Abstract
The performance of optical transmissions is intrinsically and ultimately determined by quantum noise. This study theoretically investigates the quantum-noise-limited performance of BPSK transmission using EDFAs, PSAs, or Raman amplifiers as optical repeaters. Amplifier noise, quantum noise in a coherent state, and vacuum noise accompanied with attenuation are considered. Calculations based on the theoretical analysis qualitatively show that bidirectionally pumped Raman amplification systems achieve considerably long transmission distances.