Widely Tunable Narrow-Linewidth Laser Based on a Multi-Period-Delayed Feedback Photonic Circuit

A widely tunable narrow-linewidth laser consisting of a sampled-grating distributed Bragg reflector (SG-DBR) laser and an external silica-based multi-period-delayed feedback (MPDF) photonic circuit is fabricated and experimentally demonstrated. The measured results show that a 58-nm lasing wavelength tuning range together with a more than 40 dB side-mode suppression ratio can be achieved. Notably, among the wavelength tuning range, all linewidths remain below 1 kHz, which are narrowed by more than three orders of magnitude compared to the average intrinsic linewidth of 3 MHz for the original SG-DBR laser. Besides, since the proposed MPDF structure has an ultra-dense distribution of the multi-period feedback, the linewidth reduction capability can be maintained over the entire operating wavelength range does not require free spectral range (FSR)-alignment or any extra phase match. Such widely tunable narrow-linewidth laser might offer a compact, cost-effective and easily-implemented solution for next-generation applications including ultra-wideband dense wavelength division multiplexing (DWDM) systems and light detection and ranging (LiDAR) systems.