Potential of a New, Flexible Electrode sEMG System in Detecting Electromyographic Activation in Low Back Muscles during Clinical Tests: A Pilot Study on Wearables for Pain Management.

BACKGROUND: While low back pain (LBP) is the leading cause of disability worldwide, its clinical objective assessment is currently limited. Part of this syndrome arises from the abnormal sensorimotor control of back muscles, involving increased muscle fatigability (i.e., assessed with the Biering-Sorensen test) and abnormal muscle activation patterns (i.e., the flexion-extension test). Surface electromyography (sEMG) provides objective measures of muscle fatigue development (median frequency drop, MDF) and activation patterns (RMS amplitude change). This study therefore assessed the sensitivity and validity of a novel and flexible sEMG system (NSS) based on PEVA electrodes and potentially embeddable in textiles, as a tool for objective clinical LBP assessment. METHODS: Twelve participants wearing NSS and a commercial laboratory sEMG system (CSS) performed two clinical tests used in LBP assessment (Biering-Sorensen and flexion-extension). Erector spinae muscle activity was recorded at T12-L1 and L4-L5. RESULTS: NSS showed sensitivity to sEMG changes associated with fatigue development and muscle activations during flexion-extension movements (p < 0.05) that were similar to CSS (p > 0.05). Raw signals showed moderate cross-correlations (MDF: 0.60-0.68; RMS: 0.53-0.62). Adding conductive gel to the PEVA electrodes did not influence sEMG signal interpretation (p > 0.05). CONCLUSIONS: This novel sEMG system is promising for assessing electrophysiological indicators of LBP during clinical tests.

Nonlinear chalcogenide optical fiber couplers.

We demonstrate chalcogenide optical fiber couplers with a power-dependent coupling coefficient. The couplers are designed and fabricated using an As2Se3 fiber and characterized at a wavelength of 1938 nm, leading to a critical power of 126 W, the lowest ever reported for any optical fiber coupler. These nonlinear couplers enable all-optical switching and will be useful for passive mode-locking over a wide wavelength range from the telecommunication band to the mid-infrared.

Large area Bragg grating for pump recycling in cladding-pumped multicore erbium-doped fiber amplifiers.

We demonstrate for the first time that a Bragg grating can be written over a large area inside the cladding of a multicore erbium-doped fiber amplifier to increase the power conversion efficiency (PCE) by recycling the output pump power. Our results indicate that a Bragg grating covering ∼25% of the cladding area allows us to recycle 19% of the output pump power which leads to a relative increase of the PCE by 16% for an input pump power of 10.6 W in the specific case of an eight-core erbium-doped fiber with a length of 20.3 m and one core loaded with an input signal power of 1.5 dBm.

Wearable Sensor Based on Flexible Sinusoidal Antenna for Strain Sensing Applications.

A flexible sinusoidal-shaped antenna sensor is introduced in this work, which is a modified half-wave dipole that can be used for strain sensing applications. The presented antenna is an improved extension of the previously introduced antenna sensor for respiration monitoring. The electrical and radiative characteristics of the sinusoidal antenna and the effects of the geometrical factors are studied. An approach is provided for designing the antenna, and equations are introduced to estimate the geometrical parameters based on desired electrical specifications. It is shown that the antenna sensor can be designed to have up to 5.5 times more sensitivity compared to the last generation of the antenna sensor previously introduced for respiration monitoring. The conductive polymer material used to fabricate the new antenna makes it more flexible and durable compared to the previous generation of antenna sensors made of glass-based material. Finally, a reference antenna made of copper and an antenna sensor made of the conductive polymer are fabricated, and their electrical characteristics are analyzed in free space and over the body.

Coaxial Mach-Zehnder Digital Strain Sensor Made from a Tapered Depressed Cladding Fiber.

An in-line digital optical sensor was proposed. It was built from a tapered depressed-cladding single-mode fiber and modeled as a coaxial Mach-Zehnder interferometer. The principle of operation of the optical digital sensor is based on the computation of the number of optical power transfer turning points (PTTP) from the transmission data of the component. Biconic tapers with high values of PTTP, high spectral resolution, high extinction ratio, and low insertion loss were modeled, fabricated, and characterized. As a proof of concept, an in-line digital strain sensor was fabricated and characterized. It presents a free spectral range of 1.3 nm, and produced 96 PTTP, at λ0 = 1.55 µm, under stretch of ΔL = 707 µm, therefore producing a digital resolution of 7.4 µm/PTTP. The sensor also produced a quasi-symmetric response to stretch and compression.

Silicon subwavelength grating waveguides with high-index chalcogenide glass cladding.

Silicon subwavelength grating waveguides enable flexible design in integrated photonics through nano-scale refractive index engineering. Here, we explore the possibility of combining silicon subwavelength gratings waveguides with a high-index chalcogenide glass as a top cladding, thus modifying the waveguiding behavior and opening a new design axis for these structures. A detailed investigation of the heterogeneous SWG waveguide with high-index cladding is presented based on analytical and numerical simulations. We design, fabricate and characterize silicon subwavelength grating waveguide microring resonators with an As20S80 cladding. Thanks to As20S80 negative thermo-optic coefficient, we achieve near athermal behavior with a measured minimum thermally induced resonance shift of -1.54 pm/K, highlighting the potential of subwavelength grating waveguides for modal confinement engineering and to control light-matter interaction. We also show that the chalcogenide glass can be thermally reflowed to remove air gaps inside the cladding, resulting in a highly conformal structure. These types of waveguides can find application in reconfigurable photonics, nonlinear optics, metamaterials or slow light.

Mid-infrared soliton self-frequency shift in chalcogenide glass.

Emerging applications in the mid-infrared (MIR) stimulate the growth and development of novel optical light sources. Soliton self-frequency shift (SSFS) in soft glass fiber currently shows great potential as an efficient approach toward the generation of broadly tunable femtosecond pulses in the MIR. In this work, we demonstrate a highly efficient tunable soliton source based on SSFS in chalcogenide glass. We show a simple and fully fiberized system to generate these continuously tunable Raman solitons over a broad spectral range of 2.047-2.667 µm, which consumes no more than 87 pJ per pulse. The spectral measurements suggest that the generated pulses are as short as 62 fs with a maximum power conversion efficiency of 43%. This result is realized thanks to an 8 cm long As2S3 microstructure optical fiber tapered into a microwire. Thanks to their broad transparency, their high nonlinearity, and their adjustable chromatic dispersion, chalcogenide microwires are promising components for the development of compact and highly efficient MIR optical sources with low power consumption.

Silicon-coupled tantalum pentoxide microresonators with broadband low thermo-optic coefficient.

Stable microresonators are important integrated photonics components but are difficult to achieve on silicon-on-insulator due to silicon intrinsic properties. In this work, we demonstrate broadband thermally stable tantalum pentoxide microresonators directly coupled to silicon waveguides using a micro-trench co-integration method. The method combines in-foundry silicon processing with a single step backend thin-film deposition. The passive response of the microresonator and its thermal behavior are investigated. We show that the microresonator can operate in the overcoupled regime as well as near the critical coupling point, boasting an extinction ratio over 25 dB with no higher-order mode excitation. The temperature dependent wavelength shift is measured to be as low as 8.9 pm/K and remains below 10 pm/K over a 120 nm bandwidth.

100-W-level single-mode ytterbium-free erbium fiber laser.

We report on an ytterbium-free, erbium-doped single-mode all-fiber laser reaching a record output power of 107 W at 1598 nm, with a slope efficiency of 38.6% according to the absorbed pump power at 981 nm. The erbium-doped gain fiber, co-doped with cerium, aluminum, and phosphorus, was fabricated in-house with adjusted doping concentrations to reduce erbium ions clustering, thereby increasing efficiency while keeping the numerical aperture low to ensure a single-mode laser operation. The addition of cerium co-dopant in the core glass of an erbium system is used for the first time, to the best of our knowledge, in order to adjust the fiber's numerical aperture without increasing the erbium concentration. Numerical modeling, validated by the experimental results, demonstrates that adding aluminum and phosphorus at high concentration mitigates erbium ions clustering, with an estimated erbium paired ions of only 5.0% in the reported gain fiber.

Fabrication and characterization of laser-heated, multiplexed electrospray emitter.

We present a one-step fabrication method for a new multiplexed electrospray emitter with nine parallel micronozzles. The nozzles were formed by wet chemical etching of the end of a microstructured silica fiber containing nine 10 µm flow channels. By carefully adjusting the water flow through the channels while etching, we controlled the shape of the conical micronozzles and were able to obtain conditions under which the micronozzles, together with the flow channels, formed optical micro-axicon lenses. When 1064 nm light was guided through the flow channels and focused by the micro-axicon lenses into the Taylor cones, we were able to increase the desolvation of a model analyte and thereby increased the spray current produced by the emitter. This work paves the way towards a rapidly modulated mass-spectrometry source having a greatly enhanced throughput.

Emergence of A-Site Cation Order in the Small Rare-Earth Melilites SrREGa3O7 (RE = Dy-Lu, Y).

SrREGa3O7 melilite ceramics with large rare-earth elements (RE = La to Y) are famous materials especially known for their luminescence properties. Using an innovative approach, the full and congruent crystallization from glass process, SrREGa3O7 transparent polycrystalline ceramics with small rare earth elements (RE = Dy-Lu and Y) have been successfully synthesized and characterized. Interestingly, compared to the classic tetragonal (P4̅21m) melilite structure composed of mixed Sr/RE cationic sites, these compositions can crystallize in a 3 × 1 × 1 orthorhombic (P21212) superstructure. A detailed study of the superstructure, investigated using different techniques (synchrotron and neutron powder diffraction, STEM-HAADF imaging, and EDS mapping), highlights the existence of a Sr/RE cation ordering favored by a large Sr/RE size mismatch and a sufficiently small RE cation. An appropriate control of the synthesis conditions through glass crystallization enables the formation of the desired polymorphs, either ordered or disordered. The influence of this tailored cationic ordering/disordering on the RE luminescent spectroscopic properties have been investigated. A stronger structuration of the RE emission band is observed in the ordered ceramic compared to the disordered ceramic and the glass, whose band shapes are very similar, indicating that the RE environments in the glass and disordered ceramic are close.

Label-Free Ultrasensitive and Environment-Friendly Immunosensor Based on a Silica Optical Fiber for the Determination of Ciprofloxacin in Wastewater Samples.

Emerging contaminants, including pharmaceutical compounds, are receiving research attention as a result of their widespread presence in effluents and wastewater treatment plants (WWTPs). The antibiotic ciprofloxacin (CIP) is extensively employed to treat infections in animal and human medicine. Both CIP and its metabolites are common contaminants found in WWTPs. In this study, a label-free ultrasensitive U-bent optical fiber-based immunosensor for the determination of CIP in wastewater samples was developed using the properties of the conducting polymer polyaniline (PANI). The anti-CIP immunoglobulin G (IgG) was deposited on a silica optical fiber surface previously functionalized with PANI. Scanning electron microscopy and micro-Raman spectroscopy were used to investigate the surface of the immunosensor. The analysis of CIP in wastewater was performed without the use of an organic solvent or sample preparation steps, with only the sample dilution in saline buffer (pH = 7.4). The linear range for CIP was from 0.01 to 10,000 ng L-1. The detection limit was 3.30 × 10-3 ng L-1 and the quantification limit was 0.01 ng L-1. The immunosensor provided a high average recovery of 91% after spiking wastewater samples with CIP at a concentration of 9,100 ng L-1. The method was applied in triplicate to wastewater samples from Quebec (Canada), obtaining concentrations of 549 and 267 ng L-1. A comparison with a reference method showed no significant difference (t-test at 95% confidence). The new technique developed is selective, allowing a quantitative analysis of CIP in wastewater.

Curvature sensing using a hybrid polycarbonate-silica multicore fiber.

We report on the development of a novel hybrid glass-polymer multicore fiber integrating three 80 µm polyimide-coated silica fibers inside a 750 µm polycarbonate cladding. By inscribing an array of distributed FBGs along each segment of silica fiber prior to the hybrid fiber drawing, we demonstrate a curvature sensor with an unprecedented precision of 296 pm/m-1 around 1550 nm, about 7 times more sensitive than sensors based on standard 125 µm multicore fibers. As predicted by theory, we show experimentally that the measured curvature is insensitive to temperature and strain. Also, a more precise equation to describe the curvature on a simple bending setup is presented. This new hybrid multicore fiber technology has the potential to be extended over several kilometers and can find high-end applications in 3D shape sensing and structural health monitoring.

Erbium-doped aluminophosphosilicate all-fiber laser operating at 1584 nm.

We report on an ytterbium-free erbium-doped aluminophosphosilicate all-fiber laser, producing an output power of 25 W at a wavelength of 1584 nm with a slope efficiency of 30% with respect to the 976 nm absorbed pump power. The simple cavity design proposed takes advantage of fiber Bragg gratings written directly in the gain fiber. The single-mode erbium-doped aluminophosphosilicate fiber was fabricated in-house and was doped with 0.06 mol.% of Er2O3, 1.77 mol.% of Al2O3 and 1.04 mol.% of P2O5. The incorporation of aluminium and phosphorus into the fiber core allowed for an increased concentration of erbium without inducing significant clustering, while keeping the numerical aperture low to ensure a single-mode laser operation.

Co-sputtered Pr3+-doped Ga-Ge-Sb-Se active waveguides for mid-infrared operation.

This work reports on the properties of luminescent waveguides based on quaternary Ga-Ge-Sb-Se amorphous thin films doped with praseodymium. The waveguides were fabricated via magnetron co-sputtering, followed by inductively coupled plasma reactive ion etching. The initial thin film thickness and optical properties were assessed and the spectroscopic properties of the waveguides were measured. The measurements show promising results-it is possible to obtain mid-infrared fluorescence at 2.5 and 4.5 µm by injecting near-infrared light at 1.5 µm as the pump beam. By comparing waveguides with various praseodymium concentrations, the optimal doping content for maximum fluorescence intensity was identified to be close to 4100 ppmw. Finally, correlation between the intensity of mid-infrared emission and the width/length of the waveguide is shown.

Etchless chalcogenide microresonators monolithically coupled to silicon photonic waveguides.

Integration of chalcogenide waveguides in silicon photonics can mitigate the prohibitive nonlinear losses of silicon while leveraging the mature complementary metal-oxide-semiconductor (CMOS)-compatible nanophotonic fabrication process. In this work, we demonstrate, for the first time, to the best of our knowledge, a method of integrating high-Q chalcogenides microring resonators onto the silicon photonics platform without post-process etching. The method uses micro-trench filling and a novel thermal dewetting technique to form low-loss chalcogenide strip waveguides. The microrings are integrated directly inside silicon photonic circuits through evanescent coupling, providing an uncomplicated hybrid integration scheme without the need to modify the existing photonics foundry process. The microrings show a high quality factor exceeding 6×105 near 1550 nm and propagation losses below 0.7 dB/cm, indicating a promising solution for low-cost, compact nonlinear photonic devices with applications in various fields such as telecommunications and spectroscopy.

Anodic bonding of mid-infrared transparent germanate glasses for high pressure - high temperature microfluidic applications.

High pressure/high-temperature microreactors based on silicon-Pyrex® microfabrication technologies have attracted increasing interest in various applications providing optical access in high-pressure flow processes. However, they cannot be coupled to infrared spectroscopy due to the limited optical transparency (up to ~2.7 µm in the infrared region) of the Pyrex® glass substrate employed in the microreactor fabrication. To address this limitation, the alternative approach proposed in this work consists in replacing the Pyrex® glass in the microreactor by a mid-infrared transparent glass with thermal and mechanical properties as close as possible or even better to those of the Pyrex®, including its ability for silicon-wafers coupling by the anodic bonding process. Glasses based on germanate GeO2, known for their excellent transmission in the mid-infrared range and thermal/thermo-mechanical properties, have been thus evaluated and developed for this purpose. The optical, mechanical, thermal and electrical conductivity properties of adapted glass compositions belonging to five vitreous systems have been systemically investigated. The glass composition 70GeO2-15Al2O3-10La2O3-5Na2O (mol.%) was defined as the best candidate and produced in large plates of 50 mm diameter and 1 mm thickness. Anodic bonding tests with Si-wafers have been then successfully conducted, paving the way for the development of fully mid-infrared transparent silicon-glass microreactors.

Non-Enzymatic Impedimetric Sensor Based on 3-Aminophenylboronic Acid Functionalized Screen-Printed Carbon Electrode for Highly Sensitive Glucose Detection.

A highly sensitive glucose sensor was prepared by a one-step method using 3-aminophenyl boronic acid as a unit of recognition and a screen-printed carbon electrode (SPCE) as an electrochemical transducer. Scanning Electron Microscopy confirmed the success of the functionalization of the SPCE due to the presence of clusters of boronic acid distributed on the carbon surface. In agreement with the Electrochemical Impedance Spectroscopy (EIS) tests performed before and after the functionalization, Cyclic Voltammetry results indicated that the electroactivity of the electrode decreased 37.9% owing to the presence of the poly phenylboronic acid on the electrode surface. EIS revealed that the sensor was capable to selectively detect glucose at a broad range of concentrations (limit of detection of 8.53 × 10-9 M), not recognizing fructose and sucrose. The device presented a stable impedimetric response when immediately prepared but suffered the influence of the storage time and some interfering species (dopamine, NaCl and animal serum). The response time at optimized conditions was estimated to be equal to 4.0 ± 0.6 s.

A Portable Wireless Communication Platform Based on a Multi-Material Fiber Sensor for Real-Time Breath Detection.

In this paper, we present a new mobile wireless communication platform for real-time monitoring of an individual's breathing rate. The platform takes the form of a wearable stretching T-shirt featuring a sensor and a detection base station. The sensor is formed by a spiral-shaped antenna made from a multi-material fiber connected to a compact transmitter. Based on the resonance frequency of the antenna at approximately 2.4 GHz, the breathing sensor relies on its Bluetooth transmitter. The contactless and non-invasive sensor is designed without compromising the user's comfort. The sensing mechanism of the system is based on the detection of the signal amplitude transmitted wirelessly by the sensor, which is found to be sensitive to strain. We demonstrate the capability of the platform to detect the breathing rates of four male volunteers who are not in movement. The breathing pattern is obtained through the received signal strength indicator (RSSI) which is filtered and analyzed with home-made algorithms in the portable system. Numerical simulations of human breath are performed to support the experimental detection, and both results are in a good agreement. Slow, fast, regular, irregular, and shallow breathing types are successfully recorded within a frequency interval of 0.16-1.2 Hz, leading to a breathing rate varying from 10 to 72 breaths per minute.

Linearly polarized vector modes: enabling MIMO-free mode-division multiplexing.

We experimentally investigate mode-division multiplexing in an elliptical ring core fiber (ERCF) that supports linearly polarized vector modes (LPV). Characterization show that the ERCF exhibits good polarization maintaining properties over eight LPV modes with effective index difference larger than 1 × 10-4. The ERCF further displays stable mode power and polarization extinction ratio when subjected to external perturbations. Crosstalk between the LPV modes, after propagating through 0.9 km ERCF, is below -14 dB. By using six LPV modes as independent data channels, we achieved the transmission of 32 Gbaud QPSK over 0.9 km ERCF without any multiple-input-multiple-output (MIMO) or polarization-division multiplexing (PDM) signal processing.