PURPOSE: To suppress scattering on the flank of a fiber, to lessen the degradation in diffraction effect and to obtain reproduced images having a good resolution by polishing the projecting parts generated by the intrinsic property of a crystal and removing these parts.

CONSTITUTION: The fiber 2 having the projecting parts, such as ridges, is first subjected to lapping. Namely, the fiber is ground at, for example, about 10μm/min speed by using a wheel attached with diamond abrasive grains. Work strains are generated in the fiber at the time of grinding if the wheel having a low grinding power is used. The fiber is subjected to polishing after the lapping. The fibers from which the ridges are removed is obtd. if the polishing is executed by dropping a grinding agent over the entire part of the polishing wheel and polishing the fiber at about 0.5μm/min speed. The reproduced images having the high resolution are obtd. by removing the projecting parts generated on the fiber flank in the growth process of the single crystal in such a manner.