Low-frequency acoustic anomalies in lithium niobate Mach–Zehnder interferometers

Abstract
Anomalous variation in the frequency response of z-cut and x-cut Mach–Zehnder traveling-wave optical modulators near 50 MHz has been observed. Measurements of loss in the coplanar electrode and coupling to an adjacent acoustic transducer indicate the effect is due to surface acoustic waves in the device. Application of an acoustic absorber reduces the frequency response variation.