  The lensless endoscope represents the ultimate limit in miniaturization of
imaging tools: an image can be transmitted through a (multi-mode or multi-core)
fiber by numerical or physical inversion of the fiber's pre-measured
transmission matrix. However, the transmission matrix changes completely with
only minute conformational changes of the fiber, which has so far limited
lensless endoscopes to fibers that must be kept static. In this letter we
report for the first time a lensless endoscope which is exempt from the
requirement of static fiber by designing and employing a custom-designed
conformationally invariant fiber. We give experimental and theoretical
validations and determine the parameter space over which the invariance is
maintained.
