A strain fiber optic sensor is proposed and exper-1 imentally demonstrated in this letter. The sensor operates in 2 reflection mode, and its assembly relies on a single splice point 3 between a thin core fiber and polarization-maintaining fiber. The 4 system offers competitive sensitivities of 14.68 and 6.9 pm/με, 5 determined by the PM-fiber length. In addition, the one-way 6 ANOVA analysis indicates a minimal error (MSE=0.34) and low 7 probability of measurement overlap (Prob > F = 5.59882 × 8 10 −85 ). The fabrication, the sensor dimensions, and the statistical 9 analysis make the proposed sensor an attractive alternative for 10 monitoring strain. 11 Index Terms-Strain fiber optic sensor, polarization maintain-12 ing fiber, interferometric all fiber-optic device. 13 I. INTRODUCTION 14 S TRAIN receives special attention from the fiber-optic 15 sensor community due to exciting applications such as 16 biomechanical monitoring [1], medical surgery [2], structural 17 health monitoring [3], robotics [4], metal deforming [5], and 18 art preservation [6]. Diverse strain fiber optic sensors have 19 been demonstrated over almost four decades. One of the first 20 approaches to detect strain was the well-known Fiber Bragg 21 Grating (FBG). These devices generally have a one integer 22 digit sensitivity in terms of pm/με [7]; Over the last decade, 23 many efforts have focused on improving this sensitivity by 24 modifying the FBG shape or combining it with interferometric 25 devices [8]. Tapered optical fibers are another option to detect 26 strain [9]. This thin fiber shows an improved sensitivity but 27 needs delicate opto-mechanical handling. 28 Interferometric all-fiber devices emerge as a strain detection 29 alternative with high sensitivity. Fabricating these devices 30 Manuscript