Analysis of Coherence in Widely Broadened Supercontinuum Generation in Highly Nonlinear Dispersion Shifted Fiber

The broadband supercontinuum (SC) with high coherence enables to realize the accurate optical frequency standard. We generate the SC from 1200 nm to 2200 nm using the polarization maintaining highly nonlinear dispersion shifted fiber (PM-HNL-DSF). It is expected that coherence can be complicated because of the fluctuations in the input pulse. We measure coherence as a function of wavelength across the SC spectrum by using the interferometer. The interference fringes can be observed and degree of coherence is calculated with their peak value of them. In case of the short fiber, degree of coherence is independently of the input power. On the other hand, in case of the long fiber, degree of coherence degrades and the spectral fine structure arises as the input power increases. We also analyze the coherence of SC with numerical simulations using the nonlinear Schrodinger equation and numerical results are similar to the experimental ones. The spectral fine structure which is the results of the cross-phase modulation (XPM) can affect coherence degradation because it is very sensitive to the fluctuations in the input pulse.