Work Package 1

Presentation

One of the key points of this project is the study of the transmission matrices of multimode fibers. This mathematical object perfectly characterizes the light propagation in the fiber. However, its measurement is very sensitive to the accuracy with which we can generate the modes of the fiber.  This is particularly true in the case of low coupling between the modes since the matrix contains many weak off-diagonal components. Small inaccuracies in the preparation of the modes lead to large discrepancies in the estimation of the mode coupling and the mode dependent losses.

Our first objective is to develop new tools to accurately excite the modes of multimode fibers. Compared to applications in scattering media, a high resolution is not necessary, but the accuracy of the amplitude and phase modulation is of major importance. Moreover, the refresh rate of current liquid crystal modulators does not exceed 100 frames per second. It forbids the fast characterization of the channels, which is required for telecommunications applications. We plan to use a high-speed micro-mirror modulator for a fast and accurate generation of the modes of multimode fibers. We also want to be able to optimize the system to adapt to the defects of the optical system using a feedback loop.

A typical setup for exciting the fiber modes using a Digital Micro-mirror Device with a spatial frequency filtering system to achieve amplitude and phase modulation.

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