The device and method of manufacturing

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PROBLEM TO BE SOLVED : To prevent deposit from being stripped or destroyed due to rapid impregnation with a solution and to enable whole surface of the preform to be uniformly impregnated with the solution when soot-shaped deposit being optical fiber preform is impregnated with a solution of rare-earth compound in order to dope the deposit with rare earth element or the like, for example. SOLUTION : An impregnating solution 18 is stored in a storage tank 40 from a solution supply vessel 30 via a pump 24 and is poured into an impregnating bath 16 from the storage tank 40 by dead load through a divergence adjusting valve 38. A quartz glass tube 14 in which soot-shaped optical fiber preform is deposited is dipped into the impregnating solution 18 to be impregnated with the solution. The impregnating solution 18 in the impregnating bath 16 is circulated to the impregnating bath 16 through a recovery tank 44 and the pump 24. The opening degree adjusting valve 38 controls a pouring rate of the impregnating solution, that is, impregnation amount to the optical fiber preform to prevent the deposit being the preform from being stripped or destroyed due to rapid permeation of the impregnating solution.