Confined Illumination Through Apertureless And Nano-Structured Tapered Optical Fibres

Progress in bionanotechology and in optogenetics requires the production of spots of light with a very precise and controlled intensity profile, polarization and duration. In order to illuminate not more than some tens of rod disks in photoreceptors we have set-up an illumination system consisting of apertureless tapered optical fibres (TOFs) and a laser system. The figure displays isolated intact rod from the Xenopus laevis retina, where the inner segment is drawn inside a suction electrode with a TOF positioned at 90°(left) and SEM image of an apertureless TOF (right). A variety of new TOFs were designed and fabricated generating spots of light with different profiles, ranging from gaussian beam, multispot, Bessel and top hat front wave. Apertureless TOFs or TOFs with very small holes act like an axicon lens. Laser illumination with rapid micro-to milli-second power modulation over 5 orders of magnitude was achieved with a computer controlled assembly of a laser at 491nm, an acousto-optic modulator, a rapid filter wheel equipped with a set of neutral density filters and three ports for optical fibres.