Soliton Dynamics Could Lead to New On-Chip Signal Processing Apps

Researchers have found a way to manipulate a soliton on a silicon chip at both the source and reception end of an optical fiber without altering the wave shape. They used a Bragg gated structure on a silicon substrate. The discovery, which is the result of a collaboration between researchers at the University of Sydney Nano Institute and Singapore University of Technology and Design, could potentially allow for faster photonic communications devices and infrastructure.

Researcher Sahin Ezgi from the Singapore University of Technology and Design holds one of the experimental chips. Courtesy of Singapore University of Technology and Design.

The researchers demonstrated soliton dynamics on an ultra-silicon-rich nitride (USRN) device fabricated in Singapore using optical characterization tools at Sydney Nano. They used a novel, on-chip cladding-modulated Bragg grating design and a CMOS-compatible USRN platform to enable a soliton-effect pulse compression factor of ×5.7, leading to the generation of subpicosecond pulses and time-resolved measurements of soliton fission on a CMOS-compatible photonic circuit platform. These observations were made possible by the combination of the cladding-modulated Bragg grating design and the high nonlinearity and low nonlinear loss of compositionally engineered USRN.

“Solitons of this nature — so-called Bragg solitons — were first observed about 20 years ago in optical fibers but have not been reported on a chip because the standard silicon material upon which chips are based constrains the propagation,” professor Ben Eggleton said. “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.”

Artist’s impression of the Bragg gated structure on a silicon substrate. Courtesy of the University of Sydney and Singapore University of Technology and Design.

“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 we used,” professor Dawn Tan said. “This platform prevents loss of information, which has compromised previous demonstrations.”

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. The silicon-based nature of the Bragg grating device ensures compatibility with CMOS processing. The ability to reliably initiate soliton compression and fission could allow ultrafast phenomena to be generated with longer pulses. Chip-scale miniaturization could also increase the speed of optical signal processes in compact applications.

The research was published in Laser & Photonics Reviews (https://doi.org/10.1002/lpor.201900114).