens is driven in a direction perpendicular to the direction of extension of the recording trace and in a plane parallel to the signal plane of the recording medium, so that the difference signal described above is minimized. optical information signal reproducing device.