Nonlinear analysis of Y-junction laser arrays

An analysis of Y-junction arrays above threshold is presented. The analysis incorporates nonlinear gain saturation and shows that the gain becomes nonuniform above threshold even if the array is otherwise ideal. The nonuniform, nonlinear gain saturation causes the near field and the radiation patterns to deteriorate with increasing output power. Although the far-field lobe width does not necessarily increase greatly above threshold, the Strehl ratio may decrease significantly depending on the device design. Empirically, it is found that, when the Strehl ratio decreases to approximately 0.7, the second-order array mode attains threshold and both the first and second array modes lase simultaneously. An improved design, whose far-field Strehl ratio remains 0.85 even well in excess of 1 W output power and in which the second-order array mode never attains threshold, is discussed