Fiber-tip bubble-structure microcavity sensor

A Fabry-Perot interferometer sensor based on a fiber-tip bubble-structure micro-cavity is proposed, fabricated, and demonstrated for hydrostatic pressure sensing and transverse load sensing. A segment of a well-cleaved multimode fiber with a core diameter of 62.5 mu m is processed with chemical etching based on a solution of HF 40% and the bubble-structure micro-cavity is fabricated by using arc discharge at the end of the processed multimode fiber. The sensor can be considered as a two-beam Fabry-Perot interferometer with one beam from the silica-air interface on the left side of the bubble and the other from the air-silica interface on the right side of the bubble. The broadband light is injected into the fiber-tip bubble-structure micro-cavity by splicing the multimode fiber with the bubble-structure micro-cavity to a 3-dB optical coupler and the reflective spectrum of the bubble-structure micro-cavity is measured by an optical spectrum analyzer. Both hydrostatic pressure sensing with a sensitivity of similar to 0.1 nm/MPa and transverse load sensing with sensitivity of 3.64 nm/N are experimentally demonstrated based the proposed fiber-tip bubble-structure micro-cavity sensor. The proposed sensor is demonstrated with a relative low temperature sensitivity of about 2 pm/degrees C. Properties of the fiber-tip bubble-structure micro-cavitys with different sizes are investigated. The sensor has the advantages of low-cost, ease of fabrication and compact size, which make it a promising candidate for hydrostatic pressure sensing or transverse load sensing in harsh environments.