Research On The Nonlinearity And Application Of Microstructured Optical Fiber

Microstructured optical fiber(MOF)as the excellent optical medium in the new generation has unique optical characteristics that the traditional optical fibers cannot match,such as adjustable dispersion,high nonlinearity,large mode field area,and high birefringence,etc.The combination of the ultrashort laser pulses and MOF can produce abundant optical nonlinear phenomena,which has become a hotspot in the fields of nonlinear optics and photonics.It has wide application prospects in various aspects,such as all-optical signal processing,optical fiber communication,optoelectronic integration,optical fiber devices,and so on.In this paper,the dispersion and nonlinearity characteristics of the MOF and the related applications are theoretically and experimentally investigated.The main works and contribution are as follows:First,the V-shape MOF(VMOF)with high birefringence and high nonlinearity is proposed.The fabrication of VMOF is convenient by designing of circular air holes and silica material.The birefringence,dispersion,and nonlinear coefficients of the V-MOF are analyzed using the full-vector finite element method.The fiber structure parameters are further optimized to obtain higher birefringence and stronger nonlinear coefficient in the communication window.In addition,the zero-dispersion wavelength is increased from 1.15 to 1.55 μm,and the anomalous dispersion region contains the working wavelength of the Ti:sapphire laser,which is very conducive to carry out the nonlinear experiments and has important applications in the nonlinear optics and photonics.Second,the Yb-doped V-shaped MOF(Yb-VMOF)with low dispersion and high nonlinearity is theoretically and experimentally investigated.The tunable anti-Stokes signal(ASS)based on phase-matched four-wave mixing is effectively generated in the visible band by coupling femtosecond pulses into the fundamental mode of the Yb-VMOF.The ASS is in the wavelength range from 562 nm to 477 nm,and the tunable wavelength range is over 100 nm.The maximum power ratio of the anti-Stokes signal at 477 nm wavelength and the remaining pump at 830 nm wavelength can reach 23.9:1,and the conversion efficiency is above 80%.The effects of pump wavelength and power on the signal conversion are experimentally demonstrated.The research results are helpful for further research and application of ultra-short pulse light sources in ultrafast optoelectronics and spectroscopy.Third,the generation of the ultra-wideband supercontinuum(SC)is investigated by coupling the ultra-short laser pulses near 800 nm wavelength into the silica MOF.In the normal dispersion region near the zero-dispersion wavelength of the fundamental mode,the SC is generated from the ultraviolet to visible wavelength through the interaction of nonlinear effects,including degenerate four-wave mixing,cross-phase modulation,and stimulated Raman scattering,etc.More than 40%of the incident pump power is converted into the ultraviolet to visible spectral region,when the center wavelength is 800 nm and the average power is 500 mW for the pump input pulse.The evolution of the SC at different fiber lengths is studied,and its nonlinear transmission mechanism is further analyzed.The SC generation from the ultraviolet to visible spectral region has important applications in the biophotonics and spectroscopy.Fourth,the near-infrared SC generation is experimentally investigated by coupling the femtosecond pulses at wavelength 1550 nm into the fundamental mode of all-normal dispersion(ANDi)silica MOF.The generated SC covers the communication band with the bandwidth of 435 nm.The nonlinear dynamics in the SC generation process are dominated by the self-phase modulation and optical wave breaking.This broadband SC as a light source will have an important potential application in photonic network system.Fifth,the second and third harmonics are simultaneously generated in MOF with high nonlinearity and low dispersion.When the pump wavelength is 790 nm and the pump power is 450 mW,the second and third harmonics from the deep ultraviolet to visible spectral region are simultaneously generated based on the phase-matching between the fundamental mode and higher-order modes,and the generated harmonics are located at 294 nm,502 nm,and 618 nm,respectively.The total conversion efficiency is up to 10.59%in the wavelength range from 294 nm to 618 nm.The generated harmonics as multi-frequency light source will have important application in ultrafast photonics and spectroscopy.Sixth,the characteristics of the tapered MOF and cascade tapered MOF are numerically analyzed.The influences of pump pulse parameters such as pulse width and peak power on the SC generation are systematically analyzed,which provides the important theoretical basis for the experiments research of the tapered MOF and cascade tapered MOF.The tapered MOF and cascade tapered MOF are prepared by using the post-processing technology of MOF,and they are used to study the wavelength conversion.The effects of input pump power and wavelength on the conversion efficiency are analyzed.The experimental results show that the higher conversion efficiency can achieve when the pump wavelength is closer to the zero-dispersion wavelength of the tapered waist.For the input pump pulse,when the input wavelength is 800 nm and the power is 0.4 W,the maximum power ratio between the generated anti-Stokes signal and the residual pump pulse is 6.3:1.The research results have a good reference for the development and application of new optical devices in ultrafast photonics.