Simon Fleming

Wearable devices are becoming increasingly important, addressing needs in both the fitness and the medical markets. In this paper, we describe a novel sensing platform based on a hollow-core polyurethane optical fiber, operating through capillary guidance, that acts as a conformal sensor of pressure or deformation. The novelty is achieved by combining a simple structure (hollow capillary) and a simple detection technique (intensity-based measurement) with unconventional material properties (extreme deformability and high optical absorbance). Used on the wrist and ankle, the sensor allows detailed features of the cardiac pulse wave to be identified with high fidelity, while on the chest it allows the simultaneous measurement of breathing rate and walking cadence. Used together, an array of such sensors (with others) could be incorporated into clothing and provide physiologically rich real-time data for health monitoring.

Wearable devices are becoming increasingly important, addressing needs in both the fitness and the medical markets. In this article, we describe a novel sensing platform based on a hollow-core polyurethane optical fiber, operating through capillary guidance, that acts as a conformal sensor of pressure or deformation. The novelty is achieved by combining a simple structure (hollow capillary) and a simple detection technique (intensity-based measurement) with unconventional material properties (extreme deformability and high optical absorbance). Used on the wrist and ankle, the sensor allows detailed features of the cardiac pulse wave to be identified with high fidelity, while on the chest it allows the simultaneous measurement of breathing rate and walking cadence. Used together, an array of such sensors (with others) could be incorporated into clothing and provide physiologically rich real-time data for health monitoring.

Optical technologies capable of real-time quantitative analysis of tissue structure and biochemical composition have the potential to revolutionize medical diagnostics. Histology is the gold standard for clinical diagnostics, but it can often involve painfully invasive biopsies, long turn-around times, and qualitative decision making. Established noninvasive imaging technologies, such as computed tomography, magnetic resonance imaging, and ultrasound, offer faster, reliable, and easily interpreted anatomical data with some compositional information. However, these modalities suffer from a variety of limitations including long acquisition times, ionizing radiation exposure, poor contrast between soft tissue types, the need for use of exogenous contrast agents, and large and expensive hardware.^{1 – 3} Alongside these methods, a range of optical techniques that utilize custom-engineered exogenous fluorescent markers of disease have emerged; these include small molecule organic fluorophores,⁴ quantum dots,⁵ carbon nanotubes,⁶ and various other nanomaterials.^7,8 However, considerable scope remains for developing minimally invasive spectroscopic devices [e.g., based on autofluorescence (AF) or diffuse reflectance (DR)] that can be used in the absence of specific probes or dyes.

We develop an intuitive understanding for the various properties and guiding mechanism of M-type fibers. We also report the approximate expression for the V-parameter (normalized frequency) to predict the modal-cutoffs for the M-type fibers, for the first time. This work demonstrates the potential of the M-type fibers for novel applications such as tailoring the transmission spectrum of photonic bandgap fibers, bend-induced effective area reduction for non-linear applications, and all-fiberized filters.

Thermal fiber drawing is an efficient technique for producing optical fiber tapers whose operation regime gradually varies between multi-mode and single-mode. Here we present a comprehensive theoretical analysis of tapering optical fibers through changing their drawing speed on a standard fiber draw tower. We analytically calculate the drawing speed, drawing acceleration, and time needed to produce different kinds of fiber tapers and analyze the derived expressions to find the optimal fabrication parameters for the tapers. The obtained results inform how to most efficiently draw optical fiber tapers of different adiabatic shapes using the minimal pulling force for a given tapering ratio.

There is a growing demand for polymer fiber scaffolds for biomedical applications and tissue engineering. Biodegradable polymers such as polycaprolactone have attracted particular attention due to their applicability to tissue engineering and optical neural interfacing. Here we report on a scalable and inexpensive fiber fabrication technique, which enables the drawing of PCL fibers in a single process without the use of auxiliary cladding. We demonstrate the possibility of drawing PCL fibers of different geometries and cross‐sections, including solid‐core, hollow‐core, and grooved fibers. The solid‐core fibers of different geometries are shown to support cell growth, through successful MCF‐7 breast cancer cell attachment and proliferation. We also show that the hollow‐core fibers exhibit a relatively stable optical propagation loss after submersion into a biological fluid for up to 21 days with potential to be used as waveguides in optical neural interfacing. The capacity to tailor the surface morphology of biodegradable PCL fibers and their non‐cytotoxicity make the proposed approach an attractive platform for biomedical applications and tissue engineering.

We propose a novel approach of exploiting the LP02 mode in ultra-high NA confined-doped M-type fibers to ensure effective single-mode operation, thereby breaking the trade-off between mode-area scaling and ultra-high NA. This novel approach opens the door to highly rare-earth doped fibers suitable for power scaling applications. Therefore enabling, simultaneously scaling of power and slope efficiency of fiber lasers.

Analytical modeling of soft pneumatic actuators constitutes a powerful tool for the systematic design and characterization of these key components of soft robotics. Here, we maximize the quasi-static bending angle of a soft pneumatic actuator by optimizing its cross-section for a fixed positive pressure inside it. We begin by formulating a general theoretical framework for the analytical calculation of the bending angle of pneumatic actuators with arbitrary cross-sections, which is then applied to an actuator made of a circular polymer tube and an asymmetric patch in the shape of a hollow-cylinder sector on its outer surface. It is shown that the maximal bending angle of this actuator can be achieved using a wide range of patches with different optimal dimensions and approximately the same cross-sectional area, which decreases with pressure. We also calculate the optimal dimensions of thin and small patches in thin pneumatic actuators. Our analytical results lead to clear design guidelines, which may prove useful for engineering and optimization of the key components of soft robotics with superior features.

We describe the fabrication of metamaterial magnifying hyperlenses with subwavelength wire array structures for operation in the mid-infrared (around 3 mu m). The metadevices are composed of approximately 500 tin wires embedded in soda-lime glass, where the metallic wires vary in diameter from 500 nm to 1.2 mu m along the tapered structure. The modeling of the hyperlenses indicates that the expected overall losses for the high spatial frequency modes in such metadevices are between 20dB to 45 dB, depending on the structural parameters selected, being promising candidates for far-field subdiffraction imaging in the mid-infrared. Initial far-field subdiffraction imaging attempts are described, and the problems encountered discussed. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement