Liquid-level sensor based on flat-shaped plastic optical fiber assisted by a long-period grating

A corrugated surface long-period grating (LPG) was imprinted on a flat-shaped plastic optical fiber (POF) as a liquid-level sensor. The flat shape was processed on commercial POF by a simple heat-pressing method, and the LPG was fabricated by a mechanical die-press-print method. The liquid-level sensing performance of the sensor with different structural parameters was evaluated. It was shown that the thinner flat-shaped POF assisted by an LPG exhibits better sensing performance. The LPG with deeper groove depth achieved higher sensitivity, and theoretical calculations were consistent with these results. The highest sensitivity of -0.2332dB/mm was obtained while the flat-shaped POF with a thickness of 500μm, on which was assisted by the LPG with a period of 300μm and a groove depth of 103μm. The results demonstrated that flattening the POF assisted an LPG could improve the liquid-level sensing performance.