PURPOSE: To increase optical input power at a low bit rate by giving distortion distributed in the lengthwise direction to a transmission medium in the coherent light transmission system employing a single mode optical fiber as the transmission medium.
CONSTITUTION: The direct modulation system and the external modulation system are adopted for the transmission system and the non-polarized wave control system, the polarized wave control system and the polarized wave diversity system are adopted for the reception system. A distortion provision optical fiber cable in which distortion is distributed in the lengthwise direction is employed for the transmission medium. Let a critical input at a spectrum width V0 for induction Brillouin scatter at no distortion be I0 and a critical input when a periodic distortion of ±Δ is given to an optical fiber be I, then the relation of I/I0=(Δ/BV0)+1 exists and a 13dB critical optical input power is increased in the case of V0 at 40MHz. Thus, the optical input power limit due to the induction Brillouin scatter in the coherent optical transmission at a low bit rate possible for reception of a low reception level is relaxed and the long span transmission having large input power and low reception level is attained.
TADA HIDENOBU
YABUTA TETSUO
