In an optical signal transmission system which can perform high-speed optical transmission not lower than 1 Gbps, VCSEL has light-emission points. A core diameter of an optical fiber GI-POF is set to not lower than 200 .mu.m, and the light-emission points of VCSEL are arranged inside an outer periphery at an end face of GI-POF. A polymerization composition material constituting the core of GI-POF is made of a compound containing deuterated poly methacrylic ester. A wavelength of the light beam of VCSEL is set to the range of 770 nm to 810 nm.