Design Of Dispersion Flattened Microstructure Fibers And Research On Four-Wave Mixing In Microstructure Fibers

Microstructure fiber, also called photonic cystal fiber or holey fiber, possesses many intriguing properties that are hardly achievable in traditional fiber. It is a research hotspot in the area of fiber optics. Microstructure fiber with flattened dispersion shows lots of application potentials in dense wavelength division multiplexing, supercontinuum generation and wavelength conversion, etc. Thus, dispersion falttened microstructure fiber is one of the most important research directions in microstructure fiber optics. However, due to a large number of design parameters and the dispersion's strong dependence on precision of the fiber structure, it is a difficult task to design and fabricate dispersion flattened microstucture fiber. In addition, other properties are usually needed to incorporate with the flattened dispersion property to enhance the system performance. In view of this situation, in this thesis, structural parameters' influrences on the optical properties of microstructure fiber are analyzed. Fabrication fridenly dispersion flattened microstructure fibers incorporated with other intriguing properties are designd. The main contents are described as follows:First, the error of treating group velocity dispersion of microstructure fiber as sum of material and waveguide component is computed, its relation with structural parameters is analyzed. Taken 5% and 5 ps/km/nm as relative and absolute error limit, the valid micorstrcture fiber structural boundries of employing the normalized method in dispersion calculation are proposed. Based on Maxwell equation, normalized effective mode area expression of microstructure fiber is also deduced. By employing the expression, simulation complexity of mode area is reduced.Second, large cladding air holes are prone to deformation in fiber fabrication and the dispersion of the realized fiber would be influrenced. To deal with this problem, double cladding microstructure fibers, whose dispersions are insensitive to the deformation of large outer cladding air holes, are proposed. By employing multipole method, the diseprsioon and loss property of double cladding microstucture fiber is analyzed with an emphasis on two issues listed below: first, disperison's dependence on deformation of outer cladding air holes with different number of inner air-hole layers; second, the ratio of the loss of fundamental mode to that of second order mode with different outer cladding air-hole pitch. Several dispersion flattened double cladding microstructure fibers are designed. By further adjusting the outer air-hole pitch, the fibers can also support sinlge mode transmission.Third, effective mode areas of two different kinds of microstructure fibers, whose core are formed by omitting one or seven air holes, respectively, are computed by normalized mode area expression. Their relations to the cladding air filling fraction and wavelength are analyzed. It is found that efefective mode area can be reduced tremendously if the air-hole number in the first inner ring is increased and the channel between two air holes is narrowed. According to the analysis, dispersion flattended highly nonlinear microstructure fibers in telecommunication band are designed. Their cores are either formed by omitting seven or by nineteen air holes.Fourth, dispersion flattended highly nonlinear microstructure fiber in 800 nm band is proposed. Due to large absolute value of silica's dispersion and its nonlinear relation to wavelength around 800 nm, it is difficult to counterbalance the material dispersion of silica by waveguide dispersion. More air-hole diameters have to be employed to enhance the design freedom. Highly nonlinear microstructure fiber with flattened dispersion and single-mode transmission in 800 nm band can be achieved by enlarging the air holes in first inner ring, decreasing the cladding air-hole pitch, etc.Fifth, four-wave mixing is observed both in microstructure fiber with two zero dispersion wavelengths and in dispersion shifted microstructure fiber by using Ti: sapphire fs pulse as pump. The experimental results are explained by theoretical analyses and the theoretical analyses agree well with experimental results.