Fiber borehole strainmeter based on Michelson interferometer

The measurement of borehole strain is the main approach to observe crustal stress condition and its variation. It is an important way in understanding the relationship between the earth strain abnormality and the geological calamity. A fiber borehole strainmeter based on a Michelson interferometer is developed, in which the earth strain is transformed to the change in length of an optical fiber. Another one optical fiber, acting as the reference arm, is used to reduce the influence resulted from temperature and environment. Experimental results show that the strain sensitivity is 117 nm, which has much room for improvement. This sensor has advantages over traditional ones, and can be further developed for use in field observation stations.