An electromagnetic survey sensing device, comprising: at least two electrodes disposed at spaced apart locations; an electrical to optical converter electrically coupled to the at least two electrodes, the converter configured to change a property of light from a source in response to voltage imparted across the at least two electrodes; and an optical fiber optically coupled to an output of the electrical to optical converter, the optical fiber being in optical communication with a detector; characterized in that the electrical to optical converter comprises means for changing the length of two optical paths associated with the optical fiber in response to the voltage imparted across the at least two electrodes; wherein the means for changing the optical path lengths comprises: a first piezoelectric element electrically coupled to the at least two electrodes, a first mirror functionally associated with the first piezoelectric element and disposed proximate an end of the first optical path associated with the optical fiber, such that electrical actuation of the first piezoelectric element by the voltage causes corresponding change in distance between the end of the first optical path and the first mirror; and a second piezoelectric element electrically coupled to the at least two electrodes, a second mirror functionally associated with the second piezoelectric element and disposed proximate an end of the second optical path associated with the optical fiber, such that electrical actuation of the second piezoelectric element by the voltage causes corresponding change in distance between the end of the second optical path and the second mirror opposite to the change in distance between the end of the first optical path and the first mirror. at least two electrodes disposed at spaced apart locations; an electrical to optical converter electrically coupled to the at least two electrodes, the converter configured to change a property of light from a source in response to voltage imparted across the at least two electrodes; and an optical fiber optically coupled to an output of the electrical to optical converter, the optical fiber being in optical communication with a detector; characterized in that the electrical to optical converter comprises means for changing the length of two optical paths associated with the optical fiber in response to the voltage imparted across the at least two electrodes; wherein the means for changing the optical path lengths comprises: a first piezoelectric element electrically coupled to the at least two electrodes, a first mirror functionally associated with the first piezoelectric element and disposed proximate an end of the first optical path associated with the optical fiber, such that electrical actuation of the first piezoelectric element by the voltage causes corresponding change in distance between the end of the first optical path and the first mirror; and a second piezoelectric element electrically coupled to the at least two electrodes, a second mirror functionally associated with the second piezoelectric element and disposed proximate an end of the second optical path associated with the optical fiber, such that electrical actuation of the second piezoelectric element by the voltage causes corresponding change in distance between the end of the second optical path and the second mirror opposite to the change in distance between the end of the first optical path and the first mirror. a first piezoelectric element electrically coupled to the at least two electrodes, a first mirror functionally associated with the first piezoelectric element and disposed proximate an end of the first optical path associated with the optical fiber, such that electrical actuation of the first piezoelectric element by the voltage causes corresponding change in distance between the end of the first optical path and the first mirror; and a second piezoelectric element electrically coupled to the at least two electrodes, a second mirror functionally associated with the second piezoelectric element and disposed proximate an end of the second optical path associated with the optical fiber, such that electrical actuation of the second piezoelectric element by the voltage causes corresponding change in distance between the end of the second optical path and the second mirror opposite to the change in distance between the end of the first optical path and the first mirror.