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　　熔锥型光纤器件的流变成形机理、规律与技术研究

　　作者姓名：帅词俊

　　论文题目：熔锥型光纤器件的流变成形机理、规律与技术研究

　　作者简介：帅词俊，男，1976年10月出生，2002年9月师从于中南大学钟掘教授，于2006年12月获博士学位。

　　中文摘要

　　熔锥型光纤器件是光纤通信中最具代表性也是构成其他器件的基础器件，熔融拉锥流变成形是制造光纤耦合器、波分复用器、光滤波器等光纤器件的通用方法。从国内外的研究现状来看，目前对熔锥型光纤器件的光学原理与光学设计分析较多，而从制造科学角度研究熔融拉锥流变制造过程的机理与规律仍不足，尤其对制造工艺参数与器件的微观结构及光学性能的相关机制缺乏基础研究，使制造过程某些工艺效果仍由技艺和经验决定。以致器件的性能不理想，效率和成品率低，成本高。我国目前的熔锥型光纤器件的制造技术、熔融拉锥装备主要依赖进口。

　　熔锥型光纤器件中最为典型的器件是光纤耦合器，其用量在光无源器件中居第二位，其功能是使传输中的光信号在特殊结构的熔锥区发生耦合，实现分(合)光。其制造过程为：将两根去除涂覆层的单模(或多模)光纤以一定的方式靠拢，在高温下加热熔融，同时向两侧拉伸，最终产生一段双向圆锥结构，入射的光功率在这个双锥体结构的熔锥区发生光功率再分配，一部分光功率从“直通臂”继续传输，另一部分光从“耦合臂”传输到另一光路，实现光功率的分配。

　　论文以光纤耦合器为代表，针对目前市场上广为应用的光纤器件存在的性能问题，如合格产品的光学性能差异，成品率不高所反映的制备工艺优化与稳定问题，如何进一步降低附加损耗等，从光纤耦合器流变成形制造的角度，分析了流变制造工艺参数如拉锥速度与熔融温度及其扰动对流变制造成形过程、微观结构与器件光学性能的影响，发现现有燃烧气体火焰的加热方式不能满足高性能光纤器件的流变制造技术要求，提出、设计并制造了一种新型的电阻加热系统和熔融拉锥机。

　　论文具体的创新性研究有：

　　1.在熔融拉锥机上，实验获得了温度外场、拉锥速度等制造工艺参

　　数对器件光功率损耗、分光比等性能参数的影响规律。

　　2.在扫描电子显微镜下，实验发现了光纤耦合器表面存在微裂纹与析晶等缺陷，获得了工艺参数对熔锥区微观形貌的影响规律，找到了微观形貌与器件性能之间的关联规律。

　　3.以光纤玻璃微观结构的基本单元Si-O-Si键为研究对象，基于分子振动与红外光谱理论，建立了1100cm-1红外特征峰与Si-O-Si键角的关联数学模型。

　　4.利用显微红外光谱仪，实验发现并查明了器件折射率分布不均匀、分光比一致性差等光学性能变异的根本原因在于制造过程材料分子结构的变化。

　　5.针对光纤玻璃在转变温度区域的流变行为与粘弹松弛特性，提出了面向有限元分析的松弛函数的转换算法，解决了理论模型中粘弹松弛模量的表达和数值分析中的参数变换问题。

　　6.建立了光纤耦合器熔融拉锥有限元计算模型，实现了光纤拉锥流变全过程数值仿真，可预测分析器件制造参数对流变制造过程的影响。

　　7.发现制造过程影响熔融拉锥体光传输性能提高的物理本质是：现有生产装备与工艺所提供的流变外场不能提供符合熔锥均匀连续流变的三维能场状态，熔锥流变不均匀使分子结构参数变化差异，内应力的产生与残留影响光学性能的部分丧失。

　　8.提出一种制造区光纤温度均匀化，内应力极小化的温度外场模型和结构实现，研制了一种新型电阻加热器和其温控系统，将熔融温度的稳定性由原来的5~30℃提高到小于1.5℃。

　　9.基于新型的电阻加热器，研制了一种高品质的新型熔融拉锥机，成倍地提高了器件性能的一致性，其中光功率损耗的一致性提高5倍、分光比的一致性提高4倍、拉锥长度的一致性提高20倍。

　　关键词： 熔融拉锥，光纤耦合器，流变成形，粘弹性，非晶体

　　The research on the mechanism, rule and technology of rheological formation

　　for fused-taper fiber devices

　　Shuai cijun

　　ABSTRACT

　　Fused-taper fiber device is the most typical fiber device and also a basic

　　part of other devices. Fused biconical taper (FBT) is the common fabrication

　　method of fiber coupler, wavelength division multiplex, optical filter and so

　　on. View from the present research at home and abroad, the optical theory and

　　design have been achieved a great improvement. But from the view of

　　manufacturing science, the mechanical behavior of rheological manufacturing

　　process is studied insufficiently, especially the relationships between

　　rheological manufacturing technological parameters, and between microstructure

　　of device and optical performance. The FBT technology is still at empirical

　　stage. The performance of fiber device is not ideal, such as low efficiency and

　　yield rate, and high cost price. At present, our country’s fabrication technique

　　and fabricatation setup of fused taper fiber device are depend on importing.

　　Fiber coupler is one of the most important devices among fused taper fiber

　　devices. Its usage ranks second among the optical passive devices. It is used

　　for separating or coupling light. At present, it is fabricated with fused

　　biconical taper technology at large. Its fabrication process is: two parallel

　　fibers are positioned very close to each other, heated by burning the

　　combustible gas, drawn at a certain speed by a micro-machine and formed a

　　biconical taper. The fused region will become slim during the heating and

　　drawing processes and become a biconical taper at last. The tranmitting light

　　signal is coupled and restributed in the fused taper region. A part of light

　　power is transmitted through ”straight arm”; the other part is transmitted

　　through ”coupling arm”.

　　Taking the fiber coupler as represent, aiming at the performance problem of

　　the fiber coupler which is used in the market, such as the optical performance

　　differences of accepted products, technological optimization and stability

　　reflected by the low rate of finished products, how to reduce excess loss, and

　　so on. From the view of manufacture of rheological formation, the research of

　　experiment and theory has been developed. The effects of rheological

　　technological parameters such as drawing speed and fused temperature on the

　　optical performance, microstructure and the process of rheological formation

　　have been investigated. It is discovered that the present heating mode of

　　combusting gas can’t satisfy with the rheological manufacturing technological

　　need of high performance fiber devices. A new resistance heating system is put

　　forward, designed and manufactured, and a new fused biconical taper machine is

　　developed.

　　The main innovation researches in the paper are as followed:

　　1. The changing rules between the different technological parameters (such

　　as drawing speed and fused temperature) and the performance of fiber coupler

　　optical fiber coupler (such as light power loss and coupling ratio) have been

　　studied with the six-axes optical fiber coupler machine.

　　2. The surface topography of fiber coupler fabricated at different

　　technological condition is tested by the scanning electron microscope (SEM). The

　　effect of technological parameters on surface topography is studied. The

　　essential relationship between surface topography and performance of the fiber

　　coupler is demonstrated.

　　3. Based on molecular vibration theory and infrared spectrum theory, the

　　mathematical model on 1100cm- 1 wave number of infrared characteristic peak and

　　the bonding angle of unit of Si-O-Si of fiberglass is set up.

　　4. It is discovered that the essential reason of different optical

　　performance such as uneven refractive index distribution and different coupling

　　ration is the change of molecular structural in the fabrication process with the

　　micro infrared spectroscope.

　　5. Aiming at the theological behavior and the viscoelastic relaxation

　　character of fiberglass in the transition region, a fitting method on relaxation

　　modulus facing the finite element analysis is put forward. The transition of

　　parameters lain in expression of viscoelastic relaxation and finite element

　　analysis are solved.

　　6. The numerical analysis model of fiber coupler in the process of fused

　　biconical taper (FBT) is constructed successfully. The numerical analysis of

　　fiber coupler in the process of fused FBT is accomplished with finite element

　　software. The effects of technology parameters such as fused temperature and

　　drawing speed on stress, strain and geometry in the manufacturing process are

　　acquired.

　　7. It is found that the essential cause to hinder improve the performance

　　of the light transimit is that the outfield provided with the present setup

　　can’t satisfy with the exact performances. The uneven stress results in the

　　distortion of microstructure and loss part of optical power.

　　8. A model of temperature outfield and construction realization with even

　　temperature and minimize internal stress is built. A novel electrinic resistance

　　heater and temperature controlling system are developed. The fused temperature

　　is improved from 5~30℃ to 1.5℃, whose stability is improved.

　　9. Based on the novel resistance heater, a new fused biconical taper

　　machine with high quality is developed. The consistency of performance is

　　improved exponentially. The consistency of power loss is increased by 5 folds,

　　the consistency of coupling ratio is increased by 4 folds, and the consistency

　　of drawing length is increased by 20 folds.

　　Key words: fused biconical taper, fiber coupler, rheological formation,

　　viscoelastic, noncrystalline

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