Miniature tunable Airy beam optical meta-device

Tunable Airy beams with controllable propagation trajectories have sparked interest in various fields,such as optical manipulation and laser fabrication.Existing research approaches encounter challenges related to insufficient compactness and integration feasibility,or they require enhanced tunability to enable real-time dynamic manipulation of the propagation trajectory.In this work,we present a novel method that utilizes a dual metasurface system to surpass these limitations,significantly enhancing the practical potential of the Airy beam.Our approach involves encoding a cubic phase profile and two off-axis Fresnel lens phase profiles across the two metasurfaces.The validity of the proposed strategy has been confirmed through simulation and experimental results.The proposed meta-device addresses the existing limitations and lays the foundation for broadening the applicability of Airy beams across diverse domains,encompassing light-sheet microscopy,laser fabrication,optical tweezers,etc.

Broadband high-efficiency dielectric metalenses based on quasi-continuous nanostrips

Benefiting from the abrupt phase changes within subwavelength thicknesses,metasurfaces have been widely applied for lightweight and compact optical systems.Simultaneous broadband and high-efficiency characteristics are highly attractive for the practical implementation of metasurfaces.However,current metasurface devices mostly adopt discrete micro/nano structures,which rarely realize both merits simultaneously.In this paper,dielectric metasurfaces composed of quasi-continuous nanostrips are proposed to overcome this limitation.Via quasi-continuous nanostrips metasurface,a normal focusing metalens and a superoscillatory lens overcoming the diffraction limit are designed and experimentally demonstrated.The quasi-continuous metadevices can operate in a broadband wavelength ranging from 450 nm to 1000nm and keep a high power efficiency.The average efficiency of the fabricated metalens reaches 54.24%,showing a significant improvement compared to the previously reported metalenses with the same thickness.The proposed methodology can be easily extended to design other metadevices with the advantages of broadband and high-efficiency in practical optical systems.

Time-sequential color code division multiplexing holographic display with metasurface

Color metasurface holograms are powerful and versatile platforms for modulating the amplitude,phase,polarization,and other properties of light at multiple operating wavelengths.However,the current color metasurface holography can only realize static manipulation.In this study,we propose and demonstrate a multiplexing metasurface technique combined with multiwavelength code-division multiplexing(CDM)to realize dynamic manipulation.Multicolor code references are utilized to record information within a single metasurface and increase the information capacity and security for anticracks.A total of 48 monochrome images consisting of pure color characters and multilevel color video frames were reconstructed in dual polarization channels of the birefringent metasurface to exhibit high information density,and a video was displayed via sequential illumination of the corresponding code patterns to verify the ability of dynamic manipulation.Our approach demonstrates significant application potential in optical data storage,optical encryption,multiwavelengthversatile diffractive optical elements,and stimulated emission depletion microscopy.

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.

Meta-device:advanced manufacturing

Metasurfaces are one of the most promising devices to break through the limitations of bulky optical components.By offering a new method of light manipulation based on the light-matter interaction in subwavelength nanostructures,metasurfaces enable the efficient manipulation of the amplitude,phase,polarization,and frequency of light and derive a series of possibilities for important applications.However,one key challenge for the realization of applications for meta-devices is how to fabricate large-scale,uniform nanostructures with high resolution.In this review,we review the state-of-the-art nanofabrication techniques compatible with the manufacture of meta-devices.Maskless lithography,masked lithography,and other nanofabrication techniques are highlighted in detail.We also delve into the constraints and limitations of the current fabrication methods while providing some insights on solutions to overcome these challenges for advanced nanophotonic applications.

All-optical nanoscale thermometry with silicon carbide color centers

All-optical thermometry plays a crucial role in precision temperature measurement across diverse fields.Quantum defects in solids are one of the most promising sensors due to their excellent sensitivity,stability,and biocompatibility.Yet,it faces limitations,such as the microwave heating effect and the complexity of spectral analysis.Addressing these challenges,we introduce a novel approach to nanoscale optical thermometry using quantum defects in silicon carbide(SiC),a material compatible with complementary metal-oxide-semiconductor(CMOS)processes.This method leverages the intensity ratio between anti-Stokes and Stokes emissions from SiC color centers,overcoming the drawbacks of traditional techniques such as optically detected magnetic resonance(ODMR)and zero-phonon line(ZPL)analysis.Our technique provides a real-time,highly sensitive(1.06%K^(-1)),and diffraction-limited temperature sensing protocol,which potentially helps enhance thermal management in the future miniaturization of electronic components.

Advanced manufacturing of dielectric metadevices

Metasurfaces,composed of two-dimensional nanostructures,exhibit remarkable capabilities in shaping wavefronts,encompassing phase,amplitude,and polarization.This unique proficiency heralds a transformative paradigm shift in the domain of next-generation optics and photonics,culminating in the development of flat and ultrathin optical devices.Particularly noteworthy is the all-dielectric-based metasurface,leveraging materials such as titanium dioxide,silicon,gallium arsenide,and silicon nitride,which finds extensive application in the design and implementation of high-performance optical devices,owing to its notable advantages,including a high refractive index,low ohmic loss,and cost-effectiveness.Furthermore,the remarkable growth in nanofabrication technologies allows for the exploration of new methods in metasurface fabrication,especially through wafer-scale nanofabrication technologies,thereby facilitating the realization of commercial applications for metasurfaces.This review provides a comprehensive overview of the latest advancements in state-of-the-art fabrication technologies in dielectric metasurface areas.These technologies,including standard nanolithography[e.g.,electron beam lithography(EBL)and focused ion beam(FIB)lithography],advanced nanolithography(e.g.,grayscale and scanning probe lithography),and large-scale nanolithography[e.g.,nanoimprint and deep ultraviolet(DUV)lithography],are utilized to fabricate highresolution,high-aspect-ratio,flexible,multilayer,slanted,and wafer-scale all-dielectric metasurfaces with intricate nanostructures.Ultimately,we conclude with a perspective on current cutting-edge nanofabrication technologies.

A platform for integrated spectrometers based on solution-processable semiconductors

Acquiring real-time spectral information in point-of-care diagnosis,internet-of-thing,and other lab-on-chip applications require spectrometers with hetero-integration capability and miniaturized feature.Compared to conventional semiconductors integrated by heteroepitaxy,solution-processable semiconductors provide a much-flexible integration platform due to their solution-processability,and,therefore,more suitable for the multi-material integrated system.However,solution-processable semiconductors are usually incompatible with the micro-fabrication processes.This work proposes a facile and universal platform to fabricate integrated spectrometers with semiconductor substitutability by unprecedently involving the conjugated mode of the bound states in the continuum(conjugated-BIC)photonics.Specifically,exploiting the conjugated-BIC photonics,which remains unexplored in conventional lasing studies,renders the broadband photodiodes with ultra-narrowband detection ability,detection wavelength tunability,and on-chip integration ability while ensuring the device performance.Spectrometers based on these ultra-narrowband photodiode arrays exhibit high spectral resolution and wide/tunable spectral bandwidth.The fabrication processes are compatible with solution-processable semiconductors photodiodes like perovskites and quantum dots,which can be potentially extended to conventional semiconductors.Signals from the spectrometers directly constitute the incident spectra without being computation-intensive,latency-sensitive,and error-intolerant.As an example,the integrated spectrometers based on perovskite photodiodes are capable of realizing narrowband/broadband light reconstruction and in-situ hyperspectral imaging.

Optical metasurfaces:fundamentals and applications

Optical metasurfaces are currently an important research area all around the world because of their wide application opportunities in imaging,wavefront engineering,nonlinear optics,quantum information processing,just to name a few.The feature issue“Optical Metasurfaces:Fundamentals and Applications”in Photonics Research allows for archival publication of the most recent works in optical metasurface and provides for broad dissemination in the photonics community.

Special issue on meta-lenses

About a decade ago,the unveiling of generalized Snell’s laws heralded a significant advancement in nanophotonics,leading to the emergence of metasurfaces1−6.This revolutionary milestone has set the stage for the development of advanced optical devices,particularly metalens7−11.Researchers are already well-versed in the fundamental principles and functions of meta-lenses,which exemplify the concept of phase discontinuities with clarity.However,the exploration of meta-lenses is far from over.

Arbitrary polarization conversion dichroism metasurfaces for all-in-one full Poincare sphere polarizers

The control of polarization,an essential property of light,is of broad scientific and technological interest.Polarizers are indispensable optical elements for direct polarization generation.However,arbitrary polarization generation,except that of common linear and circular polarization,relies heavily on bulky optical components such as cascading linear polarizers and waveplates.Here,we present an effective strategy for designing all-in-one full Poincare sphere polarizers based on perfect arbitrary polarization conversion dichroism and implement it in a monolayer all-dielectric metasurface.This strategy allows preferential transmission and conversion of one polarization state located at an arbitrary position on the Poincare sphere to its handedness-flipped state while completely blocking its orthogonal state.In contrast to previous methods that were limited to only linear or circular polarization,our method manifests perfect dichroism of nearly 100%in theory and greater than 90%experimentally for arbitrary polarization states.By leveraging this attractive dichroism,our demonstration of the generation of polarization beams located at an arbitrary position on a Poincare sphere directly from unpolarized light can substantially extend the scope of meta-optics and dramatically promote state-of-the-art nanophotonic devices.

Risk assessment of Giardia in rivers of southern China based on continuous monitoring

The occurrence and risks of Giardia in China have been unclear to date,which has made it difficult to properly manage source water as well as to create reasonable drinking water standards.The levels of Giardia in river networks of several cities in Zhejiang Province,China were found to be in the range of 0-5 oocysts/10 L in the rainy season in 2008.The mortality due to Giardia infection for people in this region was calculated to be from 0 to 1.95 × 10？8 persons using a conditional probability equation.Based on multiple unboiled water intake routes,the disability-adjusted life years（DALYs） due to Giardia infection for people who consumed conventionally treated water was 0.625（95% CI：0.137-2.05） per 105 persons,with the symptom of hospitalization making the highest contribution to total DALYs（0.56 per 105 persons;95% CI：0.122-1.84）.The DALYs decreased to 0.425（95% CI：0.137-2.05） per 105 persons per year for those consuming water treated with advanced technology.These values were lower than the acceptable risk（1.97 × 10？5 DALYs per year）.This study revealed the risk of Giardia infection to the people in river networks of Zhejiang Province for the first time,and provides a method to evaluate the risk of Giardia infection.The results are useful for the modification of drinking water quality standards based on cost-benefit analysis.

Phase characterisation of metalenses

Metalenses have emerged as a new optical element or system in recent years,showing superior performance and abundant applications.However,the phase distribution of a metalens has not been measured directly up to now,hindering further quantitative evaluation of its performance.We have developed an interferometric imaging phase measurement system to measure the phase distribution of a metalens by taking only one photo of the interference pattern.Based on the measured phase distribution,we analyse the negative chromatic aberration effect of monochromatic metalenses and propose a feature size of metalenses.Different sensitivities of the phase response to wavelength between the Pancharatnam-Berry phase-based metalens and propagation phase-reliant metalens are directly observed in the experiment.Furthermore,through phase distribution analysis,it is found that the distance between the measured metalens and the brightest spot of focusing will deviate from the focal length when the metalens has a low nominal numerical aperture,even though the metalens is ideal without any fabrication error.We also use the measured phase distribution to quantitatively characterise the imaging performance of the metalens.Our phase measurement system will help not only designers optimise the designs of metalenses but also fabricants distinguish defects to improve the fabrication process,which will pave the way for metalenses in industrial applications.

Direct observation of chaotic resonances in optical microcavities

Optical microcavities play a significant role in the study of classical and quantum chaos.To date,most experimental explorations of their internal wave dynamics have focused on the properties of their inputs and outputs,without directly interrogating the dynamics and the associated mode patterns inside.As a result,this key information is rarely retrieved with certainty,which significantly restricts the verification and understanding of the actual chaotic motion.Here we demonstrate a simple and robust approach to directly and rapidly map the internal mode patterns in chaotic microcavities.By introducing a local index perturbation through a pump laser,we report a spectral response of optical microcavities that is proportional to the internal field distribution.With this technique,chaotic modes with staggered mode spacings can be distinguished.Consequently,a complete chaos assisted tunneling(CAT)and its time-reversed process are experimentally verified in the optical domain with unprecedented certainty.

Suppressing meta-holographic artifacts by laser coherence tuning

A metasurface hologram combines fine spatial resolution and large viewing angles with a planar form factor and compact size.However,it suffers coherent artifacts originating from electromagnetic cross-talk between closely packed meta-atoms and fabrication defects of nanoscale features.Here,we introduce an efficient method to suppress all artifacts by fine-tuning the spatial coherence of illumination.Our method is implemented with a degenerate cavity laser,which allows a precise and continuous tuning of the spatial coherence over a wide range,with little variation in the emission spectrum and total power.We find the optimal degree of spatial coherence to suppress the coherent artifacts of a meta-hologram while maintaining the image sharpness.This work paves the way to compact and dynamical holographic displays free of coherent defects.

Phyllotaxis-inspired nanosieves with multiplexed orbital angular momentum

Nanophotonic platforms such as metasurfaces,achieving arbitrary phase profiles within ultrathin thickness,emerge as miniaturized,ultracompact and kaleidoscopic optical vortex generators.However,it is often required to segment or interleave independent sub-array metasurfaces to multiplex optical vortices in a single nano-device,which in turn affects the device’s compactness and channel capacity.Here,inspired by phyllotaxis patterns in pine cones and sunflowers,we theoretically prove and experimentally report that multiple optical vortices can be produced in a single compact phyllotaxis nanosieve,both in free space and on a chip,where one meta-atom may contribute to many vortices simultaneously.The time-resolved dynamics of on-chip interference wavefronts between multiple plasmonic vortices was revealed by ultrafast time-resolved photoemission electron microscopy.Our nature-inspired optical vortex generator would facilitate various vortex-related optical applications,including structured wavefront shaping,free-space and plasmonic vortices,and high-capacity information metaphotonics.

Risk assessment of Giardia from a full scale MBR sewage treatment plant caused by membrane integrity failure

Membrane bioreactors（MBR） are highly efficient at intercepting particles and microbes and have become an important technology for wastewater reclamation. However, many pathogens can accumulate in activated sludge due to the long residence time usually adopted in MBR, and thus may pose health risks when membrane integrity problems occur.This study presents data from a survey on the occurrence of water-borne Giardia pathogens in reclaimed water from a full-scale wastewater treatment plant with MBR experiencing membrane integrity failure, and assessed the associated risk for green space irrigation. Due to membrane integrity failure, the MBR effluent turbidity varied between 0.23 and 1.90 NTU over a period of eight months. Though this turbidity level still met reclaimed water quality standards（≤ 5 NTU）, Giardia were detected at concentrations of 0.3 to 95 cysts/10 L, with a close correlation between effluent turbidity and Giardia concentration. All β-giardin gene sequences of Giardia in the WWTP influents were genotyped as Assemblages A and B, both of which are known to infect humans. An exponential dose–response model was applied to assess the risk of infection by Giardia. The risk in the MBR effluent with chlorination was9.83 × 10-3, higher than the acceptable annual risk of 1.0 × 10^-4. This study suggested that membrane integrity is very important for keeping a low pathogen level, and multiple barriers are needed to ensure the biological safety of MBR effluent.

Lanthanide-doped nanocrystals in high-Q microtoroids for stable on-chip white-light lasers

The plentiful energy states of lanthanide(Ln^(3+))-doped nanomaterials make them very promising for on-chip integrated white-light lasers.Despite the rapid progresses,the Ln^(3+)-based white upconversion emissions are strongly restricted by their low upconversion quantum efficiency and the color stability.Herein,we combine the CaF_(2):Yb_(35)Tm_(1.5)Er_(0.5)nanocrystals and the high-Q microtoroids,and experimentally demonstrate the chip-integrated stable white-light laser.By optimizing the sizes,density,and distributions of Ln^(3+)-doped nanocrystals,the Q factors of Ln^(3+)-doped microtoroids are maintained as high as 5×10^(5).The strong light matter interaction in high-Q microtoroids greatly enhances the upconversion emission and dramatically reduces the laser thresholds at 652 nm,545 nm,and 475 nm to similarly low values(1.89-2.10 m J cm^(-2)).Consequently,robust white-light microlaser has been experimentally achieved from a single microtoroid.This research has paved a solid step toward the chip-scale integrated broadband microlasers.

Enhancing magnetic dipole emission with magnetic metamaterials

Magnetic dipole（MD） transitions are important for a range of technologies from quantum light sources and displays to lasers and bio-probes. However, the typical MD transitions are much weaker than their electric counterparts and are usually neglected in practical applications. Herein, we experimentally demonstrate that the MD transitions can be significantly enhanced by the well-developed magnetic metamaterials in the visible optical range. The magnetic metamaterials consist of silver nanostrips and a thick silver film, which are separated with an Eu3＋：polymethyl methacrylate（PMMA） film. By controlling the thickness of the Eu3＋：PMMA film, the magnetic resonance has been tuned to match the emission wavelength of MDs. Consequently,the intensity of MD emission has been significantly increased by around 30 times at the magnetic resonance wavelength, whereas the intensity of electric dipole emission is well-preserved. The corresponding numerical calculations reveal that the enhancement is directly generated by the magnetic resonance, which strongly increases the magnetic local density of states around the MD emitter and can efficiently radiate the MD emission into the far field. This is the first demonstration, to the best of our knowledge, that MD transitions can be improved by an additional degree of magnetic freedom, and we believe this research shall pave a new route towards bright magnetic emitters and their potential applications.