Beam control of broad-area semiconductor lasers using high-order sidewall gratings

Abstract

This study systematically investigates the beam quality degradation in conventional broad-area semiconductor lasers, which arises from the excitation of higher-order transverse modes under high injection currents. To address this fundamental limitation, we propose and demonstrate a novel lateral surface grating structure integrated on both sides of the ridge waveguide. Through comprehensive numerical and experimental analyses, we first examine the optical loss characteristics induced by the grating structure. Subsequently, we explore the mode modulation mechanism by systematically varying the separation distance between the gratings and the ridge waveguide. Our results reveal that reducing this critical distance significantly enhances the grating's ability to suppress higher-order transverse modes. This improvement manifests in two key aspects: (1) a notable reduction in the transverse divergence angle in the far-field pattern, and (2) a more concentrated energy distribution in the near-field profile. These findings demonstrate the effectiveness of our proposed approach in achieving superior beam quality while maintaining stable laser operation.