PURPOSE: To increase the reflectivity and to make it possible to change a selection wavelength by applying periodic refractive index changes to a specific core by irradiation with light to form diffraction gratings.

CONSTITUTION: An optical fiber structure having the core consisting of a polymer or polysilane dispersed with a low molecular compd. is constituted by imparting the periodic refractive index changes to the core by irradiation with light, thereby forming diffraction gratings. The optical fiber structure in such a case means a structure obtd. by covering the core having a high refractive index with a clad having a low refractive index and includes not only such a three-dimensional optical waveguide as represented by an optical fiber in a narrow sense but a two-dimensional optical waveguide as well. As the low molecular compd., a compound which generates, for example, charges and a charge transfer with the polymer to change the refractive index when the compd. is irradiated with the light of the prescribed wavelength, is used. The polymer is not particularly limited and various kinds of the polymers are usable.