Long-Wave Infrared Transceivers for High Speed Free Space Optical Communications in Adverse Weather Conditions

Given the ever-growing need for high-data rate, low-latency, secure, wireless communications driven by applications ranging from vehicle automation to ad-hoc battlefield command and control, free-space optical (FSO) communication links operating outside of the regulated and crowded radio-frequency (RF) bands are increasingly in demand. Recent research has verified that there are advantages to using long-wave infrared (LWIR) wavelengths for FSO links through the atmosphere. When the channel transmission is affected by fog, clouds, dust, or wind, a near-IR (~ 1.55-micron wavelength) FSO link suffers relative to systems operating at longer wavelengths. LWIR systems near 10 to 11 microns benefit from a wavelength (l) larger than the typical droplet, placing the scattering effects in the Rayleigh limit where scattering losses drop with l-4, as well as the coincidence of relatively low atmospheric absorption there. Long-wave systems also benefit from the reduced impact of turbulence-driven scintillation and beam broadening, which decrease by approximately 1/l. If the transmitter and receiver components can be developed to meet the FSO link requirements, this would enable lower latency than satellite links, greater security than RF, longer range than mm-wave, and greater availability in adverse weather than near-IR systems. We propose to develop quantum cascade laser (QCL) - based transmitter (Tx) and resonant cavity infrared detector (RCID) - based receiver (Rx) components that will enable up to 40 Gb/s communication over a FSO communication link operating in the LWIR To maximize the spectral efficiency, and therefore the data throughput of a limited-bandwidth free-space link, we propose linear, LWIR, E/O and O/E transducers. These linear modules will enable software-defined-radio methods to maximize the data throughput based on the available optical channel.