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1. Optical characterization of disordered Yb-doped silica glass Anderson localizing optical fiber

   https://doi.org/10.1364/JOSAB.444214  

   Bassett, Cody; Tuggle, Matthew; Ballato, John; Mafi, Arash (March 2022, Journal of the Optical Society of America B)

   We investigate and report the optical and laser characteristics of a ytterbium-doped transverse Anderson localizing optical fiber to develop a fundamental understanding of the light propagation, generation, and amplification processes in this novel fiber. Ultimately, the goal based on the measurements and calculations conducted herein is to design and build a random fiber laser with a highly directional beam. The measurements are based on certain observations of the laser pump propagation and amplified spontaneous emission generation in this fiber. Judicious approximations are used in the propagation equations to obtain the relevant desired parameters in simple theoretical fits to experimental observations, without resorting to speculations based on the intended construction from the fiber preform. 

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2. Impacts of Hydrostatic Pressure on Distributed Temperature-Sensing Optical Fibers for Extreme Ocean and Ice Environments

   https://doi.org/10.3390/photonics11070630  

   Tyler, Scott W; Silvia, Matthew E; Jakuba, Michael V; Durante, Brian M; Winebrenner, Dale P (July 2024, Photonics)

   Optical fiber is increasingly used for both communication and distributed sensing of temperature and strain in environmental studies. In this work, we demonstrate the viability of unreinforced fiber tethers (bare fiber) for Raman-based distributed temperature sensing in deep ocean and deep ice environments. High-pressure testing of single-mode and multimode optical fiber showed little to no changes in light attenuation over pressures from atmospheric to 600 bars. Most importantly, the differential attenuation between Stokes and anti-Stokes frequencies, critical for the evaluation of distributed temperature sensing, was shown to be insignificantly affected by fluid pressures over the range of pressures tested for single-mode fiber, and only very slightly affected in multimode fiber. For multimode fiber deployments to ocean depths as great as 6000 m, the effect of pressure-dependent differential attenuation was shown to impact the estimated temperatures by only 0.15 °K. These new results indicate that bare fiber tethers, in addition to use for communication, can be used for distributed temperature or strain in fibers subjected to large depth (pressure) in varying environments such as deep oceans, glaciers and potentially the icy moons of Saturn and Jupiter. 

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3. Quantifying Localized Stresses in the Matrix of a Fiber‐Reinforced Composite via Mechanophores

   https://doi.org/10.1002/macp.202300298  

   Haque, Nazmul; Gohl, Jared; Chang, Chia‐Chih; Chang, Hao Chun; Davis, Chelsea S. (December 2023, Macromolecular Chemistry and Physics)

   Abstract Understanding the stress distribution within fiber‐reinforced polymers (FRPs) is critical to extending their operational lifespan. The integration of mechanoresponsive molecular force probes, referred to as mechanophores, presents a potential solution by enabling direct monitoring of stress concentrations. In this study, spiropyran (SP) mechanophores (MPs) are embedded within a polydimethylsiloxane (PDMS) matrix to visualize stress localization during loading within a single fiber‐reinforced framework. The SP mechanophore undergoes a transition from a non‐fluorescent state to an active state (merocyanine) through isomerization in response to mechanical forces. Using a single fiber mounted axially within the matrix, the fundamental failure modes observed in conventional fiber‐reinforced composites are replicated. Samples are strained under uniaxial tensile loading along the fiber direction and the localization of stresses is observed via MP activation. Stresses are concentrated in the matrix near the fiber region that gradually decreases away from the fiber surface. Confocal microscopy is used to visualize mechanophore activation and quantitatively assess fluorescence intensity. Finite element modeling is used to develop a calibration to quantify the stresses based on the observed fluorescence intensity. These outcomes underscore the viability of employing these mechanoresponsive molecules as a potential means to visualize real‐time stress distribution, thereby facilitating the design of high‐performance composites. 

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4. Fiber formation mechanisms of jet-assisted wet spinning (JAWS)

   https://doi.org/10.1063/5.0232428  

   Pan, Zehao; Venkateswaran, Barath; Nunes, Janine K; Brun, Pierre-Thomas; Stone, Howard A (December 2024, Applied Physics Letters)

   In fiber spinning of photopolymers, surface tension limits the diameter of the fiber that can be produced due to the Rayleigh–Plateau instability. Submerging a pre-fiber jet in a miscible environment liberates the system from capillary effects, thus allowing the jet to be stretched into thin threads without instability. In this work, we systematically investigated a spinning method using miscible liquids, called jet-assisted wet spinning (JAWS), where stretching is achieved by a nearby submerged liquid jet. The diameter of the pre-fiber jet is a function of its flow rate and position relative to the assisting submerged liquid jet. A particular case where the main jet is modeled as the Landau–Squire jet is used to demonstrate the tracer-like thinning behavior of the pre-fiber jet. Experiments show that buoyancy has a significant impact on the pre-fiber jet diameter because of its influence on the entrainment trajectory. Overall, our results demonstrate the potential for the parallelization of JAWS for high-throughput fiber production. 

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5. High resolution, fast response fiber-optic temperature sensor with reduced end conduction effect

   https://doi.org/10.1364/OL.405604  

   Sheng, Qiwen; Li, Bo; Uddin, Nezam; Mitul, Abu_Farzan; Zhu, Yupeng; Qiu, Zhen; Han, Ming (November 2020, Optics Letters)

   We report a fiber-optic silicon Fabry–Perot temperature sensor with high speed by considering the end conduction effect, which refers to the unwanted heat transfer between the sensing element and the fiber stub delaying the sensor from reaching thermal equilibrium with the ambient environment. The sensor is constructed by connecting the narrow edge surface of a thin silicon plate to the edge of the microtube attached to the fiber tip. Compared to the traditional design where the silicon plate is attached to the fiber end face on its large plate surface, the new sensor design minimizes the heat transfer path to the fiber stub for improved sensor speed. It has the additional benefit of increased cavity length for improved resolution. We show that, compared with the sensor of traditional design, the sensor of the new design shortened the characteristic response time in still air from 83 ms to 13 ms and improved the sensor resolution by a factor of 12, from 0.15 K to 0.012 K. 

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