This paper studies how Hawking radiation can be produced in a laboratory analogue made from light in an optical fibre. The team combined theory and experiment to identify a simple, direct mechanism that generates Hawking-like pairs of light waves and to measure how producing that radiation takes energy from the field that created it — a phenomenon called backreaction.

In the experiment a strong short light pulse travels down a glass fibre and slightly changes the glass’s refractive index through the Kerr effect. That moving change in refractive index acts like a flowing medium. A weak probe beam sent into the fibre interacts with the pulse. In a reference frame that moves with the pulse, the place where the probe’s wave speed matches the pulse speed becomes the analogue of a black‑hole horizon for the probe waves.

The basic physics is controlled by a Doppler shift between the laboratory frame and the frame moving with the pulse. The co‑moving frequency ω′ is related to the laboratory frequency ω roughly by ω′ = (1 − n u / c) ω, where n is the refractive index, u is the pulse speed, and c is the speed of light. When the effective medium moves faster than the phase speed of light in the fibre, the co‑moving frequency can be negative. Pairs are produced with opposite co‑moving frequencies: one positive‑frequency wave that escapes (seen in the lab as infrared light, roughly 1100–1860 nm in this setup) and one negative‑frequency partner that appears in the ultraviolet (around 233 nm for probes in the 1100–1600 nm range).

The authors say that, unlike previous ideas that invoked complicated cascades of processes, the dominant mechanism in their fibre system is a simple, direct one. They identified the specific nonlinear optical processes responsible on theoretical grounds and then measured stimulated Hawking radiation in the lab by sending in a probe. They also observed the backreaction — the recoil or energy loss of the pulse that creates the moving medium — showing that the emitted radiation takes energy from the field that produced the horizon analogue.