Study On Doped Micro-structure Light Diffuser

Light diffuser has played an important role in spatially modulating the intensity of the incident beam to meet the requirements through the reflection,scattering,refraction or diffraction.Light diffuser has been used for beam shaping,flat panel display and solid-state lighting(organic / inorganic light-emitting diodes),photovoltaic devices,etc.The directional diffuser is widely used in airborne laser detection and ranging systems,bar code scanners,biometric scanners and directional projectors due to the directional diffusion characteristics.Based on the soft lithography,two types of light diffuser were fabricated by ultra-violet imprinting technique with PDMS molds: the particle-doped light diffuser and the selfassembly of microsphere induced by microstructure light diffuser.The optical properties of the fabricated diffuser were also characterized in this thesis.Details are listed as following:(1)Monte Carlo method(LightTools software)was used to simulate the performance of the diffusers composed of the organosilicone particle / UV curable resin and polystyrene particle / UV curable resin,respectively.The relationship between the transmittance and the particle size,doping concentration,residual layer thickness was analyzed.The optimal diameter of the doped organosilicone particle was in the range of 1-5 ?m according to the simulation results.When the particle size is 2 ?m,the doping concentration is 1 wt%-10 wt% and the residual layer thickness is less than 50 ?m,the transmittance is greater than 95%.Similar,results can be obtained by simulating the polystyrene particle / UV curable resin diffuser.However,because the refractive index of the organosilicone is less than that of the polystyrene,the transmittance of the latter is lower than that of the former.The theoretical results provide guidance for the fabrication of the proposed particle-doped light diffuser.(2)The particle-doped light diffuser was fabricated by using soft lithography technique.The fabrication procedure includes four steps: photolithography and thermal reflow,PDMS soft mold preparation,light diffusing agent-UV curable resin mixing and soft lithography.The doping mass fraction of the diffusing agent(such as organosilicone particle and polystyrene particle)is chosen as 1 wt%,3 wt%,5 wt%,7 wt%.The observed results of scanning electron microscopy and 3D confocal microscopy showed that the microstructure was uniformly transferred from the PDMS mold,and the surface roughness was measured as 0.28 ?m.When the doping mass fraction was 7 wt%,the transmittance and haze are 96.9% and 48.9%,respectively.The maximum scattering angle is 80 ° for the diffuser composed of cylindrical lens array.By changing the imprint pressure,different residual layer thickness can be obtained.When the thickness is 40 ?m and doping mass fraction is 5 wt%,the transmittance and haze were 97.43% and 74.78%,respectively.When the thickness is 10 ?m,the transmittance and haze were 96.32% and 43.51% respectively.The optical diffusing pattern was tested with a 650 nm red laser point and a white LED.The experimental results show that the engineered particle-doped light diffuser has capability of management of the incident scattering angle,brightness uniformity and haze.(3)The self-assembly microsphere induced by the microstructure light diffuser was fabricated by combining with the soft lithography and the scrape technique.The fabrication steps include photolithography,PDMS soft mold preparation,soft lithography and scrape technique.The width of the microgroove was 12 ?m,18 ?m,8 ?m,8 ?m and the height was 6 ?m.The results of scanning electron microscopy showed that the linear or polygonal edge shape of the microgroove can enhance the filling factor of the microspheres.The patterned microgroove and the filled microsphere can directionally diffuse the incident light.The microspheres filled in the microgroove can serve to smooth the optical diffusing pattern.Since the grating duty factor and the micro-nanostructure size are governed by the diffractive optics,the diffractive spots are still be clearly observed in the received screen.The influence of the microstructure groove and micro sphere on the optical performance of the diffuser needs to be further studied.The novel method of fabricating composite light diffuser is studied in this paper.The method has the advantage of low cost compared with the existing technology.The obtained composite light diffuser combined with refraction,diffraction through microstructure and the scattering effect of the diffusion particle,which can achieve high transmittance,haze can be tuned,directional diffusion.The research results of the paper can pave the way for the design and fabrication of the composite multi-functional light diffuser.