Single-Fiber Endoscope Provides Four-Fold Resolution

The researchers predict that by boosting the resolution, a fiber endoscope about two-tenths of a millimeter in diameter—just thicker than a human hair—could resolve about 80,000 pixels at a resolution of about three-tenths of a micrometer.

The working prototype is a rigid endoscope that uses a multimode optical fiber; random patterns of light generated by a spatial light modulator pass through a fiber and illuminate a region near the fiber tip. The light reflecting off the object returns through the fiber to a computer, which in turn measures the reflected power of the light and uses adaptive algorithms to reconstruct an image. Surprisingly, the researchers found that the random intensity patterns mixed the modes that can propagate through the fiber, producing four times as much detail in the image. The study describing the fiber endoscope was published on January 15, 2013, in Optics Express.

“Previous single-fiber endoscopes were limited in resolution to the number of modes in the fiber, so this is a fourfold improvement,” said lead author Joseph Kahn, PhD, a professor of electrical engineering at the Stanford. “The unconventional algorithm we used for image reconstruction was the key to revealing the hidden image detail.”

The main limiting factor at this point is that the fiber must remain straight, since bending a multimode fiber scrambles the image beyond recognition. To keep it so, the fiber is placed in a thin needle for insertion. The result is a combination of a rigid endoscope, which uses relatively thick, rod-shaped lenses to yield good images, and a flexible endoscope that usually employs bundles of tens of thousands of individual fibers, each conveying a single pixel of the image. Both types of endoscopes are bulky and have limited resolution.

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