An embeddable, robust and cost-effective optical interferometric strain sensor with nano-scale strain resolution isreported in this paper. The principal structure of the sensor consists of an optical fiber, a quartz rod coated with a thingold layer, and two metal shells employed to transfer the strain, orient and protect the optical fiber and quartz rod. Theoptical fiber endface, combining with the gold-coated surface forms an extrinsic Fabry-Perot interferometer. When thesensor is subjected to an external compressive/tensile stress, slide between the two metal shells will occur, resulting in acavity length variation of the interferometer. A temperature compensation design is employed in the structure tominimize the temperature crosstalk of the sensor. The sensor was firstly calibrated, and the result showed that ourprototype sensor can realize a measurement resolution of 30 nanostrain (nε) and a sensitivity of 10.01 με/m over arange of 1000 με. After calibration of the sensor, monitoring the shrinkage strain of a cubic brick of mortar in real timeduring the drying process was conducted. The strain sensor was compared with a commercial linear variabledisplacement transducer, and the comparison results in four weeks demonstrated that our sensor had much highermeasurement resolution and gained more detailed and useful information. Due to the advantages of the extremely simple,robust and cost-effective configuration, it is believed that the sensor is significantly beneficial to practical applications,especially in structural health monitoring.
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