High-resolution aberration-free imaging through GRIN fiber using speckle illumination and compressive sensing

Graded index (GRIN) lenses are essential for <i>in vivo</i> imaging and endoscopy. Implantable probes made from short segments of standard GRIN fiber offer important benefits over commercial GRIN lenses; however, they struggle with aberrations. This study introduces a technique that combines structured speckle illumination with compressive sensing (CS) to enable aberration-free imaging with GRIN fiber-based probes. We develop a wave-optic mode-expansion model to simulate the propagation of coherent illumination and incoherent fluorescence response in an aberrated GRIN probe. Through numerical experiments involving sequential speckle illumination and CS for image reconstruction, we achieve high-resolution, aberration-free imaging throughout the entire field of view (FOV). In contrast to standard microscopy methods, the reconstructed image quality is independent of the fiber length. The proposed method opens avenues to minimally invasive single- and multisite deep brain microscopy.