Soft mold-based hot embossing process for precision imprinting of optical components on non-planar surfaces

Patterning micro- and nano-scale optical elements on nonplanar substrates has been technically challenging and prohibitively expensive via conventional processes. A low-cost, high-precision fabrication process is thus highly desired and can have significant impact on manufacturing that leads to wider applications. In this paper, we present a new hot embossing process that enables high-resolution patterning of micro- and nano-structures on non-planar substrates. In this process, a flexible elastomer stamp, i.e., PDMS, was used as a mold to perform hot-embossing on substrates of arbitrary curvatures. The new process was optimized through the development of an automated vacuum thermal imprinting system that allows non-clean room operation as well as precise control of all process parameters, e.g., pressure, temperature and time. Surface profiles and optical properties of the fabricated components, including micro-lens array and optical gratings, were characterized quantitatively, e.g., RMS ~λ/30 for a micro-lens, and proved to be comparable with high cost conventional precision processes such as laser lithographic fabrication.