We propose a pair of related new techniques for measuring the modal power distribution (MPD) of light launched into a multimode fiber (MMF). For modern applications involving laser launches, our method has several potential advantages over ray optics-based methods such as  and recent extensions of them . Instead of relying on a time-averaged measurement of near-field intensity with a CCD camera to spatially resolve the launched power, our method uses a specially designed probe fiber to temporally resolve the launched power. If the source can be modulated fast enough (as is necessary for 10 Gbps serial transmission, for instance), the measurement is straightforward and the calculation of the MPD is trivial. For slower sources,a more involved measurement and inversion algorithm are required.
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