Ultrahigh numerical aperture meta-fibre for flexible optical trapping

Strong focusing on diffraction-limited spots is essential for many photonic applications and is particularly relevant for optical trapping;however,all currently used approaches fail to simultaneously provide flexible transportation of light,straightforward implementation,compatibility with waveguide circuitry,and strong focusing.Here,we demonstrate the design and 3D nanoprinting of an ultrahigh numerical aperture meta-fibre for highly flexible optical trapping.Taking into account the peculiarities of the fibre environment,we implemented an ultrathin meta-lens on the facet of a modified single-mode optical fibre via direct laser writing,leading to a diffraction-limited focal spot with a recordhigh numerical aperture of up to NA≈0.9.The unique capabilities of this flexible,cost-effective,bio-and fibre-circuitrycompatible meta-fibre device were demonstrated by optically trapping microbeads and bacteria for the first time with only one single-mode fibre in combination with diffractive optics.Our study highlights the relevance of the unexplored but exciting field of meta-fibre optics to a multitude of fields,such as bioanalytics,quantum technology and life sciences.

Coherent interaction of atoms with a beam of light confined in a light cage

Controlling coherent interaction between optical fields and quantum systems in scalable,integrated platforms is essential for quantum technologies.Miniaturised,warm alkali-vapour cells integrated with on-chip photonic devices represent an attractive system,in particular for delay or storage of a single-photon quantum state.Hollow-core fibres or planar waveguides are widely used to confine light over long distances enhancing light-matter interaction in atomic-vapour cells.However,they suffer from inefficient filling times,enhanced dephasing for atoms near the surfaces,and limited light-matter overlap.We report here on the observation of modified electromagnetically induced transparency for a non-diffractive beam of light in an on-chip,laterally-accessible hollow-core light cage.Atomic layer deposition of an alumina nanofilm onto the light-cage structure was utilised to precisely tune the high-transmission spectral region of the light-cage mode to the operation wavelength of the atomic transition,while additionally protecting the polymer against the corrosive alkali vapour.The experiments show strong,coherent light-matter coupling over lengths substantially exceeding the Rayleigh range.Additionally,the stable non-degrading performance and extreme versatility of the light cage provide an excellent basis for a manifold of quantum-storage and quantumnonlinear applications,highlighting it as a compelling candidate for all-on-chip,integrable,low-cost,vapour-based photon delay.

Influence of non-Hermitian mode topology on refractive index sensing with plasmonic waveguides

We evaluate the sensing properties of plasmonic waveguide sensors by calculating their resonant transmission spectra in different regions of the non-Hermitian eigenmode space.We elucidate the pitfalls of using modal dispersion calculations in isolation to predict plasmonic sensor performance,which we address by using a simple model accounting for eigenmode excitation and propagation.Our transmission calculations show that resonant wavelength and spectral width crucially depend on the length of the sensing region,so that no single criterion obtained from modal dispersion calculations alone can be used as a proxy for sensitivity.Furthermore,we find that the optimal detection limits occur where directional coupling is supported,where the narrowest spectra occur.Such narrow spectral features can only be measured by filtering out all higher-order modes at the output,e.g.,via a single-mode waveguide.Our calculations also confirm a characteristic square root dependence of the eigenmode splitting with respect to the permittivity perturbation at the exceptional point,which we show can be identified through the sensor beat length at resonance.This work provides a convenient framework for designing and characterizing plasmonic waveguide sensors when comparing them with experimental measurements.

Longitudinally thickness-controlled nanofilms on exposed core fibres enabling spectrally flattened supercontinuum generation

Nonlinear frequency conversion is a pathway to unlock undiscovered physics and implement tailored light sources for spectroscopy or medicine.A key challenge is the establishment of spectrally flat outputs,which is particularly demanding in the context of soliton-based light conversion at low pump energy.Here,we introduce the concept of controlling nonlinear frequency conversion by longitudinally varying resonances,allowing the shaping of soliton dynamics and achieving broadband spectra with substantial spectral flatness.Longitudinally varying resonances are realised by nanofilms with gradually changing thicknesses located on the core of an advanced microstructured fibre.Nanofilms with engineered thickness profiles are fabricated by tilted deposition,representing a waveguidecompatible approach to nano-fabrication,and inducing well-controlled resonances into the system,allowing unique dispersion control along the fibre length.Key features and dependencies are examined experimentally,showing improved bandwidth and spectral flatness via multiple dispersive wave generation and dispersionassisted soliton Raman shifts while maintaining excellent pulse-to-pulse stability and coherence in simulations,suggesting the relevance of our findings for basic science as well as tailored light sources.