LAUSR

An 850-nm multi-mode vertical cavity surface emitting laser (VCSEL) bare chip with high-indium-density InGaAs/AlGaAs quantum-well pairs is demonstrated for directly encoded QAM-OFDM transmission in multi-mode fiber (MMF). By directly encoding the 850-nm VCSEL bare chip with a pre-leveled 14-GHz 16-QAM OFDM data, >50-Gb/s transmission over 100-m-long OM4 MMF can be realized without using data recovery circuit. Increasing the bias current of the VCSEL beyond 7.5I_th improves the signal-to-noise ratio (SNR) and the bit error ratio (BER) of received QAM-OFDM data to 15.5 dB and $2.9\times 10^{-3}$ , respectively. The 100-m-long OM4 MMF transmission degrades the SNR with its covered bandwidth reducing to 13 GHz. The OFDM subcarrier pre-leveling technique with a slope of 0.2 dB/GHz ensures the 16-QAM-OFDM data transmission with an error vector magnitude of 17.1% and a BER of $3.4\times 10^{-3}$ .