Study On Ionic Liquids Optofluidic Waveguide Build And Its Optical Transmission Properties And Light Manipulation

With the development of science and technology, the miniaturization of equipment has becomes an inevitable trend for the future science. The study of miniaturized tunable optoelectronic devices is becoming an important and concerned area for people. Optofluidic is the marriage of optics and fluidics, which generates a new cross-frontier field. Using the advantages of fluid such as soft, controllable, real-time and reconfigurability, scientists can build adaptive optofluidic waveguides, lens, laser and other functional devices in a few square centimeters or less chip. Optofluidic provides a new ideas and methods for building miniaturization, dynamic control, integrated and low-cost of optical devices. The optofluidic waveguide is the key for building other optofluidic devices and systems. Building a low-loss optical waveguide, implementing the light directional transmission and real-time manipulation are the priorities for the present research. Room temperature ionic liquids have many attractive advantages, such as non-toxic, wide liquid temperature range (-50-300℃) designability, low volatility, high conductivity, thermal stability, stable physical and chemical properties and wide range refractive index (1.40-1.56). Especially parts of the ionic liquids have good optical transmittance at the visible wavelength, even at part of the near-infrared wavelength and far-infrared wavelength. Mentions above the characteristics of ionic liquids indicate that it is well suited as fluid materials for building optofluidc waveguide and other optofluidic devices to manipulate light. In addition, the ionic liquids have been widely used in the design of electroactivity devices; it has potential possibility to build electrically active optofluidic devices, due to their many advantages in electrical.In this paper, two different optofluidic waveguides were builded on microfluidic chip using ionic liquids as optical transmission medium, one of the waveguide is ionic liquids as core liquids and solid material PDMS as cladding, which is named liquid core waveguides (LCW); another liquid-liquid (L2) waveguide is ionic liquids as core liquid and water as cladding liquid. Then, the loss of the two waveguides are measured with fluorescence analysis method. The law of LCW loss is obtained with different cross section. In the L2 waveguide of ionic liquids as core, the waveguide loss and optical transmission proprieties are obtained at different liquids flow; obtain the optical transmission and light path manipulate law at different liquid flows.In the L2 waveguide of ionic liquids as core and water as cladding, the optical transmission characteristics was further studied at low flow. By controlling the flow of the core and cladding, the mutual diffusion can creates refractive index gradients in both transverse and longitudinal directions, the light focusing effect is observed in such waveguide. Build the theory model of optical transmission in the L2 optofluidic waveguide; three types of numerical simulations were calculated by using the finite element technique, where the Navier-Stokes and the convection-diffusion equations were solved simultaneously when the velocity, mutual diffusion coefficient and other factors were taken into account, especially the change of fluid dynamic viscosity, density with core liquids concentration were taken into account. The flow characteristics of the core and cladding fluids was obtained and analyzed, then the trajectories of the light beams in the gradient refractive index distribution L2 waveguide is obtained with the geometrical optics method. After obtained the relationship of those parameters between self-foucsing lengths, an optofluidic method for estimating mutual diffusion coefficient between two fluids is proposed based on the L2 optical waveguide. Firstly, the mutual diffusion coefficients of aqueous solutions of ethylene glycol at different volume fractions were measured and compared the measurements against the data in available literature, the result reveals the proposed method is validity. Then, mutual diffusion coefficients of eight 1,3-methylimidazolium ionic liquids-water binary systems were estimated at 298.2 K and its law. After the optofluidic chip’s temperature is controlled with external Peltier element, the mutual diffusion coefficients of three ionic liquids-water binary systems of at different temperatures were measured, and their relationships with temperature is obtained. This method provides a "green", "efficient" and "cheap" means of measurement for measuring the two liquids mutual diffusion coefficient. The obtained diffusion coefficients data provides important theoretical design parameters for designing microfluidic and optofluidic devices that rely on precise transport of molecules.By using the unique electro-optical phenomenon of ionic liquids that we found in experiment, the optofluidic waveguide with simple two-terminal electrode geometry was proposed to manipulate optical waveguide transmission power in microfluidic chip at room temperature under low voltage operation (0 to 4 V). The unique electro-optical phenomenon law the 1,3-methylimidazolium cation ionic liquids were investigated using two waveguide geometries. The first waveguide geometry was used to investigate the position-dependent modulation along the waveguide; the second waveguide geometry was used to improve the optical power manipulation efficiency. The electro-optical phenomenon law of ionic liquids at three wavelengths (663,1330 and 1530nm) are investigated, and obtained the change law of optical power for seven ionic liquids. It is obtained the relation of the optical power change with the voltage magnitude, polarity of the voltage and the physical characteristics (conductivity, viscosity) of ionic liquids. The physical explanation of the phenomenon was discussed finally. The use of ionic liquids to achieve fluid waveguide optical power manipulation provides a new methods and ideas for the design of new optical fluidic devices. The use of an electric field to control the fluid nature for achieving light manipulation, it needn’t microfluidic pump, insensitive to external environment and can be highly integrated in microfluidic chip, which is an ideal way for achieving low energy consume and portable light manipulation devices.In conclusion, the use of ionic liquids as an optical transmission medium configured fluid can greatly extend the optical window of optofluidic waveguide (visible, near infrared or far infrared), and has a low volatility, wide temperature range and other advantages. For different needs, by selecting the appropriate anions and cations or changes the anions and cations substituents, the ionic liquids can be designed for satisfying particular optical window, transmittance characteristics required and refractive index. The electro-optical phenomena of ionic liquids provide new ideas and methods for designing optical power control devices on a microfluidic chip with the electric field control. The study of light manipulation in optofluidic waveguide based on ionic liquids has certain practical value for designing other optofluidic devices.