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- ItemSide-view holographic endomicroscopy via a custom-terminated multimode fibre(Washington, DC : Soc., 2021) Silveira, Beatriz M.; Pikálek, Tomáš; Stibůrek, Miroslav; Ondráčková, Petra; Jákl, Petr; Leite, Ivo T.; Čižmár, TomášMicroendoscopes based on optical fibres have recently come to the fore as promising candidates allowing in-vivo observations of otherwise inaccessible biological structures in animal models. Despite being still in its infancy, imaging can now be performed at the tip of a single multimode fibre, by relying on powerful holographic methods for light control. Fibre based endoscopy is commonly performed en face, resulting in possible damage of the specimen owing to the direct contact between the distal end of the probe and target. On this ground, we designed an all-fibre probe with an engineered termination that reduces compression and damage to the tissue under investigation upon probe insertion. The geometry of the termination brings the field of view to a plane parallel to the fibre’s longitudinal direction, conveying the probe with off-axis imaging capabilities. We show that its focusing ability also benefits from a higher numerical aperture, resulting in imaging with increased spatial resolution. The effect of probe insertion was investigated inside a tissue phantom comprising fluorescent particles suspended in agarose gel, and a comparison was established between the novel side-view probe and the standard en face fibre probe. This new concept paves the way to significantly less invasive deep-tissue imaging.
- ItemOrders of magnitude loss reduction in photonic bandgap fibers by engineering the core surround(Washington, DC : Soc., 2021) Upendar, S.; Ando, R.F.; Schmidt, M.A.; Weiss, T.We demonstrate how to reduce the loss in photonic bandgap fibers by orders of magnitude by varying the radius of the corner strands in the core surround. As a fundamental working principle we find that changing the corner strand radius can lead to backscattering of light into the fiber core. Selecting an optimal corner strand radius can thus reduce the loss of the fundamental core mode in a specific wavelength range by almost two orders of magnitude when compared to an unmodified cladding structure. Using the optimal corner radius for each transmission window, we observe the low-loss behavior for the first and second bandgaps, with the losses in the second bandgap being even lower than that of the first one. Our approach of reducing the confinement loss is conceptually applicable to all kinds of photonic bandgap fibers including hollow core and all-glass fibers as well as on-chip light cages. Therefore, our concept paves the way to low-loss light guidance in such systems with substantially reduced fabrication complexity.
- ItemUnraveling the Impact of High-Order Silk Structures on Molecular Drug Binding and Release Behaviors(Washington, DC : ACS, 2019) Wongpinyochit, Thidarat; Vassileiou, Antony D.; Gupta, Sukriti; Mushrif, Samir H.; Johnston, Blair F.; Seib, F. PhilippSilk continues to amaze: over the past decade, new research threads have emerged that include the use of silk fibroin for advanced pharmaceutics, including its suitability for drug delivery. Despite this ongoing interest, the details of silk fibroin structures and their subsequent drug interactions at the molecular level remain elusive, primarily because of the difficulties encountered in modeling the silk fibroin molecule. Here, we generated an atomistic silk model containing amorphous and crystalline regions. We then exploited advanced well-tempered metadynamics simulations to generate molecular conformations that we subsequently exposed to classical molecular dynamics simulations to monitor both drug binding and release. Overall, this study demonstrated the importance of the silk fibroin primary sequence, electrostatic interactions, hydrogen bonding, and higher-order conformation in the processes of drug binding and release. © Copyright © 2019 American Chemical Society.
- ItemPolarization-resolved second-harmonic generation imaging through a multimode fiber(Washington, DC : OSA, 2021) Cifuentes, Angel; Pikálek, Tomáš; Ondráčková, Petra; Amezcua-Correa, Rodrigo; Antonio-Lopez, José Enrique; Čižmár, Tomáš; Trägårdh, JohannaMultimode fiber-based endoscopes have recently emerged as a tool for minimally invasive endoscopy in tissue, at depths well beyond the reach of multiphoton imaging. Here, we demonstrate label-free second-harmonic generation (SHG) microscopy through such a fiber endoscope. We simultaneously fully control the excitation polarization state and the spatial distribution of the light at the fiber tip, and we use this to implement polarization-resolved SHG imaging, which allows imaging and identification of structural proteins such as collagen and myosin. We image mouse tail tendon and heart tissue, employing the endoscope at depths up to 1 mm, demonstrating that we can differentiate these structural proteins. This method has the potential for enabling instant and in situ diagnosis of tumors and fibrotic conditions in sensitive tissue with minimal damage.
- Item2 MW peak power generation in fluorine co-doped Yb fiber prepared by powder-sinter technology(Washington, DC : Soc., 2020) Leich, Martin; Kalide, André; Eschrich, Tina; Lorenz, Adrian; Lorenz, Martin; Wondraczek, Katrin; Schönfeld, Dörte; Langner, Andreas; Schötz, Gerhard; Jäger, MatthiasWe report on the first, to the best of our knowledge, implementation of a fluorine co-doped large-mode-area REPUSIL fiber for high peak power amplification in an ultrashort-pulse master oscillator power amplifier. The core material of the investigated step-index fiber with high Yb-doping level, 52 µm core and high core-to-clad ratio of 1:4.2 was fabricated by means of the REPUSIL powder-sinter technology. The core numerical aperture was adjusted by fluorine codoping to 0.088. For achieving high beam quality and for ensuring a monolithic seed path, the LMA fiber is locally tapered. We demonstrate an Yb fiber amplifier with near-diffraction-limited beam quality of M2 = 1.3, which remains constant up to a peak power of 2 MW. This is a record for a tapered single core fiber. © 2020 Optical Society of America
- ItemHybrid Optical Fibers – An Innovative Platform for In‐Fiber Photonic Devices(Weinheim : Wiley-VCH, 2015) Alexander Schmidt, Markus; Argyros, Alexander; Sorin, FabienThe field of hybrid optical fibers is one of the most active research areas in current fiber optics and has the vision of integrating sophisticated materials inside fibers, which are not traditionally used in fiber optics. Novel in-fiber devices with unique properties have been developed, opening up new directions for fiber optics in fields of critical interest in modern research, such as biophotonics, environmental science, optoelectronics, metamaterials, remote sensing, medicine, or quantum optics. Here the recent progress in the field of hybrid optical fibers is reviewed from an application perspective, focusing on fiber-integrated devices enabled by including novel materials inside polymer and glass fibers. The topics discussed range from nanowire-based plasmonics and hyperlenses, to integrated semiconductor devices such as optoelectronic detectors, and intense light generation unlocked by highly nonlinear hybrid waveguides.
- ItemSurface, interphase and tensile properties of unsized, sized and heat treated basalt fibres(London [u.a.] : Institute of Physics, 2016) Förster, T.; Sommer, G.S.; Mäder, E.; Scheffler, C.Recycling of fibre reinforced polymers is in the focus of several investigations. Chemical and thermal treatments of composites are the common ways to separate the reinforcing fibres from the polymer matrices. However, most sizings on glass and basalt fibre are not designed to resist high temperatures. Hence, a heat treatment might also lead to a sizing removal, a decrease of mechanical performance and deterioration in fibre-matrix adhesion. Different basalt fibres were investigated using surface analysis methods as well as single fibre tensile tests and single fibre pull-out tests in order to reveal the possible causes of these issues. Heat treatment in air reduced the fibre tensile strength in the same level like heat treatment in nitrogen atmosphere, but it influenced the wetting capability. Re-sizing by a coupling agent slightly increased the adhesion strength and reflected a decreased post-debonding friction.
- ItemThermal tuning of a fiber-integrated Fabry-Pérot cavity(Washington, DC : Soc., 2021) Singer, Clemens; Goetz, Alexander; Prasad, Adarsh S.; Becker, Martin; Rothhardt, Manfred; Skoff, Sarah M.Here, we present the thermal tuning capability of an alignment-free, fiber-integrated Fabry-Pérot cavity. The two mirrors are made of fiber Bragg gratings that can be individually temperature stabilized and tuned. We show the temperature tuning of the resonance wavelength of the cavity without any degradation of the finesse and the tuning of the individual stop bands of the fiber Bragg gratings. This not only permits for the cavity’s finesse to be optimized post-fabrication but also makes this cavity applicable as a narrowband filter with a FWHM spectral width of 0.07 ± 0.02 pm and a suppression of more than -15 dB that can be wavelength tuned. Further, in the field of quantum optics, where strong light-matter interactions are desirable, quantum emitters can be coupled to such a cavity and the cavity effect can be reversibly omitted and re-established. This is particularly useful when working with solid-state quantum emitters where such a reference measurement is often not possible once an emitter has been permanently deposited inside a cavity.
- ItemOptimized diamond inverted nanocones for enhanced color center to fiber coupling(Melville, NY : American Inst. of Physics, 2021) Torun, Cem Güney; Schneider, Philipp-Immanuel; Hammerschmidt, Martin; Burger, Sven; Munns, Joseph H. D.; Schröder, TimNanostructures can be used for boosting the light outcoupling of color centers in diamond; however, the fiber coupling performance of these nanostructures is rarely investigated. Here, we use a finite element method for computing the emission from color centers in inverted nanocones and the overlap of this emission with the propagation mode in a single-mode fiber. Using different figures of merit, the inverted nanocone parameters are optimized to obtain maximal fiber coupling efficiency, free-space collection efficiency, or rate enhancement. The optimized inverted nanocone designs show promising results with 66% fiber coupling or 83% free-space coupling efficiency at the tin-vacancy center zero-phonon line wavelength of 619 nm. Moreover, when evaluated for broadband performance, the optimized designs show 55% and 76% for fiber coupling and free-space efficiencies, respectively, for collecting the full tin-vacancy emission spectrum at room temperature. An analysis of fabrication insensitivity indicates that these nanostructures are robust against imperfections. For maximum emission rate into a fiber mode, a design with a Purcell factor of 2.34 is identified. Finally, possible improvements offered by a hybrid inverted nanocone, formed by patterning into two different materials, are investigated and increase the achievable fiber coupling efficiency to 71%. © 2021 Author(s).
- ItemQuantifying texture evolution during hot rolling of AZ31 Twin Roll Cast strip(London [u.a.] : Institute of Physics, 2015) Gorelova, S.; Schaeben, H.; Skrotzki, Werner; Oertel, Carl-GeorgMulti-pass rolling experiments with an AZ31 Twin Roll Cast (TRC) alloy were performed on an industrial scaled four-high rolling mill. Within the rolling with an intermediate annealing the evolution of texture was investigated. To quantify the extent of preferred crystallographic orientation experimental X-ray pole figures were measured after different process steps and analyzed using the free and open Matlab® toolbox MTEX for texture analysis. The development of the fiber texture was observed and analyzed in dependence on rolling conditions. In the initial state the specimen exhibits a texture composed of a weak basal texture and a cast texture with {0001}-planes oriented across the rolling direction. During the following rolling process a fiber texture was developed. The expected strength increment of the fiber texture was quantitatively confirmed in terms of volume portions of the orientation density function around the fiber and in terms of the canonical parameters of fitted pseudo Bingham distributions. On the results of this work a model for prediction of the texture evolution during the strip rolling of magnesium in the examined parameter range was developed.