High-quality fiber microaxicons fabricated by a modified chemical etching method for laser focusing and generation of Bessel-like beams

The fabrication method of the high-quality fiber microaxicons (FMAs) on the endface of the optical fiber was developed. Using several types of the commercially available optical fibers we experimentally demonstrated the fabrication of a high-quality FMA focusing a laser beam into a tiny spot with a FWHM≈0.6λ and Bessel-like field distribution. It was also demonstrated that choosing the appropriate chemical composition of the etching solution makes it possible to change the shape of the FMA tip from conical to hemispherical. This allows one to change the spatial distribution of the output laser beam, which can represent both the Bessel-like beam with a depth of focus of up to 49λ and a very tiny focal spot close to the diffraction limit size. Experimentally measured focusing characteristics of the fabricated FMAs obtained using a homemade collection-mode scanning near-field optical microscope setup demonstrate good agreement with numerical simulations based on the 3D finite-difference time-domain simulations.