Fiber coupled optical isolator for high average power and high pulse energy lasers

Aqwest proposes to develop innovative fiber-coupled isolators (FCI) that can handle high-average and peak powers in 2 µm pulsed fiber amplifiers now being developed by the U.S. Air Force (USAF) as a part of an all-fiber pulsed laser system. The FCI design will support the inclusion of common fiber components such as fiber tap couplers, mode field adapters, and spectral filters. Our FCI concept offers 1) Drastic reduction in thermal lensing and birefringence, 2) Commercially available Faraday material, 3) Active cooling to remove heat deposited by the laser beam, 4) Reduced likelihood of optical damage, and 5) Active temperature control to optimize optical isolation. The proposed project will leverage Aqwest earlier work in optical isolators (OI) and extensive 2 µm laser testing capabilities. In Phase I, we will conduct analytical and experimental validation of the innovative FCI concept to show that the Aqwest design can provide the capabilities targeted by the USAF. In particular, a pre-prototype FCI will be constructed and evaluated over the 1.9-2.1 um range. Using this data, we will anchor our models, refine the concept, generate a preliminary design for a prototype FCI to be developed in Phase II. Our efforts to-date already validated the magnetics and produced large size Faraday material. This early work at Aqwest offers a basis for accelerated development in Phase I.    In Phase II, Aqwest will 1) develop and demonstrate a production prototype of a multi-component FCI meeting the objective requirements and 2) deliver it to AFRL/RDLT for assessment and testing. In Phase III, Aqwest will work with RDLT and industry partners to make their isolator design available to the DoD customer base as well as DoD industrial partners.