Israeli scientists have found a new way to obtain images through “scattering” materials such as frosted glass or leather and even “see in the corners.”
Many studies in recent years have focused on correcting distraction, especially for medical applications.
But the new trick reported in Nature Photonics, is fast, simple and uses natural light, not lasers.
It uses a so-called spatial light modulator to “cancel” scattering, which makes objects opaque or non-reflective.
A camera that can “see around the corners” attracted a lot of attention in 2010, using a series of synchronized laser pulses to illuminate a scene and understand what was around the corner from the time of the reflections.
The prototype device was just one of many research efforts trying to solve the distraction problem.
But for some applications, the “flight time” approach used by the laser camera is not enough.
“If you want to look to see an embryo developing inside an egg, but the eggshell scatters everything, or you want to look through the skin, scattering is the main enemy there, and flight time is not a good solution.” explained senior author of the study Prof. Yaron Silberberg.
For these problems, Prof. Jaron Silberberg and colleagues at the Weizmann Institute of Science in Israel have expanded the scope of what spatial light modulators (SLMs) can do.
SLMs modify the so-called incoming light beam phase. Like a series of waves in the ocean that race over rocks or surfers, waves in the light can be slowed down or redirected when they hit scattering materials.
SLMs consist of an array of pixels that can correct this by selectively slowing down some parts of the beam and allowing others to pass intact – when an electric field is applied to a pixel, it changes the speed at which light passes through it.
Prof. Jaron Silberberg and his team first created their SLM by illuminating a normal lamp through a highly scattering plastic film and allowing the computer to fine-tune the SLM until they could see a clear image of the lamp through the film.
By keeping SLM like this, they were able to obtain clear images of other objects through the film – SLM effectively turns the film back into a blank slate.
“What we’ve shown is that you don’t need lasers – everyone else did it with lasers, and we’ve shown that you can do it with incoherent light from a lamp or the sun – natural light.” Prof. Jaron Silberberg.
But then the team realized that the same approach could work in reflection – that is, not by passing through a scattering material, but by bouncing off it, like the case of light bouncing off a wall in a corner.
They then showed that the procedure worked just as well when light from an object bounced off a sheet of paper; SLM can “learn” how to eliminate the distracting effect of paper, making it an almost perfect reflector.
As Prof. Jaron Silberberg says: “You can take a piece of wall and effectively turn it into a mirror, and that’s the part that makes everyone raise their eyebrows.”
However, he said the main use of the technique would be in biological and medical research – especially to deal with highly scattered white matter in neurological images – and not in the business of looking through thin materials or around corners.
“I do not want to say that he solves the problems of secret organizations and Peeping Toms, etc., it will not be so simple. But the principle is there.
“We haven’t started dealing with these things … but I see how much interest this arouses, and I think maybe we should.”