Optimization control of modulation-instability gain in photonic crystal fibres with two-zero dispersion wavelengths

We design three kinds of photonic crystal fibres (PCF)with two zero-dispersion wavelengths (ZDWs) using the improved fullvector index method (FVIM) and finite-difference frequency domain(FDFD) techniques. Based on these designed fibres, the effect offibre structure, pump power and wavelength on the modulationinstability (MI) gain in the anomalous dispersion region close tothe second ZDW of the PCFs is comprehensively analysed in this paper.The analytical results show that an optimal MI gain can be obtainedwhen the optimal pump wavelength (1530~nm) is slightly shorter thanthe second ZDW (1538~nm) and the optimal pump power is 250~W.Importantly, the total MI gain bandwidth has been increased to 260~nmfor the first time, so far as we know, for an optimally-designed fibrewith Λ = 1.4~nm and d/Λ = 0.676, andthe gain profile became much smoother. The optimal pump wavelengthrelies on the second ZDW of the PCF whereas the optimal pump powerdepends on the corporate operation of the optimal fibre structure andoptimal pump wavelength, which is important in designing the mostappropriate PCF to attain higher broadband and gainamplification.