Amplifying Power at Light Speed

LOCSET

Scaling single element fiber laser or optical amplifier systems to high power can often be limited due to damaged thresholds of optical materials, size, heating and cooling issues.

One approach to achieving high optical powers is to accept the power limitation of a single optical amplifier, and look for ways to efficiently combine the outputs of multiple optical amplifier sources.

This approach, known as Locking of Optical Coherence by Single-detector Electronic-frequency Tagging (LOCSET) is a method pioneered by the Air Force Research Laboratory that optimally combines multiple optical beams into a single coherent high power beam.

In LOCSET, each beam of the optical array is phase-modulated at a unique radio frequency (RF). A portion of each beam is picked off via a beam sampler and interfered onto a single photodetector.

The interference beat note measured by the photodetector is then processed by the feedback electronics, where the relative phase error of each array element with respect to all other array elements is electronically isolated from the beat note and fed to the phase adjusters of the optical array.

Each phase adjuster in the array applies the appropriate phase correction to coherently combine the optical beams on the photodetector. The LOCSET architecture and hardware have been shared with other government agencies and their contractors for laboratory demonstrations.

It is becoming the preferred method for phase-locking multiple optical amplifiers. This method is being sought out by multiple large defense system integrators for system insertion.

The primary application of this technology is to combine multiple lower power coherent light sources into a single higher power light source. This is intended primarily for directed energy applications that require long-range standoff and precision engagement of difficult targets for the military, but is also of use for industrial applications such as precision cutting, welding and materials processing.

The ability to combine multiple low-power optical amplifiers into one high-power beam is much more economical and technologically stable than trying to build one large optical amplifier.

Additionally, the LOCSET electronic feedback design can be used for other closed loop locking applications where highspeed convergence of many channels is required.

LOCSET is a well-established research grade technology. It has been tested and successfully demonstrated with several cutting-edge beam combination techniques over the past couple of years by organizations such as Northrop Grumman, Lockheed Martin, Raytheon, and DARPA.

LOCSET is currently implemented using discrete off-the-shelf radio frequency components used in standard commercial cable television modulation architectures.

Commercial development of LOCSET will include monolithic integration of RF functions onto custom integrated circuits and tailored printed circuit boards with graphical user interface functionality.

Fiber laser-based technology is slated for insertion on multiple military platforms, including fighter jets and unmanned aerial vehicles (UAVs), and is considered by many as the nirvana of lasers for long-range strike applications.

LOCSET’s architecture creates an enabling technology for precision engagement of critical military targets that minimizes collateral damage.

It answers the question—why bomb the building when you only need to disable the cell phone antennas mounted on the top?

The LOCSET architecture is being sought by multiple large defense system integrators for system insertion.