Photo-induced flexible semiconductor CdSe/CdS quantum rods alignment

The anisotropic absorption and emission from semiconductor CdSe/CdS quantum rods(QRs)provide extra benefits among other photoluminescence nanocrystals.Using photo-induced alignment technique,the QRs can be oriented in liquid crystal polymer matrix at a large scale.In this article,a 2D Dammann grating pattern,within“SKL”characters domains aligned QRs in composite film,was fabricated by multi-step photo exposure using several photo masks,and a continuous geometric lens profile pattern aligned QRs was realized by the single step polarization converting holographic irradiation method.Both polarized optical microscope and fluorescence microscope are employed to determine the liquid crystal director profiles and QRs anisotropic excitation properties.We have been able to orient the QRs in fine binary and continuous patterns that confirms the strong quantum rod aligning ability of the proposed method.Thus,the proposed approach paves a way for photoinduced flexible QRs alignments to provide a highly specific and difficult-to-replicate security application at a large scale.

Spatiotemporal Fourier transform with femtosecond pulses for on-chip devices

On-chip manipulation of the spatiotemporal characteristics of optical signals is important in the transmission and processing of information.However,the simultaneous modulation of on-chip optical pulses,both spatially at the nano-scale and temporally over ultra-fast intervals,is challenging.Here,we propose a spatiotemporal Fourier transform method for on-chip control of the propagation of femtosecond optical pulses and verify this method employing surface plasmon polariton(SPP)pulses on metal surface.An analytical model is built for the method and proved by numerical simulations.By varying space-and frequency-dependent parameters,we demonstrate that the traditional SPP focal spot may be bent into a ring shape,and that the direction of propagation of a curved SPP-Airy beam may be reversed at certain moments to create an S-shaped path.Compared with conventional spatial modulation of SPPs,this method offers potentially a variety of extraordinary effects in SPP modulation especially associated with the temporal domain,thereby providing a new platform for on-chip spatiotemporal manipulation of optical pulses with applications including ultrafast on-chip photonic information processing,ultrafast pulse/beam shaping,and optical computing.

Microfabrication,surface modification,and laser guidance techniques to create a neuron biochip

In this report we illustrate our application of soft lithography-based microfabrication,surface modification,and our unique laser cell-patterning system toward the creation of neuron biochips. We deposited individual forebrain neurons from Day 7 embryonic chicks into two rows of eight in a silicon microstructure aligned over a microelectrode array (MEA). The polydimethylsiloxane (PDMS) membrane with microstructures to confine cells and guide network connectivity was aligned to the electrodes of a MEA. Both the MEA and the PDMS membrane were treated with O2 plasma,Poly-L-Lysine,and Laminin to aid in cell attachment and survival. The primary advantage of our process is that it is quicker and simpler than previous cell-placement methods and may make highly defined neuronal network biochips more practical.

Angular momentum holography via a minimalist metasurface for optical nested encryption

Metasurfaces can perform high-performance multi-functional integration by manipulating the abundant physical dimensions of light,demonstrating great potential in high-capacity information technologies.The orbital angular momentum(OAM)and spin angular momentum(SAM)dimensions have been respectively explored as the independent carrier for information multiplexing.However,fully managing these two intrinsic properties in information multiplexing remains elusive.Here,we propose the concept of angular momentum(AM)holography which can fully synergize these two fundamental dimensions to act as the information carrier,via a single-layer,non-interleaved metasurface.The underlying mechanism relies on independently controlling the two spin eigenstates and arbitrary overlaying them in each operation channel,thereby spatially modulating the resulting waveform at will.As a proof of concept,we demonstrate an AM meta-hologram allowing the reconstruction of two sets of holographic images,i.e.,the spin-orbital locked and the spin-superimposed ones.Remarkably,leveraging the designed dual-functional AM meta-hologram,we demonstrate a novel optical nested encryption scheme,which is able to achieve parallel information transmission with ultra-high capacity and security.Our work opens a new avenue for optionally manipulating the AM,holding promising applications in the fields of optical communication,information security and quantum science.

AI-assisted cell identification and optical sorting[Invited]

Cell identification and sorting have been hot topics recently.However,most conventional approaches can only predict the category of a single target,and lack the ability to perform multitarget tasks to provide coordinate information of the targets.This limits the development of high-throughput cell screening technologies.Fortunately,artificial intelligence(AI)systems based on deep-learning algorithms provide the possibility to extract hidden features of cells from original image information.Here,we demonstrate an AI-assisted multitarget processing system for cell identification and sorting.With this system,each target cell can be swiftly and accurately identified in a mixture by extracting cell morphological features,whereafter accurate cell sorting is achieved through noninvasive manipulation by optical tweezers.The AI-assisted model shows promise in guiding the precise manipulation and intelligent detection of high-flux cells,thereby realizing semiautomatic cell research.

Single-layered non-interleaved spin-insensitive metasurfaces for wavefront engineering

Metasurfaces,two-dimensional(2D)or quasi-2D arrays of dielectric or metallic meta-atoms,offer a compact and novel platform to manipulate the amplitude,phase,and polarization of incoming wavefronts in a desired manner by engineering the geometry of meta-atoms.In polarization control,spin-insensitive metasurfaces have attracted significant attention due to the robustness of circular polarization against the beam misalignment and multi-path effects.Till now,several efforts have been made to realize polarization-insensitive metasurfaces for circularly polarized(CP)wavefront manipulation;however,these metasurfaces only consider the cross-polarization channels and keep the co-polarization channels abandoned.Such metasurfaces cannot be considered truly spin-insensitive,as one has to carefully choose the analyzer at output.Here,by combining the polarization-insensitive geometric phase and engineered propagation phase,we propose a spin-insensitive design principle based on metasurfaces that can perform identical functionality(on co-and crosspolarization channels)irrespective of the handedness of incident/transmitted light.As a proof of concept,we design and numerically realize two types of spin-insensitive wavefront engineering devices:(1)spin-insensitive meta-hologram and(2)spin-insensitive beam deflector with power splitting functionality.The proposed work is expected to open up new avenues for developing spin-independent metasurfaces-based devices.

Temporal compressive super-resolution microscopy at frame rate of 1200 frames per second and spatial resolution of 100 nm

Various super-resolution microscopy techniques have been presented to explore fine structures of biological specimens.However,the super-resolution capability is often achieved at the expense of reducing imaging speed by either point scanning or multiframe computation.The contradiction between spatial resolution and imaging speed seriously hampers the observation of high-speed dynamics of fine structures.To overcome this contradiction,here we propose and demonstrate a temporal compressive super-resolution microscopy(TCSRM)technique.This technique is to merge an enhanced temporal compressive microscopy and a deep-learning-based super-resolution image reconstruction,where the enhanced temporal compressive microscopy is utilized to improve the imaging speed,and the deep-learning-based super-resolution image reconstruction is used to realize the resolution enhancement.The high-speed super-resolution imaging ability of TCSRM with a frame rate of 1200 frames per second(fps)and spatial resolution of 100 nm is experimentally demonstrated by capturing the flowing fluorescent beads in microfluidic chip.Given the outstanding imaging performance with high-speed super-resolution,TCSRM provides a desired tool for the studies of high-speed dynamical behaviors in fine structures,especially in the biomedical field.

Dynamic polarization rotation and vector field steering based on phase change metasurface

Polarization rotation and vector field steering of electromagnetic wave are of great significance in modern optical applications.However,conventional polarization devices are bulky,monofunctional and lack of tunability,which pose great challenges to the miniaturized and multifunctional applications.Herein,we propose a meta-device that is capable of multi-state polarization rotation and vector field steering based on phase change metasurface.The supercell of the meta-device consists of four Ge2Sb2Te5(GST)elliptic cylinders located on a SiO2 substrate.By independently controlling the phase state(amorphous or crystalline)of each GST elliptic cylinder,the meta-device can rotate the polarization plane of the linearly polarized incident light to different angles that cover from 19.8°to 154.9°at a wavelength of 1550 nm.Furthermore,by merely altering the phase transition state of GST elliptic cylinders,we successfully demonstrated a vector field steering by generating optical vortices carrying orbital angular momentums(OAMs)with topological charges of 0,1 and–1,respectively.The proposed method provides a new platform for investigating dynamically tunable optical devices and has potential applications in many fields such as optical communications and information processing.

A new member of the structured light family:optical spatiotemporal vortices

The burgeoning growth of structured light has opened up new possibilities for harnessing the spatiotemporal coupling effects in light.Optical spatiotemporal vortices,as a subset of spatiotemporal light,have emerged as a focal point of recent research,owing to their distinctive characteristics and vast range for application.This unique structured light will endow photons with a new degree of freedom,promising to revolutionize researchers’understanding of photonics.Conducting thorough research on optical spatiotemporal vortices will establish a solid foundation for the development of innovative physical mechanisms and advanced applications in photonics.

Nonlinear optical trapping effect with reverse saturable absorption

Nonlinear responses of nanoparticles induce enlightening phenomena in optical tweezers. With thegradual increase in optical intensity, effects from saturable absorption (SA) and reverse SA (RSA) arise insequence and thereby modulate the nonlinear properties of materials. In current nonlinear optical traps,however, the underlying physical mechanism is mainly confined within the SA regime because thresholdvalues required to excite the RSA regime are extremely high. Herein, we demonstrate, both in theory andexperiment, nonlinear optical tweezing within the RSA regime, proving that a fascinating composite trappingstate is achievable at ultrahigh intensities through an optical force reversal induced through nonlinearabsorption. Integrated results help in perfecting the nonlinear optical trapping system, thereby providingbeneficial guidance for wider applications of nonlinear optics.

On-chip sorting of orbital angular momentum beams using Bloch surface wave structures

Owing to their unique optical properties and new degrees of freedom,orbital angular momentum(OAM)beams have been applied in various fields.Detection of the topological charges(TCs)of OAM beams is the key step for their applications.However,on-chip sorting of OAM beams with large TCs still remains a challenge.In this paper,Bloch surface wave(BSW)structures with five semi-ring shaped nanoslits are modeled.A spatial separation of 135 nm on the chip is obtained between two neighboring OAM states.OAM beams with TCs up to 35 can be successfully sorted by the BSW structures,which is much larger than that using metallic structures(only seven).BSW structures exhibit better OAM sorting performances than metallic structures.We systematically show how the lower attenuation of BSW structures leads to far superior separation ability compared to surface plasmons propagating on metallic structures.In addition,sorting of two OAM beams with different TCs simultaneously can be achieved in this way.Our results reveal that BSW structures should be an excellent solution for OAM sorting with large TCs,which is beneficial for applications in integrated on-chip devices and optical communications.

In vivo spatial-spectral photoacoustic microscopy enabled by optical evanescent wave sensing

In addition to offering morphological visualizations via capture of the spatial distributions of optical absorption,photoacoustic imaging technology can reveal abundant physical information about biological particles,including their orientation,density,and viscoelasticity,through analysis of the pressure transients in the spectral domain.However,the low-amplitude wideband photoacoustic signals of intrinsic microscopic optically-absorbing objects under the action of confined photoacoustic excitation power continue to hinder simultaneous photoacoustic structural imaging and spectroscopic analysis of the nonfluorescent chromophores in living biological tissues because of the inadequate responses to photoacoustic impulses observed in most photoacoustic imaging setups that include piezoelectric transducers.Building upon a recently-developed optical evanescent wave sensor that can respond to ultrasound with high sensitivity over a broad frequency range,we propose in vivo spatial-spectral photoacoustic microscopy for recovery of structural imaging in three dimensions and characterization of anatomical features in the acoustic frequency domain.Label-free photoacoustic images of a living zebrafish are acquired in which spectroscopically-resolved differentiation of the microarchitecture is accessed,along with isometric micrometer-scale volumetric visualizations.The proposed imaging technology could potentially provide more comprehensive evaluations of the physiopathological status of living small animals.

Diffractive optical elements 75 years on:from micro-optics to metasurfaces

Diffractive optical elements(DOEs)are intricately designed devices with the purpose of manipulating light fields by precisely modifying their wavefronts.The concept of DOEs has its origins dating back to 1948 when D.Gabor first introduced holography.Subsequently,researchers introduced binary optical elements(BOEs),including computer-generated holograms(CGHs),as a distinct category within the realm of DOEs.This was the first revolution in optical devices.The next major breakthrough in light field manipulation occurred during the early 21st century,marked by the advent of metamaterials and metasurfaces.Metasurfaces are particularly appealing due to their ultra-thin,ultra-compact properties and their capacity to exert precise control over virtually every aspect of light fields,including amplitude,phase,polarization,wavelength/frequency,angular momentum,etc.The advancement of light field manipulation with micro/nano-structures has also enabled various applications in fields such as information acquisition,transmission,storage,processing,and display.In this review,we cover the fundamental science,cutting-edge technologies,and wide-ranging applications associated with micro/nano-scale optical devices for regulating light fields.We also delve into the prevailing challenges in the pursuit of developing viable technology for real-world applications.Furthermore,we offer insights into potential future research trends and directions within the realm of light field manipulation.

Massive individual orbital angular momentum channels for multiplexing enabled by Dammann gratings

Data transmission rates in optical communication systems are approaching the limits of conventional multiplexing methods.Orbital angular momentum(OAM)in optical vortex beams offers a new degree of freedom and the potential to increase the capacity of free-space optical communication systems,with OAM beams acting as information carriers for OAM division multiplexing(OAM-DM).We demonstrate independent collinear OAM channel generation,transmission and simultaneous detection using Dammann optical vortex gratings(DOVGs).We achieve 80/160 Tbit s^(-1) capacity with uniform power distributions along all channels,with 1600 individually modulated quadrature phase-shift keying(QPSK)/16-QAM data channels multiplexed by 10 OAM states,80 wavelengths and two polarizations.DOVG-enabled OAM multiplexing technology removes the bottleneck of massive OAM state parallel detection and offers an opportunity to raise optical communication systems capacity to Pbit s^(-1) level.

Optical vortices 30 years on:OAM manipulation from topological charge to multiple singularities

Thirty years ago,Coullet et al.proposed that a special optical field exists in laser cavities bearing some analogy with the superfluid vortex.Since then,optical vortices have been widely studied,inspired by the hydrodynamics sharing similar mathematics.Akin to a fluid vortex with a central flow singularity,an optical vortex beam has a phase singularity with a certain topological charge,giving rise to a hollow intensity distribution.Such a beam with helical phase fronts and orbital angular momentum reveals a subtle connection between macroscopic physical optics and microscopic quantum optics.These amazing properties provide a new understanding of a wide range of optical and physical phenomena,including twisting photons,spin–orbital interactions,Bose-Einstein condensates,etc.,while the associated technologies for manipulating optical vortices have become increasingly tunable and flexible.Hitherto,owing to these salient properties and optical manipulation technologies,tunable vortex beams have engendered tremendous advanced applications such as optical tweezers,high-order quantum entanglement,and nonlinear optics.This article reviews the recent progress in tunable vortex technologies along with their advanced applications.

Integrated(de)multiplexer for orbital angular momentum fiber communication

The quickly increasing data transfer load requires an urgent revolution in current optical communication. Orbital angular momentum(OAM) multiplexing is a potential candidate with its ability to considerably enhance the capacity of communication. However, the lack of a compact, efficient, and integrated OAM(de)multiplexer prevents it from being widely applied. By attaching vortex gratings onto the facets of a few-mode fiber, we demonstrate an integrated fiber-based OAM(de)multiplexer. A vortex grating fabricated on the fiber facet enables the direct multiplexing of OAM states at one port and the demultiplexing of OAM states at the other port. The measured bit error rate of the carrier signal after propagating through a 5-km few-mode fiber confirms the validity and effectiveness of the proposed approach. The scheme offers advantages in future high-capacity OAM communication based on optical fiber.

On-chip plasmonic spin-Hall nanograting for simultaneously detecting phase and polarization singularities

Phase and polarization singularities are important degrees of freedom for electromagnetic field manipulation.Detecting these singularities is essential for modern optics,but it is still a challenge,especially in integrated optical systems.In this paper,we propose an on-chip plasmonic spin-Hall nanograting structure that simultaneously detects both the polarization and phase singularities of the incident cylindrical vortex vector beam(CVVB).The nanograting is symmetry-breaking with different periods for the upper and lower parts,which enables the unidirectional excitation of the surface plasmon polariton depending on the topological charge of the incident optical vortex beam.Additionally,spin-Hall meta-slits are integrated onto the grating so that the structure has a chiral response for polarization detection.We demonstrate theoretically and experimentally that the designed structure fully discriminates both the topological charges and polarization states of the incident beam simultaneously.The proposed structure has great potential in compact integrated photonic circuits.

Versatile on-chip light coupling and(de)multiplexing from arbitrary polarizations to controlled waveguide modes using an integrated dielectric metasurface

Metasurfaces have found broad applicability in free-space optics,while its potential to tailor guided waves remains barely explored.By synergizing the Jones matrix model with generalized Snell’s law under the phase-matching condition,we propose a universal design strategy for versatile on-chip mode-selective coupling with polarization sensitivity,multiple working wavelengths,and high efficiency concurrently.The coupling direction,operation frequency,and excited mode type can be designed at will for arbitrary incident polarizations,outperforming previous technology that only works for specific polarizations and lacks versatile mode controllability.Here,using silicon-nanoantenna-patterned silicon-nitride photonic waveguides,we numerically demonstrate a set of chip-scale optical couplers around 1.55μm,including mode-selective directional couplers with high coupling efficiency over 57%and directivity about 23 d B.Polarization and wavelength demultiplexer scenarios are also proposed with 67%maximum efficiency and an extinction ratio of 20 d B.Moreover,a chip-integrated twisted light generator,coupling free-space linear polarization into an optical vortex carrying 1 h orbital angular momentum(OAM),is also reported to validate the mode-control flexibility.This comprehensive method may motivate compact wavelength/polarization(de)multiplexers,multifunctional mode converters,on-chip OAM generators for photonic integrated circuits,and high-speed optical telecommunications.

Optical meta-waveguides for integrated photonics and beyond

The growing maturity of nanofabrication has ushered massive sophisticated optical structures available on a photonic chip.The integration of subwavelength-structured metasurfaces and metamaterials on the canonical building block of optical waveguides is gradually reshaping the landscape of photonic integrated circuits,giving rise to numerous metawaveguides with unprecedented strength in controlling guided electromagnetic waves.Here,we review recent advances in meta-structured waveguides that synergize various functional subwavelength photonic architectures with diverse waveguide platforms,such as dielectric or plasmonic waveguides and optical fibers.Foundational results and representative applications are comprehensively summarized.Brief physical models with explicit design tutorials,either physical intuition-based design methods or computer algorithms-based inverse designs,are cataloged as well.We highlight how meta-optics can infuse new degrees of freedom to waveguide-based devices and systems,by enhancing light-matter interaction strength to drastically boost device performance,or offering a versatile designer media for manipulating light in nanoscale to enable novel functionalities.We further discuss current challenges and outline emerging opportunities of this vibrant field for various applications in photonic integrated circuits,biomedical sensing,artificial intelligence and beyond.