Phase-locked arrays of diode lasers are attractive as high-power coherent sources due to their all monolithic nature and intrinsic redundancy. Initially, due to ease in fabrication, gain-guided arrays were analyzed. However, gain-guided arrays, just as individual gain-guided devices, proved inherently unstable due to optical-mode dependence on the injected-carrier profile and thermally induced gradients. Positive-index-guided devices were next studied. It was quickly found that, due to gain-loss considerations, such devices prefer to operate in the out-of-phase condition. Significant efforts were spent to make the devices operate in-phase, but with limited success: 50-100 mW in diffraction-limited patterns. The real breakthrough occurred with the successful implementation of leaky-mode (antiguided) resonant optical waveguide laser arrays.
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