In a groundbreaking stride toward revolutionizing light-based technology, researchers at the University of Pennsylvania have engineered a novel photonic system that channels light through intricate crystalline structures, impervious to disruptions caused by imperfections or structural anomalies. This pioneering work, led by physicist Bo Zhen along with postdoctoral researcher Li He and collaborators, unveils a new horizon in controlling photons within engineered materials, allowing light to navigate a “secret tunnel” that protects it from scattering or absorption, common obstacles in conventional photonic devices.
Traditional approaches to guiding light through photonic circuits have long been constrained by the delicate nature of photons, which, unlike electrons, readily scatter, merge in complex ways, or vanish. The very essence of these quantum particles makes manipulating them a formidable challenge because they do not adhere to conservation laws in the same way electrons do. Instead of meticulously polishing photonic materials to reduce imperfections—a path that rapidly encounters practical limits—Zhen’s team reimagined the problem entirely. By harnessing the principles of topological physics, they have engineered a system that inherently shields light from defects and irregularities rather than attempting to eliminate these flaws.
Central to their innovation is the construction of a photonic crystal, a semiconductor patterned with a periodic array of holes, which is driven by circularly polarized lasers. This configuration induces a dynamic, so-called Floquet topological phase that empowers photons to travel along prescribed edges of the crystal in a unidirectional, or “chiral,” manner. Unlike typical photonic devices, where imperfections can scatter or absorb light, this topological protection guarantees uninterrupted forward motion, akin to a highway unaffected by potholes or traffic jams. This effect, characterized by a nonzero Chern number (C=1), signals the emergence of a robust one-way light channel forged under periodic driving—an experimental realization that confirms theoretical predictions made years earlier.
The journey toward this achievement was neither straightforward nor swift. Initially hypothesized in 2019 through theoretical frameworks, the experimental realization required precise control over ultrafast lasers to drive and probe the photonic crystal. This endeavor coincided with global disruptions caused by the COVID-19 pandemic, complicating equipment delivery and experimental setup. Despite these obstacles, including partial shipments and complex overseas coordination, the team persevered, eventually stabilizing the system by 2022 with critical support from colleagues at the University of California Santa Barbara.
Analyzing the experimental data involved reconstructing the photonic band structure from laser spectroscopy measurements. When driven with linear polarization, the system’s energy bands remained gapless, indicating no special conductive channels. However, applying circularly polarized light opened a sizable bandgap—a hallmark of a topologically nontrivial phase—with edge states that permitted unidirectional photon flow immune to backscattering and disorder. This observation not only validated their theoretical model but demonstrated a practical method for engineering optical isolators and lasers that can operate stably without cumbersome magnetic components or complex feedback suppression.
Moreover, this photonic platform exploits the inherent nonlinear interactions unique to light. Unlike electrons, photons can combine or split into different frequencies within nonlinear optical media, enabling phenomena such as frequency doubling or parametric down-conversion. Such versatility paves the way for novel information processing schemes that transcend what is possible with purely electronic devices. By establishing a stable topological phase for photons, the researchers have essentially rewritten the rules of optical device design, envisioning a future where quantum information and photonics coexist on robust, interference-resistant platforms.
Looking ahead, the team envisions scaling their approach beyond two-dimensional crystals into three-dimensional architectures, potentially expanding operational frequencies into the microwave regime where component sizes increase, easing fabrication and integration efforts. Extending topological protection to these domains could unlock applications in quantum computing, secure communications, and advanced sensing technologies. Protecting fragile quantum states of light from environmental disturbances is particularly enticing, offering a pathway to durable quantum networks and photonic processors.
The implications for telecommunications, nano-optics, and sensing are vast. Sturdier lasers free from destabilizing reflections promise clearer signals, while optical chips that guide light flawlessly around imperfections could drastically enhance bandwidth and energy efficiency. Devices leveraged from these principles may no longer require painstakingly defect-free fabrication, reducing costs and accelerating innovation cycles. By embedding topological protection into the fabric of photonic devices, the researchers open the door to a new era of light-based technologies with unprecedented reliability and performance.
Bo Zhen, serving as the Jin K. Lee Presidential Associate Professor of Physics and Astronomy at Penn, emphasizes that their experimental verification marks a critical leap from abstract theory to tangible technology. “We’ve shown it’s possible,” he remarks, underscoring the transition from conceptual design to applied science. Li He, a key postdoctoral contributor who will be joining Montana State University as an assistant professor, acknowledges the formidable technical hurdles surmounted during the project, highlighting the interdisciplinary collaboration essential for success.
This research draws inspiration from foundational discoveries in electronic topological insulators, work advanced significantly by Eugene Mele, a distinguished Penn professor involved in this study. Translating concepts that once applied exclusively to electrons into the domain of photons required both theoretical insight and meticulous experimental engineering. The result is a shining example of how principles of condensed matter physics and optical engineering can coalesce to create groundbreaking photonic materials.
Financial and institutional support played an instrumental role in realizing this achievement. The project benefitted from funding provided by the U.S. Office of Naval Research, Army Research Office, Department of Energy, National Science Foundation, and the Air Force Office of Scientific Research. This broad backing underscores the strategic importance placed on photonics and quantum technologies at the national level, reflecting their transformative potential across defense, communication, and technological sectors.
In sum, this advance in guided photonics harnesses the dynamic, topologically protected states of light to overcome longstanding challenges in optical communication and device stability. Through the meticulous orchestration of crystalline design, polarization control, and nonlinear optics, the University of Pennsylvania team has delivered a transformative blueprint for next-generation photonic systems, foreshadowing a future where light navigates complex environments unimpeded, ushering in revolutionary applications in science and technology.
Subject of Research: Photonics, Topological Insulators, Nanophotonics
Article Title: Towards Floquet Chern insulators of light
News Publication Date: 5-Sep-2025
Web References:
- https://www.nature.com/articles/s41565-025-02003-1
- https://live-sas-physics.pantheon.sas.upenn.edu/people/standing-faculty/bo-zhen
- https://www.sas.upenn.edu/
- https://live-sas-physics.pantheon.sas.upenn.edu/people/standing-faculty/eugene-mele
- https://penntoday.upenn.edu/news/beyond-topological-insulators
References:
Zhen, B., He, L., Jin, J., Lu, J., Bowers, J. E., Chang, L., Shang, C., & Mele, E. (2025). Towards Floquet Chern insulators of light. Nature Nanotechnology. https://doi.org/10.1038/s41565-025-02003-1
Image Credits: Eric Sucar / University of Pennsylvania
Keywords
Nanophotonics, Nanotechnology, Photonics, Solid state physics, Topological insulators, Optics
