Numerical and experimental study on the impact of chromatic dispersion on O-band direct-detection transmission

The recent emergence of efficient O-band amplification technologies has enabled the consideration transmission beyond short reach. Despite being a low chromatic dispersion (CD) window, impact CD will become increasingly significant when extending reach direct-detection (DD) systems. In this work, we first numerically investigate 3-dB bandwidth single-mode fibers (SMF) and CD-restricted in intensity-modulation DD systems, confirming difference between low- high-dispersion wavelengths. We then carry out experimental studies over SMF for distances up to 70 km at two different wavelengths, low-dispersion 1320 nm more dispersive 1360 nm, by use an bismuth-doped fiber amplifier as preamplifier receiver. compare three 50-Gb/s optical formats, namely, Nyquist on-off keying (OOK), 4-ary pulse amplitude modulation (PAM4) Kramers–Kronig detection-assisted single-sideband quadrature phase shift (KK-QPSK) half-cycle subcarrier modulation. Our results show that both OOK QPSK exhibit better bit error rate performance than PAM4. When transmitting 70-km less wavelength offers 1.5-dB power sensitivity improvement photodiode (PD) compared QPSK. Conversely, required PD can be reduced 3 dB using instead OOK.