Multitasking fibers weave a new
story for imaging systems
CAMBRIDGE, Mass. – Imagine walkingto work one day and, for no obvious reason, you get a feeling that everyone islooking at you. You ignore the feeling fora while, but it persists, despite the fact thatnone of the people bustling around nearbyare casting a single glance at you andyou’ve gotten used to the growing numberof surveillance cameras filling every cityblock. Now you feel silly, perhaps even alittle paranoid. But you might not bewrong – a new imaging technology hasbegun to weave itself into the fabric ofeveryday life.
In the lab of professor Yoel Fink of thematerials science and engineering department at MIT reside swaths of wovenstrands of optical fibers. Not off-the-rollfibers ordered from a catalog, but customlines drawn from a preform crafted byFink’s group. Interwoven like a patch ofcloth, the fibers combine to form a lensless, flexible camera.
The researchers made the fiber usingpolyethersulfone as the base materialand alternating layers of semiconductingAs40Se60 or As40Se54Te6. Contacts made oftin were attached to the semiconductorrings. After deposition, the layers wererolled together onto a tube. After makinga series of these tubes, the engineersstacked them, joined the ends by heatingthem and drew them out into their finalfiber diameter (see figure). The preformswere about 3 cm in diameter, while theprocessed fibers ranged from 100 μm to
1 mm in diameter.
When an external electric field is applied to the contacts, which act as electrodes, the semiconductor layers becomeresponsive to light via the photocurrent effect. A single layer of the material can discriminate the incoming light’s angle of incidence; a second layer distinguisheswavelength. A third layer, in theory, wouldadd RGB information to the mix.
According to Fabien Sorin, a memberof Fink’s group representing MIT’s electronics lab, the semiconductor bandgapcan be adjusted so that wavelengths fromthe UV to the visible to the IR can be detected.
The investigators tested the fiber’s ability to form an imaging system by arranging them into a 32 ; 32 grid, with about1 cm between each pair of strands. Powered up, the optical fiber “fabric” patchcould image an object with features assmall as 100 nm.
“The size [of the grid] was limited forconvenience of use in the lab,” Sorin said,“but could be made much larger, withsmaller spacing between fibers.” Thatwould significantly improve image resolution.
Fink’s group sees strong potential forthis technology – which its members havedubbed “multimaterial fibers” – in suchapplications as large-area medical imaging, remote sensing, industrial control andintelligent fabrics.
It may even show up as watchful sew-on patches on clothes and baseball caps,giving their wearers an extra eye withwhich to watch the world and you something to be wary of on your walk to work.
A group at MIT has developed a multimaterialoptical fiber that can detect the components of anylight that strikes it. Woven together, the fibers makea flexible, lensless camera. Courtesy of FabienSorin, MIT.