Optical Communication Research Articles

Experimental Demonstration and Practical Application of a Real-Time Full-Duplex Underwater Wireless Optical Communication Transceiver

Experimental Demonstration and Practical Application of a Real-Time Full-Duplex Underwater Wireless Optical Communication Transceiver

Modulation of Bessel-like vector vortex beam using the resonant magneto-optical effect in rubidium vapor

Abstract The Bessel-like vector vortex beam (BlVVB) has gained increasing significance across numerous applications. However, its practical application is restricted by manufacturing difficulties and polarization manipulation. Thus, the ability to manipulate its degrees of freedom is highly desirable. In this paper, the full-domain polarization modulation of BlVVB within a hot atomic ensemble has been investigated. We begin with the theoretical analysis of the resonant magneto-optical effect of atoms with a horizontal linear polarized beam and experimentally demonstrate precise manipulation of the polarization state across the entire domain of the BlVVB, achieving an error margin of less than 3° at various cross-sectional points. Our study provides a novel approach for the modulation of BlVVB based on atomic media, which holds potential applications in sensitive vector magnetometers, optical communications, and signal processing.

Design and analysis of 2D photonic crystals based all optical logic gates

Abstract All-optical basic logic gates play a pivotal role in the development of ultra-fast and energy-efficient computing systems. In this communication, we have designed an alternative method of all-optical logic OR, AND, XOR, and XNOR gates using 2-dimensional photonic crystals with a hexagonal lattice structure. The OptiFDTD software and finite-difference time-domain (FDTD) method has been used to verify the proposed designs and analyzed by calculating the contrast ratio and bit rate. The contrast ratios of the OR, AND, XOR, and XNOR gates are 43.20 dB, 36.40 dB, 41.46 dB and 37.63 dB, respectively. The output of the proposed logic gates may efficiently enhance the optical communication system.

Ultra‐Large Bandwidth and Ultra‐High Sensitivity Germanium/Silicon Avalanche Photodiode

AbstractGermanium/silicon (Ge/Si) avalanche photodiode (APD) has emerged as a highly desirable component for optical communication, sensing, and computing, attributed to its inherent gain. Conventional schemes typically suffer from limited bandwidth and significant excess noise due to the high gain, restricting the high‐sensitivity detection in burgeoning high‐speed applications. Here, a Ge/Si APD is developed with an ultra‐large bandwidth at an optimal gain. This breakthrough is achieved by implementing an extremely narrow multiplication layer to enhance the space charge effect, overcoming the intrinsic bandwidth limitation in conventional APDs while elaborately harnessing the gain to a moderate value to ensure the optimal sensitivity. The device possesses a bandwidth of 67 GHz at an optimal gain of 6.6 and enables data reception of 240 Gb s−1 four‐level pulse amplitude modulation signal—the largest bandwidth and highest single‐channel bitrate among all reported APDs. The presented APD suggests promising applications for high‐speed and high‐sensitivity data communication owing to its competitive performance, cost‐effectiveness, and high‐yield production.

31W Linear broadband 3.4 to 4.4 GHZ high power class-j GaN HEMT amplifier

The recent upsurge in wireless communication systems requiring high-power transmitters for numerous applications such as electronic warfare (EW), RADAR, Satellite and optical communications has further underscored the importance of linear broadband high-power Class-J power amplifiers. This paper proposes a 31W linear broadband 3.4 to 4.4 GHz high-power Class-J GaN HEMT(gallium nitride high electron mobility transistor)amplifier. The power amplifier was designed based on Cree's commercially available 10WGaN HEMT power transistor device (CGHV40010F) using Keysight Advanced Design System (ADS) software and simulated. The transistor was biased withadrain supply voltage of 48V at aquiescent drain-to-source current of 0.58A,which makes the power transistor suitable for high voltage transmitter operations and foreclosed the need for voltage upgrade, thereby reducing thecost of operation. The power amplifier (PA) operates from 3.4 to 4.4 GHz with a centre frequency of 3.9 GHz. The PA has an output power of 31W, drain efficiency of 36.3%, power added efficiency of 35.3% and power gain of 12.9 dB at an input power of 32 dBm. The PA small signal gain stood at 10.6 dB at acentre frequency of 3.9 GHz. The PA maintained a peak envelope power of 56.2W at aninput power of 31 dBm at atwo-tone Frequency of 3.895 GHz. The proposed PA will find applications in wireless communications, military and aviation transmitters.

Numerical Approaches in Nonlinear Fourier Transform‐Based Signal Processing for Telecommunications

ABSTRACTWe discuss applications of the inverse scattering transform, also known as the nonlinear Fourier transform (NFT) in telecommunications, both for nonlinear optical fiber communication channel equalization and time‐domain signal processing techniques. Our main focus is on the challenges and recent progress in the development of efficient numerical algorithms and approaches to NFT implementation.

From Theory to Practice: Implementing Meta-Learning in 6G Wireless Infrastructure

The vision of the sixth generation of communication systems, commonly known as 6G, entails a connected world that provides ubiquitous connectivity and fosters the digital transformation of society. As the number of devices, services, and users continues to grow, intelligent solutions are expected to facilitate this transformation. This paper considers meta-learning as a pivotal paradigm for 6G systems, detailing its principles, algorithms, and theoretical underpinnings. The methodology involves integrating meta-learning with three potential 6G technologies: RF-based communication systems, optical communication systems, and molecular communication systems. The findings reveal the distinct characteristics of these technologies and demonstrate the potential benefits and challenges of incorporating meta-learning algorithms. Practical implications highlight how meta-learning can enhance the efficiency and adaptability of 6G systems, addressing the growing demand for intelligent and seamless communication networks.

Fabrication of broadband-emissive micro/nanostructures using two-photon lithography.

The development of broadband emissive micro/nanoscale structures has enabled unprecedented opportunities to innovate multifunctional devices with applications in lighting, display, sensing, biomedical, photovoltaics, and optical communication. Realization of these micro/nanostructures require multi-step processing, and depends on sophisticated, complex, time-consuming, expensive, and conventional nanofabrication techniques such as mask-based photolithography, electron beam lithography, reactive ion etching. Precise control over z-axis features with a subwavelength resolution for the fabrication of 3D features is a challenge using these methods. Thus, the traditional methods often fall short of meeting these requirements simultaneously. Fabrication of emissive structures demand techniques that offer material compatibility, high resolution, and structural complexity. Here, we report single-step fabrication of 1D, 2D, and 3D broadband emissive micro/nanostructures using two-photon lithography (TPL). The broadband emissive resin used for fabricating these structures is made by combining synthesized functionalized carbon quantum dots (CQDs) with a commercially available acrylate-based resin. The resulting structures demonstrate excellent broadband emissive properties in the visible range under UV-Vis excitation.We have observed consistent emission across the fabricated structures along with good thermal and optical stability. Furthermore, we can tune the emission properties of the micro/nanostructures by modifying the functionalization/doping of the quantum dots. These micro/nanostructures have the potential to be used as fundamental components in photonics, particularly in the fields of biophotonics, sensing, and optoelectronics, and could drive new innovations in these areas.

Carbon Dots with Charge Storage Ability Promote the Red Emission of TFB via Carrier Secondary Injection.

Dual-emission light-emitting diodes (DEDs) have great promising applications in medical imaging, optical communication, data storage, and three-dimensional display. The precise material design and advanced packaging technology for the construction of DEDs are still key challenges for practical application. We demonstrate a straightforward strategy to construct DEDs that deviates from traditional approaches, utilizing commercially available luminescent material of poly(9,9-dioctylfluorene-co-N-(4-(3-methylpropyl))diphenylamine) (TFB) and carbon dots (CDs). In the DEDs, the mixture of CDs and TFB was used as the luminescent layer, which exhibits dual-wavelength emission located at 436 and 632 nm, respectively. Notably, the CDs, with charge storage ability, can store the interfacial charges, reinject the carriers into TFB, and then facilitate the long-wavelength (632 nm) emission from TFB. This work provides a new way for the design and construction of fresh DEDs through the CD-based interfacial charge transport process.

Silicon-based three-dimensional waveguide mode switch based on phase change material

The mode division multiplexing (MDM) technology can transmit multiple modes simultaneously in a few-mode fiber or waveguide, which can effectively improve the data transmission capacity in the process of optical communication. In this paper, we report a silicon-based three-dimensional waveguide mode switch based on phase change material (PCM), which uses a two asymmetric directional couplers (ADCs) structure. The two ADCs use a common few-mode waveguide as the underlying bus waveguide, and the upper layer is composed of two different single-mode waveguides covered with a thin PCM as the access waveguides. By using this structure and changing the crystal phase of the PCM, it is possible to achieve mode switching between the mode TE11 to TE21 and the mode TE11 to TE12. The designed 3D mode switch has excess losses <2.64dB and crosstalk <−15.4dB in the operating wavelength of 1500–1600 nm.

Single-longitudinal mode quadruple wavelength C+L-band erbium-doped fiber laser based on the pairs of reflective fiber bragg gratings

Abstract Flatness of lasing wavelengths of a multi-wavelength fiber laser (MWFL) is an important design constraint that is considered attractive in various applications of photonics and optical communication systems. In this work, we propose a single-longitudinal mode (SLM) quadruple wavelength C+L-band Erbium-doped fiber laser (EDFL) with high output power flatness. It is implemented with a short piece of Erbium-doped fiber (EDF) pumped by conventional 980 nm laser diode and four pairs of reflective fiber Bragg gratings (FBGs) through numerical simulations. The reflectivities of FBGs are adjusted such that SLM quadruple wavelengths are obtained at the output of EDFL with flatness of 0.9 dB, optical signal-to-noise ratio (OSNR) in the range of 44.5–53.2 dB, and linewidths (LWs) in the range of 5.4–7.3 MHz. Slope efficiency (SE) of around 24% is achieved considering the total power of all lasing wavelengths generated. Moreover, the power variation around 0.1 dB for lasing wavelengths of 1540.2 nm and 1605.7 nm is noticed for twelve iterations each repeating after five-minute interval. The proposed SLM quadruple wavelength EDFL has promising application prospects for distributed sensing and optical communication systems due to excellent performance metrics.

Coupling efficiency of electromagnetic hermite non-uniformly correlated beams into a single-mode fiber in a turbulent atmosphere

We present a theoretical formula to analyze a single-mode fiber coupling efficiency of electromagnetic hermite non-uniformly correlated (EMHNUC) beams propagating through the turbulent atmosphere and investigate the effects of initial beam parameters, including the beam width, coherence length, beam order, and ratio of field amplitude on fiber-coupling efficiency. We find that a single-mode fiber coupling efficiency initially decreases, increases sharply to the maximum value, and gradually decreases after a long propagation distance. This behavior is attributed to the co-work of the characteristics of such vector non-uniform correlated structural beam and their diffraction broadening in atmospheric turbulence. Adjusting beam parameters can effectively improve the single-mode fiber-coupling efficiency. Our results will benefit the fiber-coupling systems in free-space optical communication.

Dynamic Control of Airy Beams Using Real-Time Phase-Amplitude Encoding on a Spatial Light Modulator

Airy beams showing curved paths have found extensive applications in fields such as optical trapping, biomedical analysis, and material processing. Despite their utility, dynamic control of Airy beams poses a significant challenge. This work investigates the experimental realization of dynamic steering of Airy beams by utilizing computer-generated holograms with phase-amplitude encoding on a phase-only spatial light modulator (SLM). We successfully generated and controlled Airy beams by imposing dynamic phase masks that manipulated both the phase and amplitude of the field, which sets our approach apart from conventional methods with only phase manipulation. By directly encoding in situ such a hologram and transferring it to an SLM, we are able to control the initial position and rotational orientation of Airy beams without relying on mechanical movement or traditional optical setups involving lenses and apertures. Generating Airy beams in any initial position and rotational direction is anticipated to significantly impact applications such as optical trapping, optical communication, and biomedical imaging by providing a flexible platform for dynamic Airy beam manipulation.

Polarization-insensitive ultra-wideband tunable perfect absorber based on a vanadium dioxide metasurface

This paper provides a polarization-insensitive ultra-wideband tunable perfect absorber based on a patterned vanadium dioxide (VO2) metasurface. The absorption bandwidth reaches 18.5 THz, surpassing that of most previous studies, through integrating two distinct region patterns (A and B). The proposed absorber features a three-layer sandwiched structure and a simpler metasurface pattern, demonstrating the advantages of lower manufacturing cost and a simplified photolithography process. In addition, by optimizing geometric parameters and manipulating VO2 conductivity, the absorption spectrum reveals three specific perfect absorption peaks with the absorptance of 99.06%, 99.85%, and 99.85% at 10 THz, 14 THz, and 21.5 THz and shows polarization-insensitive performance due to the C4 rotational symmetry of the metasurface pattern. Furthermore, we illustrate that the intrinsic mechanism of the proposed perfect absorber arises from the lossy localized surface plasmon polarization (LSPP) excited by the incident wave, with the Fabry–Perot (FP) cavity enhancing LSPP absorption. The absorber reveals a good impedance matching with the free space, where the real and imaginary parts are close to 1 and 0, which also explains the perfect absorption from the perspective of the impedance matching theory. The device can transition between perfect absorption mode and total reflection mode, with relative absorptance also adjustable via manipulating the VO2 conductivity. Ultimately, the absorber displays an excellent angle tolerance maintaining absorptance above 90% in the range of 0°–50°. Consequently, the proposed polarization-insensitive ultra-wideband tunable perfect absorber can be applied in optical switching, object cloaking, and wireless communication.

Tunable Optical Filter Based on Thin Film Lithium Niobate Photonic Crystals

In this paper, we propose a tunable optical filter with a high Q factor based on photonic crystal technology, achieving a Q factor of 442.85 using thin film lithium niobate technology. By proportionally adjusting the dimensions of the unit structure, this filter enables coarse tuning across the 1520–1570 nm range (C band). Furthermore, by utilizing the thermo-optic effect of lithium niobate, we can achieve fine-tuning of the optical filter within a temperature range of 300 K to 600 K, allowing for a center wavelength tuning capability of up to 3.7 nm. This design not only enhances the filter’s performance but also broadens its potential applications in optical communication and optical signal processing.

Performance Analysis of Multiple UAV-Based Hybrid Free-Space Optical/Radio Frequency Aeronautical Communication System in Mobile Scenarios

Free-space optical (FSO) communication with unmanned aerial vehicles (UAVs) as relays is a promising technology for future aeronautical communication systems. In this paper, a multiple UAV-based aeronautical communication system is proposed, wherein a hybrid FSO/radio frequency (RF) link is established to connect the Airborne Warning and Control System (AWACS) with the mobile ground station (GS). Initially, we consider the velocity variance of both AWACS and the mobile GS, along with the influence of the Doppler effect. Furthermore, four relay selection modes are proposed, and exact closed expressions are derived for the end-to-end outage probability and bit error rate (BER) of the considered system. Numerical simulations demonstrate the impact of velocity variance variation on system performance. Additionally, we analyze the applicability of these four relay modes under different platform mobility characteristics through simulation results, while discussing the optimal numbers and the deployment altitude of UAVs. Finally, effective design guidelines that can be useful for aeronautical communication system designers are presented.

Behavior of TE and TM propagation modes in nanomaterial graphene using asymmetric slab waveguide

Abstract In this article, the conduction of transverse electric/transverse magnetic (TE/TM) propagation modes in nanomaterial graphene utilization of asymmetric dielectric slab waveguide was studied in terms of their applicability in optical fiber communication. Nano-graphene film was deposited on silica substrate and air cladding. Three layers were exposed to electromagnetic waves with a 1.55 µm wavelength and 1 µm thick nanographene film, silica, and air covering to study the performance and optical properties of graphene nanomaterials. The models were influenced by factors such as attenuation wavenumbers, cut-off frequency, mode number, propagation wavenumbers, skin depth, and angles of total internal reflection. The impact of these parameters was assessed through numerical analysis, revealing significant correlations. The modes generated ten numbers of TE and nine numbers of TM mode dependent upon the structure of nanographene, with low loss propagation wavenumber. As the TE/TM modes increase, the decay wavenumbers of the cladding and substrate parameters diminish. This indicates that the magnetic and electric fields undergo extremely rapid decay beyond the film region, which leads to the skin depth for higher TE/TM modes traveling longer distances in the cladding and substrate than do lower-order modes. Therefore, nanographene exhibits good optical properties due to its low absorption loss. The angles of internal reflection are greater in magnitude than the substrate and cladding key angles. Still, in the tenth TE mode, the internal reflection angles are extremely close to the critical angle as a result of the small substrate decay parameter and the near operating frequency. The tenth TE mode is weakly characterized. The characteristics of TE/TM modes in an asymmetric three-layer slab waveguide structure are realized for various mode orders and various parameters of nanographene material. The field profiles of the TE/TM modes are submitted to comprehend these characteristics.

Radially polarized partially coherent beams with prescribed sinh-Gauss non-uniform correlation structure

We introduce a kind of radially polarized partially coherent beam with a prescribed sinh-Gauss non-uniform correlation structure, named a radially polarized sinh-Gauss non-uniformly correlated (RPSNC) beam. Utilizing the ordinary Huygens–Fresnel principle, we derive the analytical formulas for the spectral intensity and the spectral degree of polarization (DOP) in free space and investigate the beam’s propagation properties through numerical simulations. The results demonstrate that RPSNC beams exhibit a self-focusing property during propagation, with the focal position adjustable by varying the coherence length. Additionally, the spectral DOP in the central region forms a distinctive single-ring structure as the beam propagates. These unique properties make RPSNC beams promising for applications in free-space optical communications, beam shaping, and optical trapping.

Response time of the type-II superlattice InAs/InAsSb mid-infrared interband cascade photodetector for HOT conditions

The article presents III-V InAs/InAsSb type-II superlattice (T2SL) mid-wave infrared (MWIR, 100 % cut-off wavelength, λcut-off ∼ 7.5 μm at 333 K) interband cascade photodetector (ICIP) developed to operate at temperatures > 300 K. That device solves the low quantum efficiency (QE) problem of the typical “thick absorber” photodetectors designed for high operating temperature (HOT, > 300 K) conditions. The 5-stage epilayer was grown by molecular beam epitaxy (MBE) on the lattice-mismatched GaAs substrates where absorbers are connected by the highly doped standard n+/p+ tunnel junctions. The developed and analyzed high-speed MWIR devices should be implemented in the emerging fields such as frequency comb spectroscopy (FCS), free space optical communication (FSO) and light detection and ranging (LIDAR). The majority of the MWIR ICIPs’ research have been focused on the QE increase and dark current suppressing to improve the detectivity (D*) while the high- frequency operation (HFO) is still not completely investigated. We report on the MWIR InAs/InAsSb T2SLs ICIP where tradeoff between response time and detectivity was obtained. The time constant being limited by the carriers’ transit time reaches ∼ 16 ns corresponding to 3-dB bandwidth, f3-dB ∼ 10 MHz (detectivity ∼ 2 × 108 cmHz1/2/W without immersion GaAs lens with ∼ 0.53 μm single absorber) for λcut-off ∼ 7.5 μm at 333 K and unbiased conditions. Under 1 V time constant reaches ∼ 2.4 ns (f3-dB ∼ 66 MHz).

Generation of broadband chaotic laser based on a four-segment InP-based monolithically integrated chaotic semiconductor laser

Aiming at the problems of limited bandwidth and obvious time-delay signature (TDS) of monolithically integrated chaotic semiconductor lasers, this paper proposes a four-segment InP-based monolithically integrated chaotic semiconductor laser. The laser structure is composed of a distributed feedback (DFB1) laser region, a semiconductor optical amplifier (SOA) region, a distributed Bragg reflector (DBR) grating region and a distributed feedback (DFB2) laser region. Mutual injection between the two DFB laser regions effectively enhances the bandwidth of power spectrum. The DBR grating region is used to form a complex multi-feedback cavity to suppress the TDS caused by the fixed external cavity structure. The simulation results show that the chaotic signal with the standard bandwidth of 29.2 GHz and the TDS value of 0.094 is generated. The research in this paper can further improve the performance of monolithically integrated chaotic laser, and provide a high-quality chaotic laser source for secure optical communication, chaotic lidar and distributed optical fiber sensing.