Artificial neural networks enabled by nanophotonics

The growing demands of brain science and artificial intelligence create an urgent need for the development of artificial neural networks(ANNs)that can mimic the structural,functional and biological features of human neural networks.Nanophotonics,which is the study of the behaviour of light and the light–matter interaction at the nanometre scale,has unveiled new phenomena and led to new applications beyond the diffraction limit of light.These emerging nanophotonic devices have enabled scientists to develop paradigm shifts of research into ANNs.In the present review,we summarise the recent progress in nanophotonics for emulating the structural,functional and biological features of ANNs,directly or indirectly.

Optically Digitalized Holography: A Perspective for All-Optical Machine Learning

Holography, which was invented by Dennis Gabor in 1948, offers an approach to reconstructing both the amplitude and phase information of a three-dimensional (3D) object [1]. Since its invention, the concept of holography has been widely used in various fields, such as microscopy [2], interferometry [3], ultrasonography [4], and holographic display [5]. Optical holography can be divided into two steps: recording and reconstruction. A conventional hologram is recorded onto a photosensitive film as the interference between an object beam carrying the 3D object information and a reference beam. Thereafter, the original object wavefront is reconstructed in the 3D image space by illuminating the reference beam on the recorded hologram.

Diffractive photonic applications mediated by laser reduced graphene oxides

Modification of reduced graphene oxide in a controllable manner provides a promising material platform for producinggraphene based devices. Its fusion with direct laser writing methods has enabled cost-effective and scalable production for advanced applications based on tailored optical and electronic properties in the conductivity, the fluorescence and the refractive index during the reduction process. This mini-review summarizes the state-of-the-art status of the mechanisms of reduction of graphene oxides by direct laser writing techniques as well as appealing optical diffractive applications including planar lenses, information storage and holographic displays. Owing to its versatility and up-scalability, the laser reduction method holds enormous potentials for graphene based diffractive photonic devices with diverse functionalities.

Spin-manipulated nanoscopy for single nitrogenvacancy center localizations in nanodiamonds

Due to their exceptional optical and magnetic properties,negatively charged nitrogen-vacancy(NV−)centers in nanodiamonds(NDs)have been identified as an indispensable tool for imaging,sensing and quantum bit manipulation.The investigation of the emission behaviors of single NV−centers at the nanoscale is of paramount importance and underpins their use in applications ranging from quantum computation to super-resolution imaging.Here,we report on a spin-manipulated nanoscopy method for nanoscale resolutions of the collectively blinking NV−centers confined within the diffraction-limited region.Using wide-field localization microscopy combined with nanoscale spin manipulation and the assistance of a microwave source tuned to the optically detected magnetic resonance(ODMR)frequency,we discovered that two collectively blinking NV−centers can be resolved.Furthermore,when the collective emitters possess the same ground state spin transition frequency,the proposed method allows the resolving of each single NV−center via an external magnetic field used to split the resonant dips.In spin manipulation,the three-level blinking dynamics provide the means to resolve two NV−centers separated by distances of 23 nm.The method presented here offers a new platform for studying and imaging spin-related quantum interactions at the nanoscale with superresolution techniques.

Super-resolution optical microscope: principle,instrumentation, and application

Over the past two decades, several fluorescence-and non-fluorescence-based optical microscopes have been developed to break the diffraction limited barrier. In this review, the basic principles implemented in microscopy for super-resolution are described. Furthermore, achievements and instrumentation for super-resolution are presented. In addition to imaging, other applications that use super-resolution optical microscopes are discussed.

Three-Dimensional Direct Laser Writing of PEGda Hydrogel Microstructures with Low Threshold Power using a Green Laser Beam

Three-dimensional(3D)direct laser writing(DLW)based on two-photon polymerisation(TPP)is an advanced technology for fabricating precise 3D hydrogel micro-and nanostructures for applications in biomedical engineering.Particularly,the use of visible lasers for the 3D DLW of hydrogels is advantageous because it enables high fabrication resolution and promotes wound healing.Polyethylene glycol diacrylate(PEGda)has been widely used in TPP fabrication owing to its high biocompatibility.However,the high laser power required in the 3D DLW of PEGda microstructures using a visible laser in a high-water-content environment limits its applications to only those below the biological laser power safety level.In this study,a formula for a TPP hydrogel based on 2-hydroxy-2-methylpropiophenone(HMPP)and PEGda was developed for the fabrication of 3D DLW microstructures at a low threshold power(0.1 nJ per laser pulse at a writing speed of 10μm·s^(−1))in a high-water-content environment(up to 79%)using a green laser beam(535 nm).This formula enables the fabrication of microstructures with micrometre fabrication resolution and high mechanical strength(megapascal level)and is suitable for the fabrication of waterresponsive,shape-changing microstructures.These results will promote the utilisation of low-power 3D DLW for fabricating hydrogel microstructures using visible lasers in high-water-content environments.

Bragg-mirror-like circular dichroism in bio-inspired quadruple-gyroid 4srs nanostructures

The smooth and tailorable spectral response of Bragg mirrors has driven their pervasive use in optical systems requiring customizable spectral control of beam propagation.However,the simple nature of Bragg mirror reflection prevents their application to the control of important polarization states such as circular polarization.While helical and gyroid-based nanostructures exhibiting circular dichroism have been developed extensively to address this limitation,they are often restricted by the spectral inconsistency of their optical response.Here we present the fabrication and characterization of quadruple-gyroid 4srs nanostructures exhibiting bio-inspired Bragg-mirror-like circular dichroism:a smooth and uniform band of circular dichroism reminiscent of the spectrum of a simple multilayer Bragg-mirror.Furthermore,we demonstrate that the circular dichroism produced by 4srs nanostructures are robust to changes in incident angle and beam collimation,providing a new platform to create and engineer circular dichroism for functional circular polarization manipulation.