High Performance Optical Fibers for 100-Watts Infrared Lasers

TECHNOLOGY AREA(S): ElectronicsOBJECTIVE: Develop a high performance, low loss (less than 0.5dB/m), infrared (IR) fiber technology for transmitting high power (greater than 100 Watts CW) from a multi-band mid-infrared laser (2-6 micron).DESCRIPTION: Infrared (IR) lasers are of high importance to the US military for multiple applications including infrared countermeasures (IRCM), free space optical communications, and imaging laser radars. To provide increased capability in these areas, the Department of Defense has made significant investment in high power IR laser sources. The objective of this SBIR is to leverage the advancing laser technology for IRCM systems by developing a corresponding high-performance infrared fiber technology.Current IRCM laser systems integrate a multi-band mid-infrared laser with a pointer-tracker as a mated pair, comprising a single replaceable unit. The pointer-tracker assembly then directs the laser power to confuse and jam the attacking threat missile. Performance and reliability of current IRCM laser systems in high-power, high-stress environments is limited by thermal and vibration issues due to the use of free-space optics in the laser systems. The potential use of optical fiber to transmit the high-power laser beam to the pointer would create IRCM systems that meet the requirements of Modular Open Systems Approach (MOSA), whereby the infrared lasers and pointer-trackers become line replaceable units (LRU) connected through fibers. This would enable IRCM laser systems with simpler vibration isolation, better thermal control, higher performance and reliability, and significant cost reduction (unit, repair, and maintenance costs). Fibers with appropriate composition should be robust and reliable so that they can be made insensitive to temperature changes, vibration, and moisture. Fiber strength and resistance to mechanical damage are also important.Current fiber capabilities at these wavelengths are limited by either water absorption or other losses. In addition, fiber strength and ability to withstand adverse environments is an issue. New technology is required to advance the state of the art in mid-infrared fibers to fulfill emerging requirements. Of particular interest would be methods for providing advanced infrared transmissive materials with high performance characteristics. The ability of the material to withstand representative stresses and survive in the extreme environments found in Army applications is also of interest.The development, characterization and demonstration of fiber production, infrared transmission and advantageous material properties of fibers are key elements of any proposed research. The ability to integrate these fibers with traditional fiber components, such as connectors, multiplexers, other fibers and switches, would be advantageous. Efforts are needed to develop novel approaches to achieving development of these high performance fibers and maturation of the technology and manufacturing base. The end result of this research would be high performance optical fibers to advance the state of the art in mid-infrared laser applications.PHASE I: Design an approach to produce optical fibers capable of low-loss (less than 0.5dB/m) transmission between 2-6 micron that exceeds the current state of the art. The optical fiber must have the capacity of transmission greater than 100 Watts laser power over 5-meter long fiber with the mechanical properties to operate in military environments (vibration, temperature, and humidity). Demonstration and measurement of physical properties such as fiber strength and resistance to the environment is critical. Since there is more than one wavelength to be covered, the fiber should be able to transmit a broad range of wavelengths (2-6 micron). A clear development path toward manufacturing the new fiber technology must be presented. The Phase I deliverable will be a final report including the initial fiber technology and performance assessment.PHASE II: Demonstrate production of usable lengths of mid-infrared fiber to transmit high power (> 100 Watts CW) laser output in the 2-6 micron region with less than 0.5dB/m loss and high material strength. The minimum requirement for the constructed and demonstrated fiber prototype is 25W of optical power transmission with low-loss (