Optical thermodynamics
Under thermal equilibrium conditions, the nonlinear evolution dynamics in conservative optical arrangements with a large but finite number of modes can be rigorously described through a comprehensive thermodynamic formulation. During the process of thermalization, the total entropy always increases in such a way that the ‘internal energy’ flows from a hotter to a colder subsystem while any exchange of optical power is driven by the difference in chemical potentials.
In this respect, we derive a new set of equations of state and we cast the fundamental thermodynamic equation of entropy in terms of the extensive variables associated with the internal energy, number of modes and optical power. (Nature Photonics)
Lagrange waveguides
The guided transmission of optical waves is critical for light-based applications in modern communication and energy generation systems. Traditionally, the guiding of light waves in structures such as optical fibres has been predominantly achieved through the use of total internal reflection. However, transversely confining light in fully dielectric, non-periodic and passive configurations remains a challenge when total internal reflection is not supported.
Here we present an approach to trapping light that utilizes the exotic features of Lagrange points—a special class of equilibrium positions akin to those responsible for capturing Trojan asteroids in celestial mechanics. This is achieved in twisted arrangements in which optical Coriolis forces induce guiding channels even at locations where the refractive index landscape is defocusing or entirely unremarkable. These findings may have implications beyond standard optical waveguiding schemes and could also apply to other physical systems such as acoustics, electron beams and ultracold atoms. (Nature Physics)
𝒫𝒯 symmetry
In 1998, Bender and Boettcher found that a wide class of Hamiltonians, even though non-Hermitian, can still exhibit entirely real spectra provided that they obey parity-time requirements or 𝒫𝒯 symmetry.We report the first observation of the behaviour of a 𝒫𝒯 optical coupled system that judiciously involves a complex index potential. We observe both spontaneous 𝒫𝒯 symmetry breaking and power oscillations violating left–right symmetry. Our results may pave the way towards a new class of 𝒫𝒯-synthetic materials with intriguing and unexpected properties that rely on non-reciprocal light propagation and tailored transverse energy flow. (Nature Physics)
Airy beam
We report the first observation of Airy optical beams. This intriguing class of wave packets, initially predicted by Berry and Balazs in 1979, has been realized in both one- and two-dimensional configurations. As demonstrated in our experiments, these Airy beams can exhibit unusual features such as the ability to remain diffraction-free over long distances while they tend to freely accelerate during propagation. (Physics Review Letters)