A detailed understanding of the nitride refractive indices is essential for the modeling and design of III–N laser structures. In this article, we report on the assessment of the refractive index data available for the nitride alloys and present formulas for evaluating the refractive indices for variations in both composition and photon energy. For AlxGa1−xN, an expression is given which fits well to experimental data below x<0.38, sufficient for the molefractions found in the cladding layers of III–N lasers. Due to the almost complete lack of experimental refractive index data for InyGa1−yN, we propose an expression to give a first-order approximation for the refractive index.

We present the phase locking of an array of index-guided tapered laser diodes. An external cavity based on the self-imaging Talbot effect has been built. A volume Bragg grating is used as the output coupler to stabilize and narrow the spectrum at 976 nm. A power of 1.7 W is achieved in the in-phase single main lobe mode with a high visibility. We have checked that each emitter is locked to the Bragg wavelength with a 100 pm spectrum linewidth. The experimental results compare well with numerical simulations performed with two-dimensional wide-angle finite difference beam propagation method

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