Smaller and Faster Electro-Optic Modulator

A research team comprising members from City Univer­sity of Hong Kong (CityU), Harvard Univer­sity and renowned infor­mation tech­nologies labora­tory has success­fully fabri­cated a tiny on-chip lithium niobate modu­lator, an essential component for the opto­electronic industry. The modulator is smaller, more efficient with faster data trans­mission and costs less. The tech­nology is set to revo­lutionise the industry.

Scheme of the new tiny modulator that drives data at higher speeds and lower costs. (Source: Second Bay Studios / Harvard SEAS)

The electro-optic modulator is only 1 to 2 cm long and its surface area is about 100 times smaller than tradi­tional ones. It is also highly efficient – higher data trans­mission speed with data bandwidth tripling from 35 GHz to 100 GHz, but with less energy consump­tion and ultra-low optical losses. The invention will pave the way for future high-speed, low power and cost-effective communi­cation networks as well as quantum photonic compu­tation.

Electro-optic modulators are critical components in modern communi­cations. They convert high-speed electronic signals in compu­tational devices such as computers to optical signals before trans­mitting them through optical fibres. But the existing and commonly used lithium niobate modulators require a high drive voltage of 3 to 5V, which is signi­ficantly higher than 1V, a voltage provided by a typical CMOS circuitry. Hence an elec­trical amplifier that makes the whole device bulky, expensive and high energy-consuming is needed.

Wang Cheng, Assistant Professor in the Depart­ment of Electronic Engi­neering at CityU, and the research teams at Harvard Univer­sity and Nokia Bell Labs have developed a new way to fabricate lithium niobate modulator that can be operated at ultra-high electro-optic bandwidths with a voltage compa­tible with CMOS. “In the future, we will be able to put the CMOS right next to the modu­lator, so they can be more integrated, with less power consump­tion. The elec­trical amplifier will no longer be needed,” said Wang.

Thanks to the advanced nano fabri­cation approaches developed by the team, this modulator can be tiny in size while trans­mitting data at rates up to 210 Gbit/second, with about 10 times lower optical losses than existing modu­lators. “The elec­trical and optical properties of lithium niobate make it the best material for modulator. But it is very difficult to fabricate in nano­scale, which limits the reduction of modulator size,” Wang explains. “Since lithium niobate is chemically inert, conven­tional chemical etching does not work well with it. While people generally think physical etching cannot produce smooth surfaces, which is essential for optical trans­mission, we have proved other­wise with our novel nano fabri­cation techniques.”

With optical fibres becoming ever more common globally, the size, the perfor­mance, the power consumption and the costs of lithium niobate modulators are becoming a bigger factor to consider, especially at a time when the data centres in the infor­mation and communi­cations tech­nology industry are forecast to be one of the largest elec­tricity users in the world. This revolu­tionary invention is now on its way to commercia­lisation.

Wang believes that those who look for modu­lators with the best performance to transmit data over long distances will be among the first to get in touch with this infrastructure for photonics. “Milli­meter wave will be used to transmit data in free space, but to and from and within base stations, for example, it can be done in optics, which will be less expensive and less lossy,” he explains. He believes the invention can enable appli­cations in quantum photonics, too. (Source: CU Hong Kong)

Reference: C. Wang et al.: Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages, Nature, online 24 September 2018; DOI: 10.1038/s41586-018-0551-y

Link: Nanophotonics Group, Dept. of Electronic Engineering, City University Hong Kong, Hong Kong

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