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A Photonics Breakthrough

Photonic devices that can create, manipulate or detect light have long been used in products such as photo-detector and LED.

Now, researchers are attempting to extend photonics’ operational wavelengths to the mid-infrared range, due to the potential applications in a wide range of fields, including next-generation communications and environmental monitoring.

Scientists at Nanyang Technological University’s School of Electrical and Electronic Engineering (EEE), Centre for Micro-/Nano-electronics (NOVITAS) have created a breakthrough in photonics with their new germanium-on-silicon nitride waveguides for mid-infrared integrated photonics.

These photonics could be used in next-generation, compact sensors with mid-infrared sensing capabilities, such as advanced biochemical sensors.

The researchers led by Professor Tan Chuan Seng noted that many other platforms have been tried and evaluated, including silicon-on-sapphire and silicon-on-nitride. Since germanium has a wide transparency and unique optical properties, many germanium-based platforms have also been studied.

“Germanium-on-silicon-on-insulator has been reported to have electrical advantages, and many impressive achievements have also been made with germanium-on-silicon,” said Professor Tan.

“However, what is desired is a better, alternative germanium-based waveguide platform that will provide a larger core- clad index contrast than germanium-on- silicon, as well as a useful transparency range and smaller channel-bend radii. That is why we proposed and realised germanium-on-silicon nitride,” he said.

The researchers developed a feasible and scalable wafer bonding and layer transfer technique to create germanium-on- silicon-nitride.

This involves first bonding a silicon-nitride-deposited germanium-on-silicon donor wafer onto a silicon substrate wafer, and then using a layer transfer approach to obtain the germanium-on-silicon nitride.

Professor Tan said: “Our germanium-on- silicon-nitride platform could be used to make many small and passive photonic devices, such as photonic-integrated Mach-Zehnder interferometers and micro- ring resonators. These would be useful for compact sensor devices for mid-infrared sensing applications, as well as active devices such as micro-ring modulators.”

 

By Professor Tan Chuan Seng

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Published on: 25-October-2017 ​​​​​