Mode control of 2-D phase-locked VCSEL arrays

Abstract

Arrays of vertical cavity surface-emitting lasers (VCSELs) have recently generated considerable interest as a means of scaling up the available output power while maintaining astigmatic diffraction-limited emission. Realization of such devices will require understanding and control of the modal emission properties of phase-locked VCSEL arrays. We have performed an experimental study of the modal emission properties of 2-D VCSEL arrays and compared our results with our numerical model. The arrays were fabricated by dry etching partly through the upper mirror stack, thus creating square pixels separated by lower reflectivity channels. The near- and far-field emission patterns of regions of varying size were studied by optical pumping. The observed far-fields demonstrate out-of-phase emission into four far-field lobes, and showed decreasing lobe width and spectral width with increasing array size in agreement with our calculations. The observations indicate operation on a single-longitudinal and lateral mode for array sizes up to 10 × 10. Because of the desirability of devices that emit into a single far-field lobe, we have designed a monolithic phase shifter for the above array. This design utilizes an extra material layer on top of the upper mirror stack for alternate pixels. We expect that, with careful control of the layer thickness, the emission of each pixel will be in phase, resulting in uni-phase emission.