Materials Science and Engineering Professor Yoel Fink, who also is Director of the Research Laboratory of Electronics at MIT, described his research that led to creation of special fibers for use as laser light carriers, at the Materials Day Symposium, hosted by the Materials Processing Center Oct. 23, 2013. The daylong symposium was held in Little Kresge Auditorium on the MIT campus.
“Fibers are one of the few materials that allow you to really span and control the very fine length scale on the one hand, but also to achieve uniformity over the kilometer length scale,” Fink said.
Fink started with a vision to see what type of devices and how many he could fit into a single fiber. “Could we realize a transistor, could we realize 100 or 1,000 different functions in a single fiber strand? What non-trivial system level attributes could we realize once we combine many fibers together?” Fink asked.
The process to pull fibers to kilometer-length is similar to that used for optical fibers, but the fibers in Fink’s work involve combinations of different fibers instead of single material. “All of the limitations of optical fiber follow from the fact that you are sending light through a material. Even to this day, we have collectively only identified one transparent material, that’s silica, and even that is only at certain wavelengths. Wouldn’t it be better to just evacuate the core and send light through a tenuous gas medium?” Fink wondered. Light can travel millions of miles through a tenuous medium, like the space between stars.
Fink’s group created an omni-directional reflector – a multi-layer mirror – which had an unusual property that it would reflect light coming from all angles of incidence and polarizations. “I want to highlight the fact – that project, which happened while I was a graduate student, actually happened at the MPC, it got started here,” he said. “It was only after some time that we starting thinking about putting these into cylindrical geometries. The end result was that it did eventually work.”
Fink published his results on hollow core fiber in Nature, showing hollow core layers down to 100 nanometers or to a few microns. “The beauty of this was that the problem of transmitting light turned from a problem that involved material discovery – because you would have to discover a new transparent material – to a problem which involved engineering, layer thickness control. You could use basically the same set of materials to transmit light at very different wavelengths.
You could never do that with an index guided fiber,” Fink explained.
They eventually set upon a path of using these fibers as an optical scalpel. With medicine migrating toward minimally invasive surgery, “You need to operate through very small ports. In order to operate through a very small port, you need to visualize tissue but you also need to be able to cut remotely and in a flexible manner," Fink said.
Visible light would be too strong for internal visualization and cutting, so infrared wavelengths were chosen to minimize collateral tissue damage. “We just basically offered a flexible fiber that could guide this laser beam, and by end of this year, 100,000 patients will have been treated with this fiber.” It’s a one-time use device used in airway, ear, gynecological and head or neck surgeries.
OmniGuide Surgical, a Cambridge-based firm, now has 170 employees designing and manufacturing fibers for minimally invasive robotic surgery. Fink said it is very rewarding to see device being used in the real world.
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