Near field wavefront measurements of semiconductor laser arrays by shearing interferometry.

A reliable technique for measuring near field phase fronts of phased-array semiconductor lasers is proposed and demonstrated. Laterally sheared interferograms are generated in a ring-type interferometer with zero optical path difference between two beams, eliminating problems due to equal optical path requirements in other systems. Fourier transform methods are used to extract phase difference information from the nonuniformly illuminated interferograms, and phase discontinuities between adjacent stripes of carrierguided laser arrays are observed. Test data agree with theoretical predictions and far field interpretations.