Demonstration of decoupled farfield and efficiency optimization for 14xx Raman pump lasers

Experimental and theoretical results have been presented for buried heterostructure 14xx pump lasers with and without an extra quaternary waveguide at the n-side of the active region, pulling the mode away from the p-InP cladding layers, reducing the internal loss by up to 1.6 cm^-1. The experimental results are in agreement with the theoretical value. The farfield for the design with extra waveguide is more circular than that without an extra waveguide by 1° vertically, in agreement with the theoretical difference. These results show that using an extra waveguide at the n-side, gives the designer more flexibility to both optimise the internal loss (hence the front-facet slope efficiency) and the farfield (hence the fiber coupling efficiency). This approach has been demonstrated for a buried heterostructure design, but is applicable to other laser types as well, e.g., (buried) ridge lasers.