Abstract

Near field phase front measurements of diode laser arrays are important because they can provide data necessary for development of fundamental supermode devices with a single-lobed far field. For example, phase information is necessary in designing phase-correcting such as variable phase shift zone plates. Two-point sampling of near-field interference patterns using a Young's double-slit aperture was reported by Durkin et al.¹ In our earlier experiments, we used a Mach-Zehnder laterally sheared interferometer.² Here we apply a new design, featuring a rigorously equal path Sagnac ring interferometer. This way, problems due to equal optical path requirements and short coherence length of carrier-guided arrays are eliminated. In addition, we have improved phase retrieval from the nonuniformly illuminated interference patterns. Previously, we used a simple wave aberration theory to explain qualitatively the observed fringe patterns.² Here we adopt a Fourier transform method to retrieve the phase distribution of the array. Examples of reconstructed phase fronts of ten-stripe carrier-guided phased arrays confirm that the devices operated predominantly in the highest-order supermode. However, we have also observed strong lateral variation of spatial coherence.

© 1989 Optical Society of America