Beam expanders for coherent illumination and speckle reduction

Subject of study. Optical elements combined based on holographic optical elements and a lightguide are studied. Aim of study. The aim of the study is the development of compact optical systems to convert a collimated beam with Gaussian energy distribution from a coherent radiation source into a uniform homogeneous cross-sectional beam with enlarged dimensions. Method. Coherent radiation is coupled into and outcoupled from the lightguide using holographic optical elements. The lightguide and the matched scatterer create a multitude of secondary point sources. These sources combine through interference to generate a total field with the necessary energy distribution and aperture. Main results. The authors propose several modifications for the combined optical elements based on holographic optical elements and a lightguide. The total efficiency of these elements is 40%-45% (the diffraction efficiency of individual elements is 80%-85%) with a beam uniformity of approximately 80% and a decrease in speckle contrast to the level of 20%-30%. Practical significance. The proposed technical solutions with regard to the development of combined optical elements based on lightguides and holographic optical elements can significantly reduce the energy consumption, dimensions, and weight of visualization systems, specifically wearable virtual and augmented reality devices.(c) 2023 Optica Publishing Group