JPH10190943A - Image sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure of shielding stray light from the outside of a micro-lens, without the need for a photomask for forming a light shield layer and whose effect is not limited depending on a pattern of the micro-lens. SOLUTION: In a waveguide-type reduction image sensor, consisting of a light-emitting diode array lighting an original face, a micro-lens array 8 that collects a reflected light from the original face and makes the light incident onto a guide path, an optical guide path array leading a light collected by the micro-lens 1 and a charge-coupled element to convert reduced optical information from the optical waveguide path into an electric signal, a wedge-type grating 2 is formed to a light shield part which does not require refraction in a face of the micro-lens array 8 in which the micro-lens 1 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type reduced image sensor used in facsimile machines, digital copiers and the like, and more particularly to a one-dimensional microlens array.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional one-dimensional microlens array 8. The micro lenses 1 are formed in a row on a transparent substrate 7 by an injection molding method. The effective diameter of the lens 1 is 125 μm.

FIG. 5 is a diagram showing a structure in which a microlens array 8 and a waveguide array 9 are coupled to efficiently guide incident light to a waveguide. Light incident on each of the microlenses 1 having an effective aperture of 125 μm is condensed on the corresponding optical waveguide core section 10 having an entrance aperture of 8 μm square. Reference numeral 11 denotes an optical waveguide clad.

FIG. 6 shows a light-emitting diode (LED) array 14 and a micro-lens array 15 for making reflected light from a document surface 16 efficiently enter a waveguide.
And an optical waveguide array 13 for guiding light condensed to the microlens array 15 and a charge-coupled device (CCD) 12 for converting reduced optical information from the optical waveguide 13 into an electric signal. 1 shows an example of a waveguide type reduced image sensor. Micro lens array 15
Are designed such that each part of the image is focused on a separate optical waveguide 13.

Here, regarding the crosstalk from the adjacent lens, as shown in FIG. 7A, the numerical aperture NA ₁ = nsin α of the microlens 1 and the numerical aperture NA _wg = n ₀ sin θ of the optical waveguide core 10. = √ (n ₁ ² −n ₂ ² ). Here, n: the refractive index of the material of the microlens 1, a: the angle from the edge of the lens to the focal point is formed by a straight line, and the angle between the straight line and the optical axis of the lens, D:
Effective aperture, f: focal length of microlens, n ₀ : refractive index of the area where light enters, n ₁ : refractive index of core material,
n ₂ : refractive index of the cladding material, θ: light receiving angle. Therefore, each point in the region A in FIG. 7B forms an image on the waveguide incident surface, and is incident on the waveguide core 10. The other light 17 does not enter the waveguide core 10 because, for example, the region B has an angle larger than the angle coupled to the waveguide. Therefore, crosstalk can be prevented.

Light from the image area A on the document surface 16 is condensed by one microlens 1 corresponding to the light and enters one waveguide core 10. However, as shown in FIG. 8, light 18 passing through portions other than the microlens 1 enters the cladding portion 11 of the optical waveguide and the light receiving surface of the charge-coupled device (CCD). This results in stray light, which results in lower resolution.

Here, in order to block stray light in a one-dimensional or two-dimensional microlens array, the following methods have conventionally been proposed.

First, as a first method, a light-shielding layer having an opening with a diameter smaller than the diameter of the lens at the center of the optical axis of the lens is provided on the surface of the transparent substrate opposite to the surface on which the lens array is formed. Form. As a manufacturing method, a transparent substrate is prepared, and light is shielded by AL or the like by a lift-off method except for a part where a lens is formed. Thereafter, a microlens is formed in a portion that is not shaded by injection molding. As described above, a microlens array in which light is shielded except for the lens portion can be obtained. Next, as a second method, as shown in FIG. 9A, a support substrate 19 having an opening 19a through which useful light passes and shielding stray light is prepared. In the support substrate 19, a plurality of openings of a predetermined size are formed by photoetching a thin metal plate such as SUS, and the surface other than the openings is subjected to a re-masking process by a chemical process. Next, as shown in FIG. 9B, a resin film 20 serving as a microlens is overlaid on the support substrate 19. Further, as shown in FIG. 9C, a mold 21 in which the shape of the microlens array is inverted is arranged on the support substrate 19, and a mold 22 having a flat surface is prepared on the back side. Then, as shown in FIG. 9D, the resin film 20 is heated to a temperature equal to or higher than the glass transition point, and at the same time, the dies 21 and 22 are pressed to form the opening 19a.
And then cooled to a temperature below the glass transition point. Thereby, the microlens array 23 including the light shielding portion 19b can be obtained. (See JP-A-2-64501)

[0009]

In the case where a conventional microlens array having no light-shielding structure is used for a waveguide type reduced image sensor, light passing through portions other than the microlens does not enter the core portion of the optical waveguide. However, it becomes stray light that passes through the clad portion of the optical waveguide and reaches the light receiving surface of the charge-coupled device, making it difficult to increase the resolution.

Further, the above-described method of blocking stray light has the following problems. According to the first method, the surface of the microlens array opposite to the surface on which the lens is formed,
Since a light-shielding layer having an opening with a diameter smaller than the lens diameter is formed at the center of the optical axis of the lens, light from other than the lens can be blocked. However, in order to form a light shielding layer,
A mask having openings corresponding to the position, size, and number of microlenses is required. In this case, it is very difficult to adjust the center of the optical axis of the microlens and the center of the aperture in all lenses.

The second method is effective when there is an interval between adjacent microlenses. However, depending on the pattern of the microlens array, not only the effect of light shielding is limited, but also the manufacturing method is Very complicated.

The present invention has been made in order to solve the above-mentioned problems, and does not require a photomask for forming a light-shielding layer, and its effect is not limited by a pattern of microlenses. Provided is a structure capable of blocking stray light from outside the lens.

[0013]

According to the present invention, there is provided a light emitting diode array for illuminating a document surface, a microlens array for condensing light reflected from the document surface and entering a waveguide, and a microlens array for condensing the light. An optical waveguide array for guiding the reflected light;
Further, in a waveguide-type reduced image sensor having a charge-coupled device for converting reduced optical information from the optical waveguide into an electric signal, refraction is required among the microlens surfaces on which the microlenses are formed. A wedge-shaped grating is formed in a light-shielding portion that is not used.

In the above, the wedge-shaped grating is formed in parallel with the one-dimensional microlens array.

As described above, according to the present invention, by forming a wedge-shaped grating in a light-shielding portion that does not require refraction in a surface on which a microlens is formed, unnecessary light entering the outside of the lens can be wedge-shaped. The light is refracted out of the substrate by the lattice portion of the mold to block light to the charge-coupled device, thereby improving the resolution.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, the one-dimensional microlens array 8 is made of polymethyl methacrylate (PMMA).
865 lenses having an effective diameter of 125 μm are formed on a transparent substrate 3 having a length of 110 mm and a width of 3 mm by an injection molding method. Then, a wedge-shaped grating 2 is formed on a light-shielding portion that does not require refraction in the same surface of the transparent substrate 3 where one lens is formed. An example of a method for manufacturing the microlens array 8 will be described with reference to FIG. As shown in FIG. 2A, a mold 4 for a microlens array is manufactured by coining using a lens processing jig 5. Next, as shown in FIG. 2 (b), an lithographic processing jig 6 such as a discharge electrode is provided on a light-shielding portion which does not require refraction.
To produce a wedge-shaped grid by electrical discharge machining. Then, as shown in FIG. 2C, a microlens array and a wedge-shaped lattice are simultaneously formed from the mold 4 by injection molding. Thereby, as shown in FIG. 1, a wedge-shaped grating 2 formed in parallel with the lens array of the microlenses 1 can be integrally obtained.

The microlens array manufactured as described above is combined with an optical waveguide and a charge-coupled device, and is assembled as an optical waveguide type reduced image sensor. As shown in FIG. 3, the light reflected on the document surface 16 is focused on the entrance of the optical waveguide core 10 in the microlens 1. However, light incident on the light-shielding portion that does not require refraction, that is, light incident on the surface on which the wedge-shaped grating 2 is formed is refracted on the slope of the wedge-shaped grating 2, and the optical path is bent out of the microlens substrate. Thus, the light does not enter the light receiving surface of the charge-coupled device. Therefore, unnecessary light from outside the lens can be blocked, and the resolution is improved.

[0019]

As described above, the present invention is directed to an optical waveguide type having a structure in which a wedge-shaped grating is provided in a light-shielding portion which does not require refraction in a surface of a transparent substrate on which microlenses are formed. It is a reduced image sensor, with a simple structure, can block unnecessary light from outside the lens and improve the resolution.

[Brief description of the drawings]

FIG. 1 is a diagram showing a microlens array provided with a light shielding structure of the present invention.

FIG. 2 is a diagram illustrating a method for manufacturing a microlens array provided with a light-shielding structure of the present invention.

FIG. 3 is a diagram showing the principle of light shielding according to the present invention.

FIG. 4 is a diagram showing a conventional -dimensional microlens array.

FIG. 5 is a diagram showing a coupling structure between a microlens array and an optical waveguide array.

FIG. 6 is a conceptual diagram showing a configuration of an optical waveguide type reduced image sensor.

FIG. 7 is a diagram illustrating a state of light guide of a microlens.

FIG. 8 is a diagram illustrating stray light outside the micro lens.

FIG. 9 is a view illustrating a method for manufacturing a microlens array provided with a conventional light shielding structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Micro lens 2 Wedge-shaped grating 8 Micro lens array 9 Optical waveguide array 12 Charge-coupled device 13 Optical waveguide substrate

Claims (2)

[Claims] 1. A light-emitting diode array for illuminating a document surface, a microlens array for condensing reflected light from the document surface and entering a waveguide, and an optical waveguide array for guiding the light condensed by the microlenses. Further, in the waveguide-type reduced image sensor having a charge-coupled device for converting the reduced optical information from the optical waveguide into an electric signal, the refraction of the microlens array surface on which the microlens is formed is reduced. An image sensor characterized in that a wedge-shaped grating is formed in a light-shielding portion that is not required. 2. The image sensor according to claim 1, wherein the wedge-shaped grating is formed in parallel with the lens array of the one-dimensional microlenses.