Research On Novel Photonic Crystal Fibers And The Relative Techniques Towards Their Applications

Ever since 1996, photonic crystal fibers (PCFs) have been attracting the interests of scientists all over the world owing to their unique properties. Along with the appearance of different kinds of PCFs and the progress of their fabrication techniques, a number of potential applications of PCFs have been developed. Up to now PCFs have been applied in a wide range of areas, such as optical communication, fiber sensor, and optoelectronics and so on. With the expansion of their application, many kinds of novel high performance PCFs are required to be developed, and some problems such as fabrication, splicing and testing systems for PCFs need to be broken through.This dissertation is supported by National Nature Science Foundation Program "Study on the integrated broadband dispersion and dispersion slope compensation photonic crystal fibers and their applications" and the National 973 Program "Research on the theory and key techniques of optical fiber devices towards the optical switching networks". It mainly focuses on the theoretical and experimental investigations on the novel PCFs and their fabrication and splicing techniques, the M-Z fiber interferometers based on the developed PCF and its sensing applications. The main achievements are listed as follows:1. Based on full vector finite element method, novel dual-concentric core dispersion compensation PCF is designed by inducing Ge-doped inner core. For the first time the influences of the central index dip in the inner core which is caused by the fabrication of fiber preform on the fiber dispersion is analyzed. Numerical results demonstrate that the effect of the central index dip of the inner core should not be neglected due to its effect on the phase matching wavelength shifts.2. A kind of novel DCPCF with pure silica in the inner core and fluorine-doped rods in the ring core is proposed. It has large mode field area and is easy to keep the optical properties of this DCPCF during the fabrication process. Moreover, the transmission loss can be further lowed due to pure silica inner core.3. Based on the home-made Ge-doped core PCF, the simple structured M-Z interferometers are successfully fabricated. They are applied in the experiment of low and high temperature sensing and strain sensing. The experimental results indicate that the Ge-doped core PCF interferometer has high temperature sensitive coefficient which reaches to-43pm/℃in the low temperature (20～140℃) experiment and-34.64pm/℃in high temperature (800～1050℃) measurement, and the interference spectrum shifts towards the short wavelength as the temperature increase. The highest measuring temperature is as high as 1030℃. In the strain sensing, the interferometer has good linearity and low strain sensitive coefficient. With its high temperature sensitive coefficient, this interferometer can be used as strain-insensitive temperature sensor.4. Based on the analysis of the resonant coupling theory, a new type of single-polarization single-mode PCF is proposed. Numerical results show that the bandwidth of the single-polarization single-mode PCF is great than 1000nm and much wider than the existing structures. The output mode field of this PCF is nearly Gaussian distribution, and the mode area of this PCF is similar to that of SMF which is helpful to reduce the splice loss between this PCF and SMF. In addition, the increment of central core refractive index is determined from the analysis. Through optimizing the confinement loss, the confinement loss of x-polarized mode can be increased more than 30dB which can efficiently ensure the single-polarization properties of the fiber.5. With the stack-draw method, various kinds of PCF such as Ge-doped core PCFs, polarization maintaining PCF, single-polarization single-mode PCF, dispersion compensation PCF, and photonic crystal dual-cladding fiber are successfully fabricated. By optimizing the fusion parameters, the low splicing loss between Ge-doped core PCF and SMF can be realized by using a conventional arc fusion splicer.