A method and an apparatus for measuring a profile of a beam output from a randomly-coupled multi-core fiber are provided. An apparatus includes a light source, a measurement unit, and an analysis unit. Light output from the light source is input in one or more of a plurality of spatial modes of the fiber at an input end of the fiber. The measurement unit measures a sum of intensity profiles of individual light components output from respective ones of the plurality of spatial modes by averaging a component of interference between the plurality of spatial modes in a beam profile of combined light output from the plurality of spatial modes at an output end of the fiber. The analysis unit calculates an MFD and/or Aeff of the fiber based on the sum of the intensity profiles of the individual light components obtained by the measurement unit.
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