Analysis of optical loss on blue‐violet laser diodes

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Abstract
We measured optical loss of laser diodes by taking the intensity decay of edge emitting photoluminescence with respect to the distance from cleaved edges of wafers to the position where an excitation laser was focused. Measurements were performed on wafers with different thickness of InGaN p‐waveguide. We found that optical loss of wafers was determined by absorption of Mg doped GaN for narrow InGaN waveguide and by absorption of InGaN for thick InGaN waveguide. From experimental data and fittings, we obtained 40 cm–1 for InGaN absorption at 405 nm. Therefore, we conclude that the optical losses still remain even though the Mg‐doped GaN regions are far enough from QWs and that absorption loss of InGaN layers is relatively high comparing with undoped GaN.