PHOTONICS APPLIED: DEFENSE: IR countermeasures aim for safer flights

An infrared countermeasure—a device designed to prevent a heat- or plume-seeking missile from reaching its target—generally consists of a flare, laser, or other bright illumination source and optics combination that, when placed on an aircraft or marine craft, confuses a missile’s target acquisition system.

Today, infrared countermeasure (IRCM) systems are standard equipment for most military aircraft. But although the US House and Senate introduced bills H.R. 2780 and S.1193 in 2005, each called the Commercial Airline Missile Defense Act, neither became law. Nonetheless, progress is being made in the commercial airlines arena: More powerful lasers and improved optoelectronic and optomechanical components are reducing the size and weight of IRCM systems, bringing them a step closer to accompanying you on your next flight home.

IRCM technology

While much of the technology in modern IRCM is proprietary, each system basically consists of a missile-tracking system with IR cameras and optics, the countermeasure light source or “jammer” that confuses an approaching missile (the “seeker”), a data-processing system for pattern recognition and control functions, and mechanical components that may translate/rotate the imager and light source.

“All seekers target a jet-engine plume in a somewhat narrow field of view and modulate the detected signal in order to track the location of the source energy in relation to the missile’s flight direction,” says William Caplan, engineering consultant at Netherlands Infrared Consulting and Modelling (NIRCM; The Hague, the Netherlands). “The job of the jammer is to provide a higher-intensity modulated source in the same field of view as the aircraft heat source being targeted [see Fig. 1]. In the case of directional IRCM [DIRCM], the source is mounted on a turret that directs the laser beam to the seeker. The jammer signal confuses the missile-tracking electronics, breaking their ability to lock onto the original IR source.” Caplan says that different seekers operate with different spectral bands, say 1–3 µm or 3–5 µm, for example, meaning that IRCM must broadcast a jamming signal in all bands. “MANPADS [man-portable air defense systems] technology hasn’t changed much in 20 years, and seekers typically target shortwave- to midwave-infrared [SWIR to MWIR] signals. Fortunately, imaging and visible-band seekers are not widely available to illicit [terrorist] groups,” adds Caplan. “Nonetheless, IRCM manufacturers need to anticipate probable increases in the sophistication of enemy combatant technology and design jammers with multispectral, multiband emissions that span the seeker detection bands. Considering that MANPADS can acquire and intercept a target in 2–10 s, the jammer needs to be effective and fast.”

BAE Systems’ (Nashua, NH) IRCM has been used during Desert Storm, Bosnia, Kosovo, and numerous other operations. The company’s ALQ-144A onboard jammer with offboard flares protects a target against old and new IR threats, while its AN/ALQ-212(V) advanced threat IR countermeasures/common missile warning system (ATIRCM/CMWS) suite provides protection against all IR threat bands, successfully defeating 10 of 10 IR signature analysis models in live-fire tests. BAE’s IRCM system detects an approaching missile, rejects any false alarms, and cues the onboard IR jamming system’s jam head to the missile’s location. When the jam head finds the missile with its IR tracking system, it emits a high-energy IR beam to defeat the missile’s IR seeker and incorporates one or more IR jam heads to counter multiple missile attacks.

Northrop Grumman (Rolling Meadows, IL), who built the first IR jamming laser, now has 2000 Viper lasers in service since 2002. Viper is a diode-pumped Nd:YAG laser that uses periodically poled lithium niobate (PPLN) to perform wavelength conversion in a 13 × 2 in. housing weighing less than 10 lb. Northrop Grumman calls Viper a true multiband laser, emphasizes the importance of co-alignment of the different-wavelength lasers, but like all IRCM manufacturers, cannot comment on the precise laser specifics or modulation schemes.

“We can say that lasers have made the optical break lock possible, whereby a missile violently and instantaneously turns away from its target upon seeing the laser signal,” says Jack Pledger, Northrop Grumman director of IRCM business development. “The jamming intensity to target heat-signature intensity ratio, or J/S, has grown from 10/1 for lamp-based DIRCM to nearly 1000/1 for laser-based DIRCM, upping the requirements for IRCM lasers in order to keep pace with missile detection advances. Thulium-fiber lasers and QCLs [quantum-cascade lasers] show great promise in reducing cost, weight, and increasing reliability over the -45º to +40ºC IRCM operating environment,” adds Pledger.

Multiple manufacturers are rising to the mid-IR laser challenge. “Our QCL-based JammIR laser system differs from Northrop Grumman’s Viper OPO [optical parametric oscillator], BAE Systems’ multiband laser OPO, and Elbit’s MUSIC fiber-laser pumped systems in a number of ways,” says Eric Takeuchi, director of business development for Daylight Defense (San Diego, CA). “Using QCLs in a modular architecture lets system integrators pick and choose wavelengths and power levels that suit their requirements.” Takeuchi says that QCL systems have a much smaller parts count for improved reliability and operate directly from injected current, meaning electrons in and photons out at the correct wavelengths. “Conversely, Viper OPO and thulium fiber-laser-pumped OPOs require a series of optical pumping and nonlinear frequency conversion steps in order to generate the correct wavelengths for defeating heat-seeking missiles, resulting in very complex laser systems with significant cost and reliability disadvantages.” The 9.5 lb JammIR “Series B” QCL systems, adds Takeuchi, operate over an extremely wide temperature range from -54º to +71ºC, have been flight-tested on a wide variety of military helicopters, have been demonstrated to defeat heat-seeking missiles, and operate with only solid-state thermal management—no evaporative cooling required.

ITT (Clifton, NJ) is relying on Daylight Defense’s QCL technology for the Army’s upcoming Common Infrared Countermeasures (CIRCM) competition. The program will bring IRCM capability to the Army’s 4000-plus light-to-medium weight helicopters and is valued between $1.5 and $2 billion over the next five years. “ITT was one of the first defense companies to recognize the potential of QCL technology for military IRCM processes, and we’ve been working with Daylight to get this particular laser up to military requirements,” said Bob Lawler, ITT Electronic Systems’ director of Army Programs. “QCLs offer more power and higher reliably at a lower weight than existing lasers and, for our purposes, all three of those elements are critical to a successful system,” added Lawler.

Wall-plug efficiency (WPE) is another key attribute of mid-IR QCLs. Pranalytica (Santa Monica, CA) uses its nonresonant extraction (NRE) QCL designs to achieve WPE values of 10% or better over wavelengths covering the 3.6–17 µm spectral range, in both cooled and uncooled options. Continuous-wave, room-temperature MWIR output power levels are typically >2 W at the short-wavelength end and >4 W at the long-wavelength end of interest. Pranalytica also has a multiple-wavelength system with multiwatt power output for two or more wavelengths in the MWIR region and a 2.0 µm window in the SWIR region with a collimated, collinear output beam; all modules meet MIL-STD 810G vibration/shock and temperature requirements.

Commercial obstacles and opportunities

“There are three main pillars of resistance to the deployment of IRCM on commercial aircraft: cost, weight, and drag,” says NIRCM’s Caplan. “With a complete IRCM system estimated to cost around $1 or $2 million, you can already see the limitations to widespread adoption of the technology.¹ Another figure debated in the industry is a 3% increase in fuel consumption due to system weight and increased aerodynamic drag for IRCM-equipped aircraft, which is huge for commercial airlines.”

Caplan, who worked on DIRCM implementation as a principal scientist at the North Atlantic Treaty Organization (NATO; www.nato.int) for more than a decade, sees possibility for progress in overcoming these obstacles, however. “After [9/11], the attacks on a commercial airliner in Mombasa, Kenya in 2002 and a DHL aircraft in 2003 tremendously raised awareness of the MANPAD threat to civil aviation.” In fact, a 2006 report in Aerospace America estimated that there have been 35 MANPADS attacks on civil and commercial aircraft, resulting in as many as 500 fatalities. The report also estimated that US IRCM funding was forecast to grow from just under $600 million in 2006 to nearly $1 billion in 2009 and beyond, with BAE Systems and Northrop Grumman each holding a roughly 40% IRCM market share in 2006.²