Birefringence-free photoelastic modulator with centimeter-square aperture operating at 2.7 MHz with sub-watt drive power.

Photoelastic modulators are optical devices with a broad range of applications. These devices typically utilize a transverse interaction mechanism between acoustic and optical waves, resulting in a fundamental trade-off between the input aperture and the modulation frequency. Commercially available modulators with centimeter-square apertures have operating frequencies in the vicinity of 50 kHz. In this work, we experimentally demonstrate a birefringence-free photoelastic modulator operating at approximately 2.7 MHz with a centimeter-square aperture, increasing the operating frequency substantially compared to existing approaches. Using the modulator and polarizers, we demonstrate close to π radians polarization modulation amplitude with sub-watt drive power, translating to nearly 100% intensity modulation efficiency at the fundamental (2.7 MHz) and second-harmonic (5.4 MHz) frequencies.