  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 communications. 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) temperature. 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.
