Temporal reflection as a spectral-broadening mechanism in dual-pumped dispersion-decreasing fibers and its connection to dispersive waves

We show that temporal reflections off a moving refractive index barrier play a major role in the spectral broadening of a dual-wavelength input inside a highly nonlinear, dispersion-decreasing fiber. We also find that a recently developed linear theory of temporal reflections works well in predicting the reflected frequencies. Successive temporal reflections from multiple closely spaced solitons create a blueshifted spectral band, while continuous narrowing of solitons inside the dispersion-decreasing fiber enhances Raman-induced redshifts, leading to supercontinuum generation at relatively low pump powers. We also show how dispersive wave emission can be considered a special case of the more general process of temporal reflections. Hence our findings have implications on all systems able to support solitons.

Figure 1

Dispersion parameter ${\beta }_2$ at the input end of the fiber. The circle denotes ${\nu }_0$. The zero-dispersion wavelength of the PCF is 985 nm.

Figure 2

Temporal (a) and spectral (b) evolutions of a dual-pump input inside a DDF. (a) Square root of the intensity on a linear scale in $\sqrt{\text{W}}$. (b) Normalized spectral intensity in decibels. The two pumps are separated in frequency by 400 GHz and their total power is 1 W. The dashed black line shows the distance at which ${\beta }_2=0$ at the pumps' center wavelength. Double arrows mark locations of temporal reflections in (a) together with the corresponding wavelengths in (b). The solid black line in (b) shows the theoretical prediction of the temporal reflection model discussed in the text. The dashed line shows the zero-dispersion wavelength.

Figure 3

Temporal (a) and spectral (b) evolutions of a dual-pump input under conditions identical to those in Fig. 2 except that the dispersion is kept constant along the PCF length.

Figure 4

Temporal (a) and spectral (b) evolutions under conditions identical to those in Fig. 3 except that the value of ${\beta }_2$ at the pump-center wavelength was changed to $-2.684{\text{ps}}^2/\text{km}$.