John D Joannopoulos

John Joannopoulos, pioneering MIT physicist and inventor of crystals that control light, dies at 78

John “JJ” Joannopoulos, an influential physicist who spent more than half a century at MIT and helped lay the foundations for technologies that manipulate light — with applications from surgical tools to smart fabrics — died on August 17. He was 78.

The Francis Wright Davis Professor of Physics at MIT and longtime director of the Institute for Soldier Nanotechnologies, Joannopoulos was remembered as a brilliant scientist, visionary inventor, and beloved mentor whose warmth equaled his intellect.

Nobel laureate Robert Laughlin, one of his early PhD students, said Joannopoulos had a gift for inspiring relentless curiosity: “He sprinkled a kind of transformative magic dust on people that
induced them to dedicate every waking moment to making new and wonderful things.” Born in New York City in 1947 to Greek parents, Joannopoulos was drawn early to physics precisely because it challenged him most. “I wanted to be a physics professor since I was in high school,” he recalled in a recent interview.

He attended UC Berkeley and earned his bachelor’s degree in physics in 1968 and his PhD in 1974. That same year, he joined MIT’s physics faculty, despite being warned his odds of tenure
were slim. He went on to spend his entire career at the Institute.

Initially focused on pure theory, Joannopoulos used computer simulations to understand how electrons flow through materials. For example, physicists of the 1970s understood how electrons move within a pure semiconductor crystal but were baffled by their behavior within disordered lumps of the same materials. Joannopoulos’s simulations showed them what was happening at the atomic level and how these determined macroscopic properties. His vision and scientific contributions laid the foundations for designing materials atom by atom.

In the early 1990s, he realized similar principles could be applied to the flow of light, with potentially major technological implications. He pivoted to the nascent field of “photonic crystals” and became an architect of artificial materials that allow engineers to control light, analogous to silicon microchips that control electrons. His book “Photonic Crystals –Molding the Flow of Light,” first published in 1995, was the first and remains the definitive text on photonic crystals.

One of his most celebrated breakthroughs was the “perfect mirror,” which defied expectations byreflecting light from any angle. Rolled into a hollow fiber, it enabled the first precision “optical scalpel,” a tool that has since been used in hundreds of thousands of minimally invasive surgical procedures.

He co-founded six startup companies, including Omniguide, which commercialized the scalpel, and Witricity, which specializes in wireless charging of electric vehicles. He held 126 patents and
published more than 750 scientific papers, many of them highly cited.

In 2006, Joannopoulos became director of MIT’s Institute for Soldier Nanotechnologies, where he championed projects ranging from lightweight armor to smart fabrics. Colleagues credit him with bridging academic research and practical defense applications while fostering collaborations across departments and disciplines.

“His legacy is not only in equations and innovations, but in the lives he touched, the minds he inspired, and the warmth he spread,” said Raul Radovitzky, ISN associate director.

Joannopoulos was legendary in the classroom for memorizing every student’s name after the first day of class. He urged students to pursue their own ideas, even when they challenged his. “John did not produce clones,” said Patrick Lee, MIT professor emeritus. “He showed them the way to do science by example, by caring and sharing his optimism.”

Dozens of his students went on to become professors, researchers, and entrepreneurs. Former student Josh Winn, now an astrophysicist at Princeton, said he still feels part of “the Joannopoulos academic family,” which even organized conferences to celebrate his 50th, 60th, and 70th birthdays.

His achievements earned him election to the National Academy of Sciences and the American Academy of Arts and Sciences. He was a fellow of the American Physical Society and the American Association for the Advancement of Science.

He received numerous prizes, including the Max Born Award and the Aneesur Rahman Prize in Computational Physics. At MIT, he was honored with the Buechner Teaching Prize and the Graduate Teaching Award. Earlier this year, he was awarded MIT’s Killian Achievement Award, the Institute’s highest faculty honor.

Marin Soljačić, MIT professor and former postdoc, called him “a scientific father,” adding, “He was an amazing scientist and a serial entrepreneur. Companies he co-founded raised hundreds of
millions of dollars and employed hundreds of people. But most importantly, he was always there for his student

“He chose to see the good in people, keeping his mind and heart always open,” said Yoel Fink, an MIT professor and former student. “With warmth, humor, and a never-ending optimism, JJ left an indelible impact on science and on all who had the privilege to know him.” Joannopoulos is survived by his wife, Kyri Dunussi-Joannopoulos; three daughters, Maria, Lena, and Alkisti; and their families.

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