Abstract
Supercontinuum generation in Kerr media has become a staple of nonlinear optics. It has been celebrated for advancing the understanding of soliton propagation as well as its many applications in a broad range of fields. Coherent spectral broadening of laser light is now commonly performed in laboratories and used in commercial “white light” sources. The prospect of miniaturizing the technology is currently driving experiments in different integrated platforms such as semiconductor on insulator waveguides. Central to the spectral broadening is the concept of higher-order soliton fission. While widely accepted in silica fibers, the dynamics of soliton decay in semiconductor waveguides is yet poorly understood. In particular, the role of nonlinear loss and free carriers, absent in silica, remains an open question. Here, through experiments and simulations, we show that nonlinear loss is the dominant perturbation in wire waveguides, while free-carrier dispersion is dominant in photonic crystal waveguides.
Highlights
In our recent report on supercontinuum generation in silicon wires[25] pumped around the 1550 nm telecommunication wavelength, we argued that the main perturbation to the nonlinear Schrödinger equation (NLSE) describing our measurements is two-photon absorption (2PA)
We find that nonlinear loss can induce soliton fission in indium gallium phosphide (InGaP) wire waveguides and that the impact of carriers strongly depends on the waveguide dispersion and input pulse characteristics
While we found that 2PA and higher-order dispersion (HOD) suffice to explain our results, it seems pertinent to investigate the impact of each perturbation independently in an effort to gain further physical insight into the dynamics of soliton fission in semiconductor waveguides
Summary
They correspond to localized packets that propagate unperturbed as a consequence of a balance between nonlinear self-focusing and a diffusion-like process They have been theoretically and experimentally investigated in hydrodynamics[1], plasma physics[2], biology[3] and optics[4]. This lead us to the conclusion that 2PA is the main cause for soliton decay in a silicon wire pumped around 1550 nm[25,30] Another recent report claims to experimentally observe free-carrier induced fission of higher-order solitons in InGaP photonic crystal waveguides (PhCWG)[31]. The nonlinear loss inherent to semiconductor devices results in the excitation of electron-hole pairs that subsequently impact the dynamics in two different ways They absorb photons (free carrier absorption, FCA) as well as change their wavenumber (free carrier dispersion, FCD)[33]. FCA on the other hand has less impact on soliton propagation as the induced loss is low compared to the instantaneous multi-photon absorption processes (see below)
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