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ORC’s Silicon Photonics group boosts performance of electro-optical modulators

05 Apr 2023

Improved absorption during plasma-dispersion pushes modulators to perform better.

Research by the University of Southampton’s Silicon Photonics group into silicon electro-optical modulators has been published in the prestigious Nature Photonics journal.

The paper “Harnessing plasma absorption in silicon metal oxide semiconductor (MOS) ring modulators” demonstrates that absorption during the plasma-dispersion effect can be harnessed to enhance the performance of modulators.

The work was performed within a Prosperity Partnership project jointly funded by the UK’s Engineering and Physical Sciences Research Council (EPSRC) and collaborator Rockley Photonics.

Dr Weiwei Zhang, Senior Research Fellow at the Optoelectronics Research Centre (ORC), commented, “Silicon MOS ring modulators convert electrical signals into optical signals. This is based on the plasma-dispersion effect, whereby if you increase the concentration of electrons and holes in a waveguide, you get a phase shift of the light, as well an increase in absorption. Until now, the absorption part has been considered unwanted as it increases the overall device loss and so you get less light afterwards.”

Zhang added, “Our work shows that you can use the absorption to push the modulators to perform better for the same device capacitance. As a result, we have also managed to demonstrate the fastest data transmission recorded on a device of this type so far up to 100 gigabits per second.”

Pushing performance

“One of our main research focuses is to continually push the performance of optical modulators in silicon photonics. Whilst there has been a worldwide trend to introduce other materials to do this, CMOS compatibility can be compromised potentially leading to higher production costs. Here we have shown that there are still ways to enhance the performance of all-silicon based devices that can be fabricated at relatively low cost,” said Zhang.

The innovative research has the potential to lead to new scientific opportunities. Professor David Thomson, who led the work, added: “High-bandwidth, low-power and compact silicon electro-optical modulators are essential for future energy-efficient and densely integrated optical data communication circuits. Our research has demonstrated the potential for this on one device, which modulates light at a certain wavelength.

“The compact and power efficient nature of the device allows us to densely integrate an array of these modulators on the same waveguide, with each modulating at a different wavelength. This is known as wavelength division multiplexing and it would enable you to transmit a lot more data.”

Prof. Thomson added: “We are delighted that the significance of our research has been recognised through acceptance for publication in Nature Photonics. The work has only been possible through the hard work of the team both in Southampton and Rockley Photonics in developing the concept, design and modelling, cleanroom fabrication and device characterisation. We look forward to the response to our work in the community and hope that it can lead to new collaborations and ignite other avenues of research in the field.”

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