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Graded-index (GRIN) progressive addition lens (PAL) was successfully fabricated, and GRIN's potential for aberration correction of PAL was confirmed. GRIN material was prepared by partial diffusion of methyl methacrylate (MMA (n d at polymer = 1.492)) monomer into cross-linked benzyl methacrylate (BzMA (n d at polymer=1.568)) flat gel, and GRIN-PAL was prepared by polymerization of the GRIN material attached to a mold of commercially available PAL. GRIN polymer materials have been used for various applications such as rod lenses and optical fibers. GRIN represents gradual change of refractive index in a material, which adds or reduces light focusing power of the material. PAL is a multifocal spectacle lens for presbyopia. However, some localized aberrations (especially astigmatism) in PAL have not yet been reduced satisfactorily for decades by optimizing surface geometry of a lens. In this research, we propose to employ GRIN materials for astigmatism reduction of PALs. BzMA flat gel was prepared by UV polymerization of BzMA, crosslinking agent ethylene glycol dimethacrylate (EDMA) and photopolymerization initiator DAROCURE 1173. MMA monomer was diffused into BzMA flat gel from a portion of periphery for several hours. The obtained GRIN material was attached to a mold of commercially available PAL and polymerized by UV. As a result, reduction of astigmatism was confirmed locally in the fabricated PAL and GRIN-PAL using lens meter. In conclusion, GRIN-PAL was successfully fabricated. The validity of GRIN employment for the astigmatism reduction in PAL was demonstrated experimentally.

A rational and systematic approach to estimate the load resistance and strength of various double-glass photovoltaic modules is demonstrated. The approach consists of three steps: 1) calculation of module stiffness based on a laminate effective thickness theory; 2) calculation of the highest stress concentration in the two glass plies of the module using a modified plate theory; and 3) estimation of glass breakage probability of the module against specified loads by comparing the stress concentration calculated in step 2 with allowable glass stress and associated breakage probability. In the modified plate theory, a parameter that incorporates stress mitigation by a peripheral frame and installation is introduced to enable simple and fast calculations. The allowable stress of glass in step 3 is obtained by the Weibull analysis of glass breakage data obtained by a ring-on-ring test. The calculation methodology has been validated experimentally using load tests and direct measurements of glass principal stress in a real module under load. The approach can be used for fast screening and initial design of various structures to resist specified imposed mechanical loads.