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Multimode fiber-based endoscopes have recently emerged as a tool for minimally invasive endoscopy in tissue, at depths well beyond the reach of multiphoton imaging. Here, we demonstrate label-free second-harmonic generation (SHG) microscopy through such a fiber endoscope. We simultaneously fully control the excitation polarization state and the spatial distribution of the light at the fiber tip, and we use this to implement polarization-resolved SHG imaging, which allows imaging and identification of structural proteins such as collagen and myosin. We image mouse tail tendon and heart tissue, employing the endoscope at depths up to 1 mm, demonstrating that we can differentiate these structural proteins. This method has the potential for enabling instant andin situdiagnosis of tumors and fibrotic conditions in sensitive tissue with minimal damage.

In this work, we demonstrate a four-core multicore fiber photonic lantern tip/tilt wavefront sensor. To diagnose the low-order Zernike aberrations, we exploit the ability of the photonic lantern to encode the characteristics of a complex incoming beam at the multimode facet of the sensor to intensity distributions at the multicore fiber output. Here, we provide a comprehensive numerical analysis capable of predicting the performance of fabricated devices and experimentally demonstrate the concept. Two receiver architectures are implemented to discern tip/tilt information by (i) imaging the four-core fiber facet on a 2D detector and (ii) direct power measurement of the single mode outputs using a multicore fiber multiplexer and photodetectors. For both receiver schemes, an angular detection window of$\sim <\#comment/>{0.4}^{\circ <\#comment/>}$at 1064 nm can be achieved. Our results are expected to further facilitate the development of intensity-based fiber wavefront sensors for adaptive optics systems.

The PolyOculus technology produces large-area-equivalent telescopes by using fiber optics to link modules of multiple semi-autonomous, small, inexpensive, commercial-off-the-shelf telescopes. Crucially, this scalable design has construction costs that are$><\#comment/>10\times <\#comment/>$lower than equivalent traditional large-area telescopes. We have developed a novel, to the best of our knowledge, photonic lantern approach for the PolyOculus fiber optic linkages that potentially offers substantial advantages over previously considered free-space optical linkages, including much higher coupling efficiencies. We have carried out the first laboratory tests of a photonic lantern prototype developed for PolyOculus, and demonstrated broadband efficiencies of$\sim <\#comment/>91\mathrm{\%<\#comment/>}$, confirming the outstanding performance of this technology.