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).

Ultra-broadband on-chip twisted light emitter for optical communications

On-chip twisted light emitters are essential components of orbital angular momentum(OAM)communication devices1,2.These devices address the growing demand for high-capacity communication systems by providing an additional degree of freedom for wavelength/frequency division multiplexing(WDM/FDM).Although whispering-gallery-mode-enabled OAM emitters have been shown to possess some advantages3–5,such as compactness and phase accuracy,their inherent narrow bandwidths prevent them from being compatible with WDM/FDM techniques.Here,we demonstrate an ultra-broadband multiplexed OAM emitter that utilizes a novel joint path-resonance phase control concept.The emitter has a micron-sized radius and nanometer-sized features.Coaxial OAM beams are emitted across the entire telecommunication band from 1,450 to 1,650 nm.We applied the emitter to an OAM communication with a data rate of 1.2 Tbit/s assisted by 30-channel optical frequency combs(OFCs).The emitter provides a new solution to further increase capacity in the OFC communication scenario.

Fast structured illumination microscopy via deep learning

This study shows that convolutional neural networks(CNNs)can be used to improve the performance of structured illumination microscopy to enable it to reconstruct a super-resolution image using three instead of nine raw frames,which is the standard number of frames required to this end.Owing to the isotropy of the fluorescence group,the correlation between the high-frequency information in each direction of the spectrum is obtained by training the CNNs.A high-precision super-resolution image can thus be reconstructed using accurate data from three image frames in one direction.This allows for gentler super-resolution imaging at higher speeds and weakens phototoxicity in the imaging process.

On-chip photonic Fourier transform with surface plasmon polaritons

The Fourier transform(FT),a cornerstone of optical processing,enables rapid evaluation of fundamental mathematical operations,such as derivatives and integrals.Conventionally,a converging lens performs an optical FT in free space when light passes through it.The speed of the transformation is limited by the thickness and the focal length of the lens.By using the wave nature of surface plasmon polaritons(SPPs),here we demonstrate that the FT can be implemented in a planar configuration with a minimal propagation distance of around 10 mm,resulting in an increase of speed by four to five orders of magnitude.The photonic FT was tested by synthesizing intricate SPP waves with their Fourier components.The reduced dimensionality in the minuscule device allows the future development of an ultrafast on-chip photonic information processing platform for large-scale optical computing.

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.

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.

Optical topologicallattices of Bloch-type skyrmion and meron topologies

Optical skyrmions, quasiparticles that are characterized by the topologically nontrivial vectorial textures of optical parameters such as the electromagnetic field, Stokes parameters, and spin angular momentum, have aroused great attention recently. New dimensions for optical information processing, transfer, and storage have become possible, and developing multiple schemes for manipulating the topological states of skyrmions, thus, is urgent.Here we propose an approach toward achieving dynamic modulation of skyrmions via changing the field symmetry and adding chirality. We demonstrate that field symmetry governs the skyrmionic transformation between skyrmions and merons, whereas material chirality modulates the twist degree of fields and spins and takes control of the Néel-type–Bloch-type skyrmionic transition. Remarkably, the enantioselective twist of skyrmions and merons results from the longitudinal spin arising from the chirality-induced splitting of the hyperboloid in the momentum space. Our investigation, therefore, acts to enrich the portfolio of optical quasiparticles. The chiral route to topological state transitions will deepen our understanding of light–matter interaction and pave the way for chiral sensing, optical tweezers, and topological phase transitions in quantum matter.

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.