New paper! Wavefront shaping and imaging through a multimode hollow-core fiber
Wavefront shaping and imaging through a multimode hollow-core fiber
Researchers from Nanoscale Imaging and Metrology group have made significant progress in high-resolution imaging by utilizing multimode hollow-core fibers (MHCFs). Their work introduces innovative methods to enhance imaging resolution and reduce unwanted background noise, setting the stage for advanced applications in deep-tissue imaging and fluorescence detection. The findings were published in Optics Express on October 7, 2024 [1].
Imaging techniques that allow us to see fine details, such as inside biological tissue, rely on advanced optical fibers to guide light. However, traditional solid-core fibers come with challenges: they can create unwanted signals (like auto-fluorescence) and often limit how much detail we can capture because they have a low numerical aperture (NA). NA is a measure of a fiber’s ability to focus light into sharp points, which is crucial for high-resolution imaging. To overcome these challenges, the researchers designed and tested hollow-core fibers (Fig.1) that guide light through an air-filled core rather than a solid material. This approach eliminates much of the background and allows for more precise imaging.
The team demonstrated two key breakthroughs: first, they implemented wavefront shaping, a process that corrects the way light spreads through the fiber. Light traveling through an MHCF can spread out in many directions, creating a random speckle pattern at the output. To fix this, the researchers used a device called a Digital Micromirror Device (DMD) to adjust the shape of the light phase, focusing it into diffraction-limited spots. This process, called wavefront shaping, enabled the fiber to create diffraction-limited focal points (the sharpest focus possible for the given wavelength of light). Second, they used innovative imaging methods. In raster-scan (RS) imaging, they used wavefront shaping to create small focal spots of light, which were scanned across the sample in a grid-like pattern. At each point, the light illuminated the sample, and the reflected or fluorescent signal was collected to build a complete image. In another approach, compressive imaging (CS), the researchers illuminated the sample with a series of random speckle patterns. A computational algorithm then reconstructed the full image from these patterns, making the process faster and more efficient for certain applications.
The hollow-core fibers performed exceptionally well:
- They achieved high-resolution imaging with an NA greater than 0.4, twice surpassing conventional fibers.
- The hollow-core fibers reduced unwanted signals like Raman scattering (light interaction with the material) and auto-fluorescence (spontaneous emission of light by the fiber), which are common issues in traditional fibers.
- The imaging techniques allowed for detailed visualization of fluorescent microparticles, which are tiny beads used to test optical systems.
References:
- Zhouping Lyu and Lyubov V. Amitonova, “Wavefront shaping and imaging through a multimode hollow-core fiber,” Opt. Express 32, 37098-37107 (2024)
