High power continuous and pulsed fiber lasers and amplifiers have become more prevalent in laser systems over the last ten years. In fielding such systems, strong environmental and operational factors drive the packaging of the components. These include large operational temperature ranges, non-standard wavelengths of operation, strong vibration, and lack of water cooling. Typical commercial fiber components are not designed to survive these types of environments. Based on these constraints, we have had to develop and test a wide range of customized fiber-based components and systems to survive in these conditions. In this paper, we discuss some of those designs and detail the testing performed on those systems and components. This includes the use of commercial off-the-shelf (COTS) components, modified to survive extended temperature ranges, as well as customized components designed specifically for performance in harsh environments. Some of these custom components include: ruggedized/monolithic fiber spools; detachable and repeatable fiber collimators; low loss fiber-to-fiber coupling schemes; and high power fiber-coupled isolators.
A mirror mount for adjusting and holding half-inch diameter optics is described. The intended environment for the mount is that of flight Military Lasers. This operational environment includes varying static and dynamic loading, temperatures, and pressures. The mount is angle adjustable in two orthogonal directions, though is not a true gimbal mount. Its most unique characteristics are small package size, locking features that do not impose crosstalk on the adjusted position, and extreme ruggedness and stability over the stated environment. Design and performance information is presented.
To enable the invention of new optical instruments subjected to a broad range of operating conditions, there is a need to develop improved technology to hold small mirrors and other optical elements with high dimensional stability and low cost. A previous paper described a screening experiment on small face bonded mirrors subjected to an environment of -41 to +70 degree(s)C with the intent of finding factors that influence the bond joint's contribution to angular stability. This paper describes part of the continuing experiment, specifically addressing BK-7 mirrors bonded to Aluminum mounts with a flexible adhesive. The resulting tilt errors in the mirror assemblies were measured, and showed a definite pattern with respect to bond thickness. Flexible bonds between these two CTE mismatched materials did not fail, and exhibited high stability over temperature at 0.002-inch bond thickness.
To enable the invention of higher power IRCM lasers, 3D LIDAR systems, Designator/Rangefinders and other Instruments subjected to a broad range of operating conditions, there is a need to develop improved technology to hold small mirrors, lenses, beamsplitters and other optical elements with repeatable and high dimensional stability over wide environmental temperature ranges, an do so with great economy. The intent of this effort was to begin identifying significant factors for bonding small mirrors for high stability. A screening experiment was performed in which half-inch diameter flat mirrors were face bonded to similar mirror mounts, then bolted to a reference test fixture and subjected to an environmental temperature range of -40 to +70 degrees C. Mount material, optic material, adhesive material, bond joint design, and bond thickness were varied. The resulting tilt errors in the mirror assemblies were measured. Steps were taken to isolate the bond joint stability as opposed to stability in the mounted mirror subassemblies. The effort required to minimize experimental noise was much greater than anticipated. This first experimental effort failed to identify main factors with statistical significance, however; some results are interesting. Perhaps also of interest is the progress made at characterizing the experimental setup and process, and lessons learned in control of noise factors in this kind of experiment.
As tactical military lasers become more complex and the requirement for effectiveness increases, the stability of the optics comprising those lasers becomes critical. Boresight stability requirements for individual optomechanical subassemblies are in the sub-100 microradian range with temperature excursions of up to 80 degrees C. Even the most detailed Finite Element Modeling is ineffective in predicting performance to the accuracy and resolution required. Boresight error allocations of individual optical subassemblies must be verified with test. Boresight tests were performed on several optical subsystems of a military laser required to hold boresight in an airborne military environment. The units tested were fabricated and assembled using the materials and processes prescribed for production. The purpose of the testing was to verify that the subsystems do not exceed their allocated stability tolerance. The results show angular shift in azimuth and elevation over a temperature range of -54 to +71 C. Assembly of the units was performed at approximately 23 degrees C.