Sidelobe suppression techniques for laser diode arrays

Abstract

Evanescent coupling, interconnected Y waveguides, and external cavities have been used to phase lock arrays of lasers into a coherent ensemble. The amount of energy which is coupled into the central far-field lobe is determined by the phases of the individual lasers as well as the array fill factor. This paper describes several optical methods for combining the energy of the individual laser sources into a single far-field lobe with high efficiency. One technique uses specially designed holographic diffraction gratings to couple more than 80% of the energy into the central far-field lobe independent of the array fill factor. A second technique uses a phase retarding aperture and a phase corrector plate to convert an array of low fill factor into one with an apparent fill factor of 100%. In this case, the energy from the side-lobes is effectively channeled into the central lobe. Several variations of these techniques are presented, as well as extensions to 2-D arrays.