Jelena Vuskovic delivers 2021 Dresselhaus lecture on inverse-designed photonics

As her topic for the 2021 Mildred S Dresselhaus lecture, Stanford University professor Jelena Vuskovic posed a question: Are computers better than humans at designing photonics?

Throughout his speech, presented in a hybrid format to more than 500 attendees on November 15, the Jensen Huang Professor in Global Leadership at the Stanford School of Engineering presented several examples arguing that yes, computer software Can help identify better solutions than traditional methods. Leading to smaller, more efficient devices as well as completely new functionalities.

Photonics, the science of guiding and manipulating light, is used in many applications such as optical interconnects, optical computing platforms for AI or quantum computing, augmented reality glasses, biosensors, medical imaging systems, and sensors in autonomous vehicles.

For all of these applications, Vuskovic said, multiple optical components must be integrated onto a single chip that can fit the footprint of your glasses or mobile device. Unfortunately, there are several problems with high-density photonic integration. Conventional photonic components are large, sensitive to environmental factors such as fabrication errors and temperature changes, and are designed by manual tuning with few parameters. So, Vuskovic and his team asked, “How can we design better photonics?”

His answer: Photonics inverse design. In this process, scientists rely on sophisticated computational tools and modern computing platforms to find the optimal photonic solution or device design for a particular function. In this inverse process, the researcher first considers how he or she would like the photonic block to operate, then uses computer software to find the entire parameter space of possible solutions that is optimal, within construction restrictions.

From guiding light around corners to dividing colors of light in a compact footprint, Vuskovic presented several examples to prove this process – using computer software to conduct physics-guided searches of many possibilities. Unconventional solutions are generated that increase the efficiency and/or reduce the footprint of photonic devices.

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2021 Mildred S. Dresselhaus Lecture: Jelena Vuskovic, Stanford University

Enabling New Functionalities – High-Energy Physics

State-of-the-art particle accelerators, which use microwave or radio frequency waves to propel charged particles, can be the size of a full city block; For example, Stanford’s SLAC National Accelerator Lab is two miles long. Low-energy accelerators, such as those used in medical radiation facilities, are not that large but still occupy an entire room, are expensive, and are not very accessible. “If we can use a different spectrum of electromagnetic waves with shorter wavelengths to do the same thing as accelerating particles,” Vuskovic said, “we should, in principle, reduce the size of an accelerator.” should be able to.” The solution is not as simple as reducing the size of all parts, as electromagnetic building blocks will not work for optical waves. Instead, Vuskovic and his team used the inverse design process to create new building blocks, and built a single-stage on-chip integrated laser-driver particle accelerator that is only 30 micrometers in length.

Micrograph of a micrometer-long piece of fabricated silicon.

A few-micrometer-long piece of fabricated silicon that acts as a compact stage of a particle accelerator and accelerates electrons by interacting with a coupled laser field. This structure can shrink linear accelerators on a silicon chip from miles to an inch.

Image courtesy of Jelena Vukovic.

Applying inversely designed photonics to practical environments

Autonomous vehicles have a large lidar system on the roof housing mechanics that enables the rotation of the beam to scan the environment. Vuskovic considers how it can be improved. “Could you build this system inside the footprint of a chip that would be like another sensor in your car, and could it be cheaper?” Through inverse design, his research group found optimal photonic structures to enable beams to be driven with lasers cheaper than with state-of-the-art systems, and gained 5 degrees of additional beam steering.

Next up: Scaling up a superconducting quantum processor on a diamond or silicon carbide chip. In this example, Vuskovic retracts the 2020 Dresselhaus lecture given by Harvard Professor Evelyn Hu on taking advantage of defects at the nanoscale. By relying on impurities at low concentrations in these materials, naturally trapped atoms can be very useful for quantum applications. Vuskovic’s group is working on material development and fabrication techniques that allow them to place these trapped atoms in the desired state with minimal defects.

“For many applications, letting computer software search for an optimal solution leads to better solutions than you designed or anticipated based on your intuition. And the process is material-agnostic, in line with commercial foundry.” compatible, and enables new functionalities,” Vuskovic said. “Even if you try to build something better than traditional solutions – one that is smaller in footprint or higher in efficiency – we can come up with many solutions that are equally as good or less efficient than before. better. We’re re-learning photonics and electromagnetics in the process.”

Mildred S. Honoring Dresselhaus and Jean Dresselhaus

Vuskovic was the third speaker to deliver the Dresselhaus Lecture, established in 2019 to honor the late MIT physics and electrical engineering professor Mildred Dresselhaus. This year, the lecture was also dedicated to Jean Dresselhaus, the famous physicist and husband of Millie, who passed away at the end of September 2021.

Jing Kang, a professor of electrical engineering and computer science at MIT, opened the lecture by reflecting on Dresselhaus’s scientific achievements. Kong highlights the American Physical Society’s Oliver E. Buckley Condensed-Matter Physics Prize—considered the most prestigious award given in the field of condensed-matter physics—given to both Millie (2008) and Jean (2022). “Although they worked together on many important topics,” Kong said, “it is remarkable that they received this award for separate research work. It is our privilege to follow in their footsteps.”

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