High-speed reconfigurable free-space optical interconnects with carrierless-amplitude-phase modulation and filter-enhanced spatial modulation

Optical technologies have been widely studied to satisfy the interconnect demand in high-performance computers and data centers, and free-space optical interconnects have been investigated for flexible card-to-card applications. To increase the interconnect speed and range, in this Letter we propose a reconfigurable free-space optical interconnect with 16-carrierless-amplitude-phase (16-CAP) symbol modulation and filter-enhanced spatial modulation (FE-SM). The 16-CAP increases the interconnect speed in the symbol domain, and the FE-SM scheme increases the speed in the spatial domain, even under highly correlated optical interconnect channels. A 50 Gb/s reconfigurable optical interconnect is experimentally demonstrated. The results show that the impact of FE-SM on the bit error rate (BER) is negligible, while the speed is significantly improved. Compared with the conventional SM scheme, the BER is improved by over one order of magnitude. The proposed scheme is also capable of extending the interconnect range. The results show that over 70% range extension and 50% speed increase can be achieved simultaneously. The proposed scheme with a 16-CAP and FE-SM provides a promising solution in free-space optical interconnects.