Spatial coherence research and passive speckle suppression for edge-emitting broad-area semiconductor lasers

The spatial coherence of filaments in edge-emitting broad-area semiconductor lasers (BALs) is studied based on speckle theory, and a passive speckle suppression method for BALs is demonstrated. A fly-eye lens is used to integrate the filaments and homogenize the laser beam. The speckle contrast is consistent with theoretical calculation, which proves the spatial incoherence of filaments. A light pipe is used to introduce an optical path difference between light with different incident angles, enabling more incoherent beamlets. These beamlets are then combined at different illuminating angles by a double-sided fly-eye lens and focusing lens. As a result, the subjective speckle contrast is reduced from 95.94% to 19.13% at 1.2 A while maintaining a high luminous efficiency of 77.8%. This work provides important design principles for laser display systems.