非线性Chirped光纤光栅制作与特性研究
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摘要
目前光纤通信已成为通信领域最为活跃的技术之一，它与卫星通信、移动通信共同构成现代通信技术的三大主要发展方向。随着各种通信业务不断涌现，特别是因特网业务的飞速发展，通信容量激增，大容量、高速率光纤通信系统的建设就成为必须。光纤光栅器件的出现为大容量高速率通信系统的进一步发展提供了可能。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。由于具备与光纤系统兼容、插入损耗低、易于制作、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。
首先,本文介绍了光纤光栅的基本结构和发展历程，光纤光栅在光通信系统及其它领域的应用。其中重点介绍了光纤光栅。光纤光栅是指光栅的光学周期(光栅有效折射率与折射率微扰周期的乘积)沿光栅轴向逐渐变大（小）的一种光纤光栅。在光纤光栅轴向不同位置可反射不同波长的入射光。所以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光纤光栅可作为光纤色散补偿器。非线性光纤光栅是一种新颖光纤光栅，有着许多独特的性质，但目前研究较少。本论文对非线性光纤光栅的工作原理、制备、性能和应用作了系统的研
究。
其次，在理论上，本文对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作了严格推导，并对非线性光纤光栅基本特性作了分析，得到了光纤光栅的折变量、长度和量等参量与光栅的反射率、带宽、色散值等特性之间的对应关系。为设计和制作非线性光纤光栅作了充分的准备。
在理论分析的基础上，我们提出了制作非线性光纤光栅的几种可行方法。包括：相位掩模法，温度梯度法和应变梯度应法。
相位掩模法是用相位掩膜板制作光栅，通过分析掩模板周期与非线性光纤光栅周期之间的关系，得到了掩模板的基本设计方法。同时为实现非线性光纤光栅的切趾，引入了用于线性光纤光栅的光纤掩膜板一次平移法。相位掩模法制作非线性光纤光栅，具有制作工艺简单、制作出的光栅一致性好和便于实时监控等优点。缺点是掩模板价格昂贵，制作出的光栅带宽难以调节。
温度梯度法制作光纤光栅是基于光纤光栅进行的后期制作方法，主要是利用光纤光栅对温度的敏感性，通过加热或制冷的办法在光纤光栅上建立温度梯度，从而改变光纤光栅的量，制作出光纤光栅。该方法对光栅无损伤，可以通过调节温度来调节光栅带宽。缺点是需要电力供应以维持电阻散热，而且封装后需要风扇或制冷器迅速排除多余热量。而且这种方法制作的光纤光栅带宽可调范围较小。
应变梯度法也是一种基于光纤光栅的后期制作方法。由于相位掩膜板价格较贵，温度梯度法制作的非线性光纤光栅带宽可调范围较小，我们提出用光纤光栅应变梯度法制作光纤光栅，即用氢氟酸将光纤光栅腐蚀，使其横截面积沿光栅轴向以一定函数形式逐渐变化；然后在腐蚀后的光栅两端加上拉力，从而在光纤光栅轴向建立应变梯度，制作出非线性光纤光栅。我们在理论上分析了该方法制作的光纤光栅的周期与腐蚀量以及应力的关系，并对实验装置进行了改进，以使其适应各种函数。该方法优点在于价格低廉、适用于各种函数、带宽可调。缺点在于腐蚀量的控制较困难，使用中需保持加在光栅两端的应力。
最后，在实验中，我们利用非线性光纤光栅的特性尝试解决了两个问题：矩形光栅和宽反射带光栅的制作。
在通过实验确定了各参数对非线性光纤光栅特性的影响之后，我们制作出了反射峰近似为矩形的高斯切趾光纤光栅，该光栅未加力时-1dB带宽，-20dB带宽；加0.2N应力后，-1dB带宽，-20dB带宽。在-20dB带宽未展宽的情况下，BWU值由18%提高到29%，改善幅度在60%以上。同时边模抑制比也有所提高。这种光栅在密集波分复用技术（DWDM）等领域具有良好的应用前景。另外我们利用应变梯度法制作的宽反射带光栅也获得了较好的实验结果，光栅3dB反射带宽在0.341nm到11.655nm间可调，而且在11.655nm的带宽下，仍保持比较平坦的反射峰。可以作为光纤滤波器的理想组件。
非线性光纤光栅是一种新颖的无源器件，可能具有更为良好的特性以及更为广泛的应用，还有待人们去探索。
Optical fiber communication is the most active technology of communication field. Optical fiber communication, satellite communication and mobile communication are the three main orientations of modern communication technology. At present, plenty of communication business continuously emerges, especially fast development of Internet induces rapid increase of communication capacity. Thus, it is necessary to establish large-capacity and high-speed optical fiber communication system. Fiber gratings provide possibilities for the further development of large-capacity and high-speed optical fiber communication system. 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.
In this paper we first introduced the progress of fiber grating and its applications in optical communication field . Then we introduced the basic structure and function of fiber grating. Chirped fiber grating is one type of fiber gratings whose optical period (product of grating's effective refractive index and refractive index microperturbation's period). Light with different wavelength is reflected at axial different point of chirped fiber grating. So chirped fiber gratings have broad reflection bandwidth. The group delay in chirped fiber grating reflection bandwidth changes gradually. These properties are what other type fiber gratings do not have. 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 because of the broad reflection bandwidth. Because gradual group delay, chirped fiber gratings can be used as fiber dispersion compensator for compensating fiber
dispersion. Nonlinearly chirped fiber grating is a kind of new fiber gratings, so it has many special properties. The work of this thesis is deeply studying the principle, fabrication properties and applications of nonlinearly chirped fiber gratings.
In respect of theory, we strictly deduced couple mode theory that describe the principle of fiber gratings from Maxwell equation, and analysis the properties of chirped fiber grating, obtain the relation between chirped fiber grating's parameters such as change of refractive index, length and chirp as well and the properties such as reflectivity, bandwidth and dispersion. All of these prepare for the design and fabrication of the nonlinearly chirped fiber gratings.
We give some possible methods for the fabrication of the nonlinearly chirped fiber gratings. Including the method of using phase mask, the temperature gradient method and the fiber Bragg grating strain gradient method.
The first method is using chirp phase mask, which is the normal method for fabricating fiber gratings. After analyzing the relation of the period of mask and the period of fiber gratings, we got the basic method of design phase mask for nonlinearly chirped fiber gratings. We designed to realiz fiber gratings' apodization by a simple method that we name it that fabricating apodization fiber gratings by only once moving fiber together with phase mask. The method of using phase mask has many virtues such as the easy process of fabrication, the good consistency and the easy control in fabricating. The drawbacks of this method are that the mask is too expensive and the bandwidth of fiber gratings is difficult to change.
The temperature gradient method is a kind of method that base on the Bragg fiber gratings, and it uses the temperature sensitivity of Bragg fiber gratings. By heating or cooling ,we can gain the temperature gradient in Bragg fiber gratings, so we can change the chirp extent of fiber gratings.
首先,本文介绍了光纤光栅的基本结构和发展历程，光纤光栅在光通信系统及其它领域的应用。其中重点介绍了光纤光栅。光纤光栅是指光栅的光学周期(光栅有效折射率与折射率微扰周期的乘积)沿光栅轴向逐渐变大（小）的一种光纤光栅。在光纤光栅轴向不同位置可反射不同波长的入射光。所以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光纤光栅可作为光纤色散补偿器。非线性光纤光栅是一种新颖光纤光栅，有着许多独特的性质，但目前研究较少。本论文对非线性光纤光栅的工作原理、制备、性能和应用作了系统的研
究。
其次，在理论上，本文对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作了严格推导，并对非线性光纤光栅基本特性作了分析，得到了光纤光栅的折变量、长度和量等参量与光栅的反射率、带宽、色散值等特性之间的对应关系。为设计和制作非线性光纤光栅作了充分的准备。
在理论分析的基础上，我们提出了制作非线性光纤光栅的几种可行方法。包括：相位掩模法，温度梯度法和应变梯度应法。
相位掩模法是用相位掩膜板制作光栅，通过分析掩模板周期与非线性光纤光栅周期之间的关系，得到了掩模板的基本设计方法。同时为实现非线性光纤光栅的切趾，引入了用于线性光纤光栅的光纤掩膜板一次平移法。相位掩模法制作非线性光纤光栅，具有制作工艺简单、制作出的光栅一致性好和便于实时监控等优点。缺点是掩模板价格昂贵，制作出的光栅带宽难以调节。
温度梯度法制作光纤光栅是基于光纤光栅进行的后期制作方法，主要是利用光纤光栅对温度的敏感性，通过加热或制冷的办法在光纤光栅上建立温度梯度，从而改变光纤光栅的量，制作出光纤光栅。该方法对光栅无损伤，可以通过调节温度来调节光栅带宽。缺点是需要电力供应以维持电阻散热，而且封装后需要风扇或制冷器迅速排除多余热量。而且这种方法制作的光纤光栅带宽可调范围较小。
应变梯度法也是一种基于光纤光栅的后期制作方法。由于相位掩膜板价格较贵，温度梯度法制作的非线性光纤光栅带宽可调范围较小，我们提出用光纤光栅应变梯度法制作光纤光栅，即用氢氟酸将光纤光栅腐蚀，使其横截面积沿光栅轴向以一定函数形式逐渐变化；然后在腐蚀后的光栅两端加上拉力，从而在光纤光栅轴向建立应变梯度，制作出非线性光纤光栅。我们在理论上分析了该方法制作的光纤光栅的周期与腐蚀量以及应力的关系，并对实验装置进行了改进，以使其适应各种函数。该方法优点在于价格低廉、适用于各种函数、带宽可调。缺点在于腐蚀量的控制较困难，使用中需保持加在光栅两端的应力。
最后，在实验中，我们利用非线性光纤光栅的特性尝试解决了两个问题：矩形光栅和宽反射带光栅的制作。
在通过实验确定了各参数对非线性光纤光栅特性的影响之后，我们制作出了反射峰近似为矩形的高斯切趾光纤光栅，该光栅未加力时-1dB带宽，-20dB带宽；加0.2N应力后，-1dB带宽，-20dB带宽。在-20dB带宽未展宽的情况下，BWU值由18%提高到29%，改善幅度在60%以上。同时边模抑制比也有所提高。这种光栅在密集波分复用技术（DWDM）等领域具有良好的应用前景。另外我们利用应变梯度法制作的宽反射带光栅也获得了较好的实验结果，光栅3dB反射带宽在0.341nm到11.655nm间可调，而且在11.655nm的带宽下，仍保持比较平坦的反射峰。可以作为光纤滤波器的理想组件。
非线性光纤光栅是一种新颖的无源器件，可能具有更为良好的特性以及更为广泛的应用，还有待人们去探索。
Optical fiber communication is the most active technology of communication field. Optical fiber communication, satellite communication and mobile communication are the three main orientations of modern communication technology. At present, plenty of communication business continuously emerges, especially fast development of Internet induces rapid increase of communication capacity. Thus, it is necessary to establish large-capacity and high-speed optical fiber communication system. Fiber gratings provide possibilities for the further development of large-capacity and high-speed optical fiber communication system. 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.
In this paper we first introduced the progress of fiber grating and its applications in optical communication field . Then we introduced the basic structure and function of fiber grating. Chirped fiber grating is one type of fiber gratings whose optical period (product of grating's effective refractive index and refractive index microperturbation's period). Light with different wavelength is reflected at axial different point of chirped fiber grating. So chirped fiber gratings have broad reflection bandwidth. The group delay in chirped fiber grating reflection bandwidth changes gradually. These properties are what other type fiber gratings do not have. 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 because of the broad reflection bandwidth. Because gradual group delay, chirped fiber gratings can be used as fiber dispersion compensator for compensating fiber
dispersion. Nonlinearly chirped fiber grating is a kind of new fiber gratings, so it has many special properties. The work of this thesis is deeply studying the principle, fabrication properties and applications of nonlinearly chirped fiber gratings.
In respect of theory, we strictly deduced couple mode theory that describe the principle of fiber gratings from Maxwell equation, and analysis the properties of chirped fiber grating, obtain the relation between chirped fiber grating's parameters such as change of refractive index, length and chirp as well and the properties such as reflectivity, bandwidth and dispersion. All of these prepare for the design and fabrication of the nonlinearly chirped fiber gratings.
We give some possible methods for the fabrication of the nonlinearly chirped fiber gratings. Including the method of using phase mask, the temperature gradient method and the fiber Bragg grating strain gradient method.
The first method is using chirp phase mask, which is the normal method for fabricating fiber gratings. After analyzing the relation of the period of mask and the period of fiber gratings, we got the basic method of design phase mask for nonlinearly chirped fiber gratings. We designed to realiz fiber gratings' apodization by a simple method that we name it that fabricating apodization fiber gratings by only once moving fiber together with phase mask. The method of using phase mask has many virtues such as the easy process of fabrication, the good consistency and the easy control in fabricating. The drawbacks of this method are that the mask is too expensive and the bandwidth of fiber gratings is difficult to change.
The temperature gradient method is a kind of method that base on the Bragg fiber gratings, and it uses the temperature sensitivity of Bragg fiber gratings. By heating or cooling ,we can gain the temperature gradient in Bragg fiber gratings, so we can change the chirp extent of fiber gratings.
引文
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