Analysis Of The Tunable Gradient Refractive Index And Device Design Based On Optofluidics

As a new technology, optofluidics is the subjects accumulation of microfluidics and integrated optics, which has an extensive practicing prospect in chemical analysis, biological detection and integrated optics. The lab-on-a-chip application can both reduce the cost of chemical or biological detection and improve the analysis accuracy.In this paper, a tunable liquid gradient refractive index(L-GRIN) microlens was proposed based on the laminar liquid convection and diffusion effect. The effect of various liquid/device factors, including the structure and size of device, the flow velocity, concentration, viscous resistance and temperature of liquids, etc., on the diffusion convection process of liquids, as well as the concentration and refractive index distribution of L-GRIN microlens under different conditions was simulated by Finite element method(FEM). Furthermore, the correlation between the diffusion convection process of fluid dynamics and the optical property of microlens was established by simulating the features of wave-manipulation of L-GRIN microlens using ray tracing method, and the investigations provided more understanding to the tuning mechanism of L-GRIN microlens at molecular level.Three kinds of tunable L-GRIN microlens were designed to realize different focusing effect by adjusting the diffusion coefficient, solution concentration and flow rates of core and cladding inlet, and the light transmission process and focusing effect of devices was analyzes using ray tracing method. It was found that the focal length of the microlens varied from 942 μm to 11 μm when the mass fraction of ethylene glycol solution varied from 0.05 to 0.4, while the focal length changed from 127.1 μm to 8μm by varying the flow rate of core liquid from 0.5×103 pL/s to 5×103 pL/s when there are no slip between core and cladding inlet. As the flow rate of core inlet increasing rapidly with that of cladding inlet being constant, the refractive index will keep unchanged at the centre of the area, thus the focal spot of output light will maintain a steady diameter of 23.5 μm. The adjustment of focal spot size can be implemented in the same manner. In addition, both one-dimensional(1D) and two-dimensional(2D) tunable L-GRIN microlens are designed. 1D light deflection was achieved by adjusting the flow rate of one-sided cladding inlet with that of other cladding inlet and core inlet being constant, and the focal length varied from 0μm to 58μm with the flow rate of right cladding inlet ranging from 5 ? 103pL/s to 5? 103pL/s. While 2D adjustable L-GRIN microlens performed the function of light deflection and focusing in two dimension by adjusting the flow rate of cladding inlet in four directions.In conclusion, the optical performance of L-GRIN microlens were studied using FEM, and several devices were designed to realize different functions, such as adjustable focal length, focal spot and focal direction, which will have great value in the chip-on-a-lab detection system and the design and application of novel self-adaptive optical waveguide devices.