Theory And Experimental Study Of Novel Microstructure Optical Fibers With Birefringence And Nonlinearity

Birefringence and nonlinearity are two of the most important properties of microstructure optical fiber. So far, there have been a lot of studies on birefringence and nonlinear characteristics of MOF. In this thesis, the relationship between birefringence and nonlinearity of MOF is explored, innovative design concepts for birefringent and nonlinear MOF is proposed, nonlinear process of femtosecond laser pulse in highly birefringent and nonlinear MOF is researched experimentally. The main contents are described as follows:Firstly, the transmission process of femtosecond laser pulses in the designed highly nonlinear MOF is studied by solving the nonlinear Schr?edinger equation. Based on the simulation results, the impacts of the peak-power, width, wavelength and frequency chirping of femtosecond pulses on the superconinuum generation in MOF are investigated.Secondly, a novel MOF with octagonal cladding and elliptic fiber core is proposed. The diameter of cladding air holes and the fiber core’s long and short axis ratio impacts on the birefringence and nonlinearity of the MOF are analyzed, respectively. Our analyses show that birefringence of the MOF is mainly attributed to the asymmetrical fiber core instead of octagonal symmetrical cladding. To enhance fiber birefringence, anamorphic octagonal cladding is employed and two MOFs with large central holes and rectangle-like fiber core are proposed. The influences of the holes diameter, the distance between the holes and the core’s long and short axis ratio on the birefringence, non-linearity, and dispersion of these two MOFs are analyzed. Based on these studies, it is found that to improve the birefringence and nonlinearity of the MOFs, reducing the distance between the holes is more effective and the width of the output pulse increases with the increase of the core’s long and short axis ratio.Thirdly, the properties of a V-shape MOF designed and fabricated by our group are numerically simulated by finite-element method. It is found that nonlinearity and birefringence of this V-shape MOF are very high. The transmission process of femtosecond laser pulses in the MOF is studied experimentally. The impacts of the dispersion and birefringence of the fiber, as well as the power and central wavelength of the incident light, on the supercontinuum generation are investigated for the fiber.Fourthly, the transmission process of femtosecond laser pulses in a high birefringent and nonlinear MOF, whose cladding is composed of randomly arranged air holes, is investigated by experiments. It is found for the first time that the incident light pulse with central wavelength located in the normal dispersion regime of MOF can also generate Stokes and anti-Stokes wave. The mechanism for Stokes and anti-Stokes wave generation can be explained by phase-matching theory of four-wave mixing. Experimental results also show that the intensity, central position and conversion efficiency of both Stokes and anti-Stokes wave can be effectively regulated by the phase-matching condition, the polarization direction, the average power and the central wavelength of the incident light pulse.Finally, the impacts of MOF’s structure parameters on the position of zero-dispersion wavelengths are analyzed through numerical calculation. The relationship between phase-matching and dispersion property of single or double zero-dispersion MOFs are analyzed. Experiments of spectrum transmission are performed in the MOF with double zero-dispersion. The impacts of the number and position of the zero-dispersion wavelength of the MOF on the wavelength conversion of the four-wave mixing are validated.