  Entanglement is the quantum signature of Hawking's particle pair-creation
from causal horizons, for gravitational and analog systems alike. Ambient
thermal fluctuations, ubiquitous in realistic situations, strongly affects the
entanglement generated in the Hawking process, completely extinguishing it when
the ambient temperature is comparable to the Hawking temperature. In this work,
we show that optical analog systems have a built-in robustness to thermal
fluctuations which are at rest in the laboratory. In such systems, horizons
move relative to the laboratory frame at velocities close to the speed of
light. We find that a subtle interplay between this relative velocity and
dispersion protects the Hawking-generated entanglement -- allowing ambient
temperatures several orders of magnitude larger than the Hawking temperature
without significantly affecting entanglement.
