In this report, we summarize our recent achievements in free-space communications in the mid-infrared (MIR) region enabled by directly modulated quantum cascaded laser (QCL) at 4.65 µm (~65 THz). We have experimentally demonstrated a multigigabit free-space transmission link in the lab environment with the QCL operating at room temperature. The QCL chip is mounted on a commercial QCL mount with a water-cooled Peltier element. Multilevel modulation formats at different baud rates are generated and combined with the laser driving current at a custom-made bias-tee to drive and modulate the QCL. A commercial mercury cadmium telluride (MCT, HgCdTe) photovoltaic (PV) MIR detector with a built-in trans-impedance amplifier was used to receive the MIR free-space signal. With the receiver to be the bottleneck of the system bandwidth, the end-to-end 3-dB bandwidth was measured to be around 320 MHz, and the 6-dB bandwidth was around 450 MHz. We have successfully demonstrated up to 6 Gbps free space transmission with multilevel modulation formats, assisted with effective digital equalization techniques despite the limited bandwidth.
Modern IoT and 5G applications are driving the growth of Internet traffic and impose stringent requirements to datacenter operators for keeping pace with the increasing bandwidth and low-latency demands. At the same time, datacenters suffer from increasing number of interconnections dictating the deployment of novel architectures and high-radix switches. The ratification of 400 GbE standard is driving the market of optical transceivers nevertheless, a technology upgrade will be soon necessary to meet the tremendous traffic growth. In this paper, we present the development of 800 Gb/s and 1Tb/s optical transceivers migrating to 100 Gbaud per lane and employing wafer-scale bonding of InP membranes and InP-DHBT electronics as well as advanced co-packaging schemes. The InP membrane platform is also exploited for the development of novel ultra-fast optical space switches based on a modular architecture design for scaling to large number of I/O ports.
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