Large-capacity Optical Communication Research Articles

Effective regulation of the interaction process among three optical solitons

Abstract The interaction between three optical solitons is a complex and valuable research direction, which is of practical application for promoting the development of optical communication and all-optical information processing technology. In this paper, we start from the study of the variable-coefficient coupled higher-order nonlinear Schrödinger equation (VCHNLSE), and obtain an analytical three-soliton solution of this equation. Based on the obtained solution, the interaction of the three optical solitons is explored when they are incident from different initial velocities and phases. When the higher-order dispersion and nonlinear functions are sinusoidal, hyperbolic secant, and hyperbolic tangent functions, the transmission properties of three optical solitons before and after interactions are discussed. Besides, this paper achieves effective regulation of amplitude and velocity of optical solitons as well as of the local state of interaction process, and interaction-free transmission of the three optical solitons is obtained with a small spacing. The relevant conclusions of the paper are of great significance in promoting the development of high-speed and large-capacity optical communication, optical signal processing, and optical computing.

Hybrid WDM/MDM (De) multiplexer based on Fabry–Perot resonators with Bragg grating reflectors

The traveling-wave-like Fabry–Perot (TW-like F-P) resonators, utilizing transverse-mode conversion, have been thoroughly investigated as on-chip filters. However, the asymmetric directional coupling (ADC) between the phase shifter and the output waveguide in this structure is not fully utilized, resulting in a rare implementation of hybrid wavelength division multiplexing (WDM) and mode division multiplexing (MDM). In this paper, using the transfer matrix method (TMM), we investigate methods to effectively enhance the quality factor (Q-factor) of TW-like F-P resonators. This is achieved by increasing the phase shifter length and reducing the coupling coefficient between these waveguides, without significantly impacting the channel drop efficiency. MDM can be achieved by adjusting the width of the output waveguides, utilizing the ADC between the phase shifter and the output waveguide. We design nine-channel hybrid WDM-MDM multiplexers based on TW-like F-P resonators. The variational-finite-difference time-domain (varFDTD) method is utilized to analyze the device’s performance, and its single channel extinction ratio (ER) values can reach −20dB. This work paves the way for TW-like F-P-resonator-based large capacity optical communications and interconnections.

Multi-Core Fiber Bragg Grating and Its Sensing Application.

With the increase in the demand for large-capacity optical communication capacity, multi-core optical fiber (MCF) communication technology has developed, and both the types of MCFs and related devices have become increasingly mature. The application of MCFs in the field of sensing has also received more and more attention, among which MCF fiber Bragg grating (FBG) devices have received more and more attention and have been widely used in various fields. In this paper, the main writing methods of MCF FBGs and their sensing applications are reviewed. The future development of the MCF FBG is also prospected.

Archimedes spiral optical vortex array emitter.

Optical vortex arrays (OVAs) are important for large-capacity optical communications, optical tweezers, and optical imaging. However, there is an urgent need to generate an optical vortex emitter to construct a specific OVA with a functional structure for the accurate transport of particles. To address this issue, we propose an Archimedes spiral OVA emitter that uses an Archimedes spiral parametric equation and coordinate localization techniques to dynamically regulate the position of each optical vortex. We discuss the phenomena of the location coordinates and Archimedes spiral from unclosed to closed on the OVA emitter. Furthermore, the propose of multiple OVA emitters demonstrates a chiral structure that has the potential for optical material processing. This study lays the foundation for generating OVAs with functional structures, which will facilitate advanced applications in the complex manipulation, separation, and transport of multiple particles.

Generation of arbitrarily structured optical vortex arrays based on the epicycle model.

Optical vortex arrays (OVAs) are complex light fields with versatile structures that have been widely studied in large-capacity optical communications, optical tweezers, and optical measurements. However, generating OVAs with arbitrary structures without explicit analytical expressions remains a challenge. To address this issue, we propose an alternative scheme for customizing OVAs with arbitrary structures using an epicycle model and vortex localization techniques. This method can accurately generate an OVA with an arbitrary structure by pre-designing the positions of each vortex. The influence of the number and coordinates of the locating points on customized OVAs is discussed. Finally, the structures of the OVA and each vortex are individually shaped into specifically formed fractal shapes by combining cross-phase techniques. This unique OVA will open up novel potential applications, such as the complex manipulation of multiparticle systems and optical communication based on optical angular momentum.

Wavelength-tunable Tm:Y2O3 ceramic vortex laser with a changeable orbital angular momentum state.

Wavelength-tunable orbital angular momentum (OAM) lasers with controllable topological charges have the potential for serving as light sources for large-capacity optical communication by combining conventional wavelength division multiplexing (WDM) with OAM mode-division multiplexing (OAM-MDM). In this study, we demonstrate a wavelength-tunable Tm-bulk laser that can control OAM states in the 2-µm spectral range. The excitation conditions for different Laguerre-Gaussian (L G 0,l ) modes in a bulk laser cavity are theoretically determined by measuring the spatial propagation dynamics of the annular pump beam. As a proof-of-principle study, we experimentally generate OAM states of |ℏ| and |2ℏ| from a T m:Y 2 O 3 ceramic laser with a tunable emission wavelength using a Lyot filter (LF). The spatial properties of the scalar optical vortices are well conserved during wavelength tuning, indicating the feasibility of our approach for producing wavelength-tunable structured light. These OAM laser sources, which are characterized by their robustness and compactness, have potential applications in various areas such as optical communications, quantum optics, super-resolution microscopes, and more.

Electro-optical modulator based on lithium niobate notched-ring plasmonic metasurface coated with electro-optical polymer

High speed and large capacity optical communication technology requires various optical devices, including optical modulators. Herein, an electro-optical (EO) modulator based on lithium niobate notched-ring plasmonic metasurface (LNPM) coated with EO polymer is demonstrated. The transmission and reflectance characteristics of the LNPM are simulated by finite element method (FEM), and the results show that the LNPM coated with EO polymer has resonant peaks at the operating wavelengths of 1.59 and 1.62 μm for the TM and TE polarized lights, respectively. The parameter optimizations indicate that the resonant peaks of the LNPM move towards higher frequency when the period (P) decreases or the notched-ring diameter (D) increases. The EO modulation performances show that the EO wavelength tuning (EOWT) of the HEOT-LNPM is 90 pm/V, and the maximum modulation depth (MD) is 17.5 dB with an extinction ratio (ER) of 20.2 dB. The LNPM coated with EO polymer provides a feasible EO modulation scheme for the optical communication, optical signal processing, and optical network links. Furthermore, it has promising applications in the fields of 5G communication, cloud computing, internet-of-ting, and artificial intelligence.

Flexible generation of broadly wavelength- and OAM-tunable Laguerre-Gaussian (LG) modes from a random fiber laser.

Broadband wavelength tunable Laguerre-Gaussian (LG) mode with flexibly manipulated topological charge is greatly desired for large-capacity optical communication. However, the operating wavelengths achieved for the current LG modes are significantly restricted either by the emission spectrum of the intracavity gain medium or by the operation wavelengths of mode-conversion or modulation components. Here, broadband wavelength-tunable LG modes with a controllable topological charge are generated based on a random fiber laser (RFL) and a digital micromirror device (DMD). The RFL can produce broadly wavelength-tunable laser emissions spanning from 1044 to 1403 nm with a high spectral purity and an excellent beam quality, benefiting from the cascaded random Raman gain starting from a ytterbium fiber based active gain. A commercially available broadband DMD is then utilized to excite the LG modes with a flexibly tunable topological charge of up to 100 order through the super-pixel wavefront shaping technique. The combination of the RFL and the DMD greatly broadens the operating wavelength region of the LG modes to be achieved, which facilitates the capacity scaling-up in the orbital angular momentum multiplexed optical communication application.

Mode division (de)multiplexer based on transverse mode conversion in photonic crystal using asymmetric directional couplers.

Mode division multiplexing technology has the potential to increase the channel capacity of a single wavelength carrier. Attaining cost-effective high-bandwidth-density devices with small footprints is a concern, and photonic crystal based devices are promising for ultra-small on-chip communications. This paper presents a 2D photonic crystal based mode division (de)multiplexer on a silicon on insulator platform. The device comprises two coupling regions of asymmetric directional couplers that perform mode conversion operations between the fundamental mode and higher-order modes. Each coupling section is dedicated to converting a specific mode. Mode conversion is achieved by designing a multimode waveguide to satisfy the phase-matching condition of the desired mode with the single mode waveguide. Two linear adiabatic tapers are introduced for the smooth transition of modes between waveguide sections. The device is designed and simulated for three-channel modes at 1550nm using the finite-difference time-domain technique. The obtained insertion loss and cross talk are <0.41d B and <-20.14d B, respectively. The overall size of the proposed mode division (de)multiplexer is 328.5µm 2. A fabrication tolerance study for the proposed device is performed by varying the rod radius and position in the device structure's taper and bus waveguide regions. The proposed 2D photonic crystal based mode division (de)multiplexer has the potential to be used in large-capacity optical communication systems.

High-order OAM states unwrapping in multiplexed optical links

To accurately unwrap the high-order orbital angular momentum (OAM) for multiplexed vortex beams is a challenge. In this work, over ±160 order OAM topological charges have been unwrapped in multiplexed optical links. Optical imaging based discrepancy identification enables the multiplexed OAM modes separating in physics, and the intelligent pattern recognition further promotes its unwrapping in numerical domain. Particularly, the combination of annular phase grating and auxiliary beams features compound spiral stripes, which paves the way for optical intensity recognition with low-complexity and high-commonality. Moreover, the spiral direction characterizes the symbol of the OAM states, which dramatically broadens the amount of multiplexed links. Here, optical separating means assisted by intelligent pattern recognition opens up a new route to high-speed and large-capacity optical communication, which may shed new light on 6G application.

Optical Logic Gates Excited by a Gauss Vortex Interference Beam Based on Spatial Self-Phase Modulation in 2D MoS2.

Vortex beams with optical orbital angular momentum have broad prospects in future high-speed and large-capacity optical communication. In this investigation of materials science, we found that low-dimensional materials have feasibility and reliability in the development of optical logic gates in all-optical signal processing and computing technology. We found that spatial self-phase modulation patterns through the MoS2 dispersions can be modulated by the initial intensity, phase, and topological charge of a Gauss vortex superposition interference beam. We utilized these three degrees of freedom as the input signals of the optical logic gate, and the intensity of a selected checkpoint on spatial self-phase modulation patterns as the output signal. By setting appropriate thresholds as logic codes 0 and 1, two sets of novel optical logic gates, including AND, OR, and NOT gates, were implemented. These optical logic gates are expected to have great potential in optical logic operations, all-optical networks, and all-optical signal processing.

Design and fabrication optimization of low-crosstalk silicon arrayed waveguide gratings with 32 channels and 100-GHz spacing

To satisfy the stringent requirements of large-capacity optical communication systems, the high-performance silicon arrayed waveguide gratings (AWG) with 32 wavelength channels and 100 GHz spacing are designed and fabricated. First of all, three types of arrayed waveguides are designed for seeking better performances, including rectangular-type, arc-type, and S-type ones. During fabrication, the taper connector is then introduced and the waveguide sidewall is further smoothed. Among the samples fabricated using E-beam lithography (EBL), the one with rectangular-type arrayed waveguides is characterized with better performance, showing a crosstalk of −14 dB and an insertion loss of 7.5 dB. Then, the target design with rectangle arrayed waveguides is further optimized and fabricated using 180-nm lithography platform for massive production. Outstanding results are achieved with an insertion loss of 4.5 dB, a channel uniformity of 0.95 dB, and a crosstalk as low as −20.4 dB, respectively. As far as we know, the AWGs might be the first compact silicon one fabricated by commercial lithography platform, characterized by comprehensive specifications (i.e., lowest crosstalk, highest channel uniformity, lowest insertion loss) for massive 100-GHz wavelength multiplexing/de-multiplexing.

60 nm Span Wavelength-Tunable Vortex Fiber Laser with Intracavity Plasmon Metasurfaces

Wavelength-tunable vortex fiber lasers that could generate beams carrying orbital angular momentum (OAM) hold great attention in large-capacity optical communications. The wavelength tunability of conventional vortex fiber lasers is, however, limited by a range of ∼35 nm due to narrow bandwidth and/or insertion loss of mode conversion components. Optical metasurfaces apart from being compact planar components can flexibly manipulate light with high efficiency in a broad wavelength range. Here, we propose and demonstrate for the first time, to the best of our knowledge, a metasurface-assisted vortex fiber laser that can directly generate OAM beams with customizable topological charges. Due to the designed broadband gap-surface plasmon metasurface, combined with an intracavity tunable filter, the laser enables an OAM beam with a center wavelength continuously tunable from 1015 to 1075 nm, nearly twice of other vortex fiber lasers ever reported. The metasurface can be designed at will to satisfy requirements for either low pump threshold or high slope efficiency of the laser. Furthermore, the cavity-metasurface configuration can be extended to generate higher-order OAM beams or more complex structured beams in different wavelength regions, which greatly broadens the possibilities for developing low-cost and high-quality structured-beam laser sources.

An integrated device for electro-optic modulation and dense wavelength division multiplexing based on photonic crystals

We proposed an integrated device for electro-optic (EO) modulation and dense wavelength division multiplexing (DWDM) based on photonic crystals (PhCs). The transmittance performance of the designed structure was modelled and analyzed according to the time-domain coupled mode theory (CMT), using three-dimensional finite-difference time-domain (3D-FDTD) method to calculate the parameters of the proposed device for verification. The numerical results show that the proposed integrated device can realize the functions of “on”, “off” modulation and DWDM with a channel spacing of 0.8 nm at the operating wavelengths of 1555 nm and 1554.2 nm. The minimum insertion loss, channel crosstalk and modulation voltage are 0.7 dB, − 29.04 dB and 0.88 V, respectively. The maximum extinction ratio and modulation speed are 21.51 dB and 29.4 GHz. The designed integrated device has the advantages of low loss, compact size (41.28μm×11.18μm), narrow channel spacing, large extinction ratio, which can be easily expanded the number of channels and used in highly integrated large-capacity optical communication systems and data center.

Editorial: Laser field manipulation and its advanced applications

Laser field manipulation is currently one of hot topics in the field of photonics. A wide variety of novel beams, for instance, vectorial vortex beams [1], orbital angular momentum (OAM) comb [2], toroidal vortices [3], high-dimensional beam arrays [4], can be well generated through tailoring various spatial and temporal degrees of freedom (DoFs) as OAM, spin angular momentum (SAM), phase, time/frequency, amplitude, and wave vector. Such novel beams from laser field manipulation have inspired lots of advanced applications covering classical and quantum physics as large-capacity optical communications, lidar, optical tweezer, laser processing, high-dimensional quantum entanglement, and also gravity wave detection [5]. In recent years, many efforts have been paid on laser field manipulation and achieve a leaping development. Hence, to show recent advances in laser field manipulation and their enabled applications, we organize this research topic, and expect to motivate more state-of-art scenarios.The seven published papers in this topic involve both fundamental and engineering research, regarding complex laser field tailoring and applications. M. Zhang et al. In summary, this research topic collects seven representative work of state-of-art laser field manipulation and its advanced applications. We expect this topic will build a bridge of distinct sub-areas integration, and further promote the development of laser field manipulation.

Multi-Level Phase Noise Model for CO-OFDM Spatial-Division Multiplexed Transmission

Spatial division multiplexed (SDM) transmission systems with coherence communication technology have become an important issue in meeting the demands for the capacity of fiber. However, research on the phase noise from lasers is mainly focused on single-channel systems or single-carrier SDM systems. In this paper, a phase noise model comprising common laser phase noise, in addition to the core phase drifts induced by the SDM, is introduced and analyzed for a coherence orthogonal frequency-division multiplexing (CO-OFDM) spatial-division multiplexed transmission (SDM) system. Based on the phase noise model, the applicability of the blind phase search algorithm and the pilot-aided phase estimation algorithm is discussed and demonstrated via simulation. The results show that these two algorithms can work well when considering combined laser linewidths with core phase drifts for CO-OFDM 7-core multi-core fiber (MCF). The results mean that with the SDM phase noise model, phase noise estimation in other cores can be transferred from one core to lower the complexity with the help of the model. This research provides a proper application of the phase noise analysis of large-capacity optical communication based on a weak-coupled MCF.

Adjusted EfficientNet for the diagnostic of orbital angular momentum spectrum.

Orbital angular momentum (OAM) is one of multiple dimensions of beams. A beam can carry multiple OAM components, and their intensity weights form the OAM spectrum. The OAM spectrum determines complex amplitude distributions of a beam and features unique characteristics. Thus, measuring the OAM spectrum is of great significance, especially for OAM-based applications. Here we employ a deep neural network combined with a phase-only diffraction optical element to measure the OAM spectrum. The diffraction optical element is designed to diffract incident beams into distinct patterns corresponding to OAM distributions. Then, the EfficientNet, a kind of deep neural network, is adjusted to adapt and analyze the diffraction pattern to calculate the OAM spectrum. The favorable experimental results show that our proposal can reconstruct the OAM spectra with high precision and speed, works well for different numbers of OAM channels, and is also robust to Gaussian noise and random zooming. This work opens a new, to the best of our knowledge, ability for OAM spectrum recognition and will find applications in a number of advanced domains including large capacity optical communications, quantum key distribution, optical trapping, rotation detection, and so on.

Quasi-bound states in the continuum-based switchable light-field manipulator

Nonlocal metasurfaces, which support a collective mode, can be applied to manipulate the wavefront within the narrow band spectrum and do not operate other wavelengths. However, once fabricated, the tunability of those meta-devices is still a challenge. Here, we demonstrated a switchable all-dielectric nonlocal metasurface based on quasi-bound states in the continuum controlled by symmetry breaking. This device realizes the spatial light beam manipulation in the narrow band with switchable resonant wavelengths in different environment dielectric. We designed a nonlocal metasurface for beam focusing with a tunable wavelength in the communication band. We also designed a nonlocal metasurface for the generation of non-diffraction Airy beams with tunable wavelength. These results will have potential applications in see-through display, large-capacity optical communications, nonlinear optics and imaging.

Off-axis pumped Tm:YLF vortex laser with continuously tunable wavelength

In this paper, HG mode conversion and etalon are used to achieve a 1.9 μm vortex beam output in a Tm:YLF laser while achieving a certain range of wavelength continuous tuning. In theory, the wavelength tuning characteristic and tuning capability of the etalon are analyzed. In the experiment, the HG1,0 mode laser is achieved by off-axis pump, and the optical field distribution and beam quality are relatively consistent with the theoretical state. After the HG1,0 mode laser passes through the π/2 mode converter, the LG1,0 vortex beam output is realized. The optical field distribution and beam quality of the vortex beam are relatively close to the theoretical state. The threshold of the laser at LG1,0 mode is 3.2 W, the slope efficiency is 37.7%, the optical–optical conversion efficiency is 34%, and a laser output of 8.6 W is obtained at the highest pump power of 25.3 W. On this basis, the continuous wavelength tuning of the LG1,0 mode vortex beam from 1937 nm to 1921 nm was achieved by rotating the etalon. Through comparison, it can be found that the optical field distribution and output power of each wavelength are relatively close during the wavelength tuning process. Finally, the topological charge of the vortex beam is measured by the interference of the vortex beam with the spherical wave and the plane wave. This article is of great significance for the further research of multi-dimensional tuning to realize large-capacity optical communication.

Image information transfer with petal-like beam lattices encoding/decoding

Orbital angular momentum (OAM) presents an additional degree of freedom for enhancing the information capacity in optical communications. To make full use of the OAM states, mode-division multiplexing (MDM) technology based on multiplexing multiple OAM modes has been adopted. However, numerous recent studies indicate that the recognition of multiplexed optical vortices is sensitive to the misalignment and requires complicated calculations, which severely restricts the decoding efficiency of a communication system. In this paper, a novel optical lattice that contains spatial positions and modes information is specially-designed and applied for short-haul free-space optical communications. Specifically, at the transmitter, the lattices with four different superposition modes (±1, ±2, ±3, ±4) and positions information are obtained and utilized to code the 8-bit length sequences into each 256-ary symbol. And at the receiver side, the initial information sequences can be decoded by directly identifying the captured intensity patterns (i.e., incoherent detection method). In the proof-of-concept experiment, a 64 × 64 pixel Lena gray image is successfully transmitted over a 3 m indoor optical communication link. The bit error among all received symbol sequences is evaluated, and zero bit error rate (BER) is observed, showing favorable link communication performance. Due to the mode and spatial paralleling, this work exhibits great potential in the future high-dimensional large capacity optical communications.