A fiber-optic sensor, a method of configuring a fiber-optic sensor, and a method of using a fiber-optic sensor are provided. The fiber-optic sensor includes an optical fiber coil having a length and a laser source optically coupled to the coil. The laser source has a coherence length. Light from the source is transmitted to the coil as a first signal propagating along the coil in a first direction and a second signal propagating along the coil in a second direction opposite to the first direction. The optical paths of the first signal and the second signal are substantially reciprocal with one another and the first signal and the second signal are combined together after propagating through the coil to generate a third signal. The coherence length is greater than 1 meter or is in a range between 200 microns and 10 centimeters.