A team of scientists at the MIT Media Lab in the USA have developed an imaging device made from a bundle of optical fibres without lenses or an enclosure. The fibres are loose meaning they could potentially pass through micrometre gaps to image across porous membranes.
The device operates by time-of-flight, but uses the technique not to give depth information but to determine the fibres’ relative locations in the bundle. This position information can then be used to resolve an image of what the fibre bundle is pointing at.
The researchers envision that a bundle of these fibres could inspect inside pipelines, such as oil pipes or plumbing, or create thinner endoscopes, as the imaging system needs no additional electronics.
Speaking to the MIT News Office, Barmak Heshmat, a postdoc in the Camera Culture group at the Media Lab who led the work, commented: ‘Time-of-flight, which is a technique that is broadly used in our group, has never been used to do such things. Previous works have used time-of-flight to extract depth information. But in this work, I was proposing to use time-of-flight to enable a new interface for imaging.’
The work was published in Nature Scientific Reports.
The experimental setup involved pointing 1,100 fibres at a screen with symbols projected onto it. Two ultrafast lasers fired pulses of light perpendicular to the fibre tips and to each other. A high-speed camera recorded the arrival time of the laser pulses along each fibre and, because the light came from two directions, the differences in arrival time meant a 2D map of the fibre tip positions could be calculated. This information was then used to unscramble the image taken with a conventional camera through the fibre bundle. A beam splitter directed the light onto the two cameras.
The 1,100-fibre prototype gave an image roughly 33 x 33 pixels; the resolution can be increased by adding more fibres. The images produced in the experiments were fairly blurry, according to MIT, because of some ambiguity in the image reconstruction process. The image quality could be improved by interferometric methods, the researchers said.
In a commercial application, the aim would be that the time-of-flight pulses of light would be sent along individual fibres. More pulses would be required to form an accurate picture of the fibres’ positions.
Relying on laser light piped down the fibres themselves ‘is harder than what they have shown in this experiment’, Mona Jarrahi, an associate professor of electrical engineering at the University of California at Los Angeles told MIT News. ‘But the physical information is there. With the right arrangement, one can get it.’
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