High voltage sensors using integrated optic devices have advantages to be compact and simple. A passive sensor without any electronic component to give eletrical biases and any capacitive voltage divider is preferred, since it is immune to electromagnetic interferences and it is not affected by the fluctuations in the divider ratio. In this thesis, an integrated optic high voltage sensor using a Z-cut $LiNbO_3$ channel-waveguide cutoff modulator is presented. It is a passive device that does not need any electrical bias and any capacitive divider to achieve a wide range of sensing voltage. Its sensing voltage range exceeds ac 1,000 V peak-to-peak.