Fig. 10: VCSELs with metastructures for polarization control.

a Schematic cross-sectional layout of the VCSEL with the top mirror consisting of a freely suspending HCG and four pair DBRs¹⁶⁵. b The cross section of a VCSEL with HCGs for beam shaping¹⁶⁶. c Schematic of a VCSEL featuring a chiral metasurface as the top reflector for circularly polarized emission; the top-left inset shows a top view of the metasurface unit cell, with the geometric parameters labeled¹⁶⁷. d VCSEL with a-Si metasurface on top facet. Device can simultaneously generate RCP and LCP beams when operating as a laser (forward biased)¹⁶⁸. Device can also distinguish helicity of incident light when operated as a photodetector (reverse biased). Figure a is reprinted from ref. ¹⁶⁵. with permission from the Springer Nature. Figure b and c are reprinted from ref. ¹⁶⁶. and ref. ¹⁶⁷. respectively with permission from the he Optica Publishing Group. Figure d is reprinted from ref. ¹⁶⁸. with permission from the John Wiley and Sons