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 $\pi$ 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.