Characterisation of the optical response to seismic waves of submarine telecommunications cables with distributed and integrated fibre-optic sensing.

We present the first controlled-environment measurements of the optical path-length change response of telecommunication submarine cables to active seismic and acoustic waves. We perform the comparison among integrated (optical interferometry) and distributed (distributed acoustic sensing, DAS) fibre measurements and ground truth data acquired by 58 geophones, 20 three-axis seismometers and 7 microphones. The comparison between different seismic acquisition methods is an essential step towards full validation and calibration of the data acquired using novel cable-based sensing techniques.

Roadmap on optical sensors.

Optical sensors and sensing technologies are playing a more and more important role in our modern world. From micro-probes to large devices used in such diverse areas like medical diagnosis, defence, monitoring of industrial and environmental conditions, optics can be used in a variety of ways to achieve compact, low cost, stand-off sensing with extreme sensitivity and selectivity. Actually, the challenges to the design and functioning of an optical sensor for a particular application requires intimate knowledge of the optical, material, and environmental properties that can affect its performance.

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.

Fast, selective, and sensitive detection of 2,4-dichlorophenol by an imprinted polymer functionalized core-offset U-shaped fiber sensor.

Pollution monitoring in waterways and oceans is often performed in a laboratory on samples previously taken from the environment. The integration of molecular imprinting polymer nanoparticles (MIP-NPs) with a novel, to the best of our knowledge, fiber optic interferometer allowed a fast and selective detection of water pollutant 2,4-Dichlorophenol (2,4-DCP). The proposed sensor with an increased surface-to-volume ratio of MIP-NPs provided an enhanced sensitivity of 17.

Variable ratio blue/red upconversion in Yb-Tm codoped fluorosilicate glasses.

Simultaneous blue-red emission in a fiber pumped by a single wavelength source is perceived as a great challenge because of the large energy difference of the emitted photons. This Letter reports the dependence of the blue-to-red upconversion (UC) emission ratio in Yb-Tm codoped fluorosilicate glasses (FSGs) under the excitation of a 980-nm laser on the host glass silica content. Photoluminescence spectra and SEM-EDS are used to clarify the UC mechanism, indicating that the probability of the cross-relaxation (CR) process G+ F→H+ F is key to the dominance of the blue or red emissions.

Compact high-resolution FBG strain interrogator based on laser-written 3D scattering structure in flat optical fiber.

We demonstrate a fiber Bragg grating (FBG) strain interrogator based on a scattering medium to generate stable and deterministic speckle patterns, calibrated with applied strain, which are highly dependent on the FBG back-reflection spectral components. The strong wavelength-dependency of speckle patterns was previously used for high resolution wavemeters where scattering effectively folds the optical path, but instability makes practical realization of such devices difficult. Here, a new approach is demonstrated by utilizing femtosecond laser-written scatterers inside flat optical fiber, to enhance mechanical stability.

Optical sensors, 2022: introduction to the feature issue.

This feature issue of Optics Express highlights contributions from authors who presented their latest research at the OPTICA Optical Sensors and Sensing Congress, held in Vancouver, British Columbia, Canada from 11-15 July 2022. The feature issue comprises 9 contributed papers, which expand upon their respective conference proceedings. The published papers introduced here cover a range of timely research topics in optics and photonics for chip-based sensing, open-path and remote sensing and fiber devices.

High resolution compact spectrometer system based on scattering and spectral reconstruction.

In this Letter, we present a compact scattering spectrometer system based on fluorosilicate glass ceramics. By the algorithmic spectral calibration and reconstruction, we achieve wavelength detection with a resolution of 0.1 nm.

Extruded TOPAS hollow-core anti-resonant fiber optimized for THz guidance at 0.9THz.

A hollow-core anti-resonant fiber for the THz regime is proposed and demonstrated. The proposed fiber is the hexagonal core shape which is directly extruded using a conventional 3D printer. Experimental results show that by using cyclic olefin copolymer (COC), the proposed fiber design provides a low attenuation of ∼3 dB∕m at ∼ 0.

Long Range Raman-Amplified Distributed Acoustic Sensor Based on Spontaneous Brillouin Scattering for Large Strain Sensing.

A Brillouin distributed acoustic sensor (DAS) based on optical time-domain refractometry exhibiting a maximum detectible strain of 8.7 mε and a low signal fading is developed. Strain waves with frequencies of up to 120 Hz are measured with an accuracy of 12 με at a sampling rate of 1.

Polarization fading mitigation in distributed acoustic sensors based on a high-speed polarization rotator.

A distributed optical fiber acoustic sensor based on interferometric demodulation technique with no polarization fading is demonstrated. A polarization diversity scheme based on a high-speed polarization rotator is used to eliminate signal fading due to polarization mismatch in the Rayleigh backscattered signal between adjacent points on the sensing fiber. This technique yields a spatially uniform response to the applied strain.

Low bend loss femtosecond laser written waveguides exploiting integrated microcrack.

We introduce the fabrication and use of microcracks embedded in glass as an optical element for manipulating light propagation, in particular for enhancing waveguide performance in silica integrated optics. By using a femtosecond laser to induce a strong asymmetric stress pattern in silica, uniform cracks with set dimensions can be created within the substrate and propagated along a fixed path. The smoothness of the resulting cleave interface and large index contrast can be exploited to enhance waveguide modal confinement.

Numerical Modelling of a Distributed Acoustic Sensor Based on Ultra-Low Loss-Enhanced Backscattering Fibers.

In this study, a distributed acoustic sensor (DAS) was numerically modeled based on the non-ideal optical components with their noises and imperfections. This model is used to compare the response of DAS systems to standard single-mode fibers and ultra-low loss-enhanced backscattering (ULEB) fibers, a fiber with an array of high reflective points equally spaced along its length. It is shown that using ULEB fibers with highly reflective points improves the signal-to-noise ratio and linearity of the measurement, compared with the measurement based on standard single-mode fibers.

Room-temperature watt-level and tunable ∼3 µm lasers in Ho/Pr co-doped AlF-based glass fiber.

A room-temperature watt-level continuous-wave-output power mid-infrared fiber laser operating at $\lambda\sim 3\; \unicode{x00B5}{\rm m}$ is demonstrated using a ${{\rm Ho}^{3 +}}/{{\rm Pr}^{3 +}}$ co-doped ${{\rm AlF} _3}$ based glass fiber as a gain fiber. This fixed-wavelength laser had maximum output power of 1.13 W with a slope efficiency of 10.

Enhanced 3.9 µm emission from diode pumped Ho/Eu codoped fluoroindate glasses.

The use of codoping for enhancing the :→ emission in fluoroindate glasses shows that could depopulate the lower laser state : while having little effect on the upper state :, resulting in greater population inversion. The / codoped glass has high spontaneous transition probability (6.31) together with large emission cross section (7.

High-sensitivity, fast-response ethanol gas optical sensor based on a dual microfiber coupler structure with the Vernier effect.

A high-sensitivity ethanol gas sensor based on two microfiber couplers and the Vernier effect is examined in this Letter using the unique variation rate conversion point characteristics. The output spectrum of the two couplers connected in parallel are superimposed to form a symmetrical envelope curve, showing high responsivity to variations in the external environment. Ethanol sensitivity was achieved by coating the waist region of the coupler with a mixture of Nile red and polymethyl methacrylate.

152 km-range single-ended distributed acoustic sensor based on inline optical amplification and a micromachined enhanced-backscattering fiber.

In this Letter, a distributed acoustic sensor (DAS) with a sensing range in excess of 150 km is reported. This extended sensing range is achieved by adding a low-loss enhanced-backscattering fiber at the far end of a standard single-mode fiber. A conventional DAS system along with inline optical amplifiers are used to interrogate the sensing fiber.

High-Performance Ultrafast Humidity Sensor Based on Microknot Resonator-Assisted Mach-Zehnder for Monitoring Human Breath.

Monitoring the dynamic humidity requires sensors with fast response and anti-electromagnetic interference, especially for human respiration. Here, an ultrafast fiber-optic breath sensor based on the humidity-sensitive characteristics of gelatin film is proposed and experimentally demonstrated. The sensor consists of a microknot resonator superimposed on a Mach-Zehnder (MZ) interferometer produced by a tapered single-mode fiber, which has an ultrafast response (84 ms) and recovery time (29 ms) and a large dynamic transmission range.

Broadband 2.7 µm mid-infrared emissions in Er-doped PbO-PbF-BiO-GaO glasses.

Broadband emission at 2.7 µm is observed in an -doped --- glass. The measured emission band full-width-at-half-maximum (FWHM) is ∼184.

Singlemoded THz guidance in bendable TOPAS suspended-core fiber directly drawn from a 3D printer.

Terahertz (THz) technology has witnessed a significant growth in a wide range of applications, including spectroscopy, bio-medical sensing, astronomical and space detection, THz tomography, and non-invasive imaging. Current THz microstructured fibers show a complex fabrication process and their flexibility is severely restricted by the relatively large cross-sections, which turn them into rigid rods. In this paper, we demonstrate a simple and novel method to fabricate low-cost THz microstructured fibers.

Tm-doped fluorotellurite glass microsphere resonator laser at 2.3 µm.

In this Letter, we report lasing at 2.3 µm in Tm-single-doped and Tm/Ho-codoped fluorotellurite glass microsphere resonators. By employing a 793 nm diode laser as a pump and exploiting whispering gallery mode microresonators (WGMRs), dual-wavelength lasing at 1.

100-km-sensing-range single-ended distributed vibration sensor based on remotely pumped Erbium-doped fiber amplifier.

In this Letter, we report a single-ended distributed vibration sensor with the 100 km sensing range. This sensing range is achieved by remotely pumping two pieces of Er-doped fibers incorporated along the sensing fiber with a 1480 nm Raman fiber laser at the front end. A strain resolution of 100 nϵ combined with a spatial resolution of 2.