Observation and all-optical manipulation of replica symmetry breaking dynamics in a multi-Stokes-involved Brillouin random fiber laser photonic system.

In this paper, we propose and demonstrate an all-optical control of RSB transition in a multi-wavelength Brillouin random fiber laser (MWBRFL). Multi-order Stokes light components can be subsequently generated by increasing the power of the Erbium-doped fiber amplifier (EDFA) inside the MWBRFL, providing additional disorder as well as multiple Stokes-involved interplay. It essentially allows diversified laser mode landscapes with adjustable average mode lifetime and random mode density of the 1st order Stokes, which benefits the switching between replica symmetry breaking (RSB) and replica symmetry (RS) states in an optically controlled manner. Results show that the average mode lifetime of the 1st order Stokes component gradually decreases from 250.0 ms to 1.2 ms as high orders from the 2nd to the 5th of Stokes components are activated. Meanwhile, the order parameter q of the 1st order Stokes random lasing emission presents distinct statistical distributions within the selective sub-window under various EDFA optical powers. Consequently, all-optical dynamical control of the 1st Stokes random laser mode landscapes with adjustable average mode lifetime turns out to be attainable, facilitating the RSB transition under an appropriate observation time window. These findings open a new avenue for exploring the underlying physical mechanisms behind the occurrence of the RSB phenomenon in photonic complex systems.

Highly stabilized fiber Bragg grating accelerometer based on cross-type diaphragm.

A fiber Bragg grating (FBG) accelerometer based on cross-type diaphragm was proposed and designed, in which the cross-beam acts as a spring element. To balance the sensitivity and stability, the accelerometer structure was optimized. The experimental results show that the designed device has a resonant frequency of 556 Hz with a considerable wide frequency bandwidth of up to 200 Hz, which is consistent with the simulation. The sensitivity of the device is 12.35 pm/g@100 Hz with a linear correlation coefficient of 0.99936. The proposed FBG accelerometer has simple structure and strong anti-interference capability with a maximal cross-error less than 3.26%, which can be used for mechanical structural health monitoring.

Hierarchical Porous Carbon Based on Waste Quinoa Straw for High-Performance Supercapacitors.

This work presents a novel porous activated carbon electrode based on quinoa straw (QSC), which is derived from the Qinghai-Tibet Plateau. The QSC is prepared through simple precarbonization and potassium carbonate (K2CO3) activation processes and is intended for use in supercapacitors. The QSC-3 exhibits a high specific capacitance of 469.5 F g-1 at a current density of 0.5 A g-1, as well as a high specific surface area of 1802 m2 g-1. Additionally, symmetrical supercapacitors assembled using QSC-3 samples demonstrate a superior energy power density. In a 3 M KOH electrolyte, the energy density can reach 15.0 Wh kg-1 at a power density of 689.7 W kg-1. In a 1 M Na2SO4 electrolyte, the power density reaches 999.00 W kg-1, and the energy density is 39.68 Wh kg-1. Furthermore, the device shows excellent cycle life in both 3 M KOH and 1 M Na2SO4 electrolytes, with capacitance retentions of 97.55% and 96.20% after 10 000 cycles, respectively. This study provides an excellent example of utilizing waste quinoa straw to achieve low-cost, high-performance supercapacitor electrode material for sustainable electrochemical energy storage systems.

Vibration-insensitive polarimetric fiber optic current sensor based on orbital angular momentum modes in an air-core optical fiber.

Current or magnetic field sensing is usually achieved by exploiting the Faraday effect of an optical material combined with an interferometric probe that provides the sensitivity. Being interferometric in nature, such sensors are typically sensitive to several other environmental parameters such as vibrations and mechanical disturbances, which, however, inevitably impose the inaccuracy and instability of the detection. Here we demonstrate a polarimetric fiber optic current sensor based on orbital angular momentum modes of an air-core optical fiber. In the fiber, spin-orbit interactions imply that the circular birefringence, which is sensitive to applied currents or resultant magnetic fields, is naturally resilient to mechanical vibrations. The sensor, which effectively measures polarization rotation at the output of a fiber in a magnetic field, exhibits high linearity in the measured signal versus the applied current that induces the magnetic field, with a sensitivity of 0.00128 rad/A and a noise limit of 1×10-5/H z. The measured polarization varies within only ±0.1% under mechanical vibrations with the frequency of up to 800 Hz, validating the robust environmental performance of the sensor.

Distributed optical fiber magnetic field sensor based on polarization-sensitive OFDR.

A distributed optical fiber magnetic field sensor based on a polarization-sensitive optical frequency domain reflectometer (POFDR) is proposed. It extracts the accumulated Faraday rotation by combining the Stokes vectors and the backward Mueller matrices from the measured states of polarization (SOPs) and obtains the magnetic field component. This method avoids adjusting the input polarization during the magnetic field sensing process. It overcomes the drawback of the conventional POFDR scheme, which requires at least two sets of different input SOPs for each sensing. Finally, the aforementioned effectiveness has been experimentally verified by using a single-mode sensing fiber. The results show that the sensor has good repeatability and linearity. The measurement error of the magnetic field sensor is 19.4 mT. The measured magnetic field variations agree with the applied ones with similarities higher than 0.98.

Heterogeneous integrated optical fiber with side nickel core for distributed magnetic field sensing.

A design of a heterogeneous integrated optical fiber with side nickel core (SNCF) has been proposed and demonstrated for distributed fiber-optic magnetic field sensing. Experimental results show that magnetic properties of nickel can be preserved well after the high temperature drawing process. The functionality of the SNCF has been well verified, with the sensitivity for DC magnetic field being up to -2.42 µÎµ/mT (below 8 mT). Besides, the SNCF finally presents magnetostriction saturation under a certain magnetic field, which agrees with the simulation. The proposed direct thermal drawing method to produce metal-heterogeneous integrated optical fiber paves the way for a simple and scalable means of incorporating metallic materials into fibers, as well as providing a promising candidate for long-distance distributed magnetic field sensing.

Towards high-sensitivity and high-accuracy forward Brillouin scattering-based optomechanical temperature sensing in thin-diameter fibers.

We numerically and experimentally demonstrated a high-sensitivity and high-accuracy temperature sensor based on guided acoustic radial modes of forward stimulated Brillouin scattering (FSBS)-based optomechanics in thin-diameter fibers (TDF). The dependence of the FSBS-involved electrostrictive force on the fiber diameter is systematically investigated. As the diameters of the fiber core and cladding decrease, the intrinsic frequency of each activated acoustic mode and corresponding FSBS gain are expected to be accordingly increased, which benefits the significant enhancement of its temperature sensitivity as well as the optimization of the measurement accuracy. In validations, by utilizing TDFs with fiber diameters of 80 µm and 60 µm, the proof-of-concept experiments proved that sensitivities of the TDF-based FSBS temperature sensor with radial modes from R0,4 to R0,15 increased from 35.23 kHz/°C to 130.38 kHz/°C with an interval of 8.74 kHz/°C. The minimum measurement error (i.e., 0.15 °C) of the temperature sensor with the 60 µm-TDF is 2.5 times lower than that of the 125 µm-SSMF (i.e., 0.39 °C). The experimental and simulated results are consistent with theoretical predictions. It is believed that the proposed approach with high sensitivity and accuracy could find potential in a wide range of applications such as environmental monitoring, chemical engineering, and cancer detection in human beings.

Two-photon 3D printing diaphragm-integrated ring waveguide coupler for ultrasound detection.

We demonstrate a diaphragm-integrated ring waveguide coupler fabricated by the two-photon direct laser wring technique as an ultrasonic sensor, which is integrated on an optical fiber tip. The device consists of a micro-ring waveguide with a diameter of 5 µm functionalized as an optical fiber tip light reflection mirror and a straight waveguide connecting a diaphragm. The evanescent field coupling can be realized between the two waveguides, and the coupling efficiency can be changed due to the variation of the coupling gap induced by ultrasound. Accordingly, the light reflection can be changed. Based on the plate vibration theory, the vibration frequency can be changed through optimizing the diaphragm size. The experiments show that the device exhibits a high sensitivity and low noise equivalent acoustic signal level of 1.07 mPa/Hz1/2 at 100 kHz, which has great potential in various acoustic wave sensing applications.

Sub-kHz high-order mode Brillouin random fiber laser based on long-period fiber grating and distributed Rayleigh scattering in a half-open linear cavity.

We demonstrate a narrow-linewidth high-order-mode (HOM) Brillouin random fiber laser (BRFL) based on a long-period fiber grating (LPFG) and distributed Rayleigh random feedback in a half-open linear cavity. The single-mode operation of the laser radiation with sub-kilohertz linewidth is achieved thanks to distributed Brillouin amplification and Rayleigh scattering along kilometer-long single mode fibers whilst a few mode fiber-based LPFGs enable the transverse mode conversion among a broadband wavelength range. Meanwhile, a dynamic fiber grating (DFG) is embedded and incorporated to manipulate and purify the random modes, which hence suppresses the frequency drift resulting from random mode hopping. Consequently, the random laser emission with either high-order scalar or vector modes can be generated with a high laser efficiency of 25.5% and an ultra-narrow 3-dB linewidth of 230 Hz. Furthermore, the dependence of the laser efficiency and frequency stability on the gain fiber length are also experimentally investigated. It is believed that our approach could provide a promising platform for a wide range of applications such as coherent optical communication, high-resolution imaging, highly sensitive sensing, etc.

Quasi-distributed vibration sensing using OFDR and weak reflectors.

We proposed a quasi-distributed vibration sensing technique using in-line weak reflectors and optical frequency domain reflectometry (OFDR). As a result, we achieved an 8 kHz measurable vibration frequency with a 15-20 cm spatial resolution employing a low repetition rate (∼8 Hz). Moreover, a measurable frequency of 30 kHz was achieved for a 1.5 m spatial resolution. The ability of the system to determine the frequency and amplitude of several sections vibrating simultaneously is evaluated for different configurations. Because of the simple arrangement, high detectable frequency, and high sensitivity, this approach is expected to be especially well suited for mechanical vibration sensing applications, particularly in medium-sized structures.

Fast demodulation of OFDR based long length FBG sensing system for noisy signals.

The high spatial resolution, high accuracy, as well as real-time capability of distributed fiber-optic sensors are important for real-time structural health monitoring. As one of the promising technologies, the optical frequency domain reflectometry (OFDR) based sensors, have attracted lots of attention. Currently, for the demodulation, the conventional method based on short time Fourier transform requires long computational time, while a recent method based on group delay can remarkably improve the calculation speed but has low noise tolerance. In this study, we propose a fast demodulation method which employs the cross correlation, weighted sliding windowed Fourier transform and logistic activation function based thresholding process. This approach keeps good balance among the high spatial resolution, high accuracy, and the real-time capability that is expected to further improve the applicability of OFDR based sensors.

Self-Evaluation of PANDA-FBG Based Sensing System for Dynamic Distributed Strain and Temperature Measurement.

A novel method is introduced in this work for effectively evaluating the performance of the PANDA type polarization-maintaining fiber Bragg grating (PANDA-FBG) distributed dynamic strain and temperature sensing system. Conventionally, the errors during the measurement are unknown or evaluated by using other sensors such as strain gauge and thermocouples. This will make the sensing system complicated and decrease the efficiency since more than one kind of sensor is applied for the same measurand. In this study, we used the approximately constant ratio of primary errors in strain and temperature measurement and realized the self-evaluation of the sensing system, which can significantly enhance the applicability, as well as the reliability in strategy making.

Dependence of measurement accuracy on the birefringence of PANDA fiber Bragg gratings in distributed simultaneous strain and temperature sensing.

By both simulation and experiment, we studied the relationship of the measurement accuracy and the birefringence of the distributed simultaneous strain and temperature sensor using polarization-maintaining fiber Bragg gratings (PANDA-FBGs). The PANDA-FBGs were applied to an optical frequency domain reflectometry (OFDR) which is capable of distributed measurement at high spatial resolution and sampling rate. The simulated results had agreement with the experimental results that the measurement accuracy of both strain and temperature were improved by increasing the birefringence. Additionally, the efficiency of the accuracy improvements decreased when accuracy increased.