| For the past ten years or so, photonic crystal fibers (holey fibers, microstructured fibers) have become a focus of attention in the field of optoelectronics worldwide for their brand-new concept, excellent performance and potential prospect of application. They will be widely used in the fields of optical communication, nonlinear optics, ultrashort laser pulses and harmonics, atomic spectroscopy, photonic crystal physics, high-precision spectroscopy, photonic biology and optical data transfer. The properties of photonic crystal fiber (PCF) made it an excellent medium for supercontinuum generation. The need for a supercontinuum light source is immense, with applications extending into the fields of high-precision laser spectroscopy, ultrashort pulse compression, femtosecond-pulse phase stabilization, ultrahigh-resolution optical coherence tomography and optical Doppler tomography, high-precision optical frequency metrology, sensor technology, multiwavelength optical sources, optical communications and laser colour display. Hence there is great scientific and application value in the experimental study on supercontinuum generation in PCF.The summary of the dissertation is as follows:1. Chapter I of this dissertation introduces the history and development of the studies of photonic crystal fibers and their applications. And this chapter stresses on the optical properties and application studies of PCF.2. Chapter II starts from the Maxwell's equation, discusses the physical processes of laser pulse propagation in fused-silica fibers. And this chapter focuses on the linear and nonlinear properties of optical fiber that alter the intensity and phase of laser pulses. The major phenomena that affect propagation through fiber are material absorption, dispersion, and nonlinear x(3) effects associated with fused-silica. The nonlinearSchr dinger equation (NLSE) is an approximate scalar form of the Maxwell's wave equation and can explicitly accounts for absorption, dispersion and nonliearity. The derivation of this equation is given in this chapter. And this chapter provides an introduction to a very powerful method in numerically solving the NLSE, known as the split-step Fourier method (SSFM).3. Chapter III studies numerical model of random PCF. With the model this chapter discusses theoretically optical properties of PCFs with randomly distributed air holes in the cladding. A suggestion to develop PCFs in silica media with random gas-line is also introduced.4. In chapter IV, for the first time using random PCF, we accomplished experimental studies of supercontinuum spectra as follows, a) Experimental study of supercontinuum generation in PCF with random cladding and core distributions; b) Experimental study of supercontinuum generation in PCF with combination core and random cladding. Both study achieved supercontinuum output spectra extending from 350nm to more than 1700nm. To the best of our knowledge, this is the broadest supercontinuum generation with PCF in the world.Our experimental studies have other originalities or new discoveries as follows. (1) The wavelength and power of visible light ranging in supercontinuum can be tuned by adjusting the input end of random PCF (to change pump incident point or incident angle). (2) In particular, white light has been observed. (3) The polarization states of the visible light change with adjustment of pump incident point or incident angle. (4) We observed high-order waveguide modes.These findings have great scientific value. (1) They confirmed experimentally that periodicity is not needed for efficient supercontinuum generation in PCF. (2) PCFs with randomly distributed air holes have generated many unusual features such as SC wavelength tunable notpresented in periodical PCF. (3) The SC wavelength tunable property in the random PCF can provide a novel answer to optical parameter oscillator and tunable laser. (4) Visible light of various wavelengths generated in the random PCF provide... |
PDF Full Text Request