Ever growing importance of optical fiber technology in the fields of data transfer, sensors, imaging or advanced light generation pushes the effort of integration of functional microoptical elements in the fiber based systems . Here we present a femtosecond (fs) pulse based 3D laser lithography (3DLL) of free-form polymeric structures on tips of single mode optical fibers. Fabricated objects include both microoptical elements (for instance aspheric microlenses) and woodpile photonic crystals. Also, freeform 3D monoliths, combining several of these elements into one functional component, are integrated on the tip of the fiber [2, 3]. Methods allowing enhancement and large scale fabrication, such as advanced fiber holders or synchronization of linear stages and galvo-scanners, are discussed.
In contrast to standard lithographic techniques, fs 3DLL can be employed for processing a wide array of materials, including otherwise non-processable (non-photosensitized) polymers. It is relevant to the most of the fields where microoptics are applied, as photoinitiators introduce additional short wavelength (<400 nm) absorption to the material, resulting in information loss, lower optical damage threshold, parasitic fluorescence and, therefore, should be avoided if possible. One material that could be structured in this fashion is hybrid organic-inorganic zirconium containing SZ2080 which displays many favourable qualities such optical transparency and low shrinkage . Here we provide notes on peculiarities of 3DLL of a pure SZ2080. Experimental results show that compared to photosensitized counterpart photoinitiator-free polymer has comparable characteristics when it comes to fabrication throughput, optical properties (transmission spectra and surface roughness), mechanical strength (structure survival rate and adhesion to the substrate) as well as others. A physical phenomenon behind fs structuring of pure material such as interplay between multiphoton absorption and avalanche ionization  is highlighted.
Optical resiliency of microoptical elements created with this technology is investigated and their feasibility in applications reliant on high light intensities is shown. The most resistant material was found to be non-photosensitized SZ2080 as microlenses produced out of such material can withstand peak intensities of 515 nm 300 fs 200 kHz laser in range of GW/cm^2 within minutes to hours . Such results tie well with earlier findings showing that optical damage threshold of pure materials films are in fact higher than that of a photosensitized material . Additionally, CW 405 nm laser operating at the intensity of 8.66 GW/cm^2 cannot damage microoptical elements produced out of SZ2080 in pure and photosensitized form even after tens of hours of continuous exposure. Further comparison with the optical resiliency of microoptical elements fabricated out of other lithographic materials such as Ormocer and SU8 are made.
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With fast development of interdisciplinary fields relying on various micro- and nano-structures (for instance, microfluidics, micromechanics or biomedicine) the pressure is on for the fabrication technologies to meet the ever increasing demands for the manufacturing throughput and applicable materials. Glass is one of the key substances used through the ages for creation of various objects, yet till this day the possibilities to process it in micro-scale in 3D fashion is limited. Here, we provide examples of structures that can be created out of glass by applying fs laser assisted selective etching. These include molds for micromechanical part creation, high-quality microchannels and microneedle arrays. The possibilities, limitations and perspectives of this microfabrication technology are discussed, comparisons with additive manufacturing are provided.