A method that can spatially characterize gratings with grating strength |k|L up to 10 is presented. The grating is thermally chirped, which increases the transmissivity through the grating. The complex reflectivity spectrum is measured using optical-frequency-domain reflectometry, and the spatial profile is reconstructed using the time-domain layer-peeling algorithm. The spatial profiles of a uniform grating with grating strength |k|L = 8.25 (-66-dB minimum transmissivity) and a distributed-feedback fiber laser grating with grating strength |k|L = 7.5 are accurately reconstructed from the measured complex reflection spectrum.
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