February 6, 2020 -- A team of researchers in Japan has developed a technique using multimode fiber in combination with an optical phased-array chip for single-pixel imaging in biomedical applications. The work will be presented at the 2020 Optical Fiber Communication Conference and Exhibition, held March 8 to 12 in San Diego.
The researchers from the University of Tokyo apply pseudorandom speckle patterns using ultrathin endoscopy and in vivo neural imaging. This enhances the spatial resolution of the preexisting equipment.
"This is because unlike a focused spot, the random speckle illumination consists of interference patterns that contain higher spatial frequency elements," said Taichiro Fukui, a doctoral student at the University of Tokyo, in a press release.
Integrating multimode fiber with output on an optical phased-array chip splits light into independent phase shifters, creating different random patterns to illuminate the target. This process dramatically increases the resolution used with the optical phased array, according to Fukui.
A simple matrix multiplication operation applied to the output allows for a quick reconstruction of the target. For example, the team was able to image 490 resolvable points using 128 phase shifters and 600 illumination patterns. This result is comparable to other multimode fiber methods, but with a smaller, cheaper, and faster technique.
Pending several improvements -- such as reducing the on-chip losses by integrating optical amplifiers on the optical phased-array chip -- the technique can be used to develop small, high-speed, low-cost, and high-resolution imaging technologies. Applications of the technology might include optical sensing and imaging such as flow cytometry and optical coherence tomography.