A novel all-fiber Multimode Interference (MMI) liquid level sensor is proposed and demonstrated. We show that MMI effects can be effectively applied for multiplexed liquid level sensing, and by selecting an adequate fiber, discrete and continuous level sensing is feasible. Using a standard 105/125 multimode fiber a simple discrete level sensor was fabricated, which can also can also discriminate the refractive index of the liquid. When a specialty fiber, know as NoCore fiber is used, both continuous and discrete level sensing can be achieved. We can also modify at will the continuous level range by increasing the No-core fiber by the appropriate length, while retaining the ability to determine the refractive index of the liquid during the level measurement. The MMI liquid level sensors are not only inexpensive, but their fabrication is quite simple.

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