Graduate Students

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 �鶹ӰԺ 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 �鶹ӰԺ 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)

Sharafuddin earns Ryland Graduate Fellowship for control theory research

Charles Ferrer — Mon, 06 Oct 2025 16:10:37 +0000

Sharafuddin earns Ryland Graduate Fellowship for control theory research Charles Ferrer Mon, 10/06/2025 - 10:10

Charles Ferrer

Evan Sharafuddin, a first-year electrical engineering PhD student, has been selected as the recipient of the Dwight E. and Jessica D. Ryland Graduate Fellowship for the 2025-26 academic year.

Established by Dwight and Jessica Ryland, this fellowship supports a full-time PhD student in their first year of studies at the College of Engineering and Applied Science. Dwight Ryland, a CU �鶹ӰԺ School of Education graduate, and his late wife Jessica endowed the fellowship to invest in the next generation of engineering researchers.

“Earning this fellowship is an incredible honor and privilege,” Sharafuddin said. “This is an indispensable opportunity to help me pursue wind turbine control research as a first-year PhD student.”

His research focuses on applying control theory to wind turbines specifically for floating wind turbines using wind speed previews from lidar.

Sharafuddin joined the Control Systems, Sensor Fusion and Robotics lab led by Professor Lucy Pao in the Electrical, Computer and Energy Engineering Department.

“I am passionate about applying control theory to meaningful applications such as renewable energy and medicine,” Sharafuddin said. “Our lab does a lot of applied work across industries and I hope my research produces tangible impacts.”

With wind energy playing an increasingly critical role in the transition to renewable power, Sharafuddin’s work on wind turbine control could have significant real-world impact. Beyond research, Sharafuddin is committed to making control theory more accessible.

“Control theory, like many areas in electrical engineering, is quite abstract,” he said, “and I hope to help others get excited about control theory through STEM outreach and being a teaching assistant.”

As he looks ahead to continuing his studies, Sharafuddin remains grateful for the mentors and peers who have supported his journey.

“I would like to thank my advisor Dr. Pao and lab mates Sofia and Mandar for their support,” he said. “I would also like to thank Dr. Janet Sorrells at Washington University in St. Louis, for her guidance with the application process, and my family for always being there for me!”

Evan Sharafuddin, a first-year electrical engineering PhD student, has been selected as the recipient of the Dwight E. and Jessica D. Ryland Graduate Fellowship for the 2025-26 academic year who is pursuing wind turbine control research.

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Exciting news: MS-EE degree becomes MS-ECE starting fall 2025

Rossette Reid — Fri, 14 Mar 2025 16:26:25 +0000

Exciting news: MS-EE degree becomes MS-ECE starting fall 2025 Rossette Reid Fri, 03/14/2025 - 10:26

Beginning fall 2025, the �鶹ӰԺ’s Department of Electrical, Computer & Energy Engineering is excited to announce that the Master of Science in Electrical Engineering (MS-EE) will be officially renamed the Master of Science in Electrical and Computer Engineering (MS-ECE).

Why the change?
This new title better reflects the comprehensive graduate coursework and innovative faculty expertise offered within the department. By incorporating 'Computer Engineering' into the degree title, the department now more effectively showcases the specialized knowledge and skills students acquire, providing a distinct competitive advantage. This change ensures that graduates are better positioned to stand out in a rapidly evolving job market.

What this means for the future
The updated MS-ECE degree name is part of a larger effort to ensure that the department’s degree titles reflect the full scope of innovative research and learning opportunities available while also aligning with the evolving needs of students and employers in today’s interconnected world.

Note: The degree requirements will remain the same; only the diploma name is changing.

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Marena Trujillo awarded prestigious NSF graduate fellowship

Anonymous — Tue, 02 Jan 2024 07:00:00 +0000

Marena Trujillo awarded prestigious NSF graduate fellowship Anonymous (not verified) Tue, 01/02/2024 - 00:00

Charles Ferrer

Marena Trujillo, a third year doctoral student, has earned a Graduate Research Fellowship through the National Science Foundation for her promising research in power system stability and dynamics.

The Graduate Research Fellowship Program (GRFP) recognizes outstanding graduate students from across the country in science, technology, engineering and mathematics (STEM) fields, paving the way for their continued work exploring some of the most complex and pressing issues of our time.

Each GRFP recipient will receive three years of financial support, including an annual stipend of $37,000, as well as professional development and research opportunities.

We sat down with Trujillo to share some thoughts on her journey and how we can better understand power systems dynamics.

Where did your academic journey begin and how did you choose to study electrical engineering?

In middle school, my science teacher played a video about climate change and renewable technologies. I thought the idea of generating electricity from solar energy was amazing, and since then I’ve been hooked on the idea of doing my part to mitigate the effects of the climate crisis by replacing unsustainable technologies with renewable ones. I’ve always enjoyed math and physics, so the decision to pursue electrical engineering was a natural one.

What experiences have been important in your professional journey?

I was an intern at Sandia National Laboratories for several summers as an undergraduate student, and then an intern at the National Renewable Laboratory (NREL) for a summer before graduate school. These internships gave me a real appreciation for research and further cemented my interest in the power grid.

What made you decide to pursue your PhD at CU �鶹ӰԺ?

As someone interested in renewable energy, I greatly admired the mission of NREL, and as I was doing research on different graduate programs, I learned that my future advisor, Dr. Bri-Mathias Hodge, had a joint appointment with NREL. This connection has provided an invaluable opportunity to collaborate with NREL researchers, which I am very grateful for.

Can you describe your research area within electrical engineering?

My work is chiefly concerned with power system stability and dynamics. Wind, solar, and storage resources operate in a fundamentally different way from traditional generation like coal or gas. Studying the stability and dynamics of modern power systems (with high shares of renewable energy) is important for ensuring the reliability of the grid.

What do you hope to accomplish with your NSF graduate research fellowship?

Through my research, I hope to play a part in advancing knowledge in the field of power systems engineering, specifically in regards to stability and dynamics. There are many important unanswered questions in this field, and to make progress towards answering these questions would be really exciting. Afterall, the better we understand the dynamics of power systems, the sooner we can deploy renewable resources.

What does this fellowship mean to you?

This fellowship makes it possible for me to pursue research projects that I find most interesting and that are the best suited for my skill set. Every morning I wake up excited to be doing research I find valuable and compelling!

What’s next after you finish your PhD?

Eventually, I would like to pursue a tenure-track position. I truly enjoy doing research in an academic setting and I’d love the opportunity to teach.

Any hobbies you like to pursue while you’re not researching?

In my free time, I like to read and knit as well as go skiing with my husband. I didn’t grow up skiing, but I couldn’t live in Colorado and not give it a try. Now I love it!

Marena Trujillo has earned a Graduate Research Fellowship through the National Science Foundation for her promising research in power system stability and dynamics.

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PhD student receives competitive Department of Defense fellowship

Anonymous — Mon, 11 Jul 2022 15:53:46 +0000

PhD student receives competitive Department of Defense fellowship Anonymous (not verified) Mon, 07/11/2022 - 09:53

Electrical engineering PhD student Michelle Pirrone has won a prestigious Department of Defense fellowship for her promising research in microwave engineering and machine learning.

National Defense Science and Engineering Graduate (NDSEG) Fellowships provide three years of funding for tuition and fees, as well as a monthly stipend and travel budget. The DoD awards approximately 500 fellowships each year to students across the country.

We asked Pirrone to share some thoughts on her journey in electrical engineering and advice for those considering a PhD path.

How did you originally choose to study electrical engineering?

I originally started as a mechanical engineering major in my undergrad but had an electrical engineering professor recruit me for research on antennas and 3D printing. I thought it would be a good opportunity to try something new, so I gave it a shot and loved working on microwaves engineering so much that I switched majors and decided to continue with the work in my PhD.

What made you decide to pursue your PhD at CU �鶹ӰԺ?

After working on the antenna research in undergrad, I felt that I had only just scratched the surface with microwaves engineering and really wanted to learn more and try to solve many of the questions or problems I had encountered in my original research. When I came to CU �鶹ӰԺ for visit week, it was my first time in Colorado, and I fell in love with the region. Both the professors and the students in the microwaves program were very welcoming and worked well together, which was a camaraderie that I had not seen at any other program. I decided then to take the leap, not only with going for a PhD, but also moving across the country to Colorado.

Tell us about the project you’re working on now. What do you find most interesting or satisfying about the work?

I am currently working on integrating machine learning techniques into microwaves systems that change in real time. As the requirements for things like communication systems and reconfigurable networks continue to increase, we are hoping to address these demands by allowing machine learning techniques to dynamically improve system performance as operating conditions vary. I originally started the PhD program working solely on microwave design, but I love the challenge of having to work on two very technical and different topics as microwaves engineering and machine learning are. Not many people have tried to put these topics together before like we are doing, and the projects are forcing me to take new approaches to problems in totally different ways than I would never have had to before.

What is your favorite part about working with your faculty co-advisors, Taylor Barton and Emiliano Dall’Anese?

Both of my advisors have been really great about being open-minded and giving me the room to make some of my own decisions and choices as we work on projects. However, I also always feel like they are there for me when I need support or am stuck on a part of my research and don't know how to continue. I believe we have struck up a really good balance of independence and mentorship, and the three of us work very well on capitalizing on each other's strengths for the research.

What’s next after you finish your PhD?

I still have a few years to go before finishing my PhD, and I like to always keep my opportunities open until it's time to make the final decision. I think I am currently considering going into industry to get some new experience after spending several years in the academic sphere, but only time will tell.

What advice would you give students considering pursuing their PhD?

For most of my time in undergrad, getting a PhD was not on my radar. It wasn't until I found a topic of interest that I really enjoyed that I started to seriously consider graduate school. And even though I work on totally different topics than I did in my undergrad research, there has always been a level of engagement with my work in which I always had been asking questions on if something was possible or how something worked, and now I could actually answer these questions that no one had before. Getting a PhD requires always trying to solve problems or innovate, and I think anyone considering getting a PhD needs to ask themselves if they will enjoy both the frustrations and the satisfaction that comes with forging their own path forward on things no one has really done before.

Do you have any hobbies you’d like to share?

As probably a large portion of Colorado shares, I love being outdoors and in particular love hiking. It's amazing to me how many beautiful hikes are such a short drive away from this area, and I really like doing long hikes that get you far away from the typical hustle bustle of our everyday lives. In addition to that, I really like to cook and try to make foods I've tried at restaurants at home and also like to weight lift.

Anything else you want readers to know about you or your work?

I really didn't expect to be where I am in my life right now or working on what I do, but I took some chances on trying new things along the way, and I'm hoping to continue to push the limits in my research of what's out there now and what we can accomplish.

Michelle Pirrone has won a prestigious National Defense Science and Engineering Graduate (NDSEG) Fellowship for her promising research in microwave engineering and machine learning.

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New program: Earn a professional master's in embedded systems

Anonymous — Wed, 11 Nov 2015 16:53:37 +0000

New program: Earn a professional master's in embedded systems Anonymous (not verified) Wed, 11/11/2015 - 09:53

Most of us will casually encounter dozens of embedded systems by mid-morning each day throughout our residences, roadways, workplaces and retail stores. These intelligent machines are a permanent part of our global landscape, and are continuously being expanded and upgraded by a world of forward-thinking engineers and entrepreneurs.

To help our students, alumni and industry friends keep pace with these technology trends – including the Internet of Things – the Department of Electrical, Computer and Energy Engineering has expanded its options in embedded systems design, starting in fall 2015.

The Embedded Systems Engineering (ESE) professional master’s program is structured to provide students with a broad, versatile skillset and coupled with industry input for continuous curriculum updates. Current trends covered in the program include:

ARM Processors
Capacitive Touch
Computer/Machine Vision (Industrial)
Consumer Wearables
FPGA/SoC Home Automation (Industrial)
Imaging
Memory/Storage
Sensors/MEMS
Smartphone Apps
Solid State Lighting
Transportation Autonomy
Web-enablement (Internet of Things)
Wireless Protocols & Devices

This new program is offered under the College of Engineering and Applied Science’s Master of Engineering degree. Through flexible core course options and electives, students enrolled in the ESE program may pursue a 9-credit hour certificate or a 30-credit hour degree at an introductory cost of $860/credit hour (residents) or $990/credit hour (non-residents).

With our newly added ESE classes, students now have access to all of the courses they need to complete a master’s degree in this dynamic field.

Visit the Embedded Systems webpage for more on available courses, program options and more.

To help our students, alumni and industry friends keep pace with technology trends – including the Internet of Things – the Department of Electrical, Computer and Energy Engineering has expanded its options in embedded systems design, starting in fall 2015.

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PhD student's startup takes home $275K MIT Clean Energy Prize

Anonymous — Tue, 12 May 2015 06:00:00 +0000

PhD student's startup takes home $275K MIT Clean Energy Prize Anonymous (not verified) Tue, 05/12/2015 - 00:00

OptiBit's technology helps data centers save 10% on energy use while also increasing performance.

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CU-�鶹ӰԺ faculty accept Google/IEEE Little Box Challenge

Anonymous — Thu, 15 Jan 2015 07:00:00 +0000

CU-�鶹ӰԺ faculty accept Google/IEEE Little Box Challenge Anonymous (not verified) Thu, 01/15/2015 - 00:00

ECEE Assistant Professor Khurram Afridi and his team were notified by Google in December 2014 that they had received a grant to compete in the Little Box Challenge, a million-dollar prize competition funded by Google and judged by the IEEE Power Electronics Society.

The contest's goal is to dramatically change the technology of solar power inverters, and it has attracted significant attention, with 10 teams from around the world selected to receive the grant from Google.

Now, Prof. Afridi and his team has less than a year to build a power inverter that is at least 10 times smaller than the current picnic cooler-sized inverters commonly used in photovoltaic solar power systems and other green energy applications.

The 2-kVA inverter, which must fit within a 40 in3 rectangular metal enclosure, is also required to have efficiency greater than 95%, an enclosing case temperature of under 60°C without external cooling, and must conform to a number of other requirements and standards.

But Afridi isn't daunted. In fact, he says it was the demanding timeline and project requirements that piqued the team's interest in competing.

"It was aggressive enough in terms of requirements that it made for a good challenge," he said. "The power density challenge is quite aggressive, especially when you add to it other requirements like thermal management and electromagnetic interference and the fact that you're discouraged from using limited life, but high energy density, electrolytic capacitors."

Afridi also saw the challenge as a good opportunity for collaboration across disciplines. His Team Flatiron will include ECEE researchers Professor Bob Erickson, Professor Dragan Maksimovic and Dr. Dan Seltzer, as well as Associate Professor Ronggui Yang from mechanical engineering, and a number of graduate students.

While they obviously can't give away much about their approach, Afridi said they're going to use a unique energy-buffering scheme and innovative inverter topology, which should allow them to exceed the required specifications.

Because of the tight timeline, the team won't have much time for iterations. Instead, Afridi said, they will have to run all pieces of the project in parallel, which will require close collaboration.

"It basically has to be running well on the first try," he said.

In the coming July, the Team Flatiron will submit their technical approach and their little box to the judges. Eighteen finalists will then be selected to test their inverters in October at the National Renewable Energy Laboratory (NREL) in Golden, Colorado.

Because the grant from Google will only cover equipment and parts, the team will be looking for volunteer undergraduate researchers to join them in the lab. If you are interested, contact Prof. Afridi atkhurram.afridi@colorado.edu.

Afridi and his team have less than a year to build a power inverter that is at least 10 times smaller than the current picnic cooler-sized inverters commonly used in photovoltaic solar power systems and other green energy applications.

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PhD student wins top prize for research demo

Anonymous — Sun, 19 Oct 2014 06:00:00 +0000

PhD student wins top prize for research demo Anonymous (not verified) Sun, 10/19/2014 - 00:00

First-year PhD student Saad Pervaiz recently beat out nine students from around the world to take home the Best Demo Award at the Institute of Electrical and Electronics Engineers' 2014 Energy Conversion Congress and Expo (ECCE) in Pittsburgh.

ECCE introduced the student hardware demo event in 2011 for students to showcase their research outcomes and interact with academia and industry. This year, teams from Virginia Tech, Iowa State, North Carolina State, City University of Hong Kong and KTH Sweden were among those to present their posters, hardware and videos at the event.

Pervaiz demonstrated an electrolytic-free offline led driver with a ceramic-capacitor-based compact stacked switched capacitor (SSC) energy buffer, a project he has been working on with Assistant Professor Khurram Afridi. He was supported by Yu Ni, a recent graduate of the ECEE master's program, and Minjie Chen, a student Afridi is co-advising at the Massachusetts Institute of Technology.

LED drivers are used in commercial and residential lighting to regulate power to an LED or string of LEDs.

"Most LEDs are guaranteed for 40 years, but the drivers only last four or five years before they need to be replaced," Pervaiz said. "We're creating a driver that will last longer."

During their demonstration, Pervaiz and his team pitted their driver against one with electrolytic capacitors. They showed that theirs achieved the same performance as the electrolytic version, while reducing the passive volume by a factor of two.

In addition to winning a cash award, Pervaiz said the conference was also a great networking opportunity.

"During my presentation, I got to meet some of the top researches of my field," he said. "I also made some good industry connections"

Learn more about Pervaiz's project in his demonstration report.

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