Multi-Segment Photonic Power Converters for Energy Harvesting and High-Speed Optical Wireless Communication

TL;DR

This work demonstrates that partitioning GaAs photonic power converters into multiple series-connected subcells reduces capacitance and raises bandwidth, enabling simultaneous energy harvesting and high-speed data reception in eye-safe optical wireless links. By implementing 2-, 4-, and 6-segment GaAs PPCs with OFDM-based adaptive loading over a 1.5 m link, the system achieves a world-record data rate of $3.8$ Gbps and harvests up to $39.7\%$ of incident optical power. The study quantifies the trade-offs between segmentation, current matching, and PCE, showing that higher segmentation improves bandwidth and SNR but can degrade energy harvesting under nonuniform illumination, emphasizing the need for precise illumination control for practical backhaul and 6G networks. The results indicate that multi-segment PPCs offer a viable path for integrated energy delivery and high-speed communication in compact, eye-safe devices, with explicit ocular safety validation per IEC standards.

Abstract

The demand for energy-efficient high-speed wireless communication, coupled with the rapid rise of IoT devices, requires systems that integrate power harvesting with optical data reception to eliminate the need for charging or battery replacements. Recent advances have explored the use of solar cells as optical receivers for high-speed data detection alongside power harvesting. \acs{GaAs}-based \acp{PPC} provide six times greater electron mobility than silicon- or cadmium telluride-based cells, enabling faster data detection and improved power efficiency. However, their bandwidth is constrained by junction capacitance, which increases with active area, creating a trade-off between power output and data rate. To address this, we propose and test multi-segment \acs{GaAs}-based \Acp{PPC} that serve as both energy harvesters and data detectors. By segmenting the active area into 2, 4, or 6 subcells, forming circular areas with diameters of 1, 1.5, or 2.08~mm, we reduce capacitance and boost bandwidth while preserving light collection. Fabricated on a semi-insulating \ac{GaAs} substrate with etched trenches for electrical isolation, the series-connected subcells optimize absorption and minimize parasitic effects. The \Acp{PPC} were used for an eye-safe 1.5~m optical wireless link, employing \ac{OFDM} with adaptive bit and power loading. The system achieved a world record data rate of 3.8~Gbps, which is four times higher than prior works. The system converts 39.7\% of optical power from a beam of 2.3~mW, although the segmentation increases the sensitivity of the alignment. These findings provide new solutions for off-grid backhaul for future communication networks, such as 6th generation (6G) cellular.

Figures (6)

• Figure 1: Comparison of state-of-the-art studies on PV cell-based receivers with this works result using a 4-segment GaAs-based cell.
• Figure 2: Multi-segment GaAs photovoltaic receiver structures: a, Schematic of the epitaxial structure and interconnection scheme. b, Measured spectral response of a single segment. c, Example current-voltage curves of single- and only partially interconnected segments as well as of an entire 6-segment device measured under monochromatic 809-nm illumination at uniform and similar irradiance.
• Figure 3: QAM symbol constellations and measured SNR performance of the PPC-based receiver: (a) Ideal transmitted symbols (red dots) and received symbols (blue dots) for QAM modulation orders $M = 2, 4, 16,$ and $32$; (b--d) measured SNR of the PPC-based receiver with adaptive bit allocation, implemented on a GaAs device with a circular active area of diameter $d = 2.08~\mathrm{mm}$, for configurations with (b) 2 segments, (c) 4 segments, and (d) 6 segments.
• Figure 4: Experimental setup and characteristics: (a) Block diagram for the proposed GaAs-based PPC receiver system; (b) Photograph of the experimental setup of the eye-safe infrared wireless communication system with a link length of 1.5 meters; (c) Measured characteristics of the VCSEL laser source; (d) Colored photographs of example devices. Circular sectors are interconnected outside the circular active area across isolation trenches (white dashed lines) from terminals underneath the active junction (green) to front-side contacts (yellow). Larger pads at one side (“+” and “–“) enable electrical contacting of the entire series-connected string via thin wire bonding.
• Figure 5: Recorded measurements for the PPC-based GaAs receiver. The receiver features circular active areas with diameters $d$ of 1 mm, 1.5 mm, and 2.08 mm. The figure presents: a. measured SNR for various numbers of segments; b.BER results versus data rate for different segment counts; and c.PPC I-V curve measured using a transmitter with an emitted optical power of $2.3$ mW, a DC bias of 1.78 V and a current of 6 mA.