Soliton Photonic Waves on a Silicon Chip

A colla­boration between the University of Sydney Nano Institute and Singapore Uni­versity of Tech­nology and Design has for the first time manipulated a light wave, or photonic information, on a silicon chip that retains its overall shape. In detail, the team has for the first time observed soliton dynamics on an ultra-silicon-rich nitride (USRN) device fabri­cated in Singapore using state-of-the-art optical charac­terisation tools at Sydney Nano.

Artist’s impression of the Bragg gated structure on a silicon substrate. (Source:
U. Sydney / SIngapore U. of Tech. & Des.)

This founda­tional work is important because most communi­cations infra­structure still relies on silicon-based devices for propagation and reception of information. Mani­pulating solitons on-chip could potentially allow for the speed up of photonic communications devices and infra­structure. Ezgi Sahin, a PhD student at SUTD conducted the experiments with Andrea Blanco Redondo at the University of Sydney. “The obser­vation of complex soliton dynamics paves the way to a wide range of applications, beyond pulse compression, for on-chip optical signal processing,” Sahin said. “I’m happy to be a part of this great partner­ship between the two insti­tutions with deep colla­boration across theory, device fabri­cation and measurement.”

The Director of Sydney Nano, Ben Eggleton, said: “This represents a major breakthrough for the field of soliton physics and is of funda­mental techno­logical importance. “Solitons of this nature – the Bragg solitons – were first observed about 20 years ago in optical fibres but have not been reported on a chip because the standard silicon material upon which chips are based constrains the propa­gation. This demon­stration, which is based on a slightly modified version of silicon that avoids these constraints, opens the field for an entirely new paradigm for mani­pulating light on a chip.”

Dawn Tan said: “We were able to convin­cingly demon­strate Bragg soliton formation and fission because of the unique Bragg grating design and the ultra-silicon-rich nitride material platform (USRN) we used. This platform prevents loss of information which has compromised previous demon­strations.” Solitons are pulses that propagate without changing shape and can survive collisions and interactions. They were first observed in a Scottish canal 150 years ago and are familiar in the context of tsunami waves, which propagate thousands of kilometers without changing shape.

Optical soliton waves have been studied since the 1980s in optical fibres and offer enormous promise for optical communi­cation systems because they allow data to be sent over long distances without distortion. Bragg solitons, which derive their properties from Bragg gratings, can be studied at the scale of chip tech­nology where they can be harnessed for advanced signal processing. Bragg solitons were first observed in 1996 in Bragg gratings in optical fibres. This was demon­strated by Eggleton while he was working on his PhD at Bell Labs.

The silicon-based nature of the Bragg grating device also ensures compa­tibility with complem­entary metal oxide semi­conductor (CMOS) processing. The ability to reliably initiate soliton compression and fission allows ultrafast phenomena to be generated with longer pulses than previously required. The chip-scale minia­turisation also advances the speed of optical signal processes in applications neces­sitating compactness. (Source: U. Sydney)

Reference: E. Sahin et al.: Bragg Soliton Compression and Fission on CMOS‐Compatible Ultra‐Silicon‐Rich Nitride, Laser & Phot. Rev., online 2 July 2019; DOI: 10.1002/lpor.201900114

Link: Institute of Photonics and Optical Science, School of Physics, University of Sydney, Sydney, Australia

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