Ultra-high-speed imaging serves as a foundation for modern science. While in biomedicine, optical-fiber-based endoscopy is often required for in vivo applications, the combination of high speed with the fiber endoscopy, which is vital for exploring transient biomedical phenomena, still confronts some challenges. We propose all-fiber imaging at high speeds, which is achieved based on the transformation of two-dimensional spatial information into one-dimensional temporal pulsed streams by leveraging high intermodal dispersion in a multimode fiber. Neural networks are trained to reconstruct images from the temporal waveforms. It can not only detect content-aware images with high quality, but also detect images of different kinds from the training images with slightly reduced quality. The fiber probe can detect micron-scale objects with a high frame rate (15.4 Mfps) and large frame depth (10,000). This scheme combines high speeds with high mechanical flexibility and integration and may stimulate future research exploring various phenomena in vivo.

Single fiber imaging has evolved into a powerful method for detecting minute objects in narrow spaces. However, existing systems are not conducive to imaging dynamic objects at depth due to their bulky probes, time-consuming scanning acquisition methods, and transmissive illumination mode. Minimally invasive reflection mode imaging with high spatial and temporal resolution remains an open challenge. Here, a precise and high-speed imaging scheme without scanning is proposed. Multimode fiber imaging technology is incorporated into an all-fiber aberration-free precision detection system. High temporal resolution (5000 fps) detection of tiny natural scenes is experimentally realized by optimizing the approximation of the inverse transmission matrix in a simple and compact setup. The system can display the detected screen in real-time and the computational imaging with a large depth of field (1 mm) is enabled by jointly learning. The recovery results are superior compared to typical deep neural networks. The demonstrated scheme offers a new possibility for many applications, for example, microendoscopy, all-optical computing, and remote high-speed video transmission.

Multimode fibers with high information capacity and ultra-thin diameter offer new possibilities for non-invasive endoscopy and remote high-speed secure communication. However, due to their sensitivity, special demands are thus raised on the light sources, which act as both lighting and information carrier. We build a single-arm multimode fiber image transmission system. The impact of five different sources on transmission quality is systematically compared and analyzed. High-quality transmission of complex grayscale patterns is achieved with inverse transmission matrix. The measured structural similarity exceeds 0.65. Experimental results indicate that random fiber laser with high time-domain stability is suitable for single-fiber imaging. This work is conducive to further study of fiber imaging and provides guidance for novel fiber communication and flexible endoscopy.

The realization of beam self-cleaning in a cavity is more challenging than in the outside cavity. The peak power of intracavity pulses needs to be high to reach the threshold of beam self-cleaning, which usually relies on additional diffraction grating to compress pulses in a positive-dispersion cavity. Here, it is first experimentally and numerically demonstrated that self-cleaning can be observed in an all-fiber high peak-power Er-doped spatiotemporal mode-locked (STML) laser at all-negative-dispersion. Through the nonlinear compression of graded-index multimode fiber, the pulses are compressed along with the emergence of beam self-cleaning. Besides, the inherent disorder of multimode fiber accelerates the self-cleaning process. The intracavity pulse energy of ≈13 nJ with a pulse duration of 734.5 fs is derived under a highly multimode excitation, with an output pulse energy of 2.33 nJ. The pulse energy is a nearly fourfold improvement over the previous report in all-fiber STML at 1.5 𝛍m. Temporal-dependent characteristics and nonlinear polarization dynamics of beam self-cleaning are also experimentally uncovered. It is demonstrated that the STML fiber laser will enable new insights into nonlinear pulse propagation in cavities and related applications.