Time-asymmetric loop around an exceptional point over the full optical communications band

Abstract

Topological operations around exceptional points-time-varying system configurations associated with non-Hermitian singularities-have been proposed as a robust approach to achieving far-reaching open-system dynamics, as demonstrated in highly dissipative microwave transmission and cryogenic optomechanical oscillator experiments. In stark contrast to conventional systems based on closed-system Hermitian dynamics, environmental interferences at exceptional points are dynamically engaged with their internal coupling properties to create rotational stimuli in fictitious-parameter domains, resulting in chiral systems that exhibit various anomalous physical phenomena. To achieve new wave properties and concomitant device architectures to control them, realizations of such systems in application-abundant technological areas, including communications and signal processing systems, are the next step. However, it is currently unclear whether non-Hermitian interaction schemes can be configured in robust technological platforms for further device engineering. Here we experimentally demonstrate a robust silicon photonic structure with photonic modes that transmit through time-asymmetric loops around an exceptional point in the optical domain. The proposed structure consists of two coupled silicon-channel waveguides and a slab-waveguide leakage-radiation sink that precisely control the required non-Hermitian Hamiltonian experienced by the photonic modes. The fabricated devices generate time-asymmetric light transmission over an extremely broad spectral band covering the entire optical telecommunications window (wavelengths between 1.26 and 1.675 micrometres). Thus, we take a step towards broadband on-chip optical devices based on non-Hermitian topological dynamics by using a semiconductor platform with controllable optoelectronic properties, and towards several potential practical applications, such as on-chip optical isolators and non-reciprocal mode converters. Our results further suggest the technological relevance of non-Hermitian wave dynamics in various other branches of physics, such as acoustics, condensed-matter physics and quantum mechanics.

Light‐Directed Soft Mass Migration for Micro/Nanophotonics

“…Many of the exotic optical functionalities, such as omnidirectional imaging, deep‐subwavelength‐scale light 3D focusing, SPP color pixels, and highly efficient outcoupling of LEDs are due to the unfolding of such peculiar morphological complexity (iv)Fourth, the rapidly growing field of PT‐symmetric non‐Hermitian optics (i.e., EPs and bound states in the continuum (BIC)) can also benefit from the unique ability of azomaterials to simultaneously manipulate the physical morphology (e.g., SRGs) and molecular orientation . A one‐step illumination of a polarization interference pattern onto a flat azopolymeric thin film offers a versatile and unmatched method of independently controlling Re(ε) and Im(ε).…”

“…Accordingly, the relevant materials and light‐engineering processing have been limited to conventional applications. However, as briefly introduced in Section , the overall field of micro/nanophotonics is rapidly growing and shifting in a direction toward unprecedented control of light with the advent of new paradigms, including metasurfaces, BIC, and topological approaches . Therefore, the methodology of light‐directed soft mass migrations should become accordingly adaptable to these recent research areas.…”

“…The seminal work of Bender and Boettcher first showed a Hamiltonian system with “Parity‐Time” (PT) symmetry can have completely real‐valued energy spectra even under non‐Hermitian conditions . Since then, considerable efforts have been made to implement this non‐Hermitian Hamiltonian in optical system because it enables various fascinating optical phenomena, such as nonreciprocity, unusual dynamics, and unidirectionality . Even though the materialization of non‐Hermitian optical structures has recently shown considerable progress along with recent advances in photonic crystals, metamaterials, and metasurfaces, achieving real and imaginary permittivity, ε, (or refractive index) profiles of opposite spatial parities (i.e., Δε*(− x ) = Δε( x ) with a 90° phase difference while simultaneously satisfying ΔRe(ε) = ΔIm(ε)) for a PT‐symmetric function is still nontrivial .…”

Experimental Observation of an Exceptional Surface in Synthetic Dimensions with Magnon Polaritons

“…At the EP, both the eigenstates and eigenvalues of the system coalesce, distinguishing it from regular mode degeneracy. EPs have been studied in a wide range of systems, including coupled resonators or waveguides in the optical [2][3][4][5], microwave [6][7][8][9], magnetic [10], or mechanical domains [11,12]. Novel properties have been discovered around or at the EP, ranging from topological mode transfer [11] and asymmetric mode conversion [3,9,13] to extraordinary sensitivities [4,5] and directional lasing [14].…”

Vector Exceptional Points with Strong Superchiral Fields

“…The EPs have been observed in many photonic systems, such as optical microcavities [29,30], coupled optical waveguides [31][32][33], photonic crystal slabs [34][35][36][37] and unidirectionally coupled resonators [38,39]. Many novel properties are also found at or near the EPs, such as loss-induced suppression and revival of lasing [40][41][42], unidirectional transmission or reflection [43][44][45][46][47][48], topological chirality [49][50][51] and laser mode selectivity [52][53][54]. Recently, the photonic nanostructures, which sustain higherorder EPs, have been demonstrated to be achievable and can be used for ultra-sensitive nanoparticle sensing [55][56][57][58][59][60][61].…”