Integrated Photonic In-Plane Beam Converter for Bessel-Gaussian Beam Generation

We present an integrated photonic in-plane beam converter generating a Bessel-Gaussian (BG) beam with a strong localized intensity along its propagation axis. The device is designed in two stages: the first stage transforms the waveguide mode into the Gaussian-distributed slab mode; the second stage produces the BG beam via an in-plane axicon. This axicon consists of apodized subwavelength gratings, expanding the vertical beam waist to minimize divergence. Our simulation generates a BG beam, achieving a diffraction-free zone over 2 mm that can be used for atomic-photonic hybrid integration.