JPS58111138A - Focusing detecting device - Google Patents

Abstract

PURPOSE:To simplify the structure of a titled device and to reduce the size and weight by using sensitive characteristics changed in accordance with the incident angle of light to an optical detector inclined to the optical axis of light reflected by an object to be irradiated. CONSTITUTION:When a disc 6 is located on the focusing position of an objective lens 5, both of light flux made insident to respective photodetecting areas 14A, 14B of a photodetector 13 are in parallel with the optical axis O, respectively and their incident angles are equal, so that the sensitivity of respective photodetecting areas 14A, 14B are made equal. If the disc 6 is shifted from the focusing position in the direction of (a), the light flux reflected by a polarizing prism 3 is made to the light flux having inclination components shown by max. a1-a2 to the photodetector 13, so that the incident angle of the incident light a1 to the photodetecting area 14A is reduced smaller than theta, and the incident angle of the incident light a2 penetrated into the photodetecting area 14B is increased larger than theta. When the disc 6 is shifted from the focusing position in the direction of (b), the incident angle of the incident light b2 to the photodetecting area 14B is reduced smaller than theta.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an apparatus for reading information by focusing a reading light spot using an objective lens onto an information track recorded in a spiral or concentric pattern on a recording medium, for example.
The present invention relates to a focus detection device that detects the focus state of an objective lens on a recording medium.

The above-mentioned information reading device is known from the prior art, and recording media having information tracks include, for example, books called video discs. This video disc contains video and audio signals encoded in information tracks.
It is recorded as optical information such as optical transmission characteristics, reflection characteristics, and phase characteristics. The information recorded on the video disc is rotated at high speed, and the laser light emitted from a laser light source is focused onto an information track through an objective lens, and the transmitted or reflected light transmitted by the information track is detected. and read it. One of the features of such recording media is that the information recording density is extremely high, so the width of each information track is extremely narrow, and the width of each information track is extremely narrow.
The spacing between successive information tracks is also very narrow. In order to accurately recover the original information from information tracks with such narrow width and pitch, the objective lens must be kept in focus on the video disk surface, and the light spot on the top of the disk must be focused. The diameter must always be minimized. This requires an optical reading device! In this system, a force shifting control is performed in which the defocus of the objective lens with respect to the disk surface is detected, and the objective lens is displaced in the direction of its optical axis based on this defocus signal.

Fig. g is a diagram showing an example of a focus detection device in a conventional optical reading scattering device etc. proposed earlier by the applicant. The light A= emitted from the laser light source 1 (linearly polarized in the plane of the paper) is made into parallel light by a collimating lens, and a polarizing prism with a polarizing film 3. A 1/4 wavelength plate and an objective lens! through which the information track is focused onto the disc containing the information track.

This light beam is reflected by the information track C (sickle surface) 7, which has an uneven bit shape, and is reflected by the objective lens! The light enters the polarizing prism J through the light beam and the 1/4 wavelength plate.

The reflected light incident on the polarizing prism 3 is passed through a 14-wavelength plate...
Because the light is polarized in a direction perpendicular to the plane of the paper due to the action of h, this light is reflected by the polarizing prism J. Polarized priz A
The parallel light beam reflected by the reflective surface 9 enters the detection beam t, and the light beam reflected by the reflective surface 9 is received by the detector 10.The reflective surface 9 detects the incident light beam (parallel light beam) in the focused state. The angle is set so that the angle is approximately the critical angle. In this way, in the focused state, all the rays reflected by the polarizing prism J will be totally reflected by the reflecting surface D (actually, since the condition of the reflecting surface is not perfect, some light will be reflected in the direction n shown in the figure). ), when the disc 6 deviates from the focused state in the direction a, the polarizing prism J
The nine luminous fluxes reflected by the reflective surface 9 have a maximum of ai1 to a1
This results in a beam of light having an inclination component shown by 2. t disk 6
When the disc 4 deviates from the focused state in the direction b, the incident light beam on the reflective surface 9 becomes a bundle of rays with an inclination component shown by bil'' The light rays change continuously before and after the critical angle, except for the central ray on the optical axis (dotted chain line).Therefore,
When the disc ≦ is displaced in the a and b directions and is out of focus, the reflection intensity at the reflective surface t changes rapidly with a slight change in the angle of incidence near the critical angle, and the light flux incident on the reflective surface t changes rapidly. There is a brightness and darkness in the reflection intensity along the plane perpendicular to the plane of the paper containing the central ray, and the brightness and darkness are reversed depending on the direction of movement of the focal point. On the other hand, in the focused state, the light is totally reflected uniformly, so no such brightness or darkness appears.
The photodetector 10 detects changes in the light intensity distribution of the reflected light from such a reflecting surface, so it divides the central ray (optical axis) into blocks, as shown in the plan view in FIG. It is composed of two divided light receiving areas lOm and lOB.

Now, when the disk 6 is displaced in the direction a, among the lights that are incident on the reflective surface 9 of the detection prism l, the light flux below the center ray in the figure is led by the outermost incident light II ail. As, the angle of incidence of all incident rays is smaller than the critical angle. Therefore, there is transmitted light in this part,
A bundle of light rays including the outermost transmitted light ray "tl to nt" is transmitted.The outermost reflected light 1Ia is equal to this transmitted amount.
The intensity of the reflected ray bundle including from the beam r to the central beam a is weakened.

On the other hand, among the light incident on the reflective surface D of the detection prism L,
For the luminous flux above the central ray in the figure, the incident angles of all the incident rays are larger than the critical angle with the outermost incident ray ail as the basket head. Therefore, there is no transmitted light in this part, and all the incident light rays are reflected as being included in the light flux including the outermost reflected light Mars to the central light 4I. Therefore, in this case, the light intensity distribution on the photodetector /# is such that the light receiving area 10mm becomes dark and the light receiving area 〆0mm becomes dark.
B remains bright and does not change.

On the other hand, when the disk 4 is displaced in the b direction, the reflective surface! The relationship between the inclinations of the incident light beams on the photodetector 10 is opposite to that in the a direction described above, and therefore the area 10 of the photodetector 10 is
The relationship between the brightness and darkness of lOH is reversed, and the light-receiving area lσm remains bright (11), but the light-receiving area 10B becomes dark. In this case, the reflected light and the transmitted light at the reflective surface t are indicated by the symbols brl a t) rB and btR, respectively.

Note that in the focused state, the light receiving area IOkat of the photodetector 10
o The amounts of light incident on B are equal.

Therefore, by detecting the difference between the outputs of the light receiving areas 10M and 10B using the differential amplifier II, a focus error signal representing the amount and direction of the shift can be obtained from the amount and polarity of the difference, and this signal Based on this, focusing control can be performed to control the movement of the objective lens S in the optical axis direction, and the sum of the outputs of the light receiving areas 10 and 10B is detected by an adder 12 and recorded on the disk 1. information signals can be detected. Moreover, in the focused state, there is almost no transmitted component on the reflective surface 9, so the loss of light quantity is extremely small, and when the focus is out of focus, the light beam on either side of the center ray is completely absorbed. light receiving area 1 because the reflected intensity of the light beam on the other side is extremely reduced.
The difference in light amount at 0m and /DB becomes significant. Therefore, focus detection can be performed with sufficient accuracy.

In the case shown in FIG. A 4Jl one-point error signal can be obtained by receiving the light with J photodetectors or by receiving the reflected light and transmitted light with rtJ photodetectors.

However, a drawback of the focus detection device having the above-mentioned configuration is that since the critical angle detection prism 1 is used, the optical head becomes larger and weighs 4 times more. Furthermore, since the reflective surface 9 of the critical angle detection prism l must be set at a critical angle, it is not easy to set the optical position of the critical angle detection prism or adjust the angle of the reflective surface in the detection prism. It is.

The fourth object of the present invention is to provide a focus detection device with a simple configuration that solves the problems in the conventional example as described above.

The focus detection device of the present invention includes a light source, and the light beam from the light source is focused and irradiated onto the irradiated object as a minute spot light!
an object lens, a means for guiding the reflected light flux of the minute spot light obtained through the objective lens by the irradiated object in a direction different from the light source; a photodetector that is provided at an angle with respect to the optical axis of the reflected light flux so as to receive the reflected light flux, and is divided into at least one segment with a direction intersecting the optical axis as a boundary; It is configured to correspond to the incident angle of the reflected light beam obtained from each light receiving area based on directional sensitivity characteristics, and to use the difference between the respective output signals as a focus-difference signal of the objective lens with respect to the irradiated object. It is characterized by:

The present invention will be described in detail below with reference to the drawings.

FIG. 2 is a diagram showing the configuration of essential parts of an example of the focus detection device of the present invention, and the same parts as those of the conventional device shown in FIG. 1 are designated by the same reference numerals.

That is, l is a light source such as a laser light source, c is a collimating lens, 3 is a polarizing prism having a polarizing film, and 1/4 is a polarizing prism.
A wave plate, S is an objective lens, and 4 is an object to be irradiated, for example, a video disk. Note that the polarizing prism J is an objective lens! gh corresponds to a means for guiding the reflected light flux from the disk ≦ captured by in a direction different from the laser light source l.
t 7t /J is provided so as to be inclined at an angle f0 with respect to the optical axis O so as to receive the reflected light beam from the disk 4 which is guided in a direction different from the direction of the laser light source by the deflection prism J, And the direction intersecting the optical axis 0 (
The photodetector is divided into one area symmetrically with respect to, for example, the optical axis 0, with a boundary (direction perpendicular to the plane of the paper) as a boundary, and consists of an optical area /11 and l#B.

In the above configuration, A* light (
Let's assume a turtle that prioritizes straight lines on the page. ) is converted into parallel light by a collimating lens, passes through a polarizing prism J having a polarizing film and a wavelength plate, and then passes through an objective lens! The beam is focused into a tiny spot of light and projected onto a disk containing information tracks. This light flux is reflected by the information track (recording surface) 7, which has an uneven bit shape, causing browning of the objective lens! and polarizing prism J via l/4 wavelength plate reference.
incident on . Disc incident on this polarizing prism J ≦
The reflected light flux from the %1/a wavelength plate is polarized in the direction perpendicular to the plane of the paper, so it is reflected by the polarizing film of the polarizing prism J and guided in the true direction of the -f light source, This reflected light beam enters a photodetector /3 provided to receive the light.

As shown in the plan view in Figure 1, the photodetector/J is
It is symmetrically divided into at least one light-receiving area l-mushi and l-B with respect to light-〇, and as explained earlier, it is arranged at an angle of 0 with respect to the optical axis 0 of the reflected light beam. be. However, the individual light-receiving regions 1# and 4B constituting the photodetector @/J are composed of, for example, photodiodes, and are designed to operate independently.

Sensitivity changes depending on the angle of incidence of light based on the directional characteristics of the sensor. Although the directional characteristics differ depending on the form of the cage, the directional characteristics for a case where the package surface is a flat glass and a lens with a flat surface are shown in FIG. Each light receiving area l#
The sensitivities of M and B vary independently according to the directional characteristics shown in FIG. 3 depending on the angle of incidence of the incident light.

In Figure 2, disk ≦ is the objective lens! ) When in the in-focus position, each light-receiving area array and l of photodetector II
Since the light beams incident on the reference B are both parallel to the optical axis 0 and have the same angle of incidence, the sensitivities of the respective light receiving areas l#m and /#B are equal. Now, when the disk 6 deviates from the in-focus position in the direction a, the nine beams reflected by the polarizing prism 3 are transmitted to the photodetector 1.
3, the incident light a1 becomes a bundle of rays with a maximum slope component represented by al -al, and the angle of incidence of the incident light a1 on the light receiving area l#m becomes smaller than 0 by an order of magnitude, and conversely, it enters the light receiving area /lB. The incident angle of the incident light a20 becomes larger than -. When the disc ≦ deviates from the in-focus state in the b direction, the photodetector 13
The incident light beam becomes a bundle of light beams having tilt components shown by b1 to b2, and the incident angle of the incident light b1 to the light-receiving area l-m is -
, and the angle of incidence of the incident light bl on the light receiving area te B becomes smaller than zero. That is, when the objective lens S is in focus with respect to the disk 6, the incident angle of the incident light entering each light receiving area is -;
deviates from the focused state, the incident angle of the incident light to each light-receiving area, except for the central ray on the optical axis 0, changes continuously around the incident angle 0 at the time of focus, depending on the direction of the focus shift. do. Therefore, the sensitivity of each light-receiving area l#m, /$B of the photodetector /J also changes according to the nine directivity characteristics shown in Fig. 3, depending on the incidence of the incident light incident on each. The relationship between the sensitivity of each light-receiving area #1 and B and the displacement amounts a and b of the disk 6 is as shown in FIG. That is, when the disk 4 shifts in the direction a, the sensitivity of the light receiving area/lm increases as well as the sensitivity of the other light receiving area 4B.
When the disk 4 shifts in the b direction, the opposite characteristics occur.In the in-focus state, each light-receiving area l#
The sensitivities of #B and /#B become equal. Therefore, as shown in Figure 1, each output of each light receiving area /#A, l#B of the photodetector 13 is guided to the differential amplifier 1) //, the difference between these two forces is taken, and this is calculated as the focus error. If extracted as a signal, this focus error signal will be the output of the differential amplifier n, that is, when the disk 4 is displaced in the a direction as shown in FIG. 5, and when the disk 4 is displaced in the b direction. Since the polarity of the focus error signal is reversed, the direction of defocus can be detected based on this polarity, and the amount of deviation of the disc base from the focus can be detected based on the amplitude of the focus error signal. Since the focus error signal becomes zero, the in-focus state can be easily detected.

In the above-mentioned embodiment, as shown in FIG. The output signal is an information signal reproduced from the disk t.

As explained above, according to the present invention, the in-focus state is determined by utilizing the sensitivity characteristic that changes depending on the light incidence angle of the photodetector provided at an angle with respect to the optical axis of the reflected light from the irradiated object. The detection prism has a reflecting surface set at a critical angle as shown in FIG. can be omitted, which not only simplifies the structure, makes it smaller and lighter, but also allows the angle of inclination of the reflected light beam of the photodetector with respect to the optical axis to be set so precisely, and the permissible range of the angle is wide. Therefore, the effects of the present invention are extremely large, such as ease of manufacturing and easy optical adjustment.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the main parts of an example of the configuration of an optical focus detection device developed by the author first, and FIG. 2 shows the main parts of the structure of an example of the focus detection device according to the present invention. Figures 1 and 3 are curves showing an example of the directional characteristics of a photodetector, and Figure 3 is a curve showing the relationship between each light reception of the nine photodetectors and the amount of deviation between the Shiro device and the distal. 3 are curve diagrams showing the relationship between the focus error signal and the pointless shift amount obtained by the present invention. ! ...laser light source, collimating lens, 3.
...polarizing prism, da...1/4 wavelength plate,! ...Objective lens, t...Video disk, 7...Information track, ll...Difference 1 amplifier, 12...Adder, /
3... Photodetector, 1llAll#B... Light receiving area of the photodetector. Figure 1 Figure 2 Figure 8 Incidence * (71) Figure 4 Figure 5

Claims (1)

[Claims] L: a light source, an objective lens that focuses a light beam from the light source and irradiates it onto an irradiated object as a minute spot light, and a light beam reflected by the irradiated object of the minute spot light obtained through the objective lens. means for guiding in different directions, and a direction that is inclined with respect to the optical axis of the reflected light beam so as to receive the reflected light beam guided by the means in a direction different from that of the light source, and a direction that intersects with the optical axis. and a photodetector divided into at least co-divided parts with the boundary being , and a difference between respective output signals corresponding to the incident angle of the reflected light beam obtained from each light receiving area based on the directivity part f% of the photodetector. What about the objective lens? A focus detection device characterized in that it is configured to generate a focus error signal for a projectile object.