Microfluidic Devices Based On Micro-structured Fibers

Silica optical fibers are the basis of the information society,which are widely used in optical communication and sensing.However,the traditional optical fibers cannot meet the growing demand of practical applications anymore.Moreover,silica fibers possess problems of nonlinearity,Rayleigh scattering,dispersion,laser induced damage,unavailable in ultraviolet and infrared wavelengths due to their intrinsic defects.In order to avoid these intrinsic defects,the researchers embark on exploring new-type optical fibers.Numerous micro-structured optical fiber has been proposed and applied to the areas of lasers,sensors,biology and chemistry.Microfluidics refer to the gas or liquid flowing in micron-scale channels.The volume of microfluidics is nano-liter to femto-liter generally.Microfluidics possess unique features different to the macroscopic fluid,such as low Reynolds number,multi-field coupling,low dimension,laminar flow.Micro-structured optical fibers,such as microfibers and hollow core micro-structured fibers,have their distinct advantages in microfluidic applications.On the one hand,we can achieve microfluidic detection by the interaction between the evanescent field and fluid.On the other hand,the hollow core can be used as a common channel for the light and fluid,which avoids complex processes to machine micro-channels.Meanwhile,we can enhance the action intensity between the light and the fluid by extending fiber length.In this paper,we achieve the optical detection of microfluidics using three different micro-structured fibers.These fibers are microfiber,hollow core microfiber and negative curvature hollow core fiber with large aperture,respectively.The main research results are as follows:1.We tabricated the hollow core microfibers by oxyhydrogen flame heating and drawing method.The diameter of the microfibers can be less than 1 micrometer.Meanwhile,such hollow core microfibers have relatively low transmission loss.We fabricated hollow core microfibers without pumping inert gases based on the fabrication device of standard communication optical fibers.The temperature of oxyhydrogen flame and the drawing speed of the translation to fabricate hollow core microfibers is higher than solid core microfibers.2.We achieved the controllable manipulation of suspended particles using a 1-um-diameter microfiber.A laser beam at 980 nm was divided onto two coherent beams after an adjustable ratio fiber coupler.These two beams were coupled into the both ends of the microfiber.Particles near the waist area were attracted to the surface of the microfiber under the gradient force.Meanwhile,the particles were propelled along the microfiber due to the scattering force.The direction of the scattering force was controlled through the adjustable ratio fiber coupler.3.We investigated the fluorescence intensity of micro fluidics with an effective detection volume of 300 fL using a homemade hollow core microfiber.Lights among visible and near infrared band can be guided in hollow core microfibers with an inner diameter comparable to wavelength.The transmission loss of a 5-?m-outer-diameter hollow core microfiber is 2.4 dB/mm at 400 nm.The hollow core of microfibers can be used as a common channel for the light and fluid.The interaction strength between the light and fluid is enhanced by the direct interaction.Meanwhile,the detection volume is greatly reduced due to the small size of the fluid channel.4.We achieved the rapid injection of fluid and detection of heavy metal ions using a negative curvature hollow core fiber with a large hole.We detected the concentration of Cu2+ ion quantitatively.The negative curvature hollow core fiber consists of an air core and a circle of un-contacted capillary surrounding the air core.The large air core was used as a common channel for the light and the fluid.The injection rate of the liquid and the repetition rate of fiber are greatly improved,and the interaction strength between the light and the liquid was enhanced by extending the length of the fiber.