Image delivery through multimode fibers (MMFs) suffers from modal scrambling which results in a speckle pattern at the fiber output. In this work, we use Deep Neural Networks (DNNs) for recovery and/or classification of the input image from the intensity-only images of the speckle patterns at the distal end of the fiber. We train the DNNs using 16,000 images of handwritten digits of the MNIST database and we test the accuracy of classification and reconstruction on another 2,000 new digits. Very positive results and robustness were observed for up to 1 km long MMF showing 90% reconstruction fidelity. The classification accuracy of the system for different inputs (phase-only, amplitude-only, hologram intensity etc.) to the DNN classifier was also tested.
We demonstrate multimode fiber probe that accomodates dual modality properties for high power ultrashort pulse delivery. A commercially available multimode graded-index (GRIN) fiber is used for two-photon imaging and/or femtosecond laser ablation of Cochlea hair cells. Lensless focusing and digital scanning of ultrashort pulses through the optical fiber is realized using the transmission matrix technique. We investigate the performance and the limitations of the GRIN probe in terms of focusing efficiency and peak power delivery. Selective laser ablation guided by the twophoton image obtained through the GRIN fiber is realized by proximally-only control of the femtosecond laser beam.
We show that a multimode fiber which can be either a graded index fiber or fiber bundle can be used to deliver shaped light to build useful complex parts in areas difficult or impossible to reach with conventional manufacturing tools. We will show complex objects of micrometer scale that are made by additive manufacturing with either a single photon or a 2 photon process. The large effective core area of the multimode fiber allows two orders of magnitude higher pulsed energy transfer while maintaining a spatial and temporal diffraction limit. This enable both subtractive and additive manufacturing.
We demonstrate high power ultrashort pulse delivery through a commercially available multicore fiber (MCF) and a multimode graded-index fiber (GRINF) for imaging and laser ablation. Lensless focusing and digital scanning of ultrashort pulses through the optical fibers is realized using wavefront shaping. We compare the performance of the two systems in terms of focusing efficiency and peak power delivery. Furthermore, we investigate the limitations that nonlinearities induce when high peak power ultrashort pulses are launched in MCFs and GRIN fibers. Proximally-only controlled two-photon fluorescence imaging and laser ablation are demonstrated through both investigated systems.
The need for ultrathin fiber-based devices that can deliver light to confined places in order to perform imaging and/or laser ablation of a desired target has been a research area of significant interest. The current endoscopic devices are based on distal optics and scanning mechanisms to focus and scan the light in the end of the fiber. The distal components are limiting factors for decreasing the size of the device. However, using wavefront shaping techniques, lensless focusing and scanning of a laser focus spot through the fiber can be achieved, enabling a smaller endoscopic tool. In our case, a high power focus spot is created by wavefront shaping of the light through a multicore fiber (MCF), providing the possibility of two-photon fluorescence (TPF) imaging. Femtosecond laser ablation through the endoscopic device can be also a powerful tool for a range of applications. Therefore, we investigate limitations in the maximum peak power that can be delivered through the MCF due to nonlinear effects induced in the fiber cores in the ablation peak power regime. After characterizing the capabilities of our system, we demonstrate that femtosecond pulsed laser ablation can be performed through the MCF.