Theoretical Analysis Of Dispersion Properties Of Photonic Crystal Fibers

A new type of fiber, known as photonic crystal fiber, has emerged in the past several years. These fibers are characterized by wavelength-scale air holes running along the entire fiber length in the cladding region, which have resulted in some unusual properties unattainable with conventional optical fibers. In particular, photonic crystal fibers can display anomalous dispersion in the visible and near-infrared wavelength range, and, therefore, have great potential in the field of femtosecond laser technology. The dispersion properties of photonic crystal fibers are investigated theoretically in the present dissertation. The main results are summarized as follows. 1 The dispersion properties of photonic crystal fibers are investigated using a fully vectorial effective index method (FVEIM) that we proposed. In analogy to conventional mode classification, the fundamental space filling mode of photonic crystal fibers is classified as HE1 1mode. With optimized fiber parameters, FVEIM yields results in agreement with experimental data and other numerical values, while the scalar effective index method causes considerable discrepancies. 2 A semi-vectorial finite difference method (SFDM) is used to characterize the dispersion of photonic crystal fibers. Numerical results by SFDM agree well with those measured and by other methods. The influence on photonic crystal fiber dispersion of the size of air holes in different rings within the cladding is studied. It is demonstrated that photonic crystal fiber dispersion is most sensitive to the air hole size variation in the first two rings. In addition, the angular and radial deviations of the air holes from their ideal positions are investigated separately, revealing that the former has less influence on fiber dispersion than the latter. Finally, the dispersion characteristics of hole-assisted lightguide fibers are analyzed. It is found that more air holes, larger air holes, and air holes closer to the fiber core all help to reduce the zero dispersion wavelength. 3 Photonic crystal fibers with zero dispersion and flattened dispersion around 800 nmare designed. The normalized dispersion technique is shown for the first time to our knowledge to be applicable under different scaling parameters, and then used in combination with FVEIM to design photonic crystal fibers with zero dispersion and flattened dispersion around 800 nm.