A photoelastic modulator, comprising a driving block and a driver transducer for perturbing said block in a predefined direction to establish a standing wave extending longitudinally in said block and hence perpendicularly to said predefined direction. The transducer is affixed to said block at two regions of the transducer mutually displaced in said predefined direction, to minimize the coupling of lateral perturbation perpendicular to the predefined direction. A recess or gap may be provided under the transducer.