Optical Wireless Transmission Research Articles

Research on the Use of an Ocean Turbulence Bubble Simulation Model to Analyze Wireless Optical Transmission Characteristics

Research on the Use of an Ocean Turbulence Bubble Simulation Model to Analyze Wireless Optical Transmission Characteristics

Photovoltaic, wireless wide‐field epiretinal prosthesis to treat retinitis pigmentosa

AbstractPurposeTo develop and evaluate a photovoltaic, wireless wide‐field epiretinal prosthesis for the treatment of retinitis pigmentosa.MethodsA mosaic array of thinned silicon‐based photodiodes with integrated thin‐film stimulation electrodes was fabricated with a flexible polyimide substrate film to form a film‐based miniaturized electronic system with wireless optical power and signal transmission and integrated electrostimulation. Manufactured implants were characterized with respect to their optoelectronic performance and biocompatibility following DIN EN ISO 10993.ResultsA 14 mm diameter prosthesis containing 1276 pixels with a maximum sensitivity at a near infrared wavelength of 905 nm and maximized stimulation current density 30–50 μm below the electrodes was developed for direct activation of retinal ganglion cells during epiretinal stimulation. Fabricated prostheses demonstrated mucosal tolerance and the preservation of both metabolic activity, proliferation and membrane integrity of human fibroblasts as well as the retinal functions of bovine retinas. Illumination of the prosthesis, which was placed epiretinally on an isolated perfused bovine retina, with infrared light resulted in electrophysiological recordings reminiscent of an a‐wave (hyperpolarization) and b‐wave (depolarization).ConclusionsA photovoltaic, wireless wide‐field epiretinal prosthesis for the treatment of retinitis pigmentosa using near infrared light for signal transmission was designed, manufactured and its biocompatibility and functionality demonstrated in vitro and ex vivo.

Cross-Water–Air Optical Wireless Communication Using Orthogonal Time–Frequency Space Modulation

This paper examines the communication difficulties encountered in cross-media wireless optical transmission through simulated research on the utilization of orthogonal time and frequency space (OTFS) modulation technology. Our analysis and comparison demonstrate that OTFS significantly improves the reliability and throughput of data transmission in intricate multipath channel settings. In contrast to conventional orthogonal frequency division multiplexing (OFDM) technology, OTFS displays better resilience and transmission effectiveness. We foresee additional enhancements and progress in OTFS technology to present a sturdier and more efficient resolution for wireless communication, thereby providing valuable perspectives and encouragement for associated research initiatives. Our results underscore the capability of OTFS technology to transform wireless communication systems in demanding multipath channel conditions.

Optical Wireless Power Transmission under Deep Seawater Using GaInP Solar Cells

Optical wireless power transmission (OWPT) attracts attention because it enables wireless power transfer over longer distances than current wireless power transfer methods, irradiating laser light to a light-receiving element. In this study, an OWPT system was investigated under water and deep seawater using visible lasers with low optical absorption loss in water. Three laser beams (450 nm, 532 nm, and 635 nm) were transmitted through 30 cm, 60 cm, and 90 cm long tanks filled with tap water and deep seawater and were irradiated to 1.0 × 1.0 cm2 GaInP solar cells. The light reaching rate (ηop) of laser light and the system efficiency (ηsys) of the system (excluding the laser efficiency) were investigated. GaInP solar cells showed photo-electric conversion efficiencies of 30.6%, 40.3%, and 39.3% for 450 nm, 532 nm, and 635 nm irradiations, respectively. As a result, a 532 nm laser through a 90 cm water tank in tap water showed a 78.4% ηop and a 30.8% ηsys. Under deep seawater, a 532 nm laser through a 90 cm tank exhibited a 58.3% ηop and a 23.5% ηsys. A 532 nm green laser showed a higher efficiency than the other 450 nm and 635 nm lasers in this underwater system using GaInP solar cells.

Synthesis and optical wireless communication application of high efficiency extreme blue CsPbBr3 nanoplates

Extreme blue 435 nm emission, 97% PLQY CsPbBr3 nanoplates and up to 150 Mbps optical wireless communication data transmission rate.

Структура и элементная база приёмо-передающего модуля для организации подводной оптической беспроводной системы передачи данных

In the paper, the results of theoretical study of a wireless optical data transmission channel, as well as experimental study of its characteristics, taking into account different configurations of the optical component base of receiving and transmitting modules, were presented. The model of the wireless underwater optical communication channel with pulse-position modulation (4 bits per symbol) of digital data traffic with 100 Mbps is proposed. The model showed that to organize a communication channel on a 10 m path, the use of an array of light-emitting diodes (LEDs) is requires (the amount is up to 20 LEDs). For this case, a sufficiently large route budget will be provided, even with additional factor that reduce the efficiency of light propagation in seawater. The LEDs were chosen to organize the data transmission channel, since they have a wide radiation pattern and allow the implementation of a relatively simple driver circuit. The required optical radiation power is realized with the use of an array of LEDs. Schematic diagrams of the LEDs driver and power supply for the receiving and transmitting modules have been designed. A measuring layout with optical transmitter and receiver blocks has been implemented. The test signal is a regular sequence of pulses with a duty cycle of 2, and a frequency of 1 MHz. In the receiving module, the signal from the output of the pin photodiode is amplified using a wideband operational amplifier. Sets of 3 pin photodiodes and 10 LEDs were selected and tests were carried out to determine options for optical components that provide the best time characteristics of the output electrical signal in terms of delay time, rising and falling edges of pulses in a wireless optical airborne communication channel. Also, measurements were done on an air path with a length of 0.25-3 m using one or two LEDs as part of the transmitting module. It has been experimentally confirmed that the organization of a communication channel with a length of up to 10 m requires about 15-20 light-emitting diodes. Further study involves the designing and testing of a driver for the LEDs array and a prototype transceiver module.

Freeform concentrator design for IR wireless-to-fiber link communications.

Airplanes use heavy wired harnesses to provide multimedia services to the seats. Optical wireless communications (OWC) are a natural choice to reduce the amount of weight, reduce the wiring complexity, and avoid possible spurious electromagnetic radiation that risks affecting the airplane's navigation systems. The light's dual use as lighting and optical communications functionalities allows for providing light and multimedia content through the reading lamp. Thus, an optical system using optical fibers to replace wires and a reading lamp can provide a cabin seat with lighting and onboard connectivity. However, changing shielded harnesses by optical fibers is-from an optical design point of view-a challenging task as the reading lamp must also meet the stringent requirements to link the optical wireless transmissions to the optical fiber. The difficulty up to now lies in injecting the light emitted from the passenger's device into the optical fiber using the reading lamp as the receiving antenna and light injector. Here, we describe a proof-of-concept device that experimentally allowed for establishing a link between a transmitter and a photodetector coupled to an optical fiber-end, i.e., the link consisted of an optical wireless communication and the launching of the light modulated signal into an optical fiber. Additionally, from the experimental experience, we will describe the optical design strategies permitting designing a compound freeform concentrator to allow optical free space-to-fiber links.

Efficient LED-Array Optical Wireless Power Transmission System for Portable Power Supply and Its Compact Modularization

Optical wireless power transmission (OWPT) has been a promising solution for remote power supply, eliminating the need for power cables or batteries. In this paper, we propose a light emitting diode (LED) array based OWPT system with improved transmission efficiency and compact system dimension. In this experiment, the proposed four-LED-array collimation scheme achieved a lens system efficiency as high as 70%, while obtaining an electrical power of 0.8 W from a 50 × 50 mm2 GaAs solar cell at 1 m. The emitting side with the lens system was integrated into a 120 × 114 × 61 mm3 portable device by 3D printing. In addition, the thermal performance of the integrated module and the effective surface irradiance at the receiving side were analyzed in detail. The proposed system exhibits high efficiency and portability, with the advantageous potential to temporarily power remote devices.

Compensation of emulated atmospheric disturbance and tracking of a moving object by a real-time digital phase conjugate mirror using a liquid crystal spatial light modulator

We developed a fast-response digital phase conjugate mirror using a 700 Hz high-speed liquid crystal spatial light modulator and a high-speed camera. The total delay from signal light acquisition to phase conjugate light generation was 9.7 ms at 1246 × 1024 and 5.9 ms at 640 × 512. The tracking experiment performed on a target moving at a constant distance perpendicular to the optical axis, produced an error of 2%. Furthermore, a heated soldering iron, used to compensate for artificially generated air disturbance, showed that beam wandering and intensity fluctuations were reduced by 86% and 55%, respectively, compared to a phase conjugate mirror with added delay. Phase conjugate light irradiation of a continuously moving target at a maximum speed of 0.9 mm s−1 was also performed. This study shows that real-time digital phase conjugate mirrors can correct wavefront distortion caused by air fluctuation, which is a major challenge in long-distance wireless optical transmission in the turbulent atmosphere, without complicated control, and prevent beam quality degradation in the presence of atmospheric disturbance.

Cross-Perspective Human Behavior Recognition Based on a Joint Sparse Representation and Distributed Adaptation Algorithm Combined with Wireless Optical Transmission

Traditional human behavior recognition needs many training samples. Signal transmission of images and videos via visible light in the body is crucial for detecting specific actions to accelerate behavioral recognition. Joint sparse representation techniques improve identification accuracy by utilizing multi-perspective information, while distributional adaptive techniques enhance robustness by adjusting feature distributions between different perspectives. Combining both techniques enhances recognition accuracy and robustness, enabling efficient behavior recognition in complex environments with multiple perspectives. In this paper, joint sparse representation has been combined with distributed adaptation algorithm to recognize human behavior under the fusion algorithm, and verify the feasibility of the fusion algorithm through experimental analysis. The research objective of this article is to explore the use of the combination of joint sparse representation technology and distributed adaptive technology in the recall and accuracy of human detection, combined with the cross perspective human behavior recognition of wireless optical transmission. The experimental results showed that in the process of human detection, the recall and precision of the fusion algorithm in this paper reached 92% and 90% respectively, which are slightly higher than the comparison algorithm. In the experiment of recognition accuracy of different actions, the recognition accuracy of the fusion algorithm in this paper was also higher than that of the control algorithm. It can be seen that the fusion of joint sparse representation and distributed adaptation algorithms, as well as wireless communication light technology, are of great significance for human behavior recognition.

Underwater Wireless Optical Communication System Channel Modelling With Oceanic Bubbles and Water Constituents Under Different Wind Conditions

Optical wireless data transmission from an autonomous underwater vehicle (AUV) to a sea-surface buoy has become a viable solution to support the increasing needs for many applications in the field of marine technology. Despite having unique characteristics and advantages, underwater wireless optical communication remains a challenging field due to the difficulties associated with the harsh marine environments and severe attenuation caused by the bubbles and particulates. This study aims to evaluate the uplink UWOC system in the presence of particles and bubbles under various wind speeds. To calculate the link distances and signal loss between a transmitter and a receiver of the UWOC system, simulations were performed with the inputs of the water optical properties obtained from the Bay of Bengal and Southern Ocean waters and bubble properties derived from the Hall-Novarini (HN) model. Consequently, the normalized received power were calculated for the different receiver configurations and oceanic conditions without and with bubbles. Our results showed that the received power decreased with the increasing wind speeds and smaller bubble populations. The angular and spatial distributions of the received beam increased for smaller bubble populations under high wind speeds. When compared to the clean bubbles, the received power slightly decreased for the non-absorbing coated bubbles with different film thicknesses (0.01 ∼ 1.0 μm) and increased for the absorbing coated bubbles with higher thicknesses (≥1 μm). These results will significantly help the system designer to develop and optimize an UWOC system under different bubble populations and wind speed conditions.

Implementation of 23 Gbps optical wireless link for 750 km inter-aircraft communications

Optical device research and development is crucial for the implementation of miniaturized wireless optical transmission systems that are capable of transmitting large amounts of data at fast speeds. This work presents the design and evaluation of an optical link for the inter-aircraft interconnects. At the transmitter, the vertically cavity surface emission laser (VCSEL) is used to generate a directly modulated non-return to zero (NRZ) signal. In the receiver, direct detection and Gaussian low-pass filtering are used. The system’s performance is evaluated and compared with and without the use of filtration at the detector. BER, sensitivities, and data transmission capability are used to evaluate the performance of optical wireless systems using optisystem software. The range and data rate are enhanced 9-fold and 4-fold, respectively, in comparison to earlier schemes. The results presented show a transmission range of 750 km at a 23 Gbps data rate with a BER of 10−29.

Effect of Water and Aerosols Absorption on Laser Beam Propagation in Moist Atmosphere at Eye-Safe Wavelength of 1.57 μm

To realize optical wireless power transmission, atmospheric propagation of eye-safe wavelength (1.57μm) laser beams was theoretically investigated. Laser beams are affected by the presence of water vapor and aerosols which absorb and scatter the laser energy. The scattering coefficients of water molecules and aerosols were estimated to be about 6.3 × 10^-7 and 5.6 × 10^-5 m^-1, respectively, at wavelength (λ₀) of 1.57μm. Furthermore, the absorption coefficients of moist air at 30% relative humidity and aerosols were estimated to be about 6.16 × 10^-3 and 2.52 × 10^-5 m^-1, respectively, at λ₀ = 1.57μm. Then simulation of laser beam propagation in the moist atmosphere at λ₀ = 1.57μm was performed using these coefficients. Under the condition of no wind, the beam intensity decreases rapidly with increasing the length <i>z</i> and the rate of decrease slows down as the beam radius (ω) increases. When <i>z</i>_h is defined as the <i>z</i> where the normalized intensity is halved, the <i>z</i>_h (= 25 m) at ω = 20 mm when input power <I>P</I> = 10 W is about three times longer than that (= 8 m) when <I>P</I> = 100 W. This result indicates that the thermal distortion of laser beams due to accumulated heat around the <i>z</i> axis becomes more conspicuous as the optical power increases. The effect of this thermal beam distortion can be weakened when the laser beam is subject to crosswinds. Under the condition of gentle uniform wind with wind velocity <i>v</i> = 5 m/s, propagation of laser beams with ω = 20 mm was studied when <I>P</I> = 100 W. The <i>z</i>_h (= 105 m) when <i>v</i> = 5 m/s is about 13 times longer than that (= 8 m) when <i>v</i> = 0 m/s. Thus, under conditions of <i>v</i> = 5 m/s and 30% relative humidity, laser beams with <I>P</I> = 100 W and ω = 20 mm can propagate over 100 m without damaging the initial beam shape at λ₀ = 1.57μm.

Implementation of 10 Gbps optical wireless link for 200 km inter-aircraft optical communications

Abstract The enhancements related to optical devices are highly required for high-speed compact wireless optical transmission systems. This paper focuses on development and analysis of the communication system for inter-aircraft applications. The vertical cavity surface emitting laser (VCSEL) is employed at the transmitter for generating directly modulated non-return to zero (NRZ) signal. Direct detection along with Gaussian low pass filtering is employed in the receiver. The performance of the system is examined as well as compared with and without application of filtering at the receiver. The performance of optical wireless system is analyzed in terms of BER, eye-pattern, sensitivity, SNR, and Q-factor. The data rate is enhanced by 4-fold and transmission distance is improved by 250% in comparison with earlier inter-satellite links.

Mixed THz/FSO Relaying Systems: Statistical Analysis and Performance Evaluation

In this paper, the performance of a mixed Terahertz/free-space optical (THz/FSO) wireless transmission system is studied, where the joint effects of channel fading and pointing errors are considered for both THz and FSO links. Employing the semi-blind amplify-and-forward protocol, we derive the cumulative distribution function and probability density function of the end-to-end signal-to-noise ratio. By applying the derived statistics, exact expressions for the outage probability (OP), average bit error rate (BER), and average channel capacity are obtained. In order to attain useful physical insights, asymptotic OP and average BER expressions are also presented. Based on them, the diversity gain is determined, which is shown to depend on channel fading and pointing errors of both links. In addition, by taking into account the hardware impairments, the OP of the non-ideal hardware system is derived. Moreover, the analysis is extended to multi-antenna scenarios and the asymptotic OP is obtained. Finally, illustrative numerical results are plotted and it can be observed that the path loss, channel fading, pointing errors and hardware impairments lead to a considerable degradation in system performance.

Wireless optical power transmission based on the off-axis VECSEL of long resonator

We present laser generation in a several-meters-long air cavity using an optically pumped semiconductor gain chip for wireless optical power transmission applications. Theoretical calculations showed that stable laser oscillation can be realized in long laser oscillation cavities of more than 500 cm. Moreover, the laser oscillation can be maintained even when the output mirror of the laser is off-axis, which is useful in the alignment of energy charging terminals. A lens was inserted into the cavity to adjust the intra-cavity beam, and the beam radius on the gain chip surface sufficiently increased to match a large pump spot and achieve high output power. Laser generation in an external air cavity of 200 cm was realized, and the maximum output laser power of more than 705.4 mW was achieved. The off-axis range of the output mirror surpassed 19 mm. Moreover, the output laser power decreased by 5.5 % (from 586.4 to 554.2 mW) when the length of the external air cavity was increased from 100 to 200 cm. However, the off-axis range increased by 40.7 % (13.5 to 19 mm). Thus, the longer external cavity laser made it easier to align the laser beam and charging terminal.

Preliminary Characterization of Robust Detection Method of Solar Cell Array for Optical Wireless Power Transmission with Differential Absorption Image Sensing

In an optical wireless power transmission (OWPT) system, position and size of the photovoltaic device (PV) should be accurately determined from the light source position. Even though the detection of PV for OWPT has been studied and reported in some literature, the methods reported thus far are not so robust against varying background illumination. This study aims to solve such problems utilizing an image sensor which generates a differential absorption image from two wavelength images. Unnecessary background illumination presented in the two images is subtracted in the differential image. The differential image of the Si substrate target, which simulates PV, was detected by this sensor from a 104.5 cm distance. Signal illumination intensity was less than 1 μW/cm2 on the target, and detection accuracy was 3.1% for the diameter of the substrate and about 6.3% for the area. The system level requirement is derived, and they were verified by these results. The detection range of this sensor is shown to be expandable at the cost of, for example, increasing the receiver diameter of the image sensor or controlling the transmitter beam’s divergence. With the simple experiment apparatus, preliminary results of performance assessment were obtained and issues for performance improvement and potential of this image sensor were recognized.

Long-Distance High-Power Wireless Optical Energy Transmission Based on VECSELs

Wireless charging systems are critical for safely and efficiently recharging mobile electronic devices. Current wireless charging technologies involving inductive coupling, magnetic resonance coupling, and microwave transmission are bulky, require complicated systems, expose users to harmful radiation, and have very short energy transmission distances. Herein, we report on a long-distance optical power transmission system by optimizing the external cavity structure of semiconductor lasers for laser charging applications. An ultra-long stable oscillating laser cavity with a transmission distance of 10 m is designed. The optimal laser cavity design is determined by simulating the structural parameters for stable operation, and an improved laser cavity that produces an output of 2.589 W at a transmission distance of 150 cm is fabricated. The peak power attenuation when the transmission distance increases from 50 to 150 cm is only approximately 6.4%, which proves that this wireless power transfer scheme based on a vertical external cavity surface-emitting laser can be used to realize ultra-long-distance power transmission. The proposed wireless energy transmission scheme based on a VECSEL laser is the first of its kind to report a 1.5 m transmission distance output power that exceeds 2.5 W. Compared with other wireless energy transmission technologies, this simple, compact, and safe long-distance wireless laser energy transmission system is more suitable for indoor charging applications.

Automatic Gbps Receiver for Mobile Device in Beam-Steered Infrared Light Communication System

This work presents a beam-steered infrared light communication (BS-ILC) system that enables high data rate wireless optical transmission to individual mobile users. The BS-ILC system comprises arrayed waveguide grating router-based optical antennas, camera-based user localization, and optical receivers (each integrated with an infrared tag). A high-speed photodetector has typically a small active area to minimize its junction capacitance, but this small size will result in a very limited field of view (FoV), which is detrimental to an optical wireless system aimed to provide some degree of mobility to users. Thus, the desired BS-ILC system requires precise and automatic alignment to establish a high-performance optical link between users and optical antennas. In this work, we propose an optical wireless receiver that can automatically align its orientation with respect to the optical antenna to ensure the light angle of incidence within the receiver’s FoV. The automatic receiver consists of a motorized actuator and an optimization control algorithm. The actuator controls the orientation of the receiver, and the optimization algorithm is developed to accelerate the searching process of the actuator. In an indoor laboratory system setup, the amount of less than 200 ms has been demonstrated to establish gigabit-per-second optical link, and seamless transmission has also been realized for the mobile receiver while on the move with the FoV of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm 0.6^{\circ }$</tex-math></inline-formula> .

Design of Plasmonic Yagi-Uda Nanoantennas for Chip-Scale Optical Wireless Communications.

Optical wireless transmission has recently become a major cutting-edge alternative for on-chip/inter-chip communications with higher transmission speeds and improved power efficiency. Plasmonic nanoantennas, the building blocks of this new nanoscale communication paradigm, require precise design to have directional radiation and improved communication ranges. Particular interest has been paid to plasmonic Yagi–Uda, i.e., the optical analog of the conventional Radio Frequency (RF) Yagi–Uda design, which may allow directional radiation of plasmonic fields. However, in contrast to the RF model, an overall design strategy for the directional and optimized front-to-back ratio of the radiated far-field patterns is lacking. In this work, a guide for the optimized design of Yagi–Uda plasmonic nanoantennas is shown. In particular, five different design conditions are used to study the effects of sizes and spacing between the constituent parts (made of Au). Importantly, it is numerically demonstrated (using the scattered fields) that closely spaced nanoantenna elements are not appropriated for directional light-to-plasmon conversion/radiation. In contrast, if the elements of the nanoantenna are widely spaced, the structure behaves like a one-dimensional array of nanodipoles, producing a funnel-like radiation pattern (not suitable for on-chip wireless optical transmission). Therefore, based on the results here, it can be concluded that the constituent metallic rib lengths must be optimized to exhibit the resonance at the working wavelength, whilst their separations should follow the relation , where indicates the effective wavelength scaling for plasmonic nanostructures.