Unidirectional lasing in up–down and left–right directions based on unidirectional bound states in the continuum

Achieving asymmetric transport of photonic structures is of particular interest in many photonic applications in grating couplers and antennas for light detection and ranging. To achieve unidirectional lasing in either up-down or left-right directions, we design a one-dimensional photonic crystal slab with a parity-time symmetric configuration. Under non-Hermitian modulation and breaking of mirror symmetry, the far fields of the slab have asymmetric polarization vortex in the up-down and left-right directions, respectively, which leads to the formation of unidirectional bound states in the continuum (BIC). The plane wave incidence produces the unidirectional lasing in the up-down directions. The light incidence from the line source results in unidirectional lasing in the left–right directions. All of the unidirectional lasing is dependent on the unidirectional BIC.