Mode Multiplication of Cylindrical Vector Beam Using Raytracing Control

Cylindrical vector beams(CVBs)hold significant promise in mode division multiplexing communication owing to their inherent vector mode orthogonality.However,existing studies for facilitating CVB channel processing are confined to mode shift conversions due to their reliance on spin-dependent helical modulations,overlooking the pursuit of mode multiplication conversion.This challenge lies in the multiplicative operation upon inhomogeneous vector mode manipulation,which is expected to advance versatile CVB channel switching and routing.Here,we tackle this gap by introducing a raytracing control strategy that conformally maps the light rays of CVB from the whole annulus distribution to an annular sector counterpart.Incorporated with the multifold conformal annulus-sector mappings and polarization-insensitive phase modulations,this approach facilitates the parallel transformation of input CVB into multiple complementary components,enabling the mode multiplication conversion with protected vector structure.Serving as a demonstration,we experimentally implemented the multiplicative operation of four CVB modes with the multiplier factors of N=+2 and N=−3,achieving the converted mode purities over 94.24%and 88.37%.Subsequently,200 Gbit/s quadrature phase shift keying signals were successfully transmitted upon multiplicative switching of four CVB channels,with the bit-error-rate approaching 1×10^(−6).These results underscore our strategy’s efficacy in CVB mode multiplication,which may open promising prospects for its advanced applications.

Harpoon-shaped topological photonic crystal for on-chip beam splitter

The advancement of integrated optical communication networks necessitates the deployment of on-chip beam splitters for efficient signal interconnections at network nodes.However,the pursuit of micron-scale beam splitting with large corners and reducing the device footprint to boost connection flexibility often results in phase mismatches.These mismatches,which stem from radiation modes and backward scattering,pose significant obstacles in creating highly integrated and interference-resistant connections.To address this,we introduce a solution based on the topological valley-contrasting state generated by photonic crystals with opposing valley Chern numbers,manifested in a harpoon-shaped structure designed to steer the splitting channels.This approach enables adiabatic mode field evolution over large corners,capitalizing on the robust phase modulation capabilities and topological protection provided by the subwavelength-scale valley-contrasting state.Our demonstration reveals that beam splitters with large corners of 60°,90°,and 120°exhibit insertion loss fluctuations below 2.7 dB while maintaining a minimal footprint of 8.8μm×8.8μm.As a practical demonstration,these devices facilitate three-channel signal connections,successfully transmitting quadrature phase shift keying signals at 3.66 Tbit/s with bit error rates below the forward error correction threshold,demonstrating performance comparable to that in defects scenarios.By harnessing the unidirectional excitation feature,we anticipate significant enhancements in the capabilities of signal distribution and connection networks through a daisy chain configuration.

Photonic crystal-connected bidirectional micro-ring resonator array for duplex mode and wavelength channel(de)multiplexing

The progress of on-chip optical communication relies on integrated multi-dimensional mode(de)multiplexers to enhance communication capacity and establish comprehensive networks.However,existing multi-dimensional(de)multiplexers,involving modes and wavelengths,face limitations due to their reliance on single-directional total internal reflection and multi-level mode conversion based on directional coupling principles.These constraints restrict their potential for full-duplex functionality and highly integrated communication.We solve these problems by introducing a photonic-like crystal-connected bidirectional micro-ring resonator array(PBMRA)and apply it to duplex mode-wavelength multiplexing communication.The directional independence of total internal reflection and the cumulative effect of the subwavelength-scale pillar within the single-level photonic crystal enable bidirectional mode and wavelength multiplexed signals to transmit among multi-pair nodes without interference,improving on-chip integration in single-level mode conversion.As a proof of concept,we fabricated a nine-channel bidirectional multi-dimensional(de)multiplexer,featuring three wavelengths and three TE modes,compactly housed within a footprint of 80μm×80μm,which efficiently transmits QPSK-OFDM signals at a rate of 216 Gbit/s,achieving a bit error rate lower than 10^(-4).Leveraging the co-ring transmission characteristic and the orthogonality of the mode-wavelength channel,this(de)multiplexer also enables a doubling of communication capacity using two physical transmission channels.

Highly efficient nonuniform finite difference method for three-dimensional electrically stimulated liquid crystal photonic devices

Liquid crystal(LC)photonic devices have attracted intensive attention in recent decades,due to the merits of tunability,cost-effectiveness,and high efficiency.However,the precise and efficient simulation of large-scale three-dimensional electrically stimulated LC photonic devices remains challenging and resource consuming.Here we report a straightforward nonuniform finite difference method(NFDM)for efficiently simulating largescale LC photonic devices by employing a spatially nonuniform mesh grid.

Mold-free self-assembled scalable microlens arrays with ultrasmooth surface and record-high resolution

Microlens arrays(MLAs)based on the selective wetting have opened new avenues for developing compact and miniaturized imaging and display techniques with ultrahigh resolution beyond the traditional bulky and volumetric optics.However,the selective wetting lenses explored so far have been constrained by the lack of precisely defined pattern for highly controllable wettability contrast,thus limiting the available droplet curvature and numerical aperture,which is a major challenge towards the practical high-performance MLAs.Here we report a mold-free and self-assembly approach of mass-production of scalable MLAs,which can also have ultrasmooth surface,ultrahigh resolution,and the large tuning range of the curvatures.The selective surface modification based on tunable oxygen plasma can facilitate the precise pattern with adjusted chemical contrast,thus creating large-scale microdroplets array with controlled curvature.The numerical aperture of the MLAs can be up to 0.26 and precisely tuned by adjusting the modification intensity or the droplet dose.The fabricated MLAs have high-quality surface with subnanometer roughness and allow for record-high resolution imaging up to equivalently 10,328 ppi,as we demonstrated.This study shows a cost-effective roadmap for mass-production of high-performance MLAs,which may find applications in the rapid proliferating integral imaging industry and high-resolution display.

Cylindrical vector beam multiplexer/demultiplexer using off-axis polarization control

The emergence of cylindrical vector beam(CVB)multiplexing has opened new avenues for high-capacity optical communication.Although several configurations have been developed to couple/separate CVBs,the CVB multiplexer/demultiplexer remains elusive due to lack of effective off-axis polarization control technologies.Here we report a straightforward approach to realize off-axis polarization control for CVB multiplexing/demultiplexing based on a metal–dielectric–metal metasurface.We show that the left-and right-handed circularly polarized(LHCP/RHCP)components of CVBs are independently modulated via spin-to-orbit interactions by the properly designed metasurface,and then simultaneously multiplexed and demultiplexed due to the reversibility of light path and the conservation of vector mode.We also show that the proposed multiplexers/demultiplexers are broadband(from 1310 to 1625 nm)and compatible with wavelength-division-multiplexing.As a proof of concept,we successfully demonstrate a four-channel CVB multiplexing communication,combining wavelength-division-multiplexing and polarization-division-multiplexing with a transmission rate of 1.56 Tbit/s and a bit-error-rate of 10^(−6) at the receive power of−21.6 dBm.This study paves the way for CVB multiplexing/demultiplexing and may benefit high-capacity CVB communication.

Orbital angular momentum mode logical operation using optical diffractive neural network

Optical logical operations demonstrate the key role of optical digital computing,which can perform general-purpose calculations and possess fast processing speed,low crosstalk,and high throughput.The logic states usually refer to linear momentums that are distinguished by intensity distributions,which blur the discrimination boundary and limit its sustainable applications.Here,we introduce orbital angular momentum(OAM)mode logical operations performed by optical diffractive neural networks(ODNNs).Using the OAM mode as a logic state not only can improve the parallel processing ability but also enhance the logic distinction and robustness of logical gates owing to the mode infinity and orthogonality.ODNN combining scalar diffraction theory and deep learning technology is designed to independently manipulate the mode and spatial position of multiple OAM modes,which allows for complex multilight modulation functions to respond to logic inputs.We show that few-layer ODNNs successfully implement the logical operations of AND,OR,NOT,NAND,and NOR in simulations.The logic units of XNOR and XOR are obtained by cascading the basic logical gates of AND,OR,and NOT,which can further constitute logical half-adder gates.Our demonstrations may provide a new avenue for optical logical operations and are expected to promote the practical application of optical digital computing.

Controllable photonic spin Hall effect with phase function construction

Photonic spin Hall efect(SHE)provides new opportunities for achieving spin-based photonics applications.However,flexibly manipulating the spin-dependent sltting(SDS)of photonic SHE and imposing extra phase modulation on the two spin components are always a challenge.Here,a controllable SHE mechanism based on phase function construction is reported.It is conduded that the phases with specific functional structures performing a coordinate translation are equivalent to integrating a gradient phase to the original phases.Hence,the original phase can be used for independent phase modulation,and the gradient phase originating from the co-ordinate translation is capable of manipulating the SDS.A metasurface with Pancharatnam-Berry phase that can impose conjugate phases to the two spin components of light is fabricated to verify this mechanism.By shifing the light position,the SDS is continuously manipulated in the visible region,which is successfully used for detecting the polarization llipticity.The extra phase modulation is also performed with the original phase and thus enables measuring singular beams.It is anticipated that the controllable SHE manipulation method may open new avenues in the fields of spin photonics,optical sensing,optical communications,etc.

Neural network-based surrogate model for inverse design of metasurfaces

Metasurfaces composed of spatially arranged ultrathin subwavelength elements are promising photonic devices for manipulating optical wavefronts,with potential applications in holography,metalens,and multiplexing communications.Finding microstructures that meet light modulation requirements is always a challenge in designing metasurfaces,where parameter sweep,gradient-based inverse design,and topology optimization are the most commonly used design methods in which the massive electromagnetic iterations require the design computational cost and are sometimes prohibitive.Herein,we propose a fast inverse design method that combines a physicsbased neural network surrogate model(NNSM)with an optimization algorithm.The NNSM,which can generate an accurate electromagnetic response from the geometric topologies of the meta-atoms,is constructed for electromagnetic iterations,and the optimization algorithm is used to search for the on-demand meta-atoms from the phase library established by the NNSM to realize an inverse design.This method addresses two important problems in metasurface design:fast and accurate electromagnetic wave phase prediction and inverse design through a single phase-shift value.As a proof-of-concept,we designed an orbital angular momentum(de)multiplexer based on a phase-type metasurface,and 200 Gbit/s quadrature-phase shift-keying signals were successfully transmitted with a bit error rate approaching 1.67×10^(-6).Because the design is mainly based on an optimization algorithm,it can address the“one-to-many”inverse problem in other micro/nano devices such as integrated photonic circuits,waveguides,and nano-antennas.

Optically induced atomic lattice with tunable near-field and far-field diffraction patterns

Conventional periodic structures usually have nontunable refractive indices and thus lead to immutable photonic bandgaps. A periodic structure created in an ultracold atoms ensemble by externally controlled light can overcome this disadvantage and enable lots of promising applications. Here, two novel types of optically induced square lattices, i.e., the amplitude and phase lattices, are proposed in an ultracold atoms ensemble by interfering four ordinary plane waves under different parameter conditions. We demonstrate that in the far-field regime, the atomic amplitude lattice with high transmissivity behaves similarly to an ideal pure sinusoidal amplitude lattice, whereas the atomic phase lattices capable of producing phase excursion across a weak probe beam along with high transmissivity remains equally ideal. Moreover, we identify that the quality of Talbot imaging about a phase lattice is greatly improved when compared with an amplitude lattice. Such an atomic lattice could find applications in alloptical switching at the few photons level and paves the way for imaging ultracold atoms or molecules both in the near-field and in the far-field with a nondestructive and lensless approach.