【作者】 谭彦楠；

【导师】 关柏鸥；

【作者基本信息】 大连理工大学 ， 光学工程， 2012， 博士

【摘要】 随着当今信息社会的快速发展,对环境监测、过程控制以及基础设施安全性要求的不断提高,人们对监测需要的传感器的要求越来越高。现代传感器技术正在向着小型化、网络化、多参量化和集成化方向发展。光纤传感器作为传感器家族中的生力军,以其在抗电磁干扰、灵巧和组网能力等方面的优势而日益受到人们的重视,并已在军事和民用领域被广泛应用,发挥着越来越主要的作用。光纤光栅传感器更是以其可靠性高、稳定性强、制作技术成熟和利用波分复用技术可以实现大面积多点测量的优点,被广泛应用于大型建筑物内部,对其结构的完整性、安全性、载荷疲劳、损伤程度等状态进行连续实时监测。近年来,有源光纤光栅激光传感器更是以其带宽窄,信噪比高,从而可以实现更高的准确度和分辨率而备受关注。传统的光纤光栅激光传感器大多采用波长编码,与光纤光栅传感器具有相似的工作原理类似,需要昂贵的波长解调设备来分辨微小的波长变化,极大地增加了系统的成本。由于波长编码灵敏度较低,干涉技术被用来分辨其微小的波长变化,进而提高其传感器的灵敏度和分辨率,但是大大增加了解调系统的复杂程度,并且很大程度上增加了系统的成本。本论文正是在此基础上,提出并实现了一系列新颖的基于偏振外差法的光纤激光传感器,并对偏振外差法光纤激光传感技术及其频分复用能力进行了深入的理论和实验的研究。为未来基于偏振外差法光纤激光传感器及其频分复用传感网络技术与应用打下了坚实的基础。本论文的主要研究工作和取得的成果如下：1.提出了一种新型的光纤激光水听器——偏振外差法光纤激光水听器,其以单纵模双偏振DBR光纤激光器为传感核心单元,以偏振拍频信号为传感信号,具有频率编码、易于解调,并能在同一根光纤上利用频分复用技术复用多个传感器组成传感阵列的特点。该水听器最小可测声压为0.03Pa,对应的声音信号频率为400Hz。其频响曲线的上下浮动为±7dB。2.结合本水听器的结构和实际应用的需求,提出了一种对水声、液压和温度同时测量的传感器。我们利用光纤激光器的波长首先将温度标定出来,然后将拍频静态漂移量中温度项引起的变化量去除掉,进而获得静压力的具体数值。最后利用拍频中的动态漂移量来探测环境中的声音信号。从而实现了对液压、温度和水声的同时测量。3.我们采用内部开发型结构,设计并实现了一种液体静压力不敏感DBR光纤激光水听器,可以不受液压的影响在深海进行工作。弹性膜片只将声压转化为侧压力而不将液压转化为侧压力,因此拍频信号只对声压灵敏。此水听器最小可探测声压为0.15Pa,对应的声音信号频率为400Hz。4.设计并实现了一种新颖的温度和应变同时测量的光纤激光传感器。其传感探头由两个串联的超短DBR光纤激光器组成。总长仅为1.8cm。两个激光器都完全单纵模双偏振态运转。每个激光器将在射频领域产生一个偏振拍频信号,且由于两个拍频信号具有不同的应变和温度响应,因此可以实现对应变和温度的同时测量。5.实现了一种应变不敏感温度传感器。其传感单元为一单纵模双偏振态运转的DBR光纤激光器。通过对其偏振拍频温度响应进行测量我们得到了一个温度传感器,其温度灵敏度为-78.46kHz/℃。然而,这个传感器却对应变完全不敏感。对此,我们进行了理论分析,给出了合理的理论解释。6.为了实现并提高DBR光纤激光器的的频分复用能力。我们提出了旋转熔接拍频主动控制技术。其原理为：将光纤激光器分成两个部分,然后旋转一定角度后再对准在一起,由于每个偏振态光程的变化,拍频可以连续的进行调节,当到达需要的拍频再将两部分熔接在一起,从而获得目标拍频的光纤激光器。我们实现了2.05GHz到289MHz的调谐范围。此种方法可以实现大范围的拍频调制,进一步提高了DBR光纤激光器的复用能力。由于可以实现拍频的连续调节,这种方法还可以作为一种光生微波的方法,用来制作射频信号发生器。更多还原

【Abstract】 With the rapid development of the information society, and the continuous improvement of the requirements for environmental monitoring, process control and infrastructure safety, people need higher performance sensor. Mordern sensor technology is developing to small size, network, multiple parameters and integrated. Fiber optical sensors as one of the most important sensors have been interested in and applied in military and cilvil fields, because of their advantage such as anti-electromagnetic interference, dexterity and multiplexing. Because of high reliability, strong stability, mature production technology and multiplexing ability by using of wavelength division multiplex, fiber grating sensors have been widely applied in the large structure for their integrity, security, load fatigue, injury severity and the state of real-time monitoring. Recently, fiber grating laser sensors as active optical fiber device have attracted much consideration, because of their narrow bandwidth and high signal to noise ratio, which permit more accuraty and resolution. Traditional fiber grating laser sensors is wavelength encoding. Like the principle of the fiber grating sensors, the equipments for wavelength demodulation are required, which is very expensive. Because of the small sensitivity of the wavelength encoding, the interferometric detection is required to read out the small wavelength shift. This greatly complicates the sensor multiplexing and increases the cost.In this paper, we propose and demonstrate a series of novel polarimetric heterodyning fbier grating laser sensors theoretically and experimentally. The multiplexing ability of the sensors based on frequency division multiplex is also investigated. The investigation has laid a solid foundation for the polarization heterodyne fiber laser sensor and its frequency division multiplexing sensor network to apply in future. The main research work and achievements are as follows:1. A novel fiber optic hydrophone based on polarization fiber grating laser is proposed and experimentally demonstrated. The principle of the proposed hydrophone is different in nature from the reported wavelength encoded fiber laser hydrophones. It uses dual polarization fiber grating laser as sensing element and converts acoustic signal into a change in the beat frequency between the two polarization modes from the laser. The proposed hydrophone has advantages of ease of interrogation, absolute frequency encoding, and capability to multiplex a number of sensors on a single fiber by use of frequency division multiplexing technique. The minimum detectable signal is0.03Pa at 400Hz. The frequency response exhibits a±7dB variation across the measurement bandwidth.2. Based on the structure of hydrophone, we propose and experimentally demonstrate a simultaneous measurement of temperature, hydrostatic pressure and acoustic signal sensor using a single DBR fiber laser. The acoustic wave induces a frequency modulation (FM) of the carrier in radio frequency (RF) range generated by the fiber laser and can be easily extracted by using the FM demodulation technique. The temperature can be determined by the laser wavelength. The hydrostatic pressure can be determined by monitoring the static shift of the carrier frequency and deducting the effect of the temperature.3. A hydrostatic pressure insensitive fiber optic hydrophone based on the integration of a dual polarization fiber grating laser and an elastic diaphragm is proposed and experimentally demonstrated. The diaphragm converts acoustic pressure into transversal force onto the fiber laser but shows no response to the hydrostatic pressure. Therefore, the beat frequency is sensitive to acoustic signal but insensitive to the hydrostatic pressure. It can be used in deep water.4. A novel simultaneous strain and temperature fiber optic sensor is proposed and experimentally demonstrated. The sensing head is formed by two concatenated ultra-short distributed Bragg reflector lasers that operate in single longitude mode with two polarization modes. The total length of the sensing head is only18mm. The two lasers generate two polarization mode beat notes in the radio-frequency range which show different frequency response to strain and temperature. Simultaneous strain and temperature measurement can be achieved by radio-frequency measurement.5. A strain-insensitive temperature sensor based on a dual polarization fiber grating laser is demonstrated. The measured temperature sensitivity is-78.46kHz/℃. In contrast, the sensor is almost insensitive to applied axial strain. The theoretical analysis is conducted, which give a reasonable explanation.6. To improve the frequency division multiplex ability of DBR fiber laser, we demonstrate a rotary-welding method to tune the beat frequency. By slicing the laser cavity into two sections and then aligning them with a rotated angle, the output beat frequency can be continuously tuned in a multi-octave frequency range as shown in the experiment from2.05GHz down to289MHz, as a result of the induced change in optical length for each polarization mode. Because the beat frequency can be continuously tuned in a multi-octave frequency range, this method can be used for a tunable RF signal generation.更多还原