While most kids growing up in the 1960s were playing with Lincoln Logs and bouncy balls, a young Herbert Winful was mesmerized by the laser. "When I started high school the laser was quite young, just a few years old," he says, "and I dreamt of someday inventing an X-ray laser!" This laser science leader had the great fortune as an electrical engineering sophomore at MIT to have as his mentor Hermann A. Haus, another laser pioneer in the field of optical communications (and a National Medal of Science honoree). "I went up to him and asked can I work in your lab?" Winful recalls. Haus agreed, but only if his future protégé enrolled in his course. "That was the start of my career. I've taken him as my example as I've tried to mentor students."
And what a career it has been. Winful, who grew up in Cape Coast, Ghana, and received his PhD from the University of Southern California in 1981, worked in industry for six years before he joined the faculty of the University of Michigan in 1987. He became a full professor in the College of Engineering in 1992 and was named a Thumau Professor one year later. He is a Fellow of the APS, OSA, and the Institute of Electrical and Electronic Engineers, and among his many awards, received the Presidential Young Investigator Award.
As a graduate student, Winful remembers looking for a problem to solve for his thesis. "One day I realized one could combine nonlinearity with a periodic structure and get optical bistability," he says. "The idea just came to me and I mentioned it to one of my professors, John Marburger, who later became Bush's Science Advisor, and he said 'Wow, that's the best new idea I've heard in the field in years.'" Winful's work on nonlinear periodic structures opened up a whole new field and led to novel all-optical switching devices and the discovery of certain optical pulses known as "gap solitons".
On the laser landscape, Winful is best known for nonlinear optics and solving the scientific paradox of quantum tunneling time, where particles pass through classically impenetrable barriers. For almost 75 years, scientists were perplexed as to why electrons seemed to travel faster than light speed when they pass though physical barriers, but not so when they move through empty space. Furthermore, "as you increase the length of the barrier, the tunneling time does not increase," he comments. With these tantalizing conditions in mind, Winful began working on an analogy between tunneling electrons and optical pulses and theoretically determined that electrons were not going faster than the speed of light. He proved that what was actually being measured was not the time it took for the particles to pass though the obstacle, "but the time it takes to empty the barrier of energy already stored in the barrier." This concept is known as "group delay."
"This work can shed light on the ultimate speed of electronic devices," he illuminates, "and it has widespread ramifications because tunneling is a phenomenon that can occur with all sorts of waves: light waves, sound waves, electron waves, etc...We are going to understand better the fundamental limits."
But if tunneling time blows your mind, Winful jests that "I also have my practical side" when it comes to his laser investigations. For years, he has been "studying problems involving the coherent combining of many lasers into an array such that you can get a whole lot more power than what you can get from an incoherent sum," he explains. The outcome could lead to revolutionary innovations in materials processing and other industrial arenas, as well as medical applications, such as surgery.
The future guarantees many laser advances, but Winful is especially excited about the potential of metamaterials, artificial substances that do not have typical, natural properties. Metamaterials are currently being explored by scientists for various uses, although one of the more well-known applications thus far has been to make certain objects appear invisible. To date most of the demonstrations of these exotic properties have been in the microwave region. "Extension of this cloak of invisibility to the wavelength regime of visible lasers would be a tremendous advance," he predicts.
When not pondering theoretical problems in laser science, Winful likes to relax at the piano, playing the music of Bach, Chopin, and Brahms. "It is my greatest joy, next to my work."