Stable in-Phase Mode Operation in Coherent VCSEL Array With an Integrated Phase Shifter

Implant-defined coherent vertical-cavity surface-emitting laser (VCSEL) arrays with an integrated phase shifter that can convert the out-of-phase mode into the in-phase mode were demonstrated. The measured angular full-width at half-maximum (FWHM) from a {9} \times {9} coherent VCSEL array in the far-field lobes is only 0.82°. The intensity of the central lobe is about 2.9 times than that of surrounding sidelobes, showing excellent beam quality. The FWHM of the spectrum of a {9} \times {9} array is only 0.02 nm, showing a single-mode operation. It provides a potential method to fabricate larger in-phase coherent VCSEL arrays. A remaining challenge is enhancing output power via solving the heat problem.