Electrically pumped semiconductor laser with low spatial coherence and directional emission

Abstract

We design and fabricate an on-chip laser source that produces a directional beam with low spatial coherence. The lasing modes are based on the axial orbit in a stable cavity and have good directionality. To reduce the spatial coherence of emission, the number of transverse lasing modes is maximized by fine-tuning the cavity geometry. In a cavity with the size of hundreds of micrometers, 1000 transverse modes lase simultaneously and independently, reducing the speckle contrast to 0.03. Decoherence is reached in a few nanoseconds as a result of frequency detuning of lasing modes. Such rapid decoherence will facilitate applications in ultrafast speckle-free full-field imaging.