Intellectual Merit: Photonic crystal fiber represents a new frontier in fiber-optic research. This project aims to investigate a novel platform concept based on core-to-cladding-to-core mode coupling and recoupling enabled by long-period fiber gratings inscribed in this type of fiber for resonance laser absorption spectroscopy. Specific project activities will include simulation of mode properties of select platform designs such as field distribution, overlap, and propagation loss using commercial codes; simulation-guided laser inscription and optical measurements of the platform structures for the realization of mode coupling and recoupling at prescribed resonance wavelengths; and measurements and assessment of the sensing capabilities of the optimal platform structures via resonance laser absorption spectroscopy of environmentally significant gases. This project will lead to a wealth of information on optimization of the platform structures for strong cladding mode coupling and recoupling and for resonance wavelength control so as to facilitate robust resonance laser absorption spectroscopy.
Broader Impacts: This project will provide a knowledge foundation for practical exploitation of novel fiber-optic sensing schemes. Successful outcome of the project has the potential to usher in a new sensing paradigm that fundamentally transforms the conventional fiber-optic evanescent field sensing approach. In addition, this project will provide an excellent opportunity for the training of a doctoral student as well as for valuable research experiences of a high school science teacher and several high school students in a frontier research area. The university-industry partnership under the GOALI mechanism will significantly enhance the translational prospect of university research, ultimately leading to commercial applications.
Photonic crystal fiber (PCF) represents a new frontier in fiber-optic research. Long-period grating (LPG) structure inscribed in this category of fiber greatly expands the realm of their applications especially for multi-parameter sensing. This three-year program encompassed simulation, fabrication, and measurements of PCF-LPG for fundamental understanding of mode coupling and for sensing and process monitoring in gas and liquid media. Key findings and outcomes are highlighted as follows: (1) Excitation of cladding modes by LPG has been shown to greatly expand the mode-field interaction with an analyte medium in PCF. With optimized PCF-LPG design, unprecedented field power overlap with low loss is achievable in the cladding modes. (2) LPG inscribed via asymmetrical or symmetrical laser irradiation is shown to exhibit significantly different mode field distribution in the coupled cladding modes. Symmetrical LPG inscription should be carried out for uniform and symmetric mode field distribution in the cladding structure of PCF that is less susceptible to variations in other parameter. (3) Properly designed and fabricated PCF-LPG has been demonstrated to exhibit high sensitivity to changes in the index of refraction of a gas phase that may result from variations in gas pressure, gas type or composition. Cascaded LPG has proven an effective means of enhancing the sensing resolution. (4) PCF-LPG has been further demonstrated to be a robust index transduction platform to sense and detect molecular binding events in liquid medium using a model immunoassay, illustrating its significant promise for label-free biological detection. (5) PCF-LPG has been shown to be a powerful optofluidics platform for the investigation of layer-by-layer assembly of functional polyeletrolyte thin films in confined geometry, a field of great relevance to device development of nano- sensors and nano-actuators. Our research findings have been published in five peer-reviewed journal articles (with one more under preparation) and presented as invited seminars and talks at numerous technical conferences. The project was carried out in collaboration with OFS Laboratories, an industrial leader in specialty fiber optic research and product development and with the Institute of Photonics and Electronics, the Academy of Sciences of the Czech Republic, where significant theoretical expertise in specialty fiber simulation resides. From the educational and outreach perspective, the project enabled the training of two doctoral students, who also had significant industrial as well as international exposure in the course of the investigation. One high-school science teacher actively participated in the project and was a co-author of a peer-reviewed publication for her technical contributions. This teacher also brought with her several students from her school to gain summer laboratory experiences in our group. The research outcome has been used as case studies in the graduate courses we teach and featured as success stories of graduate research for incoming students in the PI’s department.
