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Mode-group multiplexing (MGM) can increase the capacity of short-reach few-mode optical fiber communication links while avoiding complex digital signal processing. In this paper, we present the design and experimental demonstration of a novel mode-group demultiplexer (MG DeMux) using Fabry-Perot (FP) thin-film filters (TFFs). The MG DeMux supports low-crosstalk mode-group demultiplexing, with degeneracies commensurate with those of graded-index (GRIN) multimode fibers. We experimentally demonstrate this functionality by using a commercial six-cavity TFF that was intended for 100 GHz channel spaced wavelength-division multiplexing (WDM) system.

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.

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.