Transformation of the intensity profile for a step-index multimode fiber core

The launch light conditions for the 200-mu m core step-index multimode fiber have been defined by the International Electrotechnical Commission. However, we found conditions that give results outside the specified values, even when the launch lights are within the standardized encircled angular flux requirements. We report the transformation of the intensity profile for the fiber core showing non-uniform intensity distributions at practical link lengths. These distributions cause a gap compared to classical geometric models. We verified our proposed approach for a launch light study by using far- and near-field patterns of the fiber.