Optical interferometric microfiber sensor for in situ flow velocity measurement in microfluidic chips

Here, we introduce an optical interferometric microfiber sensor for in situ measurement of flow velocity in a microfluidic chip. The interferometric sensor is fabricated by fusing and tapering a standard single-mode optical fiber, and then embedded into a microfluidic chip, where the sensor element intersects vertically with the liquid flow channel. As the liquid flows through the channel, it applies pressure to the sensor’s sensitive surface, causing a wavelength shift in the transmission spectrum proportional to the flow velocity. Real-time monitoring and analysis of this wavelength shift enable precise flow velocity measurement. Results show that the proposed sensor chip exhibits excellent measurement performance within a average flow velocity range of 0–30.391 cm/s, with a average sensitivity of 0.094 nm/(cm/s). The resolution of average flow velocity measurement can reach 1.2 cm/s and the accuracy exceeds 90%.