Seeing through multimode fibers with real-valued intensity transmission matrices

Image transmission through multimode optical fibers has been an area of immense interests driven by the demand for miniature endoscopes in biomedicine and higher speed and capacity in telecommunications. Conventionally, a complex-valued transmission matrix is obtained experimentally to link the input and output light fields of a multimode fiber for image retrieval, which complicates the experimental setup and increases the computational complexity. Here, we report a simple and high-speed method for image retrieval based on our discovery of a pseudo-linearity between the input and output light intensity distributions of multimode fibers. We studied the impact of several key parameters to image retrieval, including image pixel count, fiber core diameter and numerical aperture. We further demonstrated that a wide variety of input binary images could be faithfully retrieved from measured output speckle patterns using this method, promising to be useful for highly miniaturized endoscopy in biomedicine and spatial-mode-division multiplexing in telecommunications.