JPS6028035A - Focus error detector for optical information reproducer - Google Patents

Abstract

PURPOSE:To facilitate a focus detection by dividing the information light given from a recording medium into two optical components to form images on a prescribed focal plane respectively and projecting two spots to the photodetecting parts set at the areas out of the focal point. CONSTITUTION:The information light given from a disk 1 is separated into the +1 order light and the -1 order light through a step phase type holographic lens 12 to form focal points F+ and F- respectively. Then the +1 order light and the -1 order light form spots 15a and 15b on the photodetecting surfaces 14a and 14b of a detector 14 set outside the points F+ and F-. The states of formations of these spots differ by the displacement amount Z from the reference position of the disk 1. The difference of photoelectric outputs of parts 14a and 14b, i.e., the focus error output If has a gentle inclination within a comparatively large range of the amount Z. This facilitates a focus detecting action and improves the detecting accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a focus error detection device in a recorded information reproducing device K for optically reproducing information recorded on a recording medium.

(Background of the Invention) Various types of so-called optical memory devices are known that record information on a recording medium using light and reproduce the recorded information using light. For example, a beam of laser light is narrowed down to create a light spot, which creates an image with a width of about 1 μm on the recording disk.
It is used to write audio or document information, or to read out information by irradiating the light spot onto a video disc or audio disc. Furthermore, there are also discs that allow erasing and self-recording of the information that has been sworn to the recording disc.

In this type of optical memory device, it is necessary to accurately focus a light spot onto a recording medium and to accurately track the focused light spot to an information track on the recording medium.

Various methods are known for detecting focusing and tracking errors, such as Document 1,
July, 1978/vol. 17, No, 13/Ap.
It is described in detail in pliedOptics. Here, in order to clarify the description of the present invention, a focusing error detection method using a knife knife as a conventional example will be described with reference to FIGS. 1 and 2.

FIG. 1 shows an example of an optical head device. 1 is a recording medium,
2 is a light source such as a laser, 3 is a collimator lens, 4 is a beam splitter, 5 is an objective lens, 6 is a convex lens, 7 is a light-shielding knife engine, and 8 is a photoelectric detector.

The diverging light beam emitted from the light source 2 passes through the collimator lens 3
The parallel light beam is converted into a parallel light beam by the beam splinter 4, and then is irradiated onto the surface of the recording medium 10 by the objective lens 5 as a minute light spot. This light spot is used to reproduce, record, and record information on the information track on the surface of the recording medium.
It is used for erasing, etc., and its diameter is usually 1 to 1.
．． It is about 5 μm. In order to irradiate the recording medium 1 with such a minute amount of light, the recording medium 1 and the objective lens 5 must be
The interval must be set to an accuracy of about 1 to 2 μm. However, in order to improve information efficiency, the recording medium 1 is often made of inexpensive materials such as plastic, and there are also limits to the accuracy of the mechanism (not shown) that supports and rotates the recording medium. . Therefore, in reality, as shown in FIG.
With respect to lref, it shifts toward the objective lens or away from the objective lens, causing a focusing error. As a result, stable information recording, reproduction, and erasure cannot be performed. Therefore, in order to prevent focusing errors from occurring, it is necessary to move a part or the entire optical head device including the objective lens 5 in the direction of the optical axis 11 of the objective lens 5 in accordance with the displacement of the recording medium.

Therefore, it is desirable to provide the optical sensor itself with a function for detecting focus errors.

The convex lens 6, knife lens 7, and detector 8 shown in FIG. 1 are provided for this purpose. The detector 8 consists of light receiving sections 8a and 8b divided into two by a gap 8C. This gap 8C is a portion that does not have a photoelectric conversion function. The gap 8c and the edge portion 7a of the knife edge 7 are parallel and arranged on the optical axis 11.

The principle of focus detection is as described below. First, in FIG. 1, which shows the case where there is no focus error, the light beam reflected by the recording medium 1 is again converted into a parallel light beam by the objective lens 5, and enters the convex lens 6 through the beam splitter 4.

Half of the light beam focused by the convex lens 6 is blocked by the knife technology 7, and the remaining half enters the detector 8. When there is no focus error, a light beam 9a is generated across the light receiving sections 8a and 8b. 1h. If there is a focus error, the reflected light from the recording medium 1 indicates that the recording medium 1 is deviated from the reference position [1ref. The recording medium 1 is at the reference position filre with respect to the objective lens 5.
When the distance is more than f, a semicircular light spot 9b is projected onto the light receiving portion 8a as shown in FIG.

On the other hand, when the recording medium 1 approaches the objective lens 5, a semicircular light spot 9 is formed on the light receiving section 8b as shown in FIG.
C is projected. Light receiving section 8a. , 8b photoelectric output I8a
, I8b are differentially amplified by a differential amplifier IO to become a focus error output (I8a-I8b). FIG. 4 shows the relationship between the intensity I of the focus error output (18a-I8b) and the displacement interval ΔZ of the recording medium 1 with respect to the reference position (jllrcf).

The intensity of the focus error output is zero when the recording medium 1 is located at the reference position, and when the recording medium 1 is displaced toward the reference position or downward b, the intensity varies depending on the direction of the displacement and the displacement △Z. Changes with positive or negative polarity. Therefore, focus error output (I8a-I8
The optical head device is servo-controlled by the focus error output in order to move the entire optical head device including the objective lens 5 up and down in the direction of the optical axis 11 so that b) is achieved. In this case, the laser beam will continue to be focused on the recording medium 1 with a microscopic groove of 1 to 1.5 μm in diameter.

However, focus error output (I8a-I8b)
In Fig. 4, the range in which is proportional to 2 to the displacement I (range with linearity) is only between points (5) and ) on the horizontal axis, and this is converted to the displacement of the recording medium 1. Sir. This is a narrow range of about 5 μm. That is, the light spot changes from the point-shaped sub-section (9a) shown in the first figure to the semi-circular sub-section (shown in the second or third figure)}.
This means that the displacement ΔZ required to reach 9b or 9c is extremely small. On the other hand, servo control of the optical head device in the optical axis direction requires a servo retraction operation. To perform this servo pull-in, the servo control function is temporarily stopped, the entire optical head device is brought closer to the recording medium, and when the servo control function is brought close enough to obtain a linear focus error output, the servo control function is activated. In order to enter the servo pull-in operation, if the range in which a linear focus error output can be obtained (focus error detection range) is narrow, the servo pull-in becomes difficult and there is a risk that the optical head device will collide with the recording medium. 1).

Furthermore, the range in which a linear focus error output can be obtained depends on the diameter of the light spot projected onto the detector 8 and the gap 8.
Determined by the width of c. A change in these values of only about 1 μm causes a large change in the range in which linearity can be obtained. In fact, the diameter of the light spot projected onto the river detector 8 is
When the amount of displacement ΔZ is 10, it is about 20 μm, and the width of the gap 8C is about 10 μm, so high precision is required for alignment between the detector 8 and the optical band projected here.

However, since this alignment work is difficult, variations in alignment accuracy occur (second drawback).

(Objective of the Invention) An object of the present invention is to provide a focus error detection device that solves the drawbacks listed in L.

(Summary of the Invention) In order to achieve the above object, the present invention provides a means for irradiating a light beam onto a recording medium having an information track; Optical means having the function of dividing light into light components and imaging at least two of the light components on different predetermined focal planes:
a light-receiving section that is arranged at a location other than the predetermined focal plane and on which at least two light spots whose size changes depending on the position of the recording medium are projected by the action of the optical means; and A focus error detection device is provided, comprising: means for generating a focus difference output in accordance with a photoelectric output, and the size of the light receiving section is set so as to receive light from a predetermined area of the light spot.

(Examples) Hereinafter, the present invention will be described based on Examples. 5 to 8 are diagrams showing the optical configuration of the first embodiment of the present invention. In the figure, members that act in the same way as in FIG. 1 are given the same reference numerals.

A beam emitted from a laser light source 2 is made into a parallel beam by a collimator lens 3, reflected upward by a beam splitter 4, and then irradiated onto a recording medium (disc) 1 as a light spot by an objective lens 5. This light spot is reflected by the disk 1 and returned to the objective lens 5.
becomes a parallel beam of light. This parallel light flux passes downward through the beam splitter IJ notation 4 and enters a detector 14 such as a photodiode via a convex lens 6 and a holographic lens 12. Hereinafter, the light beam reflected by the disk 1 and directed toward the detector 14 will be referred to as information light. The knife edge 7 is placed close to the bottom surface of the holographic lens 12. The light receiving surface of the detector 14 is located at a position that coincides with the focal plane of the convex lens 6 or is conjugate with the focal plane. Detector 14
The light receiving sections 14a, 14b are divided into two parts, and both the light receiving sections 14a, 14b are arranged with a predetermined gap 14c. Further, the bisector of this gap intersects with the optical axis O. The reason for providing this gap will be described later.

The holographic lens 12 has a known Fresnel zone pattern (drawn as a black/white pattern in FIG. 9) formed on its surface as shown in FIG. Examples of Fresnel zone patterns include ■
The pattern 12a blocks the light flux and the pattern 12b transmits the light flux, and the pattern 12a and 12b both transmit the light flux, but a certain phase difference is created between the light fluxes transmitted through the patterns 12a and 12b. But that's fine. These patterns 12a and 12b (transparent/opaque 75
(a person or an object that causes a phase difference), it is distributed in a step-like manner as shown in FIG. However, other than this, a continuous K (eg, sinusoidal) distribution may be used. From the point of view of optical performance, ease of manufacture, etc., the above-mentioned type ① holographic lens (step phase holographic lens) that utilizes phase difference is most suitable, and in the embodiment of the present invention, , all will be explained using step-phase holographic lenses. It is clear from the avowed optical theory that such a holographic ink lens acts as a lens having a focal length depending on the order of interference due to the interference of light beams from each zone. This situation is explained in Fig. 10. Light 13al'j: 0th-order light that does not undergo any lens action, light 1abh is 11th-order light that undergoes convex lens action, and light 13c has concave lens action. It is received - primary light. Although not shown, in addition to the θ-order light and the ±1st-order light, there are also ±2nd-order light, ±3rd-order light, and the like. In the step-phase holographic lens, the θ-order light and the ±1st-order light with respect to the intensity of the incident light are determined by the area ratio of the pattern 12a and the pattern 12b in FIG. The intensity ratio (diffraction efficiency) can be appropriately designed. An example in which a plane wave is incident at an area ratio of 1:1 is shown in the table below. In the table, λ is the wavelength of the laser light.

In FIGS. 5 to 8, the holographic lens 12
The optical path difference is λ/2, the diffraction efficiency θ of the θ-order light, and the diffraction efficiency of the +1st-order light and the -1st-order light are each 40.5.
% is used. In addition, the remaining luminous flux of about 20 units is
The light flux is ±3rd order, ±5th order (according to known optical theory, when a plane wave is incident, no corner order light flux is generated), but the diffraction efficiency is small compared to ±1st order light, and , the focal length is also different, so ignore it.

In this way, as shown in FIG. 5, 40.5% of the information light incident on the holographic lens 12 is
The second light) is subjected to the action of a convex lens to the front side of the detector 140,
That is, the focal point (F+) is set on the optical axis between the detector l4 and the holographic lens 120. Furthermore, another 40 of the information lights
．． The 5% luminous flux (-1st-order light) is focused (F-) on the rear side of the detector l4, that is, on the lower optical axis, under the effect of a concave lens.

In this case, depending on how the focal lengths of the convex lens 6 and the holographic lens l2 are selected, as shown in FIG.
The light flux subjected to the concave lens action by the holographic lens 12 becomes diverging light, and the focal point (F-) of the diverging light may be formed on the optical axis between the holographic lens 12 and the convex lens 6, but in principle , those in Figure 5 and all
It's the same.

Note that the following description will refer to FIGS. 5, 7, and 8. FIG. 5 shows that a parallel beam of light enters the objective lens 5 via the collimator lens 3 and the beam splitter 4.
A state in which the light is accurately focused on the surface of the disk 10 by the objective lens 5 is shown. In this case, on the light receiving surface of the detector 14, a semicircular spot (left semicircle) 15a due to the 1,011th order light and a semicircular spot (right semicircle) 15b due to the -1st order light are generated, respectively. FIG. 7 shows a state in which the disk 1 is displaced upward from the position shown in FIG. 6 (predetermined position). At this time, the +1st order light forms a semicircular spot 15a on the light receiving surface of the detector 14, but the -1st order light forms a semicircular spot 15a.
5b. FIG. 8 shows a situation in which the disk 1 is displaced downward from a predetermined position. At this time, on the light receiving surface of the detector 14, the +1st order light forms a point 15a, while the 11st order light forms a semicircular spot 15b.

FIGS. 11(a) to 11(g) show in detail the behavior of the optical substrate on the light-receiving surface of the detector 14 when the distance between the objective lens 5 and the disk 1 changes. FIG. 11(d) shows a state in which the disc 1 is located at the predetermined position and the laser beam is accurately focused on the disc surface (focused state Fl4).

In this focused state, the semicircular light spots 15a and 15b formed by the +1st order light and the 11th order light complement each other to form one circular spot. In this embodiment, this circular spot is divided into two by a bisector of the gap 14C between the light receiving sections 14a and 14b. Therefore, the light spot 15a is divided into a part projected onto the light receiving part 14a and a part projected into the gap 14e, and the light spot 15b is also divided into a part projected onto the light receiving part 14b and a part projected into the gap 14c. It can be divided into The positional relationship between the optical disc 1 and the objective lens 5 and the state of the light beam at this time are as shown in FIG. Now, when the disk 1 is gradually displaced upward from the predetermined position shown in FIG.
4, the light stub 15a due to the +1st-order light gradually becomes larger, and conversely, the light stub 15b due to the -1st-order light becomes larger.
becomes gradually smaller. When the disk 1 is further displaced upward, the optical spot 15a becomes even thicker, as shown in FIG. 11(b), and the optical spot 15b finally reaches a point where it is projected only onto the gap 14c. At this time, the positional relationship between the disk 1 and the objective lens 5 and the state of the light beam are as shown in FIG. These Figures 7 and 11 (
In the state shown in b), the optical spot 15b has the minimum diameter, and when the disk 1 is further displaced upward, the optical spot 15b is now projected as a semicircular spot toward the light receiving section 14a. When the disk 1 is further displaced upward, the optical socket 15a becomes even larger as shown in FIG.
It begins to form to the side. Next, when the disk 1 is gradually displaced downward from the predetermined position shown in the sixth figure,
As shown in FIG.
The light beam 15b due to the primary light gradually becomes smaller by K.

When the disk 1 is further displaced downward, as shown in FIG. 11(f), the optical spot 15a becomes a point that is projected only onto the gap 14C, and the optical spot 15b
becomes even larger. The positional relationship between the disk 1 and the objective lens 5 and the state of the light beam at this time are as shown in FIG. In the state shown in FIG. 8 and FIG. 11(f), the optical slot 15a has the minimum diameter, and when the disk 1 is further displaced downward, the optical slot 15a now becomes a semicircular spot toward the light receiving section 14b. It will be projected. When the disk 1 is further displaced downward, the optical slot 15b becomes even larger as shown in FIG. 11(q), and the optical slot 15a is now formed toward the light receiving section 14b. Note that the size of the optical slots 15a and 15b varies depending on the amount of displacement of the disk 10 with respect to a predetermined position filHc. The amount of light on the light receiving surface is constant regardless of the size of the light spot because it changes in inverse proportion to the size of the light spot. The relationship between the displacement amount ΔZ and the focus error output If will be explained with reference to FIG. 12.

Focus error output is If=(I14a-I14'b)
It is obtained by the operation of In FIG. 12, the vertical axis is the intensity of each of the outputs Il4a, I14b, If, and the horizontal axis is the displacement Δ2. When the amount of displacement is zero, that is, light spot 1
When 5a and 15b are in the condition shown in Fig. 11(d), the first
As shown by point (d) on the horizontal axis of FIG. 2, the intensities of the photoelectric output beam forces I14a and I14b are equal to each other and have a certain value. On the other hand, when the amount of displacement increases toward the left on the horizontal axis, that is, the optical slot 15al15b becomes the 11th
It changes to the size shown in Figure (c) + (b) t (a).
Then, the photoelectric output I14a gradually increases, and conversely, the photoelectric output I14b gradually decreases and finally reaches zero K. Here, points (C), (b), and (a) on the horizontal axis are the 11th
Diagram (C)? (b) and (a) correspond to each other. On the other hand, as the amount of displacement increases to the right on the horizontal axis, the light spots 15a and 15b change as shown in FIGS.
g) As it changes to the magnitude shown by K, the photoelectric output I
14b gradually increases, and conversely, the photoelectric output 114a gradually decreases and finally reaches zero. Here, (e) + (f) + (gl point on the horizontal axis is (e) + (f
)+(g), respectively. The correspondence relationship between the displacement amount ΔZ and the photoelectric outputs I14a and I14b described above is K as shown by curves Ii4a and I141) in FIG. 12, respectively. The focus error output IP corresponding to the difference between the photoelectric outputs I14a and 14b has a gentle slope between point (a) and point (gl) on the horizontal axis, as shown by the curve If in FIG. The output will be

The effect of the gap provided between the light receiving sections 14a and 14b will be explained below. Now, suppose the width of the space @14c is the light receiving part 1.
11(b) and 11(f), and the diameter of the light spots 15a and 15b in FIGS. 11(b) and 11(f) is approximately 20 μm. In the situations b) to (f), the light receiving part 14a
, 14b respectively receive more than half of the light spots 15a, 15b. Light spot on the light receiving surface}15
As mentioned earlier, the light intensity of the light spots 15a and 15b is constant regardless of the size of the spot, so the light intensity of the light spots 15a, 1
11(C), (d) and I(e), the intensities of the photoelectric outputs I14a and I14b are almost equal.

Therefore, in the range from point (C) to point (e) in FIG. 12, the focus error output If hardly changes for a displacement of 2, resulting in a decrease in the accuracy of focus error detection. Therefore, the width of the gap 14C is widened to increase the area on which the light spots 15a and 15b are projected onto this gap, that is, to reduce the area on which the light spots 15a and 15b are projected onto the light receiving sections 14a and 14b. The width of this gap 14C is the width of the optical slot 15a for the displacement △2,
It is necessary to make an appropriate selection by taking advantage of the fact that the change in diameter of 15b is almost proportional. For example, this gap is 1/2 of the total intensity of the light spot incident on the detector 14 when ΔZ=O.
The width should be enough to block the degree of damage. In this way, the amount of displacement △Z
The intensity changes of the photoelectric outputs I14a and 14b for the first
As shown in Figure 2, it is almost straight and symmetrical about the vertical axis.

Therefore, the focus error output If has substantially linearity in the range from point (a) to point (g) in FIG. 12. In contrast to the focus error output shown in FIG. 4, the focus error output shown in FIG.
Converting to approximately ±1 dragon. This is because the light spot projected onto the light receiving surface of the detector 14 is made thicker, and the area of the light spot received by the light receiving sections 14a and 14b is adjusted to reduce the focus error detection sensitivity. This is achieved by

Note that the range (a) to (g) is the holographic lens l2
It can be set to a desired value depending on the size of the light spots 15a, 15b of the +1st-order light and the -1st-order light projected by and the gap 14C. Furthermore, the diffraction efficiency of the holographic lens 12 for ±1st-order light is 40.5.
1, so no matter how the values in the range (a)-(g) are set, when the displacement amount z=O, the focus error output IF=O.

FIG. 13 shows another embodiment of a detector for receiving a spot of information light. In this embodiment, the detector 16 consists of light receiving sections 16a and 16b formed by dividing a circular light receiving surface into two and providing a hole (emergency light section) 16C in the center of the light receiving surface. The size of the non-light-receiving portion 16e may be a circle having the same diameter as the circle formed by the optical slits }15a and 15b when the displacement amount ΔZ=O, or a circle having a smaller diameter than that. This detector 16 can also obtain a focus error output having the characteristics as shown in FIG.

Next, a second embodiment of the present invention will be described. In this embodiment, the optical system other than the detector is the same as that shown in Figure 5, and by using the detector shown in Figure 14, the two photoelectric outputs and the focus error output can be separated. It is extracted using a method. In Fig. 14, detector 1
7 consists of rectangular light receiving portions 17a and 17b placed opposite each other with a gap 17C made as narrow as possible. Light receiving section 17
The width of a and 17b is the light spot 1 when the displacement △Z20
Parts of 5a and 15b are set so as to protrude from the light receiving section. The amount of this protrusion may be approximately 1/2 of the total intensity of the light spot incident on the detector 17. Figure 15(a)~
(g) shows the light beam on the light receiving surface of the detector 17}15a,
15b behavior. In addition, Fig. 15 (a) to (g)
The light spots 15a and 15b in the second position are shown in FIG.
Assume that it was generated under the same circumstances as (g). Therefore,
Assuming that the disk 1 gradually descends from a certain point above the reference position, matches the reference position, and then moves further downward from the reference position, the optical sub-box 15a
, 15b deforms from (a) to (g) in FIG. As the +1st-order light beam 15a goes from (a) to (e) in FIG.
In FIG. 15(f), the point straddles the light receiving sections 17a and 17b, and in FIG. 15(g), it is projected onto the light receiving section 17b. On the other hand, the light block 15b due to the −1st-order light is the 15th
The light spot 15a goes from (g) to (a) in the figure.
transforms in the same way. Since the photoelectric output is determined by the amount of received ±1st order light, the photoelectric outputs I17a and I17b are the 16th
It changes by 5K as shown by curves I17a and I17b in the figure, respectively. Here, when the respective photoelectric outputs of the light receiving sections 17a and 17b are I17a and I17b, the focus error output IF is the differential amplification of the photoelectric outputs 117a and I17b (
IF=Summer 17a-117b). In FIG. 16, the vertical axis represents the photoelectric output 117a. I17
b and the intensity I of the intrusion force If of the focus v4, and the displacement Δ2 is plotted on the horizontal axis. (a) on the horizontal axis of Figure 16
Corresponding to each displacement mark at points 1 to 15 (g), optical slots} 15m and 15b are shown in FIGS.
) r - The state shown is reached.

Now, the amount of displacement of disk 1 and the photoelectric output 117abI17
The relationship with b is as described below.

(1) While the disk 1 is descending from the position corresponding to (a) to (b) in FIG. t gradually increases. (2) When the disk 1 descends to the position corresponding to FIG.
Since approximately half the amount of light of the secondary light spot 15b is projected, the photoelectric output 117b is only generated at this point.

And its strength is extremely great. (3) When the disk l descends a little further from the pair position shown in FIG. 15a, only the +1st-order light spot 15a is projected. Therefore, the intensity of the photoelectric output 117a is as shown in FIG.
The intensity of the -1st-order light decreases to the extent that approximately half of the total intensity of the -1st-order light is subtracted from the intensity. (4) Disk 1 is shown in Figure 15 (C
), (d), and (e), and then descends to the corresponding position in FIG. 15(f), the photoelectric output 117a gradually increases and the photoelectric output 117
b is gradually divided downward.

Incidentally, in the case of FIG. 15(d), the photoelectric output 117a. I17
b will be equal. (6) When the disk 1 descends to the corresponding position shown in FIG. 15(f), approximately 1,000 times the optical spot of the +1st-order light is projected onto the light receiving section 17a, so that the optical power 117
At this time, a becomes maximum. On the other hand, +1 to Ukuro 17b
The photoelectric output 117b rapidly increases because the remaining average light intensity of the light spot of the secondary light and a part of the light intensity of the −1st order light spot are projected. (6) Then, disk l is Jl5
When the light receiving part 1 is lowered a little further than the corresponding position in figure (f),
Since no light spot is projected on 7a, the photoelectric output I
17a becomes zero. (7) Further, as the disk 1 descends toward the corresponding position in FIG. 15(g), the photoelectric output I1
7b gradually decreases.

The focus error output If obtained by differentially amplifying the photoelectric outputs I17a and I17b obtained in this way is shown in FIG.
It becomes linear within the range from point bl to point fJ.

FIG. 17 shows another embodiment of the detector. In this embodiment, the detector 18 consists of light receiving sections 18a and 18b formed by dividing a circular light receiving surface into two parts by a gap 18C. Gap 1
8C is made as narrow as possible. Also, the diameter of the circular light-receiving surface is 15
Set to be equal to or smaller than the diameter of the circle formed by a, 15bK. In this way, two photoelectric outputs and a focus error output having the characteristics shown in FIG. 16 can be obtained.

Next, a third embodiment of the present invention will be described.

In this embodiment, the holographic lens and detector described below are used, and the other optical systems are the same as those shown in FIG. In this case, the holographic lens 12
, the optical path difference between adjacent zones (for example, even-numbered zones and odd-numbered zones counting from the center zone) is λ/3, and the diffraction of the O-order light, +1st-order light, and -1st-order light The efficiency is equal to 29 cm each (see table above). In FIG. 18, the detector 19 is located in the gap 19C.
It consists of rectangular light-receiving parts 19a and 19b arranged side by side. On the light receiving surface of this detector 19, there are a light slot 150a for +1st order light, a light slot 150b for -1st order light,
And a light spot 150C of O-order light is projected. Light receiving parts 19a, 19b, gap 19c, and optical X box}15
The relationship with 0a, 150b, and 150C is as follows.

In other words, the width of the gap 19c is approximately equal to the diameter of the optical block 150c of the 00th order light when the displacement amount Z=00}, and the size of the light receiving parts 19a and 19b is the same as the width of the displacement {±1st order when the fE amount ΔZ=00} The amount of light is sufficient to receive all of the light beams 160a and 150b (excluding the portion projected onto the gap 19C).

FIGS. 19(a) to (e) show that when the displacement ΔZ changes, the optical substrata 150a, 150b, 150c
9 shows how it changes on the light receiving surface. Since the holographic lens does not have a lens effect on the O-order light, when the displacement ΔZ=0, the light beam 150c is projected into the gap 19c as shown in FIG. 19(C), while the light The spots 150a+150b each form a left semicircle and a right semicircle with the same radius, which complement each other to form one circular spot. As the disk 1 is displaced upward from this state, the optical spot 150a increases the diameter of the left semicircle, the optical spot 150b reduces the diameter of the right semicircle, and the optical spot 150c increases the diameter of the left semicircle. It becomes a circle and its diameter increases. Then, as shown in FIG. 19(b), the light spots 150a and 150c are located on the light receiving portion 19a. The area of the light spot 150b is increased so that the light spot 150b is projected into the gap 19c. When the disk 1 further rises, the optical spot 150b also becomes a left semicircle, and the optical spots 150a, 150b, and 150c are all projected onto the K light receiving section 19a, as shown in FIG. 19(a). Now, as the disk 1 is displaced downward from the displacement amount ΔZ=0, the diameter of the right semicircle of the optical slot 150b increases, and the optical slot 150b increases.
50a reduces the diameter of the left semicircle, and also adds a light socket}150c
becomes a right-hand semicircle and its diameter increases. And the first
As shown in FIG. 9(d), light spots 150b and 150c
has increased its area on the light receiving part 19b, and the light slot
150a is buried in the gap 19C. As the disk 1 further descends, the light spot 150a also becomes a right semicircle, and the light spots 150a, 150 as shown in FIG. 19(e)
b, 150C are both projected onto the light receiving section 19b.

FIG. 20 shows the relationship between the displacement lΔ2, the intensity of the photoelectric output of the light receiving sections 19a and 19b, and the focus error output If. For curved people, the photoelectric output of the light receiving section 19a ■ + of 19a
The difference (I
19a-I19b) Represents ten. Curve B is photoelectric output■1
Of 9a, the output component that depends on the -1st order light and the photoelectric output I1
9b, the difference from the output component that depends on the -1st order light (■19
a-I19b) Represents one. Curve C is the photoelectric output I1
Output component dependent on O-order light of 9a and photoelectric output I19
The difference between the output component of b that depends on the O-order light (I19a-
I19b) represents 0. (a) to (on the horizontal axis of Fig. 20)
The amount of displacement at point e) corresponds to the displacement views in FIGS. 19(a) to 19(e), respectively. As is clear from FIG. 20, the output components (I19a-I19b)+, (I19a-
The changes in I19b)- and (I19a-I19b)o are shown in (b), (e), and (d) in Figure 20, respectively.
Near the point, the distance changes linearly with changes in the distance between the disk 1 and the objective lens 50. By the way, since information light enters the detector 19 without distinction between O-order light and ±1st-order light, the difference between the photoelectric outputs of the two light receiving sections 19a and 19b, that is, the focus error output If is shown in FIG. K as shown by curve D. Note that the focus error output If is the 20th
The focal length of the holographic lens is appropriately set so that it changes almost linearly in the range of points (a) to (d) in the figure. In addition, the range in which the focus error output changes almost linearly with respect to the displacement ΔZ is when the holographic lens is not used (shown by curve C j(I19a-I1
9b) Same as θ), it is almost three times larger.

Next, an application example of the present invention will be explained. This application example detects the deviation (hereinafter referred to as tracking error) between the center of the information track formed on the surface of the disk 10 and the center of the optical spot of the laser beam irradiated onto the disk 1 (hereinafter referred to as the reading optical spot). It is something to do.

The general principle of tracking error detection will be explained below. As shown in FIG. 21, the information track is formed by forming continuous projections 1a (FIG. 21(a)) or intermittent projections 1b (FIG. 2(b)) on the surface of the disk 10. be. For example, in the case of a reflective disk, the protruding twill (phase difference) of this protrusion is about 1/4 to 1/8 of the wavelength of light. In the figure, the arrow indicates the direction in which the information track moves (running direction) relative to the optical head device.

The information track may have a rectangular cross section as shown in FIG. 21, or may have a triangular or round shape.

Fig. 22 qualitatively shows the diffraction pattern of the laser beam and the distribution of the intensity ID of the diffracted light due to such an information track. The same is true for discs. When the center of the light spot and the center of the information track match, the intensity distribution of the diffracted light becomes symmetrical, as shown in Figure 22(b) K, but when the center of the reading light spot and the center of the information track match, the intensity distribution of the diffracted light becomes symmetrical. If the center shifts, the image shown in Fig. 22(a) or Fig. 22(
As shown in C), the intensity distribution of the diffracted light becomes asymmetrical depending on the direction of the shift. When using a disk with such an information track, the knife edge (7) is used to detect tracking errors using the embodiment shown in FIG.
is placed perpendicular to the direction of movement shown by the arrow in FIG. In this way, asymmetry in the intensity distribution of the diffracted light due to the shift between the center of the reading light irradiated onto the disk 1 and the center of the information track will occur in the direction perpendicular to the plane of the paper in FIG. As a result, there is no adverse effect on the detection of the focus error described above. FIG. 23 qualitatively shows the intensity distribution of the diffracted light due to the shift between the center of the reading light spot and the center of the information track (1a) when the displacement position ΔZ=O. Figure 23(b) shows the case where there is no deviation at all, and Figures 23(a) and (C) respectively show the case where there is deviation in the opposite direction.
The dotted hatched areas in a) and (C) correspond to areas where the intensity is reduced due to, for example, asymmetry in the intensity of the diffracted light. FIG. 23(a) shows that the intensity of the upper half of the light beam passing through the convex lens 6 in FIG. This is the case. In this case, the +1st order light from the holographic lens 12 forms a single image at the focal point F+ before reaching the detector 14. The intensity of the luminous flux is reduced in the lower half 15a-2 of the light spot 15a, while the −1st-order light forms an image behind the light-receiving surface of the detector l4. Strength is decreasing. By the way, the deviation between the center of the reading light spot and the center of the information track is
If it is not so large, the intensity of the information light incident on the light receiving surface of the detector 14 can be considered to hardly change. Therefore, in FIG. 23(a), the upper half of the light spot 15a 15a-1 and the lower half 15b- of the optical eyelet 5b.
2, the intensity is increased compared to the same part in the case of FIG. 23(b) without any of the above deviation (S).
C) shows the case of the same figure (al) and the case of deviation in the opposite direction.As is clear from the above explanation, in order to detect the deviation of the reading light spot and the information track, the second
The intensity I of the photoelectric output corresponding to each part 15a-1, 15b-1, 15b-2 of the optical tube 1, 2, and 15b-2 in Fig. 3 is Ial, Ia2:i, respectively.
For example, (Ial+Ib2)-(
The tracking error output It can be obtained by the calculation Ia2+Ibl).

FIG. 24 shows the characteristics of the tracking error output It. The horizontal axis in FIG. 24 is the deviation ΔX between the center of the reading light spot and the center of the information trunk, and the vertical axis is the intensity I of the tracking difference output. The (a) I (b) l (Cl points on the horizontal axis correspond to the cases of (a)), (b) 1 (CI) in Fig. 20, respectively.The intensity of this tracking error output is set to zero. Furthermore, by driving the reading light spot in a direction perpendicular to the traveling direction, the reading light spot can be made to follow the information track.

Hereinafter, a first application example for detecting a focus error and a tracking error will be described based on the first embodiment shown in FIG. 5.

In FIG. 25, the detector 14 consists of eight light-receiving parts. The light receiving parts A and E are the light receiving part 14 in FIG.
a, and the light receiving sections D and H correspond to the light receiving section 14b in FIG. Further, the light receiving portions B, C, F, and G are formed at portions corresponding to the gap 14C in FIG. 11. Hikari Suboc}1
5a is caused by the +1st order light, and the light subbox 15b is -1
They are each generated by the next light. Light receiving part A
Assuming that the photoelectric outputs IA to IH can be obtained from the outputs IA to H, respectively, the focus error output If and the tracking error output It can be calculated as follows.

If-(IA+TE)-(ID±I}{)...
(1) It=(IA+IB+IG+IH)-(IC+I
D+IE+IF) (2) FIG. 26 is an electric circuit diagram for calculating equations (1) and (2). The operational amplifier 20 has photoelectric outputs IA, IE, ID.
, IH is operated manually to calculate the formula (1) to generate the focus error output If, and the operational amplifier 21 outputs the photoelectric output IA.
The trunking error output It is generated by calculating the equation (2) using TH or TH manually. Incidentally, since the information recorded on the track of the disk 1 is included in the entire optical field 15a, 15b projected on the detector 14K, the operational amplifier 22 adds up all of the photoelectric outputs IA to IH and outputs the information. Generate Id.

FIG. 27 shows another embodiment of the detector 14, which is composed of five light-receiving parts D. The light receiving parts A, DI, and H are the same as those shown in FIG. 25, and the light receiving part K is the same as the light receiving parts B and H shown in FIG.
It is a combination of C, F', and G. In this case, the focus error output If can be determined by equation (1). Also, the tracking error output It is Iz=(IA+IH)-(ID×IE)...(
It can be obtained by the calculation in 3).

A second application example for detecting a focus error and a tracking error based on the second embodiment of the present invention shown in FIGS. 14 and 15 includes the detector 14 shown in FIG.
can be used as is. That is, the focus error output is If = (IB + IF) - (Ic + IG) (
4), and the toranoking error output is (
2) Obtained by calculating Eq.

Furthermore, as is clear from FIG. 12 and FIG. 16, the focus error output obtained using the detector 14 (FIG. 11) and the focus obtained using the detector 17 (FIG. 15) The error output has the slope reversed. Therefore,
As shown in equation (5), by subtracting the difference between the focus error outputs obtained by equations (1) and (4), a more sensitive focus error output Ifl can be obtained. That is, If+-(iA+IC+IE+IG)-(IBfID+IP+I}{) (5) This situation is shown in FIG. Curve (1) t(4
)+(5) represent focus error outputs obtained by equations (1), (4), and (5), respectively. 1-1 Next, a third application example for detecting focus errors and tracking errors based on the third embodiment of the present invention shown in FIGS. 18 to 20 will be described. For this purpose, a detector 19 shown in FIG. 29 is used.

The detector 19 consists of a light receiving section P to S divided into four parts,
A gap 19c having the width as described above is provided between the left semicircular light receiving portions P, R and the right semicircular light receiving portions Q, S.

The photoelectric output of each of the light receiving sections P to S is p, IQ,
(2) Dividing R and Is, the focusing error output If and the dragging error output It can be determined as follows.

If=(Ip+IR)-(IQ+IS)-■-(6)■
t=(IP+IS)-(IQ+IR)...Seal/(7) plot=Isei3)~(7)<Kyr. T performance'Jlics. (1
゜,, In the above explanation, it was assumed that the holographic lens 12 and the knife edge 7 were used, but instead of the knife edge 7, a grism (for example, a Foucault grism) 25 was used, as shown in Fig. 30. It may also be a configuration. In FIG. 30, the light beam emitted from the holographic lens 12 is divided into halves by the prism 25 (in FIG. 30K, it is distributed to the right and left). Each of the distributed luminous fluxes behaves in exactly the same way as described above, so when the displacement amount of disk 1 △Z-o for each luminous flux, +
Detectors are installed at positions 26a and 26b, respectively, where the light spots formed by the primary light and the -1st order light have the same size. As each detector, e.g.
What is shown in FIG. 25, FIG. 27, or FIG. 29 may be used. Then, two focus error outputs Ifl, If2,} racking error output Lth, It2, and information reproduction output Idl, I obtained from each detector are obtained.
Adding each d2, If=Ifl+If2,It
If =Itl+It2 and Id=Idl+Id2 are obtained, twice the sensitivity can be obtained compared to the case where the knife edge 7 is used.

Note that even if the wavelength of the laser beam changes, the holographic lens only changes the size of the light spot on the light-receiving surface of the detector, and the focal length does not change, so it is effective for changing the wavelength. Further, in the present invention, by using a holographic lens, a plurality of beams with different focal lengths, ie, +1st order light and -1st order light, are obtained.
For example, a double-point lens using real birefringence may be used.

(Effects of the Invention) According to the present invention described below, (1) the focus error detection range can be appropriately widened, so that the distance between the disk and the optical head auxiliary device when entering the servo pull-in operation can be widened. can do. Therefore, not only can the stability of the servo retraction operation be increased, but also the risk of the optical head device colliding with the disk can be reduced. (2) Furthermore, since the diameter of the light spot projected onto the light-receiving surface of the detector can be made appropriately large, the alignment accuracy of the projected position of the light spot with respect to the detector can be made more relaxed than before. This facilitates this alignment work.

[Brief explanation of drawings]

1 to 3 are diagrams for explaining the optical system of a conventional optical head device and the principle of detecting a focus error using this optical system. FIG. 4 is a diagram showing characteristics of focus error output obtained by a conventional optical head device. 5 to 8 are diagrams for explaining the optical system of the optical head device according to the first embodiment of the present invention and the principle of detecting a focus difference using this optical system. FIGS. 9 and 10 are diagrams for explaining the holographic lens used in the first embodiment. FIG. 11 is a diagram for explaining the behavior of the light beam on the light-receiving surface of the detector in the first embodiment. The graph 12 is a diagram showing the characteristics of the focus error output obtained by the first embodiment. FIG. 13 is a diagram showing another embodiment of the detector in the first embodiment. FIG. 14 is a diagram for explaining the second embodiment of the present invention, particularly its detector. FIG. 15 is a diagram for explaining the behavior of a light spot on the light receiving surface of the detector in the second embodiment. FIG. 16 is a diagram showing the characteristics of the focus error output obtained by the second embodiment. FIG. 17 is a diagram showing another embodiment of the detector in the second embodiment. FIG. 18 is a diagram for explaining the third embodiment of the present invention, particularly its detector. FIG. 19 is a diagram for explaining the photographing movement of the light bulb on the light-receiving surface of the detector in the third embodiment. FIG. 20 is a diagram showing the characteristics of the focus error output obtained by the third embodiment. FIG. 21 is a diagram for explaining the structure of an information track on a disc. FIG. 22 is a diagram for explaining the state of diffracted light due to the information track of the disk and the intensity distribution of the diffracted light. FIG. 23 is a diagram for explaining the principle of tracking error detection. FIG. 24 is a diagram showing the characteristics of the tracking error output. FIG. 25 is a diagram for explaining a first application example for detecting a focus error and a tracking error based on the first embodiment of the present invention, particularly a detector thereof. FIG. 26 is an electrical circuit diagram used in the first application example. FIG. 27 is a diagram illustrating another embodiment of the detector in the first application example. FIG. 28 is a diagram showing the characteristics of the focus error output obtained by the combination of the first application example and the second application example. FIG. 29 is a diagram for explaining a third application example for detecting focus error output and tracking error output based on the third embodiment of the present invention, particularly a detector thereof. FIG. 30 is a diagram for explaining the optical system of an optical head device according to another embodiment of the present invention and the principle of detecting focus error output and tracking error output using this optical system. (Explanation of symbols of main parts) 1; disk, 2; laser light source, 3; collimator lens, 4; beam splitter, 5; objective lens, 6; convex lens, 7; knife edge, 8, 14, 16, 17, 18
, 19; Detector 209-Procedural Amendments (December 2, 1980) To Mr. Kazuo Wakasugi, Commissioner of the Japan Patent Office 〆' 16 Indication of Case 1982 Patent Application No. 136158 2. Name of the invention Focus error detection device for optical information reproducing device 3. Person making the amendment Related to the case Patent applicant Shigetada Fukuoka, 3-2-3 Marunouchi, Chiyoda-ku, Tokyo (411) Nippon Kogaku Kogyo Co., Ltd. Futaoka Shigetada Labor 1 Chief 4. Agent Address: 1-6-3 Nishi-Oi, Shinagawa-ku, Tokyo 140 Japan Kogaku Kogyo Co., Ltd. Oi Seisakusho (7818) Patent Attorney Takashi Watanabe I [Takuya Telephone (773) 1111 5. "Detailed Description of the Invention" column e of the specification subject to amendment Drawing 6. Contents of amendment (1) Page 14, line 12 and line 16 of the specification, page 15, line 3 and line 17, page 16, line 15, and page 17 of the specification Correct the "predetermined position" in the 14th and 19th lines to "reference position 1refJ." 2. Change r20umJ in the 15th line of page 19 to r200.
, 14+11". (3) Correct "±lnJ" in the fourth line of page 21 to "±50μ box". {4} In the 9th line of page 40 of the same document, the phrase "the holographic lens" is corrected to "if the holographic lens is used as in the above embodiment." (5) Replace Figures 2, 3, 7, 8, and 26 with the attached ones. -211-

Claims (1)

[Scope of Claims] Means for irradiating a light beam onto a recording medium having an information track; dividing the information light emitted from the recording medium by the irradiation of the light beam into at least two light components; optical means having the function of focusing two light components onto different predetermined focal planes;
a light receiving section that is arranged at a location other than the predetermined focal plane and on which at least two light spots whose size changes depending on the position of the recording medium are projected by the action of the optical means; and What is claimed is: 1. A focus error detection device comprising: means for generating a focus error output according to a photoelectric output; the size of the light receiving section is set so as to receive light from a predetermined area of the light spot.