Ultra-sensitive micro-displacement sensor based on a U-shaped bent SMF

Sensors based on irregularly shaped bent optical fiber devices have attracted considerable interest in many applications. However, the effective interference length and bent radius of the irregular shape fiber have not been given accurately. Here an equivalent arc model is proposed to define the effective interference length and bent radius of the U-shaped fiber device: the U-shaped optical fiber is equivalent to a regular arc. We found that the effective interference length of devices varies greatly with the structure's height changes in some special structure sizes, which is highly useful for micro-displacement measurement. In terms of this model, an ultra-sensitive micro-displacement sensor of -1.2838nm/µm in a measurement range of 0-60 µm has been realized. The sensitivity of this device is one order of magnitude higher than that in any previously reported bent optical fiber work. More importantly, the analysis strategy of the equivalent arc model can be generalized to various irregular bent fiber micro-displacement sensors and other sensing fields.