2.488 GB/S-318 KM REPEATERLESS TRANSMISSION USING ERBIUM-DOPED FIBER AMPLIFIERS IN A DIRECT-DETECTION SYSTEM

We have achieved 2.488 Gb/s-318 km repeaterless transmission without any fiber dispersion penalty through a nondispersion-shifted fiber in a direct-detection system. The system was loss limited with a T-R power budget of 57 dB. Three key components enabled us to achieve this result: 1) a Ti:LiNbO3 external amplitude modulator enabling a dispersion-free transmission, 2) erbium-doped fiber amplifiers increasing the transmitting power to +16 dBm, and 3) an erbium-doped fiber preamplifier enabling a high-receiver sensitivity of PBAR = -41 dBm (or eta-PBAR = -43.2 dBm) for 10(-9) BER. To our knowledge, this result is the longest repeaterless transmission span length ever reported for direct detection at this bit rate. From the experimental results and a theoretical model, we identified the sources of the receiver sensitivity degradation from the quantum limit (-48.6 dBm) and estimated the practically achievable receiver sensitivity of approximately -44 dBm (approximately -124 photons/bit) for 2.5 Gb/s optical preamplifier detection.