Step-adaptive accelerated demodulation algorithm for LFM-pulse-based distributed acoustic sensing.

We propose a novel, to our knowledge, step-adaptive cross-correlation algorithm tailored for distributed acoustic sensing systems based on linear frequency modulation pulses, aiming for rapid demodulation. This algorithm adjusts its step length through an adaptive "successive refinement" search strategy, which greatly improves computational efficiency by reducing the number of cross-correlation computations. Experimental results have shown that the demodulation time can be reduced by approximately 15 times compared to the conventional method, while maintaining the same demodulation result.

Multimodal-Responsive Circularly Polarized Luminescence Security Materials.

Nations, industries, and aspects of everyday life have undergone forgery and counterfeiting ever since the emergence of commercialization. Securing documents and products with anticounterfeit additives shows promise for authentication, allowing one to combat ever-increasing global counterfeiting. One most-used effective encryption strategy is to combine with optical-security markers on the required protection objects; however, state-of-the-art labels still suffer from imitation due to their poor complexity and easy forecasting, as a result of deterministic production. Developing advanced anticounterfeiting tags with unusual optical characters and further incorporating complex security features are desired to achieve multimodal, unbreakable authentication capacity; unfortunately, this has not yet been achieved. Here, we prepare a series of stable circularly polarized luminescence (CPL) materials, composed of toxicity-free, high-quality-emitting inorganic quantum dots (QDs) and liquid crystals, using a designed helical-coassembly strategy. This CPL system achieves a figure of merit (FM, assessing the performance of both luminescence dissymmetry and quantum yield) value of 0.39, fulfilling practical demands for anticounterfeiting applications. Based on these CPL structures, we produce a type of multimodal-responsive security materials (MRSMs) that exhibits six different stimuli-responsive modes, including light activation, polarization, temperature, voltage, pressure, and view angle. Thus, we show a proof-of-principle blockchain-like integrated anticounterfeiting system, allowing multimodal-responsive, interactive/changeable information encryption-decryption. We further encapsulate the obtained security materials into a fiber to expand our materials to work on flexible fabrics, that is, building an intelligent textile with a color-adaptable function along with environmental change.

Evolution of the time delay signature of chaos generated in three types of optical injection systems.

The time delay signature (TDS) of chaos generated in three schemes of optical injection has been investigated, and the mechanism of TDS suppression (TDSS) is revealed. The first scheme is a continuous-wave (CW) laser unidirectionally injecting into a chaotic laser, and the TDS of the chaotic laser is suppressed below 0.08 in this structure. The second scheme is a chaotic laser unidirectionally injecting into a CW laser, where the parameter range of TDSS lower than 0.06 of this structure is the largest among the three schemes. The third scheme is two CW lasers coupling to each other, and two chaotic lasers with TDS (T D S<0.1) suppression can be obtained simultaneously. For the further analysis of the mechanism of TDSS, the quasi-linear relationship between the synchronization coefficient and TDS is revealed. This study will provide insight into the generation of chaotic lasers by optical injection and promote the application of chaotic lasers.

Construction and function of a high-efficient synthetic bacterial consortium to degrade aromatic VOCs.

Aromatic volatile organic compounds (VOCs) are a type of common pollution form in chemical contaminated sites. In this study, seven aromatic VOCs such as benzene, toluene, ethylbenzene, chlorobenzene, m-xylene, p-chlorotoluene and p-chlorotrifluorotoluene were used as the only carbon source, and four strains of highly efficient degrading bacteria were screened from the soil of chemical contaminated sites, then the synthetic bacterial consortium was constructed after mixing with an existing functional strain (Bacillus benzoevorans) preserved in the laboratory. After that, the synthetic bacterial consortium was used to explore the degradation effect of simulated aromatic VOCs polluted wastewater. The results showed that the functional bacterium could metabolize with aromatic VOCs as the only carbon source and energy. Meanwhile, the growth of the synthetic bacterial consortium increased with the additional carbon resources and the alternative of organic nitrogen source. Ultimately, the applicability of the synthetic bacterial consortium in organic contaminated sites was explored through the study of broad-spectrum activity.

Enhancing propionic acid production in the acidogenic fermentation of food waste facilitated by a fungal mash under neutral pH.

Fungal mash derived from Aspergillus spp. is a green enzymatic additive for food waste (FW) valorization. In this study, the production of volatile fatty acids (VFAs) and the proportion of propionic acid (PA) in VFAs were increased by utilizing a complex enzyme (CE) obtained from Aspergillus oryzae. Results showed that CE addition significantly promoted SCOD concentration in the hydrolysis at a wide pH range from 4 to 9. In contrast, the production of VFAs was influenced by pH, and the highest yields of VFAs and PA were found at pH 7. At the CE dosage of 0.2 g/g VSS, the concentration of VFAs in the FW fermentation liquid reached 38.1 g COD/L with the PA proportion up to 42.7%, which increased by 107.9% and 63.7%, respectively, relative to that in the zero-dosage group. With CE continuing to be added, the C/N ratio declined, and the primary metabolic pathway was converted from acetic acid-type to PA-type. Further investigation of the dominant microbial communities and their metabolic capacities showed that the acrylate-mediated pathway was the potential metabolic reaction in PA-type fermentation. These results indicated that CE pretreatment was a feasible strategy to enhance the PA-rich fermentation of FW under neutral pH conditions.

Broadband chaos generation utilizing a wavelength-tunable monolithically integrated chaotic semiconductor laser subject to optical feedback.

We demonstrate a broadband and wavelength-tunable chaotic laser by using a monolithically integrated wavelength-tunable chaotic semiconductor laser subject to optical feedback. The chip consists of a gain section, a distributed Bragg reflection grating section, a semiconductor optical amplifier section, and a phase section. By applying an optical feedback loop to the chaotic semiconductor laser chip, a nonlinear frequency mixing is stimulated in the laser cavity, and the chaos bandwidth is expanded to 33.6 GHz, which is 4.4 times larger than the bandwidth without optical feedback. Furthermore, the effect of feedback optical power on the bandwidth is investigated. The results show that the wide power spectrum of chaotic laser is available in a large wavelength range from 1556.44 nm to 1566.42 nm. This work explores a broadband and wavelength-tunable chaotic semiconductor laser for the wavelength division multiplexing to enlarge the capacity in chaotic secure optical communications.

Recognition of centimeter-level length changes using the intensity of probe light in BOTDA.

We proposed a method based on the Brillouin optical time domain analysis (BOTDA) system to demodulate the length changes of the heating region using the intensity of probe light, under the premise that the temperature in the heating region does not change and the Brillouin frequency shift (BFS) of the heating region is known. This method can realize the recognition of small length under the condition of wide pulse width. The theoretical analysis shows that the different lengths of the heating region will lead to different gains when the spatial resolution corresponding to the pulse width of the pulsed light is larger than the length of the heating region. And through theoretical derivation and simulation, it is concluded that the relationship between the intensity of probe light and the length of the heating region satisfies the exponential growth. Further experiments verify that the exponential growth is approximately linear in the range of small length changes. The length of the heating region can be inversely deduced by using the linear relationship by detecting the intensity of probe light. When the length of sensing fiber is 100 m and the heating region changes from 2 cm to 8 cm, 1 cm heating region changes can be identified.

Centimeter-level spatial resolution Brillouin optical time domain analyzer using mono-pulse self-difference.

To break through the limitation of pulse width on spatial resolution in the Brillouin optical time-domain analysis system (BOTDA), a novel, to the best of our knowledge, scheme based on mono-pulse self-difference (MPSD) is proposed for centimeter-level spatial resolution. It is performed by the self-difference of the temporal trace generated by a single-shot long pulse in the conventional BOTDA. The concept-proof of the proposed approach is demonstrated, and experimental results are presented where distributed temperature sensing with a 5-cm spatial resolution is realized based on a 40-ns pulse along a 2-km sensing fiber.

Effect of resolution bandwidth and video bandwidth on the characterization of chaos in a radio-frequency spectrum analyzer.

The effect of resolution bandwidth (RBW) and video bandwidth (VBW) of a radio-frequency spectrum analyzer on the characteristics of a power spectrum for chaos generated by a semiconductor laser with external optical feedback is investigated experimentally and numerically. We describe the spectral characteristics with effective bandwidth and time-delay signature (TDS) quantificationally. The experimental results demonstrate that the ratio of VBW to RBW has a significant impact on the smoothness of the power spectrum and effective bandwidth of chaos. Meanwhile, the RBW affects the resolution of periodical peaks of the power spectrum and the TDS of chaos, which is obtained by the power spectrum. The incorrect characterization of chaos can be avoided by setting the RBW to no more than 0.1 times as much as the resonance frequency of the external cavity of chaos and setting the VBW/RBW to no more than 0.01. The simulation results qualitatively agree with the analysis of the experiment.

Extracting Brillouin frequency shift accurately based on particle swarm optimization and a cross-correlation method.

A fitting algorithm based on particle swarm optimization (PSO) and the cross-correlation method (XCM) was proposed to accurately extract features of the Brillouin scattering spectrum. Both the simulation and experiment were conducted to verify the validity of the proposed algorithm. The results show that the algorithm achieves high demodulation accuracy and is suitable for Brillouin scattering spectra with different signal-to-noise ratios, full width at half-maximums, frequency sweep intervals, and spectral symmetries. Compared with the Lorenz curve fitting and XCM algorithm, the extraction error of the PSO-XCM can be optimized up to 99.98% and 99.93%, and the fitting degree can be improved by 98%. Moreover, based on the proposed algorithm, the minimum temperature measurement error can reach 0.06°C and the Brillouin frequency shift measurement error is 0.07 MHz in 10 km sensing fiber for the Brillouin optical time domain analysis (BOTDA) sensing system.

Recent Progress in Long-Range Brillouin Optical Correlation Domain Analysis.

Distributed optical fiber sensing technology has been widely applied in the areas of infrastructure health monitoring, national defense security, etc. The long-range high-spatial-resolution Brillouin optical correlation domain analysis (BOCDA) has extensive development and application prospects. In this paper, long-range BOCDAs are introduced and summarized. Several creative methods underpinning measurement range enlargement, including the interval enhancement of the adjacent correlation peak (CP), improvements in the signal-to-noise ratio, and the concurrent interrogation of multiple CPs, are discussed and experimentally verified, respectively. The main drawbacks in the present BOCDA schemes and avenues for future research and development have also been prospected.

Rapid noise removal based dual adversarial network for the Brillouin optical time domain analyzer.

We propose a dual adversarial network (DANet) to improve the signal-to-noise ratio (SNR) of the Brillouin optical time domain analyzer. Rather than inferring the conditional posteriori distribution in the conventional maximum a posteriori (MAP) framework, DANet constructs a joint distribution from two different factorizations corresponding to the noise removal and generation tasks. This method utilizes all the information between the clean-noisy image pairs to preserve data completely without requiring traditional image priors and noise distribution assumptions. Additionally, the clean-noisy image pairs produced by the generator can expand the original dataset to retrain and enhance the denoising effect. The performance of DANet is verified using the simulated and experimental data. Without spatial resolution deterioration, an SNR improvement of 35.51 dB is observed in the simulation, and the Brillouin frequency shift (BFS) uncertainty along the fiber is reduced by 3.56 MHz. Experiments yield a maximum SNR improvement of 19.08 dB, with the BFS uncertainty along the fiber reduced by 0.93 MHz. Significantly, DANet has a processing time of 1.26 s, which is considerably faster than conventional methods, demonstrating its potential for rapid noise removal tasks.

Experimental observation of chaotic Brillouin dynamic grating.

We experimentally observe the local Brillouin dynamic grating (BDG) based on a chaotic laser in a polarization-maintaining fiber for the first time, to the best of our knowledge. The grating length of the chaotic BDG can be adjusted by changing the optical spectral width of the chaotic laser. The characteristics of the reflection spectrum versus the grating length are further analyzed, which agrees with the theory of fiber Bragg grating. Temperature distributed measurements based on the chaotic BDG have been demonstrated with a spatial resolution of an order of centimeter.

Screening of silicon-activating bacteria and the activation mechanism of silicon in electrolytic manganese residue.

Electrolytic manganese residue (EMR) is a kind of solid waste with a high silicon content. Most of the silicon in EMR, however, exist in the state of SiO2, which cannot be directly absorbed by plants. Currently, it is very challenge to recover the silicon from EMR. In this study, a preliminary screening of strains with silicon-activating ability was conducted, and four strains were screened out and isolated from the soil around the tailings pond of EMR. Then, single factor experiments were conducted to obtain the optimal growth conditions of the four strains, and the results indicated that the Ochrobactrum sp. T-07 had the best silicon-activating ability from EMR after nitrosoguanidine mutagenesis (Ochrobactrum sp. T-07-B). The available silicon (in terms of SiO2) in the leaching solution was up to 123.88 mg L-1, which was significantly higher than that produced by Bacillus circulans and Paenibacillus mucilaginosus, the two commercial available pure culture strains. Results of direct/indirect contact experiments between Ochrobactrum sp. T-07-B and EMR revealed that bioleaching was promoted under the synergistic effect of bacteria growth on the surface of and metabolism within EMR. The newly isolated strains with silicon-activating effect are different from the existing-known silicate bacteria and may be used for more efficient silicon activation in silicate minerals.

Effect of chaotic time delay signature on Brillouin gain spectrum in the slope-assisted chaotic BOCDA.

In the chaotic Brillouin optical correlation domain analysis (CBOCDA) system, the broadband chaotic laser naturally widens the Brillouin gain spectrum (BGS), which provides an enhanced range for dynamic strain measurement via slope-assisted technology. However, inherent off-peak amplification at the time delay signature (TDS) position results in a deteriorated gain envelope. The mechanism behind the sub-peak of chaotic BGS is first analyzed and the negative correlated relationship between the value of main-sub-peak ratio (MSPR) and magnitude of TDS has been experimentally demonstrated. The limitation of sub-peak on the dynamic range is investigated, where the range is not greater than 400 µÎµ at MSPR < 0 dB, and 600 µÎµ at MSPR > 0 dB. Meanwhile, by eliminating the TDS, the BGS without sub-peak is obtained and a dynamic strain of 1200 µÎµ is successfully identified. Moreover, the application of optimized chaotic BGS in a multi-slope assisted system to realize the enlargement of dynamic strain range is also discussed.

Generation of a broadband chaotic laser by active optical feedback loop combined with a high nonlinear fiber.

We propose and demonstrate a method to generate a flat broadband chaotic laser by using an active optical feedback loop combined with a high nonlinear fiber. The feedback strength and nonlinear effect, especially the four-wave mixing effect of high nonlinear fiber, are studied to improve the bandwidth and flatness of chaos. When the feedback strength is 6.6 and injected fiber power is 1.0 W, a chaotic signal with a frequency range over 50 GHz, 80% bandwidth of 38.9 GHz, and flatness of 4.2 dB are experimentally achieved.

Dynamic strain measurement by a single-slope-assisted chaotic Brillouin optical correlation-domain analysis.

We propose a novel, to the best of our knowledge, method to enhance the measurement range of dynamic strain using a single-slope-assisted chaotic Brillouin optical correlation-domain analysis. The broadband chaos provides a Gaussian-shape pump-probe beat spectrum so that not only the centimeter-level spatial resolution is achieved but also the linewidth of the chaotic Brillouin gain spectrum is naturally broadened. Thus, the enlarged linear region could be employed to dynamically measure a large-range stretched strain. This experiment is the first to accurately identify the maximal strain of 1200 $\unicode{x00B5}\unicode{x03B5}$µÎµ with a high spatial resolution of 3.45 cm using the single-slope-assisted technology. The dynamic frequency is 4.67 Hz in the highest but limited by the practical devices.

Temperature accuracy and resolution improvement for a Raman distributed fiber-optics sensor by using the Rayleigh noise suppression method.

A novel Rayleigh noise suppression method is proposed to improve temperature accuracy and resolution for Raman distributed fiber-optics sensors. The proposed temperature demodulation method can eliminate temperature measurement inaccuracy caused by Rayleigh noise. The experimental results indicate that the temperature accuracy is optimized from 6.2°C to 1.7°C at a sensing distance of 9.1 km by using the proposed method, and the temperature resolution leads to about 1.5°C improvement compared with the tradition demodulation method at a sensing distance of 10.0 km. The proposed method provides a robust and reliable high performance for long sensing ranges.

Signal-to-noise ratio improvement of Brillouin optical time domain analysis system based on empirical mode decomposition and finite impulse response.

We propose a denoising algorithm based on empirical mode decomposition (EMD) and finite impulse response (FIR) to improve the signal-to-noise ratio (SNR) of Brillouin optical time domain analysis. Denoising results indicate EMD-FIR can effectively reduce noise, and the maximum SNR improvement is 11.69 dB, which is 4.98 dB and 4.26 dB larger than the maximum SNR improvement of wavelet and Butterworth. The temperature uncertainty along the heated section is reduced to 0.62°C by EMD-FIR. The improvement of SNR opens opportunities to apply high measurement accuracy to Brillouin optical time domain analysis and other distributed sensing fields.

Temperature Resolution Improvement in Raman-Based Fiber-Optic Distributed Sensor Using Dynamic Difference Attenuation Recognition.

There is an optical interference noise in the conventional Raman-based fiber-optics distributed sensing, which results in a poor temperature resolution performance. In addition, the traditional whole-fiber demodulation principle complicates the operation steps of the system. In this paper, a novel dynamic difference attenuation recognition (DDAR) principle is operated in the DDP scheme (dual demodulation principle) and the SDP scheme (self-demodulation principle) respectively. It not only helps to eliminate the optical interference noise, but also omits the whole-fiber calibration process. In this experiment, a temperature resolution of 0.30 °C (17.0 km) is achieved through using the DDP scheme based on the DDAR principle, and the measurement time can be shortened to 1.5 s. Meanwhile, a temperature resolution of 0.18 °C (17.0 km) is obtained for the SDP scheme under the DDAR principle. The SNR of DDP and DSP schemes can be optimized to 12.82 dB and 13.32 dB by the proposed DDAR technology. Furthermore, the temperature resolution performance under a large temperature measurement range (0-1000 °C) is theoretically analyzed. The results indicate that the temperature responsivity for DDP and SDP schemes are parabolic and linear type respectively, which causes the temperature resolution of the two schemes to show a different trend with the change of temperature. The proposed DDAR method also can improve the temperature resolution in such a large temperature measurement range.