High-Speed Reconfigurable Free-Space Optical Interconnects with Carrierless-Amplitude-Phase Modulation and Space-Time-Block Code

High-speed interconnects are highly demanded in data centers and high-performance computing, and the use of optical interconnects to replace electrical interconnects has been proposed and widely studied. For medium-range board-to-board communications, free-space based optical interconnects provide the additional advantage of reconfigurability and flexibility, compared with traditional waveguide or fiber-based counterparts. However, the bit rate and interconnection range in free-space optical interconnects are typically limited. In this paper, we propose a carrierless-amplitude-phase (CAP) modulated and space-time coded free-space optical interconnect scheme to overcome these limitations. Up to 80 Gb/s (2 x 40 Gb/s) interconnection with reconfigurability and flexibility is experimentally demonstrated for a maximum error-free distance exceeding 50 cm, showing about 65% improvement over previous demonstrations. The receiver sensitivity of the space-time coded system is measured as well, and results show that the space-time-block code (STBC) is capable of improving the receiver sensitivity and suppressing the inter-channel crosstalk. The impact of air turbulence, which exists in typical interconnect environments, is also experimentally investigated and results show that its impact on the proposed scheme is negligible. The proposed reconfigurable free-space optical interconnects with CAP and STBC can be further scaled up to provide higher speed and further extended interconnection range.