| 摘要 |
PROBLEM TO BE SOLVED: To improve quality in data transmission and to perform an optical communication over a long distance by surely suppressing backscattered light occurring due to stimulated Brillouin scattering with simple constitution. SOLUTION: A transmission data signal Sa is sent out to a light emitting element 21 through a driving circuit 23, a modulation circuit 24 in a control circuit 22, and an optical signal from it is sent out through an optical fiber 27, a circulator 25 and the optical fiber 28. Stokes light (backscattering light) occurring due to the stimulated Brillouin scattering is made incident on a photodetector 26 from the port P2 through the port P3 of the circulator 25, and a detection signal Sb of a level corresponding to its light intensity is outputted to the modulation circuit 24 in the control circuit 22. When the level of the detection signal from the photodetector 26 becomes large, a driving current to the light emitting element 21 is modulated so that the emission spectrum line width of the light emitting element 21 is broadened, and the light emission spectrum line width of the light emitting element 21 is broadened. Thus, the threshold value causing the stimulated Brillouin scattering is set high, and the occurrence amount of the Stokes light is reduced. |
