Semi-Empirical Characterization of Freeform Microlens Arrays
Microlens arrays (MLA) are used since long for imaging and non-imaging applications. Because of the small dimensions of they can be cost-effectively replicated onto flexible thin-film substrates and retain great deal of the substrate flexibility.
Standard quasi-spherical microlenses can be realized using photolithography and subsequent self-assembled photoresist thermal reflow. Nevertheless, such microlenses fail to comply with stringent requests such as for example non-symmetrical beam shapes, which require more advanced non-symmetrical aka freeform microlens arrays (FMLA). Despite being compatible with cost-effective replication processes, the manufacturing of FMLA molding tools conveys a rather high cost which all too often increases markedly with increasing tool area. In addition, it is rarely the case that the first design meets the specifications and often several design-fabrication-testing cycles are required thus pushing-up the cost beyond the reach of many Companies.
Unfortunately, the experimental characterization of small samples is normally unrealistic due to handling issues and experimental errors (e.g. alignments, output power, large source beam diameter, small detector aperture, etc.).
Here, we propose a method to overcome these limitations based on 3D surface sampling, computer generation of a ray-traceable model and ray-tracing performance simulation. The proposed approach is demonstrated for several commercially available freeform asymmetric thin-film diffusers.