DD269615A1 - METHOD FOR GENERATING LARGE BREAKDOWN DIFFERENCES IN COMPACT GLASSES - Google Patents

Abstract

The invention relates to a method which is suitable for generating high refractive index differences in compact glass samples by ion exchange of M exp + ions (M exp +: Li, Na, K, Rb) against Ag ions, with unusually low attenuation of the light propagation in achieved by interdiffusion modified areas of large lateral extent. According to the invention, this object is achieved in that glasses are used in the ion exchange process, which have an alkali content of 20-35 mol .-% and a content of M * O ind 3 (M exp III: B, Al, Ga), so the molar ratio M * O ind 3: M * O * is 0.8. The exchanged layers show no noticeable discoloration up to exchange temperatures of 400 degrees C, although refractive index differences of 0.1 to 0.15 are achieved. The attenuation (* 632nm) in the generated waveguiding layers is less than 1 dB / cm. These glasses are suitable for the production of inhomogeneous optical media in the field of imaging gradient optics or in fiber optic micro-optics.

Description

Field of application of the invention

The invention relates to a method which allows the generation of high refractive index differences of large lateral extent in compact glasses.

For this reason, this method for the production of inhomogeneous optical media, for. B. in the field of imaging gradient optics or optical fiber micro-optics suitable.

Characteristic of the known technical solutions

The generation of refractive index gradients by exchange of M ⁺ ions for Ag ions below the transformation state temperature of a glass is known and has already been described several times in the literature. Although in many cases relatively large exchange depths are achieved with at the same time sufficient refractive index changes, the transmission of the regions of large lateral extent modified in this way of interdiffusion is negatively influenced. Ag ⁺ ions interact with highly polarizable terminal oxygen ions on glass-forming anions? intense self-absorption (Jansen, M.-Angew. Chem. 91 [1979] 500), which is associated with a large Transmissiunreinschränkung in these glasses. In addition, colloidal particle staining caused by reduction of silver ions is frequently found (Peters, E. Diss. Clausthal, 1979; Giallorenzi, TG et al., Appl. Optics 12 (1973) 1240; Lagu, RK and Ramaswamy, O. Appl. Phys., Lett., 45, [1984] 117. The formation of such colouration caused by silver colloids increases with increasing basicity of the glass (Bastres, AW, J. Amer., Ceram., Soc., 30, [1947], 52 This effect is used technically in color pickling.

Guaker, R. and Urnes, S. (Phys. Chem. Glass 12, [1971] 64) on an aluminosilicate glass as a result of an exchange of Na ⁺ for Ag ⁺ ions by the action of an AgNO ₃ melt at 300 ° C colorless , but received a total of grayish-tinted glass samples, so that even in this case, a partial reduction could not be excluded.

Object of the invention

The aim of the invention is to develop a method for producing large refractive index differences in compact glasses, in which a transmission limitation is effectively prevented by color effects.

Explanation of the essence of the invention

The object of the invention is to achieve, by means of a large M / Ag interdiffusion coefficient in reasonable times, a sufficient exchange depth for use in the field of imaging gradient optics or optical waveguide microoptics with at the same time high transmission of the glass regions modified by ion exchange. According to the invention the object is achieved in that in the M ⁺ / Ag ⁺ ion exchange method, oxide glasses having an alkali oxide content of 20-35 mol% and a content of Mi ¹¹ O ₃ (M " ¹ : B, Al, Ga) are used in that the molar ratio Mj ¹¹ O ₃ to MjO sO, is 8 (M ¹ : Li, Na, K, Rb), in which case preference is given to glasses with a mixture of the oxides M] ¹¹ O _3. Such glasses are in contact with Silver or silver-containing mixtures, such as alloys, molten salts or solutions of all kinds, are then subjected to a heat treatment which corresponds to the particular intended use.

According to the invention, discoloration in the visible spectral range is effectively prevented in the process of MVAg ⁺ exchange by using the specially selected glasses by means of displacement of the absorption edge in the UV region and suppression of colloid formation.

embodiment

The essence of the invention will be explained in more detail by the following examples.

Table 1 lists, under the names 1 to 4, a selection of glasses and corresponding ion exchange conditions and the properties achieved in the exchange process: substrate glass refractive index n "; Refractive index increase at the

Surface An _n ,,,; Penetration depth x, ₀ % at which Δη has dropped to 1/10 of the surface value; Wavelength X ₅₀ (measured parallel to the direction of diffusion) at which the transmission is 50% and attenuation D (λ = 632 nm, measured perpendicular to the direction of diffusion) in the ion-exchanged layer.

Table 1

Glass 1 2 (AgNO ₃ J ₉₁ (NaNO ₃ 423 3 4 property 40.0 Composition in mol% 25 30 1.5100 25 30 Na ₂ O 25 30 0.15 25 30 Al ₂ O ₃ 12.5 30 450 50 30 B ₂ O ₃ 37.5 10 395 - 10 SiO ₂ 0.34 molar ratio 1.5 2 3 2 M ₂ O ₃ : M ₂ O *>. 9 Exchange with: 410 347 283 Austauschtemperat'jr / ° C 40.0 23.5 38.3 Replacement time / h 1.5096 1.502 1,510 η _o (λ = 632 nm) 0.11 0,055 0.15 An _mix (\ = 632 nm) 570 40 110 Penetration depth x _{) 0} % / um 350 360 - Aso / nm 0.7 - - Damping D / dB cm " ¹

Claims (2)

1. A method for producing large refractive index differences in compact, optically highly transparent glass bodies, characterized in that glasses with an alkali oxide content of 20-35 mol% and a content of Mi ¹¹ O ₃ (M ¹ ": B, Al, Ga) are used , so that the molar ratio M " ¹ to M ₂ O (M ¹ : Li, Na, K, Rb)> 0.8, and that these glasses brought into contact with silver or silver-containing mixtures such as alloys, molten salts or solutions of all kinds be subjected to a temperature corresponding to the intended use. 2. The method according to item 1, characterized in that the glasses used additionally contain up to 2 mol% of ZnO or P ₂ O ₅ or Nb ₂ O ₅ or TiO ₂ .