Now, silicon has become the preferred integrated photonics platform due to its transparency at telecommunication wavelengths, its ability to electro-optically and thermo-optically, and its compatibility with existing semiconductor manufacturing technologies. Although silicon nano-photonics has made great progress in the fields of optical data communications, phased arrays, lidars, and quantum and neural circuits. There are still two major problems with integrating photons into these systems on a large scale.

The existing silicon phase modulator can change the phase of the optical signal, but this process comes at the cost of high optical loss (electro-optic modulation) or high power consumption (thermo-optical modulation). Recently, Michal Lipson, Eugene Higgins Professor of Electrical Engineering and Professor of Applied Physics at Columbia University, announced that they have discovered a new method for controlling the phase of light using two-dimensional materials: atomic-level thin materials, only 0.8 nanometer, which is 1/100,000th of the hair and can achieve extremely low power consumption without changing its amplitude.

On February 24, according to a new study published in the journal Natural Photonics, researchers demonstrated that simply placing thin materials on top of passive silicon waveguides can make them behave like existing silicon phase modulators. The phase of light is strongly changed, and the loss and power consumption of light can be reduced a lot.

Professor Lipson said:”Phase modulation in optical coherent communication is still a big challenge due to the high optical loss of the phase change. Now we have discovered a material that only changes the phase.”

Semiconductor two-dimensional materials, such as transition metal dihalogen compounds (TMDs), have optical properties that change significantly with free carrier injection (doping) near their exciton resonance peaks (absorption peaks). However, at telecommunication wavelengths far from these exciton resonances, little is known about the effect of doping on the optical properties of TMDs, because at these exciton resonances, the material is transparent and can therefore be used in photonic circuits.

Members of the Columbia team include James Hone, a professor of mechanical engineering at the Columbia Institute of Engineering, and Dimitri Basov, a professor of physics at the university. They explore the electro-optical properties of TMD by integrating a low-loss silicon nitride optical cavity with a semiconductor single layer and a doped single layer using an ionic liquid response. They observed large phase changes due to doping, while light loss had the smallest change in the transmission response of the ring cavity. They show that the phase change caused by doping is about 125 relative to the change in TMD absorption of a single layer, which is significantly higher than the phase change that can be observed in current mainstream silicon photonic modulators (including Si and III-V on Si) materials. And the accompanying insertion loss is negligible.

Ipshita Datta, a doctoral student at Lipson and the lead author of the paper, said: “We are the first to observe strong electrical refraction changes in these thin monolayers. We use low-loss silicon nitride (SiN) -TMD composites. The waveguide platform achieves pure optical phase modulation, and the optical mode of the waveguide interacts with the single layer. So now, as long as these single molecular films are simply placed on the silicon waveguide, we can change the phase of the same order of magnitude, but reduce it by 10,000 times. This is very encouraging for photonic circuits and low-power lidar scales. ”

Researchers are continuing to explore and better understand the underlying physical mechanisms of the strong electrical refraction effect. They are currently using their low-loss and low-power phase modulators to replace traditional phase shifters to reduce power consumption in large-scale applications such as optical phased arrays, neural and quantum circuits.