Comparison of freeform manufacturing techniques in the production of monolithic lens arrays

Monolithic lens arrays are used in applications such as hyper-spectral imaging, Shack-Hartmann wavefront sensors, and lens replication molds, where lens-to-lens registration is critical. Traditionally, monolithic lens arrays are produced by diamond turning one lens at a time on axis. This process requires the substrate to be shifted to a new position before the next lens is machined. This intermediate step increases production time and makes it difficult to achieve lens-to-lens registration accuracy. Freeform diamond machining allows lens arrays to be produced in a single setup. Since there are no intermediate shifts of the substrate, the lens-to-lens registration is inherent to the program and machine accuracy. The purpose of this paper is to compare different freeform manufacturing processes in the production of a three-element germanium lens array. Freeform machining technologies including Slow Tool Servo (STS), Fast Tool Servo (FTS) and Diamond Micro-Milling (DMM) will be used to produce this lens array. The results for process times, figure, and finish characteristics will be compared across all three techniques.