The influence of waveguide design on performance of nitride based laser diodes (LDs) grown by plasma assisted molecular beam epitaxy is studied. A large improvement in threshold current density and slope efficiency of LDs is observed when an InGaN interlayer with 8% In content is introduced between multi-quantum-well region and electron blocking layer. This dependence is attributed to reduction of internal losses due to lower optical mode overlap with highly absorptive Mg-doped layers. This led to demonstration of blue LD operating at λ=450 nm with high optical power of 500 mW per facet.