Vortex Grating Research Articles

Dual perfect vectorial vortex beam generation with a single spin-multiplexed metasurface

Perfect optical vortex beams (POVBs) carrying orbital angular momentum (OAM) possess annular intensity profiles that are independent of the topological charge. Unlike POVBs, perfect vectorial vortex beams (PVVBs) not only carry orbital angular momentum but also exhibit spin angular momentum (SAM). By incorporating a Dammann vortex grating (DVG) on an all-dielectric metasurface, we demonstrate an approach to create a pair of PVVBs on a hybrid-order Poincaré sphere. Benefiting flexible phase modulation, by engineering the DVG and changing the input-beam state we are able to freely tailor the topological OAM and polarization eigenstates of the output PVVBs. This work demonstrates a versatile flat-optics platform for high-quality PVVB generation and may pave the way for applications in optical communication and quantum information processing.

Full-duplex cylindrical vector beam multiplexing communication using spin-dependent phase modulation metasurfaces

Cylindrical vector beam (CVB) has recently gained attention as a promising carrier for signal multiplexing owing to its mode orthogonality. However, the full-duplex multiplexing communication has not been previously explored for the lack of effective technologies to parallelly couple and separate CVB modes. Herein, we present a full-duplex solution for CVB multiplexing communication that utilizes spin-dependent phase modulation metasurfaces. By independently phase-modulating the two spin eigenstates of CVBs with the metasurface via spin-dependent orbital interactions, and loading two binary Dammann vortex gratings, we enabled an independent and reciprocal wave vector manipulation of CVBs for full-duplex (de)multiplexing operation. To demonstrate this concept, we constructed a 16-channel (including 4 CVB modes and 4 wavelengths) full-duplex CVB multiplexing communication system and achieved the bidirectional transmission of 800 Gbit/s quadrature-phase shift-keying (QPSK) signals over a 5 km few-mode fiber. Our results demonstrate the successful multiplexing and demultiplexing of 2 radial CVB modes and 2 azimuthal CVB modes in full-duplex communication with the bit-error-rates approaching 1.87 × 10−5.

Signal quality enhanced and multicast transmission via cylindrical vector beams with adaptive optics compensation in free space optical communications

Signal quality is critical in free space optical (FSO) communications. Many technologies and methods are applied to enhance the signal quality of an optical communication system, which might require one of the methods employing structured light. We introduce structured light of cylindrical vector beams with adaptive optics compensation to improve signal quality in FSO communications. The multiplexing/demultiplexing of coaxial cylindrical vector beams is used to increase the capacity of the communication channel. Adaptive optics compensation and cylindrical vector beams are applied to mitigate influence of the turbulent atmospheric disturbances and improve the signal quality. An optical vortex grating is employed to demultiplex signal beams and then send the signals to a receiver plane to measure the bit-error-rate. Consequently, the signal quality of the cylindrical vector beams multiplexing/demultiplexing in FSO communication systems improves.

Phase control scheme of the coherent beam combining system for generating perfect vectorial vortex beams assisted by a Dammann vortex grating.

Based on Dammann vortex grating and adaptive gain stochastic parallel gradient descent algorithm, we theoretically proposed a phase control technology scheme of the coherent beam combining system for generating perfect vectorial vortex beams (VVBs). The simulated results demonstrate that the discrete phase locking for different types of VVBs (including vortex beams, vector beams, and generalized VVBs) can be successfully realized. The intensity distributions, polarization orientation, Pancharatnam phases, and beam widths of different |Hm,n〉 states with the obtained discrete phase distribution further prove that the generated beams are perfect VVBs. Subsequently, the phase aberration residual for different VVBs is evaluated using the normalized phase cosine distance function, and their values range from 0.01 to 0.08, which indicates the obtained discrete phase distribution is close to the ideal phase distribution. In addition, benefitting from the high bandwidth of involved devices in the proposed scheme, the influence of dynamic phase noise can be negligible. The proposed method could be beneficial to realize and switch flexible perfect VVBs in further applications.

Polarization-dependent phase-modulation metasurface for vortex beam (de)multiplexing

Abstract Vortex beams (VBs) carrying orbital angular momentum (OAM) have shown promising potential in enhancing communication capacity through the possession of multiple multiplexing dimensions involving the OAM mode, polarization, and wavelength. Although many research works on multidimensional multiplexing have been conducted, the (de)multiplexer compatible with these dimensions remains elusive. Following the expanded concept of the Pancharatnam–Berry (PB) phase, we designed a polarization-dependent phase-modulation metasurface to phase-modulate the two orthogonal linearly polarized components of light, and two Dammann vortex gratings with orthogonal polarization responses were loaded to simultaneously (de)multiplex OAM mode and polarization channels. As a proof of concept, we constructed a 16-channel multidimensional multiplexing communication system (including two OAM modes, two polarization states, and four wavelengths), and 400 Gbit/s quadrature-phase shift-keying (QPSK) signals were transmitted. The results demonstrate that the OAM mode and polarization channels are successfully (de)multiplexed, and the bit-error-rates (BERs) are below 1.67 × 10−6 at the received power of −15 dBm.

Phase Off-Axis Modulation Metasurface for Orbital Angular Momentum Mode Multiplexing/Demultiplexing

Orbital angular momentum (OAM) mode multiplexing provides a promising solution for enlarging communication capacity density. Although various OAM mode multiplexing technologies have been investigated, (de)multiplexers possessing a wide spectral response and polarization insensitivity to combine wavelength division multiplexing (WDM) and polarization division multiplexing (PDM) remain elusive. Herein, we propose a phase off-axis modulation strategy for OAM mode (de)multiplexing by encoding the binary Dammann optical vortex grating (DOVG) phase into a geometric phase metasurface that consists of metallic nanoantennas with spatially varying orientations on a dielectric-metal substrate. We show that four OAM modes (−2, −1, 1, 2) were successfully multiplexed and demultiplexed by virtue of the multilevel diffraction of DOVG and its reverse process. The working wavelength of this metasurface ranges from 1260 nm to 1675 nm due to the dispersion-free geometric phase, moreover, the mode symmetry of DOVG and the conjugate modulation of the geometric phase yield polarization insensitivity. As a proof of concept, an OAM mode multiplexing communication system combining WDM and PDM was constructed, and 1.56 Tbit/s QPSK signals were transmitted with the bit-error-rate approaching 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−6</sup> . These results demonstrate that this phase off-axis modulation metasurface can effectively (de)multiplex OAM modes and shows good compatibility with WDM and PDM, which may promote the practical application of OAM communication and all-optical interconnection.

Broadband decoupled spin and orbital angular momentum detection via programming dual-twist reactive mesogens.

The introduction of spin and orbital angular momentum mode division multiplexing to existing wavelength division multiplexing will significantly enlarge the capacity of optical networks. Therefore, components compatible with the above techniques are in high demand. Here, a geometric phase combined a Dammann vortex grating, and a polarization grating is designed and encoded to a dual-twist reactive mesogen. It can generate a couple of vortex channel arrays highly efficiently in broadband. Meanwhile, orthogonal spins are spatially separated, facilitating spin identification. A vortex will recover to a Gaussian beam when it is diffracted to an order with opposite topological charge, which enables the detection of orbital angular momentum. It supplies a parallel and efficient way for decoupled spin and orbital angular momentum detection operating at the entire visible range, and the design may be extended to many other compatible optical communication components.

Visible and Online Detection of Near‐Infrared Optical Vortices via Nonlinear Photonic Crystals

AbstractNear‐infrared (NIR) optical vortices (OVs), which carry specific orbital angular momentum, are believed to greatly increase the capacity of conventional optical communication systems. However, due to the equipment limits in invisible wavelengths, NIR OVs detection remains a great difficulty. Here, the up‐conversion imaging technology is exploited to circumvent using NIR detectors. A lithium niobate crystal with its quadratic susceptibility modulated by a specially designed Dammann vortex grating is fabricated to realize the frequency conversion—from NIR to the visible region—while converting multiplexed OVs to Gaussian modes in specific multichannels. During the detection process, the most of energies of the detected OVs are preserved, which can be considered as online detection. Additionally, at least 400 nm applicable wavelength range of this method is experimentally demonstrated, as well as up to 25 independent detection channels. Compared with existing solutions, this scheme enables a large‐broadband wavelength, low energy loss, and multiprocessing channels platform for visible detection of NIR OVs, showing great potential to be applied in optical communication systems.

Femtosecond laser direct writing continuous phase vortex gratings with proportionally distributed diffraction energy

In this Letter, we propose a type of continuous phase vortex gratings (CPVGs), which are able to generate a series of vortex beams with equal or proportional diffracted energies and different topological charges (TCs). A set of CPVGs with dimensions (60 × 60 × 1.1 μm3) are directly designed by mathematical equations, which avoids the use of iterative algorithms. The CPVGs are fabricated by femtosecond laser direct writing (FsLDW) with photoresist, and the experimentally generated vortex beams are in good agreement with the theoretical designs, exhibiting high optical efficiencies. In addition, we realized a CPVG onto the tip of a composite fiber for integrated optical systems. Our work paves the way for applications in optical communications, optical manipulations, and high-performance integrated optics.

Noncoaxially propagating discrete data by coding/decoding orbital angular momentum of vortex beam through multiple channels

A concept of noncoaxially propagating discrete data by coding/decoding orbital angular momentum (OAM) of vortex beam through multiple channels is proposed. Four independent channels along different directions (diffraction orders/angles) are established by a series of specially designed holograms. Sixteen vortex beams are used to code each sequence with the length of 4 bits into an OAM mode in each channel. The theoretical analysis (simulation) demonstrates that the proposed scheme is reliable. In addition, an experiment is also designed and performed for practically certifying the feasibility of the proposed scheme. A 16-bits-length sequence, which is coded into four OAM modes in four channels (one channel with one OAM mode), is successfully received/decoded by observing the intensity-profile arrays (OAM-mode spectrum) generated by a specially designed Dammann vortex grating. The measured results show that the proposed concept is also viable in practice. Moreover, the received/recovered images indicate that the performance of the system decreases as the atmosphere turbulence strength increases when a color image and a gray-scale image are simultaneously propagated. Besides, the measured bit error rate (BER) gradually decreases with the increase of bit rate or propagation distance. The acceptable BER under the threshold of forward error correct can be achieved for a short-distance communication network.

Orbital angular momentum mode detection of the combined vortex beam generated by coherent combining technology.

Coherent beam combining (CBC) technology has distinct advantages in generating high power vortex beam. In this paper, a circularly arranged coherent beam array (CBA) with discrete vortex phases is constructed to generate vortex beams. We demonstrated that the combined vortex beam (CVB) generated by the CBA is a multiplexing vortices optical field, which sidelobe is the coaxial interference pattern of these spiral harmonic components. Using the designed Dammam vortex grating (DVG), the orbital angular momentum (OAM) spectrum of the CVB is detected. Moreover, taking the target OAM mode purity of the CVB as the evaluation function of active phase control system, we realized the closed-loop phase control of the CBA and obtained the phase-locked output of the CVB.

Broadband Multichannel Optical Vortex Generators via Patterned Double-Layer Reverse-Twist Liquid Crystal Polymer

The capacity of an optical communication system can be greatly increased by using separate orbital angular momentum (OAM) modes as independent channels for signal transmission and encryption. At present, a transmissive OAM mode generator compatible with wavelength division multiplexing is being highly pursued. Here, we introduce a specific double-layer reverse-twist configuration into liquid crystal polymer (LCP) to overcome wavelength dependency. With this design, broadband-applicable OAM array generators are proposed and demonstrated. A Damman vortex grating and a Damman q-plate were encoded via photopatterning two subsequent LCP layers adopted with oppositely handed chiral dopants. Rectangular and hexagonal OAM arrays with mode conversion efficiencies exceeding 40.1% and 51.0% in the ranges of 530 to 930 nm, respectively, are presented. This provides a simple and broadband efficient strategy for beam shaping.

High-dimension data coding and decoding by radial mode and orbital angular momentum mode of a vortex beam in free space

A novel coding/decoding concept based on the orbital angular momentum (OAM) mode and radial mode of a vortex beam is proposed for short-haul free-space optical communication. Sixty-four kinds of vortex beams, which are comprised of sixteen OAM modes and four radial modes, are employed and utilized for coding each of 6-bits-length sequences into one of the 64-ary symbols. A specially-designed Dammam vortex grating (DVG) is utilized to generate an intensity-array profile, where the received vortex beam is demodulated into Gaussian beam in the related coordinate (order). In one of the coordinates, the received vortex beam can be converted into a bright spot (Gaussian beam) with a certain number of intensity rings. According to the coordinate and number of intensity rings, the received vortex beam can be identified and then decoded into the initially-propagated information sequence. The corresponding theory analysis/simulations and experiments demonstrate that the proposed concept is valid and feasible. In addition, the measured results also demonstrate that the performance of the proposed concept declines as the transmission rate/ atmosphere turbulence strength/propagation distance increases. By adopting advanced devices and approaches, the performance of the proposed scenario can be significantly improved, and then the proposed concept can be potentially utilized for short-haul free-space optical communication in the future.

Coding and decoding data by multiplexing vortex beams in free space

A novel concept of coding/decoding data is proposed by multiplexing vortex beams for short-haul-free-space light communication. Eight vortex beams carrying different orbital angular momentum (OAM) modes (-5, 3, -2, 1, 5, -3, 2, -1) are employed to code the initial information sequences into each 256-ary symbols by different multiplexing approaches. A specially-designed Dammam vortex grating is utilized to decode the received vortex beams into the initial information sequences. In order to certifying the validity and feasibility of the proposed concept in practice, a proof-of-concept experiment is also proposed and established. The measured results demonstrate that a 128 × 128 gray-scale image (“Lena”) can be perfectly propagated over a 10 m free space by the proposed concept. In order to further evaluate the performance of the proposed concept, bit error rate (BER) against the received optical signal-to-noise ratio (OSNR) is also employed to analyzing the influences of some parameters on the system performances. The measured BER distributions demonstrate that the BER performance decreases as the data rate/propagation distance/atmosphere turbulence strength increases, respectively.

Optical Generation/Detection of Broadband Microwave Orbital Angular Momentum Modes

In this article, a novel electrically controlled optical broadband phase shifter (ECO-BPS) is proposed and experimentally investigated for broadband microwave orbital angular momentum (OAM) mode generation. Based on the proposed ECO-BPS and a 17-element circular antenna array, the effect of the phase error on the OAM mode quality is studied by comparing the OAM modes respectively synthesized by three phase schemes: ideal phase shifts, ECO-BPS phase shifts, and optical true time delay phase shifts. In addition, the crosstalk caused by the phase error in applications of OAM modes multiplexing is investigated in a Dammann vortex grating based OAM modes demultiplexing system. All numerical simulation results demonstrate the feasibility of the ECO-BPS in broadband microwave OAM applications.

Spin-Dependent Optical Geometric Transformation for Cylindrical Vector Beam Multiplexing Communication

Given by the Shannon theorem, the data rate in a single mode fiber is approaching the capacity limit of 100 Tbit/s, which even applies to all existing wavelength division multiplexing and advanced modulation formatting techniques. Optical vortex beams, including orbital angular momentum (OAM) beams with phase singularities and cylindrical vector beams (CVBs) with polarization singularities, are orthogonally structured light beams providing new degrees of freedom for multiplexing optical communication, for which the multiplexer is the key component. Although there are various OAM detection approaches such as the optical geometric transformation and vortex grating, CVB sorting with high efficiency and large dynamic range has not been demonstrated before. In this work, we propose and demonstrate an efficient approach for multiple coaxial CVB sorting based on the spin-dependent optical geometric transformation using the Pancharatnam–Berry optical element device fabricated with the photoaligned liquid crystal....

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.

Progress of detecting orbital angular momentum states of optical vortices through diffraction gratings

Optical vortices are a new kind of laser beam and receiving more and more attention currently.The complex amplitudes of optical vortices comprise a helical term exp (il),with l being the topological charge and the azimuthal angle.Each photon in optical vortices carries the orbital angular momentum (OAM) with a value of lħ,where ħ is the Planck's constant divided by 2.The topological charge l is the eigenvalue of optical vortices,and determines the helical wavefront distribution,thus also known as OAM state.Moreover,such an OAM state can be an infinite integer state. And vortices with various OAM states are orthogonal to each other,making it possible to be employed in high capacity data-transmission system.In addition,the above unique features contribute to their widely applications in lots of areas such as optical tweezers and spanners,rotation detection,quantum entanglement,etc.In these applications,detecting OAM states is basic,and greatly significant.Recently researchers have developed lots of approaches to detecting the OAM states,including the methods of interference,diffraction gratings,metasurface,etc.Of such approaches,the scheme of diffraction gratings is the simplest and most widely used,where one or more diffraction gratings are employed. When optical vortices propagate through such gratings,the OAM states are acquired immediately through capturing and analyzing the distinct OAM-related diffraction patterns.In this review,we focus on the techniques of detecting OAM states through diffraction gratings,which have been demonstrated by our group and other researchers.Some of the main detection gratings,including double-slit,triangle aperture and slit,angular slit,cylindrical lens,graduallychanging-period grating,annular grating,are introduced.In addition,schemes like composite fork grating,Dammann vortex grating and integrated Dammann grating,are presented to detect the OAM state for coaxial multiplexed vortices. Besides diagnosing OAM state,measuring the intensity proportion of each OAM channel,known as OAM spectrum, in multiplexed vortices is also necessary in some cases.Therefore we also introduce the ways to measure the OAM spectrum,e.g.the OAM mode sorter,the gray-scale algorithm.

Optical vortex with a small core and Gaussian intensity envelope for light-matter interaction

Optical vortices with a vortex core size that is at least two orders of magnitude smaller than the laser beam waist is presented. The optical vortex is generated by a spiral phase plate (SPP) and counterrotating optical vortex pairs are created in a modified Mach–Zehnder interferometer surrounded by a 4f lens arrangement. The azimuthal variation of the counterrotating optical vortex forms a sinusoidal intensity modulation for which the winding number of the optical vortex is deduced accurately and precisely by fitting it to a sinusoidal function. These results are of interest in designing novel optical vortex gratings for manipulating matter waves (e.g., in Kapitza–Dirac scattering). A theory of atomic angular Kapitza–Dirac scattering with optical vortices is presented. The large beam waist combined with a small optical vortex core size would also be of interest when using an optical vortex to perform spectroscopy in a wide range of matter systems including solid, liquid, atomic, and molecular systems, as well as in short-range optical communication.

Volumetric Generation of Optical Vortices with Metasurfaces

Recent advances in metasurfaces, i.e., two-dimensional arrays of engineered nanoscale inclusions that are assembled onto a surface, have revolutionized the way to control electromagnetic waves with ultrathin, compact components. The generation of optical vortex beams, which carry orbital angular momentum, has emerged as a vital approach to applications ranging from high-capacity optical communication to parallel laser fabrication. However, the typically bulky elements used for the generation of optical vortices impose a fundamental limit toward on-chip integration with subwavelength footprints. Here, we investigate and experimentally demonstrate a three-dimensional volumetric optical vortices generation based on light–matter interaction with a high-efficiency dielectric metasurface. By employing the concepts of Dammann vortex gratings and spiral Dammann zone plates, a 3D optical vortex array with micrometer spatial separation is achieved from visible to near-infrared wavelengths. Importantly, we show that...