JPH0252310B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] This is 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 blurring condition of the hologram is generated. By detecting 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, it relates to a method for detecting information on an uneven surface that is free from distortion and provides an image with good contrast. be.

Recently, with the development of a highly information-oriented society, various technologies related to the security of information processing systems have been developed. For example, personal identification systems that use fingerprints to replace conventional ID cards are beginning to be introduced to control access to computer rooms.

[Conventional technology]

As a means for inputting personal information such as fingerprints, an uneven surface information detection device using a total reflection filtering method as shown in FIG. 3 has been developed. This is composed of a transparent flat plate 1, a light source 2, a hologram 3, a detector 4, etc., and its function is as follows: When a finger 5 pressed against the transparent flat plate 1 is illuminated by the light source 2 from below the transparent flat plate 1, Since the light 7 scattered by the concave portion 6 of the fingerprint of the finger 5 passes through the air layer, the condition of total reflection is not satisfied within the transparent flat plate 1, and all of the light 7 is emitted to the outside.
On the other hand, among the light diffusely reflected from the convex portion 8 of the fingerprint, the light 9 reflected under the total reflection condition repeats total reflection within the transparent flat plate 1 and propagates to the right, and is reflected by the hologram 3 provided at the right end of the transparent flat plate 1. The total internal reflection condition is broken and the light is emitted to the outside. The detector 4 receives this light and can immediately detect the fingerprint. (Refer to Japanese Patent Application No. 60-41437) [Problems to be Solved by the Invention] In the conventional method for detecting uneven surface information using the total internal reflection filtering method described above, astigmatism occurs due to the difference between the created wavefront and the reproduced wavefront of the hologram. The drawback was that aberrations occurred and 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 little aberration and distortion.

[Means for solving problems]

Therefore, in the present invention, the transparent flat plate 10 and
Using an uneven surface information detection device equipped with a light source 11, a hologram 12, and a detector 13, the light scattered by the uneven object 14 pressed against the transparent flat plate 10 is guided directly to the hologram 12, and the blurring conditions of the hologram are determined. The convex information light that fills the area is guided to the detector 13,
The light from the concave portions and the other light from the convex portions are not guided to the detector 13 to obtain uneven surface information.

[Effect]

By reducing the distance between the subject and the hologram during hologram reproduction, it is possible to reduce aberrations due to differences between the hologram creation wavefront and reproduction wavefront, as well as differences in image aspect ratio.

〔Example〕

FIG. 1 is a diagram for explaining an embodiment of the present invention.

The apparatus used in this embodiment is similar to the conventional example explained in FIG. 3 in that it includes a transparent flat plate 10, a light source 11, a hologram 12, and a detector 13. Of the reflected light from the convex portion 15 of the specimen 14, the light 16 that 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 and the aspect ratio and astigmatism difference of the obtained image 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. Curve A represents the aspect ratio, and curve B represents the astigmatism difference. Indicated.

As shown in the figure, the shorter the optical path length, the better the astigmatism difference.
Also, the dotted line shown in the figure represents the permissible range of aspect ratio error, but if the permissible value is 5%, the optical path length is 27 mm.
It turns out that the following is good.

In this embodiment configured as above, as shown in FIG.
An object 16 that satisfies the bragg condition is diffracted by the hologram 12 and reaches the detector 13 as indicated by ◯. However, since all of the light 18 from the recess 17 of the subject 14 does not satisfy the Bragg condition, most of it passes through the air layer like a circle according to Snell's law. Also, some of it is diffracted like a circle, but because it is not blurred, 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 17 mm using the conventional total reflection filtering method explained in Figure 3,
If the angle of use of the scattered light from the object is set to 45 degrees and one total internal reflection is performed to distinguish between concave and convex portions, the thickness of the transparent flat plate will be approximately 6 mm, and there will be a difference between the detected image and the actual one. It is impossible to obtain an image because the object overlaps with the object.

〔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. This method has the advantage that there is no burden on verification, and is extremely useful in practice.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining an embodiment of the present invention,
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 diagram showing a conventional uneven surface information detection device. In FIG. 1, 10 is a transparent flat plate, 11 is a light source, 12 is a hologram, 13 is a detector, and 14 is a subject.

Claims (1)

[Claims] 1 Transparent flat plate 10, light source 11, and hologram 1
2 and an uneven surface information detecting device equipped with a detector 13, an uneven surface information detection device 1 is pressed against a transparent flat plate 10.
4 is directly guided to the hologram 12, the convex information light that satisfies the hologram blurring condition 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. A method for detecting uneven surface information, characterized in that uneven surface information is obtained in the following manner.