High-Resolution Liquid Level Sensor Based on Microwave Photonics Technique Interrogated Multicore Fiber Interferometer

We propose and experimentally demonstrate a high-resolution liquid level sensor based on a seven-core fiber Michelson interferometer (MI), which is constructed with a pair of symmetric outer cores of the seven-core fiber. The angular position calibrated MI is securely affixed to a cantilever beam, such that variation in liquid level will change the curvature of the cantilever beam, leading to phase difference variation between the two interfering arms. Thanks to the used high-resolution microwave photonics filter (MPF) measurement system, significantly enhanced measurement resolution is achieved compared to the traditional optical wavelength demodulation methods. As a result, the measured sensitivity in 10.97 MHz/cm and the liquid level resolution is 0.04558 cm, when a 500 kHz measurement resolution of vector network analyzer (VNA) is employed. Furthermore, liquid level measurement range of up to +14 cm is achieved, which can be significantly increased by extending the length of the cantilever beam. The proposed sensor possesses the unique advantages of high sensitivity, high resolution and large measurement range, making it very promising for high-precision liquid level measurement applications in the future.