Amplified O-band direct-detection transmission using bismuth-doped fiber amplifiers

The recent emergence of bismuth-doped fiber amplifiers (BDFAs) enables the reach extension of high-speed O-band communication links In this work, our recent efforts on amplified O-band direct-detection (DD) transmission using BDFAs are reviewed. We first present the performance of a four-channel O-band coarse wavelength-division multiplexed (CWDM) transmission over 50-km length of single-mode fiber (SMF), showing that the chromatic dispersion (CD) which has long been neglected in O-band transmission, will degrade the transmission performance of dispersive O-band channels. In this context, we quantify the relative benefits of different DD formats at 50 Gb/s over up to 70-km length of SMF in a BDFA pre-amplified O-band system. The considered formats include Nyquist on-off keying (OOK), Nyquist 4-ary pulse amplitude modulation (PAM4), and Kramers-Kronig (KK) detection assisted subcarrier modulation using quadrature phase-shift keying (QPSK), and they are evaluated over both the low CD 1320-nm wavelength and the more dispersive 1360-nm wavelength It is demonstrated that OOK exhibits the best receiver sensitivity over all distances up to 70 km at the 1320-nm channel, whereas KK-QPSK achieves the optimal transmission performance at the 1360-nm wavelength when the reach is extended beyond 50 km. We consider that our results provide useful insights into possible future implementations of longer-reach O-band WDM systems.