光纤MEMS法布里—珀罗压力传感器的解调和复用

【作者】 倪小琦；

【导师】 王鸣；

【作者基本信息】 南京师范大学 ， 物理电子学， 2007， 硕士

【摘要】 光纤微机电系统(MEMS)法布里—珀罗(F-P)传感器作为一种高精度的干涉型光纤传感器，具有体积小、灵敏度高、性能稳定、不受电磁干扰、适用于恶劣环境、能远程信号处理以及可以复用等众多优点，在城市建设、土木工程、环境监测、电力系统、航空航天、医学及生物方面得到了广泛的应用。在光纤法—珀传感器的测量系统中，解调技术是系统实现的关键。光纤法—珀传感器的信号解调主要有强度解调与相位解调两大类。强度解调一般利用单色光源，根据强度变化求解出腔长；而相位解调则是应用宽带光源或是波长可调谐光源，通过相位变化求出腔长。实际使用中常需要用多个光学传感器测量温度、应力和压力等物理量，这就使得多路复用成为光学传感器的一个重要问题。复用使得单个传感器的成本大幅度降低，提高了光学传感器对传统的电子传感器的竞争力。但是法—珀传感器由于受其原理限制，不管采用强度法还是相位法来解调，复用技术都十分困难。因此，论文提出基于强度法的波分复用方案和基于相位法的空分复用方案，对于进一步推进光纤传感技术的发展，具有明显的学术意义和应用前景。本文研究了基于强度解调原理的光纤F-P传感器的双波长解调方法。理论分析了双波长解调的基本原理，实验研究了光纤MEMS压力传感器的解调技术。研究结果证明双波长解调法可以补偿传感器光网中和波长无关的变动引起的误差。进一步研究了基于相位解调法的光纤F-P传感器的傅里叶变换方法，通过傅里叶变换后的频谱与腔长的关系解调传感器，并通过实验进行验证。实验结果表明：傅里叶解调法受光源强度波动的影响较小，解调精度高，跟双波长方法比最大的优点在于能直接解调出腔长的绝对值。提出和研究了基于双波长解调原理的光纤MEMS法—珀压力传感器的波分复用方法，建立了相应的复用解调系统，实现了光纤MEMS法—珀压力传感器的准分布式测量。实验结果表明，该系统具有好的线性、灵敏度和精度，复用能力强且传感器间无串扰。进一步提出和研究了基于傅里叶解调法的空分复用方法，利用光开关来实现复用解调。和其他频分波分复用系统相比，该系统优点是：传感器的反射信号包含光源的全光谱，携带完整的信息，因此解调结果具有更高的精度。更多还原

【Abstract】 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.更多还原