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Improved Coupling Efficiency Optical Pump Combiners for Fiber Laser Systems



OBJECTIVE: Design and develop novel materials, processes and/or geometries of optical pump combiner to increase coupling efficiency. 

DESCRIPTION: Lasers and optical amplifiers are pumped with shorter wavelength light to excite electrons required for the amplification of optical signals. The pump light needs to get into the center of the laser fiber in order for it to be absorbed and excited by the laser ions. If the pump light does not get into the core, it is converted to waste heat. Any waste heat must be removed. With the rapid improvement in laser and amplifier power seen in the past two decades, kilowatts of power are routinely achieved. With this high power, heating due to coupling inefficiencies presents real problems. If the coupling efficiency were improved from 90% to 95%, there would be fifty fewer Watts of heat to remove from the coating of a 1 kW pump fiber. This two-fold reduction could be the difference between water- and air-cooling of the contact area. The simplicity of the air-cooled system might be the tipping point needed in a candidate laser system to show the value of laser solutions to military problems. This SBIR announcement calls for novel methods and geometries that could increase coupling efficiency. If greater coupling efficiency designs could be created that have similar, or even improved reliability, these new pump combiners could be used in future weapons systems. Pump light is produced at expense, and any gain in coupling efficiency would also reduce the burden on the pump lasers. 

PHASE I: Design and develop novel materials, processes and/or geometries of optical pump combiner. Provide theoretical justification for the method(s) selected and utilize mathematical modeling to predict coupling efficiencies. Prepare a preliminary manufacturability and validation/testing plan in preparation for Phase II. 

PHASE II: Optimize design(s) based on the output of Phase I. Construct prototype device(s) based on the most promising methods. Conduct experimentation and evaluation testing. Compare data to modeling predictions and make recommendations for further design iteration if warranted. Provide prototype hardware and final report. 

PHASE III: Collaborate with ARDEC engineers for possible prototype integration for TRL7 demonstration and/or transition to military program. Industrial lasers must also remove waste heat, industry would benefit from more efficient energy conversion. Other uses include applications in which energy is at a premium, such as satellites or undersea applications, such as amplifying optical signals in transatlantic communications cables. In industrial lasers, uncoupled pump light can exit the fiber and add to unwanted heating of a larger material surface as light exits the fiber, so increased efficiency would improve the precision of the laser machining process. 



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KEYWORDS: Laser, Fiber, Pump, Coupling, Efficiency 

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