JPS6274177A - Uneven surface information detecting method - Google Patents

Abstract

PURPOSE:To decrease an aberration caused by a difference of a generated wave front of a hologram and a reproduced wave front, and a difference of as aspect ratio of an image, by making a distance of a body to be inspected and the hologram approach at the time of reproducing the hologram. CONSTITUTION:Uneven surface information is obtained by using an uneven surface information detecting device which has been provided with a transparent plate 10 against which an uneven surface is pressed, a light source 11 for illuminating this uneven surface, a hologram 12, and a detector 13. This detecting device is constituted so that a beam which has been scattered by an uneven body to be inspected, which has been pressed against the transparent plate 10 is led directly to the hologram 12, and a projecting part information beam for satisfying a Bragg condition of the hologram 12 is led to the detector, but a beam from a recessed part and other beam from a projecting part are not led to the detector 13.

Description

[Detailed Description of the Invention] [Summary] A method for detecting information on an uneven surface, in which light scattered by an uneven object pressed against a transparent flat plate is guided directly to a hologram, and convex information light that satisfies the Bragg condition of the hologram is obtained. By detecting this with a detector, it is possible to obtain a distortion-free image with good contrast.

[Industrial application field]

The present invention relates to a method for detecting information on an uneven surface for detecting fingerprints, etc., and more specifically, to a method for detecting information on an uneven surface that is free from distortion and provides an image with good contrast.

Recently, various technologies related to the security of information processing systems have been developed with the development of a highly information-oriented society. For example, personal verification systems using fingerprints, etc., are beginning to be introduced to control entry into computer rooms, instead of the conventional ■D card.

[Conventional technology]

As a means for inputting personal information such as fingerprints, an uneven surface information detection device using a total internal reflection filtering method as shown in FIG. 3 has been developed. This consists of a transparent flat plate 1, a light source 2,
It is composed of a hologram 3, a detector 4, etc., and its action is such that when the finger 5 pressed against the transparent flat plate 1 is illuminated by the light source 2 from below the transparent flat plate 1, a concave area 6 of the fingerprint of the finger 5 is illuminated.
Since the light 7 scattered by the transparent plate 1 passes through the air layer, total reflection conditions are not met within the transparent flat plate 1, and all of the light 7 is emitted to the outside.

On the other hand, out of the light diffusely reflected from the convex part 8 of the fingerprint, the total immersion 1.1
The light 9 reflected under the condition repeats total reflection within the transparent flat plate 1 and propagates to the right, and the total reflection condition is broken by the bologram 3 placed at the right end of the transparent flat plate 1, ζ, = installed, to the evening part. Emits light. The detector 4 receives this light and can immediately detect the fingerprint. (Patent application 1986-41437
(Refer to the publication) [Problems to be solved by the invention] In the conventional method for detecting uneven surface information using the total internal reflection filter + moon/g method, astigmatism due to the difference between the created wavefront and the reproduced wavefront of the hologram 1 is caused. The problem was that the image was not clear.

The present invention was created in view of the above points, and an object of the present invention is to provide a method for detecting information on an uneven surface that has a simple configuration and can obtain an image with less aberration and distortion.

[Step F to solve problems]

, In the present invention, the transparent flat plate 10 and the light source 1
Using an uneven surface information detection device equipped with 1, 12 and 12, and a detector 13, we directly detect the light scattered by the object 14 that is pressed against the surface of the transparent V. 12, and the convex information light that satisfies Bragg stripe I/1 of the hologram is guided to the detector 13, and the light from the four parts and the other light from the convex parts are not guided to the detector 13 to obtain uneven surface information. It is characterized by obtaining.

[For production]

By reducing the distance between the plugged body and the hologram during hologram reproduction, it is possible to reduce the hologram's creation wavefront and re-L [aberrations due to differences in wavefronts and differences in image aspect ratio by 4].

〔Example〕

FIG. 1 is a detailed illustration of the present invention.

The apparatus used in this embodiment is the same as the conventional example explained in FIG. Of the reflected light from the convex portions 15 of 14, lTh l 6 (which satisfies the Bragg condition) is directly guided to the hologram 12 and detected by the detector 13.

FIG. 2 shows the relationship between the optical path length, image aspect ratio, and astigmatism difference in this embodiment.

In the figure, the horizontal axis represents the optical path length, the vertical axis on the left represents the aspect ratio, and the vertical axis on the right represents the astigmatism difference.
6. 2 shows the aspect ratio, and curve B shows the astigmatism difference.

As shown in the figure, the shorter the optical path length, the better the astigmatism difference.

Furthermore, the dotted line in the figure represents the permissible range of the aspect ratio error, and it can be seen that if the permissible value is 5%, the optical path length should be 27 m1 or less.

In this embodiment configured as described above, as shown in FIG. 1, out of the light from the convex portion 15 of the subject 14, light 16 that satisfies the Bragg condition is diffracted by the hologram 12 and detected as shown in It reaches vessel 13. However, since all of the light 18 from the recess 17 of the subject 14 does not satisfy the Bragg condition, most of the light 18 passes through the air layer -1 as 0 according to Snell's law. Also, some of it is diffracted like O, but because it is non-Bragg, it is weak and deviates in a different direction. Therefore, only the convex information light is detected and a fingerprint image is obtained.

In addition, when the optical path length is set to around 17111 by the conventional total reflection filtering method explained in Fig. 3, the utilization angle of the scattered light from the object is set to 45 degrees, and -times total reflection is performed to divide the light into four parts. In order to discriminate between convex portions, the thickness of the transparent flat plate would be approximately 6 mm, and the detected image would overlap with the actual object, making it impossible to obtain 7 images.

〔Effect of the invention〕

As described above, according to the present invention, a clear image can be obtained using an extremely simple method with less astigmatism difference than the conventional method, and there is no need for correction because the obtained image is free from distortion. The advantage is that there is no burden on verification.
Practical-L Extremely useful.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the present invention in detail, Fig. 2 is a diagram showing the relationship between the optical path length, the aspect ratio of the obtained image, and the astigmatism difference, and Fig. 3 is a conventional uneven surface information detection device. FIG. In FIG. 1, 10 is a transparent flat plate, 1] is a light source, 12 is a hologram, 13 is a detector, and 14 is a subject. 10...Transparent flat plate 11...Light source 12...Hologram 13...Detector 14...Object optical path length and length and width of obtained image Figure 2 shows the relationship between the ratio and astigmatism difference. Figure 3 shows the conventional uneven surface information detection device.1... Transparent flat plate 2... Light source 3... Hologram 4... Detector 5... ...Finger 6...Four parts of the fingerprint 7...Reflected light from the recesses 8...Protrusions of the fingerprint 9...Reflected light from the protrusions

Claims (1)

[Claims] 1. Using an uneven surface information detection device equipped with a transparent flat plate (10), a light source (11), a hologram (12), and a detector (13), an uneven object ( 14) The light scattered by the hologram (12)
The convex information light that satisfies the Bragg condition of the hologram is guided to the detector (13), and the light from the concave part and other light from the convex part are not guided to the detector (13) to obtain the uneven surface information. A method for detecting uneven surface information, characterized in that: