Properties of a fiber optic pressure sensor in the Sagnac interferometer configuration with a birefringent photonic crystal fiber

Przedstawiono czujnik ciśnienia w układzie interferometru Sagnaca z dwójłomnym światłowodem fotonicznym typu PM-1550-01. Analitycznie wyznaczono jego charakterystykę przetwarzania. Zbadano właściwości metrologiczne czujnika w zakresie ciśnień 0-0.45 MPa. Zmierzono charakterystykę przetwarzania dla różnych długości fali w zakresie 1460-1600 nm i wyznaczono czułość ciśnieniową czujnika. Zbadano wpływ długości fali na czułość ciśnieniową czujnika. Przedstawiono możliwości jego zastosowania.A pressure sensor in the Sagnac interferometer configuration with a polarization maintaining (PM) photonic crystal fiber (PCF) of the PM-1550-01 type is presented. The application of the PM-PCF instead of a conventional PM fiber provides the sensor with a very low temperature sensitivity and also decreases the required length of the PM fiber because of the higher modal birefringence that can be achieved in a PM-PCF. The scheme of the sensor is shown in Fig. 1. The pressure acting on the PM-PCF causes the output spectrum to shift in the direction of higher wavelengths because of the sensitivity of modal birefringence to hydrostatic pressure. One of the fundamental qualities of the sensor is the fact that the sensitivity to pressure is independent of the length of the birefringent fiber in the Saganc loop. The conversion characteristic of the sensor was calculated analytically. The metrological properties of the sensor were examined in the pressure range: 0 - 0.45 MPa. The conversion characteristic was measured for different wavelengths in the range of 1460-1600 nm and for different lengths of the birefringent fiber. On that basis the pressure sensitivity of the sensor was determined. It was also investigated how the pressure sensitivity varied with the wavelength in the range: 1460-1600 nm. Other features of the sensor are: high sensitivity (3.6 to 3.0 nm/MPa in the wavelength range: 1460-1600 nm), simple mechanical and optical configuration, frequency output insensitive to amplitude interference, lack of a mechanical transducer (pressure acts directly on the optical fiber) and ability to change the conversion sensitivity by changing the length of the fiber segment subjected to pressure