Translation memory effect in square-core multimode optical fibers

Endoscopy is a family of in vivo in-depth imaging methods. It involves inserting a probe (usually a bundle of fibers) into an organism or tissue to guide the light to the surface and make the image. In order to reduce the diameter (and therefore the invasive character) of the probe, it has recently been proposed to use a single multimode fiber: it could transmit images of a few thousand pixels with the diameter of a hair (100 µm). However, the input image is not faithfully transmitted by a fiber, as different modes propagate through the fiber at different speeds. Several methods have been proposed to overcome this difficulty, but all rely on a fiber calibration, which is very sensitive to its state (geometry, temperature, etc.). In this thesis, we have highlighted and characterized an effect, called memory effect, which connects a transformation of the luminous pattern in fiber input to the pattern in output. This phenomenon exists in square-core multimode fibers and would potentially allow imaging without calibration.

Jury :

M. SYLVAIN GIGAN
M. ESBEN RAVN ANDRESEN
Mme PATRICIA SEGONDS
Mme ELISE GHIBAUDO