【作者】 牛忠国；

【导师】 张玉书；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2004， 硕士

【摘要】 光纤光栅是光纤纤芯折射率受到周期性微扰而形成的一种新型全光纤无源器件。由于具备高波长选择性、与光纤系统兼容、插入损耗低、结构简单、体积小、成本低廉等优点，光纤光栅在光纤通信和传感领域均有着广阔的应用前景。因此，从第一支光纤光栅的研制成功到现在，光纤光栅的制备和应用一直是人们关注的热点。Chirped光纤光栅是指光栅的光学周期（光栅有效折射率neff与折射率微扰周期Λ的乘积）沿光栅轴向逐渐变大（小）的一种光纤光栅。在chirped光纤光栅轴向不同位置可反射不同波长的入射光。所以，chirped光纤光栅具有宽的反射带宽，在反射带宽内具有渐变的群时延等其它类型的光纤光栅所不具备的特点。这些独到的特点使chirped光纤光栅在光纤通信和传感领域有着独到的应用。如宽的反射带宽这一特点使chirped光纤光栅成为光纤中的宽带反射镜，可用于制作光纤带通滤波器等光纤通信系统中的关键器件；在反射带宽内具有渐变的群时延这一特点使chirped光纤光栅可作为光纤色散补偿器，补偿光纤通信系统中光纤色散，将因光纤色散而展宽的光脉冲压缩，从而延长通信系统中两个中继站之间的距离。本论文对chirped光纤光栅的工作原理、制备以及在传感领域的应用作了深入地研究，主要有以下几点：在理论上，从麦克斯韦方程组到描述光纤光栅工作原理的耦合模方程 了严格推导，并对chirped光纤光栅的特性作了分析。得到了chirped光纤光栅的折变量、长度和chirp量等参数与光栅的反射率、带宽、色散值等特性之间的对应关系，说明光栅的色散值由光栅的chirp量决定。较详细地介绍了chirped光纤光栅制作方法和应用情况。Chirped光纤光栅是一种应用较广的光纤光栅，制作上一般采用全息法、相位<WP=63>掩模法、二次曝光法、腐蚀法，而我们则采用相位掩模法和腐蚀法制作chirped光纤光栅。chirped光纤光栅在光纤色散补偿、超短光脉冲放大、掺铒光纤放大器、光纤滤波器以及光纤传感器中具有较广泛的应用。本论文重点研究chirped光纤光栅在传感领域中的应用，及简单的测试方法。实验上，我们制作了三种不同的chirped光纤光栅。第一种，将光纤光栅前端固定在石英板上，后段裸露。光纤光栅在受到沿光纤轴向应力或应变作用时，由于前段固定在宽度远远大于光纤直径的石英板上，所受的应变小到可以忽略的程度，因此光纤光栅前段对应的反射波长不随所加的应力或应变而变化。而光栅后段对应的波长受到应力或应变的作用向长波方向移动。这就导致了光纤光栅的反射光谱变宽，反射功率增大。当轴向应变增大时，光栅反射谱中间发生劈裂，劈裂宽度也随着应力或应变增大而变宽，并引起反射功率减小。在一定范围内，光栅反射谱的总功率随应力或应变的改变而线性变化，所以通过对反射功率的测量就可以得到应力或应变的大小。当光纤光栅周围温度变化时，由于石英板与光纤具有相同的热膨胀系数，整支光纤光栅对温度具有相同的敏感系数。光纤光栅波长随温度的变化而改变，但是反射谱带宽不变，反射功率也会不改变。第二种，光纤光栅直径沿轴向逐渐减小，当光纤光栅受到轴向应力或应变作用时，相当于腐蚀法制作chirped光纤光栅。在光栅中心波长向长波方向移动的同时，光栅的反射带宽和反射功率都增大。在一定范围内，光栅的功率与光纤光栅受到的应力或应变大小成正比，而且功率检测同样不受温度变化的影响，因此这种温度不敏感的传感器能够实现对应力或应变的测量。第三种，将前两种光栅结合，即光纤光栅前段也被固定在一块宽度远远大于光纤直径的石英板上，后段的直径沿光纤轴向逐渐减小。根据上述的分析，在相同的轴向应力应变作用下，这种光纤光栅具有<WP=64>比前两种结构光栅更宽的光谱，反射光信号的功率更大。对上述三种光纤光栅传感器进行了不同应力或应变下光栅反射谱测试，实验表明随着应力的增大，光栅中心波长向长波移动，带宽展宽。同时测量了反射功率随应力的变化曲线，在应力小于1.6N时，反射功率随应力呈线性变化，并且不随温度的改变而改变。chirped光纤光栅是一种性能优异的无源器件，实验中采用测试反射功率测量应力的应力或应变传感器结构简单，利用功率检测的方法降低了成本，又成功的解决了应变与温度交叉敏感的问题。由于功率检测没有波长检测精确，所以这几种传感器适用于对应力或应变精确度要求不十分严格的测量中。而要求精度较高的测量中，还是需要测量波长等其它方法来解决，此项工作还需要进一步探索和研究。更多还原

【Abstract】 Fiber grating is a new kind of all-fiber passive device that results from that the refractive index of optical fiber core is periodicity microperturbation. Because of the excellent properties such as compatible with optical fiber, easy fabrication, little insert loss, small volume and low price, fiber gratings have wide application in optical fiber communication and sensor field. Therefore, more and more attention has been paid to the fabrication and applications of optical fiber grating since the first optical fiber grating was prepared successfully. Chirped fiber grating is a kind of fiber gratings whose optical cycle (the effective refractive index of grating neff is multiplied by the period of perturbation of refractive index Λ) becomes bigger gradually along axial direction. In chirped fiber grating, different wavelength incident lights are reflected in different position along axial direction, so chirped optical fiber grating has wide reflection bandwidth and gradual group delay which are non-existent in other kind of optical fiber gratings. It is these unique properties that make chirped fiber gratings have unique applications both in optical communication and sensor field. For example, chirped fiber gratings can be used as reflector in fiber for fabricating many key devices in optical communication such as fiber bandpass filter in terms of the broad reflection bandwidth. According to gradual group delay, chirped fiber gratings can be used as fiber dispersion compensator for compensating fiber dispersion in fiber communication system and compressing broadened light pulse, accordingly, the distance between two relay stations is extended.In this paper, we explored the operating principle and fabrication and applications in sensor field. The outlines are as follows:In respect of theory, we strictly derived couple mode theory that describes the principle of fiber gratings from Maxwell equation and <WP=66>analysed the properties of chirped fiber grating, obtained the relation between chirped fiber grating’s parameters such as change of refractive index, length, chirp value of chirped fiber grating and the properties such as reflectivity, bandwidth and dispersion value of grating, which explains that dispersion value of grating depends on chirp value of grating.We introduced the fabrication method and applications of chirped optical fiber grating in detail. Chirped fiber grating is a extensive used optical fiber grating. Generally, it can be prepared by holographical method, phase mask method, double exposure method, etching method. Its application is extensive in compensation of fiber dispersion, amplification of ultrashort light pulse, Er doped fiber amplifier, fiber filter and fiber sensor . In this paper, we emphasized its applications in sensor field and simple testing method.3. In experiment, we fabricated three different kinds of chirped fiber gratings. The first kind, the front end of optical fiber grating was fixed in quartz plate, the back end was naked. When optical fiber grating was subject to stress or strain along axial direction, corresponding reflected wavelength of front end did not changed, because the front end of optical fiber grating was fixed in quartz plate whose width is far greater than the diameter of fiber, applied strain can be negligible. But corresponding reflected wavelength of back end shifted to long wave, which caused the reflection spectrum to broaden and caused reflected power to increase. When axial stress increased, the middle of reflection spectrum splitted. Splitting width broadened and reflected power reduced with stress or <WP=67>strain increasing. In a given range, total power of reflection spectrum changed linearly with stress or strain changing. So we can obtain the magnitude of stress or strain by measuring reflected power. When the ambient temperature of optical fiber grating varied, temperature sensitivity coefficient of the entire optical fiber grating was same because thermal expansion coefficient of quartz plate is identical with that of optical fiber更多还原