Researchers have for the first time realized diffraction-limited focusing and imaging using meta-optics in the mid-infrared (mid-IR) band of electromagnetic radiation. The new way of fabricating flat optical devices could enable improved but cheaper detectors for night vision, thermal imaging, biomedical sensing and other applications. The new design and technique were developed by researchers from the Massachusetts Institute of Technology (MIT) in collaboration with teams from the University of Massachusetts (UMass) at Lowell, the University of Electronic Science and Technology of China and East China Normal University.
“Unlike conventional free-space optical components, which rely on surface curvature to shape the wave front, we use basically sub-wavelength antennae to impart phase delay and redirect the beam,” Juejun Hu, associate professor of materials science and engineering at MIT, describes the new fabrication method for flat optical devices for imaging and sensing in the mid-IR band of frequencies.
New meta-atom designs with ultra-thin profile
A number of mid-IR meta-optics have been reported previously. However, “What is new is our metasurface design and fabrication technique,” Hu points out. “Our UMass collaborators devised a new set of meta-atom designs with an ultra-thin profile — only 1/8 of wavelength.” The designs can be easily fabricated using standard microfabrication techniques and do not require deep etching. Hu explains that this kind of artificial optical interface allows for nearly arbitrary wavefront manipulation, which he says would not be possible with natural materials at macro-scales. The multi-institutional team reports they have demonstrated that such meta-optics can perform as well as their free-space counterparts — such as aberration-free aspherical lenses, for example — in terms of focusing performance or imaging quality, at least over a relatively narrow spectral band. “In other words, we realized for the first time diffraction-limited focusing and imaging using meta-optics in the mid-IR.”
The new technique could help to overcome the manufacturing challenges of previous approaches in the metasurface optics field: “High-quality mid-IR optics can be fabricated using scalable standard microfabrication techniques rather than grinding and polishing or molding,” the expert confirms.
Enabling new applications through metasurface optics
Hu agrees that the pioneering metasurface designs and fabrication technique could enable new kinds of applications, such as beam shaping or beam steering from mid-IR lasers, for example. Versatile manipulation of mid-IR radiation — e.g., both wavefront and polarization, could be another thinkable application enabled by this research advance.
Designing the next generation of metaoptics
Speaking about the potential impact of new findings on the design of future metaoptical devices, Hu says, “The ultra-thin meta-atom designs point to a path towards high-efficiency meta-optics with considerably simplified fabrication.”
The research is reported in the paper “Ultra-thin high-efficiency mid-infrared transmissive Huygens meta-optics,” published in Nature Communications.
Written by Sandra Henderson, Research Editor, Novus Light Technologies Today