Fig. 1.

Confocal imaging with a DCF. (a) Light propagation schematic. Illumination light originates from the core of the DCF defined by its MFD (taken at the 1/e² intensity point) and numerical aperture (illumination half-angle β). It is collimated with a lens of focal length f_coll and fills an objective lens (of focal length f_obj, aperture 2a_obj, illumination cone half-angle α). Light collection is performed through the inner cladding of the DCF (of diameter d). Light propagates along the z-axis and r_f, r_p and r_s define the radial coordinates at the fiber, objective lens pupil and sample planes, respectively. (b) Optical sectioning (u_1/2) for a perfect plane reflector as a function of the ratio d/MFD for different values of the pupil filling factor A. c) Excitation efficiency (η) for a perfect plane reflector at focus (u = 0) as a function of the ratio d/MFD for different values of A.