Featured Alum: David Stegall, Ph.D., Physics 1994

When Professor Becker contacted me to request an essay for the CBU Newsletter, my first thought was to look for any fine print on the diploma regarding future homework assignments. To my great disappointment, no such homework clause exists, but that has not stopped me! I always found the faculty at CBU to be personable and engaging so I feel honored to be remembered in this manner. Actually, writing this article has offered me the opportunity to reminisce about my life and how persistent progress, accidental fortunes, and singular moments led to my current circumstances.

I believe that my parents would tell you that I was like every other rowdy boy in the neighborhood -sunburned from play during the summer and flinging snowballs at every opportunity that the winter in Memphis could provide. Old toys were not to be merely thrown away, but were subjected to total dissection. Batteries, speakers, or anything else worthy of extraction from an old radio were mine to eventually take to show and tell. I don’t think my parents were aware of everything that got disassembled but at least I never burnt the house down. Maybe I scorched a sink or two. If I could pinpoint a seminal moment, it would be the age of 13. Halley’s Comet was going to swing by that year. I was eminently aware that the next time it came, I probably would not be around to see it. Mark Twain had been born on one of the comet’s prior rendezvous with Earth and he managed to live just long enough to see it come around again. Although the thought was morbid, it placed a sense of urgency in me. I appreciated that there’s no moment to delay in learning and understanding the natural world around us. We may not get a second chance to not only witness, but participate in such rare cosmic spectacles. My destiny was sealed. I was not only going to see that comet with my naked eyes, but I was going to photograph it! From that moment, I became familiar with telescopes, astrophotography, and the requisite understanding in optics (at least as much as I understood with my middle school science). Astronomy and astrophotography were to become a launching pad into my career as an optical physicist.

When I first set foot into CBU in 1992, I was put at ease by the tone set by the CBU faculty. We had small classes and the professors were so much more accessible than at some of the larger schools that I previously attended. CBU was also unusual since it offered several upper level physics courses dedicated to the field of optics. Professors like Dr. Holmes and Dr. Varriano were fantastic at teaching me the skills that I would need to become an independent researcher. I can still recall the tedious hours of time spent in the optics and dark labs, exposing and developing optical filters for my senior project. It was this kind of discipline and experience that served me well when I began my PhD at the Institute of Optics at the University of Rochester in 1994. However, I was certainly less prepared for the ten feet of snow per year that Rochester typically receives!

I wrapped up my dissertation in the fall of 2000. Under the tutelage of Professor Turan Erdogan, my dissertation delved into the topic of optical fiber Bragg gratings. You might recall that we were experiencing the arrival of the internet and the juggernaut of the .com industry. The optical fiber telecommunications industry was rapidly growing in the euphoria of the internet age and it led to my career in corporate research. In order to sustain the demand for high-speed internet bandwidth, there was a widely held belief that optical fiber communication systems were going to need to improve. I joined the laboratories at 3M, where they were developing optical fiber grating filters to serve a variety of functions – chromatic dispersion compensation, erbium-doped fiber amplifier filters, add/drop filters, etc. These were exciting times in my field. Of course, the optical telecommunications bubble burst very soon after the .com bubble’s demise and the mission of the 3M lab had to evolve.

A scanning electron micrograph of a square lattice photonic crystal fabricated with a 500 nm period

When handed a lemon, one should make lemonade. Thus, the lab adapted. The leading-edge technology that had been developed for make fiber gratings was not abandoned. For example, we had learned how to stitch together a modulation to the refractive index along the length of the fiber core such that errors were less than one part in a million. If the grating was to have a period of about one micron, then that period was accurate to within 10’s of nanometers over a length of a meter. Some fiber gratings were even longer than a meter – a cutting-edge achievement at the time. What could be done along one-dimension, we learned, could also be done along two. Consequently, the lab developed a method to fabricate two-dimensional sub-micron periodic structures over large areas. In some cases, such structures are referred to as photonic crystals. An example of such a structure is shown in the figure on the right. Photonic crystals naturally occur in nature and can be found on the wings of butterflies, the outer shells of diatoms ( a kind of plankton), and even in the hairs found on the leaves of plants, like the edelweiss. They have even been found in fossilized remains dating back hundreds of millions of years. A photonic crystal has the ability to manipulate light due to its periodic refractive index modulation. At 3M, I lead a project that is developing methods to mass-produce photonic crystals that will be used in organic light emitting diodes (OLEDs). OLEDs are a developing technology that provide advantages over more traditional sources of light. They are made of organic materials, akin to plastics, and thus do not require nearly as complicated fabrication equipment as traditional inorganic semiconductor LEDs. They are dramatically more efficient than fluorescent lights and thus will be entering into the general lighting markets in a few years. Compared to LCD displays found in televisions, monitors, and cell phones, OLEDs are more efficient , more colorful, and ultimately simpler in construction. As a matter of fact, Samsung and LG are already selling cell phones using small OLED screens. 3M is in a unique position to mass produce a technology that permits OLEDs to emit light more efficiently by using photonic crystal films. We refer to these products as light extraction films. Without a light extraction film, most of the light generated within the OLED remains trapped due to internal reflections. Light extraction films provide a very fundamental modification to the internal geometry of an OLED that permits much more light to be emitted in directions that can escape the device. The benefit to a consumer would be longer battery usage time, a longer OLED display or lighting lifetime, and even a more satisfying distribution of the emitted light. Currently, we are still in the development stages of the product, but we have been getting very encouraging feedback from our prototypes to potential customers.