JPS616615A - Distributed refractive index type lens - Google Patents

Abstract

PURPOSE:To obtain the distributed refractive index type lens which has sufficiently small spherical and coma aberrations and is easily polished and assembled by allowing the lens to meet specific requirements. CONSTITUTION:The lens 1 is made of a transparent medium, such as glass and synthetic resin, having a refractive index N(Z) at distance Z from and end surface along an optical axis; one end surface 2 which is comprised of transparent medium expressed by the equation: N(Z)=Noo+No1Z is plane and the other end surface is an axially symmetrical surface with a radius 1/C1 of curvature. This lens has a refractive index distribution wherein the refractive index varies from the center 4 of the spherical end surface 3 to the optical axis 5 continuously according to expressions (1)-(3) and is constant in the surface perpendicular to an optical axis. When parallel luminous flux 6 is made incident from the side of the spherical end surface 3 of the lens 1 the flux is converted on a point 7 with small aberrations and a light source such as a semiconductor laser is arranged at the point 7 to obtain high-precision parallel projection luminous flux. In the expression, Noo and No1 are distribution constants, and C1 and C2 are curvature values of both lens surfaces; the surface is convex when C1>0 or concave when C1<0. Further, N1 and N2 are a maximum refractive index and a minimum refractive index on the optical axis respectively and Z is the distance on the basis of the curved surface side of the lens.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an axial gradient index lens, and particularly to a lens that collimates light from a light emitting element such as a semiconductor laser or condenses parallel light beams with low aberration. Regarding.

[Technical background and problems of the invention]

Lenses used for the above applications are required to have very low monochromatic aberration, especially spherical aberration and coma aberration, and to be inexpensive. Conventionally, for this type of use, an optical system composed of three to five spherical lenses having a uniform bright refractive index is known.

However, the above-mentioned conventional spherical lens has a large number of polished surfaces, ie, 6 to G surfaces, and is very expensive because polishing and assembly are time-consuming and costly.

A single lens with a refractive index distribution in the axial direction has been proposed to improve the above problem, for example, US Pat. No. 3,729.2! No. 3 describes an axial gradient index lens that reduces third-order spherical aberration and coma aberration. However, in the case of the lens disclosed in the above-mentioned patent, the fifth-order spherical aberration is so large that it is not practical as an optical system at the diffraction limit. This point is also described in Japanese Unexamined Patent Application Publication No. 2003-222232.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a gradient index lens that has sufficiently small spherical aberration and comatic aberration, is easy to polish and assemble, and is inexpensive.

[Summary of the invention]

The gradient index lens of the present invention that achieves the above object has the following features:
The refractive index N (Z
) is made of a transparent medium represented by N(Z)-NOO+NOIZ, and is characterized by satisfying the following conditions.

(,21G 2-.

(3) N1≧Halo/Za≧N where NOO and NOI are distribution constants, C1 and C2 are the curvatures of both end surfaces of the lens, 01>0 represents a convex spherical surface, and C1<0 represents a concave spherical surface. Further, N1+N2 are the maximum refractive index and minimum refractive index on the optical axis, respectively, and the distance z is the distance with the crystal surface side of the lens as a reference. Among the conditions (1) to (3) above, condition (1)
) and (2) indicate that one end surface of the lens is a flat surface and the other end surface is a spherical surface, and since one end surface is thus flat, polishing is easy. Condition (1) is a condition in which the absolute value of the amount of unsatisfactory sine condition becomes small; if this range is exceeded, comatic aberration increases and aberration becomes large for off-axis light. Condition (3) indicates the range of the maximum refractive index and minimum refractive index on the optical axis. If the range of condition 0) is exceeded, at least one of the absolute values of the spherical aberration and the amount of unsatisfactory sine condition will become large, making it impossible to obtain an optimal lens. Curvature of both lens end surfaces, refractive index distribution constant No O+ No ]-1 Maximum refractive index N1 and minimum refractive index N2 on the optical axis are conditions (1) or l
By selecting within the range specified in I), spherical aberration and comatic aberration can be kept sufficiently small as shown in numerical examples described later.

〔Effect of the invention〕

The gradient index lens according to the present invention has very small spherical aberration and comatic aberration, as is clear from the numerical examples described below.
Therefore, it is possible to collimate light from a light emitting element such as a semiconductor laser or to condense a parallel beam of light with low aberration.

[Embodiments of the invention]

FIG. 1 shows an axially graded refractive index lens according to the present invention, in which one end surface λ of the lens made of a transparent medium such as glass or synthetic resin is flat, and the other end surface 3 has a radius of curvature of /.
/C1 is an axisymmetric spherical lens, which is given a refractive index distribution that changes continuously from the center of the spherical end surface 3 in the direction of the optical axis j according to the above formula, and in the plane perpendicular to the optical axis S, there is no refraction. rate is constant. When parallel light beam B is incident from the spherical end surface 3 side of the above lens L, it is focused on point 7 with low aberration, and
If a light source such as a semiconductor laser is placed at the zero point, a highly accurate parallel emitted light beam can be obtained.

Table 1 shows numerical examples of the present invention. In Table 1, cl,
C2 is the curvature of the lens end surface (mm-1) + t is the center thickness of the lens (mm), NOO+NO1 is the distribution constant, Fb
Hahac focus (mm) and N15N2 are the maximum refractive index and minimum refractive index on the optical axis, respectively.

Aberration diagrams corresponding to Examples &l-&B in Table 1 are shown in Figs. 2 to 7. In the figure, the solid line indicates spherical aberration, and the dotted line indicates the amount of unsatisfactory sine condition.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIGS. 2 to 7 are aberration diagrams corresponding to numerical examples of the lens according to the present invention. Figure 1 Procedures Amendment Book July 1981 lb.

Claims (1)

[Claims] Refractive index N(Z) at a distance Z from the end face along the optical axis
is made of a transparent medium represented by N(Z)=N_0_1+N_0_1Z, and satisfies the following conditions (1) 0.95<1/C_1・(N_0_0N_0_1
)/(1-N_0_0<1.05 (2) C_2=0 (3) N_1≧1.618≧N_2 However, N_0_0, N_0_1 are distribution constants, C_1, C
_2 is the curvature of both end surfaces of the lens, C_1>0 is convex, C_2<
0 represents a concave spherical surface, N_1 and N_2 represent the maximum refractive index and minimum refractive index on the optical axis, respectively, and Z represents the distance from the curved surface side.