Investigation Of Microstructured Optical Fiber Sensors Based On Azobenzene Infiltration

Microstructured optical fibers (MOFs) have been widely investigated for their unique light guiding properties, flexible design, and diversity of material choice. The periodic air-hole arrangement over the fiber cross section along the fiber axis provides a promising possibility to infiltrate functional materials into the cladding air holes. The functional material infiltration technique equips MOFs with the mutual advantages of material science and fiber optics, and thus a good variety of functional fiber-optic devices could be developed. Azobenzene-based materials have attracted considerable research interests for their distinguished cis-tra-s-isomerization-based optical properties, such as UV photosensitivity, optical nonlinearity, and photo-induced anisotropy, and have been employed in various related applications, including optical storage, optical switching, and even photo-responsive bioengineering. In this thesis, azobenzene-materials and MOF have been integrated with MOFs to achieve functional microstructured optical fiber sensors. The main contents are as follows:1. A solid-core microstructured optical fiber is infiltrated with the DY7-chloroform mixture solution, resulting in the appearance of several transmission dips. Comparison experiment was conducted to investigate the origin of the transmission dips. The temperature-and load-dependent spectral characteristics of these dips have also been studied and experimental results indicate that the transmission dips are highly temperature-sensitive, but insensitive to the variation of axially applied load. Such a compact fiber-optic device with electromagnetic immunity could be employed for load-insensitive temperature sensing applications.2. The photoisomerization effect of the azo material has been introduced into a solid-core microstructured optical fiber (MOF) by infiltrating the DR1-chloroform mixture solution into its cladding air holes. The irradiation laser power density as well as temperature effects on the transmission spectral characteristics of the solution-infiltrated MOF have been investigated. The two transmission dips exhibit opposite laser power density dependences of the peak losses. And the origin of the transmission dips has been further investigated. Owing to their highly sensitive light responsivity, our proposed fiber-optic devices could be applied in light intensity measurement with a sensitivity of 0.26468dB/(mW·cm-2).3. A dual-parameter sensor based on a liquid-infiltrated microstructured optical fiber (MOF) is constructed by selective liquid infiltration of one particular cladding air hole in the MOF. The fundamental core mode could be simultaneously coupled to several higher-order modes located in the adjacent liquid rod waveguide when the phase-matching condition is satisfied, resulting in the emergence of multiple resonance peaks with different sensing characteristics. Our proposed liquid-infiltrated MOF sensor has such desirable advantages as high sensitivity and large measurement range. Moreover, temperature/force cross-sensitivity issue that is commonly encountered in practical applications could be resolved. In addition, the proposed device provides research foundation for successive studies on azobenzene-based optical fiber devices.