Metasurface-integrated VCSEL and metalens cascade for line-shaped top-hat beam generation

Line-shaped top-hat beams with uniform one-dimensional intensity profiles are important for optical systems used in laser processing, light detection and ranging (LiDAR), and photolithography. Traditional refractive and diffractive beam-shaping devices either require bulky multi-element configurations or face fabrication challenges such as multi-level etching and higher-order diffraction. To overcome these challenges, we propose an optically cascaded system that integrates a Jones-matrix metasurface with vertical-cavity surface-emitting lasers (VCSELs) and a metalens. The Jones-matrix metasurface employs geometric-phase modulation from ideal half-wave meta-atoms together with transmission-phase control to generate a top-hat beam. A subsequent metalens further converts the square top-hat output into a line-shaped one. Experimental results indicate that the designed optical system achieves a top-hat beam with a uniformity of 72%, a conversion efficiency of 80%, and a reduced divergence angle of 0.17° along the y-axis for the line-shaped top-hat beam. Therefore, the metasurface-integrated VCSEL cascaded with a metalens offers a compact and effective beam-shaping approach to generate a line-shaped top-hat beam with a small divergence angle, showing great potential for optical communication, compact LiDAR, and other integrated photonic systems.