Label-free sensing of ultralow-weight molecules with all-dielectric metasurfaces supporting bound states in the continuum

The realization of an efficient optical sensor based on a photonic crystal metasurface supporting bound states in the continuum is reported. Liquids with different refractive indices, ranging from 1.4000 to 1.4480, are infiltrated in a microfluidic chamber bonded to the sensing dielectric metasurface. A bulk liquid sensitivity of 178 nm/RIU is achieved, while a Q-factor of about 2000 gives a sensor figure of merit up to 445 in air at both visible and infrared excitations. Furthermore, the detection of ultralow-molecular-weight(186 Da) molecules is demonstrated with a record resonance shift of 6 nm per less than a 1 nm thick single molecular layer. The system exploits a normal-to-the-surface optical launching scheme, with excellent interrogation stability and demonstrates alignment-free performances, overcoming the limits of standard photonic crystals and plasmonic resonant configurations.

Holographic planar lightwave circuit for on-chip spectroscopy

Computer-generated planar holograms are a powerful approach for designing planar lightwave circuits with unique properties.Digital planar holograms in particular can encode any optical transfer function with high customizability and is compatible with semiconductor lithography techniques and nanoimprint lithography.Here,we demonstrate that the integration of multiple holograms on a single device increases the overall spectral range of the spectrometer and offsets any performance decrement resulting from miniaturization.The validation of a high-resolution spectrometer-on-chip based on digital planar holograms shows performance comparable with that of a macrospectrometer.While maintaining the total device footprint below 2 cm2,the newly developed spectrometer achieved a spectral resolution of 0.15 nm in the red and near infrared range,over a 148 nm spectral range and 926 channels.This approach lays the groundwork for future on-chip spectroscopy and lab-on-chip sensing.

High-refractive index acrylate polymers for applications in nanoimprint lithography

The development of polymeric optical materials with a higher refractive index,transparency in the visible spectrum region and easier processability is increasingly desirable for advanced optical applications such as microlenses,image sensors,and organic light-emitting diodes.Most acrylates have a low refractive index(around 1.50)which does not meet the high perfo rmance requirements of advanced optical materials.In this research,three novel acrylates were synthesized via a facile one-step approach and used to fabricate optical transparent polymers.All of the polymers reveal good optical properties including high transparency(≥90%)in the visible spectrum region and high refractive index values(1.6363)at 550 nm.Moreover,nanostructures of these acrylate polymers with various feature sizes including nanogratings and photonic crystals were successfully fabricated using nanoimprint lithography.These results indicate that these acrylates can be used in a wide range of optical and optoelectronic devices where nanopatterned films with high refractive index and transparency are required.

Guided resonance in negative index photonic crystals: a new approach

The behavior of a negative refraction photonic crystal slab irradiated with out-of-plane incident beam is an unexplored subject.In such an experimental configuration,guided mode resonance appears in the reflection spectrum.We show that,in this case,the light coupled inside the photonic crystal is backpropagating.A relationship with the negative index properties is established using a new approach in which the guided resonance is recovered by modeling the photonic crystal layer with a simple Lorentz resonator using the Fresnel reflection formula.

Tunable rainbow light trapping in ultrathin resonator arrays

Rainbow light trapping in plasmonic devices allows for field enhancement of multiple wavelengths within a single device.However,many of these devices lack precise control over spatial and spectral enhancement profiles and cannot provide extremely high localised field strengths.Here we present a versatile,analytical design paradigm for rainbow trapping in nanogroove arrays by utilising both the groove-width and groove-length as tuning parameters.We couple this design technique with fabrication through multilayer thin-film deposition and focused ion beam milling,which enables the realisation of unprecedented feature sizes down to 5 nm and corresponding extreme normalised local field enhancements up to 103.We demonstrate rainbow trapping within the devices through hyperspectral microscopy and show agreement between the experimental results and simulation.The combination of expeditious design and precise fabrication underpins the implementation of these nanogroove arrays for manifold applications in sensing and nanoscale optics.

Ellipsometric determination of permittivity in a negative index photonic crystal metamaterial

In this work,we present the first experimental evidence of negative dielectric susceptibility in a two-dimensional silicon photonic crystal(PhC)with negative refractive index behavior.In the frequency range in which the effective refractive index neff is equal to 21,the incident light couples efficiently to the guided modes in the top surface layer of the PhC metamaterial.These modes resemble surface plasmon polariton resonances.This finding was confirmed by ellipsometric measurements,demonstrating the isotropy of the PhC resonances.Such negative index PhC materials may be of use in biosensing applications.

Coupling model for an extended-range plasmonic optical transformer scanning probe

The expansion of nanoscale optics has generated a variety of scanning probe geometries that yield spatial resolution below 10 nm.In this work,we present a physical model for coupling far-field radiation to plasmonic modes on the surface of a scanning probe,and propose a scheme for extending the working distance of such a probe.In a subsurface application,an optical transformer at the tip of a probe can be coupled to a remote near-field antenna placed inside the sample at a distance away from the surface,expanding the effective working distance up to 100 nm.

Small footprint optoelectrodes using ring resonators for passive light localization

The combination of electrophysiology and optogenetics enables the exploration of how the brain operates down to a single neuron and its network activity.Neural probes are in vivo invasive devices that integrate sensors and stimulation sites to record and manipulate neuronal activity with high spatiotemporal resolution.State-of-the-art probes are limited by tradeoffs involving their lateral dimension,number of sensors,and ability to access independent stimulation sites.Here,we realize a highly scalable probe that features three-dimensional integration of small-footprint arrays of sensors and nanophotonic circuits to scale the density of sensors per cross-section by one order of magnitude with respect to state-of-the-art devices.For the first time,we overcome the spatial limit of the nanophotonic circuit by coupling only one waveguide to numerous optical ring resonators as passive nanophotonic switches.With this strategy,we achieve accurate on-demand light localization while avoiding spatially demanding bundles of waveguides and demonstrate the feasibility with a proof-of-concept device and its scalability towards high-resolution and low-damage neural optoelectrodes.