JPS59152237A - Preparation of glass material having gradient of refractive index - Google Patents

Abstract

PURPOSE:To prepare an optically transparent glass material having gradient of refractive index free from light scattering, by sintering a porous glass material in an He gas. CONSTITUTION:In the preparation titled glass material wherein a solution of a dopant is penetrated into thin pores of a porous glass material, part of the dopant in the thin pores is eluted, so that gradient of concentration is formed in the dopant in the porous glass material, the dopant is precipitated on the thin pores, the porous glass material is dried, a solvent in the thin pores is volatilized, and the glass material is sintered to collapse the thin pores, the sintering is carried out in an He gas atmosphere. Even if a solution of a dopant having high concentration is used in stuffing, bubbles are not embedded in the glass material during sintering, and the optically transparent glass material having gradient of refractive index free from light scattering is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a glass body with a refractive index gradient, which is used as a material (preform) for optical transmission fibers or as a rod-shaped lens material.

A molecular stuff ink method is known as a method for manufacturing a glass body having a refractive index gradient. This method uses porous glass as a material and fills the pores with a dopant (refractive index modifying component).
Publication No. 07 teaches a method for manufacturing a glass body having a refractive index gradient by the molecular stuff ink method as well as a method for manufacturing porous glass as follows.

That is, by first heat-treating a borosilicate glass capable of phase separation under predetermined conditions, a phase rich in Sin, an alkali metal oxide, and B20. The phase is separated into a phase rich in Next, the glass is treated with an aqueous solution containing an acid, such as @acid, sulfuric acid, or nitric acid, to elute the easily soluble phase rich in alkali metal oxides and B2O3, and to elute the glass into continuous fine particles with the framework of the 8i02-rich phase. A porous glass having pores is prepared. Next, a dopant solution is stuffed into the pores of the porous glass body thus obtained.
A part of the dopant in the pores is eluted (unstuffed) from the h-41M side to form a concentration gradient in the donocent in the glass body, and then the dopant is precipitated in the pores and then removed from the glass body. A glass body having a refractive index gradient is obtained by drying the material and then subjecting it to a firing treatment to close the pores.

Applications of glass bodies with a refractive index gradient include rod-shaped microlenses for microlens arrays, microlenses for coupling optical communication fins and light sources, etc.
In order to obtain such a microlens, a glass body with a refractive index gradient must be optically transparent. In order to produce an optically transparent glass body using the molecular stuff ink method described above, the thermal decomposition products of the dopant precipitated within the pores must be removed before the pores are collapsed during the firing process. It is necessary to sufficiently expel the gas components from the pores.

By the way, according to the above-mentioned publication, a porous glass body is dried at a heating rate of 15 to 50”C/hour to a humidity of 50 to 150°C below the glass transition point of the porous glass body, and the temperature is After holding for 5 to 200 hours, normal pressure to 150
It has been proposed to sinter the glass body under a pressure of about mmHg at a temperature at which the π11) pores collapse. However, the firing to crush the pores is carried out at normal pressure or at
If the pressure is about mmHg, air bubbles that cause light scattering are likely to be trapped in the center of the rod in porous glass bodies stuffed with a highly concentrated dopant solution, making it difficult to form optically transparent glass bodies. It is extremely difficult to obtain.

The present inventors have discovered that the problems in the above-described firing process can be solved by firing a porous glass body in helium gas, and have created the present invention.

Accordingly, the method of the present invention provides Cs in the pores of the porous glass body.
N0. , TlN0. After stuffing a dopant solution consisting of a metal compound such as or a mixture thereof, a part of the dopant in the pores is unstuffed with or without precipitation of dopants into the pores to form a porous material. By forming a predetermined concentration gradient in the dopant within the glass body, and then immersing the porous glass body at low temperature in a solvent with low dopant solubility, such as methanol or ethanol, to replace the solvent in the pores. After stabilizing the precipitation of the dopant and then drying the porous glass body to volatilize the solvent in the pores, the glass body is fired in a helium gas atmosphere to collapse the pores, thereby creating optical properties. The process consists of obtaining a glass body that is transparent and has a refractive index gradient. In a preferred embodiment of the present invention, the dry porous glass body is heated to a temperature 50 to 100"C lower than the temperature at which the pores begin to open, in the atmosphere at normal pressure or in an oxygen atmosphere. The glass body is heated at a temperature of 1 at which it completely collapses in a helium gas atmosphere at a temperature increase rate of 50 to 150 C/hour.

According to the method of the present invention, the firing treatment of the porous glass body is performed by H
Since the process is carried out in an e-atmosphere, even if a highly concentrated dopant solution is used in the stuff ink, air bubbles are not confined within the glass body during the firing process. A transparent glass body can be obtained.

Examples will now be shown, but the present invention is not limited thereto.

Example electricity storage % Te8i0254.50, B2O334,30
, Na2O5, 20 and 206.00 was melted at 1450"C for 3 hours, stirred for about 1 hour during melting, poured into a mold, kept at 480"C for 2 hours, and then left in a furnace. After cooling, a glass block was obtained. A glass rod cut out from this block with a diameter of about 4 mm and a length of 76 mm was heat treated at 540° C. for 120° to cause phase separation.

The phase-separated glass rod was then treated in a 1.5N aqueous H2SO4 solution at a temperature of 100''C for 12 to 24 hours to form a porous glass rod.

This porous glass rod weighs 110g per 100ml of water.
of TlNO3 at a temperature of 100"C.
Stuff ink was performed by immersing it for 4 hours, and then unstuffing was performed by immersing it in an aqueous solution containing 40 volumes of ethanol at a temperature of 8° C. for 20 minutes.

The unstuffed rod was then immersed in 0''C ethanol for 3 hours to precipitate the dopant into the pores, and then dried in the air. After that, the rod was fired according to the firing schedule shown in the attached drawing. That is, heat up to 700°C in air at a heating rate of 75"C/hour, and
After holding for an hour, the inside of the furnace was replaced with helium gas, after which the rod was held at 700"C for 2 hours in a helium gas atmosphere, and then heated to 900°C at a temperature increase rate of 75°C/hour,
It was held at 900''C for 4 hours and allowed to cool in the furnace.

The nine rods thus obtained were optically transparent glass bodies without light scattering and had a refractive index gradient.

[Brief explanation of drawings]

The drawing is an explanatory diagram of the firing schedule adopted in the example. Yasutani Glass Co., Ltd. Agent Masayuki Asakura

Claims (1)

[Claims] 1. After infiltrating the pores of the porous glass body with a solution of the dome and the ent, a part of the dome and the ent in the pores is eluted to create a concentration gradient in the dome and the liquid inside the porous glass body. A refractive index gradient is formed by forming a refractive index gradient, followed by precipitating the donor into the pores, then drying the porous glass body to volatilize the solvent in the pores, and then collapsing the pores by a firing process. In the method for producing a glass body for growing a glass body, the above-mentioned firing treatment is performed in a helium gas atmosphere.