Rice graduate student Yicheng Wu demonstrates the SAVI prototype, which is able to capture fine details of an object from a distance, effectively replacing a large telephoto lens. The prototype camera is on a motorized track in the foreground at left, while a laser at right creates a speckle pattern on the target, a fingerprint. Photo by Jeff Fitlow
A unique camera that can capture a detailed micron-resolution image from a distance uses a laser and techniques that borrow from holography, microscopy and “Matrix”-style bullet time.
A prototype built and tested by engineers at Rice and Northwestern universities reads a spot illuminated by a laser and captures the “speckle” pattern with a camera sensor. Raw data from dozens of camera positions is fed to a computer program that interprets it and constructs a high-resolution image.
The system known as SAVI – for “Synthetic Apertures for long-range, subdiffraction-limited Visible Imaging” — doesn’t need a long lens to take a picture of a faraway object. The prototype only works with coherent illumination sources such as lasers, but Ashok Veeraraghavan, a Rice assistant professor of electrical and computer engineering, said it’s a step toward a SAVI camera array for use in visible light.
“Today, the technology can be applied only to coherent (laser) light,” he said. “That means you cannot apply these techniques to take pictures outdoors and improve resolution for sunlit images – as yet. Our hope is that one day, maybe a decade from now, we will have that ability.”
The technology is the subject of an open-access paper in Science Advances.
Labs led by Veeraraghavan at Rice and Oliver Cossairt at Northwestern’s McCormick School of Engineering built and tested the device that compares interference patterns between multiple speckled images. Like the technique used to achieve the “Matrix” special effect, the images are taken from slightly different angles, but with one camera that is moved between shots instead of many fired in sequence.
Veeraraghavan explained the speckles serve as reference beams and essentially replace one of the two beams used to create holograms. When a laser illuminates a rough surface, the viewer sees grain-like speckles in the dot. That’s because some of the returning light scattered from points on the surface has farther to go and throws the collective wave out of phase. The texture of a piece of paper – or even a fingerprint – is enough to cause the effect.
he SAVI team’s breakthrough was the discovery that it could put the light source on the same side as the camera rather than behind the target, as in transmission microscopy, Cossairt said. He spent three months at Rice to develop the system with Holloway and others in Veeraraghavan’s lab.
“We started by making a larger version of their microscope, but SAVI has additional technical challenges. Solving those is what this paper is about,” Veeraraghavan said.
