Rochester team develops ‘smallest’ electro-optical modulator

Based on thin film of lithium niobate bonded on silica, chip offers potential in datacoms, microwave- and quantum photonics.

Electrical engineers at the University of Rochester, NY, say they have made a significant step in addressing the problem of reducing the size of photonics integrated circuits enough to compete effectively with their miniature electronic counterparts.

Using a material widely adopted by photonics researchers – lithium niobate – the Rochester team has created what they are calling “the smallest electro-optical modulator yet.” The modulator is a key component of a photonics-based chips, controlling how light moves through circuits.

The lab of Qiang Lin, professor of electrical and computer engineering, uses a thin film of lithium niobate bonded on a silicon dioxide layer to create not only the smallest lithium niobate modulator yet, but also one that operates at high speed and is energy efficient.

The work is reported in Nature Communications.

Mingxiao Li, a graduate student in Prof. Lin’s lab, says this achievement “is a significant foundation for realizing large-scale lithium niobate photonic integrated circuits that are of immense importance for applications in data communication, microwave photonics, and quantum photonics.”

‘Workhorse material’

Because of its well-known, advantageous electro-optic and nonlinear optic properties, lithium niobate has “become a workhorse material system for photonics research and development,” said Lin.

“However current lithium niobate photonic devices, made upon either 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.”

“A major challenge lies in making high-quality nanoscopic photonic structures with high precision.”

The modulator project builds upon the lab’s previous use of lithium niobate to create a photonic nanocavity, another key component in photonic chips. At only about one micron in size, the nanocavity can tune wavelengths using only two to three photons at room temperature.

“This is the first time we know of that even two or three photons have been manipulated in this way at room temperatures,” Lin says. The modulator could be used in conjunction with a nanocavity in creating a photonic chip at the nanoscale.

This research and development project was supported with funding from the US National Science Foundation, Defense Threat Reduction Agency, and Defense Advanced Research Projects Agency (DARPA); fabrication of the device was done in part at the Cornell NanoScale Facility.