The circularly polarized laser sources are core components for many optical applications such as biomedicine, quantum technology, and AR/VR. However, conventional techniques make it difficult to further diminish the size of circularly polarized lasers. Thus, the high-contrast subwavelength chiral metasurface (HCCM) with a 980 nm operating wavelength is numerically investigated. The HCCM is composed of chiral metasurfaces modulating the circular dichroism of reflectance and 6 pairs of Distributed Bragg Reflectors (DBR) with 55% reflectivity. The reason that the HCCM has an ultra-high reflectivity (99.9%) at the operating wavelength of 980 nm is the combination of the optical refractive index difference between the GaAs metasurface and the AlOx substrate and weak destructive interference in the AlOx support layer. In addition, the circular dichroism of the chiral metasurfaces (2.1%) is mainly caused by the displacement of two square air holes in opposite directions, thus transforming the unit cell of the metasurface from C2 symmetry to chiral symmetry. The reflector has the advantages of a simple structure and miniaturization, which is expected to greatly reduce the fabrication difficulty and cost of the circular polarization VCSELs.

We propose a photonic crystal (PC) nanostructure that combines bound states In the continuum (BIC) with a high-quality factor up to 10⁷ for emitting circularly polarized beams. We break the in-plane inversion symmetry of the unit cell by tilting the triangular hole of the hexagonal lattice, resulting in the conversion of a symmetrically protected BIC to a quasi-BIC. High-quality circularly polarized light is obtained efficiently by adjusting the tilt angles of the hole and the thickness of the PC layer. By changing the hole’s geometry in the unit cell, the Q-factor of circularly polarized light is further improved. The quality factor can be adjusted from 6.0 × 10³ to 1.7 × 10⁷ by deliberately changing the shape of the holes. Notably, the proposed nanostructure exhibits a large bandgap, which significantly facilitates the generation of stable single-mode resonance. The proposed structure is anticipated to have practical applications in the field of laser technology, particularly in the advancement of low-threshold PC surface emitting lasers (PCSELs).