Ultrafast nonlinear effects in hydrogenated amorphous silicon wire waveguide

Abstract

We, for the first time, present the ultrafast optical nonlinear response of a hydrogenated amorphous silicon (a-Si:H) wire waveguide using femtosecond pulses. We show cross-phase and cross-absorption modulations measured using the heterodyne pump-probe method and estimate the optical Kerr coefficient and two-photon absorption coefficient for the amorphous silicon waveguide. The pumping energy of 0.8 eV is slightly lower than that required to achieve two-photon excitation at the band gap of a-Si:H (approximately 1.7 eV). An ultrafast response of less than 100 fs is observed, which indicates that the free-carrier effect is suppressed by the localized states in the band gap.

New CMOS-compatible platforms based on silicon nitride and Hydex for nonlinear optics

“…Although initial measurements yielded a FOM no better than c-Si (~0.5) [120,121], more recent results have shown FOMs ranging from 1 [122] to as high as 2 [123,124], allowing very high parametric gain (+26dB) over the C-band [125]. While a key problem for this material has been a lack of stability [126], very recently a-Si nanowires were demonstrated [127] that displayed a combination of high FOM of 5, high n 2 (3-4 times that of crystalline silicon) and good material stability at telecom wavelengths.…”

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

“…For silicon, almost two-octave bandwidth from 2.2 to 8.5 µm [146] is available for nonlinear applications without TPA, covering a large fraction of mid-IR range. It is important to note that amorphous silicon has a bandgap energy of 1.7 eV [32,33] and thus has TPA diminishing at a much shorter wavelength ( < 1.55 μm) than crystalline silicon. Both silicon nitride and silicon dioxide have large bandgap energies, but silicon dioxide becomes highly lossy beyond 3 µm [119].…”

“…We did not include specific data in Figure 3 for amorphous silicon, since different groups reported highly variable n 2 and nonlinear FOM values in the near-IR [31][32][33][34][35]. The n 2 value could be one order of magnitude higher than that in silicon [33], while the nonlinear FOM can be as high as 5 [35], although these may not be obtained simultaneously [34].…”

“…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].…”

Supercontinuum generation in hydrogenated amorphous silicon waveguides at telecommunication wavelengths

“…At this pump photon energy, which lies close to the half-bandgap energy of crystalline silicon, the effects of TPA and free carriers absorption are strongly reduced, thereby allowing stronger nonlinear effects. Recently, attention has focused on using hydrogenated amorphous silicon (a-Si-H) waveguides [14][15][16][17][18][19][20][21]. This material is characterized by a larger band-gap than crystalline silicon, resulting in a lower TPA absorption and a significantly higher figure of merit (…”