Coupling Performance Enhancement of GaSb-Based Single-Transverse-Mode Lasers with Reduced Beam Divergence Obtained via near Field Modulation

Symmetric narrow waveguide structure has been developed and fabricated to achieve low beam divergence and improved coupling performance of the 1.95 μm GaSb-based single-transverse-mode diode lasers. The near-field expansion effect of the narrowed 150 nm vertical waveguide design leads to a reduced fast-axis beam divergence of 44.2° full width at half maximum (FWHM) as well as 62% single-mode fiber (SMF) coupling efficiency, which has 55% relative promotion compared to the 40% efficiency of the conventional 270 nm waveguide design with 60.4° FWHM. The highest SMF coupling power of 113 mW was obtained by the 210 nm narrow waveguide lasers with lower internal optical loss at a 55% coupling efficiency, which performed balanced optimal performance with a narrowed divergence of 53.4° and a relatively high optical power of 206 mW. The high coupling efficiency and power will provide more promising prospects for the GaSb-based single-transverse-mode lasers in the widespread fiber-based and external-cavity applications.