PURPOSE: To distribute the refractive index of a light guide by forming a sectionally square rectangular optical medium containing a monomer which decreases in refractive index when made into a monomer by optical polymerization, and providing masks having specific transmittivity over two orthogonal surfaces and irradiating the surfaces with light.
CONSTITUTION: An optical liquid medium 10 is poured in a cast container 1, which is half sealed; and gaseous nitrogen is flowed an 100ml/m for 100min and then monomer vapor is flowed for 20min to evaporate part of a solvent and the monomer, forming a transparent, half-solid film sheet. Then, the masks having light transmittivity distributions along an X and a Y axis as shown by an (x) and a (y) curve in a figure are arranged on the side wall 2 and bottom wall 3 of the container 1. Then, both flanks and bottom surface of the container 1 are irradiated with planar ultraviolet rays each for 1 second and 15min in total alternately to form two light guides 11 each having a refractive index which is maximum at the center part and decreases toward the circumference. This is left at room temperature for ≥30min after exposure and dried in a vacuum drier at 90°C for 10hr. Consequently, the matching with a grated index type optical fiber is facilitated.
YAMASHITA MAKI
KATOU MITSUTAKA
