Study On Fibers As Well As Fiber Gratings With Novel Materials And Microstructured Cladding

Optical fibers have many important applications in communication systems, sensors, medical instrumentation, and various optical components due to its super transmission properties, the hot research topics shifted from the attenuation to dispersion and nonlinearity research, and numerous passive and active optical components were invented. During the past few years, the optical fibers and optical components with special structure attracted much more attentions and were used wildly specially in optical components designing for its unique transmission characteristics and flexible designing that cannot be achieved from conventional fibers.In this dissertation, theoretical and experimental research on fibers and fiber gratings with a novel matieraial such as uniaxial crystal material and the Total Internal Reflection microstructured cladding.The model of fiber and fiber Bragg grating with cladding made of uniaxial crystal material whose optical axis is parallel to the axis (z-axis) of fiber was proposed, the parameter K_cl, i.e., the ratio of the extraordinary to the ordinary ray refractive index, were introduced, the characteristic equation of the ideal normal mode were derived from the wave equation, the effective index, dispersion and power confinement factor of the HE₁₁ mode of the fiber were simulated, the reflectivity, Bragg wavelength, bandwidth and dispersion of this kind fiber Bragg gratings were examined using coupled-mode theory and numeric solution and Electro-optic Effect and Elasto-Optic Effect of the fiber were theoretically investigated. These research results provide a theoretic basis for designing optical components based on fiber and fiber Bragg grating with cladding made of uniaxial crystal material, and a novel tunable filter, wavelength selector, voltage and strain sensors and etc can been designed according to the conclusions.The transmission properties of Microstractured fiber (MF), the relationship between the filling factor and the reflectivity of fiber Bragg grating formed in the Total Internal Reflection microstructured fiber were investigated by the scalar and fully vectorial improved effective index method (FVIEIM), and the ways to increase the reflectivity were concluded. The BeamPROP (BMP) method is used to design a broadband dispersion compensation MF whose structure is three-tier air hole with different diameters. A pressure sensor based on long-period fiber grating (LPG) were designed and fabricated, a pressure sensing experiment was conducted, and the results show that the LPG pressure sensor has great performance such as excellent linearity degree and high sensitivity. A kind of long-peroid fiber grating was inscribed in the high nonlinear microstructured fiber by mechanical pressure and the relationship between the depth of the transmission spectrum and the pressure was mensurated.The main contents and achievements are as follows.1, Fibers and fiber gratings with uniaxial crystal material cladding(1) The model of fiber with cladding made of uniaxial crystal material whose optical axis is parallel to the axis (z-axis) of fiber was proposed, the characteristic equation of the ideal normal mode were derived from the wave equation, the effective index, dispersion of the HE₁₁ mode of the fiber were simulated. The research results indicate that the dispersion increases from negative to positive with the wavelength increasing, the larger K_cl is, the less the zero dispersion wavelength changes. When K_cl <1, the zero dispersion wavelength decreases rapidly, but when K_cl >1, it decreases slowly.(2) The impact of K_cl on the power confinement factor of the HE₁₁mode of the fiber and the influence of Electro-optic Effect and Elasto-Optic Effect on the power distribution of this kind of the fiber was inverstigated. The calculated results indicate that the stronger the electri field is, the less optical power transmitted in the core, and more power was concentrated in the cladding. The stronger the strain is, the more energy is transmitted in the core.(3) The influence of K_cl on the reflectivity, Bragg wavelength, bandwidth and dispersion of fiber Bragg gratings with uniaxial crystal material cladding were demonstrated, the calculated results indicate that the reflectivity of the fiber Bragg grating with cladding made of uniaxial crystal material is much higher than that with cladding made of isotropy material, the Bragg wavelength could be shifted due to different index contribution of the uniaxial crystal material cladding. More power is confined in the core of the fiber with cladding made of isotropic materials than that with cladding made of isotropic material while keeping the other parameters of the fiber as constant. For fiber Bragg grating, the power transmitted by the cladding is more easily coupled into the backward-propagating guided fundamental mode.(4) The design of Optoelectronic devices with LiNbO₃ and KDP cladding, respectively, were predicted based on the above theory, i.e., a novel tunable filter, electric field (or voltage) and strain sensors and etc were proposed due to Electro-optic Effect of LiNbO₃ and Elasto-optic Effect of KDP crystal materials.2, Total Internal Reflection Microstructured fibers and gratings(5) The effective index of MF and the reflectivity of fiber Bragg grating formed in the Total Internal Reflection microstructured fiber were investigated by the scalar and fully vectorial improved effective index method (FVIEIM), the calculated results indicate that the scalar approximation condition will not be satisfied and full vector should be used when the filling factor is more than 0.45, the effective index of the fundamental space filling mode (FSFM) decreases, the reflectivity increases and the Bragg wavelength shifts to shorter wavelength with the filling factor increasing. (6) A 10-peroids and 1.2mm-long-peroid fiber grating was inscribed in the high nonlinear microstructured fiber by mechanical pressure and the relationship between the depth of the transmission spectrum and the pressure was mensurated. The result indicates that the depth of the transmission spectrum increases with the pressure increasing, i.e., the optical energy transmitted in the core is coupled to the cladding, but when the pressure become larger, the depth of the transmission spectrum decreseas, i.e., the optical energy is coupled back to the core.(7) A pressure sensing experiment was conducted using a metal groove plate whose period can be tunable, the results show that when the pressure varies between 0 and 70N, the linearity degree of the pressure-transmission peak attenuation curve is as much as 0.9915 and the sensitivity is 0.2dBm/N.(8) The BeamPROP (BMP) method is used to design a broadband dispersion compensation MF in 1550nm wavelength range. The MSF structure is three-tier air hole with different diameters, the best structure with 100 nm bandwidth is found to compensate ordinary single-mode fiber (G.652) more than 100 times which is the largest, to our knowledge.