Sensitive Yet Tough Photonic Devices Are Now a Reality

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Engineers at the University of California San Diego have achieved a long-sought milestone in photonics: creating tiny optical devices that are both highly sensitive and durable—two qualities that have long been considered fundamentally incompatible.

This rare coexistence of sensitivity and durability could lead to a new generation of photonic devices that are not only precise and powerful but also much easier and cheaper to produce at scale. This could open the door to advanced sensors and technologies ranging from highly sensitive medical diagnostics and environmental sensors to more secure communication systems, all built into tiny, chip-scale devices.

Achieving both properties has been a challenge because devices that are sensitive enough to detect tiny changes in their environment are often fragile and prone to breaking down if even the smallest imperfections arise during manufacturing. This makes them expensive and difficult to produce at scale. Meanwhile, making such devices more rugged often means compromising their precision.

Now, a team led by Abdoulaye Ndao, a professor in the Department of Electrical and Computer Engineering at the UC San Diego Jacobs School of Engineering, has found a way to overcome this contradiction.

“Our research addresses this critical challenge,” said Ndao. “We have designed new photonic devices that are both highly sensitive to their environment and robust against fabrication errors and material imperfections.” The research was published in Advanced Photonics.

The devices rely on a physical phenomenon known as subwavelength phase singularity. This occurs when light is confined to a space smaller than its own wavelength so that it creates a point of total darkness—where the light’s intensity drops to zero—while its phase continues smoothly through a full cycle. This singularity is both highly sensitive to changes in the surrounding environment—making it ideal for sensing applications—and inherently durable enough to handle imperfections from manufacturing processes.

The subwavelength phase singularity was made possible thanks to a specially engineered nanostructure. The researchers constructed a chip-scale device made from two layers of gold nanorods sandwiching an extremely thin layer of polymer in between. The bottom layer is embedded in the polymer, while the top layer is exposed to air, where it can interact directly with target molecules for sensing. The nanorods in each layer are arranged in rows that are slightly twisted at a specific angle relative to each other. By adjusting the horizontal spacing between the two layers, researchers can precisely control how the layers interact with light.

In tests, researchers demonstrated the device’s sensitivity and durability by measuring the phase singularities. Theoretical studies and simulations were led by study co-first authors Jun-Hee Park, an electrical and computer engineering Ph.D. student at UC San Diego, and Liyi Hsu, a former postdoctoral researcher, both from Ndao’s lab. Device fabrication was performed by study co-first author Jeongho Ha and measurements were conducted by Guang Yang, who is a co-author on the study—both Ha and Yang are electrical and computer engineering Ph.D. alumni from Ndao’s lab.

One particularly interesting phenomenon is the phase singularity, where the phase of light suddenly shifts, making it extremely sensitive to external changes. This property has great potential for high-precision detectors, optical communication and imaging, but practical use has been challenging, Ndao explained. Most optical devices struggle to balance sensitivity and robustness—since sensitive designs are fragile— while robust systems tend to lack precision.

“This is the first device that’s both sensitive and robust to fabrication imperfections,” Ndao said. “We have developed tiny optical devices that are both tough and highly sensitive at the same time—a combination that was previously thought to be impossible.”

Full study: “Observation of robust subwavelength phase singularity in chiral medium”

This work was supported by the 2023 Beckman Young Investigator Award, from the Arnold and Mabel Beckman Foundation; Air Force Office of Scientific Research MURI (Award No. FA9550-22-1-0312); PAIR-UP program sponsored by ASCB, and funded in part by The Gordon Moore Foundation, with additional support from the Burroughs Wellcome Funds; 2022 Scialog: Advancing BioImaging; Kavli Innovation Grant; Silicon Valley Community Foundation (Grant No. DAF2023-331948); and cZi Dynamic imaging via the Chan Zuckerberg Donor Advised Fund (DAF) through the Silicon Valley Community Foundation.