Long-range distributed vibration sensing using phase-sensitive forward optical transmission: publisher's note.

This publisher's note contains corrections to Opt. Lett.48, 4825 (2023)10.1364/OL.500587.

Super-long-range distributed vibration sensor based on the polarimetric forward-transmission of light.

Undersea earthquake-triggered giant tsunamis pose significant threats to coastal areas, spanning thousands of kilometers and affecting populations, ecosystems, and infrastructure. To mitigate their impact, monitoring seismic activity in underwater environments is crucial. In this study, we propose a new, to the best of our knowledge, approach for monitoring vibrations in submarine optical cables. By detecting vibration-induced polarization rotation, our dual-wavelength fiber-optic sensing system enables precise measurement of acoustic/vibration amplitude, frequency, and position. As a proof of concept, a double-ended forward-transmission distributed fiber-optic vibration sensor was demonstrated with a single vibration source with a sensitivity of 3.4 mrad/µÎµ at 100 Hz (20 m fiber on PZT), limit of detection of 1.7 pε/Hz1/2 at 100 Hz, sensing range of 121.5 km without an optical amplifier, spatial resolution of 5 m, and position error as small as 34 m. The vibration frequency range tested is from 0.01 to 100 Hz. The sensing system has several advantages, including elegant setup, noise mitigation, and super-long sensing distance.

Long-range distributed vibration sensing using phase-sensitive forward optical transmission.

Long-range vibration sensing is an important tool for real-time structural health monitoring. A new, to the best of our knowledge, design of a distributed fiber-optic vibration sensor is introduced and experimentally demonstrated in this study. The proposed system utilizes the transmission of light in the forward direction for sensing, and a self-interference method for laser source simplification. To extract vibration information from phase modulation of light, two Mach-Zehnder interferometers (MZIs) are employed with a 3 × 3 coupler-based differential cross multiplication algorithm for phase calculation. A folded double-ended detection configuration allows the time-of-flight difference via cross correlation (CC) to provide vibration positioning. Experimental results demonstrate a sensing range of up to ∼80 km without optical amplification, accompanied by a position accuracy of 336 m.

Screening of Endocrine Disrupting Potential of Surface Waters via an Affinity-Based Biosensor in a Rural Community in the Yellow River Basin, China.

Overcoming the limitations of traditional analytical methods and developing technologies to continuously monitor environments and produce a comprehensive picture of potential endocrine-disrupting chemicals (EDCs) has been an ongoing challenge. Herein, we developed a portable nuclear receptor (NR)-based biosensor within 90 min to perform highly sensitive analyses of a broad range of EDCs in environmental water samples. Based on the specific binding of the fluorescence-labeled NRs with their ligands, the receptors were attached to the EDC-functionalized fiber surface by competing with EDCs in the samples. The biosensor emitted fluorescence due to the evanescent wave excitation, thereby resulting in a turn-off sensing mode. The biosensor showed a detection limit of 5 ng/L E2-binding activity equivalent (E2-BAE) and 93 ng/L T3-BAE. As a case study, the biosensor was used to map the estrogenic binding activities of surface waters obtained from a rural community in the Yellow River basin in China. When the results obtained were compared with those from the traditional yeast two-hybrid bioassay, a high correlation was observed. It is anticipated that the good universality and versatility exhibited by this biosensor for various EDCs, which is achieved by using different NRs, will significantly promote the continuous assessment of global EDCs.

A comprehensive review on electrochemical and optical aptasensors for organophosphorus pesticides.

There has been a rise in pesticide use as a result of the growing industrialization of agriculture. Organophosphorus pesticides have been widely applied as agricultural and domestic pest control agents for nearly five decades, and they remain as health and environmental hazards in water supplies, vegetables, fruits, and processed foods causing serious foodborne illness. Thus, the rapid and reliable detection of these harmful organophosphorus toxins with excellent sensitivity and selectivity is of utmost importance. Aptasensors are biosensors based on aptamers, which exhibit exceptional recognition capability for a variety of targets. Aptasensors offer numerous advantages over conventional approaches, including increased sensitivity, selectivity, design flexibility, and cost-effectiveness. As a result, interest in developing aptasensors continues to expand. This paper discusses the historical and modern advancements of aptasensors through the use of nanotechnology to enhance the signal, resulting in high sensitivity and detection accuracy. More importantly, this review summarizes the principles and strategies underlying different organophosphorus aptasensors, including electrochemical, electrochemiluminescent, fluorescent, and colorimetric ones.

Highly Transparent and Self-Healable Solar Thermal Anti-/Deicing Surfaces: When Ultrathin MXene Multilayers Marry a Solid Slippery Self-Cleaning Coating.

Solar anti-/deicing can solve icing problems by converting sunlight into heat. One of the biggest problems, which has long been plaguing the design of solar anti-/deicing surfaces, is that photothermal materials are always lightproof and appear black, because of the mutual exclusiveness between generating heat and retaining transparency. Herein, a highly transparent and scalable solar anti-/deicing surface is reported, which enables the coated glass to exhibit high transparency (>77% transmittance at 550 nm) and meanwhile causes a >30 °C surface temperature increase relative to the ambient environment under 1.0 sun illumination. Such a transparent anti-/deicing surface can be fabricated onto a large class of substrates (e.g., glass, ceramics, metals, plastics), by applying a solid omniphobic slippery coating onto layer-by-layer-assembled ultrathin MXene multilayers. Hence, the surface possesses a self-cleaning ability to shed waterborne and oil-based liquids thanks to residue-free slipping motion. Passive anti-icing and active deicing capabilities are, respectively, obtained on the solar thermal surface, which effectively prevents water from freezing and simultaneously melts pre-formed ice and thick frost. The self-cleaning effect enables residue-free removal of unfrozen water and interfacially melted ice/frost to boost the anti-/deicing efficiency. Importantly, the surface is capable of self-healing under illumination to repair physical damage and chemical degradation.

Review of Optical Humidity Sensors.

Optical humidity sensors have evolved through decades of research and development, constantly adapting to new demands and challenges. The continuous growth is supported by the emergence of a variety of optical fibers and functional materials, in addition to the adaptation of different sensing mechanisms and optical techniques. This review attempts to cover the majority of optical humidity sensors reported to date, highlight trends in design and performance, and discuss the challenges of different applications.

Femtosecond laser induced low propagation loss waveguides in a lead-germanate glass for efficient lasing in near to mid-IR.

To support the growing landscape of near to mid-IR laser applications we demonstrate a range of low propagation loss femtosecond laser (FSL) written waveguides (WGs) that have achieved guided-mode laser operation in a rare earth (RE) doped lead-germanate glass. The WGs are fabricated in both the athermal and thermal FSL writing regimes using three different pulse repetition frequencies (PRF): 100 kHz (athermal); 1 MHz; and 5 MHz (thermal). The lasing capability of Yb3+ doped lead-germanate waveguides is verified in the near-IR. The refractive index contrast (∆n) for 100 kHz WGs is ~ 1 × 10-4, while for 5 MHz, ∆n increases to ~ 5 × 10-4. The WGs in the thermal regime are less effected by self-focusing and are larger in dimensions with reduced propagation losses. For the 1 MHz repetition rate thermal writing regime we report a low propagation loss WG (0.2 dB/cm) and demonstrate laser operation with slope efficiencies of up to ~ 28%.

Light-sheet skew rays enhanced U-shaped fiber-optic fluorescent immunosensor for Microcystin-LR.

A novel U-shaped fiber-optic evanescent-wave fluorescent immunosensor was designed that exploits light-sheet excitation of skew rays in a passive fiber for sensitive microcystin-LR (MC-LR) detection in real-time. In particular, a light sheet comprising a thin plane of light can be concentrated into exciting the optimum ray group, resulting in enhanced interaction between light and fluorophores. Meanwhile, skew rays excited by transmitting light into an optical fiber with an angle offset allow a much higher number of total-internal-reflections with increased interaction length along the fiber interface, which strengthens the light-matter interactions. Under the optimal angle offset, the proposed evanescent wave fluorescent immunosensor is the first demonstration of integrating light-sheet skew rays and a U-shaped fiber-optic probe for enhanced sensitivity. The results show that fluorescence sensitivity of the U-shaped fiber-optic probe with light-sheet skew rays excitation is 16 times higher than that of collimated skew rays excitation. Combined with this newly designed light-sheet skew rays enhanced U-shaped fiber-optic fluorescent immunosensor, a sensitive and real-time MC-LR detection method was established based on the indirect competitive immunoassay principle. Real environmental water samples spiked with MC-LR were determined by the immunosensor with recovery rates between 85% and 112%. The present system could be an alternative tool for the on-site environmental monitoring, in-field food safety assurance and clinical diagnostics. It also advances the fiber-optic sensors field in terms of experimental design.

Fiber-Optic Skew Ray Sensors.

The evanescent fields along multimode fibers are usually relatively weak. To enhance the sensitivity of the resulting sensors, skew rays have been exploited for their larger number of total internal reflections and their more comprehensive spread over the fiber surface. The uniform distribution of light-matter interactions across the fiber surface facilitates high sensitivity through an increased interaction area, while mitigating the risk of laser-induced coating-material damage and photobleaching. Power-dependent measurements are less susceptible to temperature effects than interferometric techniques, and place loose requirements on the laser source. This review highlights the key developments in this area, while discussing the benefits, challenges as well as future development.

Light-Sheet Skew Ray-Enhanced Localized Surface Plasmon Resonance-Based Chemical Sensing.

A stronger absorption of pump/probe light is desirable for maximizing the sensitivity to enable accurate measurements of trace chemical elements. We introduce a new sensing technique built on light-sheet excitation of skew rays in a multimode fiber with an additional enhancement of localized surface plasmon resonance (LSPR) and its evanescent-field hotspots between gold nanospheres on the coated fiber. A skewed light-sheet (i.e., a thin plane of light) can exploit the optimum ray group, producing enhanced and uniform interactions between light and matter for higher absorption/sensitivity and higher power threshold. The heightened evanescent field couples to the localized surface plasmon resonant modes to attain even greater sensitivity. We compared this excitation method with the previously demonstrated light-sheet skew ray-based sensor without LSPR and observed an enhancement in normalized attenuation of pump light up to seven orders of magnitude for low-concentration rhodamine B. The improvement in the normalized detection limit is almost three orders of magnitude. This new sensing technique uses a functionalized fiber rather than pairing a passive fiber with added functional particles in the analyte, which offers better area-selectivity. The potentially low-cost chemical sensors can be used on a range of sensing mechanisms such as pump/probe light absorption.

Femtosecond-laser-written Microstructured Waveguides in BK7 Glass.

There is a deficiency of low-loss microstructured waveguides that can be fabricated with a single laser-pass to minimize stress build-up, which can enable enhanced functionality and higher compactness for integrated optical devices. We demonstrate, for the first time, a series of multi-ring claddings each with a pair of cores in BK7 glass. Each waveguide was fabricated using only a single laser-pass at 1 MHz pulse repetition rate, 5 mm/s translation speed, 250 fs pulse width, over a set of pulse energies. We obtained the lowest-reported propagation loss of 0.062 dB/cm, measured at 1155 nm wavelength from the waveguide written with 340 nJ pulse energy. The maximum observed numerical aperture is 0.020, measured at 1155 nm wavelength from the waveguide written with 620 nJ pulse energy. Such waveguides could be incorporated in integrated Raman laser platforms for biomedical applications.

Highly coherent free-running dual-comb chip platform.

We characterize the frequency noise performance of a free-running dual-comb source based on an erbium-doped glass chip running two adjacent mode-locked waveguide lasers. This compact laser platform, contained only in a 1.2 L volume, rejects common-mode environmental noise by 20 dB thanks to the proximity of the two laser cavities. Furthermore, it displays a remarkably low mutual frequency noise floor around 10 Hz2/Hz, which is enabled by its large-mode-area waveguides and low Kerr nonlinearity. As a result, it reaches a free-running mutual coherence time of 1 s since mode-resolved dual-comb spectra are generated even on this time scale. This design greatly simplifies dual-comb interferometers by enabling mode-resolved measurements without any phase lock.

Widely tunable, high slope efficiency waveguide lasers in a Yb-doped glass chip operating at 1 µm.

Ultrafast laser inscribed waveguide lasers can lead to highly efficient and compact optical devices. This Letter reports an average lasing efficiency of 65%±2.5% from a multi-waveguide 2.5 mol. % ytterbium-doped ZrF4-BaF2-LaF3-AlF3-NaF (Yb:ZBLAN) chip in an extended-cavity configuration. A maximum output power of 750 mW with a lasing efficiency of 68% is also achieved. A monolithic end-coupled configuration reached a maximum output power of 784 mW with a lasing efficiency of 70%. The lasing wavelength is tuned from 1001 to 1045 nm in a Littrow configured cavity. A beam propagation factor of the lowest-order transverse-mode output was routinely achieved with an M2 of 1.15.

Author Correction: Ultra-fast Hygrometer based on U-shaped Optical Microfiber with Nanoporous Polyelectrolyte Coating.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Optical Microfiber Technology for Current, Temperature, Acceleration, Acoustic, Humidity and Ultraviolet Light Sensing.

Optical microfibers possess excellent optical and mechanical properties that have been exploited for sensing. We highlight the authors' recent work in the areas of current, temperature, acceleration, acoustic, humidity and ultraviolet-light sensing based on this exquisite technology, and the advantages and challenges of using optical microfibers are discussed.

Ultra-fast Hygrometer based on U-shaped Optical Microfiber with Nanoporous Polyelectrolyte Coating.

Real-time measurement of the relative humidity of air has applications ranging from process control to safety. By using a microfiber form-factor, we demonstrate a miniature and fast-response hygrometer with the shortest-ever response time (3 ms). The sensor head consists of an optical microfiber of 10 µm diameter and 2 mm length configured to form a compact U-shaped probe, and functionalized with a polyelectrolyte multilayer coating of 1.0 bilayer. The sensing mechanism is primarily water-absorption-based optical loss. We have measured a response time of 3 ms and a recovery time of 36 ms. The sensitivity is as high as 0.4%/%RH, and the detection limit is as low as 1.6%RH. The maximum relative humidity is 99%RH, before reaching a recoverable dew-point.

Self-corrected chip-based dual-comb spectrometer.

We present a dual-comb spectrometer based on two passively mode-locked waveguide lasers integrated in a single Er-doped ZBLAN chip. This original design yields two free-running frequency combs having a high level of mutual stability. We developed in parallel a self-correction algorithm that compensates residual relative fluctuations and yields mode-resolved spectra without the help of any reference laser or control system. Fluctuations are extracted directly from the interferograms using the concept of ambiguity function, which leads to a significant simplification of the instrument that will greatly ease its widespread adoption and commercial deployment. Comparison with a correction algorithm relying on a single-frequency laser indicates discrepancies of only 50 attoseconds on optical timings. The capacities of this instrument are finally demonstrated with the acquisition of a high-resolution molecular spectrum covering 20 nm. This new chip-based multi-laser platform is ideal for the development of high-repetition-rate, compact and fieldable comb spectrometers in the near- and mid-infrared.

Photodetector based on Vernier-Enhanced Fabry-Perot Interferometers with a Photo-Thermal Coating.

We present a new type of fiber-coupled photodetector with a thermal-based optical sensor head, which enables it to operate even in the presence of strong electro-magnetic interference and in electrically sensitive environments. The optical sensor head consists of three cascaded Fabry-Perot interferometers. The end-face surface is coated with copper-oxide micro-particles embedded in hydrogel, which is a new photo-thermal coating that can be readily coated on many different surfaces. Under irradiation, photons are absorbed by the photo-thermal coating, and are converted into heat, changing the optical path length of the probing light and induces a resonant wavelength shift. For white-light irradiation, the photodetector exhibits a power sensitivity of 760 pm/mW, a power detection limit of 16.4 µW (i.e. specific detectivity of 2.2 × 105 cm.√Hz/W), and an optical damage threshold of ~100 mW or ~800 mW/cm2. The response and recovery times are 3.0 s (~90% of change within 100 ms) and 16.0 s respectively.