Vortex-Bessel beam generation by 3D direct printing of an integrated multi-optical element on a fiber tip.

Shaping light beams as they propagate out of the tips of optical fibers is a desired ability, as the light could be tailored for various applications in a miniaturized, integrated, and cost-effective manner. However, fabricating sophisticated refractive elements directly onto fibers is challenging. By using 3D-direct laser writing (3D-DLW), high-quality optical devices could be fabricated directly on top of the fiber's facet by the two-photon absorption process. Here, we demonstrate how a high-order Bessel beam carrying orbital angular momentum (OAM) could be generated by using this lithography process. The beam is shaped using an integrated micro-optical system that consists of a twisted axicon and parabolic lens in an adapted fiber configuration. This work provides the analysis and measurements of the generated beam, along with simulated predictions. The far-field pattern, at a distance of 2 mm from the fiber, was examined, and we have found that the size of the central ring remained nearly unchanged, as expected for this type of beam. The beam's OAM value was measured using either an interference pattern or a mode convertor. Furthermore, the near-field and far-field Bessel beam profiles were investigated simultaneously at various laser power values, reaching intensities of up to 3.8 MW/cm2. This work may pave the way for future integrated beam manipulation on fibers, enabling the use of higher laser outputs.

Integrated orbital angular momentum mode sorters on vortex fibers.

We design, fabricate, and characterize integrated mode sorters for multimode fibers that guide well-separated vortex modes. We use 3D direct laser printing to print a collimator and a Cartesian to a log-polar mode transformer on the tip of the fiber. This polarization insensitive device can send different modes into different exit angles and is therefore useful for space division multiplexed optical communication. Two types of fibers with two corresponding sorters are used, enabling the sorting of either four or eight different modes in a compact and robust manner. The integration of the vortex fiber and multiplexer opens the door for widespread exploitation of orbital angular momentum (OAM) for data multiplexing in fiber networks.

Structuring light using solgel hybrid 3D-printed optics prepared by two-photon polymerization.

Three-dimensional direct laser writing based on a two-photon polymerization process of hybrid organic-inorganic material was used to print micrometer-scale refractive phase elements that were designed to manipulate incoming Gaussian beams into line and square intensity-flattened profiles. Here we present new results of shaping light beams, enabled by tailoring a two-photon absorption process for printing hybrid material structures based on a fast solgel process. The optical design and calculations of the optical elements are described, along with characterization of their performance in manipulating incoming light beams. The novelty described in this work, to the best of our knowledge, is the implementation of 3D solgel materials as better and improved micro-optics. This new ability provides upgraded 3D high resolution and smooth, printed optical phase structures using tailored hybrids with improved optical and mechanical properties compared to standard common photoresists. This opens new and exciting opportunities for compact and robust beam shaping by reaching glassy material properties and overcoming limitations of organic polymers.

Tailoring lens functionality by 3D laser printing.

Conversion of a Gaussian beam into a top-hat beam or to an annular beam is demonstrated using 3D direct laser printing. Micron-scale refractive phase elements were designed and printed directly on standard commercially available lenses. These structures modify the phase of the incoming beam into either three intensity-flattened profiles, having line, square, or circular shapes, or to an annular beam profile. This method to functionalize lenses opens new and exciting opportunities for compact and robust beam shaping, as well as for reduction of the aberrations of the lens itself.

3D whispering-gallery-mode microlasers by direct laser writing and subsequent soft nanoimprint lithography.

We demonstrate the realization of 3D whispering-gallery-mode (WGM) microlasers by direct laser writing (DLW) and their replication by nanoimprint lithography using a soft mold technique ("soft NIL"). The combination of DLW as a method for rapid prototyping and soft NIL offers a fast track towards large scale fabrication of 3D passive and active optical components applicable to a wide variety of materials. A performance analysis shows that surface-scattering-limited Q-factors of replicated resonators as high as 1×105 at 635 nm can be achieved with this process combination. Lasing in the replicated WGM resonators is demonstrated by the incorporation of laser dyes in the target material. Low lasing thresholds in the order of 15 kW/cm2 are obtained under ns-pulsed excitation.

Comparative analysis of direct laser writing and nanoimprint lithography for fabrication of optical phase elements.

We report a comparison between two commercially available methods for printing phase shaping optical microstructures. Phase elements that convert a zero-order Hermite-Gaussian (HG00) mode into higher-order modes (HG10, HG01, HG20, and HG02) were fabricated by 3D-direct laser writing (3D-DLW) and nanoimprint lithography (NIL). The structures in each method were characterized and the corresponding beam qualities were analyzed. The direct comparison of equivalent optical devices enables us to reveal the limitations and advantages of the two fabrication methods in order to optimize the fabrication of useful optical microstructure devices. 3D-DLW enables sharper edges and a straightforward lithography process, while NIL enables fabrication of thinner elements, and allows using a larger variety of optical materials including sol-gel glasses, which possess better surface optical quality.

Shaping of light beams by 3D direct laser writing on facets of nonlinear crystals.

We demonstrate experimentally spatial-mode conversions of light beams generated in a quadratic nonlinear process by micron-scale structures placed on the facets of nonlinear crystals. These structures were printed on the crystal facets using a three-dimensional (3D) direct laser writing system. The functional structures were designed to modify the phase of the beam at specific wavelengths, thereby enabling conversion of a fundamental Gaussian laser beam into different high-order Hermite-Gaussian modes, Laguerre-Gaussian modes, and zeroth-order Bessel beams of the second harmonic. This facet functionalization opens exciting new opportunities for robust and compact beam shaping in a nonlinear interaction without compromising the conversion efficiency.

Gradual hydrophobization of silica aerogel for controlled drug release.

We report on the successful fine-tuning of silica aerogel hydrophobicity, through a gas-phase surface modification process. Aerogel hydrophobicity is a widely discussed matter, as it contributes to the aerogel's preservation and determines its functionality. Still, a general procedure for tuning the hydrophobicity, without affecting other aerogel properties was missing. In the developed procedure, silica aerogel was modified with trimethylchlorosilane vapor for varying durations, resulting in gradual hydrophobicity, determined by solid-state NMR and contact angle measurements. The generality of this post-synthesis treatment allows its application on a variety of aerogel materials, while having minimum effect on their porosity and transparency. We demonstrate the applicability of the gradual hydrophobization by tuning drug release rates from the silica aerogel. Two chlorhexidine salts - widely employed as antiseptic agents - were used as model drugs, one representing a soluble drug, and the other an insoluble drug; they were entrapped in silica aerogel, following hydrophobization to varying degrees. The drug release patterns showed that depending on the degree, hydrophobization can increase or decrease release kinetics, compared to the unmodified aerogel. This arises from the effect of the hydrophobic degree on pore structure, diffusional rates and wetting of the aerogel carrier. We suggest the use of the gradual hydrophobization process for other drug-aerogel systems, as well as for other aerogel applications, such as transparent insulation panels, contaminate sorbents or catalysis supports.

High Quality 3D Photonics using Nano Imprint Lithography of Fast Sol-gel Materials.

A method for the realization of low-loss integrated optical components is proposed and demonstrated. This approach is simple, fast, inexpensive, scalable for mass production, and compatible with both 2D and 3D geometries. The process is based on a novel dual-step soft nano imprint lithography process for producing devices with smooth surfaces, combined with fast sol-gel technology providing highly transparent materials. As a concrete example, this approach is demonstrated on a micro ring resonator made by direct laser writing (DLW) to achieve a quality factor improvement from one hundred thousand to more than 3 million. To the best of our knowledge this also sets a Q-factor record for UV-curable integrated micro-ring resonators. The process supports the integration of many types of materials such as light-emitting, electro-optic, piezo-electric, and can be readily applied to a wide variety of devices such as waveguides, lenses, diffractive elements and more.