Researchers used sound to shake light, in effect, by fabricating piezoelectric AlN actuators on top of ultralow-loss Si3N4 photonic circuits and applying a voltage signal on them. The signal induced bulk acoustic waves electromechanically, which can modulate the generated microcomb in the Si3N4 circuits.

Integrated silicon nitride photonic chips with aluminium nitride actuators. Source: Jijun He, Junqiu Liu (EPFL)Integrated silicon nitride photonic chips with aluminium nitride actuators. Source: Jijun He, Junqiu Liu (EPFL)Piezoelectric materials and devices are commonly used in wireless communications, global positioning, navigation and space applications. Professors from Ecole Polytechnique Federale de Lausanne (EPFL) and Purdue University led a collaboration to combine piezoelectric aluminum nitride (AIN) technology with the ultralow-loss silicon nitride (Si3N4) integrated photonics to create a new scheme for on-chip acousto-optic modulation.

The hybrid resolves the challenge of allowing wideband actuation on photonic waveguides with ultralow electrical power. Maintaining the ultralow loss of Si3N4 circuits is a key feature. "This achievement represents a new milestone for the microcomb technology, bridging integrated photonics, microelectromechanical systems engineering and nonlinear optics," says Junqiu Liu, who leads the fabrication of Si3N4 photonics chips at EPFL's Center of MicroNanoTechnology. "By harnessing piezoelectric and bulk acousto-optic interactions, it enables on-chip optical modulation with unprecedented speed and ultralow power consumption." The circuit was manufactured with CMOS-compatible foundry processes typically used for microprocessors, microcontrollers, memory chips and other digital logic circuits.

Two potential applications for this hybrid system are chip-based lidar engines driven by CMOS microelectronic circuits and magnet-free optical isolators.

An article on this work is published in Nature.