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1. Connected-tube MPP Model for unsupervised 3D fiber detection

   https://doi.org/10.2352/ISSN.2470-1173.2020.14.COIMG-305  

   Li, Tianyu; Aguilar, Camilo G.; Agyei, Ronald F.; Hanhan, Imad A.; Sangid, Michael D.; Comer, Mary L. (January 2020, Electronic Imaging)

   Fast track article for IS&T International Symposium on Electronic Imaging 2020: Computational Imaging proceedings. 

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2. Two-photon, fiber-coupled, super-resolution microscope for biological imaging

   https://doi.org/10.1063/5.0075012  

   Heffernan, Brendan M.; Riley, Peter S.; Supekar, Omkar D.; Meyer, Stephanie A.; Restrepo, Diego; Siemens, Mark E.; Gibson, Emily A.; Gopinath, Juliet T. (March 2022, APL Photonics)

   Imaging sub-diffraction dynamics of neural nanostructures involved in behaviors such as learning and memory in a freely moving animal is not possible with existing techniques. Here, we present a solution in the form of a two-photon (2P), fiber-coupled, stimulated emission depletion microscope and demonstrate its capabilities by acquiring super-resolution imaging of mammalian cells. A polarization-maintaining fiber is used to transport both the 2P excitation light (915 nm) and the donut-shaped depletion beam (592 nm), which is constructed by adding two temporally incoherent and orthogonally polarized Hermite–Gaussian fiber modes. The fiber output is insensitive to bending or temperature changes and is the first demonstration toward deep tissue super-resolution imaging in awake behaving animals. 

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3. Inverse-designed large field-of-view polychromatic metalens for tri-color scanning fiber endoscopy

   https://doi.org/10.1038/s44172-025-00377-7  

   Xie, Ningzhi; Zhou, Zhihao; Fröch, Johannes E; Carson, Matthew D; Majumdar, Arka; Seibel, Eric J; Böhringer, Karl F (December 2025, Communications Engineering)

   Abstract Metalenses, with their ultrathin thicknesses and their ease for achieving ultra small diameters, offer a promising alternative to refractive lenses in miniaturized imaging systems, such as endoscopes, potentially enabling applications in tightly confined spaces. However, traditional metalenses suffer from strong chromatic aberrations, limiting their utility in multi-color imaging. To address this limitation, here we present an inverse-designed polychromatic metalens with a diameter of 680 μm, focal length of 400 μm, and low dispersion across 3 distinct wavelengths at 643 nm, 532 nm, and 444 nm. The metalens collimates and steers light emitted from a scanning fiber tip, generating scanning beams across a 70° field-of-view to provide illumination for a scan-based imaging. The metalens provides a close-to-diffraction-limited 0.5° angular resolution, only restricted by the effective aperture of the system. The average relative efficiency among three design wavelengths is around 32% for on-axis angle and 13% averaged across the entire field-of-view. This work holds promise for the application of metalenses in endoscopes and other miniaturized imaging systems. 

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4. Ptycho-endoscopy on a lensless ultrathin fiber bundle tip

   https://doi.org/10.1038/s41377-024-01510-5  

   Song, Pengming; Wang, Ruihai; Loetgering, Lars; Liu, Jia; Vouras, Peter; Lee, Yujin; Jiang, Shaowei; Feng, Bin; Maiden, Andrew; Yang, Changhuei; et al (December 2024, Light: Science & Applications)

   Abstract Synthetic aperture radar (SAR) utilizes an aircraft-carried antenna to emit electromagnetic pulses and detect the returning echoes. As the aircraft travels across a designated area, it synthesizes a large virtual aperture to improve image resolution. Inspired by SAR, we introduce synthetic aperture ptycho-endoscopy (SAPE) for micro-endoscopic imaging beyond the diffraction limit. SAPE operates by hand-holding a lensless fiber bundle tip to record coherent diffraction patterns from specimens. The fiber cores at the distal tip modulate the diffracted wavefield within a confined area, emulating the role of the ‘airborne antenna’ in SAR. The handheld operation introduces positional shifts to the tip, analogous to the aircraft’s movement. These shifts facilitate the acquisition of a ptychogram and synthesize a large virtual aperture extending beyond the bundle’s physical limit. We mitigate the influences of hand motion and fiber bending through a low-rank spatiotemporal decomposition of the bundle’s modulation profile. Our tests demonstrate the ability to resolve a 548-nm linewidth on a resolution target. The achieved space-bandwidth product is ~1.1 million effective pixels, representing a 36-fold increase compared to that of the original fiber bundle. Furthermore, SAPE’s refocusing capability enables imaging over an extended depth of field exceeding 2 cm. The aperture synthesizing process in SAPE surpasses the diffraction limit set by the probe’s maximum collection angle, opening new opportunities for both fiber-based and distal-chip endoscopy in applications such as medical diagnostics and industrial inspection. 

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5. Fiber Seismic Network on the Moon

   https://doi.org/10.1785/0220230067  

   Wu, Wenbo; Zhan, Zhongwen; Panning, Mark; Klesh, Andrew (February 2024, Seismological Research Letters)

   Abstract Internal structures of the Moon are key to understanding the origin and evolution of the Earth–Moon system and other planets. The Apollo Passive Seismic Experiment detected thousands of lunar seismic events and vastly improved our understanding of the Moon’s interior. However, some critical questions like the state and composition of the core remain unsolved largely due to the sparsity of the Apollo seismic stations and the strong scattering of seismic waves in the top layer of the Moon. In this study, we propose the concept of a fiber seismic network on the Moon and discuss its potential in overcoming the challenges in imaging deep Moon structures. As an emerging technique, distributed acoustic sensing (DAS) can provide a cost-efficient solution for large-aperture and dense seismic network deployment in harsh environments. We compute lunar synthetic seismograms and evaluate the performance of DAS arrays of different configurations in retrieving the hidden core reflected seismic phase ScS from the strong scattered waves. We find that, compared to a sparse conventional seismic network, a fiber seismic network using tens of kilometers of cable can dramatically increase the chance of observing clear ScS by array stacking. Our results indicate that DAS could provide new opportunities for the future lunar seismic surveys, but more efforts and further evaluations are required to develop a space-proof DAS. 

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