OPTICAL WAVEGUIDE FOR AMPLIFICATION

PURPOSE:To realize an optical waveguide in which the efficiency of a gain is improved and provided with the mode selectivity of gain and that of wavelength by attaching periodicity by forming a part where either or both a refractive index and the gain are high and a part lower than that alternately in the propagating direction of the optical waveguide. CONSTITUTION:The periodicity is attached on a core part 2 by forming the part 2 where either or both the gain and the refractive index are high and the part 3 where either or both the gain and the refractive index are low alternately keeping a uniform interval along the propagating direction of signal light in an optical fiber 1. To increase the refractive index of the higher part 2, the quantity of germanium dioxide, the dopant of which being performed on the part, is increased, and to increase the gain of the lower part 3, the quantity of fluorine, the dopant of which being performed on the part, is increased. To decrease the refractive index of the lower part 3, no doping of Er ion is applied to part, or, the doping of a material with loss for the signal light is performed on the part. Thereby, since it is possible to attach the improvement of the gain and the function of wavelength selectivity and mode selectivity on the optical waveguide, a remarkably effective optical device in which a filtering function can be attached on a light amplifier or as a mode filter provided with the gain even when it is a multi-mode waveguide.