Linqing Luo

Frequency resolution quantification of Brillouin distributed optical fibre sensors

Noise analysis using Monte Carlo method is conducted in this letter to correct the relationship between the frequency resolution, the Q-factor, signal-to-noise ratio, and frequency step in the Brillouin-distributed optical fibre sensors. The quantification of the Brillouin gain spectrum is important in distributed Brillouin sensors in order to improve the Brillouin frequency resolution and the corresponding strain and temperature resolutions. Two analytical expressions are derived in order to estimate the error in the determination of the Brillouin central frequency with or without second-order polynomial fitting.

Dynamic Strain Measurement Using Small Gain Stimulated Brillouin Scattering in STFT-BOTDR

A distributed dynamic strain measurement is demonstrated using small gain stimulated Brillouin scattering (SBS) in Brillouin optical time domain reflectometry based on the short-time Fourier transform algorithm. The input power limits, frequency uncertainties for given pulse durations, fiber lengths, and the number of averaging are calculated. The output signal power and the signal-to-noise ratio of the system output are enhanced by SBS. It is found that the signal processing is faster and requires fewer averaging to achieve dynamic sensing performance along the fiber under test. A 60-Hz vibration on a 6-m fiber section at the end of a 935-m fiber is detected with the spatial resolution of 4 m with a sampling rate of 2.5 kS/s.

Time and frequency localized pulse shape for resolution enhancement in STFT-BOTDR

The data is obtained from a STFT-BOTDR setup in 23/010/2015 for localization analysis in BOTDR. It is directly sampled by a ADC with 5 GSPS with 500 us width of data in each file. Three types of pulses, Rectangular, Lorentzian, Gaussian, Triangular, are used to analysis the impact of pulse shapes on resolution. Each pulse has 50ns width and 20us period. For each pulse, we have 855 files. The files are only used to get the averaged result. The data amount is quite big for the whole files, therefore, for each pulse shape, the file_001 to file_010 are uploaded. If anyone is interested to get all of the data, please contact the authors.

Distributed fiber optics sensors for civil engineering infrastructure sensing

Abstract Distributed Fiber Optic Sensing (DFOS) is one of the promising tools for structure health monitoring. It can measure physical quantities (such as temperature, strain, and vibration) of the fiber continuously (say 5 cm interval) along its length for long distance (say 10 km) due to its low-loss characteristic. By attaching an optical fiber cable to a structure or embedding it inside a structure, it is possible to monitor the changes of ambient parameters of the structure. In this paper, the measurement principles and their state-of-the-art status in terms of their capabilities are discussed. The main advantage is its high sensitivity over large distances and the ability to interface with a wide range of measurands in a distributed manner. The systems provide thousands of “strain gauges”, “thermo-couples”, or “accelerometers” along a single fiber optic cable connected to or embedded in structures, which can then serve as a civil infrastructure nerve system. It can be applied to flexible geometries, providing the ability to design a whole range of sensors with tremendous information carrying capacity. DFOS can provide a highly effective monitoring system for both short and long term to realize our concept of “smart infrastructure”.

Quadratic Time-Frequency Transforms-Based Brillouin Optical Time-Domain Reflectometry

Linear and quadratic Time-Frequency (T-F) transforms are proposed for the signal processing of the Brillouin optical time-domain reflectometry, to improve the system performance, in terms of the transition responsivity and frequency resolution. Various T-F transforms, including linear T-F transform (short time Fourier transform) and quadratic transforms (Choi–Williams, Zhao-Atlas-Marks, smoothed pseudo Wigner–Ville, S-method, and adaptive spectrogram) are applied to the experimental backscattered time-domain spontaneous Brillouin signals. Multiple T-F approaches can be jointly applied to efficiently improve the time and frequency resolutions simultaneously. Results show that the SWPV transform provides the best transition responsivity and frequency resolution simultaneously among the six T-F transforms because of its smoothing operations on frequency and time axis for reducing the cross-term interference.

Experimental and Simulation Studies of Underground Wireless Sensor Networks

This paper summarizes the experimental and simulation results in our studies of buried wireless sensor networks (B-WSN). The goal is to choose the suitable Industrial Scientific Medical Band (ISM) frequency which can be applied in the underground environment and then to investigate the underground communication ability of wireless modules based on the chosen frequency. As a key factor in point to point radio communication in WSN, the RF path loss in soil was evaluated and the results show that the attenuation significantly increases with high operating frequency. The penetration depth versus dielectric constant with various operation frequencies was also studied in this research. The simulation result shows that the penetration depth decreases with high moisture content and high operation frequency. Simulations indicate that the operation frequency in Sub-GHz range can acquire higher penetration depth and lower path loss compared to other high operation frequencies such as 2.4 GHz. The experimental results indicate that RSSI is significantly negatively related to the depth of filled soil. The results indicate that the maximal above ground horizontal transmission distance is 1.5m when the node was buried 1.3m underground

Research data supporting “Frequency uncertainty improvement in STFT-BOTDR using highly nonlinear optical fibers”

The data is for supporting the publication of a journal paper. It is based on experiment by using BOTDR to compare the performance of nonlinear fibre and normal single mode fibre. The date is collected in July 2016. The measurement are repeated 100 times and because of the size, 10 of them are uploaded. If you need more data, please feel free to contact me.