Key Technologies Of Resonant Beam Communications

New requirements of the mobile Internet and the Internet of Things are constantly promoting the evolution of wireless communication technology from the fourth generation(4G)to the fifth generation(5G),and even to the sixth generation(6G),and also promoting the continuous improvement of wireless communication carrier frequency.In the next generation of mobile communication,ultra-high frequency,including terahertz,infrared,and visible light,will bring Tbit/s-level channel capacity.On the other hand,with the increasing requirements for mobile computing performance,battery life has become a bottleneck with respect to the development of new technologies and applications.Simultaneous wireless information and power transfer(SWIPT)makes power supply become the endogenous ability of mobile communication network,which may become an important direction of the next generation of mobile Internet.Laser-based optical wireless communications(OWC)and SWIPT can meet the demands for bandwidth,power,and transmission distance in future scenarios.However,directional laser needs the assist of beam steering,alignment,and tracking technologies.The accuracy and response speed of these technologies are important factors affecting the practicability of laser-based OWC/SWIPT.Although some promising non-mechanical beam steering methods have been developed,the existing positioning technologies are difficult to guarantee the alignment and tracking accuracy over a long distance.Especially,some high-accuracy positioning networks are expensive and complex.On the other hand,under the safety requirement,how to detect foreign body intrusion and ensure the safety of high-power laser has become an important topic.As a special intra-cavity laser,the resonant beam is generated by a spatially separated laser resonator(SSLR).Different from the conventional laser,the resonant beam features self-alignment,self-tracking,high power,and intrinsic safety,which can be used to overcome the aforementioned problems.In this paper,the resonant beam-based OWC/SWIPT system is proposed,and several topics are investigated.The contributions are as follows:1.In this paper,we propose a telecentric cat’s eye retroreflector(TCR)which possess a customizable focusing ability.Then,we propose an SSLR design based on this focusing TCR to satisfy the need for low diffraction loss,which makes it possible to generate the resonant beam over a long distance.We also reveal the mechanism of the low-diffraction-loss feature of the self-aligned/self-tracking resonant beam and propose the analytical model for calculating the end-to-end transmission power,which provides a theory basis for the research of resonant beam communications.2.We analyze the echo interference issue of the resonant beam communication system and study the causes of the echo interference and its influence on intracavity modulation.To overcome this issue,we propose an echo-interference-free system design.We also establish an analytical model for the proposed system and find that the theoretical capacity can reach 14-bit/s/Hz,verifying the feasibility of high-rate resonant beam communication.3.We also design a resonant-beam-based SWIPT system and propose an algorithm to optimize the system parameters based on Monte Carlo method and stochastic gradient descent method.We find that the resonant-beam-based SWIPT system can simultaneously achieve high-rate communication and watt-level electrical power transmission.This research expands the scope of resonant beam communications and makes it more promising in application.4.Finally,an experiment platform and a time-domain simulation algorithm are demonstrated,and the implementations of several key technologies are presented,including resonant beam generation,self-alignment,self-tracking,modulation,and power transfer.In the experiment,we realized receiving 5-W optical power,which was then converted into 0.6-W electrical power,at 2-m distance and within6°field-of-view.The experiment demonstrates the advantages of the resonant beam communication technology,such as high safety and high mobility,compared with conventional laser technologies.The experiment design and results can be good references for future works.Above all,the outcomes of the theoretical and experimental research on the resonant beam-based OWC/SWIPT provide resonant beam technology with potential competitiveness in the field of OWC/SWIPT.