An ultraslim all-fiber microendoscope for depth-resolved imaging

We demonstrate an ultraslim all-fiber microendoscope for depth-resolved imaging that integrates a gradient-index (GRIN) fiber and an imaging fiber bundle. The desired imaging depth is achieved through a high-precision adjustment of the length of the GRIN fiber. A fusion splicing of this fiber to an imaging fiber bundle, with provisions for a carefully tailored adiabatic conical transition region, keeps these fiber components robustly aligned, enabling a high-quality image transmission with no compromise on fiber-probe flexibility. With the maximum outer diameter of this microendoscope scalable down to ≈50 μm, the range of envisaged applications spans from depth-resolved brain imaging, deep optical biopsy, microendoscopy, and optical coherence tomography to single-neuron imaging and single-cell neuromodulation studies in awake animal models.