Telecom tech could protect aircraft

Infrared supercontinuum laser technology could soon help protect military helicopters from heat-seeking missiles designed to home in on IR radiation emitted by a helicopter’s engine. Built with off-the-shelf telecom fiber optics, the laser technology operates in the mid- and longer IR wavelengths. Because it emits such a broad spectrum of light, it can jam missile sensors from a distance of 1.8 miles.

Optical parametric oscillators have been used on aircraft to confuse shoulder-launched heat-seeking missiles, but this technology is expensive and fragile, not suitable for the rigors of helicopter flight. Current laser-based IR countermeasures, consisting of 84 pieces of moving optics, are not considered a practical option for helicopter flight.

Researchers are developing mid-IR supercontinuum laser technology to protect military helicopters from heat-seeking missiles. Courtesy of Omni Sciences Inc.

“We moved from complexity to simplicity,” said Mohammed N. Islam, a professor in the department of electrical engineering and computer science at the University of Michigan. “The compact system can go anywhere there is space on the helicopter. We eliminated the need for mode-locked lasers, which are expensive, and we extended the wavelength to cover the entire spectrum. We used a standard distributed feedback pump laser, and light can be piped easily through 10- to 15-m fiber. Optical amplifier technology is used to boost the signal.”

Islam and his team created an all-fiber integrated supercontinuum laser that provides up to 10.5-W time-averaged power with a continuous spectrum from approximately 0.8 to 4 µm, according to their report in the IEEE Journal of Selected Topics in Quantum Electronics, March/ April 2009. They stated that the laser is generated by a combination of standard single-mode fibers and fluoride fibers pumped by a laser diode-based cladding-pumped fiber amplifier system. They also demonstrated that the output of the supercontinuum laser pulse pattern can be adjusted by directly modulating the seed laser diode and controlling the amplifier gain with a signal feedback technique.

“This is an all-fiber integrated laser with no moving parts. It is reliable, rugged and easy to maintain. The off-the-shelf components from telephone networks are relatively inexpensive and are based on a proven technology, Islam said.”

Reliability, relatively low cost and a basis in proven technology are attractive qualities to the US Department of Homeland Security, which has been looking for better ways to protect commercial and military aircraft from shoulder-launched missile attacks. The laser system is being created at the university and at Islam’s spin-off company, Omni Sciences Inc. It is being commercialized by the company, which recently received a total of $1 million in grants from the US Army and DARPA to build a second-generation prototype, according to a press release from the university.

A second-generation prototype now in development is expected to have increased power and to be smaller and more rugged. Islam and his team are working to bring down the weight of the system from 25 to 10 lb or lower. “It is easy to scale up the power of the laser and to increase repetition rate and pump power with no real change in architecture,” he said.

Among the challenges for the technology, from the engineering standpoint, are the thermal management and packaging aspects. The US government must rate the technology as having advanced from the level at which its components are validated in a laboratory environment to the level at which its prototype is demonstrated in a relevant environment.

Scientific hurdles include the need to expand the long wavelength and increase bandwidth, Islam said. “The supercontinuum laser is a platform technology and is very flexible for a wide range of applications.” These applications could include monitoring at national borders, active remote sensing of natural gas leaks, and, in the medical field, destroying harmful fats and lipids in the human body in the fight against Type 2 diabetes.