Render of 3D single-crystalline nanomembranes integrated on silicon photonics. (Image Credit: Wenbo Mao, Yuan Meng, Zhihao Xu, Di Jia
Photonic chips use light for information transmission and processing. Silicon and silicon nitride can guide light, but they don’t provide every optical function that advanced systems need. Researchers from Washington University, EPFL, and MIT integrated single-crystalline functional materials onto silicon and silicon nitride photonic chips. By doing so, photonic chips could offer more capabilities for computing and sensing.
Usually, integrating materials with different atomic structures on photonic chips can cause crystal defects to form. Those incompatibilities may worsen performance while limiting which materials can be combined. The team solved this issue by preparing crystalline materials on individual substrates and detaching them as nanomembranes (ultrathin layers). These layers are then placed on photonic chips, vertically stacked or laterally stitched.
Their technique uses van der Waals forces, allowing the layers to stick without the atomic alignment that crystal-growth methods rely on. This is very similar to LEGO brick stacking.
To demonstrate multiple optical functions, the researchers integrated materials into silicon and silicon nitride photonic platforms. They used barium titanate to achieve electro-optic modulation so that electrical signals could control light. In a device, the half-wave voltage-length product reached 0.29 V-cm. Another one exhibited an electro-optic bandwidth that surpassed 23 GHz. Gallium arsenide and gallium nitride were also integrated into silicon nitride chips. This demonstrated photodetection across a range extending from near-ultraviolet to near-infrared wavelengths.
The team also conducted another experiment in which they combined cobalt ferrite with silicon microring resonators, enabling the magneto-optical control of light. That material supported nonreciprocal optical transmission, so that light behaves differently based on the direction it travels. Afterward, the team stacked barium titanate and cobalt ferrite above a silicon microring resonator. That device achieved electrical and magnetic control of light in the same structure.
The researchers tested their method with different crystalline materials, such as barium titanate films that were up to one inch across. Applications include data storage, sensing, photonic computing, optical communications, and quantum technologies. More tests need to be done to see how it can be used for large-scale use.
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