This paper presents a miniature Fabry-Perot voltage sensor created at the tip of an optical fiber. The sensor utilizes a micro-machined, all-silica, opto-mechanical structure that is flexed under the presence of attractive forces generated among charged bodies. The small dimensions and short response times of the structure provide an opportunity for measurement of the DC and AC voltages within the range of power grid frequencies. The experimental sensor length was less than 5 mm, and the sensor's sensitivity is sufficient for measurements of voltages in mid-voltage, and even low voltage, ranges. The sensor has a parabolic response to the applied voltage and can be adapted to a variety of voltage ranges by selecting the proper geometrical configuration. We demonstrate experimentally sensors with measurement ranges between 100 V and 1 KV (higher voltage ranges are also straightforwardly attainable) and with resolutions as low as 0.1 V.