Can silicon chips guide light with fibre-like efficiency? A new waveguide platform cuts optical losses across visible and near-infrared wavelengths.
Caltech researchers have developed a photonic platform that guides light across silicon wafers with losses approaching those of optical fibre, particularly at visible wavelengths. The development uses germano-silicate waveguides fabricated directly on 8- and 12-inch wafers and could support photonic integrated circuits for optical clocks, sensors, lasers, data-centre communications, and quantum systems.
Lower optical loss allows light to travel further through a circuit before its energy is dissipated or scattered. This can improve the performance and coherence of optical devices while reducing the energy required to move signals. For AI data centres, the approach could also help connect optical fibres and semiconductor lasers more efficiently.
The platform uses germano-silicate, a glass similar to the material used in optical fibre. Instead of fabricating straight optical paths, the researchers form the waveguides into spirals, allowing long optical paths to fit within a small chip footprint.
The researchers also use a thermal reflow process to smooth the waveguide surfaces to near-atomic levels. This reduces scattering caused by surface irregularities, which is particularly important at visible wavelengths where conventional photonic circuits can experience higher losses.
At near-infrared wavelengths, the waveguides have matched the performance of some leading silicon-nitride devices. At visible wavelengths, the platform has exceeded the previous silicon-nitride record by a factor of 20. Lasers built using the approach have also demonstrated more than a 100-fold improvement in optical coherence compared with previous designs.
The researchers fabricated ring resonators, lasers, and nonlinear resonators using the platform. Low-loss waveguides allow light to circulate repeatedly inside resonators, increasing effective optical path lengths despite the devices occupying only millimetres of chip area.
The expanded wavelength range could support chip-scale atomic sensors, optical clocks, ion-trap systems, precision gyroscopes, and quantum technologies. The researchers also see potential for more efficient optical interconnects in data-centre infrastructure.
“We have developed a method to print optical circuits, made from the same material as optical fiber, directly onto the same 8- and 12-inch wafers used for computer chips,” says Kerry Vahala, Ted and Ginger Jenkins Professor of Information Science and Technology and Applied Physics at Caltech.
