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We reported a few high-sensitivity optical sensors based on different types of in-fiber air bubbles those were fabricated by use of a commercial fusion splicer.A high-sensitivity strain sensor based on an in-fiber Fabry-Perot interferometer (FPI) with an air cavity was demonstrated by means of splicing together two sections of standard single-mode fibers.The sensitivity of this strain sensor was enhanced to 6.0 pm/με by improving the cavity length of the FPI by means of repeating arc discharges for reshaping the air cavity.Moreover, such a strain sensor has a very low temperature sensitivity of 1.1 pm/℃, which reduces the cross sensitivity between tensile strain and temperature.We also demonstrated a nanoscale silica diaphragm based fiber-tip Fabry-Perot interferometer for pressure sensing applications.The thinnest silica diaphragm with a thickness of~320 nm has been achieved by use of an improved electrical-arc-discharge technique.As a result, a high pressure sensitivity of~1036 pm/MPa at 1550nm and a low temperature cross-sensitivity of~960Pa/oC are achieved when a silica diaphragm with a thickness of~ 500 nm is employed.Moreover, a unique rectangular air bubble was demonstrated to develop a promising strain sensor with an ultrahigh sensitivity of up to 43.0 pm/με.