Binary Optical Elements For Coherent Addition Of Laser Diodes

Abstract

One-and two-dimensional laser diode arrays can currently be designed to produce large amounts of optical power. In addition to high power, however, many applications require near-diffraction-limited far-field performance. This paper reviews the role of diffractive optical elements for establishing mutual coherence between lasers and producing a single-lobed far field. Grating structures have been used to superimpose an array of laser beams producing an output with single-laser divergence and increased intensity. Alternatively, diffractive spatial filtering techniques have been employed to establish mutual coherence and reduce the amount of power contained in the far-field grating lobes. Fabrication of diffractive microlens arrays are also discussed for collimating laser diode sources and correcting for optical aberrations. These lens arrays are shown to have high efficiency and very low intrinsic aberrations. Finally, free space diffraction can be used to couple lasers and establish mutual coherence across the array. High efficiency is achieved using the self-imaging properties of periodic structures.