JPS593404A - Fiber opitcal system - Google Patents

Abstract

PURPOSE:To improve resolution by providing a transparent member between an optical fiber bundle and an original plane. CONSTITUTION:An optical fiber bundle 31 wherein glass fibers having 25mum diameter per piece are bundled is sandwiched by glass blocks 32, and glass plates 33, 35 are provided to the bottom end thereof. The surface of the plate 35 is painted black except the opening 35'. The image of an original 36 is made incident through the opening 35' to the bundle 31, from which the image is transmitted to an image sensor 34 and is read by the same. The parallel light which is made incident to the bundle from the outside by a cylindrical lens 37 condenses to the opening 35', and the original 36 is illuminated by the focusing light thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fiber optical system suitable for use in an image transmission or processing device that reads a document image as image information using an image sensor or the like.

In recent years, with the development of electronic technology, various types of image transmission and processing devices have become popular. In this glaze device, a reading unit is composed of an illumination system for illuminating the original, an imaging system for forming an image of the original, and an image sensor for converting the formed image into an electrical signal. is essential. Since an imaging lens is generally used as the imaging system, a long optical path length is required.

Therefore, looking at recent technological trends, compact document reading devices are being constructed by combining an imaging system that does not require a long optical path length and an image sensor that has the same width as the document. As an imaging system with such a short optical path length,
Fiber optics are often used. Fiber optics generally consist of a bundle of optical fibers constructed by orderly bundles of optical fibers that transmit light only along their length; When the image is incident, the image is transmitted to the other end.
2 is a glass block, 3 is an image sensor, 4 is a document surface, and 5 is illumination light. The resolution of the Koriyo 5 & fiber optical system is expressed as the highest (approximately 1/I, the reciprocal of the diameter η of one optical fiber) when the original surface 4 and the incident side end surface 1' of the optical fiber bundle are brought into close contact. It will be done. However, in this five-light configuration, there is not enough space for illuminating the document surface, so in reality, a certain distance (1) between the document surface 4 and the original fiber east end surface 1' must be maintained. The resolution at this time is the numerical aperture of one optical fiber ((N, A,) −5
inθ], as shown in Figure 2, approximately 1/(D
+21 (N, A, )) (However, considering θζ0, sin θ−tan θ is used). Here, parts common to those in FIG. 1 are given the same reference numerals. Therefore, in such a conventional fiber optic system, the end of the optical fiber on the image incidence side cannot be brought into close contact with the original, so there is a drawback that the resolution is low.

On the other hand, in the above optical system, the optical fiber part numerical aperture (N
, person, ) can improve the resolution. However, this 55-way fiber has a serious problem in that the amount of light that is effectively taken into the fiber is reduced.

The present invention was made to solve the above-mentioned drawbacks of conventional fiber optical systems, and aims to provide a bright (and high resolution) fiber optical system.

The present invention provides a fiber optical system in which an image of a document is input from one end of a bundle of optical fibers and the image is transmitted through the bundle of optical fibers, in which: The above object is achieved by arranging a transparent object having a uniform refractive index greater than 1.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 6 is a schematic diagram illustrating the invention in detail.

In order for the light ray to travel through the optical fiber 10 in FIG. 3, the refractive index of the core portion 11 of the fiber must be n
o, and when the refractive index of the cladding portion 12 is nl, the angle between the optical axis of the fiber and the light beam must be smaller than the angle ψ given by cos ψ-□(2) LO.

When a transparent parallel plate 16 outside the refracting wheel is placed on the image incident side end face of the fiber 10, the following relationship exists between the incident angle θ of the light beam incident on the parallel plate. From equations (1) and (6), ns jn
qy −n (5) is obtained, and further, from equations (2) and (4), sin θ−? (6) becomes. That is, even if a transparent flat plate is provided on the end face of the fiber on the image incidence side, the numerical aperture sin θ of the fiber optical system as a whole remains unchanged.

On the other hand, as shown in FIG.
When t is approximately equal to t, that is, when the transparent plate and the original are very close to each other, it can be considered approximately, and the larger t, the higher the resolution. Furthermore, even if a transparent object is not close to the IQ document as described above, the effect of increasing resolution can be obtained if it is placed between the input end of the original fiber and the document. be able to.

As described above, the present invention provides a fiber optical system that can improve the resolution without substantially reducing the numerical aperture and is bright (and has a high resolution).

Furthermore, if the distance I between the end surface of the optical fiber bundle on the image incidence side and the document changes, IJp, the illuminance of the document surface, and the resolution will vary greatly, so l cannot be kept constant, which is undesirable. In the conventional fiber optic system, there is nothing intervening between the end of the optical fiber bundle and the document, so it is difficult to keep l constant. In the present invention, by bringing a transparent object into close contact with the optical fiber bundle and placing it close to the original, as shown in P4 shown in FIG. It is to be kept in a safe place.

Furthermore, as in another embodiment of the present invention shown in FIG.
By providing a mask 25 with holes only at the necessary portions 24' of the document on the surface of the document 6, reflected light from unnecessary portions of the document can be restricted and resolution can be further improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in more detail below with reference to an example in which a fiber optic system of the present invention is used in a document reading device.

<Example 1> As shown in FIG. 6, an optical fiber bundle 31 consisting of a bundle of glass fibers (N, A, -0,35) each having a diameter of 25 μm is held between glass blocks 32,
At its lower end is a 5-inch glass plate 65 (1001 m thick).
) are glued with epoxy resin.

An image sensor (one pixel size 60 μm
X 6 D pm ) is provided. Further, the surface of the glass plate 650 is painted black leaving a necessary opening 65' to form a mask 65. And this opening 6
5/, the image of the original 66 is incident on the optical fiber bundle 61, the image is transmitted to the image sensor 34, and the original is read. In addition, the cylindrical lens 37 fitted to the cutout in one corner of the glass block '52 condenses parallel light incident from the outside onto the opening 65'.
It is illuminated by this focused light.

FIG. 7 shows the MTF (Modulat
ion Transfer Function) results on day 3 are shown. The conventional optical system does not have the glass plate 63 and the mask 35, and the end face of the original fiber bundle 31 and the original 36
When compared with the MTF 59 in the sub-scanning direction of a document reading device using a fiber optic system with fiber optics separated by 100 μm, it can be seen that the resolution of the fiber optic system according to the present invention is clearly improved.

<Example 2> As shown in FIG. 8, an optical fiber bundle 41 formed by bundling glass fibers similar to that in Example 1 is attached to a glass block 4.
2, the lower end of which is diagonally cut out and polished, a thin glass plate (thickness: 100 μm) 46 is adhered with epoxy resin, and the lower end is polished again. Furthermore, an image sensor 44 similar to that in the first embodiment is provided on the opposite end surface of the optical fiber bundle 410. The upper corner of the glass block 42 is also cut out like 42', so that the light incident thereon illuminates a necessary part of the document.

FIG. 9 shows the MTF (sub-scanning direction) of the document reading device of this embodiment. By comparing this figure with 68 and 69 in FIG. 7, it can be seen that even with the configuration of this embodiment, the fiber optic system of the present invention exhibits high resolution.

The fiber optic system of the present invention is applicable not only to an image reading device that uses an image sensor to read an image transmitted through a fiber as described above, but also to various devices such as a display device that directly emits a transmitted image onto a screen or the like. It can be used.

As explained above, the present invention improves resolution in conventional fiber optics by: 1) improving resolution without reducing brightness;

2) Make it easier to maintain a constant distance between the original and the fiber bundle.

6) A mask that blocks unnecessary reflected light from the original and improves resolution can be easily attached.

It has the following effects.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an example of a conventional fiber optical system used in a document reading device, Fig. 2 is a schematic diagram illustrating resolution in the conventional fiber optical system, and Fig. 6 is a detailed explanation of the present invention. FIGS. 4 and 5 are schematic diagrams showing one aspect of the present invention, respectively. FIG. 6 is a schematic diagram showing a first embodiment in which the present invention is applied to a document reading device, and FIG. 7 is a schematic diagram showing one embodiment of the present invention. 8th diagram showing the MTF versus the spatial frequency of the original in the first embodiment.
The figure is a schematic diagram showing a second embodiment in which the present invention is applied to a document reading device, and FIG. 9 is a diagram showing the MTF with respect to the spatial frequency of the document in the second embodiment. 10--Optical fiber 11--Optical fiber core portion 12--Optical fiber cladding portion 13--
・Transparent object 14...Manuscript side Applicant Canon Co., Ltd.") - H Shumoto Maki

Claims (3)

[Claims] (1) Inject the original image from one end of the optical fiber bundle,
In a fiber optic system that transmits the image through the optical fiber bundle, a transparent object having a uniform refractive index greater than 1 is disposed between the image incident side end surface of the optical fiber bundle and the original. Features a fiber optic system. (2) The fiber optic system according to claim 1, wherein the transparent object is placed in close contact with the optical fiber bundle and close to the document. (3) The fiber optic system according to claim 1, wherein a mask is provided on the surface of the transparent object (original 111) that transmits only an image of a necessary portion of the original.