Effects of LED Device Size on UV-C Short-Range LoS Optical Wireless Communication

We report systematic investigation of the device-size-dependent performance of ultraviolet C (UV-C) light emitting diodes (LEDs) for optical wireless communication (OWC). Utilizing 273 nm-wavelength devices with diameters in the range of 40 $\mu$m to 300 $\mu$m, the size-dependent electrical, optical and frequency response characteristics of AlGaN UV-C LEDs are analyzed. As the junction area scales down, the smaller devices present lower optical power but faster modulation speed. Based on a 1-m point-to-point OWC system, this study further explores the LED size effect on the communication performance including channel gain, signal-to-noise ratio (SNR), theoretical Shannon capacity, achievable data transmission rate, relevant ratio, and spectral efficiency (SE). The system employing a 60 $\mu$m diameter (micro) LED transmitter achieves the highest average SNR and SE accompanying a data transmission rate up to a 5.53 Gbps at the forward error correction floor of 3.8$\times 10<^>{-3}$. These results suggest an optimal device diameter of $\sim$60 $\mu$m for further development of high-performance UV-C short-range line-of-sight (LoS) OWC.