Optimization of pump wavelength for enhancing SC spectral broadening in silica fibers under CW-excitation

Abstract

Supercontinuum sources generated by continuous-wave excitation are very promising for many applications as they present in general higher spectral power density then their pulsed counterparts. On the other hand, the properties of supercontinuum are very difficult to be controlled as the initial broadening is driven by modulation instability. This latter one breaks-up the CW radiation into a train of ultra-short pulses whose peak power, spectral length and shape strongly depend on the power, coherence and noise of the pump and on the fiber properties. In this paper, we present a preliminary work on the role of chromatic dispersion on supercontinuum spectral broadening in order to study how to optimize SC spectral width under CW regimes. By means of a home-made tunable high-power laser we induce supercontinuum generation by pumping at different dispersion values of the fiber. We show that at low injected powers the wider spectrum is obtained when pumping just above the zero-dispersion wavelength of the fiber. By contrast, for higher injected powers, wide and squared-shaped spectra can be obtained when pumping over a larger range of anomalous dispersion values. These results seem to be very promising for a number of applications requiring smooth, squared and high-power SC spectral profiles such as optical coherence tomography.