Tunable Violet Laser Diode System for Optical Wireless Communication

we report a tunable self-injection locked violet laser diode external cavity system exhibiting a continuous wavelength tunability of 5.15 nm (400.28 - 405.43 nm) with mean side-mode-suppression-ratio (SMSR) and linewidth of ~23 dB and ~190 pm, respectively. The effects of injection current and temperature indicate a robust system besides being cost-effective and straightforward. Moreover, a successful indoor on-off keying transmission at two different locked modes on a 0.4 m free space channel showed ~10 times improvement in the bit-error-rate (BER) with value ${\sim }8\times 10^{-4}$ at 2 Gb/s, and better performance on 0.8 m channel length at 1.75 Gb/s compared to the free-running laser case. Our work is a potential step towards the realization of future high data capacity narrow-wavelength-spaced multiplexed optical wireless communication system wherein continuously tunable laser sources are expected to play a crucial role as transmitters.