Interglass Technology AG has developed a novel lens casting technology which enables embedding of functional elements into prescription spectacle lenses. Besides the important correction of ametropia, the technology provides secure protection of sensitive optical elements. Volume holograms in functional films might be used as optical combiners in augmented reality (AR) and mixed reality (MR) headsets. However, holographic diffraction gratings are susceptible to excessive heat and distortions. Therefore, mild process conditions are essential for the successful incorporation of holographic films into spectacle lenses. This study compares the standard lens casting process, which is normally used for lenses without functional films, with an optimized process, which allows better control of polymerization rate and reaction temperature. Evaluation of peak positions and diffraction efficiencies shows that both processes preserve full hologram functionality over the tested range of spherical powers. However, in terms of film adhesion, there is an obvious difference between the two processes. While the standard process leads to delaminations between film and polymer matrix during curing or lens edging, the optimized process yields reproducibly flawless lenses with sufficient adhesion. Furthermore, the effect of surface activation and lens thickness on film adhesion is analyzed. Testing analogous to ISO 15024 shows that adhesion evolution follows chemical kinetics, i.e. higher reaction temperatures during polymerization result in higher critical energy release rates. A possible explanation for this behavior is the establishment of covalent bonds between the activated film and the evolving polymer matrix.
D. Muff and L. Körner, "Casting technology for embedding optical elements into prescription spectacle lenses," Proc. SPIE 10676, Digital Optics for Immersive Displays, 1067609 (Presented at SPIE Photonics Europe: April 24, 2018; Published: 21 May 2018); https://doi.org/10.1117/12.2315802.
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