Study On High Coherent Supercontinuum Source

The supercontinuum spectrum is a kind of physical phenomenon of spectrum broadening,which involves the influence of various nonlinear effects and dispersion effects.Photonic crystal fiber has been widely used in the study of supercontinuum because of its characteristics such as controllable dispersion,no cut-off frequency single mode transmission and enhanced nonlinear characteristics,which are not found in other nonlinear media.In recent years,the generation of supercontinuum spectrum based on photonic crystal fiber has been paid more and more attention.In the fields of spectroscopy,metrology,optical wave communication and pulse compression,supercontinuum light sources with high coherence have wide application prospects,so how to further optimize supercontinuum spectrum is studied.It is necessary to improve the coherent properties of of supercontinuum spectrum to meet the requirement of practical application.In this paper,based on the existing research results,the high coherent near-infrared and mid-infrared supercontinuum spectra in photonic crystal fiber are investigated in details,and how to further improve the spectral width,flatness and coherent properties of the supercontinuum spectrum is studied.The contents of the study are as follows:1.The generation of near infrared supercontinuum spectra in the all-normal dispersive photonic crystal fibers and the coherent characteristics of supercontinuum are studied.The results show that the bandwidth,flatness and coherent characteristics of the supercontinuum spectrum can be improved by optimizing the modulation parameters of modulated Gaussian pulse.When the modulation depth is greater than 0.3,the coherence of the supercontinuum spectrum decreases sharply,and the coherent characteristics of the supercontinuum spectrum becomes better firstly and then worse with the increase of modulation frequency.When the modulation frequency is 24 THz,the coherence of the supercontinuum spectrum is the best.Under the optimal parameters of modulation pulse(modulation depth is 0.3,modulation frequency is 24 THz),the supercontinuum spectrum with 10 dB bandwidth of 1305 nm is obtained.The value of first-order coherence is larger than 0.90 within the above bandwidth,which indicates that the supercontinuum spectrum has good coherence.2.The pulse compression of near infrared supercontinuum based on grating pair compressor is studied.It is shown that the grating pair is particularly suitable for compression with linearly chirped pulses.By choosing appropriate initial chirp,the chirp of supercontinuum pulse tends to be linear,thus the compression quality of supercontinuum pulse is improved.The simulation results show that the pulse width of the compressed pulse increases with the increase of initial chirp,but the compression quality increases firstly and then decreases.When the initial chirp is 3.5,the compression quality of the pulse is the best,that is to say,the optimal initial chirp is 3.5.Under the initial chirp is 3.5 and the transmission distance is 5.8 mm,the pulse with a pulse width of 53.6 fs is compressed to 9.15 fs through the grating pair,and the compression quality of the compressed pulse is up to 95.4%.3.The generation of mid-infrared supercontinuum spectra in As2S3 photonic crystal fibers with all-normal dispersion and coherence characteristics of the supercontinuum are studied.It is shown that the shorter the pulse width of the pump pulse is,the more favorable the high coherence supercontinuum spectrum is;the higher the incident power is,the worse coherent characteristic of the supercontinuum spectrum is;the coherent characteristic of the supercontinuum can be improved by adding the initial chirp to the pump pulse.By optimizing the parameters,under the optimal chirp is-4,the incident peak power is 100 W,the fiber length is 20 cm and the input pulse width is 50 fs,the supercontinuum spectrum with 3 dB bandwidth of 2484 nm is obtained.The value of first-order coherence is above 0.89,which indicates that the supercontinuum spectrum has good coherent characteristics.