TECHNOLOGY AREA(S): Air Platform

ACQUISITION PROGRAM: PMA272 Tactical Aircraft Protection Systems

OBJECTIVE: Develop single mode polarization-maintaining fiber (PM-fiber) that covers the Mid-Wave Infrared (MWIR) wavelengths from 2um � 6um for applications that require a high polarization extinction ratio at the fiber output and is able to waveguide tens of watts of optical power through the fiber.

DESCRIPTION: Applications requiring linearly polarized light and the flexibility of fiber delivery in the MWIR region will require a fiber solution that preserve the polarization state of the launched light. Most infrared lasers are polarized. PM-fiber offers the capability of preserving the launched light polarization state as it propagates through the fiber. In conventional fibers the polarization state is not preserved due to mechanical stress, temperature induced changes, fiber fabrication imperfections, and fiber bends. Commercially available silica PM-fibers cover the visible and near-infrared spectrum; these work by creating a strong birefringence across the core of the fiber, which is responsible for preserving the polarization state of launched light as long as the polarization is aligned with one of the birefringent axes. Several different approaches can be taken in order to fabricate such specialty fibers including, but not limited to, the use of elliptical core, the addition of stress rods (Panda type and Bow-Tie type), and also by micro-structuring the optical fiber (MOF). Currently there is no commercially available PM-fiber solution for the MWIR region. A specialty fiber capable of high-power laser transmission (>10W cw) and preserving the polarization state of the input light with high polarization extinction ratio (~-30dB), high birefringence (~10-3) and with low propagation losses (<0.2dB/m) covering the MWIR wavelength spectrum is desired.

PHASE I: Determine the feasibility of an initial design of a PM-fiber approach best suited for the MWIR spectral region. Evaluate the performance of the PM-fiber design by determining if wave guidance is achieved in the spectral window of 2um � 6um, the magnitude of the birefringence, and the attenuation loss is less than 0.2dB/m. Demonstrate fabrication proof of concept and identify the steps and approach needed to fabricate the fiber design. Develop a Phase II plan. The Phase I effort will include prototype plans to be developed under Phase II.

PHASE II: Develop an initial PM-fiber prototype. Perform characterization of the optical and mechanical performance of the PM-fiber. Compare experimental results to the expected specifications. Optimize the PM-fiber design based on the characterization results and evaluation. Produce several different lengths of PM-fibers� to test the performance of the drawn fibers (i.e., 1m, 5m, 10m), which should be terminated in an optical connector that requires a minimal amount of epoxy. Ensure that the insertion loss of these fibers is less than 0.5 dB.

PHASE III DUAL USE APPLICATIONS: Finalize development and support fiber testing. Refine the fiber based upon results of testing and transition the final technology to be used with the next-generation Infrared Counter Measures (IRCMs). Successful development would benefit the medical industry for transporting high amounts of optical energy to manage drug efficacy or cells manipulation.

REFERENCES:

1. Folkenberg, J., Nielsen, M., Mortensen, N., Jakobsen, C., and Simonsen, H. Polarization Maintaining Large Mode Area Photonic Crystal Fiber. Optics Express, 2004. https://www.osapublishing.org/DirectPDFAccess/03FB670B-D83C-C517-012C0C8F20DB2EB6_79214/oe-12-5-956.pdf?da=1&id=79214&seq=0&mobile=no

2. Mendez, A., and Morse, T. �Polarization Maintaining Fibers (Chapter 8).� Specialty Optical Fibers Handbook, 2007, pp. 243-277. Elsevier Inc.: Burlington. https://www.sciencedirect.com/science/book/9780123694065#book-info

KEYWORDS: PM Fiber; Polarization; Polarization Maintaining Fiber; MID IR Fiber; PM Photonic Crystal Fiber; PM AS2S3 Fiber