Engineering 101

High-speed, Efficient, and Compact Electro-optic Modulators Target Free Space

We use electro-optic modulators for everything from sensing to metrology and telecommunications. Research tends to focus on applications that take place on chips or within fiber optic systems. But what about optical applications outside the wire?

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), in collaboration with researchers at the Department of Chemistry at the University of Washington, developed a compact and tunable electro-optic modulator for free space applications that can modulate light at gigahertz speed. They published their research in Nature Communications

Flat, compact metasurfaces are ideal platforms for controlling light in free space, but most are static, key functionality for modulators. Some active metasurfaces can effectively modulate light, but only at low speeds of just a few megahertz. For applications such as sensing or free-space communications, fast bursts of light on the scale of gigahertz are necessary. 

The high-speed modulator developed combines metasurface resonators with high-performance organic electro-optical materials and high-frequency electronic design to efficiently modulate light intensity in free space.

The modulator consists of a thin layer of an organic electro-optic material deposited on top of a metasurface etched with sub-wavelength resonators integrated with microwave electronics. When a microwave field is applied to the electro-optical material, its refractive index changes, changing the intensity of light transmitted by the metasurface in mere nanoseconds. 

The design enables light modulation 100 to 1,000 times faster than previously possible.

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