Orbital Angular Momentum Multiplexing Research Articles

Electromagnetic Vortex Imaging Based on OAM Multiplexing Beam With Orthogonal Polyphase Coding

Electromagnetic Vortex Imaging Based on OAM Multiplexing Beam With Orthogonal Polyphase Coding

All-fiber function devices for twisted lights.

Lights carrying orbital angular momentum (OAM), also called twisted lights, have been applied in fields of optical manipulation, imaging, quantum communication, and mode-division-multiplexing (MDM) optical communication systems. Traditional approaches for manipulating twisted lights carrying OAM in free space paths such as Q-plates, spiral phase plates (SPPs), and spatial light modulators (SLMs) that are usually affected by diffraction effect and imperfect alignment between different optical components, limiting the practical applications of twisted lights. Here we design, fabricated, and package all-fiber function devices for twisted light carrying OAM such as all-fiber broadband OAM generator, all-fiber OAM (de)multiplexer, all-fiber OAM & WDM coupler, and all-fiber OAM 1 × 2 coupler. Base on coupled mode theory and phase-matching condition, twisted light can be generated and detected by pre-tapered single mode fiber (SMF) fusing with multi-mode fiber (MMF). The results show that the proposed all-fiber function devices for twist light have large working broadband (at least C band), high purity (above 95%), and low insert loss (less than 3 dB). The proposed devices will open a reliable way for twisted light applied in optical fiber communications and optical interconnections.

Demultiplexing of 40 acoustic orbital angular momentum wavelength-division multiplexing (OAM-WDM) channels by an improved virtual rotating receiver method

Orbital angular momentum (OAM) multiplexing/demultiplexing technology is crucial in increasing the data transmission rate for acoustic communication. However, the existing acoustic OAM multiplexing/demultiplexing is still limited to eight channels, and its combination with other communication techniques has not been verified experimentally. Here, we experimentally demonstrate the demultiplexing of up to 40 data channels using OAM multiplexing combined with wavelength-division multiplexing (WDM). The proposed demultiplexing method is improved from the virtual rotating receiver method used to detect the rotational Doppler effect of the OAM waves by a static array of microphones. The improved method has overcome the challenges of insufficient response, cross-talk, and signal aliasing, which often hinder the existing demultiplexing methods in the low-frequency region. The proposed demultiplexing method can be used to quickly decode the massive information concealed in a large number of acoustic OAM-WDM channels. Our work also shows practical prospects in underwater communication applications, especially in long-range communication using acoustic waves at low frequencies.

Simultaneously enhancing capacity and security in free-space optical chaotic communication utilizing orbital angular momentum

Optical chaotic signals emitted from an external-cavity feedback or injected laser diode enable small-signal information concealment in a noise-like carrier for secure optical communications. Due to the chaotic bandwidth limitation resulting from intrinsic relaxation oscillation frequency of lasers, multiplexing of optical chaotic signal, such as wavelength division multiplexing in fiber, is a typical candidate for high-capacity secure applications. However, to our best knowledge, the utilization of the spatial dimension of optical chaos for free-space secure communication has not yet been reported. Here, we experimentally demonstrate a free-space all-optical chaotic communication system that simultaneously enhances transmission capacity and security by orbital angular momentum (OAM) multiplexing. Optical chaotic signals with two different OAM modes totally carrying 20 Gbps on–off keying signals are secretly transmitted over a 2 m free-space link, where the channel crosstalk of OAM modes is less than −20 dB, with the mode spacing no less than 3. The receiver can extract valid information only when capturing approximately 92.5% of the OAM beam and correctly demodulating the corresponding mode. Bit error rate below the 7% hard-decision forward error correction threshold of 3.8×10−3 can be achieved for the intended recipient. Moreover, a simulated weak turbulence is introduced to comprehensively analyze the influence on the system performance, including channel crosstalk, chaotic synchronization, and transmission performance. Our work may inspire structured light application in optical chaos and pave a new way for developing future high-capacity free-space chaotic secure communication systems.

Orbital angular momentum multiplexing holography based on multiple polarization channel metasurface

Abstract As a high-degree-of-freedom approach to manipulate the electromagnetic wave, metasurfaces are widely used in high-capacity information technology. Extensive investigations have explored multiplexing techniques using polarization, incident angle, wavelength, and infinite-dimensional multiplexing through Orbital Angular Momentum (OAM). However, due to the limited spatial resolution and array size of the metasurface, the number of multiplexing channels that can be actually realized is limited. Therefore, research on the combination of OAM multiplexing and polarization degrees of freedom is of great significance. Here, we propose and experimentally demonstrate a metasurface holography multiplexing scheme based on multiple polarization channels combined with OAM. Taking advantage of the orthogonal independence of spin angular momentum and orbital angular momentum, multiple OAM multiplexing holograms are constructed in multiple different spin-polarization channels. Utilizing the well-established compatibility between OAM multiplexing and polarization multiplexing, we successfully integrated two multiplane holograms and 15 OAM multiplexing holograms on a single metasurface. Subsequently, we introduced an optical nested encryption framework designed for parallel communication. This work facilitates high-capacity and high-security holography by employing multiplexing metasurfaces, thereby providing innovative design concepts for optical communication, information encryption, and related domains.

Optical soliton based long-haul data transmission over MMF employing OAM multiplexing technology

Optical soliton based long-haul data transmission over MMF employing OAM multiplexing technology

Free-Space Quantum Teleportation with Orbital Angular Momentum Multiplexed Continuous Variable Entanglement

Quantum teleportation is one of the fundamental primitives of quantum cryptography. In order to achieve a wider range of high-capacity information transfer, we propose a free-space quantum teleportation (QT) protocol with orbital angular momentum (OAM) multiplexed continuous variable (CV) entangled states. The preparation of the entangled states is accomplished by the spontaneous four-wave mixing (SFWM) process occurring in a hot 85Rb vapor cell, and the mode selection for the Bell-state measurement is achieved by employing the balanced homodyne detection technique. The fidelity of teleporting EPR entangled states carrying different topological charges via a Kolmogorov-type atmospheric turbulence channel is derived, and the superiority of enhancing the system channel capacity via OAM multiplexing is demonstrated. Our work provides a feasible scheme to implement high-capacity quantum communication in atmospheric environments.

Next generation PON architecture using PD-NOMA employing OAM and WDM multiplexing

In this paper, we propose and experimentally demonstrate the efficacy of a next-generation passive optical network (PON) architecture for free space optical link, which utilizes power domain (PD) non-orthogonal multiple access (NOMA) along with simultaneous orbital angular momentum (OAM) mode and wavelength-division multiplexing (WDM) techniques. In this proposed architecture, many optical network units (ONUs) are accommodated by clustering them based on their power budgets and their data streams are allocated with different powers accordingly. The clustered ONUs are served with multiple OAM modes over multiple wavelengths to maintain high capacity, low latency, and increased reliability. As a proof-of-principle experimental demonstration of the proposed architecture, we have experimentally emulated two ONU clusters having a power ratio of (near:far)−3.17dB for implementing the PD-NOMA system for downlink. Each ONU cluster uses three 50 GHz spaced WDM channels, where each WDM channel carries two multiplexed OAM modes having opposite topological charge (l=±1 and ±2) values. Each cluster’s six ONUs is delivered with a 10 Gbps On-Off Keying (OOK) signal. We have demonstrated that all users can achieve a pre-forward error correction (pre-FEC) bit error rate (BER) below the 7% overhead-FEC (OH-FEC) BER limit of 3.8×10−3. We have also measured the x-talk due to WDM and mode multiplexing, and it has been revealed that the main contribution to the power penalty (relative to the no cross-talk condition) comes from OAM mode cross-talk.

Extending orbital angular momentum multiplexing to radially high orders for massive mode channels in fiber transmission.

Orbital angular momentum (OAM) beams with different angular indices l have the potential to greatly increase communication capacity. However, the finite aperture of optical systems limits the value of the angular index. In order to fully use the orthogonal mode channels supported in the fiber for high-capacity communications, we propose extending the radial indices p of OAM modes as an additional multiplexing dimension. In this paper, we introduce spatially discrete multiple phase planes to multiplex the angular and radial OAM modes simultaneously. Due to the orthogonal property of the central symmetric OAM modes, a two-dimensional (2D) input Gaussian beams array can be converted to coaxial OAM modes through Cartesian to log-polar coordinate transformation by inverse design. For a proof-of-concept demonstration, a 10-mode multiplexer for high-order radial OAM modes was designed using five phase planes. The fabricated multiplexer generated high-quality multiplexed OAM modes with a loss of less than 5.4 dB. The multiplexed OAM modes were coupled into a specially designed ring-core fiber by mode-field matching, achieving stable mode transmission in 2 km fiber. The approach provides a scalable technology to increase the number of transmission channels and could lead to the practical applications of OAM multiplexing in communication.

Performance investigations on integrated MMF/FSO transmission enabled by OAM beams

This paper introduces a new hybrid system for high-bandwidth and high-transmission-capacity communication. The system integrates a multi-mode fiber (MMF) cable with free space optics (FSO) using orbital angular momentum (OAM) multiplexing. The proposed system uses a single wavelength to simultaneously transmit 40 Gb/s data on four distinct OAM beams ((LG0,0, LG0,17, LG0,40, and LG0,75)) with a symmetric circular shape. The performance of the system was evaluated with a fixed MMF length of 100 m and varying FSO ranges, according to extreme climate changes such as rain and fog, and atmospheric turbulences. The results indicate that the suggested system is capable of transmit up to 1250 m (100 m MMF length + 1150 m FSO range) under clear weather (CW) and weak turbulence (WT), with a minimum transmission distance of 440 m (100 m MMF length + 340 m FSO range) under heavy fog (HF). The performance of the system was also demonstrated based on actual meteorological data for two different cities, Alexandria, Egypt and Chandigarh, India, with different visibility ranges and geographical locations. Since Alexandria has a longer visibility range than Chandigarh, our proposed model could spread over a larger area than it could be in Chandigarh. The obtained ranges were within an acceptable bit error rate (BER) of less than 10−9. The system’s maximum range was 1200 m for Alexandria and 1100 m for Chandigarh. The proposed model can be suggested for use in next generation (NG) passive optical networks (PON) for supporting symmetric 40 Gb/s data.

Atmospheric Turbulence Effects on the Performance of Orbital Angular Momentum Multiplexed Free-Space Optical Links Using Coherent Beam Combining

Atmospheric effects including absorption and scattering, and turbulence could introduce signal power loss and severe mode crosstalk for the orbital angular momentum (OAM)-based free-space optical communication (FSOC). Therefore, it is of great significance to simultaneously increase signal power and mitigate mode crosstalk. In this paper, for the OAM beam from a coherent laser array with a discrete vortex (CLA-DV) based on coherent beam combining, we investigate its propagation characteristics by employing theoretical derivation and the random phase screens simulation in atmospheric propagation, respectively. The probability density and OAM spectrum are given and compared for CLA-DV and Gaussian vortex beam. The results demonstrate that the Gaussian vortex beam exhibits smaller mode crosstalk under weak atmospheric turbulence conditions, while CLA-DV shows a good performance on crosstalk mitigation for strong atmospheric turbulence conditions in long-distance links. Furthermore, with a specially designed radial phase-locked Gaussian laser array composed of two orthogonal polarized coherent laser arrays carrying different OAM states, a scheme of optical communication system possessing simultaneously polarization-division multiplexing and OAM multiplexing is proposed. The normalized energy weight matrices of all 16 non-zeroth-order OAM modes are numerically calculated. To verify the feasibility of the proposed scheme, the performance of an eight-bit grayscale Lena image facing various atmosphere turbulences is evaluated. The quality of transmitted images becomes worse with the turbulence strength and transmission distance increase, which is confirmed by the trend of average optical signal error rates. This work will provide theoretical insight for improving the performance of OAM-based FSOC under scattering conditions.

Photon-counting-based underwater wireless optical communication employing orbital angular momentum multiplexing.

Underwater wireless optical communication (UWOC) is a critical technology for underwater communication, providing high speed, low latency, and security advantages. However, the strong attenuation in the water channel still limits the UWOC systems and their performances require further improvement. In this study, an orbital angular momentum (OAM) multiplexing UWOC system that uses photon-counting detection is experimentally demonstrated. By employing a single-photon counting module to receive photon signals, we analyze the bit error rate (BER) and photon-counting statistics by building a theoretical model that fits the real system, and demodulate the OAM states in single photon level and implement signal processing using field programmable gate array (FPGA) programming. Based on these modules, a 2-OAM multiplexed UWOC link is established over a water channel of 9 m. By using on-off keying modulation and 2-pulse position modulation, we achieve a BER of 1.26×10-3 with data rate of 20Mbps and 3.17×10-4 with data rate of 10Mbps respectively, which below the forward error correction (FEC) threshold of 3.8×10-3. The total transmission loss is 37 dB under an emission power of 0.5 mW, which is equivalent to the attenuation of 283 m Jerlov I type seawater from the perspective of energy loss. Our verified communication scheme will benefit the development of long-range and high-capacity UWOC.

Near-field formation of the UCA-based OAM EM fields and short-range EM power flux profiles

Orbital angular momentum (OAM) multiplexing is a recently considered solution for enhancing wireless and free-space optical communications channel capacity, whether implemented separately or in combination with existing multiplexing techniques. The theoretically infinite number of paraxially propagating and mutually orthogonal OAM modes is expected to increase the channel capacity. However, the orthogonality for different OAM modes has been shown to decrease for far link range distances, and the paraxiality of the OAM beams is not very good for small radiating sources. Based on the current knowledge, OAM beams are most likely to be used for short-range communications. Many models of the electromagnetic (EM) fields carrying the OAM neglect the fact that the OAM beam sources could be electrically large or introduce other approximations that are appropriate for far-field analysis only. An in-depth analysis of the short-range properties of OAM EM fields is still lacking. To address this problem, we propose the use of the infinitesimal (Hertz) dipole method customized for the analysis of the OAM EM fields. This technique can model the positioning and basic radiation properties of separate antennas or antenna sub-arrays that are the building blocks of OAM arrays exactly and efficiently. Similar modeling can represent the OAM sources for free-space optical communications. We focus here on the uniform circular antenna arrays and provide an in-depth analysis of what can and cannot be expected, in the best case, in their utilization. We assume low losses, which is a common assumption for many methods, except for computationally much more demanding full-wave simulations. The obtained results indicate the need to simultaneously optimize the transmission of all planned OAM modes and allow estimates of the link distances that could provide adequate OAM wave reception in various cases.

A THz-OAM Wireless Communication System Based on Transmissive Metasurface

With the development of various emerging technologies, the capacity of current wireless communication system is gradually saturated, and terahertz (THz) and orbital angular momentum (OAM) have hereby attracted much attention as two key technologies to increase the communication capacity. In this paper, a THz-OAM wireless communication system operating at 100 GHz based on a transmissive metasurface is proposed for the first time to the best of our knowledge. The operation principle of multiplexing metasurface which allows simultaneous generation of two coaxial OAM beams at different modes of l = 1 & –1 is studied. To meet the requirements of wireless communication and OAM multiplexing, a C-shaped transmissive unit is designed with characteristics of broad bandwidth, low transmission loss and insensitive to the change of incident angle. Experimental measurements show that the generated two OAM beams feature high mode purity, providing the excellent orthogonality of modes. The generated two OAM modes are also employed as two OAM channels to transmit two independent communication signals with on-off keying (OOK) modulation, and a data rate of 10 Gbit/s is achieved at a transmission distance of 300 mm (100 λ of 100 GHz) with bit error rates (BERs) below 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . This work verifies the feasibility of the multiplexing metasurface supporting wireless communication, and makes THz-OAM wireless communication systems potential for future large capacity wireless services.

Highly Efficient 3D Nonlinear Photonic Crystals in Ferroelectrics

AbstractNonlinear photonic crystals (NPCs) with spatially modulated second‐order nonlinear coefficients are indispensable in nonlinear optics and modern photonics. To access full degrees of freedom in the generation and control of coherent light at new frequencies, three dimensional (3D) NPCs have been recently fabricated employing the femtosecond laser writing technique in ferroelectric crystals. However, the nonlinear interaction efficiencies in 3D NPCs so far are rather low, which has been a major barrier to further development. Here, fabrication challenges of large‐scale 3D NPCs have been overcome to realize more than four orders of magnitude efficiency improvement over previously reported crystals. With the generation of second harmonic vortex beam as an example, the measured conversion efficiencies as high as 2.9 × 10−6 W−1 (femtosecond pulse‐pumped) and 1.2 × 10−5 W−1 (continuous‐wave‐pumped) are comparable with those in 1D or 2D NPCs. A general approach of structural simplification to relax fabrication challenge of truly complex 3D structures without sacrificing the predesigned functions is also presented. This realization of efficient nonlinear interactions in 3D NPCs paves the way for their novel applications in nonlinear photonics and quantum optics including nonlinear orbital angular momentum multiplexing and high‐dimensional entangled source.

Orbital Angular Momentum Data Transmission Using a Silicon Photonic Mode Multiplexer

We designed and fabricated a silicon photonic orbital angular momentum (OAM) multiplexer (MUX) chip that enables simultaneous wavelength-division multiplexing (WDM) and OAM mode-division multiplexing (MDM) in optical fiber communication systems. We successfully utilized the fabricated MUX chip to demonstrate simultaneous 3 OAM MDM transmission as well as OAM MDM/WDM transmission with an 800-m OAM ring-core fiber. In both cases, 10 Gbit/s OOK signals were utilized and BERs below the 7% FEC limit were obtained.

Orbital Angular Momentum Mode-Multiplexed Amplification and Transmission Based on a Ring-Core Erbium-Doped Fiber

Recently, orbital angular momentum (OAM) multiplexing has attracted much attention for providing an exponential growth in optical fiber capacity. As an irreplaceable component to promote long-haul OAM mode fiber transmission system, the on-line OAM mode-multiplexed fiber amplifier need to be developed. In this paper, we propose a Gaussian-like erbium doping distribution design method for ring-core erbium doped fiber (RC-EDF) to optimize the differential modal gain (DMG), which can reduce the fabrication complexity of the fiber preform. With a good match with original design, the fabricated RC-EDF was characterized by all the supporting four OAM modes ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\vert l \vert$</tex-math></inline-formula> = 1, 2, 3, 4) multiplexed amplification, which achieves an ultra-low DMG less than 0.3 dB at 1550 nm. The gain is above 15 dB and DMG is less than 1.2 dB for four OAM modes across the C-band under a 500 mW pump power. As a proof for transmission, 32 channels (8 wavelengths × 4 OAM modes) carrying 32-Gbaud quadrature phase-shift keying (QPSK) OAM modes multiplexed-WDM transmission over the OAM-EDFA is demonstrated. The proposed OAM-EDFA with the average OSNR penalties of 0.34 dB may promote the practical implementation for the long-haul OAM modes fiber transmission system.

Integrated Phased Array for Scalable Vortex Beam Multiplexing

Orbital angular momentum (OAM) modes have low model interactions during fiber propagation at data center distances, and thus are suitable for ultra-high capacity systems at low digital signal processing. Generating OAM modes using free-space setups is useful for proof-of-concept experiments, but is not a scalable solution. We use an optical phased array (OPA) with two-dimensional antennas for on-chip circularly polarized OAM beam generation. Our previous work demonstrated an OAM multiplexer for lower-order modes. In this work, we demonstrate an OAM multiplexer that supports a record of 46 (23 per polarization) simultaneous spatial modes up to OAM order 11. We also improve the crosstalk performance of our multiplexer. We incorporate an intensity tuning capability that substantially improves the OAM quality by enabling a uniform power distribution across the antennas. The worst-case crosstalk for the supported OAM5 to OAM11 are found experimentally to be better than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-12$</tex-math></inline-formula> dB, with OAM10 achieving <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-17.2$</tex-math></inline-formula> dB.

Low-light-level spin–orbit splitting via structured light cross-Kerr interaction in coherent atomic media

We explore the spin–orbit coupling (SOC) mechanism for structured light in coherent atomic media with low-light-level cross-Kerr nonlinearity. Using the five-level M-type electromagnetic induced transparency (EIT) system as a prototype, we show that spin–orbit splitting for a weak spinor image can be generated by a weak trigger field carrying orbital angular momentum (OAM) at low-light intensity. By quantum-optical analogy, the paraxial focusing and defocusing of the two pseudo-spin states in the spinor image can be governed by a Pauli-like equation. More importantly, by changing the EIT parameters, especially the topological charge of the weak trigger field, the SOC-induced radial quantization of the spinor image can be rather significant, giving rise to positive or negative OAM-OAM mode separation in free space. This suggests that the separation can be flexibly controlled due to strong image-vortex interaction based on few-photon cross-Kerr modulation. Our findings may have the potential for all-optical OAM multiplexing and demultiplexing of structured light fields toward few-photon quantum control and multimode communication.

Multiple Orbital Angular Momentum Beams with High‐Purity of Transmission‐Coding Metasurface

AbstractVortex electromagnetic wave carrying orbital angular momentum (OAM) is expected to break through the shortage of spectrum resource because of its multiple independent modes. Nowadays, there are various methods to generate OAM vortex beam. Based on the concepts of digital metasurface and propagation phase, a broadband 3‐bit coding transmission metasurface is designed and illustrated by simulation and measurement. The elements exhibit the different phase by changing the size of metal patch, and the focusing phase is introduced to reduce the divergence of OAM beams. Based on the principle of phase superposition, the wide‐band, high‐purity, and multi‐beam OAM vortex waves can be generated by the transmission‐coding metasurface (TCMS). The experimental results verify that TCMS realizes the multiple OAM beams along different directions simultaneously from 9 to 10.5 GHz, which are consistent with the theoretical results. The high purity more than 90% of OAM mode is demonstrated by both the simulated and measured results. The TCMS provides a potential and effective scheme for OAM multiplexing and multi‐target positioning in wireless systems.