High-Speed Resonant-Cavity Infrared Detectors and Narrow-Linewidth Quantum Cascade Lasers for Free Space Communication in Adverse Weather Conditions

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 necessitate free space communication links (FSCLs) operating outside of the regulated and crowded RF-frequency bands. We propose to develop transmitter (Tx) and receiver (Rx) components that will enable up to 40 Gb/s communication over a free-space communication link (FSCL) operating in the long-wave infrared (LWIR). To maximize the spectral efficiency, and therefore the data throughput, of a limited-bandwidth free-space link, we propose to develop linear, LWIR, electrical-to-optical and optical-to-electrical transducers. These linear modules will enable software-defined-radio methods to maximize the data throughput based on the available optical channel. Recent research has verified that there are advantages to using LWIR wavelengths for FSCLs through the atmosphere. When the channel transmission is affected by fog, clouds, dust, or wind, a near-IR (~ 1.55 mm wavelength) FSCL suffers relative to systems operating at longer wavelengths. LWIR systems near 10 to 11 mm benefit from a wavelength larger than many fog or cloud droplets, reducing scattering, as well as the coincidence of relatively low atmospheric absorption at those wavelengths. LWIR systems also benefit from a reduced impact of turbulence-driven scintillation and beam broadening. Intraband, working with the University of Wisconsin-Madison (UW-Madison) and the Naval Research Laboratory (NRL), proposes to investigate the feasibility of FSCLs based on the UW/Intraband 1-W MOCVD-grown QCL technology and the NRL resonant-cavity infrared detectors (RCIDs), optimized for modulation bandwidth > 5 GHz, transmitter power > 1 W, narrow linewidth, and link signal to noise ratio. The RCID resonant cavity reduces the absorber thickness required to achieve high quantum efficiency in the detector. This reduced thickness reduces the dark current, increases specific detectivity, and decreases carrier transit time. The narrow LWIR optical bandwidth of the RCID also aids in rejecting background radiation but does require a QCL with narrow linewidth. Intraband will work with the UW-Madison to design and model high-power, narrow-linewidth QCLs optimized for high-speed modulation in the LWIR. NRL will investigate the feasibility of > 5-GHz bandwidth for a LWIR RCID and provide modeled characteristics for devices and for arrays. Intraband will establish the feasibility of > 5GHz LWIR QCL linear transmission through simulations and experiments.