JPS58200436A - Focus detecting device - Google Patents

Abstract

PURPOSE:To facilitate the control for setting an incident angle, by unifying at least an optical dividing element and a critical angle prism and setting the incident angle of a reflected luminous flux given from an object to be irradiated with control of the optical axis of the irradiating luminous flux. CONSTITUTION:The 2nd prism 8 and a critical angle prism 9 are formed into one body and fixed completely to each other. In such a constitution, the incident angle of an incident luminous flux to the prism 9 is set and fixed at a value equal to or little larger than the critical angle by moving a laser diode 1 by a movable fixing mechanism 14 and within a plane which is orthogonal to the optical axis O of a collimator lens 2. Therefore the position of the diode 1 is controlled and fixed so that the incident angle of the incident luminous flux to the prism 9 is set equal to or slightly larger than the critical angle to reflecting surfaces 10 and 10' of the prism 9. This can facilitate the control for setting an incident angle.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an apparatus for reading information sound by focusing a frequently used spot on nine information tracks recorded in a spiral or concentric form on a recording medium, for example, using an objective lens. In the present invention, there is provided a critical angle type focus detection device for detecting the in-focus state of an objective lens with respect to a recording medium.

The above-mentioned information reading device is conventionally known, and recording media containing information tracks include, for example, what is called a video disc. This video disc contains nine video signals and audio signals encoded into information tracks.
It is recorded as optical information such as optical transmission characteristics, reflection characteristics, and phase characteristics. The information recorded on the video disk is condensed onto the information track through the radar jtVr objective lens emitted from the radar ytis without turning it all over again, and the transmitted Xt reflected light modulated by the information track is Detect and read jobs. One of the features of such a power recording medium is that the recording density of information is very high, so that the width of each information track is extremely narrow, and the intervals between successive information tracks are also very narrow. In order to accurately retrieve the original information from an information track with such narrow convergence and pitch, the objective lens must always be in focus on the video disc surface, and the original spot on the disc surface must be kept in focus. The diameter must always be minimized. For this reason, in such an optical reading device, focus lens control is performed to detect the defocus of the objective lens with respect to the disk surface and to displace the objective lens in the direction of its optical axis based on this defocus signal.

FIG. 181 is a diagram showing the configuration of an example of a critical angle type focus detection device in a conventional optical reading *b device or the like. The multiplication table (linearly polarized in the plane of the paper) emitted from the laser light source 1 is converted into parallel light by the collimating lens 8, and the first
The light is focused through a prism 8, a quarter-wave plate 4 and an objective lens 5 onto a disk 6 containing information tracks. This light beam is reflected by the information track having a concave and convex bit shape, passes through the objective lens 5, the /4 wavelength plate 4, and the first prism 8 again and enters the second prism 8 having a deflection film. That is, since the reflected light incident on the first prism 8 is directed in the same direction perpendicular to the plane of the paper due to the action of the quarter-wave plate 4, this light passes through the polarizing film 5 and is directed to the eighth prism.
The light beam enters the critical angle prism 9 through the prism 8 of
Receives light at 1. The reflecting surface 10.10'd is set to have a critical angle with respect to the incident light beam (parallel light beam) in the focused state. In this way, in the focused state, the eighth blizzard
All the light rays that have entered the critical angle prism 9 through the beam S are totally reflected by the reflecting surface 10, 10' (actually, since the state of the reflecting surface is not optical, some light passes through), and the disc 6 deviates from the focused state in the direction a, the light beam incident on the critical angle prism 9 is reflected in the critical angle prism 90 in the direction 10.10'
It becomes a ray bundle with a tilt component in a direction that opens outward relative to the rays. When the mirror disc 6 deviates from the in-focus state in the b direction, the incident light rays on the reflecting surface 10, 10' become a bundle of light rays having an inclination component in a direction converging inward. That is, when the disk 6 deviates from the focused state, the incident light rays on the critical angle prism 90 reflecting surface 10°10' change continuously around the critical angle, except for the central ray on the optical axis (dotted chain line). . therefore,
When the disk 6 is at the first position in the a and b directions and deviates from the focused state, the reflection intensity at the reflections 1i110, 10' changes rapidly near the critical angle with a slight change in the angle of incidence, and the reflection surface 1
The reflected intensity of the light beam incident at 0 and 10' changes brightly and darkly at a plane perpendicular to the plane of the paper containing the central ray tube, and the brightness and darkness are reversed depending on the direction of movement of the focal point. On the other hand, when the light is in focus, it is totally reflected uniformly, so such brightness and darkness do not appear. Light detection @11 detects changes in the light intensity distribution of reflected light from reflection directions 10 and 10', and divides the central ray (optical axis) into two to create 92 light-receiving areas. , 11Bt.

When the disc 6 is displaced in the direction a, among the light incident on the reflective surface 10, ] 0' of the critical angle prism 9, the light beam C below the center ray in the figure is the outermost incident ray. 11, the angle of incidence of all incident rays is smaller than the critical angle. Therefore, there is a light transmittance in this part, and the intensity of the reflected light beam including the outermost reflected light ray to the center ray is weakened by the amount of light transmitted. On the other hand, among the light incident on the reflective surface 10.10' of the critical angle prism 9, the luminous flux C' above the central ray in the figure
As the outermost incident ray t-silver head, the angle of incidence of all the incident rays is also larger than the critical angle. Therefore, there is no transmitted light in this part, and all incident light rays are
It is included in a light beam that includes t from the outermost reflected ray to the center Jjt and is reflected. Therefore, in this case, the light intensity distribution on the photodetector @11 is such that the light receiving area ]1 is dark;
The light receiving area 11B remains bright and does not change.

On the other hand, when the disk 6 is displaced in the direction b, the relationship between the inclinations of the incident light beams on the reflective surfaces 10 and 10' of the critical angle prism 90 is opposite to that in the direction a described above, and therefore the light detection 9111 Area 11m.

The relationship between the brightness and darkness of the light receiving area 11B is reversed, and the light receiving area 1"1" remains bright and remains the same, but the light receiving area 11B becomes dark.

In addition, in the focused state, the light receiving areas 11 and 1 of the light detection @11
The amount of light incident on 1B becomes stronger.

Therefore, by detecting the output of each light receiving area 11 and IIB with the differential sound differential amplifier 18, it is possible to obtain a focal point I@difference signal representing the amount and direction of deviation from the l and polarity, and this signal It is possible to perform focus lens control to control the movement of the objective lens 5 in the optical axis direction based on By detecting the information signal! mouse. Moreover, in the focused state, there is almost no transmitted component at the reflective surface 10.10', so i
The loss of t is extremely small, and when the focus is out of focus, the light beam on either side of the center ray is totally reflected, and the reflected tonicity of the light beam on the other side decreases to the W end, so light is received. In region 11m, 1m of light in IIB becomes more difficult to reach.

Therefore, a 1jlK focus detection tube can be used.

In the focus detection device configured as described above, the angle of incidence of the incident light on the reflection 7110.10' of the critical angle prism 9 is set to 1-
Conventionally, the method of setting the boundary angle or a slightly smaller angle is to provide a coupling mechanism between the wI2 prism 8 and the critical angle prism 9 that can rotate the critical angle prism 8 once in the direction shown by the arrow. -field angle of incidence on the prism 9'yt
, 'gr, for example, a bale set at a critical angle, and both were fastened and fixed.

That is, in the conventional focus detection device using the critical angle method, the incident angle of the incident light beam to the critical prism 9 is set, and the critical angle prism 9 is transferred to the third prism, and then the angle of incidence is changed. Not only is it necessary to have a mechanism for connecting both pipes (6), but the mechanism is relatively large.
And it's too complicated.

Even with this constant accuracy, there is a drawback that p deviation may occur due to the 1ljjk variation over time. Especially the first prism and the second prism.
In the case of integrated prisms, the problem is that due to their heavy weight and large size, they tend to change over time, and are not fixed properly.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a focus detection device tv& in which setting of the incident angle with respect to the reflective surface of a critical angle prism is carried out on the light source side which is sufficiently smaller than the critical angle prism. It is something to do.

The focus detection device of the present invention includes a light source, an objective lens that focuses and irradiates the light from the X* onto an irradiated object, and a source from the light source that guides the light to the objective lens and is reflected by the irradiated object and is directed to the objective. a light splitting element that guides the reflected light that has returned through the lens in a direction other than the source; plane at critical angle or more
A critical angle prism set to a medium-thick haze and a critical angle prism set to a wide angle detect changes in the amount of reflected light reflected by the reflective surface of the critical angle prism, and output a focus error signal of the objective lens with respect to the irradiated object. In a focus detection device comprising a photodetector, the light splitting element and the critical angle prism 1 are at least integrated, and the central ray of the reflected light flux from the irradiated object is incident on the reflective surface of the critical angle prism. the corner,
The present invention is characterized in that the original axis of the irradiation light beam from the light source to the object to be irradiated is set by using a piece.

That is, the present invention provides a focus detection device having a conventional configuration as described in FIG. If 1 is changed, the flat beam of light coming out of the collimating lens 2 remains parallel, just like when the optical axis 1 is tilted! : This was made by focusing on the generation of an inclination, and based on this principle, the incident angle tube of the reflected light beam from the disk 6 to the reflection direction 10.10' of the critical angle prism 9, the critical angle prism 9t- Without turning the eighth prism 7 all the way, it is arranged to generally add to the critical angle or a medium or thicker angle than the critical angle with both of them tm attached.

FIG. 2 is a schematic diagram showing an example of the configuration of an embodiment of the present invention, in which the same elements as in FIG. 1 are designated by the same reference numerals.

In the figure, a light source l, such as a laser diode, is provided with movable fixing means 14 configured to be movable and fixed within a plane intersecting the optical axis 0 thereof. First, second
The prism 8 and the critical angle prism 9 are integrally formed, and the distance between them is completely [i! It looks like it has a redundant shape.

In such a configuration, the angle of incidence of the incident light beam on the critical angle prism 9 is determined by adjusting the angle of incidence of the beam of light incident on the critical angle prism 9 by adjusting the laser diode 1 to the collimating lens 2 by the movable fixing mechanism 4.
It is moved within a plane orthogonal to the 0 optical axis and set to a critical angle or slightly wider than that, and then fixed by the movable fixing means 14. That is, by moving the laser 1'11 diode lt in a plane perpendicular to the optical axis o6c, the parallel light beam from the collimating lens 2- is
81st! Tilt while maintaining parallelism as shown by the dashed line to gl! [Arises. This light flux passes through the first prism 8, the V4 wavelength plate, and the objective lens i, and then irradiates the disk 6, and the reflected light flux passes through the objective lens 5, the first prism 8, and the polarizing film again, and then the second prism 8. critical angle prism 9
incident on . In this case, the incident light beam that enters the critical angle prism 9 is a parallel light beam if the objective lens b is focused on the disk 6. Therefore, the angle of incidence of the incident light beam on the critical angle prism 9 in this parallel light beam state is
Reflection of its critical angle prism 9 iii 10 , ] 0
The position of the laser diode may be adjusted and fixed so that the critical angle (or something like that) becomes a somewhat arbitrary angle. With this configuration, when the disk 6 is in the focused state as shown in FIG.
', and the focal 1M difference signal obtained from the differential amplifier II & 13 is zero.

It is clear from FIG. 1 that when the lens deviates from the in-focus state in the a direction or the b direction, the focal point wA signal becomes opposite in polarity and becomes useless.

FIGS. 8 and 4 show how the disc The concrete means for adjusting the optical axis of the irradiation light beam for irradiation are shown in each tube.

That is, in FIG. 1, the collimating lens 2 is fixed? For example, the laser diode 1'f is moved by jtm within a plane perpendicular to the optical axis 0, thereby changing its inclination while maintaining a parallel beam. The movable fixing means 14 (see FIG. 2) is, for example, formed with a slightly thicker screw insertion hole of the laser diode 1 and movably attached to the laser diode 1f body within the same plane. The angle of incidence of the reflected light beam from the disk 6 in the focused state on the reflective surface of the critical angle prism is set in the state of focus, and after death, the body and the laser diode are fixed in twin with adhesive or the like. .

In addition, the one shown in Fig. 4 is configured such that the laser diode l and the collimating lens st are integrally formed, and can be rotated and fixed together by a suitable means. If the angle of incidence on the reflecting surface of the critical angle prism is set by adjusting the angle in the direction of K, then it is fixed.

As described above in detail, the focus detection device of the present invention integrates a critical angle prism and a third prism for guiding a reflected light beam from an object to be irradiated to the critical angle prism. This is because the angle of incidence of the light flux incident on the critical angle prism onto the reflective surface of the critical angle prism is set by adjusting the optical axis of the light flux irradiated from the light source to the irradiated object. However, there is no need for a mechanism for rotationally fastening the critical angle prism to the third prism, which is conventionally used in this type of focus detection device.

Therefore, according to the present invention, not only the structure can be simplified and the structure can be made smaller and lighter, but also the angle of incidence of the incident light beam on the reflective surface of the critical angle prism is set by the beam, so the angle of incidence can be set. It is relatively easy to adjust the angle of the lens.In addition, the critical angle prism and the second prism for guiding the reflected light flux from the disk to the critical angle prism are completely integrated. Therefore, there is an effect that the deviation of the incident angle of the reflected light beam from the disk that is incident on the critical angle prism due to static or environmental quality is reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an example of a focus detection device using a conventional critical angle method. FIG. 2 is a diagram conceptually showing the configuration of an example of an embodiment of the present invention. FIG. 4 is an explanatory diagram of different light source movable means. 1... Laser light source, 2... Collimating lens, 8...
...First prism, 4...1/4 wavelength plate, 5...
Objective Reno, 609. ,I,,21910. prejudice·:,
membrane, 8. $mt). 9...Critical angle prism, 10.10'...Reflecting surface, ]]...Photodetector, 11mm, 11B...Receiving area of photodetector, ]2...Difference Dynamic amplifier, 18...Adder, 14...V Applicant: Olympus Optical Industry Co., Ltd. Figure 3 Figure 4 Procedural amendment January 21, 1981 1, Jf display Showa 7 poems Patent Application No. 83228 2, Komei's Name Focus Detection Device: (Relationship among those who make corrections) Patent applicant (11; i7) Olympus Optical Co., Ltd., Specification page 1, No. 8 The claims in lines 11 to 4 of page 2 are corrected as follows: [2. Claim L5'e source and objective for concentrating and irradiating light from this light source onto an irradiated object. a lens, a critical angle prism configured to guide light from the light source to the objective lens, reflect it from the irradiated object, and separate the reflection in a direction other than the light source; and the critical angle prism. A focus detection device comprising a photodetector that detects a device change in reflected light reflected by the reflective surface of a prism and outputs a focus error signal of the objective lens with respect to the irradiated object, the light splitting element and the critical angle prism are integrated at least, and the incident angle of the central ray of the reflected light flux from the irradiated object that is incident in the reflection direction of the critical angle 1 rhythm is determined by the angle of incidence of the central ray of the reflected light beam from the irradiated object from the light source to the irradiated object. A focus detection device that is patented to be set by #shaping the axis.'' 2. On page 8, lines 18 to 19, ``inside the paper'' is corrected to ``in a plane perpendicular to the paper.'' 8. On page 4, lines 7 to 8, "in the direction perpendicular to the page" is replaced with "into the page," and in lines 11 to 18, [reflective surfaces 10 and 10' are... . . ” is replaced by “The critical angle prism 9 has a reflected light beam (at the time of focusing) from the disk 6 that is incident on its reflection directions 10 and 10'.
The angle of incidence of parallel light) is corrected. Naru, "conventional" in line 18, page 8, "conventional", 1st
Correct "critical prism 9" in line 4 to "critical angle prism 9" and correct "1 rhythm of @2" in line 16 to "second 71J rhythm 8." 5. On page 9, lines 16 to 18, the phrase ``Slightly thicker than the center ray of the reflected light beam'' is replaced by ``reflection of the center ray of the reflected light beam.'' The angle of incidence on the surface should be at or slightly smaller than the critical angle.'' 6. In the same @1og line 19, ``for zum 7'' is corrected to ``as for zum 8, like the conventional one'', and in line 20, ``thick'' is corrected to ``small.'' 7. “σ to critical angle prism 9” in line 11 of @111R
J' to [critical angle prism 90 reflecting surface 10.10']
And, by moving [move f4,...music...people's eyes] in line 16, the inclination of the optical axis is changed and #adjusted, and the angle of incidence in the focused state is "It should be at or slightly smaller than the critical angle," they each corrected. 8 Change “1/, wave plate” in the first line of the same No. 1 gjij to [1/
6 waves M & 4j and "large" in the 11th row "small"
and "critical angle prism" in line 16 is corrected to "critical angle prism 9." 9 "Figure 1" in line 7 of M18 Tei is changed to "Figure 8".'
In lines 1s16 to 1), change "the angle of incidence to the reflective surface of the critical angle prism" to "reflection direction of the critical prism 9, 10, I
The angle of incidence on O' is corrected to be at or slightly smaller than the critical angle. lO same mxi*M+-ff ~5 lines (IJ rllll
F angle y IJ ” and “@2 prism” in line 9 are corrected as “light splitting element, eg, second prism J”.

Claims (1)

[Scope of Claims] L: a light source; an objective lens that focuses and irradiates light from the light source onto an irradiated object; and a light source that guides the light from the light source to the objective lens, and reflects the light from the irradiated object to the object. a light splitting element that guides the reflected light that has passed through the lens and returned in a direction other than the light source; and a reflecting surface for the central ray of the reflected light beam separated by the light splitting element A critical angle prism is set at a critical angle or slightly thicker than the critical angle prism, and a light change tube detects the reflected light reflected by the reflecting surface of the critical angle prism, and the objective lens is focused on the irradiated object. A focus detection device comprising a photodetector that outputs an error signal, wherein the light splitting element and the critical angle prism are at least integrated, and the reflected light beam from the irradiated object is incident on the reflective surface of the critical angle prism. A focus detection device characterized in that an incident angle of a central ray is set by adjusting an optical axis of a beam of light irradiated from the light source onto an object to be irradiated.