Speckle contrast evaluation of multi-emitter broad area 638-nm red laser diodes

Speckle contrast of single, dual, and triple emitter broad area laser diodes (BA-LDs) with a wavelength of 638 nm was experimentally investigated. Speckle noise was relatively small near the threshold current probably due to the longitudinal mode competition. Higher output power led to smaller speckle noise owing to the spectrum widening. A wide stripe presented an advantage in terms of speckle reduction in the single emitter LDs. It is also found that wider emitter width leads to the smaller the speckle noise. A larger number of emitters decreased speckle noise due to the beam superposition effect, even for multi-emitter LDs in which the emitters are built into one chipa.