Optics

Silicon electro-optical modulator with ITO is smaller and more efficient than existing devices

April 14, 2020

Heterogeneously integrated indium tin oxide thin film in silicon photonics forms a subwavelength-sized plasmonic phase-shifter.

John Wallace

On a silicon chip (gray), electrical data (white) travels through Mach-Zehnder interferometer (MZI) based electro-optical modulators, encoding electrical data into the optical domain by means of tunable plasmonic ITO-based phase shifters (golden patches atop both MZI sections) capable of operating at multiple wavelengths of light in the telecommunication-relevant C-band (red and purple).

Researchers at the George Washington University (Washington, DC) have developed and demonstrated a silicon-based electro-optical modulator that they say is smaller, as fast as, and more efficient than state-of-the-art technologies.¹ By adding indium tin oxide (ITO) -- the transparent conductive oxide commonly found in touchscreen displays and solar cells -- to a silicon photonic chip platform, the researchers were able to create a compact device 1 μm in size and able to yield gigahertz-speed signal modulation.

The new invention is timely, as demand for data services is growing rapidly and moving towards next-generation communications networks. Taking advantage of their compact footprint, electro-optic converters can be utilized as transducers in optical computing hardware such as optical artificial neural networks.

Electro-optical modulators in use today are typically between 1 mm and 1 cm in size. Reducing their size allows increased packaging density, which is vital on a chip. While silicon often serves as the passive structure on which photonic integrated circuits are built, the light/matter interaction of silicon materials induces a rather weak optical index change, requiring a larger device footprint. While resonators could be used to boost this weak electro-optical effect, they narrow devices' optical operating range and incur high energy consumption from required heating elements.

By heterogeneously adding a thin material layer of ITO to the silicon photonic waveguide chip, researchers led by Volker Sorger, an associate professor of electrical and computer engineering, have demonstrated an optical index change 1000 times larger than silicon. Unlike many designs based on resonators, this spectrally broadband device is stable against temperature changes and allows a single fiber-optic cable to carry multiple wavelengths, increasing the amount of data that can move through a system.

Source: https://www.eurekalert.org/pub_releases/2020-04/gwu-bts041320.php

REFERENCE:

1. Rubab Amin et al., Optica (2020); https://doi.org/10.1364/OPTICA.389437.

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.