Research On Improving The Light Coupling Efficiency Of Organic Light-emitting Diode And Polymer Optical Waveguide Integrated Device

At present,integrated optoelectronic technologies based on polymer optical waveguide usually need external light sources,such as,light-emitting diode(LED)or solid-state laser,but their high cost or large volume limits the industrialization of these technologies and the miniaturization and portability of equipment.Organic lightemitting diode(OLED)is suitable for integrating light source on a chip due to its advantages of flexibility,low cost,simple preparation process and easy integration with other substrates.Therefore,for on-chip optical sensing and wearable flexible devices,directly integrating OLED on the polymer optical waveguide has important application background.But the method of directly preparing the OLED on the surface of the polymer optical waveguide makes the light coupling efficiency between them limited by the small refractive index difference of the waveguide core layer and the cladding.The grating coupling structure can effectively improve the light coupling efficiency because of the diffraction principle,this paper focuses on the use of grating coupling structure to improve the light coupling efficiency of an OLED and polymer optical waveguide integrated device.The main research contents are as follows:(1)First,taking advantage of SU-8 waveguide material's lithography,low transmission loss and high visible light transmittance,we chose SU-8 as the waveguide core.By analyzing the basic theory of polymer optical waveguide and grating coupling,we calculated the waveguide core cut-off thickness formula,the relationship between the effective refractive index of the waveguide and the core layer thickness.The initial value of the grating period was obtained according to grating coupling condition,which provided a reference for the design of the subsequent grating coupling structure.(2)Secondly,in order to further optimize the grating coupling structure,we used the FDTD Solutions simulation software based on the Finite Difference Time Domain(FDTD)algorithm to construct a simulation model of the OLED and polymer optical waveguide integrated device based on the grating coupling structure.The calculation of the light coupling efficiency of the OLED and polymer optical waveguide integrated device was determined,and it was used as an optimization index to optimize the period and duty cycle of the grating coupling structure.When the grating period was 310 nm,the duty ratio was 0.65 and the depth was 15 nm,the OLED and polymer optical waveguide integrated device could achieve a maximum light coupling efficiency of14.35%,which was 10.1% higher than that without grating coupling structure.(3)Finally,according to the simulation results,we built a laser double-beam interference optical path,fabricated grating coupling structure by laser double-beam interference lithography,and then used an atomic force microscope to characterize the shape of the grating structure,which period was 330 nm,duty cycle was 0.5 and depth was 15-18 nm.According to the actually prepared grating structure parameters,we used FDTD Solutions software to simulate the OLED and polymer optical waveguide integrated device based on the grating coupling structure.When the grating period was330 nm,the duty cycle was 0.5,and the depth was 15 nm,the light coupling efficiency of the integrated device based on the grating coupling structure was 6.3% higher than that without the grating coupling structure.In order to study the change of the light coupling efficiency based on the grating coupling structure,we built an integrating sphere optical power test system.Through the measurement of the transmitted optical power of the OLED and polymer optical waveguide integrated device with and without grating coupling structure,the light coupling efficiency of the integrated device based on grating coupling structure was about 5.5% higher than that without the grating coupling structure,which was still a deviation compared with 6.3%.The main reason is that the parameters of the prepared grating structure were not completely consistent with the simulation.The proposed integrated device has a good reference significance for the research of integrating optical sensors on a chip with flexible and low cost.