Optical Orbital Angular Momentum Modes Research Articles

Time Evolution of Orbital Angular Momentum Modes for Deep-Routing Multiplexing Channels

Optical orbital angular momentum (OAM) mode multiplexing has emerged as a promising technique for boosting communication capacity. However, most existing studies have concentrated on channel (de)multiplexing, overlooking the critical aspect of channel routing. This challenge involves the reallocation of multiplexed OAM modes across both spatial and temporal domains—a vital step for developing versatile communication networks. To address this gap, we introduce a novel approach based on the time evolution of OAM modes, utilizing the orthogonal conversion and diffractive modulation capabilities of unitary transformations. This approach facilitates high-dimensional orthogonal transformations of OAM mode vectors, altering both the propagation direction and the spatial location. Using Fresnel diffraction matrices as unitary operators, it manipulates the spatial locations of light beams during transmission, breaking the propagation invariance and enabling temporal evolution. As a demonstration, we have experimentally implemented the deep routing of four OAM modes within two distinct time sequences. Achieving an average diffraction efficiency above 78.31%, we have successfully deep-routed 4.69 Tbit·s−1 quadrature phase-shift keying (QPSK) signals carried by four multiplexed OAM channels, with a bit error rate below 10–6. These results underscore the efficacy of our routing strategy and its promising prospects for practical applications.

Synthesizing the crosstalk between OAM modes of vortex beam by simultaneously propagating a probe vortex beam in free space

To overcome the upcoming famine of channel capacity driven by explosive increases of new applications, optical orbital angular momentum (OAM) carried by a vortex beam has been considered to be a promising candidate for space-division multiplexing (SDM) in a novel physics domain. However, owing to the inescapable disturbance induced by atmosphere turbulence (AT), the performance of OAM-based free-space optical communication (FSOC) is seriously restrained, which can be ascribed to the crosstalk among different OAM modes induced by the distorted helical phase. For promoting the development of OAM-based FSOC, a synthesizing-crosstalk method is proposed for mitigating the AT by coaxially propagating an OAM-probe beam (OPB), wherein the OAM mode of the extra OPB is identical to the OAM mode of the propagated OAM-data beam (ODB). The corresponding theory analysis of the proposed method demonstrates that the conjugated distortion of the crosstalk can be generated by a hybrid of the OPB and the ODB in a photoelectric receiver/detector (PD/PR). The generated conjugate distortion of the OPB can effectively counteract the crosstalk of ODB induced by the turbulence. To verify the feasibility of the proposed scheme, an experimental setup is built. The measured results demonstrate that the bit error rate (BER) and constellation plot (CP) of the employed two OAM channels can be significantly improved under different atmosphere turbulence (AT) by utilizing the proposed scheme. A continuous 30 min-long-BER-testing results depict that the proposed concept can stably work well. The proposed concept can be also suitable for multiplexing other OAM modes as well as the employed two OAM channels. Besides, with the increase of data speed, the proposed scheme can also effectively mitigate the crosstalk and improving the system performance. Consequently, the proposed concept is valid and feasible both in theory and practice, which can be used for compensating the distorted helical phase and improving the system performance of an OAM-based FSOC in the future.

Mode Conversion Between Beams Carrying Orbital Angular Momentum With Opposite Topological Charges Using Two-Dimensional Multimode Interference Waveguides

Recently, the implementation of rectangular waveguides for generation and manipulation of orbital angular momentum (OAM) modes, has been developed to exploit the outstanding features of these modes in more complex integrated devices. Multimode interference (MMI) structures have been widely used in both one and two dimensions as the basic elements in many integrated optical devices like optical beam splitters, mode converters, couplers, wavelength-division (de)multiplexers, and switches. According to the various applications of OAM modes in quantum and classical communications, the study of their propagation properties in MMI waveguides is useful in order to facilitate the way into higher security and capacity systems. This paper presents the results of numerical investigation of a proposed integrated optical OAM mode converter which is performed based on the mode decomposition properties of propagating OAM modes in 2D MMI waveguides, as well as the fact that any order of OAM mode can be represented as superposition of an odd mode and a quarter-wave shifted even mode. The proposed device, which consists of two MMI waveguides connected by phase shifters and linear waveguides, provides mode conversion between beams carrying OAM with odd opposite topological charges. The design procedure is performed for OAM modes with topological charge values of l = ±1 and l = ±3 using beam propagation method. The proposed device is passive with reciprocal behavior and has the output mode purity of 94% and 82% for beams carrying l = ±1 and l = ±3, respectively.

Optical Encryption in the Photonic Orbital Angular Momentum Dimension via Direct-Laser-Writing 3D Chiral Metahelices.

Vortex beams, which intrinsically possess optical orbital angular momentum (OAM), are considered as one of the promising chiral light waves for classical optical communications and quantum information processing. For a long time, it has been an expectation to utilize artificial three-dimensional (3D) chiral metamaterials to manipulate the transmission of vortex beams for practical optical display applications. Here, we demonstrate the concept of selective transmission management of vortex beams with opposite OAM modes assisted by the designed 3D chiral metahelices. Utilizing the integrated array of the metahelices, a series of optical operations, including display, hiding, and even encryption, can be realized by the parallel processing of multiple vortex beams. The results open up an intriguing route for metamaterial-dominated optical OAM processing, which fosters the development of photonic angular momentum engineering and high-security optical encryption.

Miniaturized optical vortex mode demultiplexer: Principle, fabrication, and applications

Vortex beams have attracted extensive attention in recent decade due to the carried optical orbital angular momentum (OAM). Vortex beams carrying different OAM modes are orthogonal to each other, and thus have become highly promising in realizing high-capacity optical communication systems. This review is to introduce the fundamental principles of optical OAM mode demultiplexing, recent advances in the fabrication techniques and emerging applications in high-capacity optical communications. First, this review introduces the development history of the working principle of OAM mode demultiplexer. Subsequently, a variety of preparation techniques and emerging applications of OAM mode demultiplexing are discussed in detail. Finally, we provide an in-depth analysis and outlook for the future trends and prospects of the OAM mode demultiplexer.

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 mode-division 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 mode-division 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 dB , with insertion loss of less than 2.6 dB. OAM modes are sorted by the demultiplexer with mode crosstalk below − 10 dB , 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 dB. The proposed configuration is highly efficient and convenient and will be beneficial for potential applications in quantum information, information processing, and optical communications.

High-resolution optical orbital angular momentum sorter based on Archimedean spiral mapping.

We propose a generalized spiral transformation scheme that is versatile to incorporate various types of spirals such as the Archimedean spiral and the Fermat spiral. Taking advantage of the equidistant feature, we choose the Archimedean spiral mapping and demonstrate its application in high-resolution optical orbital angular momentum (OAM) mode sorting. Experimental results show 90% efficiency and cross-talk of -8.78 dB that is sufficient to separate adjacent OAM modes. This generalized transformation scheme may also find various applications in optical transformation and can be easily extended to other fields related to conformal mapping.

Generation, Transmission and Application of Orbital Angular Momentum in Optical Fiber: A Review

Optical orbital angular momentum (OAM) has become a hot research topic because of its unique properties due to its spiral distribution of phases. The production and transmission of OAM has also become a necessary condition for effective use of OAM. As an optical waveguide with good propagation properties, optical fibers are used in optical systems supporting OAM. This paper introduces the OAM generation and transmission system based on fiber, summarizes the current photonic crystal fiber, ring core fiber, fiber grating and other all-fiber systems that can support OAM modes, and explains some experimental principles. Finally, an outlook on OAM generation or transmission devices for all-fiber systems is presented, providing a useful reference for future related research.

Generation of higher-order orbital angular momentum modes and (de)multiplexing based on double-trench SOI waveguide

An ultracompact device, designed with two air-etched trenches embedded in two opposite corners of a silicon bus waveguide, for generation and (de)multiplexing optical orbital angular momentum (OAM) modes is proposed. The double-trench waveguide can generate OAM±1 and OAM±2 modes when the phase difference of two rotated orthogonal LP-like modes is equal to π/2 (or 3π/2). The operating principle and mode purity of the generated OAM modes are theoretically and systematically investigated. The simulation results show that the average purities of OAM±1 modes exceed 90%, and that of OAM±2 modes is greater than 80% over a wide wavelength range of 1.4–1.625 µm. Furthermore, an on-chip five-OAM-mode (de)multiplexer (OAM0, OAM±1, OAM±2) with a compact footprint of <200×4×4 µm3 is designed, whose main mode crosstalk is less than −20 dB. The presented OAM mode generator and (de)multiplexer are promising for applications like optical communications and quantum information processing.

Spectral self-imaging of optical orbital angular momentum modes

The Talbot self-imaging effect is mostly present in the forms of space or time, or in the frequency domain by the Fourier duality. Here, we disclose a new spectral Talbot effect arising in optical orbital angular momentum (OAM) modes. The effect occurs in the context of petal-like beams, which are typically constructed from a number of in-phase equidistant OAM modes with at least one void mode in between. When illuminating such beams on phase masks that are azimuthally modulated with Talbot phases, the initial OAM modes are self-imaged to create new OAM modes, meanwhile preserving the initial OAM spectral profile. Such a phenomenon is theoretically predicted, and a close analogy is drawn with the spectral Talbot effect of frequency combs. The prediction is also experimentally confirmed by observing versatile spectral self-imaging on various optical petal-like beams.

Ultra-dense perfect optical orbital angular momentum multiplexed holography.

Optical orbital angular momentum (OAM) has been recently implemented in holography technologies as an independent degree of freedom for boosting information capacity. However, the holography capacity and fidelity suffer from the limited space-bandwidth product (SBP) and the channel crosstalk, albeit the OAM mode set exploited as multiplexing channels is theoretically unbounded. Here, we propose the ultra-dense perfect OAM holography, in which the OAM modes are discriminated both radially and angularly. As such, the perfect OAM mode set constructs the two-dimensional spatial division multiplexed holography (conventional OAM holography is 1D). The extending degree of freedom enhances the holography capacity and fidelity. We have demonstrated an ultra-fine fractional OAM holography with the topological charge resolution of 0.01. A 20-digit OAM-encoded holography encryption has also been exhibited. It harnesses only five angular OAM topological charges ranging from -16 to +16. The SBP efficiency is about 20 times larger than the conventional phase-only OAM holography. This work paves the way to compact, high-security and high-capacity holography.

Preface

The 2021 2nd International Conference on Electrical, Electronic Information and Communication Engineering (EEICE 2021) was successfully held online through Zoom on April 16-18, 2021. Due to COVID-19 and the pandemic-related nationwide lockdowns and other coordinated restrictive measures, the organizers decided to hold a conference in a virtual format with the organization of access for all participants to the presented reports with comprehensive discussion for ensuring the event at a high scientific level.EEICE 2021 is to bring together innovative academics and industrial experts in the field of “Electrical”, “Electronic Information”, “Communication Engineering” and “Communication and Information System”, etc to a common forum. The primary goal of the conference is to promote research and developmental activities in “Electronic Information Technology”, “Communication Engineering” and another goal is to promote scientific information interchange between researchers, developers, engineers, students, and practitioners working all around the world.This scientific event brings together more than 125 national and international researchers in Electrical, Electronic Information and Communication Engineering. On top of the local participants coming from different national universities, international participants are also registered from different countries, namely Iran, Italy, Denmark and USA. During the conference, the conference model wasdivided into three sessions, including oral presentations, keynote speeches, and online Q&A discussion. In the first part, some scholars, whose submissions were selected as the excellent papers, were given about 5-10 minutes to perform their oral presentations one by one. Then in the second part, keynote speakers were each allocated 30-45 minutes to hold their speeches.In the second part, we invited four professors as our keynote speakers. Prof. WONG Hei, from Department of Electrical Engineering, City University of Hong Kong performed a speech: Device, System, and Application Prospectives of More Moore and More than Moore. This talk highlighted some of these issues with some personal remarks and prospective on the technology development in coming decades, in particular with 5G mobile technology to be introduced. And then we had Prof. Yang Yue from Institute of Modern Optics, Nankai University, China. He presented an insightful speech: Air-Core Ring Fiber Supporting Numerous Optical Orbital Angular Momentum Modes. Another two keynote speakers were Prof. Ting Yang, from School of Electrical and Information Engineering, Tianjin University, China and Prof. Wenli Shang, from School of Electronics and Communication Engineering, Guangzhou University, China. Their insightful speeches had triggered heated discussion in the third session of the conference. Every participant praised this conference for disseminating useful and insightful knowledge.The proceedings are a compilation of the accepted papers and represent an interesting outcome of the conference. Topics include but are not limited to the following areas: Electrical Engineering, Electronic Information, Communication Engineering and more related topics. All the papers have been through rigorous review and process to meet the requirements of International publication standard.We would like to acknowledge all of those who supported EEICE 2021. The help and contribution of each individual and institution was instrumental in the success of the conference. In particular, we would like to thank the organizing committee for its valuable inputs in shaping the conference program and reviewing the submitted papers.Committee of EEICE 2021Committee member, Conference Chairman, Organizing Committees, Technical Program Committees and this titles are available in this pdf.

High-Precise Fractional Orbital Angular Momentum Probing With a Fiber Grating Tip

Optical orbital angular momentum (OAM), carried by optical vortices, is a fundamental property of light that grabs broad interests. The detection of OAM modes, including fractional OAM is of great importance in diverse fields. Here, we firstly propose and develop the limited integer-component measurement method to determine the fractional topological charge (TC) of OAM states. This method indicates that a 2-integer-mode responsive device could be applied for the detection of fractional TC. An orthogonal long-period fiber grating (OLPFG) element is used as a fractional OAM TC probe to verify the Applicability. We experimentally demonstrate the fractional TC detection, ranging from −1 to 0, and recognize different fractional OAM modes with the minimum TC interval of 0.01. This scheme provides a concise, precise, continuous, and fiber-compatible fractional TC detection method that might have great potential in micro-detection, optical communication, quantum information, and chiral sensing applications.

On-chip enhanced electro-optic Kerr effect for manipulation of optical orbital angular momentum modes

The mode division multiplexing (MDM) technique using higher order orbital angular momentum (OAM) carrying modes through a channelized bandwidth provides enhanced capacity communication systems. Furthermore, encrypted channels via OAM based high-dimensional quantum key distribution (QKD) improve the transmission rate and security. In such applications, mode-selective manipulation of the spatially distributed (here, OAM) modes is a significant function to implement MDM and QKD networks. This paper proposes a novel versatile-designed chip which is configured in a Ycut periodically poled lithium niobate (PPLN) photonic wire. This integrated optical device acts as spatial mode converter for data modulated on higher order OAM = ±2ћ modes. The conversion is based on an enhanced electro-optic Kerr effect via phase-mismatched cascaded polarization coupling interactions of decomposed guided modes in two successive PPLN sections. The high-purity (91%) and low-voltage (<14.6 V) of the proposed device enable its operation in compatibility with applicable commercial modulators in OAM-based MDM and QKD systems.

Identification of optical orbital angular momentum modes with the Kerr nonlinearity of few-layer WS2

Optical vortex beams (VBs), a structured light possessing helical phase—front and carrying orbital angular momentum (OAM), have recently emerged as a promising perspective in optical manipulation, optical tweezer and optical communication. In this contribution, by taking advantage of the strong light–matter interaction, a nonlinear diffraction method is demonstrated to identify OAM modes. The nonlinear diffraction device (NDD) composed of WS2 nanosheets is employed to excite the optical Kerr nonlinear effect. Owing to the large Kerr coefficient of layered WS2, the spatial phase shift of VBs are readily regulated, resulting in controllable diffraction rings and tails, from which we can directly identify the magnitude and signs of OAM modes. The incident light intensity also expands the intensity distribution because the enhanced nonlinear phase shift will enlarge the diffraction rings, which provides an efficient way to identify the OAM and intensity of VBs simultaneously. It is anticipated that the optical nonlinearity might afford new opportunities for detecting structured lights and may have great potentials in designing all-optical OAM devices, etc.

Analysis of optical OAM mode conversion using elastic vortex wave in graded-index optical fiber

We theoretically analyze acousto-optic (AO) mode conversion between optical orbital angular momentum (OAM) modes using an elastic vortex wave (EVW) carrying OAM in a squared graded-index (GI) fiber. The AO mode conversion from the fundamental mode to the higher-order optical OAM mode is a useful technology to generate optical OAM modes in the GI fiber. This paper clarifies the contribution of each component of the dielectric constant perturbation caused by the EVW to the AO mode conversion.

Convolutional Neural Network-Assisted Optical Orbital Angular Momentum Recognition and Communication

The identification of orbital angular momentum (OAM) modes with high-accuracy and -speed is always a difficult issue in practically applying optical vortex beams (OVs). In this work, we propose and experimentally investigate a convolutional neural network (CNN) method for optical OAM mode identification and shift-keying (SK) communications. The CNN model, including convolution and pooling layers, was designed to extract mode information from the diffraction patterns produced by diffracting the OVs with a cylindrical lens. After trained with loads of studying samples, the CNN model has a good generation ability in recognizing the OAM modes of OVs ranging from −15 to 15. The recognition accuracy reaches 99% with the turbulence intensity of $C_{n}^{2} =1 \times 10^{-13}\,\,\text{m}^{-{2/3}}$ , $\Delta z=50$ m. Even under the turbulence of $C_{n}^{2} =1 \times 10^{-12}\,\,\text{m}^{-{2/3}}$ , $\Delta z=50$ m, the accuracy still exceeds 89%. By mapping and encoding a Lena gray image with the size of $100\times100$ pixels to two OAM channels, the OAM-SK signals with 900 modulation orders were successfully demodulated by the CNN model, and the image was well recovered after transmission. With an I5-8500 Central Processing Unit, this recognition process only takes $1\times 10^{-3}$ s per mode. It is anticipated that the CNN methods might provide an effective way for identifying OAM modes with high-accuracy and -speed, which may have great potentials in OAM communication, quantum information processing, and astronomical application, etc.

On-chip orbital angular momentum modes generator and (de)multiplexer based on trench silicon waveguides.

Based on an integrated silicon platform, we present an ultracompact structure to generate optical orbital angular momentum (OAM) modes, where only a waveguide with a specially designed trench is involved. Single-trench waveguide can support two orthogonal LP-like modes whose optical axes are rotated by around 45° with respect to the horizontal and vertical directions. By optimizing the structure parameters, OAM modes with topological charges of + 1 and -1 can be selectively generated by combining two orthogonal LP-like modes with different propagation constants. We study the structure parameters for both x- and y-polarizations over a wide wavelength range from 1.45 µm to 1.65 µm. The average mode purities are close to 90% for x- and y-polarizations. Moreover, we design an on-chip OAM modes (de)multiplexer (OAM0, OAM ± 1) for x-polarization based on trench silicon waveguides. It is shown that the mode extinction ratio can achieve approximately 20 dB from 1.52 µm to 1.58 µm.

Simple and Nondestructive On-Chip Detection of Optical Orbital Angular Momentum through a Single Plasmonic Nanohole

Optical orbital angular momentum (OAM) provides an additional dimension for photons to carry information in high-capacity optical communication. Although the practical needs have informed the generations of miniaturized devices to manipulate the OAM modes in various integrated platforms, it is still a challenge for on-chip OAM detection to match the newly developed compact OAM emitter and OAM transmission fiber. Here, we demonstrate an ultracompact device, i.e., a single plasmonic nanohole, to efficiently measure an optical beam’s OAM state in a simple and nondestructive way. The device size is reduced to a few hundreds of nanometers, which can be easily fabricated and installed in the current OAM devices. It is a flexible and robust way for in situ OAM monitoring and detection in optical fiber networks and long-distance optical communication systems. With proper optimization of the nanohole parameters, this approach could be further extended to discriminate the OAM information multiplexed in multiple wav...

Optical Orbital Angular Momentum Amplifier Based on an Air-Hole Erbium-Doped Fiber

We present for the first time broadband operation of an optical orbital angular momentum (OAM) erbium-doped fiber amplifier for lower order OAM modes based on an air-hole erbium-doped fiber designed and fabricated to provide significant mode splitting between the OAM │ l │ = 1 modes and the adjacent vector modes. Up to 15.7 dB gain is obtained using a cladding pumped amplifier configuration for OAM modes with topological charge │ l │ = 1 in the operational wavelength range 1545–1600 nm