A DOUBLE-DIE MODIFICATION OF MICRO-PULLING-DOWN METHOD FOR IN-SITU CLAD CORE DOPING OF FIBER CRYSTAL/

A novel technique for single-crystal fibers cladding immediately in th e course of the growth process based on the micro-pulling-down (mu-PD) method has been proposed and verified. The principle of the double-di e-mu PD implies that the capillary nozzle provides capillary feeding t o the growing fiber simultaneously from the inner pipe channel with un doped melt and from the outer surface with doped melt. The menisci sha pe, melt flow outside the nozzle, control of the doped/undoped melt ra tio and process stability are discussed in terms of capillarity. Examp les of practical crucible design are discussed in connection with radi al dopant distribution. Mn-doped lithium niobate fiber, 0.5 and 0.7 mm in diameter, having 40-60 mu m doped outer area were grown successful ly.