By Patricia Daukantas
Every scientific advancement has a story behind it. Telecommunications fibers and optical coherence tomography (OCT) are no different. Donald Keck and James Fujimoto--the first two CLEO:2011 plenary speakers--did a great job of telling those true tales.
Donald Keck, a retired Corning Inc. (U.S.A.) scientist who participated in the development of the first low-loss optical fiber, attributed the telecom boom to a “syzygy” of rapid-fire technological developments four decades ago. In addition to that first practical fiber, the earliest computer-network experiments, the room-temperature laser chip and the computer chip all appeared between 1969 and 1971.
Evoking the original notion of the laser as a “solution looking for a problem,” Keck drew chuckles by reminding the audience of schemes for laser cutting of trees, laser-made nipples for baby bottles and Arthur Schawlow’s “laser eraser” for typists. Early proposals for laser telecommunications--by sending light beams down 2-in.-wide coaxial cables--were not much more practical.
Fortunately, British government researchers asked Corning for help in creating glass fibers with attenuation below 20 dB/km, at a time (1966) when the best silica fiber suffered from signal loss of 1,000 dB/km. Drawing upon glass research from the 1930s to the 1950s, Keck and his Corning colleagues started tracking down and eliminating the sources of optical loss in fiber.
Their initial fiber-drawing equipment was crude--including a household vacuum cleaner--but effective. When Keck tested the first fiber with a loss of only 17 dB/km, he was so impressed that he wrote in his lab notebook, “Whoopee!” However, in 1970 an Applied Physics Letters reviewer initially rejected the Corning team’s paper because, Keck said, “it lacked believability.”
Today’s single-mode fibers fulfill Keck’s 1972 prediction of operation with losses of 0.2 dB/km or less at the 1,550-nm wavelength. Progress in telecommunications has come rapidly, especially after the 1984 court-ordered breakup of the old Bell-System AT&T, which created “a lot of fiber-hungry ‘baby Bells,’” Keck said. With the development of fiber that can bend around sharper corners without introducing losses, the industry is poised to use fiber in ways traditionally associated with copper wire.
OCT: Joining Optics and Clinical Science
OCT is a method of imaging using echoes of light--the optical analogue of ultrasound, said James Fujimoto of the Massachusetts Institute of Technology (U.S.A.). In terms of resolution and tissue penetration, OCT bridges the gap between ultrasound and confocal microscopy.
Although Michel A. Duguay and A.T. Mattick first suggested the technique in a 1971 Applied Optics article, the first demonstration of OCT, performed on a cadaver eye, was published two decades later, according to Fujimoto. Since then, progress has come rapidly, with the technique’s extension to living tissue and the commercial development of OCT equipment for clinical use. Today, spectral domain interferometric techniques have improved both the speed and sensitivity of OCT. High-speed CCD cameras and volumetric data-rendering techniques have added to OCT’s ability to track dynamic processes such as capillary blood flow.
OCT is now moving beyond ophthalmic procedures into the world of intravascular imaging, where the technique can identify unstable arterial plaques and guide the medical treatment of those dangerous blood-flow blockers.
Fujimoto said that there has been a huge increase in intravascular OCT procedures in the last three years. The development of tiny fiber-optic catheters and the Fourier-domain mode-locked (FDML) laser have helped make this possible.
Finally, Fujimoto drew the audience’s attention to one of this CLEO’s postdeadline papers, which reports a record imaging speed for OCT using a swept single-mode vertical-cavity surface-emitting laser (VCSEL). OCT promises to be an exciting technological field to watch in the near future.
Applied optics, Biomedical optics, CLEO/QELS, Fiber optics, Lasers, Lasers, CLEO