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.

Silicon nanophotonics for on-chip light manipulation

The field of silicon nanophotonics has attracted considerable attention in the past decade because of its unique advantages,including complementary metal–oxide–semiconductor（CMOS） compatibility and the ability to achieve an ultra-high integration density. In particular, silicon nanophotonic integrated devices for on-chip light manipulation have been developed successfully and have played very import roles in various applications. In this paper, we review the recent progress of silicon nanophotonic devices for on-chip light manipulation, including the static type and the dynamic type. Static onchip light manipulation focuses on polarization/mode manipulation, as well as light nanofocusing, while dynamic on-chip light manipulation focuses on optical modulation/switching. The challenges and prospects of high-performance silicon nanophotonic integrated devices for on-chip light manipulation are discussed.

On Negative Differential Mobility in Nanophotonic Device Functionality

A negative differential mobility (NDM) of the two-dimensional carrier-gas against some proper external regulator allowing for gradual controlled modification of the nanointerfacial environment tends to occur as interwoven with nanophotonic device functionality. In this work, several instances, in our two-decade principal research, of both experimental observation and conceptual prediction concerning nanophotonics NDM are reconsidered towards outlining a global potential for the appearance of the effect.

A Notional Duette on Nanophotonics Fundamentals

A two-part Notional Synthesis on Nanophotonics Fundamentals is being carried out: On the one hand, a rather novel depiction of the Fermionic Quantum Causality is being attempted. On the other hand, a Nanophotonic Response Encoder is being devised: Illuminated Electrons are the original Protagonists.

Optical wafer defect inspection at the 10 nm technology node and beyond

The growing demand for electronic devices, smart devices, and the Internet of Things constitutes the primary driving force for marching down the path of decreased critical dimension and increased circuit intricacy of integrated circuits. However, as sub-10 nm high-volume manufacturing is becoming the mainstream, there is greater awareness that defects introduced by original equipment manufacturer components impact yield and manufacturing costs. The identification, positioning, and classification of these defects, including random particles and systematic defects, are becoming more and more challenging at the 10 nm node and beyond.Very recently, the combination of conventional optical defect inspection with emerging techniques such as nanophotonics, optical vortices, computational imaging, quantitative phase imaging, and deep learning is giving the field a new possibility. Hence, it is extremely necessary to make a thorough review for disclosing new perspectives and exciting trends, on the foundation of former great reviews in the field of defect inspection methods. In this article, we give a comprehensive review of the emerging topics in the past decade with a focus on three specific areas:(a) the defect detectability evaluation,(b) the diverse optical inspection systems,and(c) the post-processing algorithms. We hope, this work can be of importance to both new entrants in the field and people who are seeking to use it in interdisciplinary work.

Nonlinear frequency conversion in optical nanoantennas and metasurfaces:materials evolution and fabrication

Nonlinear frequency conversion is one of the most fundamental processes in nonlinear optics.It has a wide range of applications in our daily lives,including novel light sources,sensing,and information processing.It is usually assumed that nonlinear frequency conversion requires large crystals that gradually accumulate a strong effect.However,the large size of nonlinear crystals is not compatible with the miniaturisation of modern photonic and optoelectronic systems.Therefore,shrinking the nonlinear structures down to the nanoscale,while keeping favourable conversion efficiencies,is of great importance for future photonics applications.In the last decade,researchers have studied the strategies for enhancing the nonlinear efficiencies at the nanoscale,e.g.by employing different nonlinear materials,resonant couplings and hybridization techniques.In this paper,we provide a compact review of the nanomaterials-based efforts,ranging from metal to dielectric and semiconductor nanostructures,including their relevant nanofabrication techniques.

Photoluminescence control by hyperbolic metamaterials and metasurfaces:a review

Photolu min esce nee in clud ing fluoresce nee plays a great role in a wide variety of applicati ons from biomedical sensing and imag ing to optoelectr on ics.Therefore,the enhan ceme nt and con trol of photolu min esce nee has imme nse impact on both fun dame ntal scie ntific research and aforeme nti oned applicati ons.Among various nano phot tonic schemes and nanostructures to enhance the photoluminescence,we focus on a certain type of nanostructures,hyperbolic metamaterials(HMMs).HMMs are highly ani sotropic metamaterials,which produce intense localized electric fields.Therefore,HMMs n aturally boost photolu min esce nee from dye molecules,qua ntum dots,n itroge n-vaca ncy cen ters in diam on ds,perovskites and tra nsiti on metal dichalcoge nides.We provide an overview of various con figuratio ns of HMMs,i nclud ing metal-dielectric multilayers,trenches,metallic nanowires,and cavity structures fabricated with the use of noble metals,transparent conductive oxides,and refractory metals as plasmonic elements.We also discuss lasing action realized with HMMs.

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.

Diurnal cooling for continuous thermal sources under direct subtropical sunlight produced by quasi-Cantor structure

In this paper, an optical radiative cooler with quasi-Cantor structure is theoretically proposed and analyzed. This simple and symmetrically designed optical structure operates upon continuous thermal sources in diurnal subtropical conditions, and its efficiency is much higher than natural cooling, for instance, when operating upon a typical 323.15 K continuous thermal source with a wind speed at 3 m·s^-1, it can generate a net cooling power of 363.68 W·m^-2, which is 18.26% higher than that of non-radiative heat exchange （natural cooling） under the same conditions. Additionally, several aspects are considered in its design to ensure a low cost in application, which is of great economical and environmental significance.

Topological Landau–Zener nanophotonic circuits

Topological edge states(TESs),arising from topologically nontrivial phases,provide a powerful toolkit for the architecture design of photonic integrated circuits,since they are highly robust and strongly localized at the boundaries of topological insulators.It is highly desirable to be able to control TES transport in photonic implementations.Enhancing the coupling between the TESs in a finite-size optical lattice is capable of exchanging light energy between the boundaries of a topological lattice,hence facilitating the flexible control of TES transport.However,existing strategies have paid little attention to enhancing the coupling effects between the TESs through the finite-size effect.Here,we establish a bridge linking the interaction between the TESs in a finite-size optical lattice using the Landau–Zener model so as to provide an alternative way to modulate/control the transport of topological modes.We experimentally demonstrate an edge-to-edge topological transport with high efficiency at telecommunication wavelengths in silicon waveguide lattices.Our results may power up various potential applications for integrated topological photonics.

Optical phase front control in a metallic grating with equally spaced alternately tapered slits

A technique capable of focusing and bending electromagnetic （EM） waves through plasmonic gratings with equally spaced alternately tapered slits has been introduced. Phase resonances are observed in the optical response of transmission gratings, and the EM wave passes through the tuning slits in the form of surface plasmon polaritons （SPPs） and obtains the required phase retardation to focus at the focal plane. The bending effect is achieved by constructing an asymmetric phase front which results from the tapered slits and gradient refractive index （GRIN） distribution of the dielectric material. Rigorous electromagnetic analysis by using the two-dimensional （2D） finite difference time domain （FDTD） method is employed to verify our proposed designs. When the EM waves are incident at an angle on the optical axis, the beam splitting effect can also be achieved. These index-modulated slits are demonstrated to have unique advantages in beam manipulation compared with the width-modulated ones. In combination with previous studies, it is expected that our results could lead to the realization of ootimum designs for plasmonic nanolenses.

Acoustic plasmonics of Au grating/Bi2Se3 thin film/sapphire hybrid structures

The surface plasmon polaritons of the topological insulator Bi2Se3 can be excited by using etched grating or grave structures to compensate the wave vector mismatch of the incident photon and plasmon. Here, we demonstrate novel gold grating/Bi2Se3 thin film/sapphire hybrid structures, which allow the excitation of surface plasmon polaritons propagating through nondestructive Bi2Se3 thin film with the help of gold diffractive gratings. Utilizing periodic Au surface structures,the momentum can be matched and the normal-incidence infrared reflectance spectra exhibit pronounced dips. When the width of the gold grating W(with a periodicity 2 W) increases from 400 nm to 1500 nm, the resonant frequencies are tuned from about 7000 cm-1 to 2500 cm-1. In contrast to the expected ■ dispersion for both massive and massless fermions,where q ~π/W is the wave vector, we observe a sound-like linear dispersion even at room temperature. This surface plasmon polaritons with linear dispersion are attributed to the unique noninvasive fabrication method and high mobility of topological surface electrons. This novel structure provides a promising application of Dirac plasmonics.

Daytime Radiative Cooling:Artificial and Bioinspired Strategies

Traditional cooling systems have been posing a significant challenge to the global energy crisis and climate change due to the high energy consumption of the cooling process.In recent years,the emerging daytime radiative cooling provides a promising solution to address the bottleneck of traditional cooling technology by passively dissipating heat radiation to outer space without any energy consumption through the atmospheric transparency window(8~13μm).Whereas its stringent optical criteria require sophisticated and high cost fabrication producers,which hinders the applicability of radiative cooling technology.Many efforts have been devoted to develop high-efficiency and low-cost daytime radiative cooling technologies for practical application,including the nanophotonics based artificial strategy and bioinspired strategy.In order to systematically summarize the development and latest advance of daytime radiative cooling to help developing the most promising approach,here in this paper we will review and compare the two typical strategies on exploring the prospect approach for applicable radiative cooling technology.We will firstly sketch the fundamental of radiative cooling and summarize the common methods for construction radiative cooling devices.Then we will put an emphasis on the summarization and comparison of the two strategies for designing the radiative cooling device,and outlook the prospect and extending application of the daytime radiative cooling technology.

Physiological Fluid Specific Agglomeration Patterns Diminish Gold Nanorod Photothermal Characteristics

Investigations into the use of gold nanorods (Au-NRs) for biological applications are growing exponentially due to their distinctive physicochemical properties, which make them advantageous over other nanomaterials. Au-NRs are particularly renowned for their plasmonic characteristics, which generate a robust photothermal response when stimulated with light at a wavelength matching their surface plasmon resonance. Numerous reports have explored this nanophotonic phenomenon for temperature driven therapies;however, to date there is a significant knowledge gap pertaining to the kinetic heating profile of Au-NRs within a controlled physiological setting. In the present study, the impact of environmental composition on Au-NR behavior and degree of laser actuated thermal production was assessed. Through acellular evaluation, we identified a loss of photothermal efficiency in biologically relevant fluids and linked this response to excessive particle aggregation and an altered Au-NR spectral profile. Furthermore, to evaluate the potential impact of solution composition on the efficacy of nano-based biological applications, the degree of targeted cellular destruction was ascertained in vitro and was found to be susceptible to fluid-dependent modifications. In summary, this study identified a diminution of Au-NR nanophotonic response in artificial physiological fluids that translated to a loss of application efficiency, pinpointing a critical concern that must be considered to advance in vivo, nano-based bio-applications.

The Surface Plasmons＇ Frequencies of Two Adjacent Metallic Nanospheres by Bloch-Jensen Hydrodynamical Model

The wave guides and optical fibers have long been known to transmit light and electromagnetic fields in large dimensions. Recently, surface plasmons, which are collective plasma oscillations of valence electrons at metal surfaces, have been introduced as an entity that is able to guide light on the surfaces of the metal and to concentrate light in subwavelength volumes. It has been found that periodic array of metallic nanospheres, could be able to enhance the light transmission, and guiding light at nanoscale. The coupling between two nanoparticles in these devices is very important. The Bloch-Jensen hydrodynamical method has been used for computing surface plasmons＇ frequencies of a single metallic nanosphere. It contains the entire pole spectrum automatically, so it is more exactly than the other computational methods. In this research, we have computed the surface plasmons＇ frequencies of two adjacent nanospheres by Bloch-Jensen hydrodynamical model for the first time. The results show that there are two modes for this system, which depend explicitly on interparticle spacing. In addition, we have shown that the excitation modes yield to a single mode of a nanoparticle as the interparticle spacing increases.

Nanophotonic catalytic combustion enlightens mid-infrared light source

The tunable mid-infrared source in a broad-spectrum heralds great scientific implications and remains a challenge.Nanolocalized catalytic combustion facilitates access to customizable infrared light sources.Here,we report on fabricating platinumalumina bilayer nano-cylinder arrays for methanol catalytic combustion,which enables them to act as an array of infrared point light sources,with wavelength tunable by controlling the flow rate of methanol/air mixture.We then propose a technique of integrating nanophotonic structures with catalytic combustion to engineer infrared light emission.We demonstrate a prototype of a topological photonic crystal catalyst array in which infrared emission can be enhanced significantly with highly vertical emission.This work establishes a framework of nanophotonic catalytic combustion for infrared light sources.

Recent progress on structural coloration

Structural coloration generates colors by the interaction between incident light and micro-or nanoscale structures.It has received tremendous interest for decades,due to advantages including robustness against bleaching and environmentally friendly properties(compared with conventional pigments and dyes).As a versatile coloration strategy,the tuning of structural colors based on micro-and nanoscale photonic structures has been extensively explored and can enable a broad range of applications including displays,anti-counterfeiting,and coating.However,scholarly research on structural colors has had limited impact on commercial products because of their disadvantages in cost,scalability,and fabrication.In this review,we analyze the key challenges and opportunities in the development of structural colors.We first summarize the fundamental mechanisms and design strategies for structural colors while reviewing the recent progress in realizing dynamic structural coloration.The promising potential applications including optical information processing and displays are also discussed while elucidating the most prominent challenges that prevent them from translating into technologies on the market.Finally,we address the new opportunities that are underexplored by the structural coloration community but can be achieved through multidisciplinary research within the emerging research areas.

Stepwise colloidal lithography toward scalable and various planar chiral metamaterials

Chiral metamaterials(CMs)composed by artificial chiral resonators have attracted great attentions in the recent decades due to their strong chiroptical resonance and identifiable interaction with chiral materials,facilitating practical applications in chiral biosensing,chiral emission,and display technology.However,the complex geometry of CMs improves the fabrication difficulty and hinders their scalable fabrication for practical applications,especially in the visible and ultraviolet wavelengths.One potential strategy is the colloidal lithography that enables parallel fabrication for scalable and various planar structures.Here,we demonstrate a stepwise colloidal lithography technique that uses sequential deposition from multiple CMs and expand their variety and complexity.The geometry and optical chirality of building blocks from single deposition are systematically investigated,and their combination enables a significant extension of the range of chiral patterns by multiple-step depositions.This approach resulted in a myriad of complex designs with different characteristic sizes,compositions,and shapes,which are particularly beneficial for the development of nanophotonic materials.In addition,we designed a flexible chiral device based on PDMS,which exhibits a good CD value and excellent stability even after multiple inward and outward bendings.The excellent compatibility to various substrates makes the planar CMs more flexible in practical applications in microfluidic biosensing.

Optical bound states in the continuum in periodic structures:mechanisms,effects,and applications

Optical bound states in the continuum(BICs)have recently stimulated a research boom,accompanied by demonstrations of abundant exotic phenomena and applications.With ultrahigh quality(Q)factors,optical BICs have powerful abilities to trap light in optical structures from the continuum of propagation waves in free space.Besides the high Q factors enabled by the confined properties,many hidden topological characteristics were discovered in optical BICs.Especially in periodic structures with well-defined wave vectors,optical BICs were discovered to carry topological charges in momentum space,underlying many unique physical properties.Both high Q factors and topological vortex configurations in momentum space enabled by BICs bring new degrees of freedom to modulate light.BICs have enabled many novel discoveries in light-matter interactions and spin-orbit interactions of light,and BIC applications in lasing and sensing have also been well explored with many advantages.In this paper,we review recent developments of optical BICs in periodic structures,including the physical mechanisms of BICs,explored effects enabled by BICs,and applications of BICs.In the outlook part,we provide a perspective on future developments for BICs.