A distributed and dynamic strain sensing system based on frequency-scanning phase-sensitive optical time domain reflectometry is proposed and demonstrated. By utilizing an RF pulse scheme with a fast arbitrary waveform generator, a train of optical pulses covering a large range of different optical frequencies, short pulse width, and high extinction ratio is generated. Also, a Rayleigh-enhanced fiber is used to eliminate the need for averaging, allowing single-shot operation. Using direct detection and harnessing a dedicated least mean square algorithm, the method exhibits a record high spatial resolution of 20 cm, concurrently with a large measurable strain range (80 µε, 60 demonstrated), a fast sampling rate of 27.8 kHz (almost the maximum possible for a 55 m long fiber and 60 frequency steps), and low strain noise floor (<1.8 nε/ √ Hz for vibrations below 700 Hz and <0.7 nε/ √ Hz for higher frequencies).

The phase change of back-scattered light due to external perturbations is retrieved in coherent Rayleigh-based distributed sensors by estimating the frequency shift (FS) between the traces of different measurements. The uncertainty associated with the estimator, due to the presence of system noises, can lead to an inaccurate evaluation of the FS. Additionally, in coherent Rayleigh-based sensors, the calculation of the signal-to-noise ratio (SNR) from the jagged back-scattered intensity trace using the statistical estimators can cause an erroneous determination of the absolute value of the SNR. In this work, a method to accurately evaluate the non-uniform SNR caused by the stochastic variation of the back-scattered light intensity along the fibre is presented and validated. Furthermore, an analytical expression to evaluate the uncertainty in the FS estimation using one of the standard estimators, namely cross-correlation, is presented. A direct-detection frequency-scanned phase-sensitive optical time-domain reflectometer (φ-OTDR) is employed for the experimental verification of the expression as a function of two crucial system parameters: the SNR and the spatial resolution. The performance of various distributed sensing system configurations utilising cross-correlation for determining the FS occurring due to the external perturbations can be properly predicted hereafter with the aid of the analytical expression presented in this study.

Spontaneous Brillouin scattering is measured for the first time in a hollow-core anti-resonant fibre (HC-ARF) filled with Nitrogen (N2) gas at different pressures. A Brillouin gain of 0.029 m − 1W − 1 is yielded at a pressure of 34.7 bar.

Background and Objective: Despite that inherited (thalassemia and SCA) and infectious (hepatitis B, hepatitis C and AIDs) diseases and their risk factor consanguineous marriage are widespread among Yemen population, community-based awareness studies towards premarital screening (PMS) is extremely limited, so our study is designed to elicit knowledge and attitude of engaged and recently married couples in Taiz (Yemen) toward PMS. Methods: A cross-sectional study was conducted from April to September 2021 at Taiz. A well-structured questionnaire was designed and then delivered to participants to collect data. Results: The results revealed that majority of respondents (83.60%-94.18%) had knowledge about inherited and infectious diseases, respectively, and educational institution was the main knowledge source. Females had significantly higher knowledge than males ( P ≤ .01), except about AIDs since no difference ( P = .539). The results also revealed that majority of respondents had positive attitudes toward PMS, except toward AIDs testing since 70% of males and 68.91% of females had negative attitudes. The majority of respondents agreed that screening reduces the diseases incidence. Approximately half of respondents (50.79%-56.61%) tend to go ahead for marriage in case of positive results for inherited and infectious diseases respectively. Making PMS as an obligatory step prior engagement was agreed by 47.62% of respondents (45.71% of males, 48.74% of females). Conclusion: A high level of knowledge and positive attitudes toward inherited and infectious diseases and PMS were reported. This knowledge reflected on the agreement of majority of respondents regarding PMS importance in term of reduction of diseases incidence.

Distributed temperature sensing with 10 dB back-reflection-enhanced fiber is performed based on φ-OTDR. While the temperature sensitivity of such fibers is similar to that of standard single-mode fibers, a 3-times higher temperature resolution is observed.