JPS63109401A - Image device - Google Patents

Abstract

PURPOSE:To prevent the rugged pattern working faces of Fresnel lenses from being damaged or deformed by arranging two transparent bases on which micro- Fresnel lenses are formed respectively on both front and rear faces of an image device so that the faces forming the micro-Fresnel lenses are turned to the inside of the device. CONSTITUTION:The image deice is provided with at least two transparent bases 10, 20 obtained by forming many micro-Fresnel lenses on one face of each base. These two transparent bases 10, 20 are arranged on the front and rear faces of the image device so that the faces forming the micro-Fresnel lenses, i.e. the rugged pattern working faces, are turned to the inside of the image device. The optical axes of the corresponding micro-Fresnel lenses on the front and rear faces coincide with each other. Consequently, the rugged pattern faces can be previously prevented from damage or dirt adhesion or damage for deformation due to other physical and chemical factors, so that the optical characteristics of the micro-Fresnel lenses can be maintained almost at constant values.

Description

DETAILED DESCRIPTION OF THE INVENTION Background of the Invention The present invention is used as an imaging optical system. In particular, it relates to image devices as equal-magnification imaging elements.

Rod lens arrays are known as 1-magnification imaging elements, and are widely used in optical and electrical machines such as copying machines, facsimile machines, and laser printers. As an alternative to the rod lens array, the applicant devised a smaller, lighter image device having a large number of micro-Fresnel medium lenses (for example, in Japanese Patent Application No. 61-189).
(See No. 808).

This image device includes a large number of micro Fresnel lenses as shown in FIG. 1 on both the front and back surfaces, and the lenses corresponding to one front and back are arranged so that their optical axes are aligned. As can be seen from FIG. 1, the Fresnel lens is composed of a large number of concave and convex circular patterns, both of which have a width A and a thickness D on the order of microns. Width A is several μm to 10 μm
degree.

The thickness D is often 2 μm or less. therefore.

These uneven patterned surfaces are easily damaged by dust.

There are problems in that dirt and the like are easily attached and difficult to remove. Therefore, damage to the uneven pattern due to scratches, dirt, and other physical and chemical factors.

A problem arises in that the optical characteristics of the micro Fresnel lens deteriorate due to deformation or the like.

SUMMARY OF THE INVENTION An object of the present invention is to provide a structure that can prevent damage and deformation of the concavo-convex patterned surface of a Fresnel medium lens as much as possible and maintain constant optical characteristics.

The image device according to the present invention includes at least two micro Fresnel lenses formed on the negative side.
It has two transparent substrates. These two transparent substrates are placed on both the front and back sides of the image device, and the surface on which the micro Fresnel lens is formed, that is, the surface processed with the above-mentioned uneven pattern, faces the inside of the image device. Features. The optical axes of the front and back micro Fresnel lenses corresponding to the front and back sides coincide with each other.

According to this invention, the concavo-convex patterned surface of the Fresnel lens formed on the substrate faces inside the image device and is not exposed to the outside. Therefore, this uneven pattern surface will not be scratched, dirt or other physical damage.

Damage or deformation caused by chemical factors is prevented. This makes it possible to maintain the optical properties of the micro Fresnel lens approximately constant.

DESCRIPTION OF THE EMBODIMENTS FIG. 2 shows an example of an image device according to the present invention, and FIG. 3 shows an enlarged cross-sectional view taken along the line ■--■ in FIG.

The image device shown in Figure 2 consists of two transparent substrates 1
0.20, and these transparent substrates 10 and 20 are fixed in parallel to each other with a constant interval between them by side plates 30 on both sides. Preferably.

The end face is also closed by the end face plate 3I to prevent dust from entering the inside of the image device from the outside.

A large number of micro Fresnel lenses 11.21 are arranged in two rows on the inner surfaces of the two transparent substrates 10.20. Micro Fresnel Lens 11
．． Reference numeral 21 has the same structure as shown in FIG. 1, and has a large number of concentric patterns of protrusions and recesses. Transparent base 1 & 10
．． The Fresnel lenses 11 and 21 formed in 20 do not need to be arranged in two rows, but may be in any number of rows. Preferably, the lenses in the first row and the lenses in the second row are arranged alternately (the ones shown are not staggered). Further, as shown in FIG. 3, the optical axes M of the corresponding Fresnel lenses 11 on the negative substrate 10 and the Fresnel lenses 21 on the other substrate 2° coincide with each other. FIG. 3 also shows how a same-magnification image can be obtained by the Fresnel lenses If and 21 on both the front and back surfaces. By changing the distance from the object (indicated by the solid arrow) to one of the Fresnel lenses 11, an image of arbitrary magnification (indicated by the dashed arrow) can also be obtained.

In this way, the textured LL surface of the Fresnel lens 11.21 faces inward of the device during imaging, preventing dust and dirt from adhering to its textured surface and causing damage. It can be prevented. Since the outer surfaces of the substrates 10 and 20 are flat, dust and dirt can easily adhere to them.

Can be removed. In this way, it is possible to keep the optical properties of the imaging device approximately constant.

The substrate 10.20 with Fresnel lenses in the above-described imaging device can be produced in various ways.

For example, an electron beam resist is applied onto a transparent substrate, a micro Fresnel lens φ pattern is drawn on the resist by electron beam lithography, and then.

Develop this resist. The residual resist film remaining on the substrate becomes the Fresnel lens 11 (or 21).

The remaining resist pattern on the substrate may be transferred to the substrate by dry etching to form a Fresnel lens.

Furthermore, a transparent substrate having a Fresnel lens formed on its negative side can also be produced by integrally molding it with a transparent synthetic resin using a previously prepared female mold.

This female mold can be made in various ways, for example, as follows.

An electron beam resist is applied onto a predetermined substrate, a large number of micro Fresnel lens patterns are drawn on the resist by electron beam writing, and then this resist is developed. Then, the remaining resist pattern on the substrate is transferred to the substrate by dry etching. This substrate becomes a female mold (see Japanese Patent Application No. 61-3419).

Alternatively, a female mold is formed by electroforming using the above residual film resist pattern as a male mold. That is, the remaining resist pattern is plated with metal.

After that, by dissolving the remaining film pattern and the substrate with an organic solvent, only the metal plating part is left (Tokugan Sho (i)
(See No. 1-3420).

In the production of the female mold described above, a female mold of one micro Fresnel lens is made, and a large number of identical micro Fresnel lenses are formed from plastic using this female mold,
The above substrates 10, 20 with Fresnel lenses can also be made by gluing these Fresnel lenses onto glass or plastic substrates.

In this way, a substrate with a large number of Fresnel lenses, and thus an image device.

Since mass production is possible, it can be provided at low cost.

The image device is not limited to one made of two transparent substrates with Fresnel lenses as shown in FIG. For example, a transparent substrate having a similar number of Fresnel lenses may be placed between the two transparent substrates 10 and 20. Further, by providing a partition (field stop) between adjacent Fresnel lenses from the substrate 10 to the substrate 20, it is possible to block flare light entering through the adjacent lenses.

[Brief explanation of the drawing]

Figure 1 shows the shape of the micro Fresnel lens, (A) is a perspective view, (II), (C) is (A)
It is a sectional view taken along the lines BB and C-C. FIG. 2 and FIG. 3 show an embodiment of this invention.
FIG. 2 is a partially cutaway perspective view, and FIG. 3 is an enlarged cross-sectional view taken along the line ■--■ in FIG. 10, 20...Transparent substrate. 11, 21...Micro φ Fresnel lens. Patent applicant Tateishi Electric Co., Ltd. Agent Patent attorney Kenji Ushiku (and one other person) Figure 2 Figure 3

Claims (1)

[Claims] At least two transparent substrates each having a large number of micro Fresnel lenses formed on one surface, these two transparent substrates being arranged on both the front and back surfaces of the image device, and the surface on which the micro Fresnel lenses are formed. An image device where the side faces the inside of the device.