Authors: Francesco Fedele, Joseph Brennan, Sonia…
Nonlinear optics of fibre event horizons
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.