JPS62242913A - One directional refractive index distribution type slab lens array - Google Patents

Abstract

PURPOSE:To efficiently make an incident light quantity transmit through, by superposing plural pieces of slab-shaped refractive index distribution type lenses of a focusing property, having a refractive index distribution in only one direction, along the direction of the refractive index distribution so that the refractive index distribution and the vertical surface contact, and the refractive index distribution becomes parallel to each other. CONSTITUTION:In the rectangular parallelopiped-shaped glass, the X direction and the Z direction have no refractive index gradient, only the Y direction has such a refractive index gradient as the refractive index decreases to a prescribed quantity from the center surface of the rectangular parallelopiped to the upper and lower directions, and the Z direction is taken in the optical axis, it can be taken greatly in length of the X direction as long as the manufacturing condition of a slab is allowed. Also, with respect to a light beam which has been made incident along the Z axis, the X direction has no lens effect at all, but in only the Y direction, an incident light transmits through as a sine wave. Accordingly, when length of the lens is adjusted to length of 3P.4 from P/2, an image distance and an object distance become equal in the Y direction, and an erect unmagnification real image can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a slab-shaped lens array used in the field of optical communication and optical information processing equipment.

[Prior Art] Along the radial direction from the central axis of a cylindrical glass body, the refractive index is approximately n(r) 2 = no 2 (1-g2 r2 )
(11 or n(r)=no (1-j-Ar2) +2
1 (where nr is the refractive index at radius r, no is the refractive index at the center, and Q and A are constants.) The gradient index rod lens, which decreases according to is attracting attention as In particular, microlens arrays in which a large number of such lenses are arranged are used as image-forming optical systems and transfer lenses for copying machines and mini-faxes, contributing to miniaturization of devices.

It is well known that the imaging state of such a zero rad lens body changes depending on the length of the lens. For example, [
``Development of New Ceramics'' (edited by Hiroaki Yanagita, Parti Kitano, p. 175, published by Kagaku Kogyosha). According to this, as shown in FIG. 4, the light beam incident on the rod lens 3 is transmitted as a sine wave within the meridional cross section,
If the length of one period of this optical path is P = 2π/A, then when the lens length is from P/2 to 3P/4, the image distance 11N2+ and the object distance flo become equal, and as shown in Fig. 5, the object distance 1 is On the other hand, each time an erect equal-magnification real image 2 is formed on the optical axis 4.

In addition, rod-shaped lenses that satisfy this condition are stacked in two or three stages as shown in Figure 6, and a required number of these stacked lenses are arranged in one direction to create a rod lens array. It is stated that a bright erect 1-magnification image can be formed by combining the light beams transmitted through the rod lens.

Here, the royal life-size real image formation conditions are! . =f+,
M (magnification)-1.

Such a rod lens array has a distance between the object and the image of l1l.
(Co-wavelength L"j2o +11 + +7o) is shorter than that of a normal lens, so it is useful for downsizing the transfer optical system of a copier or facsimile.

[Problems to be Solved by the Invention] However, in the conventional rod lens array, as shown in Fig. 6, the cylindrical lenses are in contact with the close lens at one point on the circumference, so the gap between the lenses is large. You can do a lot. To prevent stray light from entering and exiting between each lens,
The gap between the lenses is filled with a material that absorbs light, so
The light incident on the lens array is no longer transmitted through this portion, resulting in a loss of light intensity.

In the horizontal direction, some lens arrays do not necessarily require a single tip-shaped lens when transferring exactly the same image, for example when reading a bar code or when condensing light emitted from a linear light source such as an array light source in a straight line. There is no need to use it, and if a single-shaped lens is used, there is a drawback that the amount of light is significantly lost as described above.

[Means for solving the problem] On the other hand, in addition to the above-mentioned cylindrical lens, the gradient index lens has a refractive index lens that is almost only in the thickness direction, as already described in Japanese Patent Publication No. 61-5661). Equation (1) or (2
It is a light-converging slab-like lens that has a refractive index gradient in only one direction according to the formula.

That is, as shown in FIG. 7, the graded index slab lens 5 has no refractive index gradient in the X direction and Y direction in the rectangular parallelepiped-shaped glass, and only in the Y direction from the center plane of the rectangular parallelepiped in the vertical direction. The lens has a refractive index gradient such that the refractive index decreases according to equation (1) or (2).

Therefore, if two directions are taken as optical axes, the length in the X direction can be made as large as the manufacturing conditions of the slab lens allow. Furthermore, there is no lens effect at all in the X direction for light rays incident along the Z axis. On the other hand, since the Y direction has a refractive index gradient as in the case of a gradient index rod lens,
The incident light is transmitted as a sine wave in the Y direction. Therefore, when the lens length is adjusted from P/2 to 3P/4, the image distance in the Y direction is 111f. and object distance 111I
+ become equal, and an erect equal-size real image can be formed. This lens array is also useful for efficiently condensing light from a light source located away from the lens entrance end onto the exit side. When using a slab lens to linearly condense light rays emitted from a point light source or a line light source toward the output side, if the light source 9 and the lens are separated by a certain distance as shown in FIG. The direction, that is, the X direction! Although it can be made as large as the lighting conditions allow, there is a limit in the thickness direction, that is, in the Yl direction, so a part of the light beam is eclipsed.

Therefore, an object of the present invention is to provide a slab-like lens array that efficiently transmits the incident light D with almost no damage, and a further object of the present invention is to provide a slab-like lens array that eliminates vignetting of the luminous flux. There is.

[Means for Solving the Problems] In order to achieve the above object, the present invention comprises stacking a plurality of slab-shaped lenses in the direction of the refractive index distribution so that the perpendicular surfaces of the lenses are in contact with each other and the refractive index distributions are parallel to each other. By using a slab-like lens array realized by combining lenses, the amount of light incident on the lens array can be transmitted efficiently with almost no loss, thereby solving the problems of conventional lens arrays.

As explained with reference to FIG. 7, the graded index slab lens 5 constituting the lens array has a refractive index gradient in the rectangular parallelepiped glass in the X direction and the Y direction, but only in the Y direction from the central plane of the rectangular parallelepiped. It has a refractive index gradient such that the refractive index decreases according to formula (1) or ('2J) in the vertical direction, and if the Z direction is taken as the optical axis, the manufacturing conditions of the slab lens allow for the length in the X direction. It can be made as large as possible. Also, for light rays incident along the Z axis, there is no lens effect at all in the X direction, but incident light only in the Y direction is transmitted as a sine wave. Therefore, the lens length can be P/2 to 3P/
If you adjust the length to 4, the image distance in the Y direction! . and object distance β1 become equal, and an erect equal-magnification real image can be formed.

As shown in FIG. 1, when a large number of slab lenses 5 (three in the figure) are stacked together in the Y direction to form a lens array 10, the light beams transmitted through the lenses are combined to form a bright image in the Y direction. It becomes possible to form. Therefore, in the horizontal direction,
In other words, when an image that is exactly the same in the X direction is to be transferred, for example when reading a bar code or when condensing light emitted from a linear light source such as an array light source in a straight line, the perspective view is shown in Figure 2. As shown, there is almost no gap between the lenses and there is no boundary in the X direction as the glass is a single piece of glass, so it is possible to form an image without following the light. In terms of manufacturing, it also has the advantage that it can be manufactured through a simple process of stacking rectangular parallelepipeds, compared to stacking cylindrical lenses.

When one slab lens 5 is used to condense light rays emitted from a point light source or a line light source into a line on the output side, there is a limit in the thickness direction, that is, in the Y direction, as described with reference to FIG. As a result, part of the luminous flux is vignetted. However, as shown in FIG. 3, by combining slab lenses with a lens length of P/2 to 3P/4 in the thickness direction (Y direction with a refractive index distribution) to form a lens array 10. If we create the same magnification condition, the light from the light source located at the conjugate length position9
It is possible to always focus light on the conjugate length position in the opposite direction without waste. Of course, whether it is used as an imaging system or as a condensing system for light rays from a light source, stray light that enters from adjacent lenses beyond the aperture angle of the lens may be affected by the imaging characteristics of the lens array 10 or the condensing system. To avoid this, it is necessary to insert a coating agent between the lenses that absorbs the wavelength used, but compared to rod lens arrays that fill the gaps between cylinders, it is necessary to insert an absorbing coating agent on the upper and lower surfaces in advance. Stray light can be prevented with a simple process of stacking vapor-deposited or coated slab lenses.

[Example] Commercially available slab lens GLS25C (Cl = -, 0,0
84~0, 088, n0 = 1.47 numerical aperture N, A,
0.22, pitch length 71-75III11 thickness 3
．． 4n+a) lens with a width of 5mm.

The length is 44.5 mm, and by stacking three lenses in the direction of the refractive index distribution, that is, in the thickness direction, to form a 10.2 mm thick lens array, the same-magnification imaging condition is satisfied only in the thickness direction. An optical system with a conjugate length of 95.5 mm could be formed. When a plurality of slab lens arrays 10, which are similarly stacked in the thickness direction, are used in a light focusing system as shown in FIG. 3, the maximum angle of incidence on the slab lens is determined by the distance between the light source 9 and the lens.

When using the above commercially available slab lens, and thickness 2
．． Table 1 summarizes the distance from the light source that the lens array can receive when using a slab lens having the same optical constant as above at 5 mm, compared with the frontage angle of the slab lens.

Table 1 Relationship between possible entrance numerical aperture of slab lens array and light source distance *However, the number of frontages of slab lenses is N, A, -
0,22 Furthermore, the above commercially available slab lens GL325
When layering C, a black acrylic lacquer was sprayed as a light absorber to the adjacent surfaces, that is, the upper and lower surfaces in the thickness direction, and when these were layered, it was found that when no light absorber was used, 19 images with good contrast compared to
I was able to

[Effects of the Invention] As described above, the light-condensing slab lens array having a refractive index gradient in only one direction obtained based on the present invention transfers an equal image that fits in the lateral direction without a refractive index distribution. In some cases, it is possible not only to form an image with almost no damage to the light flux incident on the lens array, but also to form an image on the output side of the light rays emitted from a point or line light source, similar to a normal slab lens. It becomes possible to focus light on the shape of the object. Even more lens array! ! ! In terms of construction, it can be manufactured using a simple process of stacking rectangular parallelepipeds without the difficulty of stacking cylindrical lenses.

[Brief explanation of drawings]

Figure 1 is a side view of the unidirectional refractive index gradient slab lens array of the present invention, Figure 2 is a perspective view of the same slab lens used for barcode reading, and Figure 3 is a light source from the slab lens of Figure 1. Fig. 4 is a side view illustrating the optical constants of a gradient index lens, and Fig. 5 is a side view illustrating the formation of a royal equal-magnification real image using a conventional gradient index lens. 6 is a cross-sectional view of the rod lens array, and FIG. 7 is a perspective view of the gradient index slab lens.
FIG. 8 is a side view illustrating vignetting of light rays caused by a lens. 1...Object, 2...Image, 3...Rod lens, 4
...Optical axis, 5...Slab lens, 6...Object, 7
...image, 8...luminous flux, 9...light source, 10...lens array. Applicant Hoya Co., Ltd. Agent Masayuki Asakura Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. A slab-like gradient index lens having a light-concentrating property having a refractive index distribution in only one direction, with a surface perpendicular to the refractive index distribution in contact with the lens,
A slab lens array characterized in that a plurality of slab lenses are stacked along the direction of the refractive index distribution so that the refractive index distributions are parallel to each other. 2. The slab-shaped lens array according to item 1, characterized in that a material that absorbs light of the wavelength to be used is arranged on the boundary surface where the plurality of stacked slab lenses touch each other.