十字架纖芯THz光纖的研究
Study on Cross-core Terahertz Fiber

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摘要 在光譜圖中位于微波段和紅外波段之間的太赫茲（THz）輻射波，很多特殊的性質(zhì)，比如低能、透視、寬帶等，因此它在生物工程、光譜分析學(xué)、成像和通信工程等領(lǐng)域有著廣闊的應(yīng)用前景。太赫茲波在傳輸介質(zhì)中的吸收損耗很大，但在干燥空氣中的傳輸損耗幾乎為零，所以近些年來，人們致力研究和設(shè)計不同纖芯結(jié)構(gòu)的光纖，將盡可能多的太赫茲波能量限制在空氣中傳輸，比如亞波長實芯光纖、空芯光纖、多孔光纖、多孔纖芯帶隙光纖等。另一方面，聚合物光纖在傳輸太赫茲波方面具有很多優(yōu)勢，低成本、低吸收損耗的聚合物種類繁多，設(shè)計與制備工藝簡單等。因此，關(guān)于微結(jié)構(gòu)聚合物太赫茲光纖的設(shè)計、制造和特性方面的研究成為太赫茲研究領(lǐng)域的熱點。
本論文在系統(tǒng)介紹了太赫茲光纖基礎(chǔ)知識和理論研究方法的基礎(chǔ)上，設(shè)計并分析了一種新型的寬帶、低損耗太赫茲光纖——十字架纖芯太赫茲光纖。通過優(yōu)化光纖結(jié)構(gòu)，使模式能量主要分布在十字架纖芯周圍的四個大扇形空氣孔中，降低材料吸收損耗；外圍的介質(zhì)圓環(huán)將光纖固定，同時避免了外部環(huán)境對太赫茲波傳輸?shù)挠绊?；通過增加纖芯到介質(zhì)圓環(huán)的距離降低了限制損耗，實現(xiàn)了一種在0.44THz—0.84THz頻率范圍內(nèi)總損耗低于0.086dB/cm的新型太赫茲波光纖。對所設(shè)計的太赫茲光纖進(jìn)行數(shù)值模擬，得到了該光纖的有效折射率、吸收損耗、限制損耗、能量分布隨頻率變化的曲線，并討論了光纖內(nèi)直徑、介質(zhì)層厚度對光纖傳輸特性的影響。本文提出的太赫茲光纖設(shè)計思路和方法，以及軟件模擬的具體步驟，對新型太赫茲光纖的設(shè)計、特性分析和應(yīng)用具有重要意義。

關(guān)鍵詞：太赫茲波 十字架纖芯 限制損耗 數(shù)值模擬



Study on Cross-core Terahertz Fiber
Abstract The terahertz radiation that lies between the millimeter wave and infrared region in the electromagnetic spectrum, has huge potential for application in the field of biotechnology, spectroscopy, imaging, and communication, due to its unique characteristics——low energy, perspectivity, and broadband. Given that the absorption losses in dielectrics at the terahertz range are serious, while the dry air is almost transparent for terahertz wave propagation, many optical-fiber-type guiding designs have been developed with the main aim to force a large part of the terahertz radiation to propagation in air while still confine it to a waveguide, these include solid core subwavelength fibers, hollow-core fibers, porous core fibers, porous-core bandgap fibers.. Moreover, polymer microstructured optical fiber has a good advantage in transmitting the terahertz wave, including the large variety of the low-cost and relatively low absorption loss polymer, easy to design and fabricate. Thus, the design, fabrication and characterization of polymer microstructured optical fiber for applications in terahertz waveband has attracted extensive attention in the field of terahertz technology.
In the basis of introducing the fundamental knowledge and the finite element research method of terahertz optical fiber, a new structure of terahertz fiber with cross-core, broadband and low loss is proposed in this paper. By optimizing the fiber structure,it leads to a significant enhancement of the modal fields in the four big fan-shaped air holes, and as a consequence, reduction in the waveguide losses; using the outer tube cladding to fixed the fiber prevents the disturbance of the surrounding environment; by increasing the distance of core and tube cladding, the confinement loss was decreased,thus we provide a new type of terahertz fiber with a total loss lower than 0.086dB/cm in frequency range from 0.44THz—0.84THz. Make use of the software—COMSOL Multiphysics to carry out the step and programme of the numerical cross-core fiber, we obtain the curves among the effective index, absorption loss, confinement loss and power-percentage in air-holes and clad-background with the change of frequency. This paper provides a basic idea and a effective way to achieve a computer stimulation of the design and application of the new type terahertz optical fiber, and it important for the design, analysis and application of new types optical fiber.
Key words Terahertz wave cross-core fiber confinement loss numerical simulation

目錄
第一章 緒論 1
1.1 引言 1
1.2 太赫茲技術(shù) 1
1.2.1太赫茲波簡介 1
1.2.2太赫茲技術(shù)的研究現(xiàn)狀 3
1.2.3太赫茲波導(dǎo)器件的研究進(jìn)展 4
1.3課題研究的目的和意義 4
1.4論文的主要內(nèi)容 5
第二章 微結(jié)構(gòu)聚合物太赫茲光纖 6
2.1 微結(jié)構(gòu)聚合物光纖技術(shù)的發(fā)展 6
2.2 幾種微結(jié)構(gòu)聚合物光纖簡介 6
2.2.1亞波長實芯太赫茲光纖 6
2.2.2亞波長多孔太赫茲光纖 7
2.2.3空芯太赫茲光纖 8
2.3 微結(jié)構(gòu)聚合物太赫茲光纖的損耗機(jī)理 10
2.3.1吸收損耗 10
2.3.2限制損耗 10
2.4 光纖色散的簡單介紹 11
2.5 太赫茲光纖的封裝 11
2.6 有限元法 12
2.7 太赫茲光纖數(shù)值模擬的實現(xiàn)步驟 12
第三章 十字架太赫茲光纖的設(shè)計及數(shù)值模擬 14
3.1 十字架太赫茲光纖的幾何結(jié)構(gòu) 14
3.1.1光纖的結(jié)構(gòu)設(shè)計 15
3.1.2光纖的導(dǎo)光原理 15
3.2 十字架太赫茲光纖的數(shù)值模擬 16
3.2.1COMSOL Multiphysics數(shù)值模擬過程 16
3.3 對模擬結(jié)果的分析 21
3.3.1介質(zhì)條厚度d對光纖傳輸特性的影響 21
3.3.2內(nèi)直徑D對光纖傳輸特性的影響 24
3.3.5雙折射 26
第四章 總結(jié) 2..