JPS61261238A - Production of lens having refractive index distribution in axial direction - Google Patents

Abstract

PURPOSE:To obtain the titled lens, safely and readily by bringing a medium containing silver ions into contact with the surface of a plate phosphate glass material, and diffusing and introducing the silver ions thereinto by the ion exchange to form a refractive index distribution in the thickness direction of the flat glass. CONSTITUTION:A medium containing silver ions, e.g. a mixed molten salt of silver nitrate and potassium nitrate, is brought into contact with at least one side of a plate phosphate glass material, and the silver ions are diffued and introduced into the flat glass by ion exchange and form the concentration distribution of the silver ions. Thus, the refractive index gradient is formed in the thickness direction from the surface to the interior thereof. The part having the desired refractive index distribution is then cut out of the flat glass and the direction of the refractive index gradient is made in agreement with the optical axis to carry out grinding. Thus, the aimed lens having a great refractive index in the axial direction can be readily produced without using a diffusing cation having strong toxicity, e.g. thallium.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a low-aberration lens having a refractive index distribution in the axial direction.

[Prior Art] As is well known, in a spherical lens made of a homogeneous medium, the focal length of a ray passing through the periphery of the lens 1 is as shown in FIGS. 3A and 3B. This results in so-called spherical aberration, which is called shortening. There are ways to prevent this by combining lenses or using an aspherical lens, but as shown in Figure 4, it is possible to correct this by making the lens 4 from a medium that has a refractive index distribution in the optical axis direction. It is well known that this is possible (Note 1). Here, the ideal distribution of the axial refractive index distribution is nn(1+αZ)+ ・・・・・・・・・・・・(1
) (Note 1) This is a linear refractive index distribution n+αZ ・・・・・・・・・・・・・・・(
Even a distribution close to 21 is sufficiently effective in reducing spherical aberration (Note 2).

Note 1: E. W. Marchant “Gradient Index Optics” Academic Press, New York [E. W. Harchand “Gradient”
Index 0ptics ”Academic
Press New Work] (1978
) P106 Note 2: Keigo Iizuka, "Fundamentals of Modern Optical Engineering" Ohmsha (1980) P131 As for the manufacturing method of an axial gradient index lens such as S, conventionally, parallel planes were fabricated as shown in Fig. 5. A base material glass plate 3 with a base material 3 is immersed in a molten salt 2 containing cations selected from thallium (TIl), lithium (Li), and cesium (C8), and the ions are transferred to the glass plate 3 by ion exchange.
By diffusing the cations inside and forming a concentration distribution of cations, a refractive index distribution is formed in the thickness direction from the surface to the inside of the glass plate, and the necessary refraction is obtained from this base material glass as shown in Figure 6. The part with a rate distribution (the part surrounded by the dotted line 5
) is cut out and polished to make the lens 4.

[Problems to be Solved by the Invention] By using the method of immersion in the molten salt 2 containing cations selected from the above thallium, lithium, and cesium, the refractive index distribution can be approximated by equation (1) or (2). However, thallium (Tf) can be obtained as a diffused cation.
> has the problem of being highly toxic and difficult to handle, and although lithium (Li) and cesium (Os) are not toxic, TIl has the disadvantage of not being able to obtain a large refractive index difference. Furthermore, since the diffusion rate of all cations was low, it was difficult to make thick lenses.

Therefore, an object of the present invention is to easily manufacture an axially graded refractive index lens that is nontoxic and has a large refractive index difference.

[Means for Solving the Problems] In order to achieve the above object, the present invention brings a medium containing silver ions into contact with at least one side of a plate-shaped phosphate glass body, and transfers the silver ions to the glass plate by ion exchange. By diffusing into the glass plate to form a concentration distribution of silver ions, a refractive index gradient is formed in the thickness direction from the surface to the inside of the glass plate, and a portion having a desired refractive index gradient is formed from this glass plate. It is characterized in that it is cut out and polished with the direction of the refractive index gradient aligned with the optical axis.

[Effects of the Invention] The present invention uses silver ions as cations that provide a high refractive index when producing lenses with a refractive index gradient by the molten salt method, so they diffuse faster than thallium.
It is also less toxic and provides a higher refractive index difference than lithium or cesium.

Furthermore, since phosphate glass is used as the substrate glass material, coloring due to colloidal silver does not occur even if a large amount of silver ions are introduced.

[Example] Hereinafter, the present invention will be explained based on examples.

[11 As a glass substrate, P2O548%, Na202
AQN03 40%, K NO
Processed in 36G% (wt%) mixed molten salt. The refractive index distribution near the surface of this glass plate was as shown in FIG. A piece of glass was cut out from this plate at the position indicated by the dotted line in Figure 1, with a diameter of 1 cm x thickness of 1 cm, and a curvature of 1.3 cm.
When a lens with a diameter of cm is manufactured, the longitudinal aberration becomes as shown by the curve in Figure 2, and a conventional spherical lens without an axial refractive index distribution has a spherical aberration as shown in the curve a in Figure 2. can be significantly improved.

Example 2 P2O548%, N8202 in weight% as substrate glass
A glass plate containing 0
A lens with a diameter of 1.10-1, a thickness of 0.85 am, and a curvature of 1.82 cm was cut out after processing for 5 hours.
As shown by curve C in the figure, spherical aberration was significantly improved.

In any of the above Examples 1.2, no brown coloration due to colloidal silver, which normally occurs in silicates and borosilicates due to the introduction of silver ions, was observed.

[Brief explanation of drawings]

FIG. 1 is a refractive index distribution diagram of the glass plate of the present invention, FIG. 2 is an aberration characteristic diagram of the axial gradient index lens of the present invention, and FIG.
The figure is an explanatory diagram showing the spherical aberration of a normal spherical lens, No. 3B.
The figure is also a longitudinal aberration diagram, Figure 4 is an explanatory diagram showing improvement of spherical aberration by axial refractive index distribution, Figure 5 is a cross-sectional view of the manufacturing process of axial refractive index distribution glass by ion exchange method, and Figure 6 The figure is an explanatory diagram showing the refractive index distribution and the cutting position of the lens. Applicant: Hoya Co., Ltd. Representative: Tadashi Asakuraff(m)
m) fIL overturn (cm) Figure 3A Figure 3B Figure 4 Figure 5 Figure 6 Procedural amendment (Self-restraint Date of June 1985)

Claims (1)

[Claims] 1 Ag (
A refractive index gradient is created in the thickness direction from the surface to the inside of the glass plate by bringing a medium containing silver (silver) ions into contact with the glass plate and diffusing the ions into the glass plate through ion exchange to form a concentration distribution of silver ions. A method for manufacturing an axially distributed refractive index lens, comprising: forming a glass plate, cutting out a portion having a desired refractive index gradient from this glass plate, and polishing the glass plate so that the direction of the refractive index gradient coincides with the optical axis. .