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Abstract Lithium (Li) dendrite growth significantly deteriorates the performance and shortens the operation life of lithium metal batteries. Capturing the intricate dynamics of surface localized and rapid mass transport at the electrolyte–electrode interface of lithium metal is essential for the understanding of the dendrite growth process, and the evaluation of the solutions mitigating the dendrite growth issue. Here we demonstrate an approach based on an ultrasensitive tilted fiber Bragg grating (TFBG) sensor which is inserted close to the electrode surface in a working lithium metal battery, without disturbing its operation. Thanks to the superfine optical resonances of the TFBG, in situ and rapid monitoring of mass transport kinetics and lithium dendrite growth at the nanoscale interface of lithium anodes have been achieved. Reliable correlations between the performance of different natural/artificial solid electrolyte interphases (SEIs) and the time-resolved optical responses have been observed and quantified, enabling us to link the nanoscale ion and SEI behavior with the macroscopic battery performance. This new operando tool will provide additional capabilities for parametrization of the batteries’ electrochemistry and help identify the optimal interphases of lithium metal batteries to enhance battery performance and its safety.

Abstract As the population ages, the worldwide prevalence of Alzheimer's disease (AD) as the most common dementia in the elderly is increasing dramatically. However, a long‐term challenge is to achieve rapid and accurate early diagnosis of AD by detecting hallmarks such as amyloid beta (Aβ42). Here, a multi‐channel microfluidic‐based plasmonic fiber‐optic biosensing platform is established for simultaneous detection and differentiation of multiple AD biomarkers. The platform is based on a gold‐coated, highly‐tilted fiber Bragg grating (TFBG) and a custom‐developed microfluidics. TFBG excites a high‐density, narrow‐cladding‐mode spectral comb that overlaps with the broad absorption of surface plasmons for high‐precision interrogation, enabling ultrasensitive monitoring of analytes. In situ detection and in‐parallel discrimination of different forms of Aβ42 in cerebrospinal fluid (CSF) are successfully demonstrated with a detection of limit in the range of ≈30–170 pg mL−1, which is one order of magnitude below the clinical cut‐off level in AD onset, providing high detection sensitivity for early diagnosis of AD. The integration of the TFBG sensor with multi‐channel microfluidics enables simultaneous detection of multiple biomarkers using sub‐µL sample volumes, as well as combining initial binding rate and real‐time response time to differentiate between multiple biomarkers in terms of binding kinetics. With the advantages of multi‐parameter, low consumption, and highly sensitive detection, the sensor represents an urgently needed potentials for large‐scale diagnosis of diseases at early stage.

Abstract Operando monitoring of complex physical and chemical activities inside rechargeable lithium-ion batteries during thermal runaway is critical to understanding thermal runaway mechanisms and giving early warning of safety-related failure. However, most existing sensors cannot survive during such extremely hazardous thermal runaway processes (temperature up to 500 °C accompanied by fire and explosion). To address this, we develop a compact and multifunctional optical fiber sensor (12 mm in length and 125 µm in diameter) capable of insertion into commercial 18650 cells to continuously monitor internal temperature and pressure effects during cell thermal runaway. We observe a stable and reproducible correlation between the cell thermal runaway and the optical response. The sensor’s signal shows two internal pressure peaks corresponding to safety venting and initiation of thermal runaway. Further analysis reveals that a scalable solution for predicting imminent thermal runaway is the detection of the abrupt turning range of the differential curves of cell temperature and pressure, which corresponds to an internal transformation between the cell reversible and irreversible reactions. By raising an alert even before safety venting, this new operando measurement tool can provide crucial capabilities in cell safety assessment and warning of thermal runaway.

A nonmetallic plasmonic heterostructure of W18O49 nanowires on reduced-graphene oxide is reported for the efficient dehydration of isopropanol to 100% propylene. The energy barrier is found to be reduced under full-spectrum irradiation.

Operando monitoring of highly localized and rapid temperature changes during photo-involved catalysis reactions at liquid-solid interfaces via narrow bandwidth fiber-optic spectral combs.

Operando tracking the ion dynamics/states of battery is critical to understanding of electrolyte-electrode interactions. Here the authors propose to use the surface plasmon waves to rapidly screen localized electrochemical events on a sub-μm-scale thickness adjacent to the electrode interface, without perturbing battery operation.

Alzheimer's disease (AD) is one of the most common neurodegenerative illnesses displaying the highest death rate in the elderly. However, the existing AD diagnostic system remains elusive due to lack of a technology that may ensure enough sensitivity and reproducibility, detection accuracy, and specificity. Herein, a straightforward approach is reported to realize lab‐on‐fiber (LoF) technology for AD biomarker detection based on a D‐shaped single‐mode fiber combined with nanometer‐scale metal‐oxide film. The proposed sensing system, which permits the generation of lossy‐mode resonance (LMR), remarkably increases the evanescent field of light guided through the fiber, and hence the fiber‐surrounding medium interaction. Moreover, such optical sensors are highly repeatable in results and can safely be embedded into a compact and stable microfluidic system. Herein, the specific detection of Tau protein (as one of the classical AD biomarkers that is highly correlated with AD progression) in a complex biofluid with a detection limit of 10−12 m and over a wide concentration range (10−3–10 μg mL−1) is successfully demonstrated. The proposed LoF biosensor is an appealing solution for rapid, sub‐microliter dose and highly sensitive detection of analytes at low concentrations, hereby having the potential toward early screening and personalized medicine in AD.

An optical fiber biosensor displaying superfine plasmonic spectral combs and enhanced by conjugate-induced amplification enables the detection of environmental estrogens down to pg/mL estradiol equivalent concentration level.

The metal-to-dielectric transition of silver films deposited on single-mode optical fibers is monitored by measurements of the transmission spectra of tilted fiber Bragg gratings inscribed in the core of the fiber. In situ, real-time measurements of the spectrum at wavelengths near 1550 nm during the wet etching of a 50 nm thick silver coating show a sudden and temporary decrease of more than 90% in the amplitudes of the core-to-cladding mode coupling resonances when the film thickness reaches 18 nm. Confirmation that this observation corresponds to the percolation threshold is obtained from simultaneous measurements of the silver coating conductivity during etching and by simulations of the grating response. The characteristic spectral signature of the percolation threshold is only obtained for cladding modes polarized azimuthally in the fiber cross section, i.e., parallel to the film surface.

Abstract A highly sensitive fiber-optic accelerometer based on detecting the power output of resonances from the core dip is demonstrated. The sensing probe comprises a compact structure, hereby a short section of specific core (with a significant core dip) fiber stub containing a straight fiber Bragg grating is spliced to another single-mode fiber via a core self-alignment process. The femtosecond laser side-illumination technique was utilized to ensure that the grating inscription region is precisely positioned and compact in size. Two well-defined core resonances were achieved in reflection: one originates from the core dip and the other originates from fiber core. The key point is that only one of these two reflective resonances exhibits a high sensitivity to fiber bend (and vibration), whereas the other is immune to it. For low frequency (

Abstract A dual-frequency distributed Bragg reflector (DBR) fiber laser based sensor is demonstrated for low-frequency vibration measurement through the Doppler effect. The response of the proposed sensor is quite linear and is much higher than that of a conventional accelerometer. The proposed sensor can work down to 1 Hz with high sensitivity. Therefore, the proposed sensor is very efficient in low-frequency vibration measurement.

A miniature optical fiber ultrasonic sensor based on the Fabry-Perot interferometer (FPI) is proposed and experimentally demonstrated. The cavity of the interferometer is based on a section of hollow core fiber coated with a 353ND diaphragm. A well-define interference pattern is achieved, and the spectral sideband filter technique is used to interrogate the sensor. Because the thin reflective diaphragm is extremely sensitive to sound pressure, the signal-to-noise ratio of the sensor response reaches to 31.22 dB with the pulse ultrasonic excitation of 300 kHz. A clear interface information can be distinguished in physical model imaging, and the longitudinal spatial resolution is 5 mm. This proposed sensor has the advantages of being simple to fabricate, ultracompact in size, cost effective, corrosion resistance, and being highly stable.

Fibre sensors are key to many minimally-invasive detection techniques but, owing to an index mismatch, they are often limited to aqueous environments. Here, Caucheteur et al. develop a high-resolution fibre gas sensor with a tilted in-fibre grating that allows coupling to higher-order plasmon modes.

A wideband-tunable Q-switched fiber laser with a high-reflective topological insulator saturable absorber mirror (TISAM) was proposed and experimentally demonstrated. The proposed TISAM is composed of Sb2Te3 and gold films deposited over the fiber tip, and it has the advantage of compact size, easy integration over fiber, good stability, and mass production ability. The modulation depth, saturable intensity, and nonsaturable loss of the TISAM at 1550 nm are experimentally tested to be 6.2%, 143 MW/cm2, and 4.2%, respectively. By using such TISAM, we obtain laser pulses of ~400 ns in pulse width and kHz in repetition rates over the wavelength range from 1530 to 1570 nm. The experimental results indicate that the Sb2Te3 based TISAM have good potentials for Q-switched fiber lasers.

A sensitivity-improved fiber-optic strain sensor using an etched and regenerated fiber Bragg grating (ER-FBG) suitable for a large range of temperature measurements has been proposed and experimentally demonstrated. The process of chemical etching (from 125 µm to 60 µm) provides regenerated gratings (at a temperature of 680 °C) with a stronger reflective intensity (from 43.7% to 69.8%), together with an improved and linear strain sensitivity (from 0.9 pm/με to 4.5 pm/με) over a large temperature range (from room temperature to 800 °C), making it a useful strain sensor for high temperature environments.

A reflective fiber-optic interferometer for ultra-high temperature measurement is proposed and experimentally demonstrated. The device consists of a short piece of polarization-maintaining photonic crystal fiber (PM-PCF) spliced with a lead-in single mode fiber (SMF) without any offset. The hollow holes within the PM-PCF are partly collapsed due to the directional arc-heating splicing and excite two linearly polarized (LP) modes over the downstream PM-PCF. These two LP-modes are reflected at the end face of PM-PCF and backward recoupled into the lead-in SMF through the collapsed region. A superimposed interference pattern is obtained as the result of interference of the polarized modes. The proposed interferometer is demonstrated for ultra-high temperature measurement up to 1100 °C with a sensitivity of 12.3 pm/°C over repeated measurements. Meanwhile, isochronally thermal annealing has been studied to address the effect of residual stress in the sensing probe and the feasibility of further improving temperature measurement range of the device.

Plasmonic immunosensors are usually made of a noble metal (in the form of a film or nanoparticles) on which bioreceptors are grafted to sense analytes based on the antibody/antigen or other affinity mechanism. Optical fiber configurations are a miniaturized counterpart to the bulky Kretschmann prism and allow easy light injection and remote operation. To excite a surface plasmon (SP), the core-guided light is locally outcoupled. Unclad optical fibers were the first configurations reported to this end. Among the different architectures able to bring light in contact with the surrounding medium, a great quantity of research is today being conducted on metal-coated fiber gratings photo-imprinted in the fiber core, as they provide modal features that enable SP generation at any wavelength, especially in the telecommunication window. They are perfectly suited for use with cost-effective high-resolution interrogators, allowing both a high sensitivity and a low limit of detection to be reached in immunosensing. This paper will review recent progress made in this field with different kinds of gratings: uniform, tilted and eccentric short-period gratings as well as long-period fiber gratings. Practical cases will be reported, showing that such sensors can be used in very small volumes of analytes and even possibly applied to in vivo diagnosis.