The present invention is strain, the total reflection type external Fabry for measuring various physical quantities such as a pressure - directed to a ferro-optic sensors and strain measurement method using the same, in particular inserted in one end of the capillary glass tube 52, a fixed single-mode optical fiber (51) Wow; The end of the single mode optical fiber 51 is inserted in the capillary glass tube 52 and to be spaced a predetermined distance into the other end of the capillary glass tube 52, and a fixed metal-coated optical fiber (53); A laser for irradiating the light to the end groups of the single-mode optical fiber 51 is inserted into the non-capillary glass tube (52); Wherein the laser groups joined by a single-mode optical fiber 51 and the single-mode optical fiber 51 and the metal-coated optical fiber 53, an interference signal fringes of light returning to the single-mode optical fiber 51 by an air gap 54 between the but it provided with a light detector for sensing; When deformation occurs in the longitudinal direction of the capillary glass tube 52, the gap length (S) of the air gap 54 side, while the occurrence frequency and the signal level change trend of the interference fringes is varied according to the variations in size and direction. With the occurrence of interference fringe can measure the strain amount of the object to be measured, and by using the tendency of the signal level is increased or attenuated depending on the loss degree caused by the light spread in the air gap (54) deformation direction (tensile or compressive) may also be determined.
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