Advanced Optical Communication Research Articles

Diffraction-free orbital angular momentum holography

Holography offers significant potential for applications in information storage, encryption, beam-shaping, all-optical artificial intelligence, and three-dimensional displays. However, conventional holograms suffer from rapid image diffraction outside the target plane, resulting in low fidelity and detection challenges. Existing methods for generating diffraction-free beams are typically complex, inefficient, and lack Fourier transform capabilities. We propose a novel approach using an extended depth-of-focus (EDOF) flat lens to create diffraction-free holographic displays. We utilized an inverse-designed extended-depth-of-focus (EDOF) lens that achieves a depth-of-focus of 20 mm (>30,000 λ), which is 14 × greater than that of an equivalent conventional lens. This allows any incident field to be Fourier transformed and remain largely diffraction invariant over an extended depth-of-field, termed the extended spatial-frequency domain (ESFD). We further implement orbital angular momentum (OAM) as an information carrier, demonstrating diffraction-free OAM-encoded holographic images selectable by varying incident OAM modes with topological charges from −8 to 8 on a single device. We experimentally confirm that the diffraction-free OAM beam is able to self-heal in the presence of an occluder. Furthermore, we show that these beams preserve their information content after propagating through 80mm of dense fog, whereas conventional beams completely lose this information due to extreme scattering (attenuation factor of 20×). Our approach shows promising potential for high-security optical encryption, optical tweezers, and advanced optical communication systems.

Off-axis dispersion-managed metasurface for routing orbital angular momentum mode and wavelength multiplexing channels

Offering the strengths of mode orthogonality and physical independence from wavelength dimension, optical orbital angular momentum (OAM) modes hold immense potential for enhancing communication capacity through multi-dimensional channel multiplexing. Although methods using angle-separated gratings have seen advances in multi-dimensional (de)multiplexing, routing these multiplexed channels is impeded by the resultant mode-wavelength dispersion resulting from Bragg diffraction of grating. This induces not only multi-level mode conversion but also confined wavelength separation scope, posing obstacles in spatial reallocation of both OAM modes and wavelengths for routing channels. To tackle these issues, we propose a wavelength-dependent multi-foci transformation solution for OAM mode-wavelength routing that utilizes an off-axis dispersion-managed metasurface. Incorporated with composite lens phases and helical modulations, the metasurface enables the precise manipulation of OAM mode-wavelength dispersion upon multi-foci Fourier transform without multi-level diffraction, facilitating both efficient mode conversion and versatile wavelength separation. Harnessing the multi-dimensional independence, this approach establishes a high-dimensional linear mapping relationship among OAM modes, wavelengths, and spatial positions, thereby achieving the routing of mode-wavelength hybrid channels. In a proof-of-concept simulation, we demonstrated the successful routing of 20 channels with five OAM modes and four wavelengths across four depth planes, with the average channel crosstalk below -15.2 dB. Additionally, 16-ary quadrature amplitude modulation signals carried by these 20 multiplexed channels were successfully routed, and the bit-error-rates approach 1 × 10-5. Our method shows flexibility in spatial reallocation of both OAM modes and wavelengths, as further explored by altering the number of routing channels and their spatial positions, which may provide new insights for advanced OAM-based optical communications.

Examining the soliton solutions and characteristics analysis of fractional coupled nonlinear Shrödinger equations

The [Formula: see text]-dimensional fractional coupled nonlinear Schrödinger equations (FCNLSEs) are investigated in this work. This model is important as it involves applications in allowing soliton wavelength division multiplexing and pulse propagation in two-mode optical fibers. This means it is important for the study of the dynamics of solitons in dispersive, inhomogeneous, nonlinear media, and, therefore, it is a tool of prime value for the development of advanced optical communication technologies. Beta space-time fractional derivative, which is important in dielectric polarization and electromagnetic systems, is used to evaluate the FCNLSE. We capitalize a modified version of the Sardar sub-equation method for the purpose of getting different soliton solutions. Solutions take the form of optical solitons, including dark, bright, periodic, peakons, compactons, and kink soliton solutions, formulated using exponential, trigonometric, and hyperbolic functions. To make our understanding of the physical meaning of these solutions richer, we apply advanced plotting techniques, examples of which are the three-dimensional (3D), two-dimensional (2D), contour, and density plots. Such plots provide a colorful overview of the dynamic behavior of the solutions obtained. The solutions do not only pinpoint the fact that the result is an effective and accurate method application, but they also set a high standard in further probing meaning in the numerous physical phenomena. These new solutions go beyond earlier studies in the literature by incorporating beta derivatives as a modeling tool for FCNLSE. The methodology applied here functions seamlessly and can be extended to address numerous advanced models in contemporary areas of science and engineering. The anticipated usefulness of the derived solutions in various scientific domains, particularly optics, is expected to make a valuable contribution to the fiber communication system in future research endeavors.

Phosphor-converted light-emitting diodes in the marine environment: current status and future trends.

The exploitation and utilization of resources in marine environments have ignited a demand for advanced illumination and optical communication technologies. Light-emitting diodes (LEDs), heralded as "green lighting sources", offer a compelling solution to the technical challenges of marine exploration due to their inherent advantages. Among the myriad of LED technologies, phosphor-converted light-emitting diodes (pc-LEDs) have emerged as frontrunners in marine applications. At the heart of pc-LEDs lie phosphor materials, colour-converters that orchestrate the emission of light. In the marine environment, blue-green light with a wavelength of 440-570 nm exhibits the deepest penetration depth, while other wavelengths are rapidly attenuated in the shallow layer. Additionally, specific wavelengths of light are crucial for particular applications. However, the moist marine environment as well as the demand for continuous and stable lighting pose a formidable challenge to the environmental stability of the phosphors. Therefore, developing blue-green phosphors with exceptional colour purity and high thermal and moisture stability is paramount for marine applications. Herein, this review delves into the application of LED and pc-LED technology in underwater optical communication and marine fishery, exploring the development strategies of phosphors tailored for the marine environment. The insights presented serve as a valuable reference for further research on phosphors and pc-LED devices.

Performance evaluation of Hard-Isolated GPONs using regular perturbation methods

Abstract In this study, we conduct a detailed performance evaluation of hard-isolated Gigabit Passive Optical Networks (GPONs) using Regular Perturbation (RP) methods. The Nonlinear Schrodinger Equation (NLSE) is utilized to model signal propagation in optical fibers, capturing the effects of nonlinearities and dispersion. By applying RP techniques, we derive approximate solutions to the NLSE, offering a more manageable approach for performance analysis in highly nonlinear regimes. Key performance metrics such as Normalized Squared Deviation (NSD), Bit-Error Rate (BER), and Achievable Information Rates (AIR) are analyzed to validate the accuracy and efficiency of the RP models. Simulation results demonstrate that the RP method provides good accuracy in modeling nonlinear effects, particularly at lower input power levels. Additionally, the study investigates the impact of hard isolation on mitigating nonlinearities, showing significant benefits in maintaining signal integrity and reducing BER. The findings highlight the potential of RP methods as robust tools for performance evaluation and optimization in advanced optical communication systems.

Deep learning techniques for quality of transmission estimation in optical networks

A large body of research has recently examined the estimation of the quality of transmission (QoT) in optical networks with deep learning. This paper discusses a lightpath’s quality of transmission to design fiber-optic communication and networks using deep learning algorithms. We need different major estimation parameters for advanced optical fiber communication and networks, i.e., modulation formats, baud rate, and code rate. Currently, the quality of transmission for unspecified optical paths depends on different estimation techniques i.e., (1) analytical models estimating physical layer impairments (PLIs) and (2) margined formulas. This paper focuses on deep-learning techniques that can be applied to optimization and complex systems. The deep learning algorithms contain different classifiers that can simulate results and estimate the bit-error rate, and signal-to-noise ratio of unspecified optical paths with threshold values, traffic volume, and modulation format. We must train and test the datasets for various classifiers, and classification features using Korean network topology. The classifier accuracy and Area Under the ROC Curve (AUC) simulation results are carried out using MATLAB.

Investigation of optical soliton solutions for the cubic-quartic derivative nonlinear Schrödinger equation using advanced integration techniques

This paper aims to investigate optical soliton solutions in the context of the cubic-quartic derivative nonlinear Schrödinger equation with differential group delay, incorporating perturbation terms for the first time. Motivated by the need to better understand soliton dynamics in advanced optical communication systems, we employ three integration techniques: the direct algebraic approach, Kudryashov’s method with an addendum, and the unified Riccati equation expansion method. Our study reveals that, by appropriately selecting parameter values, the resulting solutions include Jacobi elliptic functions that describe straddle solitons, bright, dark, and singular solitons. We also identify the conditions under which these soliton pulses can exist. Furthermore, we provide numerical simulations to illustrate these solutions under specific parameter settings, highlighting their potential applications in optical fiber systems.

Telecom-band multiwavelength vertical emitting quantum well nanowire laser arrays

Highly integrated optoelectronic and photonic systems underpin the development of next-generation advanced optical and quantum communication technologies, which require compact, multiwavelength laser sources at the telecom band. Here, we report on-substrate vertical emitting lasing from ordered InGaAs/InP multi-quantum well core–shell nanowire array epitaxially grown on InP substrate by selective area epitaxy. To reduce optical loss and tailor the cavity mode, a new nanowire facet engineering approach has been developed to achieve controlled quantum well nanowire dimensions with uniform morphology and high crystal quality. Owing to the strong quantum confinement effect of InGaAs quantum wells and the successful formation of a vertical Fabry–Pérot cavity between the top nanowire facet and bottom nanowire/SiO2 mask interface, stimulated emissions of the EH11a/b mode from single vertical nanowires from an on-substrate nanowire array have been demonstrated with a lasing threshold of ~28.2 μJ cm−2 per pulse and a high characteristic temperature of ~128 K. By fine-tuning the In composition of the quantum wells, room temperature, single-mode lasing is achieved in the vertical direction across a broad near-infrared spectral range, spanning from 940 nm to the telecommunication O and C bands. Our research indicates that through a carefully designed facet engineering strategy, highly ordered, uniform nanowire arrays with precise dimension control can be achieved to simultaneously deliver thousands of nanolasers with multiple wavelengths on the same substrate, paving a promising and scalable pathway towards future advanced optoelectronic and photonic systems.

Design of 16-wavelength high-power heterogeneous III-V/Si laser arrays with varying stripe width and grating period

Multi-wavelength laser array is currently one of the most attractive technologies to provide high density links for advanced optical communications and computing. The conventional scheme of varying grating period is almost impossible to achieve 8-wavelength or more. And, the optical output power of heterogeneously integrated quantum dot laser can hardly meet the commercial demand. In this paper, we report a 16-wavelength high-power heterogeneously integrated quantum dot distributed feedback laser array. To the best of our knowledge, this is the first heterogeneously integrated quantum dot laser array that tunes the lasing wavelength by combining the scheme of varying the stripe width and grating period of laser units. The effective refractive index of gratings is calculated by eigenmode expansion method. When the grating period is fixed at 198 nm, and the stripe widths of laser units are 2.00 μm, 2.25 μm, 2.60 μm and 3.15 μm, respectively, the corresponding lasing wavelengths are 1307.94 nm, 1308.49 nm, 1309.06 nm and 1309.63 nm, respectively, and the wavelength spacing of the adjacent laser units is about 100 GHz. By additionally adjusting the grating period between 196 nm and 202 nm with 2 nm spacing of grating period, a 16-wavelength QD DFB laser array is designed with the wavelength range from 1294.73 nm to 1336.09 nm. In addition, asymmetric distributed feedback grating is adopted to improve the optical output power at the front-end of laser arrays. The maximum ratio of the output power at the both end of laser units is 19.6 when the grating duty cycles of the front-end and the back-end of the λ/4 phase-shift is 0.7 and 0.5, respectively, and the grating lengths is 250 μm and 450 μm, respectively. This work will promote the performance improvement of heterogeneously integrated quantum dot lasers and develop the quantum dot lasers towards multi-wavelength.

Optical mode manipulation using deep spatial diffractive neural networks

In this paper, we investigate the theoretical models and potential applications of spatial diffractive neural network (SDNN) structures, with a particular focus on mode manipulation. Our research introduces a novel diffractive transmission simulation method that employs matrix multiplication, alongside a parameter optimization algorithm based on neural network gradient descent. This approach facilitates a comprehensive understanding of the light field manipulation capabilities inherent to SDNNs. We extend our investigation to parameter optimization for SDNNs of various scales. We achieve the demultiplexing of 5, 11 and 100 orthogonal orbital angular momentum (OAM) modes using neural networks with 4, 10 and 50 layers, respectively. Notably, the optimized 100 OAM mode demultiplexer shows an average loss of 0.52 dB, a maximum loss of 0.62 dB, and a maximum crosstalk of -28.24 dB. Further exploring the potential of SDNNs, we optimize a 10-layer structure for mode conversion applications. This optimization enables conversions from Hermite-Gaussian (HG) to Laguerre-Gaussian (LG) modes, as well as from HG to OAM modes, showing the versatility of SDNNs in mode manipulation. We propose an innovative assembly of SDNNs on a glass substrate integrated with photonic devices. A 10-layer diffractive neural network, with a size of 49 mm × 7 mm × 7 mm, effectively demultiplexes 11 orthogonal OAM modes with minimal loss and crosstalk. Similarly, a 20-layer diffractive neural network, with a size of 67 mm × 7 mm × 7 mm, serves as a highly efficient 25-channel OAM to HG mode converter, showing the potential of SDNNs in advanced optical communications.

20 Watt single-frequency 509 nm laser by single-pass second harmonic generation in an LBO crystal

High power 509 nm continuous-wave (CW) lasers have important applications in science and communication. Here we demonstrate a robust high-power single-frequency 509 nm laser system based on nonlinear phase demodulation technique and single-pass second harmonic generation (SHG) configuration. In experiments, the single-frequency fundamental wave at 1018 nm was linewidth-broadened by an electro-optical modulator and then amplified to 207 W in a ytterbium-doped fiber amplifier. In subsequent single-pass SHG stage, over 20 W CW single-frequency 509 nm laser was generated in a LiB3O5 crystal with a SHG efficiency of 9.7%. To the best of our knowledge, this is the highest reported power for CW single-frequency 509 nm laser, which could be used for advanced underwater optical communication and preparation of cesium Rydberg state.

Thermal stress simulation analysis of aerospace optical fibers and connectors and related extensions to high-speed railway area

Aerospace optical cables and fiber-optic connectors have numerous advantages (e.g., low loss, wide transmission frequency band, large capacity, light weight, and excellent resistance to electromagnetic interference). They can achieve optical communication interconnections and high-speed bidirectional data transmission between optical terminals and photodetectors in space, ensuring the stability and reliability of data transmission during spacecraft operations in orbit. They have become essential components in high-speed networking and optically interconnected communications for spacecrafts. Thermal stress simulation analysis is important for evaluating the temperature stress concentration phenomenon resulting from temperature fluctuations, temperature gradients, and other factors in aerospace optical cables and connectors under the combined effects of extreme temperatures and vacuum environments. Considering this, advanced optical communication technology has been widely used in high-speed railway communication networks to transmit safe, stable and reliable signals, as high-speed railway optical communication in special areas with extreme climates, such as cold and high-temperature regions, requires high-reliability optical cables and connectors. Therefore, based on the finite element method, comprehensive comparisons were made between the thermal distributions of aerospace optical cables and J599III fiber optic connectors under different conditions, providing a theoretical basis for evaluating the performance of aerospace optical cables and connectors in space environments and meanwhile building a technical foundation for potential optical communication applications in the field of high-speed railways.

Rapidly Grown Hexagonal Organic Microtubes Using Ionic Liquids for an Enhanced Optical Waveguide Effect

AbstractAn optical waveguide that transmits the electromagnetic waves is a critical component for various optoelectrical applications including integrated optical circuits and optical communications. Among many, the 1D tubular optical waveguide structure enables efficient distant energy transfer via mode selection within the optical microcavity. However, its application is limited due to the complicated fabrication process. Herein, hexagonal tris(8‐hydroxyquinoline) aluminum (Alq3) microtubes with an average longitudinal length of ≈15 µm are self‐assembled within few minutes by utilizing 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIMBF4) ionic liquids. The swift fabrication is enabled by the high electron affinity of BMIMBF4 that forms hexagonal microrods. Also, BMIMBF4 ionic liquid etches the central region of micorods during its growth, forming microtubes with a wall thickness of ≈650 nm. The fabricated Alq3 microtubes show significantly improved waveguide characteristics with reduced optical loss coefficient (0.054 µm−1) compared to that of microrods (0.271 µm−1). The demonstrated method to fabricate Alq3 microtubes with ionic liquid is an efficient approach to utilize organic microstructures as an optoelectrical components for advanced optical communications.

Broadband wavelength conversion in Si-rich silicon nitride waveguides based on intermodal four-wave mixing

All-optical wavelength converters and frequency synthesizers represent essential components for the development of advanced and reconfigurable optical communications systems. In this respect, the exploitation of intermodal nonlinear processes in integrated multimode waveguides has received significant attention in recent years for all-optical processing applications. Here, we discuss our recent results on the realization of fully-integrated and broadband wavelength converters utilizing the Bragg scattering intermodal four-wave mixing nonlinear process in a silicon-rich silicon nitride platform.

Sb2S3-based optical switch exploiting the Brewster angle phenomenon [Invited

Optical switches based on phase change materials (PCMs) hold great promise for various photonic applications such as telecommunications, data communication, optical interconnects, and signal processing. Their non-volatile nature as well as rapid switching speeds make them highly desirable for developing advanced and energy-efficient optical communication technologies. Ongoing research efforts in exploring new PCMs, optimizing device designs, and overcoming existing challenges are driving the development of innovative and high-performance optical switches for the next generation of photonics applications. In this study, we design and experimentally demonstrate a novel optical amplitude switch design incorporating PCM antimony trisulfide (Sb2S3) based on the Brewster angle phenomenon.

Vertical Emitting Nanowire Vector Beam Lasers.

Due to the peculiar structured light field with spatially variant polarizations on the same wavefront, vector beams (VBs) have sparked research enthusiasm in developing advanced super-resolution imaging and optical communications techniques. A compact VB nanolaser is intriguing for VB applications in miniaturized photonic integrated circuits. However, determined by the diffraction limit of light, it is a challenge to realize a VB nanolaser in the subwavelength scale because the VB lasing modes should have laterally structured distributions. Here, we demonstrate a VB nanolaser made from a 300 nm thick InGaAs/GaAs nanowire (NW). To select the high-order VB lasing mode, a standing NW as-grown from the selective-area-epitaxial (SAE) growth process is utilized, which has a bottom donut-shaped interface with the silicon oxide growth substrate. With this donut-shaped interface as one of the reflective mirrors of the nanolaser cavity, the VB lasing mode has the lowest threshold. Experimentally, a single-mode VB lasing mode with a donut-shaped amplitude and azimuthally cylindrical polarization distribution is obtained. Together with the high yield and uniformity of the SAE-grown NWs, our work provides a straightforward and scalable path toward cost-effective co-integration of VB nanolasers on potential photonic integrated circuits.

Giant enhancement of the Goos–Hänchen shift assisted by merging bound states in the continuum

Bound states in the continuum (BICs) have received considerable attention in the field of nanophotonics due to their highly confined resonance and high Q factor, which effectively eliminates radiation loss. Various periodic structures have been studied to achieve BICs, with photonic crystal slabs (PCSs) being a prominent example. In PCS, multiple BICs can be merged to strongly suppress out-of-plane-scattering losses caused by fabrication imperfections. In this paper, we investigate the impact of reflection-type merging BICs on the Goos–Hänchen shift (GH shift) and demonstrate a remarkable enhancement of the GH shift, exceeding five orders of wavelength. We show the dynamic changes of the GH shifts with the isolated, merging, and merged BICs, achieving positive and negative GH shifts in different angles of peak reflectance for the same frequency. Our research highlights that even minor fabrication imperfections can result in a significant change in the GH shift, which can serve as a means for detecting manufacturing defects. Furthermore, we propose an ultrasensitive environmental refractive index sensor based on the enhanced GH shift by an isolated BIC. Our study contributes to the understanding of BICs and their potential applications in nanophotonics, including advanced optical communication devices, nanodevice fabrication, and highly sensitive sensors.

Injection-locked highly Yb3+-doped uncoupled-61-core phosphate fiber laser.

Uncoupled multicore fibers are promising platforms for advanced optical communications, optical computing, and novel laser systems. In this paper, an injection-locked highly ytterbium (Yb3+)-doped uncoupled-61-core phosphate fiber laser at 1030 nm is reported. The 61-core fiber with a core-to-core pitch of 20 μm was fabricated with the stack-and-draw technique. Each core doped with 6-wt.% Yb3+ ions has a diameter of 3 μm and numerical aperture of 0.2. Linearly polarized single-frequency output of 9.1 W was obtained from the injection-locked cavity with a 10-cm-long gain fiber at a pump power of 23.6 W. The injection locking of all 61 cores was confirmed by inspecting the longitudinal modes of the individual lasers with a scanning Fabry-Perot interferometer. The performance of the injection-locked 61-core fiber laser was characterized and compared to that of the free-running operation in terms of optical spectrum, near- and far-field intensity profiles, and relative intensity noise.

Assessment of quality of signal transmission process in focs with DWDM

The power of a group DWDM signal increases nonlinear interference in the optical path, especially the value of the interference of the FWM. These interfering factors degrade signal transmission quality and can completely disable the WDM system. Therefore, when designing a DWDM system, it is necessary to optimize the power of the transmitted signal to minimize the probability of error in the optical channel. The article presents the research results and analysis of factors affecting the quality of fiber-optic communication systems with wave separation of channels. Selecting the optimal power level of the group signal and evaluating the transmission quality of optical communication channels in WDM allows us to solve the problem of science-based design, implementation, and effective operation of advanced optical communication systems with wave division of channels.

(INVITED) Bi-doped optical fibers and fiber amplifiers

Bismuth (Bi)-doped aluminosilicate, phosphosilicate, germanosilicate and high (⩾50 mol%) germanosilicate fibers have shown luminescence around 1.15 μm, 1.3 μm, 1.45 μm and 1.7 μm, respectively. Bi-doped fibers have paved the way for developing optical amplifiers and fiber lasers in the wavelength region of 1150–1500 nm and 1600–1700 nm, where it can serve a wide range of applications in astronomy, imaging, medicine and advanced optical communications. However, spectroscopic study is required to understand the nature of near-infrared (NIR)-emitting Bi active centers (BACs) to improve the efficiency of Bi-doped fiber amplifiers and lasers. In this paper, we review the luminescence properties of Bi-doped glasses as well as Bi-doped fibers with aluminosilicate, phosphosilicate, and germanosilicate glass hosts. Absorption and emission cross-sections of Bi-doped phosphosilicate fibers are reported. In addition, we review the current state of the art of Bi-doped fiber amplifiers development in the second telecom window (O-band) and in the E-band and S-band for the next-generation high-capacity optical communications.