In many military and industrial applications, GaAs photovoltaic (PV) converters are connected in series in order to generate the required voltage compatible with most common electronics. Multimode optical fibers are usually used to carry high-intensity laser and illuminate the series connected GaAs PV converters in real time. However, multimode optical fiber illumination has a speckled intensity pattern. The series connected PV array is extremely sensitive to nonuniform illumination; its performance is limited severely by the converter that is illuminated the least. This paper quantifies the effects of multimode optical fiber illumination on the performance of series connected GaAs PV converters, analyzes the loss mechanisms due to speckles, and discusses the maximum illumination efficiency. In order to describe the illumination dependent behavior detailedly, modeling of the series connected PV array is accomplished based on the equivalent circuit for PV cells. Finally, a series of experiments are carried out to demonstrate the theory analysis. 1. Introduction An increasing application of GaAs PV converters is the conversion of monochromatic light into electrical power [1–5]. A typical application of this technology is the optical transmission of energy or power-by-light. Electrical energy delivery in power-by-light systems represents a promising alternative for copper wires [6]. In such systems, the laser light is mostly transmitted through an optical fiber and a PV receiver converts the optical energy into electrical energy. These systems are used in places where the use of electrical energy is not recommendable, taking advantage of the properties of optical fiber such as electrical insulation, immunity from EMI, RF, and lightning. Examples of these applications are found in fields such as the oil industry, remote sensing, aerospace, explosions, high voltage power lines, and nuclear plants [7, 8]. In these applications, the required voltage of the electronic circuit is generally higher than that supplied by a single GaAs PV converter; this value is about 1？V. Therefore, GaAs converters are always connected in series to match the required voltage. One of the principal advantages to pursuing this technology is that electric power can be generated in a far smaller volume than required by a DC-DC converter. This option is more compact and has the possibility of integrating the GaAs PV converters with an electronic circuit. Fiber illumination is important because some of today’s optical power transfer applications do not have line of sight between the
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