A fiber-optic differential pressure sensor and its application in liquid level measurement

This paper reports an all-fiber, all-silica differential pressure sensor based on a Fabry–Pérot interferometer (FPI) with a pressure-sensitive diaphragm. Differential pressure sensing is achieved by a custom-designed single-mode fiber, that incorporates two capillaries that are placed in parallel with the fiber core. These capillaries connect the interior of the FPI cavity to the external environment through radially fabricated venting ports, allowing for the creation of a second pressure port. The sensor was characterized experimentally as a differential pressure sensor. The sensor demonstrated a high-pressure sensitivity of − 1311 nm/bar near zero pressure (quadratic fit: ΔOPL = 499.1P 2 − 1311P, R 2 = 0.999), and fast dynamic response with time constants as low as 1.4 s, which can be reduced further to the millisecond range by increasing the custom designed single-mode fiber diameter. When employed as a liquid level gauge, the sensor achieves a resolution of 1.1 mm with negligible hysteresis over the operating range of 0–800 mm. Owing to its compact design with a short FPI cavity, the sensor eliminates the need for temperature compensation. Its fully dielectric construction and low optical power requirement (≤150 µW) make it intrinsically safe and highly suitable for deployment in potentially explosive environments, such as fuel tanks.