Photonics

Researchers build ultra-efficient optical sensors shrinking light to a chip

Charles Ferrer — Mon, 23 Feb 2026 16:37:42 +0000

Researchers build ultra-efficient optical sensors shrinking light to a chip Charles Ferrer Mon, 02/23/2026 - 09:37

Charles Ferrer

Lu at the new electron beam lithography system used to develop microresonators at COSINC.

CU ��Ĵ�ý researchers have built high performing optical microresonators opening the door for new sensor technologies.

At its simplest form, a microresonator is a tiny device that can trap light and build up its intensity.

Once the intensity is high enough, researchers can perform unique light operations.

“Our work is about using less optical power with these resonators for future uses,” said Bright Lu, a fourth-year doctoral student in electrical and computer engineering and a lead author on the study. “One day these microresonators can be adapted for a wide range of sensors from navigation to identifying chemicals.”

For this endeavor published in Applied Physics Letters, the team focused on ‘racetrack’ resonators, named for their elongated shape that resembles a running track.

Specifically, researchers used ‘Euler curves’ — a type of smooth curve also found in road and railway design. Just as cars can’t make sharp right-angle turns in motion, light can not be forced into abrupt bends.

“These racetrack curves minimize bending loss,” said Won Park, Sheppard Professor of Electrical Engineering, a co-advisor on the study. “Our design choice was a key innovation of this project.”

By guiding light smoothly through the resonator, they dramatically reduced light loss, allowing photons to circulate longer and interact more strongly inside the device.

If too much light is lost, Lu says, high light intensities can’t be achieved for these microresonators to operate at the needed performance.

Made in Colorado

Incredibly small in size, the microresonators were built using the Colorado Shared Instrumentation in Nanofabrication and Characterization (COSINC) clean room’s new electron beam lithography system.

The facility provides a highly-controlled environment required to work at the microscopic scales that can lead to reliable device performance.

Optical waveguide microresonators on a chip created in this effort, which are ten times thinner than human hair.

Many optical and photonic devices are smaller than the width of a piece of paper, meaning even tiny dust particles or surface imperfections can disrupt how light travels through a material.

“Traditional lithography uses photons and is fundamentally limited by the wavelength of light,” Lu said. “However, electron beam lithography has no such constraint. With electrons, we can realize our structures with sub-nanometer resolution, which is critical for our microresonators.”

For Lu, the hands-on fabrication process was a fulfilling aspect of the project.

“Clean rooms are just cool and you’re working with these massive, precise machines and then you get to see images of structures you made only microns wide. Turning a thin film of glass into a working optical circuit is really satisfying.”

A key success from the work was the ability of the researchers to use chalcogenides, a broad term encompassing a family of specialized semiconductor glasses.

“These chalcogenides are excellent materials for photonics because of their high transparency and nonlinearity,” said Park. “Our work represents one of the best performing devices using chalcogenides, if not the best.”

Chalcogenides were helpful since they have strong transparency for light to pass through the device at high intensities needed for microresonators.

However, the materials are not easy to process for the device, so there’s a balancing act to tread.

“Chalcogenides are difficult, but rewarding materials to operate for photonic nonlinear devices,” said Professor Juilet Gopinath, who has worked on this project with Park for more than ten years. “Our results showed that minimizing the bend loss enables ultra-low loss devices comparable to state-of-the-art in other materials platforms.”

Measuring light at the microscale

Erikson with the optical setup for capturing data measuring absorption and thermal effects.

Once fabricated, the microresonators were handed off for testing, work led by James Erikson, a physics PhD student specializing in laser-based measurements. He carefully aligned lasers with microscopic waveguides, coupling light into and out of the device while monitoring how it behaved inside.

They looked for ‘dips’ within the data in transmitted light that indicate resonance as photons get trapped. By analyzing the shape of those dips, they were able to extract properties like absorption and thermal effects.

“The most obvious indicator of device quality is the shape of the resonances and we want them to be deep and narrow, like a needle piercing through the signal background,” said Erikson. “We’ve been chasing this kind of resonator for a long time, and when we saw the sharp resonances on this new device we knew right away that we’d finally cracked the code.”

Erikson added, to make a good device you need to know how much light will be absorbed versus transmitted. Thermal effects become important when adding laser power as you run the risk of damaging the device.

“The way most materials interact with light also changes depending on the temperature of the material,” said Erikson, “so as a device heats up its properties can change and cause it to work differently.”

In the future, the microresonators could be used for compact microlasers, advanced chemical and biological sensors and even tools for quantum metrology and networking.

“Many photonic components from lasers, modulators and detectors are being developed and microresonators like ours will help tie all of those pieces together,” said Lu. “Eventually, the goal is to build something you could hand to a manufacturer and create hundreds of thousands of them.”

CU ��Ĵ�ý researchers have built high performing optical microresonators opening the door for new sensor technologies. In the future, the microresonators could be used for compact microlasers, advanced chemical and biological sensors and even tools for quantum metrology and networking.

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The fabrication cleanroom facility provides state-of-the-art instrumentation including lithography, thin-film deposition and among others. (Credit: COSINC)

An earthquake on a chip: New tech generates tiny waves, could make smartphones smaller, faster

Charles Ferrer — Wed, 14 Jan 2026 21:32:04 +0000

An earthquake on a chip: New tech generates tiny waves, could make smartphones smaller, faster Charles Ferrer Wed, 01/14/2026 - 14:32

A team of engineers has developed a new device that works like a laser but, instead of light, generates incredibly small vibrations called surface acoustic waves.

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Engineers develop real-time membrane imaging for sustainable water filtration

Charles Ferrer — Tue, 16 Dec 2025 15:49:56 +0000

Engineers develop real-time membrane imaging for sustainable water filtration Charles Ferrer Tue, 12/16/2025 - 08:49

Charles Ferrer

Observed 3D volume calcium sulfate and calcium bicarbonate crystal growth (Credit: Lange Simmons)

CU ��Ĵ�ý researchers have introduced a solution to improving the performance of large-scale desalination plants: stimulated Raman scattering (SRS).

Published Dec. 16 in the journal Environmental Science & Technology, the laser-based imaging method allows researchers to observe in real time membrane fouling, a process where unwanted materials such as salts, minerals and microorganisms accumulate on filtration membranes.

Worldwide, 55% of people experience water scarcity at least one month a year and that number is expected to climb to 66% by the end of the century.

Desalination—turning saltwater into fresh water—is critical for communities globally as demand increases.

Modern reverse osmosis (RO) plants make up about 80% of the world’s desalination facilities, placing greater importance on having them run efficiently.

“Reverse osmosis membranes are critical for desalination,” said Juliet Gopinath, professor of electrical, computer and energy engineering and physics. “Our work aims to monitor and provide early warning for membrane fouling.”

RO systems rely on thin polymer membranes to filter out buildup.

A set of three real-time, in-situ calcium sulfate crystal scaling images. The growth of three unique crystal morphologies over time emphasizes the importance of having both the image along side the chemical identification that stimulated Raman spectroscopy provides. (Credit: Lange Simmons and Jasmine Andersen)

This accumulation reduces filtration efficiency and increases both energy use and operating costs for desalination plants.

Detecting fouling early remains one of the biggest challenges in desalination.

“We can learn a lot about materials and molecules by shining light on them,” said Postdoctoral Researcher Jasmine Andersen. “Depending on the type of light you use, you’ll get different light coming back, and that tells you what’s inside the material.”

This principle underlies Raman scattering, where the color—or wavelength—of the scattered light shifts in ways that reveal a material’s molecular structure and composition.

The team used SRS to observe crystal growth on RO membranes, tracking how the molecules vibrated revealing the chemical makeup of the material.

To test the system, researchers observed calcium sulfate and calcium bicarbonate, ions commonly found in seawater. SRS provided both high-speed imaging and chemical identification.

“Watching these crystals form as it happens, getting volumetric data and identifying the chemical all at once is pretty exciting,” Andersen said. “Previously, you could get volume data or chemical identification, but not at the same time.”

Andersen notes this level of insight is something industry tools cannot currently provide.

Supporting sustainable water systems

Understanding what forms on a membrane and when can help operators maximize filtration, notes Professor Emeritus Alan Greenberg, an expert in membrane performance and characterization.

“It is well known that RO desalination plants can be more productive and operate at lower cost if fouling is reduced and cleaning is more efficient,” Greenberg said.

Beyond calcium sulfate, the team expects SRS could help study more complex mixtures of organic, inorganic and biological materials that contribute to fouling in both seawater and brackish water systems.

“As our freshwater resources shrink, we’re going to rely more on desalination,” Andersen said. “If we can make that process more efficient and sustainable, we can help ensure people have reliable access to clean water.”

Key collaborators on this project included Victor Bright, professor of mechanical engineering; Y. Lange Simmons physics doctoral graduate; and Mo Zohrabi, senior research scientist. This project received funding from the Advanced Research Projects Agency-Energy, the National Science Foundation and a CU ��Ĵ�ý Research and Innovation Seed Grant.

CU ��Ĵ�ý researchers have developed a laser-based imaging method called stimulated Raman scattering to improve the performance of desalination plants by allowing real-time detection of membrane fouling. The advance could help make desalination more efficient and reliable as global demand for clean water rises.

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