Cascaded bowknot-type taper based Mach–Zehnder interferometer for microfluidic flow rate sensing.

• Cascaded Bowknot-type taper based Mach–Zehnder interferometer (MZI) could be used for microfluidic flow rate detection. • The proposed sensor is suitable for liquids with refractive indexes ranging from 1.33 to 1.43. • The detectable water flow rate ranges from 0.66 mm/s to 10.6 mm/s. In microfluidic chip applications, the flow rate plays an important role. Here we proposed a simple liquid flow rate sensor by using two cascaded bowknot-type tapers (BTTs) to form a Mach–Zehnder interferometer (MZI) as the sensing element. As the water flows in the vicinity of the BTT, the cascaded BTTs based MZI's interference spectrum changes due to its contact with water. By comparing the time-swept spectra of the cascaded BTTs MZI from the state of one BTT in water to that of another BTT in water as the water flowing over it, the flow rate can be detected. The proposed sensor has a detectable range from 0.66 mm/s to 10.6 mm/s. [ABSTRACT FROM AUTHOR]