Scattering of a cross-polarized linear wave by a soliton at an optical event horizon in a birefringent nanophotonic waveguide

Abstract

The scattering of a linear wave on an optical event horizon, induced by a cross polarized soliton, is experimentally and numerically investigated in integrated structures. The experiments are performed in a dispersion-engineered birefringent silicon nanophotonic waveguide. In stark contrast with co-polarized waves, the large difference between the group velocity of the two cross-polarized waves enables a frequency conversion almost independent on the soliton wavelength. It is shown that the generated idler is only shifted by 10 nm around 1550 nm over a pump tuning range of 350 nm. Simulations using two coupled full vectorial nonlinear Schrödinger equations fully support the experimental results.Nonlinear interactions between linear waves and solitons attract a tremendous amount of interest in the scientific community for many years. In this framework, interactions between waves of similar group velocities particularly draw the attention of researchers for their potential useful applications such as frequency converters [1] or for future optical transistor-like devices [2]. In this particular process, the propagation of an intense solitonic pump in a Kerr medium induces a moving refractive index perturbation which in turn leads to a frequency conversion of a weak probe wave through a cross-phase modulation (XPM) process. In the context of supercontinuum (SC) generation, this process helps understanding the underlying physics of the spectral broadening [3], and has also been demonstrated to enable the generation of highly coherent broadband SC [4,5] in a complementary manner from the well-known process involving the soliton fission [6][7][8]. Recently, this nonlinear interaction has been reinterpreted as the optical analog of the event horizon of black and white holes [9,10]. As the propagation takes place in a dispersive media, the frequency conversion of the probe wave is accompanied by a modification of its group velocity, which is either accelerated or decelerated preventing any crossing between the two waves. The intense pulse thus constitutes an horizon that light can neither join nor escape. These so-called optical event horizons have thus also been largely studied for their analogy with general relativity and in particular with the Hawking radiation [9].Since its first theoretical prediction made by Yulin et al. a decades ago [11,12], and its experimental observation in the context of SC generation in optical fibers [13], numerous experimental demonstrations have been realized. We can cite studies involving the superimposition of a linear wave to an intense pump at the waveguide input [9,10,14], or the interaction between two pulses [1]. More recent studies have also investigated the interaction of an intense pulse with its own dispersive wave (DW) [15] or the trapping of a DW between two solitons [16,17]. Interactions involving higher order solitons [18] or dark solitons [19] have also been considered. Owing to the essential role played by the dispersion properties of the structure for the observation of ...

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