Theoretical Design And Characterization Of Single-mode Large-mode-area Optical Waveguides

For the solid-state lasers with ever increasing output powers,the issues of thermal management,stresses,and nonlinearities in cavity structures have become dominant in limiting the power improvement and system stability.Due to their excellent thermal dissipation property,low transmission loss,and thus high power capacity,large-mode-area(LMA)optical waveguides offers a whole new world for the development of high power solid lasers.In this dissertation,several kinds of novel optical waveguides are theoretically designed and investigated by analytical and numerical methods.Single-mode(SM)and zero birefringence conditions of LMA crystal rib waveguides are first systematically analyzed aiming for high power laser applications.The SM cut-off criterion for rib waveguide is proposed and the modal area can reach up to 300?m~2.Besides,two-dimensional rib-waveguide array structures are proposed to generate the in-phase supermode that can improve the effective modal area up to 1136.4?m~2 by coupling mode theory.An all-solid photonic crystal planar waveguide(PCPW)is then proposed to further expand the effective modal area.The birefringence of waveguide has also been discussed.Besides,the19-unit PCPW waveguide array is constructed that can support SM modal area up to 13059?m~2.A LMA-PCPW and array waveguide is presented and analyzed for the single-polarization sinlge-mode(SPSM)condition.The simulation results show that the optimized five-unit linear array can possess an“endlessly”SPSM spectrum with modal area over 2600?m~2.It is noted that a near-zero leakage loss phenomenon can be achieved at the resonant wavelength.Next,a novel kind of multi-spoke core fibers are proposed to satisfy both the SM and ultra-large modal area conditions.The influence of structural parameters on the leakage losses of the multi-spike core fiber is systematically studied.Eventually,a single-trench eight-spoke core fiber is designed tp dramatically improve the SM effective modal area up to 9171.5?m~2 with good beam quality at the wavelength of 1.064?m.Lastly,for waveguides supporing the supercontinuum generation,a photonic crystal pillar waveguide(PCPW)with relatively large modal area is designed to improve the dispersion,nonlinearity,and modal area characteristics.A flat and low dispersion profile with four zero dispersion wavelengths is obtained as the optimized wavguide design.The supercontinuum generation in waveguides is calculated based on the nonlinear schrodinger equation.The results show that an ultra-broadband spectral broadening spanning from 1-10?m is achieved when pumped with 2 k W peak power with a shorter-wavelength near-infrared pulsed laser.The outcome of this dissertation may be enlightening for designs regarding high-power solid-state lasers and amplifiers,as well as supercontinuum sources to generate lightwave outputs with LMA and high beam quality.