When you challenge a century-old belief, encountering some resistance is inevitable. This is precisely what John Joannopoulos and his team at MIT encountered in 1998, when they proposed a fresh theory on how substances can be manipulated to refract light in completely unprecedented ways.
“Due to the significant deviation from what people anticipated, we documented the theory for this, but it was quite challenging to get it published,” Joannopoulos shared with a full audience in MIT’s Huntington Hall on Friday, while he delivered the James R. Killian, Jr. Faculty Achievement Award Lecture.
Joannopoulos’ theory provided a novel perspective on a type of material known as a one-dimensional photonic crystal. Photonic crystals consist of alternating strata of refractive elements arranged in a manner that can affect how incoming light is reflected or absorbed.
In 1887, the English physicist John William Strutt, known more widely as Lord Rayleigh, formulated a theory about how light should refract through a similar construct composed of multiple refractive layers. Rayleigh anticipated that such a construct could reflect light, but only if that light originated from a highly specific angle. In essence, this type of structure could function as a mirror for light approaching from a designated direction only.
More than a century later, Joannopoulos and his team discovered that, in fact, the exact opposite was true. They theoretically demonstrated that if a one-dimensional photonic crystal comprised layers of materials exhibiting certain “refractive indices,” bending light to varying degrees, the crystal as a whole could reflect light coming from any and all angles. Such an arrangement could serve as a “perfect mirror.”
This concept was a significant departure from established scientific beliefs, and as a result, when Joannopoulos submitted the research for peer evaluation, it took time for the journal, and the broader community, to accept it. However, he and his students persevered, ultimately confirming the theory through experimental validation.
This endeavor culminated in a prominent publication, enabling the group to refine the idea into a tangible device: Using the principles they established, they effectively constructed a perfect mirror, which they molded into a tube to create a hollow-core fiber. When light was directed through it, the interior of the fiber reflected all the light, trapping it completely within the core as it bounced through the fiber. In 2000, the team established a startup to further evolve the fiber into a flexible, precise, and minimally invasive “photonics scalpel,” which has since been utilized in hundreds of thousands of medical procedures, including surgeries of the brain and spine.
“And consider this: We’ve estimated more than 500,000 procedures across hospitals in the U.S. and abroad,” Joannopoulos proudly announced, to appreciative applause.
Joannopoulos is the recipient of the 2024-2025 James R. Killian, Jr. Faculty Achievement Award and serves as the Francis Wright Davis Professor of Physics and director of the Institute for Soldier Nanotechnologies at MIT. In response to an audience member’s inquiry about what fueled him amid initial doubts, he replied, “You must persist if you are convinced what you have is accurate.”
Invaluable influence
The Killian Award was instituted in 1971 to commemorate MIT’s 10th president, James Killian. Annually, a member of the MIT faculty is recognized with the award in acknowledgment of their remarkable professional achievements.
Joannopoulos earned his PhD from the University of California at Berkeley in 1974, then promptly joined MIT’s physics faculty. In introducing his talk, Mary Fuller, professor of literature and chair of the MIT faculty, remarked: “If you do the calculations, you’ll see he just celebrated 50 years at MIT.” Throughout that extraordinary tenure, Fuller highlighted Joannopoulos’ significant influence on generations of MIT students.
“We acknowledge you as a leader, a visionary researcher, cherished mentor, and a believer in the inherent goodness of people,” Fuller stated. “Your legendary impact at MIT and the wider scientific community is immeasurable.”
Manipulating light
In his lecture, aptly titled “Working at the Speed of Light,” Joannopoulos guided the audience through the fundamental concepts underpinning photonic crystals, as well as the ways in which he and others have demonstrated that these materials can manipulate incoming light in a directed manner.
He characterized photonic crystals as “synthetic materials” that can be engineered to affect the properties of photons similarly to how physical features in semiconductors influence the movement of electrons. In semiconductors, these materials possess a specific “band gap,” or a range of energies where electrons cannot exist.
In the 1990s, Joannopoulos and his colleagues speculated whether similar effects could be achieved for optical materials, aiming to deliberately reflect, or block, certain types of light while allowing others to pass through. Even more fascinating was the possibility: Could a single material be designed to direct incoming light away from particular areas within the material in predetermined pathways?
“The response was a resounding yes,” he declared.
Joannopoulos conveyed the enthusiasm within the burgeoning field by quoting an editor from the journal Nature, who at the time stated: “If only it were feasible to create materials in which electromagnetic waves cannot propagate at particular frequencies, all kinds of almost-magical possibilities would arise.”
Joannopoulos and his team at MIT began in earnest to clarify the interactions between light and matter. They initially worked with two-dimensional photonic crystals formed from a horizontal grid-like arrangement of silicon dots surrounded by air. Silicon has a high refractive index, enabling it to bend or reflect light significantly, while air has a much lower index. Joannopoulos predicted that the silicon could be arranged to divert light away, compelling it to traverse through the air along designated routes.
Through various studies, he and his students demonstrated both theoretically and experimentally that they could design photonic crystals, for example, to bend incoming light by 90 degrees and guide light to circulate solely at the borders of a crystal within an applied magnetic field.
“Over the years, there have been numerous instances we’ve uncovered of very peculiar, extraordinary behavior of light that cannot manifest in conventional objects,” he noted.
In 1998, after demonstrating that light can be reflected from all angles by a stacked, one-dimensional photonic crystal, he and his students rolled the crystal structure into a fiber, which they analyzed in a laboratory. In a video Joannopoulos presented to the audience, a student carefully aimed the end of the long, flexible fiber at a sheet of material made from the same substance as the fiber’s casing. As light coursed through the multilayered photonic lining of the fiber and out the other end, the student used the light to gradually etch a smiley face design onto the sheet, eliciting laughter from the audience.
The video illustrated how, despite the light being strong enough to melt the material of the fiber’s coating, it was entirely contained within the fiber’s core, thanks to the multilayered design of its photonic lining. Additionally, the light was sufficiently focused to create intricate patterns as it emerged from the fiber.
“Initially, we developed this [optical fiber] as a military application,” Joannopoulos explained. “But then the clear choice was to utilize it for the civilian sector.”
“Having faith in the goodness of people and their capabilities”
He and others co-founded Omniguide in 2000, which has since evolved into a medical device firm that designs and commercializes minimally invasive surgical tools like the fiber-based “photonics scalpel.” To showcase the fiber’s significance, Joannopoulos played a news video that spotlighted its effectiveness in conducting precise and efficient neurosurgery. The optical scalpel has also been utilized in procedures within laryngology, head and neck surgery, gynecology, alongside brain and spinal surgeries.
Omniguide is just one of the several startups Joannopoulos has aided in founding, including Luminus Devices, Inc., WiTricity Corporation, Typhoon HIL, Inc., and Lightelligence. He is the author or co-author of over 750 peer-reviewed journal articles, four textbooks, and 126 issued U.S. patents. He has attained numerous accolades and honors, including his election to the National Academy of Sciences and the American Academy of Arts and Sciences.
The Killian Award citation states: “Professor Joannopoulos has been a consistent exemplar not only in his achievements but in the manner he accomplishes them. … Through all the individuals he has influenced — along with their academic descendants — Professor Joannopoulos has had a profound effect on the advancement of science in recent decades.”
At the conclusion of the lecture, Yoel Fink, Joannopoulos’ former student and frequent collaborator, now a professor of materials science, asked Joannopoulos how, especially in today’s climate, he has managed to “maintain such a positive and hopeful perspective on humanity and human nature.”
“It’s about believing in the goodness of individuals and their potential, what they can achieve, and providing an environment where they feel extremely comfortable,” Joannopoulos responded. “This includes fostering a sense of trust between the faculty and the students, which is crucial. That makes a significant difference.”