2.6 GHz high-speed visible light communication of 450 nm GaN laser diode by direct modulation

Gallium Nitride (GaN) based light emitting diodes (LEDs) has been considered as a next generation lighting source due to its high efficiency, long lifetime, and high brightness. In addition to the lighting purpose, visible light communication (VLC) on LEDs has been studied since it is easily available in the existing light infrastructure. Exponentially increasing wireless data traffic in radio frequency (RF) also motivated the need for VLC. However, the modulation bandwidth of LEDs with a long carrier recombination lifetime (∼ns) is limited up to ∼ 400 MHz even though orthogonal frequency division multiplexing (OFDM) rather than direct modulation could improve data rate up to 3 Gbit/s [1]. It can be seen that laser based VLC is necessary because the modulation bandwidth of laser diodes is limited by photon lifetime (∼ps). In addition, since Denault et al. reported 76 lm/W efficacy for 442 nm laser based white lighting, the blue laser is promising lighting source readily available for white lighting communication, which is also called light fidelity (Li-Fi) [2]. Recent progress on high-speed VLC using a 422 nm laser diode showed 1.4 GHz bandwidth and 2.5 Gbps. Even if this is about three times larger bandwidth than blue LED VLC, the system was limited by the bandwidth of the photo detector (PD) due to the absence of commercially available high speed PD covering in the blue region with enough responsivity [3]. Our study demonstrated the first novel VLC system limited by the bandwidth of 450 nm laser diode with a high-speed UV-extended PD giving 2.6 GHz modulation bandwidth and 4 Gbit/s data transmission rate.