Smart Light Management via optical microstructures created by SLM-based interference lithography

Lighting industries hold about one fifth of worldwide power consumption. Smart lighting can significantly decrease this power demand, the used resources and, finally, the corresponding costs. Optical microstructures can be used to achieve nearly arbitrary light distributions and are, therefore, optimally suitable for smart lighting applications. However, large-scale microstructures might be expensive to produce and to install. To address the need for an efficient way to produce optical microstructures, SLM-based interference lithography is a promising strategy. SLM-based interference lithography combines the advantages of achieving a high resolution and maintaining full pattern flexibility while having a higher throughput compared to other mastering techniques. Created structures serve as masters for a galvanic impression in nickel, which is finally used as a tool in precision moulding. The used SLM, or Spatial Light Modulator, is an array of cells containing liquid crystals. Each cell can be addressed via a voltage signal which aligns the liquid crystals. As liquid crystals are birefringent, the effective refractive index seen by an incident wave can be modulated for each cell. For a given grayscale structure, a program was written to determine possible cell configurations, which relate to computer-generated holograms, or CGHs for short. Microstructures created with SLM suffer from the speckle effect. In order to reduce deviations from the desired shape, hundreds of CGHs, resulting in the same structure, were used during exposure. With each of them having a different speckle characteristics, errors within the resulting structure are minimized. Placing the sample in the focal plane is critical to avoid blurriness. Therefore, in addition to showing the CGH, the SLM was utilized as a virtual lens with tuneable focal length to increase the accuracy of finding the focal position.