An optical‐maser modulator employing a transparent piezoelectric medium is described. The device is based on multiple interference in transmission or reflection, the intensity in the interference pattern being modulated by a change in thickness of the piezoelectric plate. Using barium titanate it is shown that 80% modulation and 20‐Mc bandwidths are readily attainable. A sacrifice of modulation to 10% permits bandwidths ∼200 Mc. A slight modification allows the device to operate purely as a phase modulator.In addition, an optical‐maser modulator employing a grating ruled on a piezoelectric medium is described. Spatial modulation is brought about by a change in grating constant via the piezoelectric effect. As a communication device in conjunction with an optical maser operating at 0.7&mgr;, 10% modulation and a bandwidth ∼10 Mc can be obtained using barium titanate driven near the fundamental resonance frequency.