62 research outputs found
Frequency resolution quantification of Brillouin distributed optical fibre sensors
No full textNoise analysis using Monte Carlo method is conducted in this paper to correct the relationship between the frequency resolution, the Q-factor, Signal-to-Noise Ratio (SNR), 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 polynomialfitting
Dynamic strain measurement using small gain stimulated Brillouin scattering in STFT-BOTDR
No full textA 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
Frequency uncertainty improvement in a STFT-BOTDR using highly nonlinear optical fibers
No full textThe sensitivity of a sensor to strain or the temperature variations due to distributed Brillouin scattering are partially related to the type of fibers used and the Brillouin scattering induced effective index. In this paper, a highly nonlinear fiber that can generate a higher Brillouin scattering signal is compared to a standard single mode fiber in a short-time-Fourier-transform Brillouin optical time domain reflectometer (STFT-BOTDR). The results show that much higher signal to noise ratios of the Brillouin scattering spectrum and smaller frequency uncertainties in the sensing measurement can be achieved in the highly nonlinear fiber for comparable launched powers. With a measurement speed of 4 Hz, the frequency uncertainty can be 0.43 MHz, corresponding to 10 με in strain or 0.43°C in temperature uncertainty for the highly nonlinear fiber. In contrast, for the standard single mode fiber case, the value would increase to about 1.02 MHz (25 με or 1.02°C), demonstrating the advantage of the highly nonlinear fiber for distributed strain/temperature sensing.</p
Time and frequency localized pulse shape for resolution enhancement in STFT-BOTDR
No full textShort Time Fourier Transform-Brillouin Optical Time Domain Reflectometry (STFT-BOTDR) implements STFT over the full frequency spectrum to measure the distributed temperature and strain along the optic fiber, providing new research advances in dynamic distributed sensing. The spatial and frequency resolution of the dynamic sensing is limited by the Signal to Noise Ratio (SNR) and the Time-Frequency (T-F) localization of the input pulse shape. T-F localization is fundamentally important for the communication system, which suppresses interchannel interference (ICI) and intersymbol interference (ISI) to improve the transmission quality in multi-carrier modulation (MCM). This paper demonstrates that the T-F localized input pulse shape can enhance the SNR, the spatial and frequency resolution in STFT-BOTDR. Simulation and experiments of T-F localized different pulses shapes are conducted to compare the limitation of the system resolution. The result indicates that rectangular pulse should be selected to optimize the spatial resolution, Lorentzian pulse could be chosen to optimize the frequency resolution, while Gaussian shape pulse can be used in general applications for its balanced performance in both spatial and frequency resolution. Meanwhile, T-F localization is proved to be useful in the pulse shape selection for system resolution optimization
Research data supporting “Frequency uncertainty improvement in STFT-BOTDR using highly nonlinear optical fibers”
No full textThe 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.</span
Controlled synthesis and ceramization of well-defined Fe/Si/C ceramic precursors by living anionic polymerization
No full textTwo kinds of iron-containing ceramic precursors, PFS and PS-b-PFS, were synthesized via living anionic polymerization by using ferrocenyldimethylsilane and styrene as the monomers. The structures, elemental compositions and molecular weights were characterized by FT-IR, NMR, EDS and GPC, respectively. The homopolymerization of ferrocenyldimethylsilane was simulated using computational chemistry method. The copolymerization between ferrocenyldimethylsilane and styrene was investigated by altering the ratio between monomers and initiator (n-butyllithium). The experimental results indicated that the Mn, Mw and PDi of homopolymer PFS were 6.91×103 g/mol, 8.29×103 g/mol and 1.20, respectively. Moreover, the molecular weight, structure and composition of block copolymers PS-b-PFS, were successfully controlled by changing the ratio of styrene, n-butyllithium and ferrocenyldimethylsilane. Subsequently, using such iron-containing polymers as precursors, Fe/Si/C ceramics were obtained after sintering at 1400°C. The microstructures, morphologies and elemental compositions of ceramics were characterized by SEM and EDS. The results implied the controllable preparation of spherical Fe/Si/C ceramics was achieved via the self-assembly of precursors.</p
麟慶知交手札
No full textThis study is concerned with the bibliography about 23 letters recording in "Letters to Linqing from His Old Friends" in the 19th century in China. The author has elucidated and explained following items about each letter: 1. the name and career of the writers of the letters; 2. the relation and comradeship between the writers and Linqing; 3. the month and year when the letters were written; 4. the content of the letters and the persons and events mentioned in the letters; and 5. the idioms and the source of quotations written in the letters.3KJ00006665559論文Articl
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