Single-Photon Counting Receivers for 6G Optical Wireless Communications

Optical wireless communication (OWC) offers several complementary advantages to radio-frequency (RF) wireless networks such as its massive available spectrum; hence, it is widely anticipated that OWC will assume a pivotal role in the forthcoming sixth generation (6G) wireless communication networks. Although significant progress has been achieved in OWC over the past decades, the outage induced by occasionally low received optical power continues to pose a key limiting factor for its deployment. In this work, we discuss the potential role of single-photon counting (SPC) receivers as a promising solution to overcome this limitation. We provide an overview of the state-of-the-art of OWC systems utilizing SPC receivers and identify several critical areas of open problems that warrant further research in the future.

Evaluation of SiPM based Optical Receiver for Low Energy Devices

Silicon Photomultipliers (SiPMs) are photon-counting detectors with great potential to improve the sensitivity of optical receivers. However, its recovery time and dark count rate could limit its dynamic range that effectively detects single photons, hence limiting the sensitivity. Recent studies of SiPMs in communication focus on the speed rather than the power consumption of the receiver. The gain and bandwidth of the designed receiver circuit to read out SiPM output are much higher than required for the target data rate. Additionally, the SiPM experiments for optical communication are performed using an offline method which uses instruments including oscilloscopes and personal computers to process chunks of the transmitted data. In this work, we have developed an embedded realtime system FPGA-based platform to evaluate a commercially available 1 mm-sq SiPM. Moreover, simulations for investigating the relationship between the electrical bandwidth of the receiver circuit and the target data rate to achieve a target Bit Error Rate (BER) are established. The experimental results show that the implemented real-time system achieves a Bit Error Rate (BER) of 1E-3 with less than 5 pW of incident optical power with an average of 11.35 photons per bit at 100 kbps under 620 nm LED, approaching the Poisson limit. It was found that the minimum receiver electrical bandwidth required to maintain the Poisson limit is 50 times higher than the target data rate. The analysis of the minimum receiver bandwidth in photon counting and BER enables the potential future adoption of this receiver technology in high sensitivity applications in underwater and visible light communications, especially for low energy devices.