1
Distributed Laser Charging:
A Wireless Power Transfer Approach
Qingqing Zhang, Student Member, IEEE, Wen Fang, Qingwen Liu
∗
, Senior Member, IEEE, Jun Wu, Senior
Member, IEEE, Pengfei Xia, Senior Member, IEEE, and Liuqing Yang, Fellow, IEEE
Abstract—Wireless power transfer (WPT) is a promising
solution to provide convenient and perpetual energy supplies to
electronics. Traditional WPT technologies face the challenge of
providing Watt-level power over meter-level distance for Internet
of Things (IoT) and mobile devices, such as sensors, controllers,
smart-phones, laptops, etc.. Distributed laser charging (DLC), a
new WPT alternative, has the potential to solve these problems
and enable WPT with the similar experience as WiFi com-
munications. In this paper, we present a multi-module DLC
system model, in order to illustrate its physical fundamentals
and mathematical formula. This analytical modeling enables
the evaluation of power conversion or transmission for each
individual module, considering the impacts of laser wavelength,
transmission attenuation and photovoltaic-cell (PV-cell) tempera-
ture. Based on the linear approximation of electricity-to-laser and
laser-to-electricity power conversion validated by measurement
and simulation, we derive the maximum power transmission
efficiency in closed-form. Thus, we demonstrate the variation
of the maximum power transmission efficiency depending on the
supply power at the transmitter, laser wavelength, transmission
distance, and PV-cell temperature. Similar to the maximization
of information transmission capacity in wireless information
transfer (WIT), the maximization of the power transmission
efficiency is equally important in WPT. Therefore, this work not
only provides the insight of DLC in theory, but also offers the
guideline of DLC system design in practice.
Index Terms—Wireless power transfer, distributed laser
charging, power transmission efficiency.
I. INTRODUCTION
Internet of Things (IoT) and mobile devices, such as
sensors and smart-phones, are typically powered by batteries
that have limited operation time. Sensors for IoT, especially
sensors that being deployed in special environments such as
volcanoes, are difficult to be charged. Meanwhile, carrying a
power cord and looking for a power supplier to charge mobile
devices incur great inconvenience. An alternative is thus to
transfer power wirelessly, which virtually provides perpetual
energy supplies. Hence, wireless power transfer (WPT) or
wireless charging attracts great attention recently.
Three major wireless charging technologies are surveyed
in [1, 2]. Inductive coupling is safe and simple for implementa-
tion. However, it is limited by a short charging distance from
Q. Zhang, W. Fang, Q. Liu, J. Wu, and P. Xia, are with the
College of Electronic and Information Engineering, Tongji University,
Shanghai, China, (email: anne@tongji.edu.cn, wen.fang@tongji.edu.cn, qing-
wen.liu@gmail.com, wujun@tongji.edu.cn, pengfei.xia@gmail.com).
L. Yang is with the Department of Electrical and Computer En-
gineering, Colorado State University, Fort Collins, CO 80523, USA
(email:lqyang@engr.colostate.edu).
* Corresponding author.
Inter-Drone Charge
DLC
Transmitter-2
DLC
Transmitter-1
TV
Laptop
Watch
Camera
Phone
Pad
Drone-1
Drone-2
Phone
Sensor
Fig. 1 Distributed Laser Charging Applications
a few millimeters to centimeters, which is only suitable for
contact-charging devices like toothbrush. Magnetic resonance
coupling has high charging efficiency. However, it is restricted
by short charging distances and big coil sizes, which fits
home appliances like TV. Electromagnetic (EM) radiation has
long effective charging distances. However, it suffers from
low charging efficiency and is unsafe when the EM power
density exposure is high, hence is only favorable for low-power
devices like sensors. In a nutshell, these traditional WPT tech-
nologies provide great wireless charging abilities for different
application scenarios, whereas it is still challenging to offer
sufficient power over long distance for safely charging IoT
and mobile devices, e.g., smart-sensor, smart-phone, laptop,
drone, etc., which usually need Watt-level power over meter-
level distances.
To support the power and distance requirements for IoT
and mobile devices, a distributed laser charging (DLC) system
is presented in [3], which could transfer 2-Watt power over a
5-meter distance [4]. By using inductive coupling or magnetic
resonance coupling, IoT and mobile devices, say sensors and
smart-phones, should typically be placed in a special charging
cradle with a particular position. However, the DLC’s self-
aligning feature provides a more convenient way of charging
IoT and mobile devices without specific positioning or track-
ing, as long as the transmitter and the receiver are in the line of
sight (LOS) of each other. Different from EM radiation, DLC’s
arXiv:1801.03835v3 [eess.SP] 9 Oct 2018
