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Light scattering is one of the most established wave phenomena in optics, lying at the heart of light-matter interactions and of crucial importance for nanophotonic applications. Passivity, causality, and energy conservation imply strict bounds on the degree of control over scattering from small particles, with implications on the performance of many optical devices. Here, we demonstrate that these bounds can be surpassed by considering excitations at complex frequencies, yielding extreme scattering responses as tailored nanoparticles reach a quasi-steady-state regime. These mechanisms can be used to engineer light scattering of nanostructures beyond conventional limits for noninvasive sensing, imaging, and nanoscale light manipulation.

Plant-derived polyphenols have emerged as molecular building blocks for biomedical architectures. However, the isolation of polyphenols from other components requires labor-intensive procedures, which increases costs and often raises environmental concerns. Here, we suggest that decaffeination can be a convenient and cost-effective method for enhancing the antibacterial performance of polyphenol-rich tea extracts. As a demonstration, we compared the properties of a nano-thin coating made of decaffeinated (dGT coating) and raw green tea extract (GT coating). The dGT coating exhibited enhanced antibacterial performance with regard to bacterial killing and prevention of bacterial attachment compared with the GT coating. Moreover, the chemical reactivity of the dGT coating was further utilized for secondary modifications, which enhanced the overall antibacterial performance of the modified surface. Given its intrinsic low toxicity, we envision that the developed antibacterial coating is ready for the next steps toward application in real clinical settings.

The adiabatic encirclement of exceptional points in non-Hermitian systems is known to produce surprising non-adiabatic effects. A new study finds a cheat code to exactly emulate this behaviour without ever having to produce an exceptional point.

Colorants have been utilized for precise biomarker detection in rapid and convenient colorimetric bioassays. However, the diffusion of colorants in solution often results in poor sensitivity, which is a major obstacle to the clinical translation of current colorants. To address this issue, in the current study, a unique colorant is developed that possesses adhesiveness for concentration near the target biomarker, avoiding diffusion. In nature, the synergistic interplay between catechol and amine functional groups is thought to be key for the unique mechanism of marine mussel adhesion. In addition, polymerized catecholamines are found in nature as biopigments, that is, in melanin. The dual role of catechol/catecholamine moieties in natural organics inspire to design novel colorimetric bioassays based on an adhesive colorant. Horseradish peroxidase (HRP) is used to initiate in situ polymerization of the catecholic precursors with amine-containing additive molecules and simultaneously attach them near the HRP-labeled biomarkers. This novel catecholamine-based adhesive colorant provides an excellent quantitative (naked-eye) visible signal and it also generates superb spatial information on the biomarkers on complex surfaces (e.g., cell membranes).

Nonlinear wave–matter interactions may give rise to solitons, phenomena that feature inherent stability in wave propagation and unusual spectral characteristics. Solitons have been created in a variety of physical systems and have had important roles in a broad range of applications, including communications, spectroscopy and metrology1–4. In recent years, the realization of dissipative Kerr optical solitons in microcavities has led to the generation of frequency combs in a chip-scale platform5–10. Within a cavity, photons can interact with mechanical modes. Cavity optomechanics has found applications for frequency conversion, such as microwave-to-optical or radio-frequency-to-optical11–13, of interest for communications and interfacing quantum systems operating at different frequencies. Here we report the observation of mechanical micro-solitons excited by optical fields in an optomechanical microresonator, expanding soliton generation in optical resonators to a different spectral window. The optical field circulating along the circumference of a whispering gallery mode resonator triggers a mechanical nonlinearity through optomechanical coupling, which in turn induces a time-varying periodic modulation on the propagating mechanical mode, leading to a tailored modal dispersion. Stable localized mechanical wave packets—mechanical solitons—can be realized when the mechanical loss is compensated by phonon gain and the optomechanical nonlinearity is balanced by the tailored modal dispersion. The realization of mechanical micro-solitons driven by light opens up new avenues for optomechanical technologies14 and may find applications in acoustic sensing, information processing, energy storage, communications and surface acoustic wave technology. Stable, dissipative optomechanical solitons are realized using optical fields in a whispering gallery mode resonator by balancing the optomechanical nonlinearities with a tailored modal dispersion.

Achieving non-reciprocal light propagation via stimuli that break time-reversal symmetry, without magneto-optics, remains a major challenge for integrated nanophotonic devices. Recently, optomechanical microsystems in which light and vibrational modes are coupled through ponderomotive forces have demonstrated strong non-reciprocal effects through a variety of techniques, but always using optical pumping. None of these approaches has demonstrated bandwidth exceeding that of the mechanical system, and all of them require optical power; these are both fundamental and practical issues. Here, we resolve both challenges by breaking time-reversal symmetry using a two-dimensional acoustic pump that simultaneously provides a non-zero overlap integral for light–sound interaction and also satisfies the necessary phase-matching. We use this technique to produce a non-reciprocal modulator (a frequency shifting isolator) by means of indirect interband scattering. We demonstrate mode conversion asymmetry up to 15 dB and efficiency as high as 17% over a bandwidth exceeding 1 GHz. Time-reversal symmetry is broken via an acoustic pumping scheme enabling demonstration of a frequency shifting optical isolator with 15 dB asymmetry and 1 GHz bandwidth.

Supplemental document

We demonstrate dynamic suppression of Rayleigh backscattering in a whispering gallery mode resonator by locally breaking time-reversal symmetry through a Brillouin optomechanical interaction.

We experimentally demonstrate GHz bandwidth non-reciprocal light transmission using acoustic pumping of a nanophotonic circuit. Non-reciprocity is achieved through an indirect interband optical transition as a result of photoelastic perturbation caused by an acoustic wave.

Microscale resonators that simultaneously exhibit high-Q optical and mechanical resonances are routinely used to study the coupling between light and vibration. We have learned recently that Brillouin scattering (traveling-wave light-sound interactions) within simple dielectric whispering-gallery resonators can enable nonreciprocal optical transmission through a waveguide, which can be reconfigured optically and on demand. In this talk, we describe the basic theory and experimental demonstrations of Brillouin Optomechanics, and describe how it allows the breaking of time-reversal symmetry by means of traveling phonon modes. We experimentally demonstrate ultra-low loss optical isolation using a simple resonator system. Our results demonstrate that chip-scale optical isolation is much more accessible than previously thought. (invited by Prof. Xudong Fan)

We demonstrate optomechanical cooling without added damping in a whispering gallery mode resonator by means of disorder-induced scattering. The phenomenon results from a reduction of thermal loading such that it eventually induces chirality of phonons.

Wavelike spatiotemporal modulation of discrete coupling elements creates synthetic phonons that enable nonreciprocal coupling., Inducing nonreciprocal wave propagation is a fundamental challenge across a wide range of physical systems in electromagnetics, optics, and acoustics. Recent efforts to create nonreciprocal devices have departed from established magneto-optic methods and instead exploited momentum-based techniques such as coherent spatiotemporal modulation of resonators and waveguides. However, to date, the nonreciprocal frequency responses that these devices can achieve have been limited, mainly to either broadband or Lorentzian-shaped transfer functions. We show that nonreciprocal coupling between waveguides and resonator networks enables the creation of devices with customizable nonreciprocal frequency responses. We create nonreciprocal coupling through the action of synthetic phonons, which emulate propagating phonons and can scatter light between guided and resonant modes that differ in both frequency and momentum. We implement nonreciprocal coupling in microstrip circuits and experimentally demonstrate both elementary nonreciprocal functions such as isolation and gyration, as well as reconfigurable, higher-order nonreciprocal filters. Our results suggest nonreciprocal coupling as a platform for a broad class of customizable nonreciprocal systems, adaptable to all wave phenomena.

We demonstrate dynamical induction of chiral phonon transport in optomechanical resonators by means of traveling-wave acousto-optical interaction. The phenomenon results in unidirectional defect tolerant transport and chiral cooling of high-Q phonon modes in the system.

The ultimate limits of performance for any classical optical system are set by sub-wavelength fluctuations within the host material, which may be frozen-in or even dynamically induced. The most common manifestation of such subwavelength disorder is Rayleigh light scattering, which is observed in nearly all waveguiding technologies today and can lead to both irreversible radiative losses as well as undesirable intermodal coupling. While it has been shown that backscattering from disorder can be suppressed by breaking the time-reversal symmetry in magneto-optic and topological insulator materials, common optical dielectrics possess neither of these properties. Here, we demonstrate an optomechanical approach for dynamically suppressing Rayleigh backscattering within dielectric resonators. We achieve this by locally breaking the time-reversal symmetry in a silica resonator through a Brillouin scattering interaction that is available in all materials. Near-complete suppression of Rayleigh backscattering is experimentally confirmed through two independent measurements—the elimination of a commonly seen normal-mode splitting or “doublet” effect and by measurement of the reduction in intrinsic optical loss. Additionally, a reduction of the back-reflections caused by disorder is also observed. Our results provide new evidence that it is possible to dynamically suppress Rayleigh backscattering within any optical dielectric medium using time-reversal symmetry breaking, for achieving robust light propagation in spite of scatterers or defects.

The transport of sound and heat, in the form of phonons, can be limited by disorder-induced scattering. In electronic and optical settings the introduction of chiral transport, in which carrier propagation exhibits parity asymmetry, can remove elastic backscattering and provides robustness against disorder. However, suppression of disorder-induced scattering has never been demonstrated in non-topological phononic systems. Here we experimentally demonstrate a path for achieving robust phonon transport in the presence of material disorder, by explicitly inducing chirality through parity-selective optomechanical coupling. We show that asymmetric optical pumping of a symmetric resonator enables a dramatic chiral cooling of clockwise and counterclockwise phonons, while simultaneously suppressing the hidden action of disorder. Surprisingly, this passive mechanism is also accompanied by a chiral reduction in heat load leading to optical cooling of the mechanics without added damping, an effect that has no optical analog. This technique can potentially improve upon the fundamental thermal limits of resonant mechanical sensors, which cannot be attained through sideband cooling., Chiral transport can provide robustness against disorder, resulting in improved resonant modes for sensing and metrology. Here, Kim et al. demonstrate chiral phonon transport, disorder suppression and anomalous cooling without damping in an asymmetrically-pumped optomechanical system.

Dynamical back-action cooling of phonons in optomechanical systems having one optical mode is well studied. Systems with two optical modes have the potential to reach significantly higher cooling rate through resonant enhancement of both pump and scattered light. Here we experimentally investigate the role of dual optical densities of states on Brillouin optomechanical cooling, and the deviation from theory caused by thermal locking to the pump laser. Using this, we demonstrate a room temperature system operating very close to the strong coupling regime, where saturation of cooling is anticipated.