MFSE is a highly promising endoscopic imaging system that has the potential to replace single-mode fiber and fiber bundle endoscopes due to its ultrathin footprint and high information transmission density. Over the past decades, MFSE has attracted extensive research interest and achieved substantial advancements in improving imaging performance and extending its applications. In this review, we first introduced the wavefront shaping principle to generate focal spots through MMF and procedures to implement all-optical scanning imaging without using mechanical actuators. Developments of three techniques, including transmission matrix measurement method, digital phase conjugation method and phase optimization algorithms, to acquire the mask for wavefront shaping with the SLM are reviewed in detail. Then, we focus on the scanning imaging performance of MFSE and strategies employed to enhance these performance metrics. In addition to some versatile improvements, combinations of some advanced imaging modalities, including confocal endoscopy, two-photon imaging, Raman imaging, and photoacoustic imaging modalities, with the MFSE systems to enhance the imaging performance for specific application scenarios are also presented. The applications of MFSEs that have been demonstrated in literature are introduced. Finally, we summarize the challenges faced by the current MFSE and the potential solutions. Looking forward to the future, if the mentioned problems in the current MFSE system can be overcome, MFSE could initiate its journey toward commercialization. Owing to certain trade-offs among various imaging performance metrics, it is possible to optimize the most crucial performance indicators based on specific application scenarios. The successful commercialization of MFSE is certain to substantially drive the progress of diverse application fields spanning biology, medicine, and industry.Optical endoscopy has become an essential diagnostic and therapeutic approach in modern biomedicine for directly observing organs and tissues deep inside the human body, enabling non-invasive, rapid diagnosis and treatment. Optical fiber endoscopy is highly competitive among various endoscopic imaging techniques due to its high flexibility, compact structure, excellent resolution, and resistance to electromagnetic interference. Over the past decade, endoscopes based on a single multimode optical fiber (MMF) have attracted widespread research interest due to their potential to significantly reduce the footprint of optical fiber endoscopes and enhance imaging capabilities. In comparison with other imaging principles of MMF endoscopes, the scanning imaging method based on the wavefront shaping technique is highly developed and provides benefits including excellent imaging contrast, broad applicability to complex imaging scenarios, and good compatibility with various well-established scanning imaging modalities. In this review, various technical routes to achieve light focusing through MMF and procedures to conduct the scanning imaging of MMF endoscopes are introduced. The advancements in imaging performance enhancements, integrations of various imaging modalities with MMF scanning endoscopes, and applications are summarized. Challenges specific to this endoscopic imaging technology are analyzed, and potential remedies and avenues for future developments are discussed.
(From:https://www.oejournal.org/article/)
