Fabrication Of Optical Fiber Microfluidic Devices By Femtosecond Laser And Liquid Refractive Index Sensing

In this paper, we successfully fabricate microchannels which are parallel with thefiber cores using water-assisted femtosecond laser fabrication method. Then the fibersbecome new type microfluidic devices which can measure liquid refractive index. Thefabrication method is efficient and simple. The devices are uneasily broken, temperatureinsensitive and have strong anti-interference ability. The main contents are listed asbelow.Firstly, we introduce the main advantages, classifications and the research status offiber optic sensors and summarize the research status of femtosecond lasermicromachining and its remarkable strengths. The Electromagnetic wave equations inoptical fibers are derived from Maxwell equations and the Beam Propagation Method(BPM) is used for simulating the theoretical curves. At last, the mechanism ofwater-assisted femtosecond laser fabrication is given.Secondly, we research the methods of fabricating microchannels parallel with thefiber cores and determine to use the H type‘fabrication method. By adding the throughholes, we can almost fabricate microchannels of arbitrary length. The distances betweenthe microchannels and the fiber cores also can be controlled by adjusting the distancesbetween the through holes and the fiber cores. In order to achieve the sensingcharacteristics of these sensors to liquid refractive index, we prepare a set of standardrefractive index solutions using water and glycerin. The refractive indices are from1.3406to1.4078. Then the sensing curves of the samples with different lengths ofmicrochannels as well as different distances between microchannels and the fiber coresare measured. These curves are compared with the theoretical curves simulated usingsoftware. At last, the temperature properties of the samples are investigated.By analyzing the sensing curves, we find that, as the lengths of the microchannelsbecoming longer, the light losses in the fiber cores become larger. At the same time, thesensitivities of the sensors become higher. Besides, when the microchannels and thefiber cores are closer, the light losses in the fiber cores become larger and thesensitivities of the sensors become higher. Then we compare the theoretical curves withthe sensing curves measured in experiments. They have the same trend, but the losses ofthe practical sensing curves are larger, which is mainly due to the roughness of innerwalls of the microchannels. The samples are temperature insensitive and can worknormally under the temperature of200℃.