40  km amplifier-less transmission of single wavelength 90  Gbps four-level pulse amplitude modulation signals enabled by an ultrabroadband directly modulated laser

An ultrabroadband, high linearity directly modulated laser (DML) module operated at the O-band is proposed. The effect of the package network on the DML module is first investigated. In the package network, a wire bonding compensation method is used to improve the resonance at high frequency, which can be equivalent to the channel equalization technique. Without any optical amplification, we experimentally demonstrated 90 Gb/s four-level pulse amplitude modulation transmission over 40 km standard single mode fiber, which is the longest reach to the best of our knowledge. A bit error rate of 6.74×10^−4 is achieved at a received optical power of −2.5  dBm. A receiver sensitivity of −4.5  dBm at 7% overhead forward error correction limit (3.8×10^−3) is obtained for back-to-back with a power margin of more than 8.5 dB.