Narrow-linewidth 1.55-µm-wavelength InP-based photonic-crystal surface-emitting lasers with near-diffraction-limited beam quality

We demonstrate 1.55-µm-wavelength InP-based photonic-crystal surface-emitting lasers (PCSELs) featuring narrow spectral linewidth, high output power, and excellent beam quality. PCSELs simultaneously support narrow-linewidth operation and high output power through large-area single-mode lasing in two-dimensional photonic crystals. Their stable single-mode behavior also enables a symmetric, high-quality circular beam. Here, we achieve near-diffraction-limited beam quality, with an M² factor below 1.1 and divergence angles of approximately 0.6° (1/e²), measured at output powers above 300 mW. Furthermore, we report an intrinsic spectral linewidth of 35 kHz at output powers exceeding 300 mW under continuous-wave operation at 25°C. The linewidth dependence on the inverse of output power follows the ideal behavior predicted by the single-mode laser model. These results indicate that our PCSELs are well-suited for coherent free-space optical (FSO) communication and light detection and ranging (LiDAR) applications, as well as optical fiber communication systems.