Non-instantaneous optical nonlinearity of an a-Si:H nanowire waveguide

Abstract

We use pump-probe spectroscopy and continuous wave cross-phase and cross-amplitude modulation measurements to study the optical nonlinearity of a hydrogenated amorphous silicon (a-Si:H) nanowire waveguide, and we compare the results to those of a crystalline silicon waveguide of similar dimensions. The a-Si:H nanowire shows essentially zero instantaneous two-photon absorption, but it displays a strong, long-lived non-instantaneous nonlinearity that is both absorptive and refractive. Power scaling measurements show that this non-instantaneous nonlinearity in a-Si:H scales as a third-order nonlinearity, and the refractive component possesses the opposite sign to that expected for free-carrier dispersion.

Optical nonlinearities in ultra-silicon-rich nitride characterized using z-scan measurements

“…The higher nonlinear refractive index arises from a free carrier effect excited by two step absorption in the existence of defect states in amorphous-Si 23 . The nonlinear refractive index has the same sign as the Kerr nonlinear index 24 . We postulate that the same phenomenon could explain the high nonlinear refractive index in USRN films.…”

“…It is noted that the measured nonlinear refractive index of the USRN film is higher than that in crystalline silicon. Some groups have reported that deposited amorphous Si:H has a higher nonlinear refractive than crystalline Si 23,24 . The higher nonlinear refractive index arises from a free carrier effect excited by two step absorption in the existence of defect states in amorphous-Si 23 .…”

Silicon Nanosheets: An Emerging 2D Photonic Material with a Large Transient Nonlinear Optical Response beyond Graphene

“…Concerning the nonlinear refractive response of both SiNSs, in some other studies it has been reported that amorphous Si–H possesses a larger nonlinear refractive index parameter γ ′ than crystalline Si [ 61 , 62 ]. The larger value of γ ′ was ascribed to free carrier refraction, induced by two-step absorption due to the presence of defects states in amorphous Si–H [ 62 ]. In addition, it was shown that the nonlinear refractive parameter γ ′ has the same sign as the Kerr effect, causing a refractive nonlinear response [ 62 ].…”

Nonlinear optical interactions in silicon waveguides

“…These groups have shown a multitude of demonstrations of all-optical signal processing experiments in a-Si:H waveguides [36] and even as a source for photon pair generation [46,47]. Lastly, by investigating the time-dependent response of hydrogenated amorphous silicon waveguides, it has been observed that the Kerr-like response is far from instantaneous [48].…”