MHz operation of elasto-optic phase modulators in laser-written photonic integrated circuits

Thermo-optic phase shifters in femtosecond-laser-micromachined (FLM) glass photonics suffer from limited modulation bandwidths (typically 1 kHz) and require constant power dissipation to maintain static phase shifts. We overcome these limitations by integrating piezoelectric actuators with FLM waveguides in glass substrates. A piezoelectric plate is bonded to the sample; its deformation induces controlled stress and strain on the substrate across the waveguides. This stress directly results in an elasto-optic refractive index variation, enabling both static and dynamic phase reconfiguration without static power consumption. Our approach achieves optical signal modulation frequencies up to 6 MHz, surpassing the capabilities of thermo-optic phase shifters in FLM circuits by three orders of magnitude. The technique retains key advantages of FLM fabrication: low coupling loss with standard optical fibers, flexible definition of the operating wavelength, and rapid realization without complex lithographic deposition or patterning of piezoelectric material. This provides a practical, power-efficient solution for high-speed reconfigurable photonics in applications spanning quantum simulations, quantum metrology, sensing, and classical communications.