Journal of Lightwave Technology | 2021
Photonic Crystal Structured Multi-Mode VCSELs Enabling 92-Gbit/s QAM-OFDM Transmission
Abstract
The multi-mode vertical-cavity surface-emitting lasers (MM-VCSELs) with different photonic crystal (PhC) designs in core and cladding regions are compared for transmitting the complex formatted QAM-OFDM data over 100-m OM5 multi-mode fiber (MMF). Among the designs with using flat core/cladding (denoting as Core<sub>flat</sub>/Clad<sub>flat</sub>) and/or PhC core/cladding (denoting as Core<sub>phc</sub>/Clad<sub>phc</sub>) for the MM-VCSEL, the Core<sub>flat</sub>+Clad<sub>flat</sub> VCSEL with the highest threshold current and large emission aperture provides the highest differential quantum efficiency of 0.11 and output power of 2 mW, whereas the Core<sub>flat</sub>+Clad<sub>phc2</sub> VCSEL with two periods of cladding PhC reveals the lowest threshold current of 2 mA, the highest modulation bandwidth of 15 GHz, the lowest relative intensity noise peak of -126 dBc/Hz and background level of -143 dBc/Hz. After pre-compensation, the Core<sub>flat</sub>+Clad<sub>phc2</sub> VCSEL chip can achieve the highest OFDM bandwidth of 18 GHz for 72-Gbit/s transmission in the BtB case. With additionally adding 1 period of core PhC, the Core<sub>phc1</sub>+Clad<sub>phc2</sub> VCSEL possesses a single-mode lasing spectrum to facilitate the suppression of modal dispersion after MMF propagation. Hence, the Core<sub>phc1</sub>+Clad<sub>phc2</sub> VCSEL exhibits the same bit rate of 60 Gbit/s as compared to the Core<sub>flat</sub>+Clad<sub>phc2</sub> VCSEL after 100-m OM5-MMF. After improving the analog bandwidth for waveform synthesis, the data rate of Core<sub>flat</sub>+Clad<sub>phc2</sub> VCSEL can successfully deliver 76-Gbit/s and 72-Gbit/s single-band 16-QAM OFDM data streams for BtB and 100-m OM5 MMF conditions via the pre-leveling technology. To date, the ultimate raw data rate achieves 92-Gbit/s with employing the multi-band QAM-OFDM data format.