Optical Fiber Mems Fabry - Perot Pressure Sensor Demodulation And Multiplexing,

As high-precision interferometric optical fiber sensors, the optical fiber MEMS Fabry-Perot(F-P) sensors have many advantages such as small volume, high sensitivity, stable performance, immunity to electromagnetic interference, high adaptability in harsh environments, remote signal processing, the possibility of multiplexing an so on. So they have been widely applied in city building, civil engineering, environment monitoring, electric system, aerospace, medicine and biology.In the measurement system of optical fiber F-P sensors, demodulating technique is the key factor. Demodulating methods for optical fiber F-P sensors are divided into two categories: intensity demodulation and phase demodulation. In the former method, cavity length of sensor is usually got from optical intensity variation by using monochromatic light source; and in the latter one, broadband or wavelength tunable light source is used and cavity length is got through the phase variation. In commercial measurement, several optical sensors are needed to measure temperature, stress, pressure and other physical quantities at the same time, making multiplexing of sensors necessary. By multiplexing of sensors, the cost per sensor is greatly reduced, improving the competitiveness of optical sensors against conventional electromechanical sensors. Limited by the principle, F-P sensors are hard to be multiplexed. Therefore, wavelength division multiplexing (WDM) scheme based on the intensity demodulation and space-division multiplexing scheme based on phase interrogation are presented in this paper, which will further enhance demodulating technique.Dual-wavelength interrogation based on intensity demodulation is studied in this paper. The principle of dual-wavelength interrogation is theoretically analyzed and the interrogation technique of optical fiber MEMS pressure sensor is experimentally approached. The results demonstrate that the dual-wavelength interrogation can eliminate errors resulting from wavelength-independent variations in the fiber interconnect to the sensor. Fourier transformation method based on phase demodulation is further explored. Relationship between Fourier spectrum and cavity length is used to demodulate sensors. Experimental results show that this method can prevent errors resulting from intensity variation of light source, so high precision is available. Its primary superiority over dual-wavelength method is that the absolute value of cavity length can be calculated.Wavelength division multiplexing (WDM) scheme for optical fiber MEMS pressure sensors based on dual-wavelength interrogation is presented and studied. The demodulating system is set in the library, making quasi-distributed measurement possible. Experimental results indicate that reasonable linearity, sensitivity and precision are available in this system. Many sensors can be multiplexed in this system and there is no observable crosstalk among them. A space-division multiplexing (SDM) scheme using optical switch based on Fourier transformation demodulation is presented and experimentally verified. Compared with other wavelength or frequency division multiplexing system, this system has particular merit that the reflected spectrum from the sensor is a full spectrum, with the whole information of the sensor. So, an even higher precision can be achieved.