Advances in 3D fabrication have afforded new freedoms in the design of custom optical elements. We explore a design space where the refractive index may vary freely with position in a material by considering applications in coherent beam shaping. First, we will describe experimental results where we have used femtosecond laser writing to fabricate custom GRIN waveguides in a planar geometry. We show a 2D device that converts a Gaussian beam to a flat top in one transverse direction, and is a single-mode waveguide in the other. Second, we describe a numerical method for designing 3D refractive index profiles. As an example, we will use the 3D method to design a device that transforms a circular beam with a Gaussian intensity profile into a square beam with a flat top.
W. Minster Kunkel, Ali Ghoreyshi, Glen Douglass, Simon Gross, Michael J. Withford, and James R. Leger, "Gradient-index beam shapers: fabricated devices and 3D design method," Proc. SPIE 10518, Laser Resonators, Microresonators, and Beam Control XX, 105181S (Presented at SPIE LASE: February 01, 2018; Published: 16 February 2018); https://doi.org/10.1117/12.2290909.
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