Bound electronic and free carrier nonlinearities in Silicon nanocrystals at 1550nm

Abstract

We present a detailed investigation of the different processes responsible for the optical nonlinearities of silicon nanocrystals at 1550 nm. Through z-scan measurements, the bound-electronic and excited carrier contributions to the nonlinear refraction were measured in presence of two-photon absorption. A study of the nonlinear response at different excitation powers has permitted to determine the change in the refractive index per unit of photo-excited carrier density sigma(r) and the value of the real bound-electronic nonlinear refraction n(2be) as a function of the nanocrystals size. Moreover at high excitation power, a saturation of the nonlinear absorption was observed due to band-filling effects.

Nonlinear Group IV photonics based on silicon and germanium: from near-infrared to mid-infrared

“…Silicon nano-crystals in silicon dioxide and silicon nitride have also been investigated as a nonlinear material, exhibiting higher nonlinear indices than crystalline silicon by an order of magnitude or more [36][37][38][39][40][41]. The values of n 2 , β TPA , and nonlinear FOM are also highly variable, if silicon excess, annealing temperature and wavelength change.…”

“…The values of n 2 , β TPA , and nonlinear FOM are also highly variable, if silicon excess, annealing temperature and wavelength change. We include one data point (n 2 = 4.8 × 10 -17 m 2 /W) from [38] in Figure 3. Extremely high n 2 and FOM by 3~4 orders have been obtained experimentally [41] with large silicon excess (note that the FOM in [41] is defined as the reciprocal of ours here).…”

“…This is because the guided mode extends more to the highly nonlinear thin slot layer. Note that the used n 2 value in SRO [38] is currently the one measured at 1.55 µm, so the n 2 and γ values may vary in the mid-IR, but the trend is general.…”

“…Materials engineering further enhanced the nonlinearity, e.g., in amorphous silicon under certain deposition conditions [31][32][33][34][35] and in Si-rich silicon oxide (SRO) and nitride (SRN) based on the formation of silicon nano-crystals [36][37][38][39][40][41].…”

Low TPA and free-carrier effects in silicon nanocrystal-based horizontal slot waveguides

“…A vertical slot geometry was also demonstrated to allow the introduction of an organic polymer, and this device showed optical 160 Gb/s demultiplexing capabilities [4]; however, these materials involve non-CMOS processes and impose strict temperature limitations. On the other hand, silicon-nanocrystal-based horizontal slot waveguides only require CMOS processes, and have recently demonstrated ul-trafast all-optical modulation capabilities and good nonlinear properties [13][14][15][16]. In this paper, we study the nonlinear ultrafast dynamics of this type of waveguide, where we show that the effect of carriers is greatly reduced as compared to silicon channel waveguides.…”