Orbital Angular Momentum Waves: Generation, Detection and Emerging Applications

Orbital angular momentum (OAM) has aroused a widespread interest in many fields, especially in telecommunications due to its potential for unleashing new capacity in the severely congested spectrum of commercial communication systems. Beams carrying OAM have a helical phase front and a field strength with a singularity along the axial center, which can be used for information transmission, imaging and particle manipulation. The number of orthogonal OAM modes in a single beam is theoretically infinite and each mode is an element of a complete orthogonal basis that can be employed for multiplexing different signals, thus greatly improving the spectrum efficiency. In this paper, we comprehensively summarize and compare the methods for generation and detection of optical OAM, radio OAM and acoustic OAM. Then, we represent the applications and technical challenges of OAM in communications, including free-space optical communications, optical fiber communications, radio communications and acoustic communications. To complete our survey, we also discuss the state of art of particle manipulation and target imaging with OAM beams

Performance of Spatial Diversity DCO-OFDM in a Weak Turbulence Underwater Visible Light Communication Channel

The performance of underwater visible light communication (UVLC) system is severely affected by absorption, scattering and turbulence. In this article, we study the performance of spectral efficient DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) in combination with the transceiver spatial diversity in turbulence channel. Based on the approximation of the weighted sum of lognormal random variables (RVs), we derived a theoretical exact bit error rate (BER) for DCO-OFDM systems with spatial diversity. The simulation results are compared with the analytical prediction, confirming the validity of the analysis. It is shown that spatial diversity can effectively reduce the turbulence-induced channel fading. The obtained results can be useful for designing, predicting, and evaluating the DCO-OFDM UVLC system in a weak oceanic turbulence condition

Orbital Angular Momentum-based Space Division Multiplexing for High-capacity Underwater Optical Communications

To increase system capacity of underwater optical communications, we employ the spatial domain to simultaneously transmit multiple orthogonal spatial beams, each carrying an independent data channel. In this paper, we multiplex and transmit four green orbital angular momentum (OAM) beams through a single aperture. Moreover, we investigate the degrading effects of scattering/turbidity, water current, and thermal gradient-induced turbulence, and we find that thermal gradients cause the most distortions and turbidity causes the most loss. We show systems results using two different data generation techniques, one at 1064 nm for 10-Gbit/s/beam and one at 520 nm for 1-Gbit/s/beam, we use both techniques since present data-modulation technologies are faster for infrared (IR) than for green. For the higher-rate link, data is modulated in the IR, and OAM imprinting is performed in the green using a specially-designed metasurface phase mask. For the lower rates, a green laser diode is directly modulated. Finally, we show that inter-channel crosstalk induced by thermal gradients can be mitigated using multi-channel equalisation processing.Comment: 26 pages, 5 figure

A Survey of Positioning Systems Using Visible LED Lights

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.As Global Positioning System (GPS) cannot provide satisfying performance in indoor environments, indoor positioning technology, which utilizes indoor wireless signals instead of GPS signals, has grown rapidly in recent years. Meanwhile, visible light communication (VLC) using light devices such as light emitting diodes (LEDs) has been deemed to be a promising candidate in the heterogeneous wireless networks that may collaborate with radio frequencies (RF) wireless networks. In particular, light-fidelity has a great potential for deployment in future indoor environments because of its high throughput and security advantages. This paper provides a comprehensive study of a novel positioning technology based on visible white LED lights, which has attracted much attention from both academia and industry. The essential characteristics and principles of this system are deeply discussed, and relevant positioning algorithms and designs are classified and elaborated. This paper undertakes a thorough investigation into current LED-based indoor positioning systems and compares their performance through many aspects, such as test environment, accuracy, and cost. It presents indoor hybrid positioning systems among VLC and other systems (e.g., inertial sensors and RF systems). We also review and classify outdoor VLC positioning applications for the first time. Finally, this paper surveys major advances as well as open issues, challenges, and future research directions in VLC positioning systems.Peer reviewe

Waymark in the Depths: Baseband Signal Transmission and OFDM in Underwater Acoustic Propagation Channel Models

In the intricate environment of underwater acoustic propagation, establishing reliable communication channels stands as a formidable challenge, primarily due to the medium's inherent properties, such as high path loss, multipath propagation, and time-varying channel characteristics. "Waymark in the Depths: Baseband Signal Transmission and OFDM in Underwater Acoustic Propagation Channel Models" presents an innovative exploration into enhancing underwater communication systems by leveraging advanced signal processing techniques and channel modeling strategies. At the core of this research lies the integration of Orthogonal Frequency Division Multiplexing (OFDM) with baseband signal transmission, aiming to mitigate the detrimental effects of the underwater acoustic environment on signal integrity and throughput. By dissecting the acoustic channel's unique attributes, the study devises a comprehensive channel model that encapsulates the dynamic nature of underwater acoustics, including the impact of temperature, salinity, and pressure on sound speed and signal dispersion. This model serves as a waymark, guiding the development of tailored OFDM techniques that are optimized for the underwater medium, focusing on maximizing spectral efficiency and minimizing error rates. The research meticulously examines the interplay between baseband signal processing and OFDM in this context, illustrating how their synergistic application can overcome the bandwidth limitations and frequency-selective fading characteristic of underwater channels. Through extensive simulation and experimental validation, the study demonstrates the feasibility of achieving high-speed, reliable underwater communication, highlighting significant improvements in data rates and link stability. Furthermore, the research delves into adaptive modulation schemes and coding strategies, optimized for the derived channel model, to bolster the robustness of the communication link against the unpredictable underwater environment. This pioneering work not only sheds light on the complexities of underwater acoustic signal transmission but also charts a path forward for the next generation of underwater communication systems. By pushing the boundaries of current technological capabilities and offering a solid theoretical foundation, this research contributes significantly to the field of underwater acoustics and opens new horizons for marine exploration, environmental monitoring, and submarine communication networks. Through its comprehensive analysis and innovative approaches, "Waymark in the Depths" not only addresses the technical challenges of underwater signal transmission but also lays down a crucial waymark for future endeavors in the uncharted territories of the ocean's depths

A review of gallium nitride LEDs for multi-gigabit-per-second visible light data communications

The field of visible light communications (VLC) has gained significant interest over the last decade, in both fibre and free-space embodiments. In fibre systems, the availability of low cost plastic optical fibre (POF) that is compatible with visible data communications has been a key enabler. In free-space applications, the availability of hundreds of THz of the unregulated spectrum makes VLC attractive for wireless communications. This paper provides an overview of the recent developments in VLC systems based on gallium nitride (GaN) light-emitting diodes (LEDs), covering aspects from sources to systems. The state-of-the-art technology enabling bandwidth of GaN LEDs in the range of >400 MHz is explored. Furthermore, advances in key technologies, including advanced modulation, equalisation, and multiplexing that have enabled free-space VLC data rates beyond 10 Gb/s are also outlined

Employing VLC technology for transmitting data in biological tissue

Abstract. With the development in wireless communication methods, visible light communication (VLC), a subset of Optical Wireless Communication (OWC) has garnered much attention to employ the technology for a secure short-range wireless communication. We present a feasibility study to determine the performance of VLC in short range wireless transmission of data through biological tissue. VLC is a cost efficient and secure means of transmitting high volume of data wirelessly which can considerably reduce the interference issues caused by electromagnetic pulses and external electric fields. We present a simple measurement approach based on Monte Carlo simulation of photon propagation in tissue to estimate the strength of wireless communication with body implant devices. Using light for communication brings inherent security against unauthorized access of digital data which could be acquired from the low energy body implant devices used for medical diagnosis and other studies. This thesis discusses the typical components required to establish VLC such as, transmitter, receiver and the channel mediums. Furthermore, two cases of Monte Carlo simulation of photon-tissue interaction are studied to determine a possibility if VLC is a suitable substitute to radio frequency (RF) for a more wireless communication with the body implants. The process of theoretical measurement begins with conversion of light intensity into an electrical signal and an estimation of achievable data rate through a complex heterogeneous biological tissue model. The theoretically achieved data rates of the communication were found to be in the order of megabits per second (Mbps), ensuring a possibility to utilize this technology for short range reliable wireless communication with a wider range and application of implant medical devices. Biophotonics.fi presents a computational simulation of light propagation in different types of computational tissue models comprehensively validated by comparison with the team’s practical implementation of the same setup. This simulation is also used in this thesis (5.2.2) to approximate more accurate data rates of communication in case of a practical implementation