The technological advancement of optical lenses has long been an important feature of human scientific achievements. Glasses, telescopes, cameras and microscopes have literally and figuratively enabled us to see the world in a new light. Lenses are also a fundamental part of nanoelectronics manufacturing by the semiconductor industry.
One of the most impactful breakthroughs in lens technology in recent history is the development of photonic meta-surfaces-manufactured nanoscale materials with remarkable optical properties. Georgia Tech researchers at the forefront of this technology recently demonstrated the first-ever electrically tunable photonic metasurface platform in a recent study published by nature communication†
“Meta-surfaces can de optical systems very thin, and as they become easier to operate and fine-tune, you will soon find them in cell phone cameras and similar electronic imaging systems,” said Ali Adibi, a professor in the School of Electrical and Computer Engineering at Georgia. Institute of Technology.
The pronounced alignment measures achieved by the new platform represent a critical advance towards the development of miniaturized reconfigurable meta-surfaces. The results of the study demonstrated a record 11-fold change in reflective properties, a wide range of spectral tuning for use, and a much higher tuning rate.
Warming up meta-surfaces
Metasurfaces are a class of nanophotonic materials in which a large number of miniaturized elements are designed to influence the transmission and reflection of light at different frequencies in a controlled manner.
“When viewed under high-powered microscopes, meta-surfaces look like a periodic array of poles,” Adibi said. “The best analogy would be to think of a LEGO pattern formed by connecting many similar LEGO bricks side by side.”
Since their inception, metasurfaces have been used to demonstrate that very thin optical devices can influence the propagation of light, with metalses (the formation of thin lenses) being the most developed application.
Despite impressive progress, most of the meta-surfaces showcased are passive, meaning that their performance cannot be changed (or modified) after fabrication. The work presented by Adibi and his team, led by Ph.D. candidate Sajjad Abdollahramezani, applies electrical heat to a special class of nanophotonic materials to create a platform that allows easy fabrication of reconfigurable meta-surfaces with high levels of optical modulation.
PCMs provide the answer
A wide variety of materials can be used to form meta-surfaces, including metals, oxides, and semiconductors, but Abdollahramezani and Adibi’s research focuses on phase change materials (PCMs) because they can form the most effective structures with the smallest feature sizes. PCMs are substances that absorb and release heat during the process of heating and cooling. They are called “phase change materials” because they move from one crystallization state to another during the thermal cycling process. Water changing from a liquid to a solid or gas is the most common example.
The Georgia Tech team’s experiments are considerably more complicated than heating and freezing water. Knowing that the optical properties of PCMs can be altered by localized heating, they exploited the full potential of the PCM alloy Ge.2sb2At5 (GST), a compound of germanium, antimony and tellurium.
By combining the optical design with a miniaturized electric micro-heater underneath, the team can de crystalline phase of the GST to allow active tuning of the metasurface device. The fabricated meta-surfaces were developed by Georgia Tech’s Institute for Electronics and Nanotechnology (IEN) and tested in characterization labs by illuminating the reconfigurable meta-surfaces with laser light at different frequencies and measuring the properties of the reflected light in real time.
What tunable metasurfaces mean for the future
Driven by device miniaturization and system integration, as well as their ability to selectively reflect different colors of light, metasurfaces are quickly replacing bulky optical assemblies of the past. Immediate impact on technologies such as LiDAR systems for autonomous cars, imaging, spectroscopy and sensing is expected.
With further development, more aggressive applications such as computing, augmented reality, artificial intelligence photonic chips and biohazard detection could also be considered, according to Abdollahramezani and Adibi.
“As the platform continues to evolve, reconfigurable metasurfaces will be everywhere,” says Adibi. “They will allow even smaller endoscopes to go deep into the body for better imaging and to help medical sensors detect various biomarkers in the blood.”
Sajjad Abdollahramezani et al, Electrically powered reprogrammable phase change meta-surface that achieves 80% efficiency, nature communication (2022). DOI: 10.1038/s41467-022-29374-6
Georgia Institute of Technology
Quote: Shaping the future of light through reconfigurable metasurfaces (2022, May 16) retrieved May 17, 2022 from https://phys.org/news/2022-05-future-reconfigurable-metasurfaces.html
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