Deep Seated Negative Axicon in Selective Optical Fiber Tip and Collimated Bessel Beam

In this letter, we have demonstrated the fabrication of a deep seated negative axicon (DSNA) with micrometer dimensions inside a selective optical fiber tip for the generation of optical Bessel beams (BBs). The DSNA is prepared by simple chemical etching of the fiber tip in hydrofluoric acid under the influence of capillary action. The selective optical fiber has a high numerical aperture of 0.3 and a small core diameter of about $4~\mu \text{m}$ . The higher etching rate of the optical fiber core contributes to fabricate the DSNA, which converts Gaussian-like beam into BB. The central spot of the BB shows quasi-invariant spot-size over the propagation distance of sub-millimeter and centimeter range. The self-protected DSNA can be useful for scanning optical fiber endoscopy applications as well as can be integrated into systems, where non-diffracting BB is preferred.