Research On The Characteristics And Applications Of Photonic Crystal Fiber

The air holes with wavelength scale distributed periodically or quasi-periodically in the cladding region make the photonic crystal fiber (PCF) have unique characteristics, which can not be achieved in the conventional fibers. As the excellent optical medium in the new generation, it can be extensively applied on the nonlinear optics, optical fiber communication, all-optical devices, and so on.In this paper, the dispersion, band-gap, and nonlinear characteristics of PCF are theoretically and experimentally investigated, and the studies on application are carried out. The main works and innovative fruits are as follows:First, the cladding-ring-equivalent effective index method (CREEIM) is put forward, the corresponding mathematical model is built, and the dispersion, mode cut-off, and nonlinear characteristics in two and three cladding PCFs are analyzed. By comparing the simulation numerical results with those obtained by other methods, it shows that this method can accurately analyze the multi-cladding PCF, and the calculation time can be greatly shortened due to not considering the complex electromagnetic field distributions near each air hole and the boundary conditions in the cladding region. This has significant meaning on accurately and fastly designing and analyzing the complex PCF with multi-cladding structure.Second, by deeply investigating on the mode coupling characteristics in the dual-concentric-core PCF (DCCPCF) with hybrid cladding structure, the large negative dispersion PCF around 1.55?m is designed. The PCF can simultaneously compensate the dispersion and dispersion slope, and restrain the pulse deterioration induced by the nonlinear effects in the fiber link. By the coupled-mode theory, the equivalent propagation constants of inner core fundamental mode and outer core defect mode are detailedly deduced. Whether a complete coupling is or not happening can be clearly indicated by comparing the equivalent propagation constant real and imaginary parts of two modes. This is instructive to accurately predicting the dispersion and mode characteristics of such DCCPCF in practice.Third, the band-gap and mode characteristics from near-infrared to visible wavelengths in hollow-core PCF (HC-PCF) with interstitial holes are theoretically and experimentally investigated. The remarkable influence of the glass interstitial apexes on the band-gap position is deeply analyzed, and the crucial effects of different points of the reciprocal lattice in the first Brillouin zone on the upper and down-edge forming of band-gap are indicated. The experimental result agrees well with that obtained by simulation. A kind of anti-resonance guiding PCF (ARG-PCF) which works at the nearby wave-band is designed. Through analyzing the characteristics of band-gap and mode, the influences of the cladding structures especially the high index cylinders on the the formation of band-gap and the existing case of guided-mode are shown. By the equivalent planar waveguide theory, the mode cut-off equation in such ARG-PCF is deduced, and the the resonance and anti-resonance characteristics are analyzed. These fruits provide a basis for the application of optelectronic devices based on the photonic band-gap PCF.Fourth, by three kinds of highly nonlinear PCF designed in our lab, the highly effiecient wavelength-tunable anti-Stokes signal conversions in the fundamental and second-order modes are experimentally achieved. In the second PCF, when the pump pulse with 500 mW works in the normal dispersion region closing to the zero dispersion wavelength of fundamental mode, the power ratio of 22.6:1 between the output signal and residual pump component and the conversion efficiency of 46% are obtained, which are the maximal ratio and highest conversion efficiency for the frequency conversion at short wavelengths by the fundamental mode. Through analyzing the signal conversion process, the involved nonlinear optical effects are adequately shown. In addition, the influences of working wavelength and power of pump on the signal conversion are comprehensively investigated. These fruits are beneficial to the development and application of new-style devices in ultrafast photonics.Fifth, by the PCF with central holes fabricated by extracting air from the central hole, the flat supercontinuum (SC) from 470 to 805 nm is generated in the experiment. At 585 nm and 590 nm, the corresponding maximal and minimal normalized intensities are 0.9915 and 0.9845, the relative intensity fluctuation being only 0.0071. The pump pulse with high peak power works in the anomalous dispersion region closing to the zero dispersion wavelength of fundamental mode, and three nonlinear phases in SC generation are comprehensively shown. This can provide a wide band source with good performance for the communication system at vsible wavelengths.Sixth, by> 100 fs pumping in the anomalous dispersion region closing to the zero dispersion wavelength of fundamental mode, based on the Raman solitons red-shifting above 2000 nm, the highly efficient and broadband Cherenkov radiation (CR) is experimentally generated at visible wavelengths. To the best of our knowledge, the conversion efficiency of 31% and bandwidth of 54 nm are the highest efficiency and maximal bandwidth by>100 fs short pulse. This provides an effective approach for obtaining the signal source at short wavelengths.