Dynamic full-color digital holographic 3D display on single DMD

Digital holography has high potentials for future 3D imaging and display technology.We present a method for a dynamic full-color digital holographic 3D display on single digital micro-mirror device(DMD)with full-color,high-speed and high-fidelity characteristics.We combine the square regions of adjacent micro-mirrors into super-pixels that can modulate amplitude and phase independently.Gray images are achieved by amplitude modulation and precise positioning of each color is achieved by phase modulation.The proposed method realizes a full-color imaging based on the three primary colors and achieves measured structural similarity of more than 88%and color similarity of more than 98%,while retaining the high switch speed of 9 kHz,thus achieving dynamic full-color 3D display on charge-coupled device(CCD).

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.

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.

Optical spiral vortex from azimuthally increasing/decreasing exponential phase gradients

A new type of power-exponent-phase vortex-like beams with both quadratic and cubic azimuthal phase gradients is investigated in this work.The intensity and orbital angular momentum(OAM)density distributions are noticeably different when the phase gradient increases or decreases along the azimuth angle,while the orthogonality and total OAM remain constant.The characteristics of the optical field undergo a significant change when the phase shifts from linear to nonlinear,with the variation of the power index having little impact on the beam characteristics under nonlinear phase conditions.These characteristics provide new ideas for applications such as particle manipulation,optical communications,and OAM encryption.

Nondiffractive polarization feature of optical vortices

Optical vortices have been extensively researched in recent years for applications in optical manipulation,orbital angular momentum,opti-cal mode multiplexing,and quantum information.1 When the polariza-tions(spin angular momentum)encounter the phase singularity(orbital angular momentum)of an optical vortex,spin-orbit interaction occurs,leading to the discovery of even more fascinating features such as op-tical skyrmions 2 and polarization robustness.3 Optical vortices are like a rich goldmine with many more fascinating features yet to be revealed.

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.

Generation and modulation of multiple 2D bulk photovoltaic effects in space-time reversal asymmetric 2H-FeCl_(2)

The two-dimensional(2D)bulk photovoltaic effect(BPVE)is a cornerstone for future highly efficient 2D solar cells and optoelectronics.The ferromagnetic semiconductor 2H-FeCl_(2) is shown to realize a new type of BPVE in which spatial inversion(P),time reversal(T),and space−time reversal(PT)symmetries are broken(PT-broken).Using density functional theory and perturbation theory,we show that 2H-FeCl_(2) exhibits giant photocurrents,photo-spin-currents,and photo-orbital-currents under illumination by linearly polarized light.The injection-like and shift-like photocurrents coexist and propagate in different directions.The material also demonstrates substantial photoconductance,photo-spin-conductance,and photo-orbital-conductance,with magnitudes up to 4650(nm·μA/V^(2)),4620[nm·μA/V^(2)/(2e)],and 6450(nm·μA/V^(2)/e),respectively.Furthermore,the injection-currents,shift-spin-currents,and shift-orbital-currents can be readily switched via rotating the magnetizations of 2H-FeCl_(2).These results demonstrate the superior performance and intriguing control of a new type of BPVE in 2H-FeCl_(2).

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.

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 orbital angular momentum multiplexing communication via inversely-designed multiphase plane light conversion

Multiplexing and demultiplexing of optical orbital angular momentum(OAM)are critical operations in modedivision multiplexing communications.Traditional Dammann gratings,spiral phase planes,and optical geometric transformations are regarded as convenient methods for OAM mode(de)multiplexing.However,crosstalk between the different modes and the difficulty of mode multiplexing greatly limit their application to modedivision multiplexing communications.Here,using a set of inversely-designed phase planes,we demonstrate an OAM(de)multiplexer based on multiphase plane light conversion that can enable perfect OAM multiplexing communication.The sorted patterns are Gaussian-like and can be coupled easily into single-mode fiber arrays.Inputs from the fiber array are turned into coaxial OAM modes after the phase planes.OAM mode crosstalk generated by the multiplexer is less than-20 d B,with insertion loss of less than 2.6 d B.OAM modes are sorted by the demultiplexer with mode crosstalk below-10 d B,and the sorting results are coupled to the fiber array.OAM modes carrying 10 Gbit/s on–off keying signals were transmitted in a 5 km few-mode fiber.The measured bit-error-rate curves have power penalties of less than 10 d B.The proposed configuration is highly efficient and convenient and will be beneficial for potential applications in quantum information,information processing,and optical communications.

Beam wander relieved optical switch using Bessel beams in turbulent atmosphere

The digital micro-mirror device(DMD)-based optical switch has the advantages of high-speed channels reallocation, miniaturization, stability, and large capacity for short reach optical communication in the datacenter.However, thermal turbulent atmosphere in the datacenter would cause perturbations and channel crosstalk for the optical switch. The self-healing optical beams such as the Bessel beams have the non-diffraction property to mitigate the turbulence issue. Here, we propose and demonstrate a Bessel beams enabled DMD-based optical switch to improve the stability and performance of optical communication in turbulent atmosphere. We statistically characterize the beam wanders of the Gaussian and Bessel beams in turbulent atmosphere at temperatures of 60°C and 80°C. We build the two-channel optical switch communication system and measure the bit error rate of the 15 Gbit/s on–off keying signals transmitted by the Gaussian and Bessel beams at temperatures of 60°C and 80°C, respectively. The optical switch using the Bessel beams shows lower bit error rates with weaker fluctuations compared with the Gaussian beams. The DMD-based optical switch using the Bessel beams has the potential for practical optical communication applications in the datacenter.

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.

Optical vortices and vector beams

Amplitude, phase and polarization are essential parameters of an optical field. In the past decade, with the enhancement of techniques in manipulating phase and polarization states in complex optical fields, optical vortices and vector beams are investigated in a closely coupled fashion in terms of efficient beam generation and manipulation, stable transmission and novel detection aimed at various applications. In this special issue 6 invited papers demonstrate a number of typical topics in the field, with emphasis on the vectorial beam generation and optical communication systems utilising orbital angular momentum(OAM).

Measuring the magnetic topological spin structure of light using an anapole probe

Topological spin structures of light,including the Skyrmion,Meron,and bi-Meron,are intriguing optical phenomena that arise from spin-orbit coupling.They have promising potential applications in nano-metrology,data storage,super-resolved imaging and chiral detection.Aside from the electric part of optical spin,of equal importance is the magnetic part,particularly the H-type electromagnetic modes for which the spin topological properties of the field are dominated by the magnetic field.However,their observation and measurement remains absent and faces difficult challenges.Here,we design a unique type of anapole probe to measure specifically the photonic spin structures dominated by magnetic fields.The probe is composed of an Ag-core and Si-shell nanosphere,which manifests as a pure magnetic dipole with no electric response.The effectiveness of the method was validated by characterizing the magnetic field distributions of various focused vector beams.It was subsequently employed to measure the magnetic topological spin structures,including individual Skyrmions and Meron/Skyrmion lattices for the first time.The proposed method may be a powerful tool to characterize the magnetic properties of optical spin and valuable in advancing spin photonics.

High-speed Stokes vector receiver enabled by a spin-dependent optical grating

Stokes vector direct detection is a promising,cost-effective technology for short-distance communication applications.Here,we design and fabricate a spin-dependent liquid crystal grating to detect light polarization states.By separating the circular and linear components of incident light,the polarization states can be resolved with accuracy of up to 0.25°.We achieved Stokes vector direct detection of quadrature phase-shift keying(QPSK),8 PSK,and16-ary quadrature amplitude modulation signals with 32,16,and 16 GBd rates,respectively.We integrated the system,including the grating,photodetectors,and optical elements,on a miniaturized printed circuit board and demonstrated high-speed optical communications with 16 GBd rate QPSK signals.

3D waveguide device for few-mode multi-core fiber optical communications

Space-division multiplexing based on few-mode multi-core fiber(FM-MCF)technology is expected to break the Shannon limit of a single-mode fiber.However,an FM-MCF is compact,and it is difficult to couple the beam to each fiber core.3D waveguide devices have the advantages of low insertion loss and low cross talk in separating various spatial paths of multi-core fibers.Designing a 3D waveguide device for an FM-MCF requires considering not only higher-order modes transmission,but also waveguide bending.We propose and demonstrate a 3D waveguide device fabricated by femtosecond laser direct writing for various spatial path separations in an FM-MCF.The 3D waveguide device couples the LP01 and LP11a modes to the FM-MCF with an insertion loss below 3 dB and cross talk between waveguides below-36 dB.To test the performance of the 3D waveguide device,we demonstrate four-channel multiplexing communication with two LP modes and two cores in a 1-km few-mode sevencore fiber.The bit error rate curves show that the different degrees of bending of the waveguides result in a difference of approximately 1 dB in the power penalty.Femtosecond laser direct writing fabrication enables 3D waveguide devices to support high-order LP modes transmission and further improves FM-MCF communication.

Flexible generation of femtosecond cylindrical vector beams (Invited Paper)

Femtosecond(fs)cylindrical vector beams(CVBs)have found use in many applications in recent years.However,the existing rigid generation methods seriously limit its development.Here,we propose a flexible method for generating fs-CVBs with arbitrary polarization order by employing half wave plates and vortex retarders.The polarization state,autocorrelation width,pulse width,and spectrum features of the input and generated CVB pulses are measured and compared.The results verify that the generated CVBs remain in the fs regime with no appreciable temporal distortion,and the energy conversion efficiency can reach as high as 96.5%,even for a third-order beam.As a flexible way to generate fs-CVBs,this method will have great significance for many applications.

Simultaneous dual-contrast three-dimensional imaging in live cells via optical diffraction tomography and fluorescence

We report a dual-contrast method of simultaneously measuring and visualizing the volumetric structural information in live biological samples in three-dimensional(3D) space. By introducing a direct way of deriving the 3D scattering potential of the object from the synthesized angular spectra, we obtain the quantitative subcellular morphology in refractive indices(RIs) side-by-side with its fluorescence signals. The additional contrast in RI complements the fluorescent signal, providing additional information of the targeted zones. The simultaneous dual-contrast 3D mechanism unveiled interesting information inaccessible with previous methods, as we demonstrated in the human immune cell(T cell) experiment. Further validation has been demonstrated using a Monte Carlo model.

LP modes exchange based on multiplane light conversion

Data exchange between different mode channels is essential in the optical communication network with mode-division multiplexing(MDM).However,there are challenges in realizing mode exchange with low insert loss,low mode crosstalk,and high integration.Here,we designed and fabricated a mode exchange device based on multiplane light conversion(MPLC),which supports the transmission of LP01,LP11a,LP11b,and LP21 modes in the C-band and L-band.The simulated exchanged mode purities are greater than 85%.The phase masks were fabricated on a silicon substrate to facilitate the integration with optical systems,with an insert loss of less than 2.2 dB and mode crosstalk below-21 dB due primarily to machining inaccuracies and alignment errors.We carried out an optical communication experiment with 10 Gbit/s OOK and QPSK data transmission at the wavelength of 1550 nm and obtained excellent performance with the device.It paves the way for flexible data exchange as a building block in MDM optical communication networks.