A New Fast Electro-Optical Modulator

Illustration of a fast, micrometer-size electro-optical modulator. (Source: GWU)

Researchers developed and demons­trated for the first time a silicon-based electro-optical modulator that is smaller, as fast as and more efficient than state-of-the-art technologies. By adding indium tin oxide (ITO) – a trans­parent conductive oxide found in touch­screen displays and solar cells – to a silicon photonic chip platform, the researchers were able to create a compact device 1 micrometer in size and able to yield gigahertz-fast, or 1 billion times per second, signal modu­lation.

Electro-optical modulators are the workhorses of the internet. They convert electrical data from computers and smart­phones to optical data streams for fiber optic networks, enabling modern data communications like video streaming. The new invention is timely since demand for data services is growing rapidly and moving towards next generation communi­cation 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 that mimic the human brain and a plethora of other appli­cations for modern-day life.

Electro-optical modu­lators in use today are typically between 1 millimeter and 1 centimeter 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 indium tin oxide to the silicon photonic waveguide chip, researchers at the George Washington Univer­sity, led by Volker Sorger, an associate professor of electrical and computer engi­neering, have demons­trated an optical index change 1,000 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 of light, increasing the amount of data that can move through a system. “We are delighted to have achieved this decade-long goal of demons­trating a GHz-fast ITO modulator. This sets a new horizon for next-generation photonic reconfigurable devices with enhanced perfor­mance yet reduced size”, Sorger said. (Source: GWU)

Reference: R. Amin et al.: Sub-wavelength GHz-fast broadband ITO Mach–Zehnder modulator on silicon photonics, Optica 7, 333 (2020); DOI: 10.1364/OPTICA.389437

Link: Orthogonal-Physics-Enabled-Nanophotonics Lab, George Washington University, Washington DC, USA

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