Drawing Optical Fibers
Today the optical fibers that carry phone calls and Internet traffic (as well as images of patients’ interiors through endoscopes) seem to have been around forever. Indeed, the basic idea of using glass rods to guide light dates back at least to the 1840s. But the problem of making a glass surface smooth enough to transmit light took more than a century to solve. Ultimately, it was an undergraduate’s weekend gamble that paid off.
Fibers start out smooth, but when they’re bundled together to transmit images or other data, their surfaces scratch each other, letting light ooze out. Researchers thought that a cladding, or insulation, made from a material less optically dense than glass would reflect the light back inside the fibers. But trials with materials from margarine to beeswax all disappointed.
Then Larry Curtiss had a brainstorm. In 1956, Curtiss was a University of Michigan junior, working to build a flexible fiber-optic endoscope to examine the stomach. When bare fibers didn’t work, he wondered if wrapping them in another kind of glass might. He knew that, since the glass tubing used in chemistry labs was less optically dense than the rods he was testing, it should trap light inside the fiber’s core. His idea was to slip the core rod into such tubing, melt them together and then draw out glass-clad fibers from the hot material. But several physics professors told him the glass coating would crack, making it useless. They suggested he stick to plastic instead.
On December 8, 1956, the professors left for a conference, so Curtiss decided to try the glass tubing. He melted it around a rod and walked away from the furnace pulling out a thin glass fiber. “I was 40 feet down the hall, and I could still see the glow of the fiber,” Curtiss recalls. The fiber was transmitting light all the way down the hall-much farther than necessary for an endoscope. Curtiss collected his early fibers by winding them around oatmeal boxes like the one above. Within 10 weeks gastroenterologist Basil Hirschowitz had examined a patient’s ulcers through an endoscope made from the new fibers.
Fiber-optic medical imaging was off and running. In the early 1960s, communications researchers started using glass-clad fibers to transmit voice data. But while Curtiss’s essential idea held true, the fibers used in communications had to be made from much purer glass using different technology-so the patent he received didn’t extend to that field. Based in Concord, MA, Curtiss still works as a consultant in the optical-fiber field.
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