Design of an optimized distal optic for non linear endomicroscopy

The development of a nonlinear endomicroscope is justified by the need for a non-invasive diagnosis tool to assess at the cellular level, in vivo and in live the presence of pathologies like cancer in a patient body. To do so, an important effort has to be made in the miniaturization of the distal head of the endoscope. We report in this paper our work on the characterization of a commercial gradient index (GRIN) lens, especially its possible fluorescence emission and ability to image biological structures. We show that the fluorescence of the peripheral glue of the GRIN lens does not have impact on the fluorescence images but can lead to perturbations to measure fluorescence lifetime and emission spectrum. The axial and lateral resolutions are obtained by imaging 1 μm diameter gold beads. The results show a good agreement with values from the literature. Finally, we simulate an endomicroscope combining an appropriate double-clad fibre (DCF) with the GRIN lens and a tubular piezoelectric scanner (PZT) scanning head. Variations of parameters values like fibre tilt angle and distance between the DCF and the GRIN lens allow to discuss on the performances of this device in terms of working distance (WD), magnification, field of view (FOV) and coupling efficiency.