Optical Power Transmission Research Articles

Solar Cell Detection and Position, Attitude Determination by Differential Absorption Imaging in Optical Wireless Power Transmission

In optical wireless power transmission, position, size, and attitude of photovoltaic device (PV) must be determined from light source. A method proposed in the previous report is based on selective absorption characteristics of PV, and it is detected by differentiating images of strongly absorbable wavelength and one not. In this study, using two infrared wavelengths, two kinds of targets were detected by differential absorption imaging. One was a GaAs substrate which simulates diffuse rear surface, and the other was a real GaAs PV. It was found that the substrate’s reflective characteristic was diffuse, and the solar cell’s was mainly non-diffuse and accompanied by small diffuse component supporting wide-angle reflection. Using this feature, the position of the GaAs solar cell could be determined within a wide range of angle. Its attitude could also be determined with an accuracy of ±10 degrees to its normal. The position of diffuse GaAs substrate could be determined within a wide range of angles, and its attitude determination was proposed by exploiting its varying apparent size with tilt angle. Broad reflection characteristics of the GaAs substrate enabled attitude determination for a wide-angle range, and determination around normal would be erroneous.

Ultrasensitive tapered optical fiber refractive index glucose sensor

Refractive index (RI) sensors are of great interest for label-free optical biosensing. A tapered optical fiber (TOF) RI sensor with micron-sized waist diameters can dramatically enhance sensor sensitivity by reducing the mode volume over a long distance. Here, a simple and fast method is used to fabricate highly sensitive refractive index sensors based on localized surface plasmon resonance (LSPR). Two TOFs (l = 5 mm) with waist diameters of 5 µm and 12 µm demonstrated sensitivity enhancement at λ = 1559 nm for glucose sensing (5–45 wt%) at room temperature. The optical power transmission decreased with increasing glucose concentration due to the interaction of the propagating light in the evanescent field with glucose molecules. The coating of the TOF with gold nanoparticles (AuNPs) as an active layer for glucose sensing generated LSPR through the interaction of the evanescent wave with AuNPs deposited at the tapered waist. The results indicated that the TOF (Ø = 5 µm) exhibited improved sensing performance with a sensitivity of 1265%/RIU compared to the TOF (Ø = 12 µm) at 560%/RIU towards glucose. The AuNPs were characterized using scanning electron microscopy and ultraviolent-visible spectroscopy. The AuNPs-decorated TOF (Ø = 12 µm) demonstrated a high sensitivity of 2032%/RIU toward glucose. The AuNPs-decorated TOF sensor showed a sensitivity enhancement of nearly 4 times over TOF (Ø = 12 µm) with RI ranging from 1.328 to 1.393. The fabricated TOF enabled ultrasensitive glucose detection with good stability and fast response that may lead to next-generation ultrasensitive biosensors for real-world applications, such as disease diagnosis.

Implementation of PoF-powered IoT Sensing Systems for Industry 4.0

We propose and experimentally investigate two distinct power-over-Fiber (PoF) approaches, aiming to remotely power Internet-of-Things (IoT) sensing systems for Industry 4.0 environments. The first proof-of-concept is focused on demonstrating a 1-W optical power transmission through a 50-m-fiber-optic link for powering an Arduino Uno, a temperature sensor (DS1820B), and a 433-MHz transceiver (FS1000A). The designed PoF link is able to provide up to 280 mW with power transmission efficiency (PTE) of 28.9%. The second implementation is based on a 100-m PoF link capable of transmitting over 0.6-W optical power and delivering 140-mW electrical power with PTE of 23%. In this scheme, an Arduino Pro Mini, another temperature sensor (LM35), and a 2.4-GHz transceiver (nRF24L01+) are employed. A voltage stability analysis enables to demonstrate that our PoF system is capable of delivering stable output voltage at 8.5 V and 5 V, with only 0.6% and 0.2% voltage fluctuations. In addition, an industrial oven is employed to evaluate the sensor performance considering temperature measurements from both sensing systems. The obtained results demonstrate that PoF might be considered as a potential technology to optically-power IoT wireless sensing systems for Industry 4.0 scenarios.

Retraction: A design of wet-mateable connector aiming for contactless power transfer and optical communication (IOP Conf. Ser.: Earth Environ. Sci. 1152 012016)

This article has been retracted by IOP Publishing following the discovery that large sections of it were duplicated from another paper [1] written by the authors that was submitted to another publisher in parallel and published prior to this article. The authors initially requested a retraction, but failed to provide necessary information and then withdrew the retraction request. The authors have now confirmed that redundant publication has occurred. This matter was investigated in line with COPE guidelines and IOP Publishing has decided to retract the work. The authors agree to this retraction. [1] Duan, Z., Zhang, Y., Hu, J., He, B., & Yang, C. (2023). Research on non-contact wet mateable connector for optical communication and power transmission. Retrieved from https://www.frontiersin.org/articles/10.3389/fmars.2023.1100653/full Retraction published: 27 July 2023

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.

Research on non-contact wet mateable connector for optical communication and power transmission

At present, contact watertight connectors are commonly utilized for the connection between underwater electromechanical equipment and the seabed observation network. Such traditional watertight connectors are easy to be irreversibly worn when plugging and unplugging, however, they have complicated sealing structures and limited service life. This paper designs a Non-contact Wet Mateable connector for Optical Communication and Power Transmission (OCPT-NWMC), which is based on technology of Contactless Power Transmission (CLPT) and optical communication. Docking structure of the sockets and plugs are designed, facilitating Remotely Operated Vehicle (ROV) to operate. A prototype of the OCPT-NWMC was established. The experimental results show that the connector designed can achieve 200W power transmission, with a maximum power transmission efficiency of 94%. The communication bandwidth reaches 18MHz. The OCPT-NWMC can assist the rapid and safe deployment and operation of seabed observation network.

Numerical analysis of a strip-loaded silicon rich nitride-thin film lithium niobate hybrid waveguides

Hybrid integration of silicon rich nitride and lithium niobate on insulator (SRN-LNOI) is an emerging material platform for photonic integrated circuits (PIC). In this paper, we present a systematic numerical investigation of the mode properties of a strip-loaded SRN-LNOI hybrid waveguide at 1550 nm wavelength using the full-vectorial finite difference method. Considering the anisotropic nature of the lithium niobate (LN) crystal, the effective refractive indices of the transverse electric and transverse magnetic modes of strip-loaded SRN-LN hybrid waveguides were analyzed. The single-mode condition, zero-birefringence, effective mode area, and power distribution in terms of the geometrical parameters of the strip-loaded SRN-LN hybrid waveguide are discussed in detail. Furthermore, the optical power transmission in both straight and bent waveguides, as well as the different characteristics of the optical power confinement of the fundamental modes in the SRN and LN layers were analyzed. This study provides useful information for designing high-performance photonic devices on a hybrid SRN-LNOI platform for future PIC applications.

Correction: Asaba, K.; Miyamoto, T. System Level Requirement Analysis of Beam Alignment and Shaping for Optical Wireless Power Transmission System by Semi–Empirical Simulation. Photonics 2022, 9, 452

In the original publication [...]

Relaxation of Beam Irradiation Accuracy of Cooperative Optical Wireless Power Transmission in Terms of Fly Eye Module with Beam Confinement Mechanism

In optical wireless power transmission (OWPT) systems, since beam size is finite, and relative position and attitude between transmitter and receiver is not always stationary, both beam alignment and shaping accuracies are important parameters. Analysis based on a power generation efficiency calculation model of general OWPT systems shows that their tolerances are quite demanding, especially for long range OWPT, and relaxation is inescapably necessary. This study introduces the fly eye lens as a candidate to relax these difficulties and, moreover, it features producing homogeneous irradiation onto the solar cell array. All of these are essential to OWPT systems. In this study, cooperative OWPT is discussed, in which solar cell array and power transmitter mutually align each other. Its efficiency calculation model is integrated with a fly eye module surrounded by reflective walls. System level requirements are analyzed regarding beam shaping and alignment in terms of power generation ratio, and it is clarified that this module largely relaxes requirements. In this module, beam power is confined within the module and will be eventually absorbed by the solar cell as the incident beam is within the acceptance angle. This feature avoids degradation of power generation ratio due to beam shape mismatch. These advantages bring progress towards building operational OWPT.

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.

Gold nanoparticles are capped under the IRMOF-3 platform for in-situ surface-enhanced Raman scattering technique and optic fiber sensor

Integrating noble-metal and organic-inorganic hybrid crystalline porous materials for Raman signal augmentation is crucial for surface-enhance Raman spectroscopy. This study effectively generated gold nanoparticles / metal-organic frameworks (Au NPs/IRMOF-3) hybrids. The activity of Au NPs/IRMOF-3 double component substrate was significantly enhanced under localized surface plasmon resonance (LSPR) because the hot electrons produced on Au NPs surface were incorporated with IRMOF-3 and utilized the porous structure to capture the analyte. Development much hot spots of great significance for surface-enhanced Raman scattering (SERS) technique, herein, we developed an Au NPs/IRMOF-3-based nanosensor for rhodamine B (RhB) sensing by using in-situ SERS technique. X-ray diffraction (XRD) spectrometry, surface morphology analysis, optical properties, and energy-dispersive X-ray (EDX) spectroscopy were used to examine the layer-by-layer deposited substrate. The Au NPs/IRMOF-3 multilayers generated chemical and electromagnetic amplification of Raman signals of Rhodamine B at a low concentration and high enhancement factor. In the presence of dopamine molecules, due to the strong specific affinity between the modified surface out-layer of fiber sensor and the target molecules, resulting in the obvious change of the optical power transmission signals, which can be used for dopamine sensing with high sensitivity and stability (limit of detection is 1.42 × 10 -18 M with a wide linear range from 10 -17 to 6 × 10 -8 M of dopamine). The Au NPs/IRMOF-3 nanosensor can be used as an ideal platform for real applications, especially for some gases or low-weight molecules in the future. • Using a traditional synthesis approach, low cost, and high synthesis efficiency. • This sensor has high homogeneity and a stable arrangement structure. • Determination of Rhodamine B at low detection limit of 10 -9 M along with an enhancement factor of 6.54 × 10 9 . • Limit of detection is 1.42 × 10 -18 M and measurement range with a linear response from 10 −17 to 10 −8 M.

Study on the Efficiency of Temperature/Strain Measurement for Ultra-Long-Distance Optical Fiber Composite Overhead Power Transmission Lines

The coherent optical time domain reflectometer (COTDR) is a very important instrument for distributed temperature/strain measurement along the sensing fiber with a large dynamic range and high accuracy. The length of the sensing fiber and the temperature/strain measurement range limit the system performance, especially the measurement efficiency. So, a COTDR system is constructed, and the characteristics of the obtained coherent Rayleigh noise (CRN) are analyzed. Then, in consideration of the temperature/strain measurement range, accuracy, and time efficiency, the temperature/strain demodulation algorithm in noise conditions is studied. With different noise coefficients, the array length with 11, 21, 31, 51, and 101 independent frequency sweeping points are adopted to calculate the cross-correlation coefficients along a standard reference array with 301 independent frequency sweeping points. The results demonstrate that the array length has little influence on the signal processing time, but it can decide the measurement accuracy. To balance the system measurement efficiency and accuracy, it is inferred that, for a sensing fiber with a length of 100 km or more, the optimal independent frequency sweeping points are 101 and the trace average number is 1000.

Stimulated Brillouin Scattering Threshold in Presence of Modulation Instability for Optical Pulse in Long Optical Fiber

A theoretical and experimental study on the stimulated Brillouin scattering (SBS) threshold for optical pulse in the presence of modulation instability (MI) in long optical fiber is presented. The effects of MI on the SBS gain and threshold are analyzed based on the coupled-wave equation. An analytic expression is obtained to calculate the SBS threshold in the presence of MI. Numerical simulation is conducted to study the effects of the repetition rate and amplified spontaneous emission (ASE) noise on the SBS threshold for optical pulses. An experiment is conducted, and the results agree well with the theoretical analysis. The results clearly reveal how MI affects the Brillouin gain and SBS threshold of optical pulses in long optical fiber. The SBS threshold is affected by the ASE noise level and the repetition rate of the optical pulse. The study is helpful for the power evaluation of interferometric fiber sensing systems and optical power transmission systems.

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.

Experimental Characterization of High Tolerance to Beam Irradiation Conditions of Light Beam Power Receiving Module for Optical Wireless Power Transmission Equipped with a Fly-Eye Lens System

This paper is an experimental characterization of a light-receiving module containing a fly-eye lens system with high tolerance to beam irradiation conditions. The fly-eye lens system, which is tolerant to fluctuations in beam shape, beam size, number of beams, beam incident position, and beam incident direction, was proposed, a light receiver module with a fly-eye lens system was constructed, and its characteristics were evaluated. The effect of the beam size on the fly-eye lens system was evaluated and the tolerance to misalignment of beam incident position was measured. When a GaAs solar cell was irradiated with a laser beam of 450 nm wavelength and 6 W light output through a 90 cm long water tank with tap water, a maximum output of 0.755 W was obtained as underwater OWPT. In addition, a fly-eye lens system with mirrors applied to four surfaces was proposed and fabricated as a light-receiving side module that can receive high incident angles from any direction of up, down, left, and right and its effectiveness was clarified through experiments.

Theory of Dronized Laser Source for Next Generation of Optical Wireless Power Transmission

A theory of dronized laser resonator source which can be applied effectively to achieve an efficient remote wireless optical power transmission (WOPT) for the next 6G mobile communications, internet of things (IoT) devices, and continuous flying unmanned aerial vehicles (UAV) is proposed. The proposed laser resonator composes mainly of mirrors and a gain element that can be carried individually by drones to form a relatively long cavity. The airborne components can be assembled according to a specified formation flight of drones to configure a flying laser cavity that exposes its output towards the corresponding target. The stability of the proposed device is theoretically analyzed in terms of main important intracavity parameters, such as length, g-geometrical parameters, and radius of curvature of mirrors. Accordingly, the performance of the confocal symmetric laser resonator is determined in terms of mode size, beam waist size, and beam divergence angle of the fundamental mode in presence of refractive power variation. Simulation results have shown that a stable operation over a wide range of refractive power of confocal long laser resonator can be obtained when the value of curvature of mirror approaches resonator length. In addition, an acceptable fundamental mode size at gain element and mirrors is obtained with an expected efficient gain medium excitation and low diffraction loss.

1 W High Performance LED-Array Based Optical Wireless Power Transmission System for IoT Terminals

Optical wireless power transmission (OWPT) is a promising technology for remote energy supply, especially for powering Internet of things (IoT) terminals. Light-emitting diode (LED)-based power sources of OWPT are attractive for the development of high-performance systems without the constraints of safety issues. In this paper, the electricity output of a near-infrared LED-OWPT is significantly improved. The saturation output caused by the small lens aperture in the LED array collimation scheme was analyzed. The experiment achieved a maximum electricity output of more than 1 W from a 50 × 50 mm2 GaAs solar cell at 1 m transmission distance. In addition, the thermal features also proved the feasibility of a high-output LED-OWPT system for practical applications.

System Level Requirement Analysis of Beam Alignment and Shaping for Optical Wireless Power Transmission System by Semi–Empirical Simulation

Since optical wireless power transmission (OWPT) transmits power by light, which has a narrow diffraction angle feature, it is a strong candidate for wireless power transmission systems supporting long ranges. To develop a realistic operational OWPT system, clarification of system level requirements is essential. In this study, to fill a gap between the concept/initial demonstration and an operational system, the required conditions were analyzed regarding the effects of beam alignment and shaping on the power generation ratio which is a system level efficiency factor with extension from the formerly reported one-dimensional analysis to three-dimensional to include errors in all degrees of freedom is presented. This extension is regarded as an indispensable methodology to evaluate the system level performance of general OWPT systems. Numerical requirements for beam alignment and shaping are derived for both non-cooperative and cooperative OWPT. In non-cooperative OWPT, the direction of the solar cell module is fixed, and the transmitter aligns its beam with the module. In cooperative OWPT, the module and transmitter mutually align in the same direction. Though the cooperative OWPT is more restrictive than the non-cooperative one, its advantages were clarified.

Optical Wireless Power Transmission Using a GaInP Power Converter Cell under High-Power 635 nm Laser Irradiation of 53.5 W/cm2

Optical wireless power transmission (OWPT) system is a technology that supplies energy from remote locations, having some features such as long-distance transmission, high directivity, and no electromagnetic noise interference. This study investigated the optical transmission efficiency and photoelectric conversion efficiency with a transmission distance of 10 m using GaInP power converter cells with a small area of 2.40 × 2.40 mm2 and a 635 nm high-power laser over 50 W/cm2. As a result, we achieved a photoelectric conversion efficiency of 44.7% under 6.7 W/cm2 (0.14 W) and 37.2% under 53.5 W/cm2 (1.1 W) irradiation. These results suggested that W-class optical wireless power transmission could be realized by expanding the converter cell area. Additionally, it was found that the reductions of the divergence angle of the laser and the heat generation of the power converter cell were critical issues for further lengthening the distance and increasing the power.