  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.
