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To compensate for the refractive index errors in optical carrier-based microwave interferometry (OCMI), a ranging system is designed to measure the single-arm optical path of OCMI. A high-speed photodetector and a downconversion method are used to acquire the microwave envelope of the interference signal. A Hilbert transformation is used to realize phase detection. Simulation shows the linear relationship between the phase and optical length in a period. Adjusting the microwave frequency can resolve the phase ambiguity. The experimental results show that when the maximum microwave modulation frequency is set to 1.5 GHz, the standard deviation of the measured data can be limited to the level of 10 − 5 .

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An all-polarization-maintaining Er-doped fibre laser was demonstrated using PANDA microfibre embedded in a CNT-PDMS composite. The PANDA microfibre had good extinction ratio and low insertion loss. Robust and efficient saturable absorption was confirmed. © 2020 The Author(s)

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