A system for measuring simultaneously both temperature and ac voltage and/or ac current, the system comprising: a piezo-electric sensor; and optical fiber that includes an optical strain sensor being in contact with the piezo-electric sensor and able to expand or contract therewith and an analyzer for analyzing an optical output of the fiber and strain sensor in response to an optical input, the analyzer being operable to use the optical output to determine the temperature and the ac voltage and/or ac current.