JPH05224005A - Refractive index distribution type lens array body - Google Patents

Abstract

PURPOSE:To provide an optical system which facilitates the alignment of components and has high resolution with optical information transmission by optical interconnection, etc. CONSTITUTION:Plural refractive index distribution type lenses 2 whose end axis surfaces are both flat are arranged telecentrically while making an optical in common. The lenses 2 have a refractive index distribution represented by n (r)=n0[1-(gr)2+h4(gr)<4>] and the value of the coefficient h4 of the quadriterm is in a range of (-0.2)-0.6. An optical component is interposed in a gap part between the lenses 2 and the optical pattern output of the component is transmitted to another optical components interposed in a gap between other lenses; and simulation shows that above-mentioned telecentric optical system has higher resolution above the optimum value of the quadriterm coefficient of a conventional single refractive index distribution type lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a general-purpose optical system useful for constructing an optical system in the fields of optical information processing, optical computing, optical conversion, optical interconnection, and optical measurement.

[0002]

2. Description of the Related Art When a lens, a grating, a prism and the like are combined to form an optical system, alignment adjustment of the optical axis of each component is extremely complicated and many optical components or spatial modulators (hereinafter abbreviated as "SLM"). It is almost impossible to accurately align optoelectronic components such as detector arrays, LED arrays, semiconductor laser arrays (hereinafter abbreviated as “LD arrays”).

Further, since the mechanism for aligning and fixing these parts becomes complicated, there is a problem that it is difficult to secure the reliability of the optical system in size and temperature change after assembly.

In order to solve the above-mentioned conventional problems, the present inventor has previously proposed Japanese Patent Application Nos. 2-253831 and 2-2531.
-253830 has proposed the following optical information transmission device and its manufacturing method.

That is, in the apparatus disclosed in the above-mentioned prior application, a large number of lenses are coaxially arranged at equal intervals, conjugate image planes are formed between adjacent lenses, respectively, and the conjugate image planes between the conjugate image planes are formed. The spatial transmission of the light pattern is performed. In particular, when a gradient index lens is used as each lens, since the light input / output end faces of each lens are all flat, there are many advantages such as ease of component insertion and elimination of antireflection coating.

[0006]

However, in the case of constructing the above device with such a gradient index lens, in order to obtain high resolution for image formation between desired conjugate image planes, the lens is It is necessary to optimize the refractive index distribution of

Up to now, the optimum value of the refractive index distribution for such a coaxial lens array has not been clarified, but it is necessary to form the lens refractive index distribution so as to satisfy the conditions specified in the present invention. It was found by simulation that higher resolution can be obtained.

A first object of the present invention is to solve the complexity and difficulty of alignment and adjustment, the difficulty of miniaturizing an optical system, and the low reliability, and the second object of the present invention. Is
An object of the present invention is to provide an improved technique capable of obtaining high resolution for image formation between conjugate image planes in a coaxial lens array.

[0009]

A lens array is constructed by coaxially arranging a plurality of lens bodies having a refractive index distribution symmetrical with respect to a cylindrical axis of a substantially cylindrical transparent member. In the lens body, the light incident surface and the exit surface are planes perpendicular to the cylinder axis, and the refractive index distribution in the cross section is n (r) = n ₀ [1- ( gr) ² + h ₄ when expressed as (gr) _^4], h ⁴ is used which is within the range of -0.2 ≦ h ₄ ≦ 0.6. In the gradient index lens having such optical parameters, two adjacent lenses have a telecentric arrangement.

[0010]

According to the present invention, since other components can be inserted and fixed in contact with the end surface of the gradient index lens, alignment fixing of the optical system is easy, and at this time, the refractive index distribution is optimized. Therefore, high resolution can be obtained in the image formation between the conjugate image planes.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a side view along an optical axis of a lens showing an example of a lens array according to the present invention. In the figure, reference numeral 1 denotes a substrate made of glass, ceramics, plastics, etc., on which a gradient index lens (hereinafter referred to as "rod lens") 2 is arranged and fixed.

The rod lens 2 is, for example, a lens obtained by subjecting a cylindrical glass rod to ion exchange,
It has a refractive index distribution that is rotationally symmetric with respect to the central axis of the cylinder and that decreases from the center in the radial direction in a substantially square distribution in the radial direction. Due to this refractive index gradient, the light rays are bent inward in the rod and the convex lens Acts as. Such rod lenses 2 are arranged in multiple stages with the optical axis 20 in common.

In the present invention, each rod lens 2 constitutes an equal-magnification image forming system, and further, the respective rod lenses are arranged so that the conjugate image planes I ₁ , I _2, ... Of the rod lenses arranged in multiple stages become common. Adjust and fix the distance. That is, a unity-magnification imaging system is configured such that the conjugate imaging planes of the rod lenses arranged on the coaxial 20 are common to each other. I in Figure 1
All _{1 to} I ₄ are conjugate equal-magnification image planes. In practice, one unity-magnification (-1 ×) imaging system is
The rod lenses are arranged in a telecentric arrangement.

With the telecentric optical system as shown in FIG. 2, the brightness and resolution at each point on the image plane can be made equal by, for example, providing an appropriate stop on the Fourier transform plane, and the light exits from each point on the image plane. The principal rays of light can be made parallel to the optical axis at each conjugate image plane position, and multistage cascade imaging is possible.

Further, in the present invention, in the image formation of the telecentric optical system using such a rod lens, the refractive index distribution shape of the rod lens is set so as to obtain the highest resolution. That is, in the cross section of the rod lens, the refractive index n (r) at a point at a distance r from the axis is defined as n ₀ , which is the refractive index on the cylindrical axis.

N (r) = n ₀ [1- (gr) ² + h ₄ (gr) ⁴ ] Formula 1 is described. It can be said that in Expression 1, g is a parameter representing the focusing power, and h ₄ is a parameter for controlling the magnitude of aberration.

Until now, the aberration-free condition for meridional rays propagating in the continuous medium of a rod lens has been

[Number 2] _{n (r) = n 0 sech} (gr) = n 0 {1-1 / 2 (gr) 2 +5/6 (gr) 4 -61/90 (g r) 6 + ··} Formula 2 Was obtained analytically as (for example, S. Kwakam
iand J. Nishizawa, IEEE Tra
ns. Microwave Theory and T
echniques, 16 (1968) 814).

However, in the telecentric optical system as shown in FIG. 2, the above conditions are not necessarily optimum, and the present inventors newly performed a ray tracing simulation for the telecentric optical system to obtain the optimum value of the refractive index distribution. It was

FIG. 3 is a sectional view of the optical path of the optical system used in the simulation. As an example of the optical system, the lens diameter is 4 mm,
Lens length 4.2 mm, on-axis refractive index n ₀ = 1.608, g
Parameter = 0.1533, aperture stop diameter = 2 mm,
Using h ₄ as a variable, the focused spot on the equal-magnification conjugate plane at each image height was calculated by ray tracing. The working distance Wd was set to the best position of the focused spot in the vicinity of Wd = 5.3 to 5.5 mm in each calculation.

FIG. 4 is a calculation result showing the spot diagram on the conjugate image plane in the image formation of the on-axis object point and the geometrical optical diameter of the focused spot. From the figure, h ₄ = 5/6 = 0.833 which is an aberration-free condition (equation 2) in a continuous medium.
Than in this telecentric optical system, h ₄ = 0.58
It can be seen that the aberration of 6 is smaller.

However, in the case of h ₄ = 0.586, as shown in FIG.
As shown in (3), a large astigmatism occurs in off-axis imaging. For example when you suppress low the deterioration of the focusing spot within the image height 1.2mm in the same optical system, the range of h ₄ = 0.117~-0.117 as shown in the calculation result of FIG. 6 There is a need to.

From the above results, it is desirable to set h _{4 to} 0.586 when the image surface to be used is relatively small, and h ₄ = 0.117 to − when it is relatively large.
It can be said that about 0.117 is desirable. Therefore, in combination with these, for the telecentric optical system handled in the present invention, by setting h ₄ within a range of approximately −0.2 to 0.6, it is possible to realize good imaging with high resolution. I can say.

In such a telecentric optical system, a sufficiently long rod lens is fixed on a glass or ceramic substrate, and then a slicing machine or the like is used so that the lens length and the inter-lens gap become a predetermined length. It can be manufactured by forming a groove that divides the lens. Alternatively, individual rod lenses whose end faces have been polished in advance may be coaxially arranged and fixed.

[0023]

According to the present invention, it is possible to easily insert and position an optical component, which has been extremely difficult in the past, and to construct a high resolution optical system by optimizing the refractive index distribution of the telecentric optical system.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along the optical path of the telecentric optical system 1 unit in the embodiment of FIG.

FIG. 3 is a sectional view taken along the optical path of the optical system used for the simulation.

FIG. 4 is a diagram showing a calculation result of the size of a focused spot in the on-axis imaging of the telecentric optical system of FIG.

5 is a diagram showing a result of calculating a spot diagram at each image height under the best condition of on-axis imaging of the telecentric optical system of FIG.

6 is an image height 2.4 m of the telecentric optical system of FIG.
The figure which shows the result of having calculated the size of the focused spot in the range of m.

[Explanation of symbols]

 1 substrate 2 gradient index rod lens 3 insertion optical component 20 lens optical axis

Claims (1)

[Claims] 1. A lens array in which a plurality of lens bodies having a refractive index distribution symmetrical with respect to a cylindrical axis of a transparent member having a substantially cylindrical shape are coaxially arranged, and the lens body has a light incident surface and an exit surface. The surface is a plane perpendicular to the cylinder axis, two adjacent lenses of the lens array are arranged in a telecentric manner, and the refractive index distribution of the lenses is measured in the radial direction from the cylinder axis in the cross section. When n (r) = n ₀ [1- (gr) ² + h ₄ (gr) ⁴ ] is expressed with r as a distance, h ₄ is in the range of −0.2 ≦ h ₄ ≦ 0.6. A characteristic gradient index lens array.