OpticaLabsorber And Structural Color Device By Nano/microstructure Engineering

With the development of nanophotonic,people could manipulate interaction of light and matter at micro/nano-scale,leading to extraordinary reflection,transmission,absorption and scattering at the boundary of the object.Various platforms such as binary optics,photonic crystal,metamaterial and topological material have enriched the approaches of manipulating light wave and meanwhile lots optical functional devices such as broadband absorber,structural color,optical cloaking,anomalous light deflection have been demonstrated.These developments unprecedentedly promoted the methods of manipulating electromagnetic wave including light wave.In this thesis,we focus on manipulating light wave at microscale,including broadband absorbers and its application in radiative thermal management,monolithic integration of various structural color filters and dynamic structural color display based on liquid crystals.First,based on carbon material,we propose a new technique for fabrication of broadband absorbers called self-mask etching effect Using this effect,we fabricated nanoneedle structures on the compressed carbon plate.By adjusting etching process,we could control the height of nanoneedle structures and then control absorption band and absorptance.Experimental results show that the absorptance is larger than 99%in the region from 400 nm to 10 μm.Similarly,we fabricate nanoneedle structures on flexible graphite sheet.This film shows 99%absorptance in the regime from 400 nm to 15 μm.Meanwhile,its thermal conductivity is larger than 630 Wm-1K-1.This film can also use as a thermal spreader.Compared with pristine graphite sheet,this broadband absorber has better thermal dissipation performance.Experimental results show 3.7-degree cooler with broadband graphite sheet than using pristine graphite sheet as a thermal spreader.Next,we propose a novel structural color device.With the help of stepwise structures,we can integrate various filters monolithically at chip scale.This device is an asymmetric FP cavity composed of lossy metal on top,thick silver film as bottom layer and SU8 polymer as dielectric layer.Compared to noble metals such as silver and gold,lossy metal as top layer can lead to a broader absorption band and hence a narrower reflection peak.By controlling UV exposure dose,we can adjust the thickness of the dielectric layer and different dielectric thickness result in various color filters.Besides,we also fabricate these structural color devices on flexible substrate to extend the applications.In the third part,we propose a dynamic transmissive structural color display by combining liquid crystal with grating type FP cavity.This cavity is composed of a grating layer on top and thin metal film layer at bottom.It is very sensitive to polarization due to the asymmetric geometry.By applying voltage,we can control the distribution of director of liquid crystal,thus the polarization state of incident light wave.Color can be dynamically changed according to the polarization state from blue to orange.Simulation results show the transmission peak can be up to 70%and the wavelength tuning range can be as large as 300 nm which is the largest one among various structures.In addition,the structural color can cover the whole visible region by adjusting the geometrical parameters.At last,we conclude the whole these and give some perspectives about broadband absorbers,structural color and other related works.