In the scientific and technological race for smaller, stronger, and smarter optical systems, twisted moiré photonic crystals are emerging as a revolutionary optical metamaterial. The material is unique in that its interlayer twisting and stacking precisely regulates the behavior of light, providing a new solution for miniaturization and multifunctional integration of optical devices.
The optical miracle of the Mohr effect
To understand how this material works, one can analogy with the superposition of two pieces of cloth with a regular pattern: when perfectly aligned, the original pattern is clearly visible; However, if you rotate or shift it slightly, you will create a completely new interference pattern. Twisted Moiré photonic crystals take advantage of this effect to achieve simultaneous control of optical phase, polarization, and wavelength by precisely controlling the torsion angle and layer spacing of the crystal layers. This means that what traditionally required multiple optics to do may now be possible with a single tiny device.
However, for a long time, researchers have not been able to realize the real-time active control of the angle and distance between crystal layers, which seriously restricts its practical application value.
Breakthrough: Chip-scale sensors that can be dynamically adjusted
Led by Harvard University's John Paulson School of Engineering and Applied Sciences (SEAS) and a team of researchers from Stanford University and the University of California, Berkeley, a major breakthrough was recently published in Nature Photonics. Using microelectromechanical systems (MEMS) technology, they have succeeded in developing the first chip-scale twisted Moir photonic crystal sensor that can be controlled in real time. The device is only a few millimeters in size and uses a CMOS-compatible manufacturing process with potential for mass production.
"Twisted Moir photonic crystals are ideal for creating smaller, more powerful optical systems due to their highly adjustable optical, precise light control capabilities, compact design architecture, and broad application prospects in various advanced photonic technologies." Senior author Eric Mazur, professor of physics and applied physics at Harvard University, explains.
Figure: The Harvard team breaks through the problem of real-time control of distorted photonic crystals
Multifunctional integrated optical "Swiss Army Knife"
For the first time, the research team achieved simultaneous acquisition of hyperspectral and hyperpolarization imaging by precisely adjusting the spacing and rotation angle of the photonic crystal layers with vertical and rotary actuators, where each pixel captured by the sensor contains full electromagnetic spectral information and complete polarization state data. This real-time ability to resolve the multi-dimensional characteristics of light is the first of its kind in an actively tuned device.
"Our research not only demonstrates the great potential of these materials, but also opens up a feasible path for fabricating planar optics suitable for multifunctional light manipulation and information processing." Haoning Tang, the first author of the paper and a postdoctoral fellow at SEAS, said.
Broad application prospects
This breakthrough technology is expected to be useful in areas such as quantum computing, data communications, satellite remote sensing, and medical imaging, especially in scenarios that require high-precision optical information. In the future, the research team plans to develop an advanced version with more freedom control capabilities to further expand its application boundaries.
The study received grants from the National Science Foundation, DARPA, the U.S. Air Force Research Office, and the U.S. Office of Naval Research, and sample preparation was done at the Center for Nanosystems at Harvard University. The result of this cross-agency collaboration marks a key step towards the practical application of programmable optical metamaterials.
