Military wants lightweight fiber lasers for unmanned aircraft

DARPA could offer over $6 million for advanced lighweight laser

DARPA Hummingbird uav
Military researchers are looking for a 22lb laser that can fit and operate in high-altitude unmanned aircraft. 

As you might suspect, the Defense Advanced Research Projects Agency (DARPA) is behind the laser building project known as the Fiber Laser Pulsed Source (FILPS) program that could end up being used in a number of applications from drone communications and targeting to weapons. DARPA said approximately $6.3 million will be available with the anticipation of approximately two awards for FILIPS contracts. 

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The attractive thing about fiber lasers is that they are by some estimates, two-times more efficient in that they can deliver more laser power per weight and volume than solid-state lasers. 

Technically speaking from DARPA: The FILIPS program objective is to develop a versatile fiber laser/amplifier platform that can generate sub-ns duration pulses, with greater than 10-mJ of energy per pulse, at a 25-kHz repetition rate.  The output pulse characteristics, including phase stability, pulse jitter, and laser beam quality, should be sufficient to enable efficient pulse energy scaling to the 100-mJ level via coherent combining.  The system will need to be phase-locked to an external optical reference and configurable over a wavelength band greater than 5-nm in width.    

DARPA stated that fiber laser amplifiers will enable the development of arrays of fiber amplifiers whose beams can be coherently combined into a single beam to reach very high power. The monolithic all-fiber design approach provides a robust platform that is more rugged than laser systems that employ free-space power transport. Fiber laser amplifiers will find applications in laser communications, target search and track, target identification and IFF, and ultimately high-power laser weapon applications. 

The ultra-high efficiency and near diffraction limited beam quality promised by fiber laser amplifiers can lead to high power laser systems that are more than 10 times lightweight and more compact than existing high power laser systems currently deployed by the Dodd, DARPA stated. 

Potential FILIPS developers need to address a few of the biggest hurdles in laser development. First is obviously keeping the weight down on the laser package itself. Laser-making equipment tends to be on the big and bulky side. 

Then there is the issue of controlling the beam itself. From long distances in particular, lasers tend to spread out, making precise targeting a problem.

Finally there is the need to build a laser package that can generate enough power or brightness to be useful in myriad applications FILIP will entail.

DARPA has a ton of development work in lasers. For example in July the agency said it want to develop a laser system the goes way beyond today's opto-mechanical, acousto-optical or electro-optical systems to establish photonic integrated circuit (PIC) technology that will provide video frame rate beam steering speeds, and emit multiple beams with a total output power of 10 W.

DARPA said opto-mechanical scanning devices are usually bulky and relatively slow, while acousto- and electro-optical technologies utilize devices that while small in size, cannot provide the steering speeds and versatility necessary for many of the advanced applications the military envisions.

Known as the SWEEPER, which is short for short-range wide-field-of-view extremely-agile electronically-steered photonic emitters, DARPA said it expects the new laser technology to draw from phased array concepts that revolutionized RADAR systems. 

DARPA said it expects SWEEPER will provide a compact, agile alternative to mechanically steered technology, and recognizing the recent advances in photonic device density, circuit complexity, and performance capabilities in the emerging PIC technology, the SWEEPER program should extend phased array beam steering to the optical domain in the near infra red (0.8 to 2 μm range) by developing PIC technology for optical phased arrays. Such arrays will require the integration of thousand of closely packed optical emitting facets, precise relative electronic phase control of these components, and all within a very small form factor with a total output power of 10W, DARPA stated.

DARPA has had a long interest in developing beyond-bleeding-edge laser technology. For example it currently is developing what's know as Blue Laser for Submarine Laser Communications which provides large area submarine communications at speed and depth, which no other future or existing system, or combinations of systems, can do. DARPA said.

Then there's the High Energy Liquid Laser Area Defense System which the agency defines as a novel, compact, high power laser enabling practical small-size and low-weight speed-of-light weapons for tactical mobile air- and ground-vehicles.

Large lasers have had success in blowing things up this year. In August, Boeing and the US Air Force said that a C-130H aircraft armed with Boeing's Advanced Tactical Laser (ATL) blasted a target test vehicle on the ground for the first time.  Boeing has been developing the ATL since 2008 under an Air Force contract worth up to $30 million.

According to Boeing, the C-130 fired its 12,000lb high-power chemical laser through the beam control system while flying over White Sands Missile Range, N.M. The beam control system acquired the ground target and guided the laser beam to the target.

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