Short-range Optical Communication Research Articles

Short range optical communication with GaN‐on‐Si microLED and microPD matrices

Abstract(In)GaN microLEDs have reached a high degree of maturity due to their development in the lighting industry. Their robustness and high efficiency make them ideal candidates for high‐brightness, high‐resolution micro‐displays. Beyond display applications, microLEDs are being explored for non‐display uses, including wireless Visible Light Communication (VLC) and parallel communication via multicore fiber. This study investigates short‐range chip‐to‐chip optical communication using InGaN/GaN microLEDs and micro Photodiodes (microPDs). Leveraging processes developed for micro‐displays, we address the challenges of integrating GaN microLEDs and microPDs on ASICs. We outline the main figures of merit, including expected energy efficiency, optical coupling to multicore fibers or waveguides, and the spectral efficiency of InGaN/GaN microPDs correlated with TCAD simulation and experimental transmission results. Our study highlights the potential of GaN microLEDs and microPDs for massively parallel, energy‐efficient data transmission, paving the way for innovative short‐range and energy‐efficient optical communication solutions.

Short Range Optical Communication with GaN-on-Si MicroLED and MicroPD Matrices

Short Range Optical Communication with GaN-on-Si MicroLED and MicroPD Matrices

Adaptive Information Hiding Method Based on Feature Extraction for Visible Light Communication

Visible Light Communication (VLC) is an emerging short-range optical communication technology that can alleviate spectrum congestion. However, VLC faces security problems with man-in-the-middle hijacking and bypass listening. Since the covert transmission of visible light information has the characteristics of strong concealment and difficult detection, VLC based on information hiding becomes a new paradigm to solve these security problems. This paper presents a method in which Red, Green, Blue (RGB) Light-emitting Diode (LED) is used to secure the VLC by using the information hiding technique. Specifically, a gammatone filter bank-based feature extraction method is suggested. This method extracts robust vector for information hiding and extraction. To hide and extract the information, a dither modulation information hiding scheme based on the adaptive optimization is proposed. The presented method uses dither modulation to hide information in the extracted feature vector, which can effectively improve the success rate of information extraction. On the basis of performance analysis, the superiority of the presented method is illustrated by comparing with the existing methods.

Evolution of Short-Range Optical Wireless Communications

The optical wireless communication (OWC) technology explores the broad unregulated optical spectrum to provide high-speed wireless communications, and the visible, ultraviolet and near-infrared wavelength ranges all have been investigated. Compared with the conventional radio frequency (RF) band, the spectrum in OWC systems is much less congested and the interference is much lower. The OWC technology also provides enhanced physical layer security due to the natural confinement of optical beams that makes it difficult to intercept the transmitted signal. Hence, the OWC technology has been widely studied and considered as a promising candidate in future beyond-5G communications. The OWC technology has been considered for both long-range and short-range applications, and in this paper we will introduce the fundamentals and recent developments of short-range OWC systems. In particular, we will focus on the key short-range OWC applications in indoor personal or local area communications, underwater wireless communications, wireless data center networks, and vehicular communications. We will also introduce some recent widely studied advanced techniques to boost the performance of short-range OWC systems, including the spatial domain diversity, multiplexing and modulation principles to improve the system robustness and data rate, and the machine learning algorithms and hardware accelerators to suppress both linear and nonlinear effects to improve OWC signal quality and bit-error-rate performance.

Hardware Architecture of a QAM Receiver for Short-Range Optical Communications

Short-reach optical fiber communications systems aim to achieve high throughput, in the order of tens of Gbps. The implementation of these high-speed systems requires parallel processing, which makes low-complexity designs of their subsystems a key to the successful large-scale deployment of this technology. Half-Cycle Nyquist Subcarrier Modulation (HC-SCM) was originally suggested for these systems with the goal of using as much bandwidth as possible and, therefore, achieving high communication rates. Recently, Oversampled Subcarrier Modulation (OVS-SCM) was proposed as an alternative more computational efficient than HC-SCM and also with a better spectral efficiency. This paper proposes a hardware-efficient architecture for an OVS-SCM receiver, which takes into account the inherent parallel processing of these systems. This receiver takes 16 samples in parallel from a 5 GSa/s analog-to-digital converter with a 3.2 GHz 3 dB bandwidth. Design solutions for the frame detection block, the mixer, the resampler, the fractional interpolator, the matched filter and the timing estimator are presented. Our results show that, compared to the HC-SCM receiver, this proposal reduces the computational load of the downconverter stages by 90%. FPGA implementation results are given to demonstrate that our proposal can be implemented in state-of-the-art devices.

Fault-Tolerant Cooperative Signal Detection for Petahertz Short-Range Communication With Continuous Waveform Wideband Detectors

Motivated by unique scattering properties at petahertz frequencies, we present a novel statistical model of fault-tolerant cooperative signal detection for short-range optical petahertz wireless communications, where a single-scattering assumption holds valid. We characterize the received non-line-of-sight (NLOS) signal by a fault-tolerant continuous waveform wideband detector with a non-zero failure probability. To better reflect the physical properties of the petahertz communication, both signal-independent and signal-dependent noise sources are considered in characterizing the received signal. The distribution of the received signal is quantified with each scattered path following the Málaga distribution. We leverage the location flexibility of randomly distributed collaborative users, considering each user experiences an independent channel condition. Utilizing the Neyman-Pearson criterion, we develop the binary hypothesis testing problem and subsequently derive the likelihood ratio for the test statistics. Moreover, to quantify the performance, a framework is developed for the average area under the receiver operating characteristic (ROC) curve for both single user and cooperative scenarios. An optimal decision fusion with a majority rule for fault-tolerant signal detection is applied to exploit the maximum spectrum opportunity. It is found that with the optimal voting rule and for a given target error rate, the network requires fewer collaborative secondary users than the total number of users available in an optical network. However, in the limiting case, it is shown that, as the cost function approaches its minimum or maximum value within its allowable range, the optimal number of collaborative users becomes independent of the failure probabilities. With the realistic assumption of fault-tolerant users, it is found that the false alarm probability increases faster than the detection probability.

Modeling of ultraviolet propagation from air to human epidermis with wavelength range of 200–300 nm

Ultraviolet (UV) technology plays an important role in the fields of sterilization, disinfection, and short-range wireless optical communications. In this Letter, a theoretical model to determine the UV radiation intensity (UVRI) on human skin is put forward based on the Monte Carlo method, where the UV wavelength ranges from 200 to 300 nm. Meanwhile, the UVRI evaluation algorithm is provided to reproduce the simulation results. Furthermore, the penetration depth of UV radiation in the human epidermis is investigated, which can be used to assess whether UV radiation causes damage to human health. Simulation results coincide with the existing experimental results that the 222-nm UV radiation is harmless to humans at the given dose of 1.7 mJ/cm2. This work provides theoretical guidelines for the power control of a UV system when humans are in the vicinity.

100 Hertz frame-rate switching three-dimensional orbital angular momentum multiplexing holography via cross convolution

The orbital angular momentum (OAM) of light has been implemented as an information carrier in OAM holography. Holographic information can be multiplexed in theoretical unbounded OAM channels, promoting the applications of optically addressable dynamic display and high-security optical encryption. However, the frame-rate of the dynamic extraction of the information reconstruction process in OAM holography is physically determined by the switching speed of the incident OAM states, which is currently below 30 Hz limited by refreshing rate of the phase-modulation spatial light modulator (SLM). Here, based on a cross convolution with the spatial frequency of the OAM-multiplexing hologram, the spatial frequencies of an elaborately-designed amplitude distribution, namely amplitude decoding key, has been adopted for the extraction of three-dimensional holographic information encoded in a specific OAM information channel. We experimentally demonstrated a dynamic extraction frame rate of 100 Hz from an OAM multiplexing hologram with 10 information channels indicated by individual OAM values from –50 to 50. The new concept of cross convolution theorem can even provide the potential of parallel reproduction and distribution of information encoded in many OAM channels at various positions which boosts the capacity of information processing far beyond the traditional decoding methods. Thus, our results provide a holographic paradigm for high-speed 3D information processing, paving an unprecedented way to achieve the high-capacity short-range optical communication system.

Visible Light Communications for Industrial Applications—Challenges and Potentials

Visible Light Communication (VLC) is a short-range optical wireless communication technology that has been gaining attention due to its potential to offload heavy data traffic from the congested radio wireless spectrum. At the same time, wireless communications are becoming crucial to smart manufacturing within the scope of Industry 4.0. Industry 4.0 is a developing trend of high-speed data exchange in automation for manufacturing technologies and is referred to as the fourth industrial revolution. This trend requires fast, reliable, low-latency, and cost-effective data transmissions with fast synchronizations to ensure smooth operations for various processes. VLC is capable of providing reliable, low-latency, and secure connections that do not penetrate walls and is immune to electromagnetic interference. As such, this paper aims to show the potential of VLC for industrial wireless applications by examining the latest research work in VLC systems. This work also highlights and classifies challenges that might arise with the applicability of VLC and visible light positioning (VLP) systems in these settings. Given the previous work performed in these areas, and the major ongoing experimental projects looking into the use of VLC systems for industrial applications, the use of VLC and VLP systems for industrial applications shows promising potential.

Outdoor Visible Light Communication Channel Modeling under Smoke Conditions and Analogy with Fog Conditions

Visible Light Communication (VLC) has gained popularity in research and business in the last decade. This technology aims to combine lighting and communication into a single device. For now, this technology has been thoroughly studied for an indoor environment, but it is sufficiently mature nowadays to consider its outdoor-environment potentials. The key outdoor challenges are the weather variabilities and smoke particles in cities due to pollution or fires. The aim of this is the study and quantification of the weather and smoke particles’ impact on a short-range optical communication thanks to a simulator. This article’s novelty is the inclusion of the effects of smoke in a short-range outdoor VLC system channel model. This smoke model, which comes from the fire engineering field, states that smoke attenuation is independent of the wavelength, starting from high visibility to 5 m. The visibility represents the distance up to which an object can be distinguished against the background. The effects of fog and smoke are studied in the case of two outdoor VLC scenarios. Smoke and fog models have analogous equations to express the optical attenuation they induce, using the visibility concept. Taking into account the actual light-emitting diode (LED) lamp radiation pattern, the simulator computes the power at the receiver side and the channel attenuation coefficients for a given fog or/and smoke outdoor setting. The main result drawn in this paper is that the channel attenuation levels due to fog and smoke are both in the same order of magnitude, starting from the visibility of about 1 km. The attenuation induced by fog is higher under this threshold of 1 km.

Vortex Polymer Optical Fiber with 64 Stable OAM States.

This research introduces a numerical design of an air-core vortex polymer optical fiber in cyclic transparent optical polymer (CYTOP) that propagates 32 orbital angular momentum (OAM) modes, i.e., it may support up to 64 stable OAM-states considering left- and right-handed circular polarizations. This fiber seeks to be an alternative to increase the capacity of short-range optical communication systems multiplexed by modes, in agreement with the high demand of low-cost, insensitive-to-bending and easy-to-handle fibers similar to others optical fibers fabricated in polymers. This novel fiber possesses unique characteristics: a diameter of 50 µm that would allow a high mechanical compatibility with commercially available polymer optical fibers, a difference of effective index between neighbor OAM modes of around 10−4 over a bandwidth from 1 to 1.6 µm, propagation losses of approximately 15 × 10−3 dB/m for all OAM modes, and a very low dispersion for OAM higher order modes (±l = 16) of up to +2.5 ps/km-nm compared with OAM lower order modes at a telecom wavelength of 1.3 µm, in which the CYTOP exhibits a minimal attenuation. The spectra of mutual coupling coefficients between modes are computed considering small bends of up to 3 cm of radius and slight ellipticity in the ring of up to 5%. Results show lower-charge weights for higher order OAM modes.

DLI-Based DP-QPSK Reception Scheme for Short-Range Optical Communication

The unacceptably high cost of digital coherent receivers for short-range optical communication has in recent years fueled the study of alternative transmission schemes that are simultaneously highly performing and cost-effective. However, the proposed solutions (e.g., Kramers–Kronig receiver) usually require the cooperation of a transmitting end, which is unachievable in the context of non-cooperative communication. In this work, we mainly studied a dual-polarization quadrature phase-shift-keying (DP-QPSK) non-coherent reception scheme based on a delay-line interferometer (DLI) and measures to improve the reception performance. A data recovery algorithm was proposed for DLI-based DP-QPSK demodulation. The simulation results demonstrated that the algorithm could accurately recover the raw data from the transmitter. Moreover, decreasing the differential delay of the DLI could effectively increase the chromatic dispersion tolerance of the receiver and the optimal delay scaled inversely with the chromatic dispersion. It was found that a DLI-based DP-QPSK reception scheme is a better choice for short-range, non-cooperative communication with less severe transmission impairments.

Multiuser Visible Light Communication Systems Using OFDMA

Visible light communications (VLC), a short-range optical wireless communication scheme using light-emitting diodes (LEDs) as transmitters, has been proposed to support multiple users, predominantly in indoor environments. This article explores using orthogonal frequency division multiple access (OFDMA) for VLC due to its high spectrum utilization efficiency and potentially high transmission data rate. The proposed optical OFDMA uses adjacent subcarriers as a set to support each user. Doing so allows some users to sample at a lower sampling rate and employ a smaller fast Fourier transform (FFT) to lower the computational complexity and hardware cost. A multi-cell structure is naturally obtained in VLC since more than one LED lamp is usually installed in an indoor environment. In this article, users located in different cells can reuse the same subcarrier sets, potentially causing multiple access interference. Analysis and simulation results are used to predict the subcarrier-set reuse probability over the entire indoor space. When the OFDM modulation index is optimized considering the peak-power-limit of the LEDs, the average transmission data rate is twice that of using OFDM that does not reuse the spectral resources, for the scenarios tested.

Indoor multiuser visible light communication systems using Hadamard-coded modulation.

Visible light communications (VLC) is a short-range optical wireless communication technology that uses light-emitting diodes (LEDs) as lighting devices and data transmitters. This paper describes a multiuser VLC system using Hadamard-coded modulation (HCM) for indoor data transmission. Considering the peak transmitted power limit of the LEDs, a DC-reduced HCM (DCR-HCM) is used to reduce the nonlinear clipping distortion. Since the Hadamard codewords have different bandwidth requirements for a given symbol rate, they can be assigned to users with varying hardware capabilities. Optimally assigning codewords to users is found to significantly improve the average throughput, up to twice higher than a random assignment for a typical scenario. When the number of active users is less than the size of the Hadamard matrix used, more than one codeword can be assigned per user, which further improves the throughput. This paper also examines a scenario where multiple lamps in an indoor space transmit the same data. Since the time of arrival for the received signals emitted from different lamps is different, the Hadamard codes received are no longer orthogonal, resulting in multiple access interference and inter-chip interference. The number of acceptable codewords is computed based on the specific interference experienced in different parts of the indoor space. The spatial distribution of the maximum throughput is also simulated, showing that the ratio of the maximum to the minimum data rate can be as high as 10 when considering the entire area of a typical indoor room.This article is part of the theme issue ‘Optical wireless communication’.

OFDM With Differential Index Modulation for Visible Light Communication

In this paper, orthogonal frequency division multiplexing with differential index modulation (OFDM-DIM) is proposed for visible light communication. Compared with traditional OFDM with index modulation (OFDM-IM), the proposed scheme decreases the average number of used subcarriers when transmits the same amount of information bits, therefore higher spectral efficiency can be achieved. The simulation results present that OFDM-DIM can provide higher data transmission rate and lower bit error rate (BER) over additive white gaussian noise (AWGN) optical channel. Meanwhile, simulations over reference channels of short range optical wireless communication are implemented, where OFDM-DIM performances better than OFDM-IM when line-of-sight (LOS) components are dominant.

近距离LED光通信直视信道模型研究

近距离LED光通信直视信道模型研究

Short-range optical wireless communications for indoor and interconnects applications

Optical wireless communications have been widely studied during the past decade in short⁃range applications, such as indoor high⁃ speed wireless networks and interconnects in data centers and high⁃performance computing. In this paper, recent developments in high⁃speed short⁃range optical wireless communications are reviewed, including visible light communications (VLCs), infrared in-door communication systems, and reconfigurable optical interconnects. The general architecture of indoor high⁃speed optical wire⁃ less communications is described, and the advantages and limitations of both visible and infrared based solutions are discussed. The concept of reconfigurable optical interconnects is presented, and key results are summarized. In addition, the challenges and potential future directions of short⁃range optical wireless communications are discussed.

Cogent Machine Learning Algorithm for Indoor and Underwater Localization Using Visible Light Spectrum

From last few years indoor localization has become more popular for wireless devices. The major reason for its popularity is to access current location efficiently. On the other side visible light communication is attaining interest of researchers due to high growth of wireless communication and solid state lighting. This network structure can produce high accuracy for the resident positioning electromagnetic environment. The proposed approach is viable for both air and underwater communication based on the visible light spectrum. We evaluate the technique for other supervised machine learning algorithms to analyse an accuracy, error distance and computational time for indoor localization in visible light communication network. Experimental work was made by using star topology supported by visible personal area network system based simulator, which corresponds an attribute of PHY and MAC layer for IEEE 802.15.7 standard designed for short range optical wireless communication. The evaluation was carried out for an accuracy, error distance and computational time. The results show that the suggested methodology achieves overall computational accuracy and deliver an acceptable location estimation error.

Design and simulation of integration of vertical cavity surface emitting lasers and heterojunction bipolar transistor

Vertical cavity surface emitting lasers (VCSELs) are widely used in the field of short-range optical communication and optical interconnection because of their advantages such as low threshold current, large modulation bandwidth, easy two-dimensional integration, easy coupling with optical fibers and low cost. The VCSELs and heterojunction bipolar transistor (HBT) are longitudinal current devices, so they can be well integrated on the same wafer, and the output light power can be modulated by the HBT base current. Integration of VCSELs and HBT are designed in this paper. The VCSELs and PNP InGaP/GaAs HBT form a direct series structure. The reflectivity of DBR is 99.72% at a resonant wavelength of 850 nm and 99.57% after adding HBT separately. Therefore, the addition of HBT has little influence on the reflectivity of DBR at the resonant wavelength. The electro-optical characteristics of the integrated structure are simulated by using PICS3D software. An interim collector is added into the model in order to ensure that the simulation can be carried out smoothly. Firstly, HBT is conducted and the current flows from the emitter to the interim collector. Then, the voltage across the interim collector and the N-type electrode is increased to make VCSELs conducted and the current of the transition collector drop to zero. The interim collector can be removed from the actual structure because the current is zero. The simulation results show that the current gain coefficient is 400, and the maximum modulation rate of the base current to the output light power rises up to 280 mW/mA. The maximum temperature in the active region increases with the base current increasing, and the output light power first increases and then tends to be saturated. The ac optical gain characteristics of the integrated structure is simulated by PICS3D, and the simulation result shows that cutoff frequency exceeds 1 GHz. The addition of HBT limits the modulation rate of the integrated structure, and further optimization of HBT structure parameters and geometric dimension are needed to improve the modulation rate. The integrated structure and simulation method established in this paper can also be used to integrate LED, LD, DFB or other luminescent devices with HBT.

Near-Field-Focusing Integrated Optical Phased Arrays

Integrated optical phased arrays that focus radiated light to a tightly-confined spot in the near field are demonstrated for the first time. The element phase distributions necessary for generating and steering focused beams using phased arrays are developed. Discussion and simulations detailing the effects of the array aperture and focal length on the focal spot are included. Two focusing phased array architectures are presented: (1) a one-dimensional splitter-tree-based architecture with novel focusing antennas and inline phase bumps and (2) a two-dimensional large-scale pixel-based architecture. Both architectures are used to experimentally demonstrate a variety of aperture size and focal length passive focusing arrays in a CMOS-compatible platform, including (i) a 512-antenna splitter-tree-based array with a wavelength-steerable 7 µm spot at a 5 mm focal length, (ii) a 1024-antenna pixel-based array with a 21 µm spot at a 5 mm focal length, and (iii) a 10,000-antenna pixel-based array with a 21 µm spot at a 10 mm focal length. The demonstrated focusing phased arrays present a new functional modality compared to standard optical phased arrays that generate diffracting beams in the far field of the array. This new focusing modality has the potential to advance a number of important application areas at the cutting edge of lightwave technology, as it will enable future integrated optical phased array implementations for a wide range of applications that require focusing operation. Such areas include optical trapping for biological characterization, laser-based three-dimensional printing, short-range light detection and ranging, and short-range optical data communications.