An optical voltage sensor for measuring voltage on an underground power line or for use in other scenarios in which access to a conductor is available through a blind hole. The optical voltage sensor includes a light modulating member, such as a Pockel's crystal. A reflective, conductive member is positioned at one end of the light modulating member and another conductive member is positioned at an opposed end. A voltage capacitively coupled to the reflective conductive member induces a voltage across the light modulating member, thereby impacting the amount of modulation. A beam of light is directed through the crystal and reflected back out of the crystal, where the amount of modulating can be measured. The amount of modulation indicates a measured voltage, and can be transmitted to a monitoring station where processing can determine the status of the power grid or generate other results based on the measured voltage.