Design and demonstration of a liquid level fiber sensor based on self-imaging effect

A novel liquid level fiber sensor based on self-imaging properties of the multimode interference (MMI) in no core fiber (NCF) is proposed and demonstrated. Based on the beam propagation method (BPM) simulation, a NCF of optimal length is selected to act as a sensing head and tunable filter in a ring cavity fiber laser. For high liquid level sensing, a height conversion setup based on atmospheric pressure balance principle is designed and the sensitivity is magnified 5 times. A 50 cm range of liquid level can be detected by monitoring the peak wavelength shift of output laser. The sensor exhibits an excellent linear response (R2 = 0.9999) and a sensitive response to different liquid refractive index (RI). The sensitivity of the single mode-no core- single mode (SNS) sensor is 108.8 pm/mm and the accuracy is about 1% at the resolution of 0.1 nm of detection using an OSA with the liquid RI of 1.4152, which is the highest accuracy for a 50 cm liquid level range to our best knowledge.