GaN-based lateral-coupled distributed feedback laser diode with large bandwidth and narrow linewidth

Coherent visible light communication (VLC) is emerging as a promising technology for 6G wireless networks, offering advantages of high signal-to-noise ratios, dispersion-free spatial transmission, high receiver sensitivity, and high spectral efficiency. However, its deployment has been limited by the lack of narrow-linewidth blue laser transmitters. In this work, we design and demonstrate a c -plane GaN-based lateral-coupled distributed feedback (LC-DFB) laser diode (LD) with a narrow linewidth operating at 450 nm. The device shows a threshold current of 50 mA and an output power exceeding 90 mW. At an injection current of 100 mA, a remarkably narrow linewidth of 2.6 MHz is achieved. Furthermore, the fabricated LD demonstrates excellent frequency response characteristics with a −3 dB modulation bandwidth of 5.67 GHz. Using a directly modulated LC-DFB laser as the transmitter, a VLC link with a high data rate of 20.05 Gbps is demonstrated. Such a multifunctional device, featuring both a high modulation bandwidth and a narrow linewidth, can meet the demands of various application scenarios across different transmission distances in visible light interconnects. The measured linewidth represents a significant advancement in blue semiconductor laser technology, making this device also particularly promising for other important applications, including spectroscopy, atomic systems, and quantum systems.