Integrated microfluidic flowmeter based on a micro-FBG inscribed in Co2+-doped optical fiber

Two glass capillaries and a short length of high-light-absorption Co2+-doped optical fiber were stacked inside a larger outer capillary tube. The stack was then drawn into a tapered device. Two microchannels with the diameter of ∼50 μm were formed inside the capillaries for flowing of microfluidics. An FBG was inscribed in the tapered Co2+-doped fiber with waist diameter of ∼70 μm , and acts as a flow-rate sensor. A pump laser with wavelength of 1480 nm was utilized to locally heat the μFBG, rendering the μFBG as miniature "hot-wire" flowmeter. The flow rate of the liquid in the micro-channels is determined by the induced wavelength shift of the μFBG. The experimental results achieve a minimum detectable change of ∼16 nL/s in flow rate, which is very promising in the use as part of biochips.