Modal Analysis of Large Spot Size, Low Output Beam Divergence Quantum-Dot Lasers

Large spot size ridge waveguide lasers utilizing a low modal gain single quantum dot layer emitting at 925 nm were designed and fabricated. Ridge waveguides with width <3 mum emit in a single transverse mode with a low transverse full-width at half-maximum divergence of 20deg. Wider ridges initially lase in the first-order transverse mode before collapsing to the fundamental mode. This characteristic is explained by a thermally induced increase in the refractive index of the waveguide core. All lasers operate in a single lateral mode