High-sensitivity micro-liquid-level sensor employed the sidewall anti-resonance effect in hollow-core fiber

High-precision liquid level sensing at the microscale plays a critical role in microfluidics, lab-on-a-chip systems and chemical analysis. Here, we proposed a high-sensitivity micro liquid-level sensor by leveraging the sidewall anti-resonance effect in hollow-core fiber (HCF). The probe of the sensor is formed by splicing HCF segment between two single-mode fiber (SMF) and the anti-resonance effect could be induced by optimize the parameters of HCF. As the liquid level covers the sensor region, the effective refractive index (RI) of the high-order mode in cladding changes, causing a measurable shift of the output spectrum. Consequently, the liquid level height can be directly correlated with anti-resonance dip shift. Experiments demonstrate that the micro-liquid-level sensor achieves a maximum sensitivity of 0.012 dB/μm with a high detection limit of 2.5 μm in the range from 0 to 1100 μm. The results also indicate that the sensor probe is insensitive to the velocity, temperature and the RI of the liquid. The proposed sensor probe exhibits a simple structure, compact footprint and excellent linearity. This work offers a reliable and efficient approach for detecting liquid levels at the microliter scale, demonstrating significant potential for integration into advanced micro-analytical platforms.