Low divergence tapered laser diode with integrated metalens

Abstract

High power and high beam quality laser sources are required in numerous applications such as nonlinear frequency conversion, optical pumping of solid-state and fiber lasers, material processing, and others. Here, we theoretically study and demonstrate a tapered laser diode with integrated metalens, which can greatly reduce the lateral far-field divergence of the device. A 980 nm tapered laser diode adopted in this design consists of a power-amplified tapered section and a narrow-ridged section, in which the latter restricts the lateral mode number, and the former is utilized to amplify the output power. The wavefront is carefully reshaped by preparing a one-dimensional (1D) trench metalens near the front facet of the tapered cavity. By precisely designing the length and width of the low refractive index elements at different positions, the approximate spherical wave formed by diffraction in the tapered cavity is transformed into an output plane wave while ensuring high transmittance (>90%), which reduces the divergence of the lateral far-field. The simulation results show that the lateral far-field divergence of the fundamental mode decreases from 3.2° to 2.0° (FWHM) after the integration of the metalens with a 500 μm length of tapered cavity.