Tunable lasing direction in one-dimensional suspended high-contrast grating using bound states in the continuum

We realized off-λ lasing using the Friedrich-Wintgen bound state in the continuum (FW-BIC) in a one-dimensional suspended high-contrast grating (HCG). A clear anticrossing was observed in the band diagram of the HCG corresponding to the coupling between the specific different orders of Bloch modes, and the FW-BIC with a high quality factor and large confinement factor was observed near the anticrossing point. Owing to these outstanding characteristics, the FW-BIC can serve as a robust and extraordinary cavity mode for realizing low-threshold laser operation and for achieving angle-steering laser beams. The conditions of the FW-BIC can be modulated by tuning the geometry related to the coupling modes in the anticrossing, resulting in a tunable lasing direction observed in the measurement. Furthermore, through appropriate design, the emission angle can be controlled precisely within a wide tunable range. Therefore, FW-BICs can be used to realize high-resolution directional lasing within a wide range of emission angles; they can also be applied in three-dimensional sensing for lidar applications.