Laser-based wireless power transmission technology (LWPT) is a relatively new technology for use in long-range wireless power transmission applications such as unmanned aerial vehicles and orbiting satellites.1,2 The LWPT system has two main components: a laser diode (LD) And the array of photovoltaics (PV), as shown in Figure below. 3 In any application, the overall efficiency of the system must be considered. This system efficiency includes both LD and PV matrix efficiencies, as it is responsible for reducing the efficiency of the implemented system. Most of the recent research on LWPT is focused primarily on device-level technologies and device applications. However, there are some studies that focus on enhancing the efficiency properties of the LD and PV matrix so that the system efficiency characteristic of the whole system remains ambiguous. In order to examine the system efficiency characteristic, the LWPT system in this article is designed as an optically coupled DC / DC converter, as shown in the figure below. As it can be seen from the figure that current has a direct effect on LD performance, so the system efficiency due to the input current is analyzed theoretically and measured experimentally. It is concluded that the system efficiency can be affected by the duty cycle of the LD input current, which makes some contribution to the field of LWPT technology. With the help of the relationship between transmission power and system efficiency under different operating cycle conditions of input current, a guideline for system control method can be provided. Subject to the above conditions, the system can be optimized by efficiently utilizing the LD and PV cell. Theoretical analysis of the system efficiency characteristic The efficiency characteristics of LD In wireless power transmission applications, LD can be powered by either DC (CC mode) or pulsed current (Pulse mode). 4 The figure below (above) shows the main waveform of LD under CC and pulse mode. First, we examine the relationship of LD competency and its current input, as LD performance is affected by its current input. It is evident from the figure below (below) that for the same output optical power, the smaller the duty cycle of the LD input current, the higher the efficiency of the LD. Efficiency Characteristics of PV Arrays The LD driving in pulse mode provides the advantage of high efficiency. It is therefore quite natural to investigate the mechanism of how the efficiency of the PV array changes with the continuous optical energy of the pulse incident. The voltage and current of the PV array at the maximum power point depend on the radiation level and the temperature of the cell. In standard environmental conditions, the irradiance level is 1000 W / m2 and the cell temperature is 25 ° C. Increasing the temperature degrades the efficiency of the photovoltaic cell. To overcome this problem, a cooling system is used in the LWPT system to keep the cells’ temperature as low as possible. This cooling system aids in achieving maximum photovoltaic cell performance. Hence, it was concluded that temperature can be ignored. The figure below shows the graph of the efficiency against the incident light power under different laser pulse duty cycles. It can be easily seen in the graph that the smaller the duty cycle, the higher the efficiency. Hence, it was concluded that for the effective performance of photovoltaics at high laser density, the PV array should be illuminated by the pulsed laser. System Efficiency Characteristics For an LWPT system, losses in the LD and PV array are the main contributing factors to the system rather than other components. So the efficiency of the system is determined by the efficiency of LD and PV. As mentioned earlier, the duty cycle has the same effect on the efficiencies of both the LD and PV array in the case of specialized PV cells. Therefore, the efficiency of the system will increase with the decrease in the duty cycle. Conclusion In this article, we have discussed and examined the LWPT system. There have been few studies on this system and they are considered in this article. In short, the system efficiency is directly related to the duty cycle of the LD input current; The smaller the duty cycle, the more efficient the system. Hence, controlling the duty cycle of the pulsed laser is the main factor in improving system efficiency. References 1 Evaluation of the efficiency of a laser-based wireless power transmission system. Weiyang Zhou, Department of Electrical and Computer Engineering, University of Michigan – Dearborn, USA, [email protected]; Ke Jin, College of Automation Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing, China, 2R. Mason, “The Feasibility of Transferring Laser Power to a High Altitude Unmanned Aerial Vehicle,” The Rand Corporation, 2011. 3D. E-Ripple. “High Density Laser Power Radiation for Wireless Power Transmission”, MSc Thesis, Department of Electrical and Computer Engineering, Cleveland State University, Cleveland, Ohio, May 2008. 4 Weiyang Zhou and Ke Jin, “Evaluation of laser diode efficiency in different drive modes for power transmission Wireless, IEEE Trans. Electron Force, Vol. 30, No. 11, pp. 6237–6,244, 2015.5K. J. Sauer, T. Roesslor, and CW Hansen, “Modeling the Radiation and Temperature Dependence of PV Modules in PVsyst,” IEEE Journal. From photovoltaics. , Vol. 5, No. 1, pp. 152-158, 2015.6O. Hohn, AW Walker, AW Bett, and H. Helmers, “Laser wavelength optimized to operate the laser transducer efficiently above temperature,” APLA. Phys. Lett., Vol. 108, Issue 24, Pages 1-9, 2016.