Long-Term Thermal Stability of Single-Mode VCSEL Under 96-Gbit/s OFDM Transmission

Thermal-dependent transmission performance and long-term stability of a single-transverse-mode (SM) vertical-cavity surface-emitting laser (VCSEL) with directly pre-leveled 16-quadrature amplitude modulation orthogonal frequency-division multiplexing (16-QAM OFDM) data over 100 m OM4 multi-mode-fiber (MMF) are demonstrated. Although narrowing the oxide-confined aperture to 3 μm enables the SM VCSEL with low threshold current of 0.21 mA and high modulation bandwidth of 21.4 GHz, this technology also enlarges the insulating oxide area to accumulate the heat for raising core temperature. This induces a harsh environment as the core temperature persistently increases without dissipation even under the water-cooling control at 20 °C. As a result, the SM VCSEL can only guarantee a stable operation for 1.5 h under the encoding of QAM-OFDM data for transmission. After optimization, the SM VCSEL successfully supports a back-to-back transmission capacity as high as 96 Gbit/s. With the assistance of OFDM pre-leveling technique, the 96-Gbit/s QAM-OFDM data transmission is qualified over 100 m OM4 MMF with a receiving power penalty as low as 1.3 dB.