Distributed acoustic sensing (DAS) systems have been widely employed in oil and gas resource exploration, pipeline monitoring, traffic and transportation, structural health monitoring, hydrophone usage, and perimeter security due to their ability to perform large-scale distributed acoustic measurements. Conventional DAS relies on Rayleigh backscattering (RBS) from standard single-mode fibers (SMFs), which inherently limits the signal-to-noise ratio (SNR) and sensing robustness. Ultra-weak fiber Bragg grating (UWFBG) arrays can significantly enhance backscattering intensity and thereby improve DAS performance. This review provides a comprehensive overview of recent advances in UWFBG arrays for high-performance DAS. We introduce major inscription techniques for UWFBG arrays, including the drawing tower grating method, ultraviolet (UV) exposure through UV-transparent coating fiber technologies, and femtosecond laser direct writing methods. Furthermore, we summarize the applications of UWFBG arrays in DAS systems for the enhancement of RBS intensity, suppression of fading, improvement of frequency response, and phase noise compensation. Finally, the prospects of UWFBG-enhanced DAS technologies are discussed.

The wavelength-division-multiplexed (WDM) fiber Bragg grating (FBG) array inscribed by using femtosecond laser is a promising quasi-distributed temperature sensors due to its excellent thermal resistance. We developed the femtosecond laser point-by-point (PbP) inscription method to create the high-quality WDM FBG array featuring with uniform reflectivity, low polarization dependent loss (PDL), and high side-mode suppression ratio (SMSR). The shutter and the slit were inserted into the inscription system, which can be used to decrease the PDL and increase the uniformity in reflection of FBG. Moreover, the precise control over the position of refractive index modulations (RIMs) is used to realize apodized profiles, increasing the SMSR of FBG. By using these approaches, a high-quality WDM FBG array consisting of ten gratings was fabricated successfully. In addition, the FBG arrays packaged by stainless steel microtube were welded on the steel plate. High-temperature tests were carried out. The results show that the temperature distributions of the plate can be measured by using such WDM FBG arrays. Moreover, a 40-h, 700 degrees C test and a cycling temperatures test were performed. These arrays exhibited excellent high thermal stability and good repeatability in temperature measurements. Furthermore, a thermal shock test was carried out by using the flame projector, and the maximum temperature of 1000 degrees C was achieved. During the test, the sensors can measure the temperature stably. Hence, the proposed WDM FBG array is a promising quasi-distributed high-temperature sensor, which can be applied in many fields, for example, power plants, gas turbines, and hypersonic vehicles.

Femtosecond-laser-inscribed fiber Bragg gratings (FBGs) have shown great potential for high-temperature sensing, yet accurate demodulation under extreme conditions remains challenging. Over a wide temperature range, the spectral response of FBGs becomes increasingly nonlinear, which reduces the accuracy of conventional fitting models. Sapphire fiber Bragg gratings (SFBGs) can operate at temperatures up to 1900 °C, but their multimode interference (MMI) effect and strongly nonlinear spectral behavior make high-accuracy temperature demodulation more difficult. To address these issues, a deep-learning demodulation architecture based on a convolutional attention bidirectional long short-term memory network (CAB-LSTM) is proposed. To build spectral training datasets with reliable temperature labels, fiber grating sensors with thermal responses matched to that of a thermocouple were designed and fabricated. A geometric tuning method was adopted to optimize the sensor packaging, and the package diameters of the FBG and SFBG sensors were controlled at 2.3 and 2.1 mm, respectively. This design enabled strict thermal-response alignment between the fiber sensors and the thermocouple, so that each spectrum was assigned an accurate temperature label. Experimental results show that the standard deviation (SD) of the FBG sensor remained within 0.72 °C at 700 °C. For the SFBG sensor, the SD values were 1.007 °C at 800 °C and 1.228 °C at 1600 °C. With physically aligned training data and the CAB-LSTM architecture, the proposed method provides an effective solution for real-time and high-accuracy temperature monitoring in extreme industrial environments.

Reconfigurable photodetectors featuring stable, high-speed, and nonvolatilely programmable photoresponse states are essential for in-sensor computing, yet their realization remains a significant challenge. Here, we report two-dimensional ambipolar floating-gate optoelectronic memories (2D AFGOMs) to address this limitation. By introducing an ambipolar channel, more balanced electron–hole transport is expected to facilitate carrier recombination after light removal, which is consistent with the observed fast and reversible optical modulation. Combined with the high interfacial barriers, the nonvolatilely programmed dark states remain nearly unchanged under repeated optical stimulation. As a result, the 2D AFGOMs exhibit 84 distinguishable photoresponse states (>6 bits) under 473 nm illumination, microsecond switching speeds (tr = 576 μs, td = 648 μs), and robust long-term dynamic stability (>104 s). This work provides a promising device platform for future neuromorphic vision-sensor research.

In this work, a ReMoS2 2-D material was grown on a sapphire planar substrate (FS) by chemical vapor deposition (CVD), and transferred to a gallium nitride patterned substrate (PGS) by a wet-transfer process to prepare ReMoS2/FS and ReMoS2/PGS photodetectors. Compared with the performance of the ReMoS2/FS photodetector, the ${I}_{\mathbf {light}}$ / ${I}_{\mathbf {dark}}$ of the ReMoS2/PGS photodetector is ${1.35} \times {10}^{{3}}$ , the responsivity is 91 A/W, and the detectivity is ${4.1} \times {10}^{{10}}$ Jones under the irradiation of light with a wavelength of 460 nm, which are increased by 46, 56, and 151 times, respectively. At the same time, the ReMoS2/PGS photodetector also has imaging capability and communication function.

Phase-sensitive optical time-domain reflectometry (Phi-OTDR) has been applied in distributed acoustic sensing (DAS) of many fields, such as deep-sea geological activity monitoring, oil extraction, and intelligent transportation. However, in Phi-OTDR, the continuous acquisition of broadband acoustic/vibration signals with high spatial resolution has always been a challenge. In this article, a real-time chirped-pulse (CP) Phi-OTDR based on overlap-save polyphase fast Fourier transform (OS-PFFT) optical pulse compression is demonstrated for DAS with high spatial resolution and broadband frequency response. In the proposed system, a polyphase-channel parallel approach is employed for interleaved sampling on Rayleigh backscattering (RBS) signal segments with subsequent FFT processing, thus reducing the computational load while improving data throughput. A pulse compression at a high sampling rate of 3.2 GSa/s has been achieved successfully in a field-programmable gate array (FPGA) without clock constraints. A strain resolution of 26.3 p epsilon/root Hz and a spatial resolution of 0.9 m were experimentally achieved at a distance of 25 km, and a spatial resolution of 2.5 m was achieved at 70 km. A low-frequency vibration at 0.01 Hz was detected with a signal-to-noise ratio (SNR) of 48 dB, whereas a maximum detectable frequency of 5 kHz was demonstrated. As a result, the proposed real-time DAS scheme has the potential to facilitate DAS applications with requirements for a wide-range frequency response and rapid sensing capabilities.

Addressing the urgent need for high-temperature vector vibration monitoring in extreme environments such as aerospace and oil exploration, this paper proposes and develops a novel accelerometer based on femtosecond laser-engraved eccentric fiber Bragg gratings (FBGs) and nickel-coated reflectors. This sensor employs a highly localized FBG with a 10 mm length and 1 mu m eccentricity fabricated within a single-mode fiber. It utilizes asymmetric refractive index modulation to achieve direction-sensitive cladding mode coupling. Simultaneously, a 30-nm-thick nickel film is sputter-deposited onto the fiber end-face to form a single-ended reflection structure. This design eliminates complex processes like fiber taper drawing and eccentric fusion splicing, overcoming the stability limitations of existing vector sensors at elevated temperatures. Experimental results demonstrate spectral stability across the 25 degrees C-1020 degrees C temperature range and effective vibration measurement at 800 degrees C. At the room temperature and 800 degrees C, the acceleration sensitivities are 0.169 V/g (R 2=0.993) and 0.0743 V/g (R 2=0.989), respectively, with a common frequency response range of 15 Hz-25 Hz. The maximum angular response sensitivities are 2.4 V/g and 1.2 V/g, respectively, fully validating its reliable vector detection capability across a wide temperature range. This study provides a compact, mechanically robust, and high-temperature-resistant solution for vibration monitoring in extreme environments.

Two-dimensional (2D) semiconductors offer opportunities for the development of post-Moore information devices due to their exceptional properties. Analogous to silicon-based technologies, the fabrication of wafer-scale single crystals stands as a prerequisite for their large-scale application. Herein, we demonstrate the seeded solid-phase epitaxial growth of wafer-scale single-crystalline 2H-MoTe2 arrays on diverse substrates through spatially confined single nucleation. By precisely controlling the nucleation and atomic diffusion processes, the production efficiency and quality of wafers have been significantly improved, laying the foundation for their practical applications in high-performance field-effect transistors and photodetectors. In particular, the in situ integrated 2H-MoTe2/Si p-n photodiode arrays exhibit a high photon-triggered on/off ratio of 106 and a detectivity exceeding 3 × 1012 Jones, which solves the arrays' crosstalk problem and enables near-infrared optical communication and optical imaging. This work offers a pathway toward large-scale production and integration of 2D semiconductors in the form of single crystals.

Single-frequency distributed Bragg reflector fiber lasers (DBR FLs) are attractive as sensing elements for detecting weak vibration or acoustic signals in extreme environments. However, conventional UV-written DBR FLs operate with two orthogonal polarization modes and can hardly operate in high-temperature environments. Herein, we propose the fabrication of polarization-controllable DBR FLs by using a slit beam shaping femtosecond (fs) laser point-by-point technology. High-quality fiber Bragg grating Fabry-Perot (FBG-FP) cavities with insertion loss as low as 0.2 dB are directly inscribed in Er-doped fibers to create DBR FLs. Both single-polarization and dual-polarization DBR FLs are created by changing the fs laser-induced birefringence using a mechanical slit. In addition, a DBR FL array consisting of eight DBR FLs is also successfully created. Experimental results show that the fabricated DBR FL can withstand a high temperature up to 800 degrees C and the laser linewidth increases from 1.55 kHz to 10.8 kHz as temperature raising from 25 degrees C to 800 degrees C. Furthermore, high-temperature vibration sensing at 800 degrees C is realized by using a single-polarization DBR FL, achieving an acceleration sensitivity of 0.319 rad/(m/s(2)). Moreover, a dual-polarization DBR FL is served as an ultrasonic sensor, realizing the ultrasonic non-destructive evaluation (NDE) in a 7075-aluminum plate.

Space exploration represents a critical frontier for advancing human knowledge and technology. However, the extreme space environment-characterized by wide temperature fluctuations, vacuum, radiation, atomic oxygen erosion, and micrometeoroid impacts-places exceptional demands on spacecraft materials. These conditions necessitate materials that are lightweight, thermally stable, radiation-and corrosion-resistant, and mechanically robust. High-performance fibers and fiber-reinforced composites have emerged as key candidates due to their excellent specific strength, stiffness, and tunable functionalities, finding broad use in spacecraft components, astronaut gear, and shielding systems. Despite growing interest in space-applied fiber materials, comprehensive reviews integrating material design principles, interface engineering strategies, and practical aerospace applications remain scarce. This review addresses that gap by systematically analyzing recent advances in highperformance fibers and composites for space use. It focuses on their performance under multifactorial space conditions and the impact of interfacial modification and matrix architectures on composite mechanics. Functional applications-such as atomic oxygen resistance, thermal protection systems, and electromagnetic shielding-are critically discussed, with an emphasis on limitations and challenges. Finally, we highlight future directions for material innovation, emphasizing the need for interdisciplinary approaches to advance next-generation aerospace fiber systems that not only meet demanding mission requirements but also support longterm sustainability for deep-space exploration.

Mode extraction is the inverse process of the double‐beam superposition principle in classical optics. While polarization mode extraction has been successfully demonstrated using an m‐order vector vortex beam, amplitude mode extraction remains a significant challenge due to the complex intertwinement of inherent amplitude modes. To address this challenge, a method is developed to extract arbitrary amplitude modes of a light beam in both the real and imaginary domains. By introducing competition between amplitude modes in these domains, the desired amplitude modes within a light beam can be selectively extracted in the focal region of an objective lens using an optical pen. This work demonstrates the principle of amplitude mode extraction, thereby potentially paving the way for multidimensional manipulation of light fields.

Is it possible to modulate the inherent properties of a light beam, namely amplitude, phase and polarization, simultaneously by merely its phase? Here, we solve this scientific problem by unifying all these three properties using phase vectorization and phase version of Malus’s law. Full-property spatial light modulator is therefore developed based on the unification of these three properties, which enables pixel-level polarization, amplitude and phase manipulation of light beam in a real-time dynamic way. This work not only implies that the amplitude, phase and polarization of a light beam are interconnected, but also offers a reliable answer on how to modulate these three properties of a light beam simultaneously, which will deepen our understanding about the behavior of light beam, and facilitate extensive developments in optics and relate fields.

Sapphire fiber Bragg gratings (SFBGs) are promising high-temperature sensors in many harsh environments, such as aviation, nuclear power, and furnaces. Here, we proposed and experimentally demonstrated a quasi-distributed high-temperature sensor based on an SFBG array sealed in an argon gas-infiltrated sapphire tube interrogated by using an InGaAs-based interrogator. An SFBG array including five SFBGs was inscribed using the femtosecond laser line-by-line method and sealed in an argon gas-infiltrated sapphire tube. A multi-peak auto-tracking algorithm, including the Hilbert transform and cross correlation algorithm (CCA), was employed to demodulate the array. The Hilbert transform method is introduced for the segmentation of the peak region in the reflection spectrum. The CCA was used to obtain the Bragg wavelength shift of each SFBG reflection peak. Then, we investigated the stability in demodulation of the SFBG array, and the result shows that Bragg wavelength dispersion is less than ±12 pm, which indicates that the interrogator and the proposed algorithm exhibit high accuracy and stability. Moreover, the SFBG array was calculated at high temperatures up to 1676 °C, and the thermal response curves of the SFBG array were obtained. Furthermore, the temperature distribution measurement of the blackbody radiation source was successfully carried out using the calibrated SFBGs array sensor, with a maximum test temperature of 1900 °C. Therefore, such a quasi-distributed high-temperature sensing system, including an SFBG array, interrogator, and multi-peak detection algorithm, is promising in applications with thermal gradients, such as metallurgical, aviation, and nuclear power industries.

We propose and demonstrate a high-performance DAS system using ultra-short fiber Bragg grating arrays (USFBG) and a phase-sensitive optical time domain reflectometry (phi- OTDR). A USFBG with an ultra-short length of 30 mu m was successfully fabricated in a single-mode fiber (SMF) by femtosecond laser point-by-point inscription, exhibiting a large full width at half maximum (FWHM) bandwidth of 24.6 nm. To the best of our knowledge, this is the largest grating bandwidth reported to date. The ultra-large bandwidth effectively avoids the mismatch between the wavelength of the system light source and the grating caused by temperature changes. Moreover, a USFBG array with 300 identical USFBGs and an interval of 5 m was fabricated along the SMF to enhance the backscattering signal and suppress fading noise. An optical pulse compression algorithm was also deployed in the heterodyne phi-OTDR system to improve the spatial resolution. Thanks to the combination of USFBG arrays and the pulse compression phi-OTDR system, a long-distance DAS with a sensing distance of 60 km, a spatial resolution of 5.9 m, and an improved strain resolution of 13.9 p epsilon/root Hz was achieved. Then, long-term high-temperature annealing was carried out, and the results showed that the fabricated USFBGs can withstand a high temperature of 1000 degrees C. A high-temperature DAS system capable of operating at up to 1000 degrees C was also demonstrated. As such, the proposed DAS systems could be used in harsh environments, such as aerospace vehicles, nuclear plants, and oil and gas exploration. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

Sapphire fiber Bragg gratings (SFBGs) are promising high-temperature sensors, which can be applied to measure temperature and strain in extreme environments. However, the multimode operation of SFBGs is susceptible to disturbance, leading to unreliable wavelength detection. Here, we propose by using added multimode fibers (AMMF) and tracing the longwave edge of reflection envelope to enhance the stability of wavelength detection for SFBG. The near-field profiles of transmission modes are investigated in sapphire fiber with different lengths of AMMF. It is found that the mode-field distribution of sapphire fiber can be improved by using AMMF with a length of 1000 m, which results in a reduction of relative standard deviation (RSD) from 57 % to 10 %. Then, the signal-to-noise ratio (SNR) in the reflection spectrum of SFBG is improved to 16 dB by polishing inclined end faces of sapphire fiber using the removal mechanism of hard-brittle materials. Furthermore, we detect the wavelengths of both the longwave edge and peak on the reflection envelope, which reveals lower fluctuations (i. e., SD = 0.02 nm) of the longwave edge, since lower-order modes are more stable during transmission. The effect of external disturbances (i.e., torsion and vibration) on demodulation of SFBG is also evaluated, with a maximum fluctuation of 0.06 nm (SD = 0.01 nm). A temperature experiment is carried out with the assembly and polynomial fitting curves with high fitness are obtained. Thus, our proposed methods enhance the reliability of wavelength detection in the reflection spectrum of SFBG, which is beneficial to improving the sensing performance of SFBG-based sensors.

Linear-frequency-swept (LFS) phase-sensitive optical time domain reflectometry (Φ-OTDR) can overcome the constraints between spatial resolution and signal-to-noise ratio. However, the Doppler shift induced by vibration in the Rayleigh backscattering (RBS) signal generates significant crosstalk beyond the vibration area. Here, we propose and demonstrate a Doppler-crosstalk-suppressed quasi-distributed acoustic sensor (QDAS) based on an LFS Φ-OTDR, utilizing a discrete Rayleigh-enhanced single-mode fiber (eSMF). The mechanism of Doppler-induced crosstalk was analyzed, and the effects of pulse parameters, including pulse width, sweep rate, and bandwidth, were studied. Moreover, a discrete eSMF was proposed to suppress the crosstalk by reducing the change rate in the local phase. As a proof of concept, a vibration signal with a frequency of 8 kHz was successfully detected with a spatial resolution of 10 cm, a strain resolution of 190 pε/√Hz, and an improved crosstalk suppression of 20 dB. The proposed QDAS system with Doppler-induced crosstalk suppression is promising for ultrasonic structural health monitoring, such as aerial vehicles and deep-sea submersibles.

Distributed acoustic sensing (DAS) based on phase-sensitive optical time-domain reflectometry (Φ-OTDR) enables long-reach monitoring for pipelines, geophysical exploration, and infrastructure safety. However, long-reach operation is limited by phase fading and low signal-to-noise ratio (SNR), which destabilize arctangent-based phase unwrapping and reduce far-end sensitivity. We propose a stable phase-demodulation scheme for chirped-pulse Φ-OTDR that digitally tracks optical-field evolution using an error-state Kalman filter (ESKF). On a 70-km fiber link, the scheme achieves strain resolutions of 4.9–42.2 pε/√Hz across different distances. Compared with conventional arctangent demodulation, the far-end sensitivity increases by 20 dB, yielding higher sensitivity and robustness under low-SNR conditions. The method requires no hardware changes and is fully compatible with existing Φ-OTDR systems. These results provide a practical, drop-in signal-processing pathway for long-distance, high-sensitivity DAS deployments.