Free Space Optical or Laser communications is creating a new communications revolution, that by using visible and infrared light instead of radio waves for data transmission is providing large bandwidth, high data rate, license free spectrum, easy and quick deployability, low mass and less power requirement. It also offers low cost transmission as against radio frequency (RF) communication technology and fiber optics communication.
The unique characteristics of laser such as its powerful coherent light beam, the possibility of modulating it at high frequency and the low beam divergence has made it the preferred light source for enhanced FSO applications. FSO operates on the Line-of-Sight phenomenon, consisting of a LASER at source and detector at the destination which provides optical wireless communication between them. FSO involves the transmission of data through a wireless medium using modulated near infrared light beam (with wavelength between 800 nm-1700 nm) as carrier wave. FSO communication is considered to be one of the key technologies for realizing very-high-speed multi-gigabit-per-second large-capacity communications when fibre optic cable is neither practical nor feasible.
For military, FSO is the next frontier for net-centric connectivity, as it can provide low cost, large bandwidth, high speed and secure communications in space and inside the atmosphere. There are size, weight and power (SWAP) advantages as well. Intelligence, Surveillance, and Reconnaissance (ISR) platforms can deploy this technology as they require disseminating large amount of images and videos to the fighting forces, mostly in real time.
US military has started exploring the use of laser communications systems that are harder to detect and disrupt . The current wireless networks and radio-frequency communications used for voice and data communications, sharing intelligence, targeting data, and orders have become vulnerable to Electronic Warfare capabilities of rivals like China and Russia that could pick up those transmissions and jam them, change them to confuse or deceive, or track them to target the people sending and receiving them. That’s why the Defense Department recently awarded a three-year, $45 million grant to a tri-service project for a laser communications system. Thomas and her collaborators have moved past the research equipment and are building a full-up prototype expected to be ready by 2019.
US DOD is also looking to laser communications as key technology of their Operationally Responsive Space (ORS) effort under which it is planning to replace its highly costly, capable although vulnerable satellites with cheap though more more survivable microsatellite constellations. US DOD for its future multi domain battles is also planning an interservice, regional robust command-and-control network using small and rapidly-launched satellites.
Military FSO or Laser Communications
Spectrum congestion is a growing problem, it increasingly limits operational capabilities due to the increasing deployment and bandwidth of wireless communications, the use of network-centric and unmanned systems, and the need for increased flexibility in radar and communications spectrum to improve performance and overcome sophisticated countermeasures.
Networks are said to be one of the U.S. military’s Achilles’ heels. Anthony Nigara, senior director for advanced systems at Exelis, which is working on a laser communications project for the Office of Naval Research, said in an interview that adversaries may want to block, degrade or eavesdrop on U.S. military communications. Cutting off communications through jamming or the destruction of infrastructure could be devastating to battlefield commanders. FSO communication cannot be easily intercepted, detected or jammed as FSO laser beam is highly directional with very narrow beam divergence. Unlike RF signal, FSO signal cannot penetrate walls which can therefore prevent eavesdropping. However, this technology is limited to LOS communications and is affected by atmospheric attenuation that is impossible to control. This is definitely a challenge that will impact mission capabilities.
Therefore, a viable future work would be to explore the possibility of implementing FSO relay capability as a solution for broadband communication over the horizon in tactical operations. Relay could be implemented from ground-to-air and air-to-ground paired links. The device in the air acts as a repeater to avoid physical obstructions during required ground-to-ground communications.” This solution addresses the challenge involving LOS, and transmission away from the ground reduces the effect of atmospheric scintillation to the optical link. The solution could be cascaded to further increase the eventual ground-to-ground range,” propose Lai, Jin Wei Monterey, California: Naval Postgraduate School. Caution has to be exercised when using an FSO communication system as the laser may cause damage to the human eye.
GA-ASI Successfully Tests Air-To-Space Laser Communication System
General Atomics Aeronautical Systems, Inc. (GA‑ASI) has successfully ground tested its Airborne Laser Communication System (ALCoS) by establishing a link with a satellite in Geo-synchronous Earth Orbit (GEO). GA-ASI conducted the test with Tesat-Spacecom (TESAT), the leader of space-based laser communication (lasercom), using their GEO Laser Communication Terminal (LCT), the LCT 135. This was the first demonstration of an air-to-space lasercom system with Size, Weight and Power (SWAP) that is compatible with a Medium-altitude, Long-endurance (MALE) Remotely Piloted Aircraft (RPA).
GA-ASI tested the ALCoS from an optical observatory located on Tenerife in the Canary Islands and closed link with TESAT’s LCT 135 terminal onboard the GEO satellite Alphasat. The test successfully demonstrated acquisition and tracking, and sufficient power to close the link with the LCT 135. GA-ASI is completing the development of the flight system for use on a GA-ASI-produced MQ-9 RPA.
“This test was a critical step towards enabling our aircraft with a high-bandwidth communication system that cannot be jammed or detected by an adversary,” said Linden Blue, CEO, GA-ASI. “ALCoS allows a new generation of high-performance sensors by breaking the data bottleneck of current RF SATCOM technology.”
ALCoS is the result of a five-year, GA-ASI-funded effort to deliver Low Probability of Intercept (LPI), Low Probability of Detect (LPD) communications link to the MQ-9. With 300 times the data carrying capacity of conventional RF SATCOM systems, ALCOS will be able to operate as a gateway to the Joint Aerial Network for forward-deployed forces.
The system has the capability to work in two optical wavelengths, 1064nm and 1550nm. TESAT brings more than 12 years of experience with deployed lasercom systems for space. TESAT’s LCT 135 terminals are currently in use on seven satellites in orbit. These LCTs make over 60 satellite-to-satellite links over a distance of 45,000 km per day and have logged over 30,000 links total. TESAT has proven the commercial viability of laser satellite communications.
Marines conduct field test of laser-based communications system
The 7th Communication Battalion, III Marine Expeditionary Force Information Group performed field testing of a new Free Space Optics system at Camp Hansen in Okinawa, Japan in August 2018. The FSO is designed to be highly mobile and easy to use, making it easier for Marines of all stripes able to deploy the system. It is currently designed for ground-to-ground communications but could eventually be scaled to ship-to-shore and air-to-ground, according to the U.S. Naval Research Laboratory.
Office of Naval Research tests tactical line-of-sight operational network (TALON)
Defense Department recently awarded a three-year, $45 million grant to a tri-service project for a laser communications system. “This is basically fiber optic communications without the fiber,” said lead researcher Linda Thomas, whose Naval Research Laboratory team takes home about a third of the grant money. Their TALON device transmits messages via laser over distances comparable to current Marine Corps tactical radios, but because it’s a narrow beam of light rather than a radio broadcast, it’s much harder for an enemy to pick up the transmission, let alone interfere with it.
ONR successfully tested Exelis’ tactical line-of-sight operational network (TALON) between two mountains 50 kilometers apart at Naval Air Weapons Station China Lake in California. Nigara said the TALON program has worked on synchronizing transmitters and terminals on the move, whether from ship to ship, or ship to shore. They must be able to find each other and link automatically.
Exelis’ ES division has developed TALON (Tactical Line-of-Sight Optical Network), “Our TALON product line is a free-space optical communications system that uses lasers to transmit mission-critical data to warfighters from distances of more than 30 miles and 1,000 times faster than RF technology,” says Andy Dunn, vice president of business development, integrated electronic warfare systems, Exelis ES.
“You can only push so much data, video and voice communications through the traditional RF space. When you move up to optics or laser-based communications, you can push a lot more data through the pipeline and that’s what the TALON line does.” Because heavy weather can still block laser beams, especially over long distances, Thomas emphasized you’d never want to get rid of your radios and rely exclusively on lasers.