We propose and demostrate a novel all-optical correlator based on modal dispersion in multimode fiber. The incident optical signal is copied into different modes in a large core high numerical aperture step-index multimode fiber and time delay is introduced by modal dispersion. We use a mask with slits as a space filter to select the modes needed. A correlator of the mask and input signal is achieved at the output end. Thanks to the use of modal dispersion, the correlator is nearly independent of the wavelength and bandwidth of input signal. By adjusting slits on the mask, the target patterns of the correlator can be changed easily.
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