TeraHertz operational reachback (THOR) a mobile free space optical network program

The DARPA teraHertz operational reachback (THOR) program developed and assessed a suite of technologies for application in a mobile ad-hoc free space optical communication system. The notional THOR system includes airborne and ground based full duplex active terminals and passive optical terminals that form the physical layer of a high speed ad hoc mobile optical network. THOR consists of airborne terminals networked to form a communications backbone transmitting and receiving data at 2.5Gbps as well as passive optical terminals connected as high speed edge devices with a data rate of 200Mbps. The operational objective is to enable high data rate communications between a combat theater command post and an edge terminal linked to the global information grid (GIG) located outside of theater. DARPA investments were made in compact electro-optic beam steering devices to decrease the size and weight of optical terminals, high-speed high sensitivity (-47dBm) detectors, and high power (50W) modulating laser sources. Passive optical terminal technology investments focused on highspeed modulating quantum well focal plane arrays for integration with wide field of view +/-15 degree cat's eye optical systems to enable high speed modulating retro reflectors. Networking technologies included protocol assessments and quality of service algorithms to maintain low latency data transfer over unreliable optical data channels while maintaining data rates in the 2.5Gbps range. Analysis and network simulation results demonstrated that with multiple redundant links an all-optical network could operate with atmospheric weather conditions consisting of 80% broken cloud cover.