3D diffractive elements through fs-laser direct writing
Final Report Abstract
The aim of the project was to design and fabricate computer-generated 3D diffractive optical elements similar to optically recorded volume holograms. This provides the benefits of angular and wavelength selective features without being limited to the practical constraints during physical hologram recording. Instead, computer-generated diffractive structures can be realized via femtosecond-laser direct writing in a transparent dielectric at high processing speed. Thereby, the pulsed laser is used to locally modify the refractive index inside the bulk material. This local refractive index modification, called voxel, is characterized via tomographic refractive index profiling. The evaluated refractive voxel profile works as input for the optimization algorithm. The algorithm locally activates or deactivates potential voxels in the simulated 3D bulk of the dielectric to find the best configuration for shaping the desired light field. Thereby, it simulates light propagation as realistically as possible to account for scattering effects at the voxels, thus ensuring highly efficient beam shaping. The calculated voxel distribution is fabricated inside the bulk material by femtosecond-laser direct writing. The manufactured elements are suitable for intensity shaping and reach unprecedented diffraction efficiencies of up to 80 %, while the fabrication time takes only 20 min. Furthermore, 3D diffractive optical elements were designed and experimentally demonstrated as spatial mode converters and wavelength multiplexers.
Publications
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Tomographic refractive index profiling of direct laser written waveguides. Optics Express, 29(22), 35414.
Barré, Nicolas; Shivaraman, Ravi; Ackermann, Lisa; Moser, Simon; Schmidt, Michael; Salter, Patrick; Booth, Martin & Jesacher, Alexander
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Refractive index tomography of direct fs-laser written waveguides. Advanced Fabrication Technologies for Micro/Nano Optics and Photonics XV, 4. SPIE.
Barré, Nicolas; Shivaraman, Ravi; Ackermann, Lisa; Moser, Simon; Schmidt, Michael; Salter, Patrick; Booth, Martin J. & Jesacher, Alexander
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Direct laser-written aperiodic photonic volume elements for complex light shaping with high efficiency: inverse design and fabrication. Advanced Photonics Nexus, 2(03).
Barré, Nicolas; Shivaraman, Ravi; Moser, Simon; Salter, Patrick; Schmidt, Michael; Booth, Martin J. & Jesacher, Alexander
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Inverse methods applied tot he fabrication of femtosecond laser-written spatial mode multiplexers in glass. In IEEE Photonics Society Summer topical Meeting Series (SUM)
Barré, N., Shivaraman, R., Ackermann, L., Moser, S., Schmidt, M., Salter, P., Booth, M. & Jesacher, A.
