| The supercontinuum generation is considered as an extremely important nonlinear optical phenomenon,and its wide bandwidth and high coherence characteristics make it have important value in the fields of optical communication,biomedicine,coherent measurement,and other fields.Supercontinuum is usually generated using highly nonlinear optical fibers or waveguides,and the micro-size and higher nonlinear coefficients of the waveguides are conducive to the generation of supercontinuum compared with optical fibers.Due to the current development trend of silicon-based photonics towards miniaturization and integration,the supercontinuum generation through nonlinear waveguides is more in line with current practical needs and conducives to the system stability.In this thesis,two types of nonlinear waveguides with different structures are designed using two materials.The corresponding dispersion curves are obtained through dispersion control.The effects of different factors on the generation of supercontinuum are studied.For the two types of waveguides,a set of optimal parameters is optimized,and the supercontinuum generated can reach the octave-spanning bandwidth.The main research work and innovative results of this thesis are summarized as follows:1.A strip waveguide is designed using titanium dioxide(TiO2)as the waveguide material,and the influence of waveguide structural parameters on dispersion is studied.By optimizing the size of the waveguide,a set of optimal parameters is determined,and the dispersion curve obtained has three zero-dispersion wavelengths,which are located at wavelengths 1.53μm,3.96 μm,and 5.43 μm,respectively,the nonlinear coefficient and effective mode field area within a certain wavelength range are calculated.2.Using the designed strip TiO2 waveguide,the effects of different factors on supercontinuum generation are studied.The effects of pump wavelength,peak power,pulse width,waveguide length,and noise coefficient on the generation of supercontinuum and coherence characteristic are investigated,respectively.The research results show that for the pump wavelength of 3.1μm,the peak power of 1000 W,the pulse width of 80 fs,the noise figure of 0.001,and the transmission distance of 4.2 mm,the supercontinuum generated using the titanium dioxide waveguide achieves a spectral width,whose wavelength range at-40 dB level is from 1.79 to 9.90 μm,more than 2.5 octaves.And its first-order coherence degree is 1.3.Silicon carbide(SiC)is chosen as the waveguide material and a ridge SiC waveguide with the multimodes is designed.Through dispersion control,the dispersion curves corresponding to three quasi-TE optical modes TE00,TE10,and TE20 mode are determined.The nonlinear coefficients and effective mode field areas of the three modes at different wavelengths are studied.4.Using the designed ridge SiC waveguide,the generation of supercontinuum and its influencing factors in different modes are investigated.The effects of pump wavelength,peak power,pulse width,and waveguide length on the generation of supercontinuum for different modes are simulated,and a set of optimal pump parameters is determined.The results show that when the pump wavelength is 2.3 μm,the peak power is 2 kW,the pulse width is 100 fs,and the waveguide length is 2.2 mm,the bandwidths at-40 dB level of the supercontinuum generated by the three optical modes TE00,TE10,and TE20 are 1.01～5.04 μm,1.23～4.05 μm,and 1.82-3.80 μm,respectively,the octave ranges of 2.32,1.72,and 1.06,respectively.And their first-order coherences are close to 1.The generation of octave-spanning supercontinuum in nonlinear waveguides is studied using the strip TiO2 waveguide and the ridge SiC waveguide in this thesis.Those research results provide a new implementation scheme for generating the supercontinuum in waveguides.The further studies on generating the supercontinuum and improving its performance will have important application value in the fields of nonlinear optics,coherent measurement,and optical communication. |
