A Mach-Zehnder interferometer based on seven-core fiber (SCF) and muti-mode fiber (MMF) is proposed and experimentally demonstrated. The interferometer is fabricated by splicing a segment of SCF spliced with two MMFs. The SCF length and MMF length are 5cm and 1cm, respectively. When the broadband light is injected into the interferometer through a lead-in single mode fiber, a pronounced interference pattern appears in the transmission spectrum. By monitoring the wavelength and power shifts of interference dips, simultaneous measurement of strain and torsion can be achieved. The experimental results show that the wavelengths at interference dip have a blue shift with the increases of strain, but the wavelength does not respond to the torsion. The power sensitivities of the interference dip to the strain and torsion are sensitivities are 0.001dB /° and 0.16dB/°, respectively. The simultaneous measurement of strain and torsion is demonstrated based on the sensitive matrix. The proposed MZI exhibits the advantages of easy fabrication, low cost, and simultaneous measurement of strain and torsion, which will make a significant contribution to torsion measurement.
A demodulation based on the principle of fiber Bragg grating edge filter method is used to measure impact energy of acrylic plate (PMMA) and aluminum plate in this paper. A new demodulation method based on damping attenuation principle is proposed. Fiber Bragg grating sensing system is built in the experiment. The complex vibration wave generated by impact energy is processed by using the envelope of peak value in MATLAB. The experimental results show that using the time length corresponding to the peak attenuation of 10% as the demodulation basis has a higher Goodness of fit. The linear fitness of PMMA plate and aluminium plate is 0.94 and 0.89, respectively. At the same time, it is concluded that this method can be used to preliminarily determine whether the plate is viscoelastic or not. This is a new potential demodulation method for practical impact energy detection based on fiber Bragg grating.
A high sensitivity and low cost all-fiber temperature sensor combined a single-mode-polarization maintaining-single-mode optical fiber (SPS) structure and a Sagnac loop is proposed and experimentally demonstrated. In this sensor, the SPS structure is reeled into a circle is inserted into a Sagnac loop. Experimental results show that the radius of the circle has significant influence on temperature sensitivity. The temperature sensitivity can reach up to 1.678nm/°C for the radius of 3cm.
The hybrid fiber optic interferometers are proposed and experimentally demonstrated. In our schemes, the hybrid fiber optic interferometers are constructed by single mode-multimode-polarization maintaining-single mode optical fiber (SMPS) structure and a Sagnac loop. The temperature and strain characteristics of the hybrid interferometers are studied in experiment, and the sensitivities depending on the length of polarization maintaining optical fiber (PMF) and multimode optical fiber (MMF) are detailedly investigated in experiment. The experimental results have demonstrated that the PMF and MMF lengths have low affect on the strain sensitivity but has great influence on the temperature sensitivity. The achieved strain sensitivity is 37.2pm/με for 10cm PMF and 12cm MMF. The achieved strain sensitivity is 38.0pm/με for 12cm PMF when the length of MMF is fixed at 15cm, and is 37.2 pm/με for 12cm MMF when the length of PMF is fixed at 10cm. The obtained temperature sensitivities is 1.723nm/°C when the length of MPF is 8cm with the fixed length of 15cm MMF, and the obtained temperature sensitivities reach 1.848nm/℃when the length of MMF is 12cm with the fixed length of 10cm PMF.