STTR Phase II: Chiral Long Period Grating Fiber Sensors

This Small Business Technology Transfer (STTR) Phase II project will develop a novel optical fiber sensor of temperature, pressure, extension, axial twist and various environmental factors, including liquid level, in harsh environments. The optical fiber sensor will be free of electromagnetic interference and of the hazard of igniting combustible fuels and will be capable of remotely monitoring temperatures up to and beyond 750 ýýC and of tolerating high-radiation levels. Conventional long period gratings fiber (LPGs) formed by exposing photosensitive doped optical fibers to patterned ultraviolet illumination cannot operate in harsh environments because of the fragility of the imprinted periodic structure. In contrast, the glass fiber in the dual-twist chiral fiber sensor (CFS) need not be photosensitive and will be chosen for its robustness. The chiral long-period grating (CLPG) structure of the CFS will be created in a glass-forming process in which signal and scaffolding optical fibers are twisted together to form a helix in the signal fiber as the fibers pass through a miniature oven. Transmission dips due to coupling of the light between the core and surrounding glass cladding by the chiral grating and their shift with environmental factors will be measured and calculated using an increasingly sophisticated sequence of perturbation theories. The CFS based on the dual-twist CLPG structure overcomes the disadvantages of the LPG and of the CFS based on twisting single birefringent fibers. If successful it is ideally suited for demanding applications such as found in nuclear reactors, outer space, and oil wells, as well as in medical diagnostics and treatment and in the automotive and aerospace industries. The CFS may therefore become a pervasive part of modern technology and everyday life which relies increasingly on sensing and automated decision making. By substantially raising the operation temperature of optical fiber sensors, substantial savings can be realized. Conventional power generators could run at higher temperatures where they are substantially more efficient and the recovery rate in oil reservoirs can be increased considerably. The use of high-temperature and radiation-resistant CFSs in nuclear power plants can make these facilities more efficient and safe. The enhanced range of conditions in which the CFS can function relative to conventional electrical and optical sensors will have an impact across the economy and will make the CFS a rapidly growing segment of the multi-billion dollar sensor market. The novel glass forming fabrication methods and computational approaches may find use in diverse fields including photonics, microfluidics and medical diagnostics.