SBIR-STTR Award

This Small Business Innovative Research (STTR) Phase I project will demonstrate the feasibility of an innovative optical chiral fiber sensor (CFS) technology. A double helix structure with pitch greatly exceeding the wavelength will be imposed by twisting glass fibers with noncircular cores as they pass through a miniature oven in a "twisting tower" with enhanced temperature and motion control. The chiral long period grating (CLPG) will couple core and cladding modes to produce a series of dips in transmission of the core mode. The central wavelengths and depths of these dips are sensitive measures of the strain, pressure, torque, and temperature of the fiber and of the refraction index of the material surrounding the fiber. The CPLG design will be guided by an innovative combination of analytical calculations assisted by 2-D hybrid transverse finite elements electromagnetic simulations and fully three-dimensional finite vector elements simulations of wave propagation. These simulations will yield the coupling strength between the core and cladding modes. The results of transmission measurements with varying temperature, elongation and surrounding refractive index will be used to refine the assumptions of the calculations. The improved model will be used to fabricate the CLPG and to design a transducer for a CFS. The innovative CLPGs present a clear advantage of a broad choice of glass materials, which may be selected for resistance to harsh environments at high temperatures and/or radiation levels such as those in oil wells, nuclear reactors or outer space. In contrast, conventional fiber gratings created in UV sensitive glass fibers are significantly degraded in such harsh environments. The versatile fabrication approach allows for the flexible production of a full suite of sensors functioning over a broad frequency range by a single tool by changing the computer controlled twist and draw rates. This manufacturing process will make it possible to fabricate highly sensitive uniform CLPGs while dramatically lowering the production cost relative to conventional fiber gratings, which require precise patterning of UV radiation. The improved manufacturing process will also be used to produce other devices based on chiral fibers for filter, laser, sensor and polarizer applications. The computational model developed will enhance the understanding of optical interactions with chiral fibers and thereby facilitate the development of new chiral fiber devices

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 °C 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.