1 Gbps free-space deep ultraviolet communications based on III-nitride micro-LEDs emitting at 262 nm

He, Xiangyu and Xie, Enyuan and Islim, Mohamed Sufyan and Purwita, Ardimas Andi and McKendry, Jonathan J. D. and Gu, Erdan and Haas, Harald and Dawson, Martin D. (2019) 1 Gbps free-space deep ultraviolet communications based on III-nitride micro-LEDs emitting at 262 nm. Photonics Research, 7 (7). B41-B47. ISSN 2327-9125

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    Deep ultraviolet (DUV) communications have many advantages including low background noise, large coverage area enabling non-line-of-sight (NLOS) communications and high security. However, so far the reported data transmission rates of deep UV communications are less than 100 Mbps, which is mainly limited by the low modulation bandwidth of the light sources used. In this paper we present the III-nitride micro-light emitting diodes (µLEDs) emitting in the UV-C region and their applications as light sources for deep UV communications. These µLEDs are in trapezoidal pixel form with emission area of 565.5µm^2 (equivalent area to disk shaped LEDs of diameter 26.8µm) and can sustain a high current density up to 3400 A/cm^2. At this current density, a UV-C µLED produces an optical power of 196 µW. The measured modulation bandwidth of the UV-C µLEDs increases linearly with the driving current density. At a current density of 70.73 A/cm^2, the UV-C µLED has a 3-dB electrical modulation bandwidth of 438 MHz which is 15 times higher than the reported bandwidth of deep UV LEDs. By further increasing the driving current densities, even higher modulation bandwidths are expected although those have not been directly demonstrated due to the cut-off frequency of the commercial avalanche photodiode used for the measurement. A deep UV communication system using the fabricated µLED as the light source is further demonstrated. At a 0.3 m distance, up to 744 Mbps and 1.02 Gbps error-free data transmission rates are achieved assuming on–off-keying (OOK) and orthogonal frequency division multiplexing (OFDM) modulation schemes, respectively.