| 摘要 |
PURPOSE:To widen the frequency band of a transmission signal and to increase communicatable distance by selecting the numerical aperture at which the light emitted from a light source is projected to an optical fiber smaller than the incident numerical aperture intrinsic to the optical fiber. CONSTITUTION:Laser light 13 is transmitted as the transmission signal in the core 12a of the optical fiber 12 of a step index type via a lens 14. The numerical aperture of the luminous flux entering the optical fiber 12 is set smaller than the numerical aperture intrinsic to the optical fiber 12 by selecting the distance l2 between the incident end face 15 of the optical fiber 12 and the lens 14 at the distance larger than the distance l1 between a semiconductor laser 11 and the lens 14 in this case. The number of reflections of the light progressing zigzag while reflecting in the core 12a of the optical fiber 12 is, therefore, decreased and the distortion of the incident waveform generated by a difference in the optical route in the optical fiber 12 is suppressed. The communicatable distance is thereby increased and the frequency band of the transmission signal is widened as well. |
