Resumen
Photonic-crystal surface-emitting lasers (PCSELs) have led to amazing results in overcoming the divergence limitation of semiconductor lasers. However, so far, the physical mechanism behind this promising control of far-field characteristics is still unclear. Here, we perform a theoretical study of the mechanism of the influence of photonic crystal (PhC) geometry on the far field of PCSELs. The perspective from group theory is adopted in our analysis. We explore the function of symmetry in the formation of the far-field pattern (FFP) and clarify the roles played by various PhC parameters in this process. Through our analysis, a symmetry criterion to design PCSELs with single-lobed narrow beams is shown, where an asymmetric in-plane PhC structure, a large vertical confinement factor, and a sufficient number of periods are required. Our results reveal the physical origin of the narrow beam of PCSELs, which can even reach 0.1° with a PhC cavity size of over 1000 µm at a lasing wavelength of 940 nm.