Nonlinear optics of fibre event horizons

Abstract

The nonlinear interaction of light in an optical fibre can mimic the physics at an event horizon. This analogue arises when a weak probe wave is unable to pass through an intense soliton, despite propagating at a different velocity. To date, these dynamics have been described in the time domain in terms of a soliton-induced refractive index barrier that modifies the velocity of the probe. Here we complete the physical description of fibre-optic event horizons by presenting a full frequency-domain description in terms of cascaded four-wave mixing between discrete single-frequency fields, and experimentally demonstrate signature frequency shifts using continuous wave lasers. Our description is confirmed by the remarkable agreement with experiments performed in the continuum limit, reached using ultrafast lasers. We anticipate that clarifying the description of fibre event horizons will significantly impact on the description of horizon dynamics and soliton interactions in photonics and other systems.

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

“…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].…”

“…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.…”

“…When interacting in a Kerr media, two waves with similar group velocities can lead to the generation of an idler wave set by the well-known resonant condition [10,12,13,21]:…”

Probe-controlled soliton frequency shift in the regime of optical event horizon

“…In a regime of optical event horizon, the probe DW can experience a frequency conversion to an idler wave at ω i , according to the resonance conditionD(ω i − ω s ) =D(ω p − ω s ) [6]. During the collision process, since the center frequency of the FS shifts, the phase-matched probeidler pair is modified as well.…”

“…Physically, based on the cross-phase-modulation (XPM) effect, an optical event horizon is formed when an intense pump light which gives rise to a strong refractive index barrier so a weak probe light hits the barrier will be velocity inversed as well as frequency shifted, just named in the optical analogue of physics behaviors at an event horizon [1]. Such phenomena were also understood in terms of the four-wave mixing effect [6].…”