arXiv subjects

Huizhong Ren

Publications and source records attributed to Huizhong Ren.

9 recordsLinked to original sources

arXiv2026

Unified framework of optical thermodynamics and optical pressure

Optical thermodynamics is a newly developed framework that applies principles from statistical mechanics to describe the intricate behavior of weakly nonlinear, multimode photonic systems. Utilizing this theory, the collective dynamics of complex optical arrangements can be systematically uncovered and understood. The purpose of this work is to examine fundamental aspects of optical thermodynamics, including optical pressure, and provide a unified framework that can be applied to effectively any optical setting within the domain of validity of optical thermodynamics. We find that in addition to the conservation laws, the remaining extensive and intensive parameters of the system are naturally provided by the parameters of the propagation constants. At this point, several thermodynamic approaches exist for analyzing optical forces in multimode settings. Here, we develop a new theoretical methodology that unifies these perspectives in a variety of different configurations, irrespective of whether they are discrete or continuous. We apply our theory in four different settings. By studying Su-Schrieffer-Heeger lattices, we elucidate the thermodynamics of polyatomic chains and show that intercell and intracell bonds can display different optical forces. In addition, we provide a thermodynamic formalism to predict and understand the optical pressure at equilibrium arising in arrangements characterized by a continuous index variation and apply our results to graded-index fibers.

physics.optics↗

arXiv2025

Universal Routing of Light via Optical Thermodynamics

Understanding and exploiting the dynamics of complex nonlinear systems is nowadays at the core of a broad range of scientific and technological endeavors. Within the optical domain, light evolution in a nonlinear multimode environment presents a formidable problem, as its chaotic evolution often hinders predictive insights. Recently, an optical thermodynamic framework has been put forward that, in a systematic manner, can not only predict but also harness the intricate behavior of these systems. In this work, by deploying entropic principles, we demonstrate a counterintuitive optical process in which light, launched into any input port of a judiciously designed nonlinear array, universally channels into a tightly localized ground state, a response that is completely unattainable in linear conservative arrangements. This phenomenon arises from the interplay between lattice structure and the way the kinetic and nonlinear Hamiltonian components unfold, leading to two optical thermal processes: a Joule-Thomson-like expansion followed by mode thermalization. Experimentally, this effect is demonstrated in properly configured nonlinear time-synthetic mesh lattices, where the optical temperature approaches near zero, causing light to condense at a single spot, regardless of the initial excitation position. The effect demonstrated here opens new avenues for applying the principles of optical thermodynamics in realizing novel optical functionalities, such as all-optical beam steering, multiplexing, and nonlinear beam shaping in high-power regimes, while also offering a greater understanding of the remarkable physics of light-matter interactions in multimode nonlinear systems.

physics.optics↗

arXiv2025

Observation of Joule-Thomson photon-gas expansion

In recent years, a self-consistent optical thermodynamic framework has emerged that offers a systematic methodology to understand, harness and exploit the complex collective dynamics of multimode nonlinear systems. These developments now allow consideration of a series of longstanding problems in optics, including the prospect of funnelling the entire power flowing in a multimode system into its ground state, for which no methodology currently exists. Here, we demonstrate an all-optical Joule-Thomson expansion process mediated by photon-photon interactions whereby the temperature of the optical gas drops abruptly to zero. Our experiments in various configurations of coupled multicore nonlinear waveguide arrangements illustrate how light undergoing expansion-induced cooling can be channelled from arbitrary input states into the fundamental mode with near-unity efficiency. We show that the stability of the post-expansion state is ensured through an irreversible process of energy conversion. The all-optical thermodynamic phenomena explored in this study may enable innovative techniques where various uncorrelated but identical sources are merged into a unified spatially coherent state, offering a route for direct beam combining.

physics.optics↗

arXiv2024

Rigorous analysis of optical forces in dielectric structures based on the Minkowski-Helmholtz formula

Optical forces in dielectric structures are typically analyzed by utilizing either the Maxwell stress tensor or energy-based methods from which they can be derived by means of the eigenfrequencies and the effective refractive indices involved. While the equivalence of these two methods has been discussed in several studies, it would seem that a general electrodynamic proof of this aspect is still lacking. In this work, we provide a rigorous electrodynamic derivation based on the Minkowski-Helmholtz formula and the electromagnetic variation theorem, from which one can directly conclude that under Hermitian conditions these two approaches are formally equivalent to each other. The results of our study universally apply to any dielectric waveguide or cavity configuration. In addition, this methodology can be employed in graded index systems that do not exhibit sharp interfaces. Importantly, our analysis offers a straightforward route for predicting optical forces in a variety of photonic arrangements, including dielectric scatterers and multielement array configurations.

physics.optics↗

arXiv2024

Nature of Optical Thermodynamic Pressure Exerted in Highly Multimoded Nonlinear Systems

The theory of optical thermodynamics provides a comprehensive framework that enables a self-consistent description of the intricate dynamics of nonlinear multimoded photonic systems. This theory, among others, predicts a pressure-like intensive quantity ($\hat{p}$) that is conjugate to the system's total number of modes ($M$) - its corresponding extensive variable. Yet at this point, the nature of this intensive quantity is still nebulous. In this Letter, we elucidate the physical origin of the optical thermodynamic pressure and demonstrate its dual essence. In this context, we rigorously derive an expression that splits $\hat{p}$ into two distinct components, a term that is explicitly tied to the electrodynamic radiation pressure and a second entropic part that is responsible for the entropy change. We utilize this result to establish a formalism that simplifies the quantification of radiation pressure under nonlinear equilibrium conditions, thus eliminating the need for a tedious evaluation of the Maxwell stress tensor. Our theoretical analysis is corroborated by numerical simulations carried out in highly multimoded nonlinear optical structures. These results may provide a novel way in predicting and controlling radiation pressure processes in a variety of nonlinear electromagnetic settings.

physics.optics↗

arXiv2024

Dalton's law of partial optical thermodynamic pressures in highly multimoded nonlinear photonic systems

We show that in highly multimoded nonlinear photonic systems, the optical thermodynamic pressures emerging from different species of the optical field obey Dalton's law of partial pressures. In multimode settings, the optical thermodynamic pressure is defined as the conjugate to the extensive variable associated with the system's total number of modes and is directly related to the actual electrodynamic radiation forces exerted at the physical boundaries of the system. Here, we extend this notion to photonic configuration supporting different species of the optical field. Under thermal equilibrium conditions, we formally derive an equation that establishes a direct link between the partial thermodynamic pressures and the electrodynamic radiation pressures exerted by each polarization species. Our theoretical framework provides a straightforward approach for quantifying the total radiation pressures through the system's thermodynamics variables without invoking the Maxwell stress tensor formalism. In essence, we show that the total electrodynamic pressure in such arrangements can be obtained in an effortless manner from initial excitation conditions, thus avoiding time-consuming simulations of the utterly complex multimode dynamics. To illustrate the validity of our results, we carry out numerical simulations in multimoded nonlinear optical structures supporting two polarization species and demonstrate excellent agreement with the Maxwell stress tensor method.

physics.optics↗

arXiv2022

A thermodynamic description of the near- and far-field intensity patterns emerging from multimode nonlinear waveguide arrays

Nonlinear highly multimode photonic systems are ubiquitous in optics. Yet, the sheer complexity arising from the action of nonlinearity in multimode environments has posed theoretical challenges in describing these systems. In this work, we deploy concepts from optical thermodynamics to investigate the near- and far-field emission intensity patterns emerging from nonlinear waveguide arrays. An exact equation dictating the response of a nonlinear array is derived in terms of the systems invariants that act as extensive thermodynamic variables. In this respect, the near- and far-field characteristics emerging from a weakly nonlinear waveguide lattice are analytically addressed. We show that statistically, these patterns and the resulting far-field brightness are governed by the optical temperature and its corresponding chemical potential. The extensivity associated with the entropy of such configurations is discussed. The thermodynamic results presented here were found to be in good agreement with numerical simulations obtained from nonlinear coupled-mode theory.

physics.optics↗

arXiv2021

Thermalization of light's orbital angular momentum in nonlinear multimode waveguide systems

We show that the orbital angular momentum (OAM) of a light field can be thermalized in a nonlinear cylindrical multimode optical waveguide. We find, that upon thermal equilibrium, the maximization of the optical entropy leads to a generalized Rayleigh-Jeans distribution that governs the power modal occupancies with respect to the discrete OAM charge numbers. This distribution is characterized by a temperature that is by nature different from that associated with the longitudinal electromagnetic momentum flow of the optical field. Counterintuitively and in contrast to previous results, we demonstrate that even under positive temperatures, the ground state of the fiber is not always the most populated in terms of power. Instead, because of OAM, the thermalization processes may favor higher order modes. A new equation of state is derived along with an extended Euler equation -- resulting from the extensivity of the entropy itself. By monitoring the nonlinear interaction between two multimoded optical wavefronts with opposite spins, we show that the exchange of angular momentum is dictated by the difference in OAM temperatures, in full accord with the second law of thermodynamics. The theoretical analysis presented here is corroborated by numerical simulations that take into account the complex nonlinear dynamics of hundreds of modes. Our results may pave the way towards high power optical sources with controllable orbital angular momenta, and at a more fundamental level, could shed light on the physics of other complex multimoded nonlinear bosonic systems that display additional conservation laws.

physics.optics↗

arXiv2017

Quantitative Coherence Witness for Finite Dimensional States

We define the stringent coherence witness as an observable which has zero mean value for all of incoherent states and hence a nonzero mean value indicates the coherence. The existence of such witnesses are proved for any finite-dimension states. Not only is the witness efficient in testing whether the state is coherent, the mean value is also quantitatively related to the amount of coherence contained in the state. For an unknown state, the modulus of the mean value of a normalized witness provides a tight lower bound of $l_1$-norm of coherence in the state. When we have some previous knowledge of the state, the optimal witness is derived such that its measured mean value, called the witnessed coherence, equals to the $l_1$-norm of coherence. One can also fix the witness and implement some incoherent operations on the state before the witness is measured. In this case, the measured mean value cannot reach the witnessed coherence if the initial state and the fixed witness does not match well. Based this result, we design a quantum coherence game. Our results provides a way to directly measure the coherence in arbitrary finite dimension states and an operational interpretation of the $l_1$-norm of coherence.

quant-ph↗