Abstract: Recently, lab-in-fiber (LIF) sensors have offered a new paradigm in many different scenarios, such as optofluidics, due to their ability to integrate different multiphysics sensor elements in a small space. In this Letter, the design and manufacture of a multiparameter sensing device is proposed, through the combination of an in-fiber air microcavity and a plane-by-plane fiber Bragg grating (FBG). The reflection-based sensor, with a length of less than 300 µm, is located at the end of a single-mode fiber and integrated into a surgical needle for exploitation in biomedical applications. Here we present the first (to our knowledge) ultra-short LIF sensor reported under the "touch and measure" approach. In this first prototype, the detection of axial tensile strain (6.69pm/µe in air cavity) and surrounding refractive index (11.5 nm/RIU in FBG) can be achieved simultaneously.

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