Strain distribution characteristics of sensing fiber and influence on sensitivity of a fiber-optic disk accelerometer.

In a fiber-optic disk accelerometer, the strain distribution of sensing fiber is crucial for the improvement of sensitivity. The distribution characteristics of axial and radial strain in the sensing fiber are analyzed by the finite-element method, and the influence of strain distribution on the sensitivity of accelerometer is studied. Sensors with different outer radii of sensing fiber coils are designed and manufactured, and their performance is tested. The resonant frequencies are greater than 200 Hz, and the sensitivity increases as the outer radius of the sensing fiber coil increases. The dynamic range of the sensor with maximum sensitivity is 145.8 dB@100 Hz, and the transverse cross talk is 32.5 dB. Among the sensing fiber strain calculation methods we tested to predict the value of sensitivity, using the strain of sensing fiber directly obtained by the finite-element analysis method shows the smallest error with experimental results (within 7%). It is concluded that in the optical fiber strain disk, the absolute values of axial strain and radial strain of sensing fiber decrease with the increase of disk radius, while the signs of axial strain and radial strain of the ipsilateral sensing fiber are opposite and remain unchanged. The sensitivity can be further improved by optimizing the inner and outer radius of the sensing fiber coils, which is very important for the research and design of high-sensitivity fiber-optic accelerometers.

High-resolution distributed polarization crosstalk measurement for polarization maintaining fiber with considerable dispersion.

We present a high-resolution polarization crosstalk measurement method for polarization maintaining fiber (PMF) with considerable dispersion. The birefringence dispersion of the PMF severely degrades the spatial resolution of the distributed polarization crosstalk measurement. Conventional dispersion compensation methods are effective for modest birefringence dispersion coefficients (for instance, of 0.0014 ps/nm/km). We present an iterative matched filter (IMF) method to cope with the case of considerable birefringence dispersion. We measured the distributed polarization crosstalk of a PMF coil with a birefringence dispersion coefficient of 0.235 ps/nm/km. By applying the IMF method, we obtained a spatial resolution of 0.09 m at any position of the PMF (a maximum of 12.36 m without dispersion compensation).

Simultaneous measurement of displacement and temperature using a PMF-based dual Mach-Zehnder interferometer.

A dual Mach-Zehnder interferometer (MZI) based on polarization-maintaining fiber (PMF) is described for simultaneous measurement of displacement and temperature. Two orthogonal polarization components of a beam are simultaneously transmitted in the interferometer. The sensing configuration contains a short PMF section, a lens, and a mirror. The lens can transmit the slow polarization component and reflect the fast polarization component. Each polarization component exhibits a unique phase shift in response to changes in displacement and temperature, forming a dual MZI. Experimental results show that the resolutions of displacement and temperature are 60 pm and 2×10-3°C, respectively, and measurement ranges of displacement and temperature can reach 20 cm and 70°C. The experimental result demonstrates that there is no crosstalk between displacement and temperature, and high repeatability is demonstrated experimentally. This sensor allows multiparameter measurement, high resolution, wide measurement range, and good repeatability, conferring good application potential.