Since the gradient index material has important applications at photoelectric system, imaging system, and integrated-optical system. Now, researches on gradient index material containing silver ions are more popular, it is difficult to get glass with high silver content as silver ion is extruded from molten glass at the molten temperature. Two-step ion-exchange process including Ag +- Na+ and Na+ - Ag + ion-exchange is used to get gradient index. This paper is based on the research in our lab, by adjusting the glass composition to get a series of sodium-rich glass then drawing the fusioned glass into fiber with diameter of 1mm used for ion-exchange. We used mixed molten salt for ion- exchange, then we researched on the choice of silver salt, the advantage and disadvantage of mixed molten salt and single molten salt, and the coloring up problem after ion-exchange.
The β-eucryptite glass ceramics with negative coefficient of thermal expansion (CTE) is studied in this paper. And the coefficient of thermal expansion, the crystal phases and the structure are researched by XRD and SEM. The β-eucryptite glass ceramics with negative CTE is produced by glass crystallization method, and whose negative CTE of -103.7×10-7/°C (from room temperature to 200°C) is obtained, which can be used as fiber Bragg grating (FBG) substrate. The substrate shrinks with a rise in temperature which compensates for the Bragg wavelength shift with temperature. It can be confirmed that β-eucryptite glass ceramics have suitable thermal expansion characteristics for FBG.
For making Gradient index (GRIN) glass with silver ion, it is difficult to get glass with high silver content by normal glass moltening process because silver ion will be extruded from molten glass at the high temperature. For solving this hard problem, the two-step ion-exchange process based on sodium rich glass is applied to get GRIN glass containing silver ion. In this process, the matching between the temperature of glass soft point and the highest working point of silver molten salt is one of key technologies. In this paper, the sodium-rich glass was made as the glass substrate for silver ion-exchange. Then the glass composition was adjusted to get transparent sodium-rich glass with low soft point and high chemical stability. On the other hand, the silver salt with high dissociation temperature for ion exchange was studied. At last the glass substrate with low soft point and the salt source with high dissociation temperature were matched at the suitable temperature in order to improve ion-exchange process.