We report here the characteristics of dark hollow beams (DHBs) generated using negative micro-axicons fabricated via
selective chemical etching process in the tip of optical fibers. The DHB output from the etched fibers were further
manipulated to generate single and multiple period optical bottle beams, 0th- and 1st- order Bessel beams and astigmatic
Bessel beams and beams with helical wavefront. Selective excitation of the guided modes in single and multimode
optical fibers with V-numbers ranging from 2.405 - 5.69 are etched to different negative cone dimensions and are used
to generate in a controllable way DHBs and related optical beams. Negative cones are etched in the fiber tips via
selective chemical etching process wherein the different etch rates of the fiber core and cladding dopants and dopant
concentration results in different cone angles and cone depths. Input laser beam guided through the optical fiber diffracts
and refracts at the tip generating beams with one or many bright rings surrounding the dark central spot. By positioning
the DHB in the front focal plane of a bi-convex lens we generate Bessel beams whose characteristics are compared with
that generated using positive cone etched in the fiber tip and bulk axicon. Under certain excitation conditions we also
observe helical wavefront DHBs with phase dislocation embedded in the beam.
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