Two-photon polymerization lithography for imaging optics

Optical imaging systems have greatly extended human visual capabilities,enabling the observation and understanding of diverse phenomena.Imaging technologies span a broad spectrum of wavelengths from x-ray to radio frequencies and impact research activities and our daily lives.Traditional glass lenses are fabricated through a series of complex processes,while polymers offer versatility and ease of production.However,modern applications often require complex lens assemblies,driving the need for miniaturization and advanced designs with micro-and nanoscale features to surpass the capabilities of traditional fabrication methods.Three-dimensional(3D)printing,or additive manufacturing,presents a solution to these challenges with benefits of rapid prototyping,customized geometries,and efficient production,particularly suited for miniaturized optical imaging devices.Various 3D printing methods have demonstrated advantages over traditional counterparts,yet challenges remain in achieving nanoscale resolutions.Two-photon polymerization lithography(TPL),a nanoscale 3D printing technique,enables the fabrication of intricate structures beyond the optical diffraction limit via the nonlinear process of two-photon absorption within liquid resin.It offers unprecedented abilities,e.g.alignment-free fabrication,micro-and nanoscale capabilities,and rapid prototyping of almost arbitrary complex 3D nanostructures.In this review,we emphasize the importance of the criteria for optical performance evaluation of imaging devices,discuss material properties relevant to TPL,fabrication techniques,and highlight the application of TPL in optical imaging.As the first panoramic review on this topic,it will equip researchers with foundational knowledge and recent advancements of TPL for imaging optics,promoting a deeper understanding of the field.By leveraging on its high-resolution capability,extensive material range,and true 3D processing,alongside advances in materials,fabrication,and design,we envisage disruptive solutions to current challenges and a promising incorporation of TPL in future optical imaging applications.

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.

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.