On the nanoscale, controlling light can be as challenging as catching smoke. In computing devices that exploit light, also called photonic devices, the ability to reconfigure the emission wavelength is essential for emerging applications such as adaptive optical communications and sensitive biosensors. However, achieving tuneable photoluminescence after device fabrication is not as easy as picking shades on a colour wheel, especially when stability and efficiency must be preserved.
“Photoluminescence is a process where materials absorb light and re-emit it as vivid colours, like a gemstone glowing under ultraviolet light,” said Omar A. M. Abdelraouf, a Research Scientist at the A*STAR Institute of Materials Research and Engineering (A*STAR IMRE). “We wanted to make a tiny chip that could produce brighter colours and allow those colours to be changed on demand.”
“In addition, tuneability is a crucial function for light-emission devices,” said Hong Liu, a Principal Scientist and Intelligent Nano-Optics Group Leader at A*STAR IMRE. “It enables a single compact chip to deliver on-demand display technologies, instead of requiring multiple separate devices.”
To deliver both high brightness and post-fabrication colour tuneability, the researchers built a chip-scale system as a hybrid metasurface. The device features a precisely patterned array of nano-pillars made from amorphous silicon and antimony trisulfide (Sb2S3), with nanocrystalline silicon quantum dots embedded inside.
During fabrication, the metasurface geometry can be adjusted to set the initial emission wavelength. Afterwards, additional all-optical tuning comes from the use of Sb2S3. By shining light or applying heat, the material switches between amorphous and crystalline states, each bending light differently. This enables a single chip to shift its emission wavelength by up to 24 nanometres, thus changing colour, without altering its structure.
“Sb₂S₃ exhibits a striking contrast in refractive index when it changes phase,” said Liu. “This intrinsic optical property is one of the key enablers for the large tuneability of our device.”
The team’s design also exploits bound states in the continuum (BICs), described by Abdelraouf as a ’hidden echo of light inside a material’. These optical modes trap light with minimal leakage, intensifying the local electromagnetic field.
“Our device reveals and uses two of these echoes at the same time, boosting light emission and shifting colour in a way that’s never been done before,” Abdelraouf added. “The dual-BIC design also makes the chip highly sensitive, promising for advanced medical sensors.”
Upon testing, the researchers found that their device could amplify photoluminescence by a factor of 15, with a wavelength shift of up to 105 nanometres achievable via variations to the metasurface geometry. To maintain efficiency across the tuned wavelengths, they also integrated a high-Q metalens into the metasurface. The flat lens focuses the system’s diffraction-limited spot—the fundamental resolution limit—in the near-infrared range.
“This technology can make quantum light sources more efficient and switchable at very high speeds, which is vital for next-generation computing and communications,” Abdelraouf said. “It also holds strong potential for medical sensors, where sensitivity is critical.”
Looking ahead, the team is developing patents for applications including ultrafast, all-optical neural network hardware and compact sensors, supported by A*STARTCentral gap funding.
“All-optical tuning is one of the key solutions to meet the demands of energy efficiency, speed and bandwidth in future photonics,” Liu said. “Our Group is now developing nanoscale quantum light sources and scalable nanoimprint lithography for metalenses to tackle these challenges.”
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Institute of Materials Research and Engineering (A*STAR IMRE).
