Wireless charging for mobile Internet of Things (IoT) devices such as smartphones is extremely difficult. To reduce energy dissipation during wireless transmission in mobile scenarios, laser or narrow radio beams with sophisticated tracking control are typically required. However, reaching the necessary tracking accuracy and reliability is really difficult. In this article, inspired by the features of optical resonators and retroreflectors, we develop an experiment on a self-aligned resonant beam charging system for long-distance mobile power transfer. It exploits light resonances inside a double-retroreflector-based spatially separated laser resonator (SSLR), which eliminates the requirement for any kind of tracking control. Focal telecentric cat’s eye retroreflectors are employed here. The SSLR was investigated by both theoretical calculation and experiment. We also well assembled the transmitter and the receiver and demonstrated its application in mobile smartphone charging. The results show that above 5-W optical power (also obtained more than 0.6-W electrical power) transferring with negligible diffraction loss to a few-centimeter-size receiver is realized while the receiver moves arbitrarily within 2-m vertical distance and 6° field of view from the transmitter. The maximum horizontal moving range is up to ±18 cm. This wireless charging system empowers a smartphone in mobile operation with unlimited battery life without the need for a cable.

Optical wireless communications (OWC) utilizing infrared or visible light as the carrier attracts great attention in 6G research. Resonant beam communications (RBCom) is an OWC technology which simultaneously satisfies the needs of non-mechanical mobility and high signal-to-noise ratio (SNR). It has the self-alignment feature and therefore avoids positioning and pointing operations. However, RBCom undergoes echo interference. Here we propose an echo-interference-free RBCom system design based on second harmonic generation. The transmitter and the receiver constitute a spatially separated laser resonator, in which the retro-reflective resonant beam is formed and tracks the receiver automatically. This structure provides the channel with adaptive capability in beamforming and alignment, which is similar to the concept of intelligent reflecting surface (IRS) enhanced communications, but without hardware and software controllers. Besides, we establish an analytical model to evaluate the beam radius, the beam power, and the channel capacity. The results show that our system achieves longer distance and smaller beam diameter for the transmission beyond 10 Gbit/s, compared with the existing OWC technologies.

Resonant Beam Charging (RBC) is a promising Wireless Power Transfer (WPT) technology to realize long-range and high-power charging for electronic devices. However, the safety mechanism of the RBC system has not been investigated so far. In this paper, we propose an analytical model based on electromagnetic field analysis for evaluating the performance of the RBC system with external object invasion, such as the benchmark for the WPT safety, irradiance on the invading object. For the RBC system with 5 m transmission distance and 1 W output electric power, the safety numerical analysis of radiation illustrates that the maximum irradiance on the invading object is 0.81 W/cm ² , which is approximately $1/10$ compared with 8.22 W/cm ² for the comparable laser charging system. Particularly, the peak irradiance on the invading object of the RBC system satisfies the Maximum Permissible Exposure (MPE) requirement for human skin, which is 1 W/cm ² in the standard “Safety of Laser Products IEC $60825-1$”. Hence, the RBC system can realize skin-safe WPT with Watt-level power over meter-level distance.

Simultaneous lightwave information and power transfer (SLIPT) has been regarded as a promising technology to deal with the ever-growing energy consumption and data-rate demands in the Internet of Things. We propose a resonant beam based SLIPT (RB-SLIPT) system, which deals with the conflict of high deliverable power and mobile receiver positioning with the existing SLIPT schemes. At first, we establish a mobile transmission channel model and depict the energy distribution in the channel. Then, we present a practical design and evaluate the energy/data transfer performance within the moving range of the RB-SLIPT. Numerical evaluation demonstrates that the RB-SLIPT can deliver more than 4W charging power and enable 3Gb/s achievable data rate with the moving range of 20° field of view (FOV) over 3m distance. Thus, RB-SLIPT can enable simultaneous high deliverable power and high data rate in mobile scenarios without tracking control.

Optical wireless communication (OWC) is a promising technology anticipated to play a key role in the next-generation network of networks (NoNs), especially as a complementary technology to traditional radio-frequency (RF) communications, for enhancing networking capabilities beyond conventional terrestrial networks. OWC is already a mature technology with diverse usage scenarios and can enable integrated applications via wireless access and backhaul networks, dynamic drone and satellite networks, underwater networks, inter- and intrasystem interconnecting networks, and vehicular communication networks. Furthermore, novel and emerging technological opportunities such as photovoltaic cells, orbital angular momentum-based modulation, optical reconfigurable intelligent surfaces, organic light-emitting and photo diodes, and recent advances in ultraviolet communications can help to enhance future OWC capabilities even further. Moreover, OWC networks can also support value-added services such as enhanced positioning and gesture recognition. Hence, OWC provides unique functionalities that can play a crucial role in building convergent and resilient future NoNs alongside RF and optical fiber technologies.

Both high-accuracy localization and power supply for mobile and Internet of Things (IoT) devices are demanding in the next-generation wireless networks. Recently, research on complete localization has been proposed, i.e., capturing the target’s location and identification (ID). However, the existing schemes face challenges, including: 1) improving positioning accuracy without the active emission of signals from the targets and 2) providing sufficient power for the targets to enable features such as ID. In this article, we present a simultaneous localization and power transfer (SLAPT) system relying on the resonant beam system (RBS), which can realize complete, passive, and high-accuracy positioning along with the capability of sufficient power supply. We first establish analytical models to illustrate the principles of power transfer to the target with an open-cavity laser, positioning the target, including Time-of-Flight (ToF) ranging and Angle-of-Arrival (AoA) estimation with the self-reproducing mode theory, wireless charging power conversion, and identifying the target using shutter modulation. Numerical results demonstrate that the proposed SLAPT system can achieve less than 1-cm positioning accuracy over 2-m distance in 16° Fields of View (FoVs) with 3-W wireless power supply. The proposed system allows passive and complete localization for the target without battery or power line in various IoT applications.