JPS6212633A - Glass composition suitable for producing transparent material of refractive index distribution type - Google Patents

Abstract

PURPOSE:To form a glass composition capable of producing a lens of cesium- containing refractive index distribution type having high numerical aperture, which can be produced from an existing glass composition, by ion exchange method, by adding zinc and optionally other bivalent ions to parent material glass. CONSTITUTION:A glass composition suitable for producing a transparent material of refractive index distribution type comprising 30-75mol% SiO2, 2-25mol% Cs2O and 2-40mol% ZnO as essential components and 15-0mol% Na2O, 15-0mol% Li2O, 15-0mol% K2O, 15-0mol% B2O3, 15-0mol% Al2O3, 15-0mol% TiO2, 7-0mol% ZrO2, 5-0mol% Ta2O5, 7-0mol% Nb2O3, 5-0mol% WO3, 15-0mol% La2O3+Y2O3, 25-0mol% CaO, 25-0mol% MgO, 25-0mol% SrO, 25-0mol% BaO, 25-0mol% PbO and 0.5-0mol% As2O3+Sb2O3 as arbitrary components.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a glass composition suitable for producing a gradient index lens having a high number of cesium ions by ion-exchanging cesium ions in the glass with alkali ions. Related.

By immersing the glass in molten WA salt and continuously exchanging the alkali ions X+ contained in the glass with other alkali ions X2 in the molten salt, the concentration of X+ ions gradually decreases from the central axis of the glass to the periphery. The ion exchange method, which forms a parabolic refractive index gradient, is the most commonly used method for producing gradient index lenses because it has excellent human productivity and reproducibility.

The X1 ions contained in the glass, that is, the dopant ions, have a high electronic polarizability (TIl÷, C8
+, Rb÷, etc.) and those with a large ability to polarize other ions (Li+). When Tf'' is used as a dopant, the difference in refractive index between the central axis of the glass and the periphery is large due to its high electronic polarizability, and a lens with a high numerical aperture can be manufactured. In addition, T2-containing glass has large wavelength dispersion of refractive index and large chromatic aberration.
Another drawback is that the resolution is greatly reduced when white light is used as a light source.

In addition, when Li+ is used as a dopant, the ions that replace it are larger than Li+, so internal strain remains in the glass and cracks are likely to occur after ion exchange, so lenses with a large refractive index difference are used. There is an inconvenience that it cannot be manufactured.

For these reasons, there has been a long-awaited demand for a gradient index lens that uses C8+ as a dopant and has small chromatic aberration and a large difference in refractive index. However, when a lens is made by the ion exchange method using C5+ as a dopant ion, (1) the electronic polarizability is lower than that of Tf+, and a large refractive index difference cannot be formed between the central axis and the periphery of the glass (2) the diffusion rate is slow, and long ion If Cs1fi is increased in order to increase the C3+ refractive index difference, which requires replacement time and reduces productivity, if C5202025 mol% or more, the weather resistance of the glass deteriorates significantly, causing various problems such as making it unsuitable for practical use. Therefore, conventional cesium-containing gradient index lenses have a numerical aperture of 0.61 at most.
Only a limited amount is produced.

By incorporating zinc and, if necessary, other 2 (II) ions into the base glass, the present invention can produce a cesium-containing graded index lens with a high numerical aperture that could not be obtained with conventional glass compositions. The present invention provides a glass composition that can be produced by an exchange method.

That is, the glass of the present invention suitable for manufacturing a cesium-containing gradient index lens having a high numerical aperture has a mol% of 30
~75Si02.2~25C820 and 2~40ZnO
Contains 0 to 15 Na20 as an essential component, and 0 to 15 Na20 as an optional component.
, O~151 i20, 0~15 to 20.0~15B2
0z, 0~15Aj2203, O~15"102.
0~7ZrO2, 0~5Ta205, O~7Nb203
, O~5WO3, O~15 (L a 203+Y2O
3), 0~2508010~25Mg010~25Sr
O10~25Bao10~25PbO10~0.5(A
S203 +Sbz 03 ).

Next, the glass composition limited range will be explained in detail.

First, 5iOz is required in an amount of 30 mol % or more from the viewpoint of the weather resistance of the glass, but if it exceeds 75 mol %, the melting temperature of the glass becomes too high, making it inappropriate for practical use.

Also, it is preferably 15 mol % or less in order to contain the dopant C920 at a high concentration.

If the dopant C820 (1) is less than 2 mol %, the refractive index difference formed by the ion exchange method is too small and the effect as a lens cannot be expected.As the amount of C320fil increases, the refractive index difference can be increased. If it exceeds 25 mol%, it is unsuitable because the weather resistance of the glass will deteriorate significantly.As shown in Table 1, ZnO has the effect of particularly increasing the refractive index difference and increasing the ion exchange rate. In the present invention, a range of 2 to 40 mol% is allowed.

For NazO, in order to set the melting temperature of glass in an appropriate temperature range, the total amount of alkali (20 + L to C520 + Na2O +
iz O) is added for the purpose of adjusting the content to 15 to 30 mol%. In addition, 8203 is used for the purpose of lowering glass melting humidity.
, Li2O, and 20 in the range of 0 to 15 mol%, and Aj2 for the purpose of improving the chemical durability of the glass.
20x, TfOz, Zr'02, Ta205,
Nb2O2, La20:l.

Y203, CablMQO, SrO, BadlPbO
can be contained in the above-mentioned ranges, and further AszO3 and/or 5bzO3 can be contained as a refining agent in the range of 0 to 0.5 mol%.

The glass composition of the present invention as described above can be formed into a cylindrical, plate-like or spherical glass body, and if an ion exchange method is applied to the glass body in a conventional manner, the glass composition of the present invention can be obtained approximately as shown by the following formula. A high numerical aperture condensing lens having a radial refractive index distribution can be manufactured.

n (r)2 = no2 (1-g2r2) where, n
(r): refractive index at a distance r from the optical axis in a plane perpendicular to the optical axis no: refractive index at the central axis q: positive constant Below Examples will be described.

Example 1 Raw materials were weighed and mixed to obtain about 10 kg of glass, melted in a platinum crucible at 1300°C for 10 hours while preventing the generation of bubble striae, and then poured into a mold, molded, and slowly melted. It got cold. After slow cooling, it is processed into a round bar of 15s + iφ, and this round bar is immersed in molten potassium nitrate at a temperature near the yield point of each glass for a predetermined period of time for ion exchange, and then cut into a predetermined length. Both end surfaces were rtll P to form a lens. The refractive index (no) at the center of each lens made with various glass compositions, the refractive index difference (Δn) between the center and the periphery, the numerical aperture (N, A,) and refractive index distribution of the lens are The ion exchange time required to achieve the ideal distribution (1
°E,) are shown in Tables 1 and 2.

"Examples" in Table 1 are glasses having the composition range of the present invention, and "Comparative Examples" in Table 2 are glasses other than this. From the comparison of the graphs, when using the glass with the composition according to the present invention, a lens with a refractive index difference that is more than twice as large as that of conventional glass can be obtained, and the ion exchange time required to manufacture the lens can be reduced by 1. It can be seen that it can be shortened to /3 or less. (Left below) Example 2 In mol%, 44.3 S t 02.14.3 C
520°+2.5 82 03, 8.3 N82
01 1.6 K2 012.5 ZnO, 6,
The raw materials were melted and molded in the same manner as in Example 1 so as to obtain a glass having a composition of 3PbO, 0,05Sb203.0.15Δ3203. After processing into a plate with a thickness of 3.0++ un, it was poured into a potassium nitrate molten salt. The lens was immersed in water and subjected to ion exchange for 176 hours near the yield point (500°C), and then cut into appropriate dimensions and polished on both end faces to obtain a slab lens (see Figure 1). As shown in Figure 2 (A), (B), and (C), this slab lens has a refractive index distribution that gradually decreases in one direction from the center in the thickness direction toward the outer periphery -Yo and YO. The center of the lens (
The refractive index of P) is n. -1,5624, the refractive index difference between the relevant part and the peripheral part (Q) in the thickness direction is Δn = 0.0302
9. It was a slab lens with the number of frontages (N, Δ,) = 0.306.

[Brief explanation of the drawing]

Figure 1 shows the width 2XO, thickness 2Yo, and length 2 obtained in Example 2.
FIG. 2(A) is a perspective view of Zo's slab lens;
(B) and (C) show the refractive index distribution in the X direction, Y direction, and Z direction of the slab lens shown in FIG. 1, respectively. Applicant Hoya Co., Ltd.

Claims (1)

[Claims] In 1 mol%, SiO_2 30-75 Cs_2O 2-25 ZnO 2-40 Na_2O 0-15 Li_2O 0-15 K_2O 0-15 B_2O_3 0-15 Al_2O_3 0-15 TiO_2 0-15 ZrO_2 0-7 Ta_2O_5 0-5 Nb_2O_3 0-7 WO_3 0-5 La_2O_3+Y_2O_3 0-15 CaO 0-25 MgO 0-25 SrO 0-25 BaO 0-25 PbO 0-25 As_2O_3+Sb_2O_3 0-0.5 Gradient index transparent material A glass composition suitable for the production of.