A high-visibility in-line optofluidic Fabry–Pérot (HVILOFFP) cavity was demonstrated by splicing a silica capillary tube into two standard single mode fibers (SMFs) and polishing the latter SMF. Two size-controllable microfluidic accesses in the sides of the HVILOFFP cavity allow the analyte of interest to smoothly flow into the cavity and directly interact with light without any assisting equipment to direct the analyte into the cavity. Experimental results showed that the fringe visibility of the HVILOFFP cavity was up to 24 dB in both air and water, which is higher than that of most laser-machined in-line fiber-optic Fabry–Pérot cavities because of the smoother end faces of the SMFs. The proposed HVILOFFP cavity was demonstrated by measuring the refractive indices with a sensitivity of 1148.93 nm/RIU in the range of 1.333–1.345. Moreover, the proposed HVILOFFP cavity is economical, compact (<100 μm), robust, and insensitive to temperature. These advantages make it a promising optofluidic platform in biomedical and chemical sensing applications.

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