Creating optical components that allow light to propagate in only one direction-that is, that allow non-reciprocal propagation or 'isolation' of light-is important for a range of applications. Non-reciprocal propagation of sound can be achieved simply by using mechanical components that spin. Spinning also affects de Broglie waves , so a similar idea could be applied in optics. However, the extreme rotation rates that would be required, owing to light travelling much faster than sound, lead to unwanted wobbling. This wobbling makes it difficult to maintain the separation between the spinning devices and the couplers to within tolerance ranges of several nanometres, which is essential for critical coupling. Consequently, previous applications of optical and optomechanical isolation have used alternative methods. In hard-drive technology, the magnetic read heads of a hard-disk drive fly aerodynamically above the rapidly rotating disk with nanometre precision, separated by a thin film of air with near-zero drag that acts as a lubrication layer . Inspired by this, here we report the fabrication of photonic couplers (tapered fibres that couple light into the resonators) that similarly fly above spherical resonators with a separation of only a few nanometres. The resonators spin fast enough to split their counter-circulating optical modes, making the fibre coupler transparent from one side while simultaneously opaque from the other-that is, generating irreversible transmission. Our setup provides 99.6 per cent isolation of light in standard telecommunication fibres, of the type used for fibre-based quantum interconnects . Unlike flat geometries, such as between a magnetic head and spinning disk, the saddle-like, convex geometry of the fibre and sphere in our setup makes it relatively easy to bring the two closer together, which could enable surface-science studies at nanometre-scale separations.

We propose nonreciprocal phonon lasing in a coupled cavity system composed of an optomechanical and a spinning resonator. We show that the optical Sagnac effect leads to significant modifications in both the mechanical gain and the power threshold for phonon lasing. More importantly, the phonon lasing in this system is unidirectional, that is the phonon lasing takes place when the coupled system is driven in one direction but not the other. Our work establishes the potential of spinning optomechanical devices for low-power mechanical isolation and unidirectional amplification. This provides a new route, well within the reach of current experimental abilities, to operate cavity optomechanical devices for such a wide range of applications as directional phonon switches, invisible sound sensing, and topological or chiral acoustics.

Droplets, particularly water, are abundant in nature and artificial systems. Thermal fluctuations imply that droplet interfaces behave like a stormy sea at the sub-nanometer scale. Thermal capillary-waves have been widely studied since 1908 and are of key importance in surface science. Here we use an optical mode of a droplet to probe its radius fluctuation. Our droplet benefits from a finesse of 520 that accordingly boosts its sensitivity in recording Brownian capillaries at 100-kHz rates and 1±0.025 ångström amplitudes, in agreement with natural-frequency calculation and the equipartition theorem. A fall in the fluctuation spectrum is measured below cutoff at the drop's lowest-eigenfrequency. Our device facilitates resonantly-enhanced optocapillaryinteractions that might enable optical excitation (/cooling) of capillary droplet-modes, including with the most-common and important liquid -water.Single sentence: We activate a droplet as a hybrid optocapillary resonator, and access its thermal capillaries while benefiting from resonantly-enhanced sensitivity.Thermal capillary waves [1][2][3][4][5][6] were first suggested by Smoluchowski [7] and are most

In submerged microcavities there is a tradeoff between resonant enhancement for spatial water and light overlap. Why not transform the continuously resonating optical mode to be fully contained in a water microdroplet per se? Here we demonstrate a sustainable 30-μm-pure water device, bounded almost completely by free surfaces, enabling >1,000,000 re-circulations of light. The droplets survive for >16 h using a technique that is based on a nano-water bridge from the droplet to a distant reservoir to compensate for evaporation. More than enabling a nearly-perfect optical overlap with water, atomic-level surface smoothness that minimizes scattering loss, and ∼99% coupling efficiency from a standard fibre. Surface tension in our droplet is 8,000 times stronger than gravity, suggesting a new class of devices with water-made walls, for new fields of study including opto-capillaries.

Observation of the plasmonic Rashba effect manifested by a polarization helicity degeneracy removal in a surface wave excitation via an inversion asymmetric metamaterial is reported. By designing the metasurface symmetry using anisotropic nanoantennas with space-variant orientations, we govern the light-matter interaction via the local field distribution arising in a wavelength and a photon spin control. The broken spatial inversion symmetry is experimentally manifested by a directional excitation of surface wave jets observed via a decoupling slit as well as by the quantum dot fluorescence. Rashba-type plasmonic metasurfaces provide a route for spin-based nanoscale devices controlled by the metamaterial symmetry and usher in a new era of light manipulation.