Modulation-simplified and narrow-linewidth FMCW laser using misaligned grating external cavity

We propose a frequency-modulated continuous-wave (FMCW) laser based on misaligned grating waveguide external cavity coupled with a reflective semiconductor optical amplifier (RSOA). Compared with waveguide external cavity lasers using two cascading microring resonators, which adopt vernier effect for frequency modulation, the proposed laser has a much simpler frequency modulation scheme. The proposed laser can realize linear frequency tuning through one electric control circuit, compared to that the waveguide external cavity lasers using two cascading microring resonators need more than three electric control circuits. Moreover, the proposed laser has a linewidth less than 1 kHz with the misaligned grating structure, while the linear chirp bandwidth is about 2.2GHz with non-linearity of ~10-3. This laser has been used in a laser ranging application, demonstrating a ranging accuracy of ~6.5cm. These results show that the proposed laser can be a potential solution for LiDAR, long-range optical fiber sensing, optical interferometry and coherent optical communication, etc.