Miniaturized Modulator Increases Potential of Photonic Integrated Circuits

Photonic integrated circuits promise greater speed, bandwidth, and efficiency than traditional electrical circuits, but they’re not yet small enough to be used broadly in computing and other applications.

To achieve energy efficiency and operational speed within a smaller device, electrical engineers at the University of Rochester used a thin film of lithium niobate (LN) bonded on a silicon dioxide layer to create a miniaturized LN modulator. The engineers have created what they believe to be the smallest electro-optic modulator ever reported.

A schematic drawing shows an electro-optic modulator developed in the lab of Qiang Lin, professor of electrical and computer engineering. The smallest such component yet developed, it takes advantage of lithium niobate, a 'workhorse' material used by researchers to create advanced photonic integrated circuits. Courtesy of University of Rochester/Michael Osadciwm.

Because of its outstanding electro-optic and nonlinear optic properties, lithium niobate has become a workhorse material system for photonics research and development, professor Qiang Lin said. “However, current LN photonic devices, made upon either [a] bulk crystal or thin-film platform, require large dimensions and are difficult to scale down in size, which limits the modulation efficiency, energy consumption, and the degree of circuit integration,” he said.

Lead author Mingxiao Li holds a small lithium niobate chip in an etching chamber. Courtesy of the laboratory of Qiang Lin/University of Rochester.

The LN electro-optic modulator demonstrated a tuning efficiency up to 1.98 GHz V⁻¹; a broad modulation bandwidth of 17.5 GHz; and an electro-optic modal volume of only 0.58 μm³. The device demonstrated efficient electrical driving of high-Q cavity mode in both adiabatic and nonadiabatic regimes, and achieved high-speed electro-optic switching with low switching energy.

This energy-efficient, high-speed electro-optic modulator could be a step toward realizing device miniaturization and high-density photonic integration on the monolithic LN platform, which is expected to find broad applications in communication, computing, microwave signal processing, and quantum photonic information processing.

The Rochester team’s modulator project builds on the lab’s previous use of lithium niobate to create a photonic nanocavity. Along with the modulator, the nanocavity is a key component in photonic chips. At only about 1 μm in size, the team’s nanocavity can tune wavelengths using only two to three photons at room temperature. The modulator can be used in conjunction with a nanocavity to create a photonic chip at the nanoscale.

The research was published in Nature Communications (www.doi.org/10.1038/s41467-020-17950-7).