Femtosecond Laser Fabricated In-fiber Coupled Waveguide Sensor

Optical fiber sensors have been applied for applications in measuring of physical,biomedical and chemical parameters.In order to make optical devices more compact in size,integrating waveguides in fiber cladding has become hot issues for researchers.This dissertation mainly focuses on in-fiber coupled waveguide sensors and femtosecond laser inscription of waveguides.As follows:1.The dissertation reviews the fabrication and sensing application of in-fiber waveguide devices reported in recent years,introducing the development of femtosecond laser inscription of waveguide,fabrication and applications of laser-waveguide based devices.In addition,the coupled mode theory between parallel waveguides,nonlinear interaction between femtosecond laser pulses and material,and heat accumulation effects under high-repetition-rate femtosecond laser are also included.2.The performance of in-fiber laser waveguide has been optimized by use of lowrepetition-rate femtosecond lasers(1 k Hz and 200 k Hz),with a low propagation loss of 1.2 d B/cm.The refractive index(RI)profile in the cross-section of laser waveguides has been analyzed,with a positive and negative RI modification of 0.01 and 0.025 respectively.The mode field profile and inscription of Bragg grating waveguides have also been studied in this dissertation.3.In-fiber coupled Bragg gratings waveguide has been proposed,designed and fabricated.After in-fiber Bragg grating waveguides was optimized,an X-coupler was integrated in a single mode fiber and used for coupling light from fiber core to fiber surface.A fiber Bragg grating waveguide has been fabricated near fiber surface and applied for RI measurement of surrounding mediums,whose polarization and sensing characteristics were also analyzed.4.A coupled waveguide sensor in photonics crystal fibers(PCFs)has been proposed,designed and fabricated.A femtosecond-laser-assisted selective infiltration technology has been introduced,from the splicing between special fibers and traditional single mode fibers,precisely cleaving process to the selective opening of holes.Supporting many modes transmitting in this structure,the coupled waveguide sensor integrates with a multimode interferometer and successfully applies to simultaneous temperature and strain measurement,with sensitivities of 14.73 nm/oC and 12.01 pm/?? respectively.Using Finite Element Method(FEM),hybrid coupled waveguides have been modeled by use of COMSOL soft and dispersion curves have been calculated to precisely analyze the transmitting modes in hybrid coupled waveguides and study the phase matching condition between the liquid and solid waveguides.The calculated temperature sensitivity of 14 nm/oC agrees well with that of experiments.5.A coupled waveguide in hollow core fibers(HCFs)has been proposed,designed and fabricated.After a laser waveguide was inscribed in hollow core fiber,a pair of microchannels has been created by use of femtosecond laser ablation to measure the analyte's RI in real-time.This sensor has achieved an ultra-high RI sensitivity of-112743 nm/ RIU.The theoretical RI sensitivity has also been calculated by use of FEM,with a value of-108016 nm/RIU.It turns out that simulated results agree well with that of experiments.