Strain-tunable optical microlens arrays with deformable wrinkles for spatially coordinated image projection on a security substrate

As a new concept in materials design,a variety of strategies have been developed to fabricate optical microlens arrays(MLAs)that enable the miniaturization of optical systems on the micro/nanoscale to improve their characteristic performance with unique optical functionality.In this paper,we introduce a cost-effective and facile fabrication process on a large scale up to~15 inches via sequential lithographic methods to produce thin and deformable hexagonally arranged MLAs consisting of polydimethylsiloxane(PDMS).Simple employment of oxygen plasma treatment on the prestrained MLAs effectively harnessed the spontaneous formation of highly uniform nanowrinkled structures all over the surface of the elastomeric microlenses.With strain-controlled tunability,unexpected optical diffraction patterns were characterized by the interference combination effect of the microlens and deformable nanowrinkles.Consequently,the hierarchically structured MLAs presented here have the potential to produce desirable spatial arrangements,which may provide easily accessible opportunities to realize microlens-based technology by tunable focal lengths for more advanced micro-optical devices and imaging projection elements on unconventional security substrates.

Gain enhancement of perovskite nanosheets by a patterned waveguide:excitation and temperature dependence of gain saturation

Optical gain enhancement of two-dimensional CsPbBr3 nanosheets was studied when the amplified spontaneous emission is guided by a patterned structure of polyurethane-acrylate.Given the uncertainties and pitfalls in retrieving a gain coefficient from the variable stripe length method,a gain contour g((h))ω.x)was obtained in the plane of spectrum energy(hω)and stripe length(x),whereby an average gain was obtained,and gain saturation was analysed.Excitation and temperature dependence of the gain contour show that the waveguide enhances both gain and thermal stability due to the increased optical confinement and heat dissipation,and the gain origins were attributed to the two-dimensional excitons and the localized states.