Study on the spatiotemporal coherence and passive speckle suppression of the edge-emitting broad-area laser diode

Abstract The spatiotemporal coherence of the edge-emitting broad-area laser diode was studied at different injection currents and optical path delays. Low spatiotemporal coherence was observed in the lateral direction of the laser, and it was further reduced to near zero by introducing an optical path difference. A one-dimensional refractive optical element (ROE) was designed and fabricated to destroy the spatiotemporal coherence of the laser beam in the transverse direction. Low spatiotemporal coherence was observed both in the lateral and the transverse directions when the ROE was introduced. Efficient two-dimensional speckle suppression was achieved in the experiment using a microlens array and a one-dimensional ROE. The freedom of speckle suppression attained 50.6, and the subjective speckle contrast was reduced to a low value of 6.2%. This work provides an efficient and handy method to suppress speckle passively.