J. Opt. 16, 055202 (2014)

Broadband omnidirectional electromagnetic absorbers — so-called optical black holes — have become a popular topic in recent years, especially those based on cylindrical nonlinear materials. To date, analysis has largely relied on linear transformational optics, but this is insufficient for describing extremely strong nonlinear effects in a small area. Now, Yuriy Rapoport and co-workers from Ukraine, the UK and Mexico have developed a method based on nonlinear transformation optics to investigate nonlinear optical phenomena at very high intensities. The team considered an infinitely long dielectric cylinder composed of an inner core and an outer shell. The nonlinear optical coefficient of the inner core was constant, whereas that of the outer shell varied with the radius. The scientists investigated how incident beams are focused inside the rod by accounting for the nonlinearity saturation, the nonlinear loss and the linear gain. The numerical simulation indicates that when the intensity of any beam exceeds a certain threshold, nonlinear focusing may occur. When this happens, the peak position of the intensity distribution jumps from some point inside the inner core to a point near the interface between the inner core and the outer shell.