All-fibre transmission liquid level sensor based on core-cladding propagation modes interference

This paper presents an all-fibre liquid level sensor based on the interference between cladding and core modes propagating in a fibre with reduced core. The cladding modes are generated simply by using a combination of fibres with different cores fusion-spliced with a small misalignment. The sensing fibre is then exposed to the external medium and the level measurement is made by analysing only the transmitted signal, with no need for any special configuration to generate and collect a reflected signal. This simple, stable and compact system is capable of measuring up to 90 mm of water level with a sensitivity of 5.61 pm/mm with no need for using fibre gratings or fibre circulators.