Surface plasmon polariton propagation length enhancing via second-harmonic generation

Surface plasmon polaritons (SPPs) offer promising technological applications due to their ability to confine light to subwavelength scales. To achieve advanced photonic integrations competitive with electronic ones, the ideal would be to work with short wavelengths, in the violet or ultraviolet bands. However, these wavelengths are strongly limited due to the high absorptions of any metal layers necessary to realize SPP waves. This study aims to demonstrate the possibility of extending the propagation distance of short-wavelength SPPs by exploiting the nonlinear mutual interaction with long-propagating signals. We show an IR radiation at 1064 nm coupled as an SPP wave to the interface between a metal layer and a nonlinear crystal, propagating along it. By exploiting the nonlinearities of the substrate, this wave can generate its second harmonics at 532 nm, which is able to run for a distance about 30 times longer than the propagation length of an isolated 532 nm signal.