Real-time mode-modulation enhanced stable imaging through flexible multimode fiber

Multimode fibers (MMFs) are poised to transform minimally invasive endoscopy by providing hair-thin probes capable of high-resolution imaging deep within biological tissues. Still, their dynamic instability and the limited transmission capacity of the ultra-thin core hinder their clinical use. We propose a method that overcomes both their dynamic instability and their performance limitations, enabling stable, high-fidelity real-time imaging through a flexible, ultra-thin MMF. During operation, a real-time rapid calibration routine identifies the fiber's current bending state in approximately 75 milliseconds by sequentially projecting focusing wavefronts as a state probe. This swift state recognition enables the synchronous retrieval of a corresponding singular vector from a pre-calculated database. The retrieved singular vector is then projected onto the input beam to perform mode modulation, thereby selectively exciting the fiber's internal intrinsic modes and injecting the beam into the eigenchannels for transmission. This synergy of stabilization and enhancement improves the imaging performance of flexible MMFs without introducing additional time loss, effectively overcoming the MMF's susceptibility to disturbances and successfully resolving the long-standing performance trade-off between the miniaturization of ultra-thin fibers and image quality. We validated our method by dynamically flexing 40-µm and 105-µm-core MMFs, achieving substantial improvements in image fidelity. For handwritten digits, the peak signal-to-noise ratio (PSNR) and structural similarity (SSIM) were enhanced by an average of 7.75 dB and 0.069, respectively. For complex natural scenes, the PSNR and SSIM were enhanced by 0.90 dB and 0.063. In the imaging of a biological specimen, the edge preservation index was enhanced by an average of 12.10%. By providing a robust, fast, and simple solution, our work removes a critical roadblock for MMF-based imaging and establishes a practical pathway toward the clinical deployment of flexible, high-resolution, hair-thin fiber endoscopes in dynamic environments.