Research On Supercontinuum Generation In Multimode Photonic Crystal Fiber

Supercontinuum(SC)has excellent characteristics such as high brightness,wide spectrum,and high coherence.It has broad application prospects in many fields such as bio-medicine,optical communication networks,and meteorological detection.Optical frequency comb(OFC)is a spectrum composed of a series of phase-coherent,evenly spaced frequency components.It is widely used in astronomy,optical measurement,communication,and other fields due to its high stability.Single-polarization SC is also widely concerned by the researchers.Polarization-maintaining photonic crystal fiber(PMPCF)has different dispersion characteristics in the two polarization directions,and the SC with different characteristics can be obtained through pumping in the two polarization directions.Therefore,it is an important medium to obtain the single-olarization SC.Multi-mode PCF can propagate many different modes at the same time.It is an effective solution to resolve communication congestion,and has high research value.In this paper,the multimode PCF and polarization-maintaining multimode PCF are designed by using the telluride materials,and highly coherent and octave-spanning SC and OFC are generated based on the different modes.The main research works and achievements are summarized as follows:1.Based on the study of dispersion and nonlinear coefficients,a multimode telluride PCF is designed.The effects of the pump pulse parameters(center wavelength,pulse width,and peak power)on the SC are studied by simulation when the LP01,LP02,and LP12 modes are considered.When the pump pulse parameters are set as ?0=2.5 ?m,T0=80 fs,and P0=18 kW,the SC bandwidths of the three modes are 2.56,1.39,and 1.12 octaves,respectively.The dynamic evolution of the SC in the frequency and time domains under optimal pumping conditions is desmonstarted.By analyzing the coherence,it is known that when the random noise coefficient ?<1×10-3,the coherence of the SCs generated by the three modes is approximately 1.2.When the optimized pump pulse sequence with the repetition rate of 1 GHz is used to pump the above multimode PCF,the octave-spanning OFCs for the LP01,LP02,and LP12 modes can be obtained.3.Based on the study of dispersion and nonlinear coefficients,a multimode polarization-maintaining PCF is designed.The effects of pump pulse parameters(center wavelength,pulse width,and peak power)on the SC for the LP01,LP11,and LP21 modes are studied by simulation.When the pump pulse parameters are set as ?0=2.0?m,T0=80 fs,P0=18 kW,the generated SC bandwidths in the fast and slow axes of the polarization-maintaining PCF are 2.00,1.92,and 1.28 octaves,and 2.15,2.04,and 1.46 octaves,respectively,for the LP01,LP11,and LP21 modes.The evolutions of the SCs in the fast and slow axes in the frequency and time domains for the three modes are compared,and the effects of the random noise on the coherence of the single-polarization SC are analyzed.It is found that when the random noise figure ?<1 ×10-4,the coherence of the SCs generated by the three modes is approximately 1.4.When the optimized pump pulse sequence with the repetition rate of 1 GHz is used to pump the above multimode polarization-maintaining PCF,the octave-spanning OFCs in the two polarization directions for the LP01,LP02,and LP12 modes can be obtained.In this paper,the research achievements on designing the multi-mode PCF and generating the octave-spanning SC and OFC provide the solutions for the generations of broadband,high coherence,and single-polarization SC and low noise and stable OFC.These research achievements will promote the research and development of the generation and application of the SC and OFC sources.