Etching an optical fiber fusion splice

An optical-fiber fusion-splicing method comprising the steps of:

• removing the coating of one end part of each of two optical fibers with different mode field distributions to be spliced;
• heating the exposed end part of at least one of said optical fibers, to thereby vary a mode field distribution thereof;
• cleaving the exposed end part of at least one of said optical fibers so that the mode field distributions at the cleaved end faces of said two optical fibers are substantially coincident with each other in configuration;
• fusion splicing said two optical fibers;
• and
• immersing the heated portion of the exposed end part of the fusion-spliced optical fiber in a hydrofluoric acid solution, to there effect a surface treatment thereof,
• wherein said surface treatment of said exposed end part of said optical fiber is carried out in a manner that a container of which the width is shorter than an exposed end part of a fusion-spliced optical fiber is filled with a hydrofluoric solution, and said exposed end part of said fusion-spliced optical fiber is immersed, while being held in a straightened state, in a portion of said hydrofluoric acid solution, which stands up the rim of said container by its surface tension.