【作者】 王文；

【导师】 郑建成（Kin Seng Chiang）；

【作者基本信息】 电子科技大学 ， 光学工程， 2020， 博士

【摘要】 近年来,随着互联网流量的快速增长和新应用的陆续出现,对于增加光纤的传输容量的需求十分迫切。模分复用技术是当前认为可以提高光纤传输容量的有效方法,在模分复用系统中,每个模式都是独立传输的信道。模式转换器能实现模式之间的相互转换,在模分复用系统里能发挥重要作用。利用电光（Electro-Optic,EO）或者热光效应制作的模式转换器能作为可重构的模式开关使用,灵活地实现模式转换。本论文以聚合物光波导模式转换器和开关为研究对象,探索实现高带宽的模式转换器和低开关电压的模式开关的理论与技术,论文的研究内容概述如下:（1）针对提高模式转换器的工作带宽的问题,提出利用长度切趾长周期光栅来提高模式转换器工作带宽的方案。利用有机聚合物材料设计和制作了基于侧壁光栅的LP₀₁-LP_11a模式转换器和基于表面光栅的LP₀₁-LP_11b模式转换器。LP₀₁-LP_11a模式转换器和LP₀₁-LP_11b模式转换器分别在120 nm和150 nm的波长范围内转换效率达到了99%,并在180 nm和300 nm的波长范围内转换效率超过了90%。并且这两种模式转换器对温度和偏振变化均不敏感。超宽带的模式转换器能与其他器件进行集成,在模分复用系统里发挥重要作用。（2）针对有机电光聚合物（Electro-Optic Polymer,EOP）薄膜的极化问题,提出利用石墨烯电极来极化有机电光聚合物薄膜的方案。利用石墨烯薄膜埋入芯层和包层折射率差较小的波导中不会对TM（Transverse magnetic）偏振的模式造成较大损耗的优点,取代传统金属电极来完成有机电光聚合物的极化。因此石墨烯电极与电光聚合物薄膜之间不需要缓冲层,大大减小了极化电压。采用410 V的电压极化了3.8μm厚的薄膜,极化之后,电光聚合物薄膜在1541 nm波长处的电光系数r₃₃达到了82 pm/V,在1300 nm波长处,电光系数达到了110 pm/V。而且极化之后石墨烯薄膜不会引入额外的损耗,石墨烯电极亦可以作为调制电极使用。采用石墨烯作为极化电光聚合物薄膜的电极,可以简化电光器件的设计和制作。（3）针对聚甲基丙烯酸甲酯（Polymethyl methacrylate,PMMA）支撑的石墨烯不能转移到不耐丙酮衬底的问题,提出醇类溶剂可溶的支撑材料来取代PMMA完成石墨烯的转移的方案。利用醇类溶剂可溶的聚（4-乙烯基苯酚-co-甲基丙烯酸甲酯）（Poly（4-vinylphenol-co-methyl methacrylate）,PVP-co-PMMA）和PMMA双层薄膜完成了石墨烯的转移,该转移方法能实现大面积、高品质的石墨烯转移。利用该转移方法成功将石墨烯转移到电光聚合物薄膜上,完成电光聚合物薄膜极化之后,PVP-co-PMMA和PMMA双层薄膜能被乙醇溶剂剥离。该转移方法能使得石墨烯转移到不耐丙酮的衬底上,如电光聚合物薄膜和有机半导体材料上,扩大了石墨烯的应用范围。（4）针对实现低开关电压、高带宽的模式开关,提出利用石墨烯和有机电光聚合物材料来设计电光模式开关的方案。利用石墨烯电极在折射率差较小的波导中不会对TM偏振模式的光造成较大损耗的性质,以及石墨烯电极能高效极化有机电光聚合物薄膜的优势,设计了基于石墨烯光栅电极的LP₀₁-LP_11a和LP₀₁-LP_11b模式开关。通过优化模式开关的芯层尺寸、包层和芯层折射率以及光栅电极的设计来得到低开关电压、低损耗、高转换效率的模式开关。并利用长度切趾长周期光栅电极实现了超宽带模式开关的设计。更多还原

【Abstract】 In recent years,with the rapid growth of internet traffic and the emergence of new applications,the need to increase the transmission capacity of optical fibers is very urgent.The mode-division-multiplexing（MDM）technology is currently considered as an effective method to increase the transmission capacity.In the mode-division-multiplexing system,each mode is an independent transmission channel.The mode converters that realize the mutual conversion between the fundamental mode and higher order modes can play an important role in the mode-division-multiplexing system.Mode converters realized by electro-optical or thermo-optical effects can be used as reconfigurable mode switches to flexibly realize mode conversion.This dissertation takes polymer optical waveguides as the research topic,and aims at the realization of broadband mode converters and mode conversion switches with low switching voltage.The research contents of this dissertation are summarized as follows:（1）To improve the bandwidth of mode coverters,a length-apodized long period grating is employed to increase the operating bandwidth of the grating-based waveguide mode converter.Using organic polymer materials,we designed and fabricated LP₀₁-LP_11a mode converter based on sidewall grating and LP₀₁-LP_11b mode converter based on surface grating.The fabricated LP₀₁-LP_11a and LP₀₁-LP_11b mode converters provide the conversion efficiency higher than 99%over a bandwidth of¹20 nm and¹50 nm,respectively,or the conversion efficiency higher than 90%over a bandwidth of¹80 nm and³00 nm,respectively.And these two mode converters are insensitive to temperature and polarization variations.The ultra-broadband mode converters can be integrated with other devices and play an important role in MDM system.（2）To pole the electro-optic polymer films,the scheme that using graphene as poling electrodes is proposed.The graphene film embedded in a low-index-contrast waveguide does not induce a significant loss to the transverse-magnetic（TM）waves,so graphene electrodes can replace conventional metal electrodes to realize the poling of organic electro-optic materials.Without using buffer layer between elctro-optic polymer film and electrode,the poling voltage is largely reduced.410 V voltage is applied to pole 3.8μm thick film,after poling,the electro-optic coefficient can be 82 pm/V in1550 nm,and in 1300 nm,the electro-optic coefficient can be 110 pm/V.Moreover,the graphene electrodes do not introduce excessive loss after poling,and then the graphene electrodes can be used as modulation electrodes.Using the graphene electrodes to pole the electro-optic polymer materials can simplify the design and fabrication of electro-optic devices.（3）In order to solve the problem that the graphene supported by PMMA film cannot be transferred onto the substrate that is not resistant to acetone,the scheme that alcohol-soluble supporting materials are used to replace PMMA to complete the transfer of graphene is proposed.Alcohol-soluble PVP-co-PMMA and PMMA double-layer films are used to realize the transfer of graphene.This transfer method can achieve large-area and high-quality graphene films.Graphene films are transferred onto the electro-optic polymer film by using this transfer method,after poling,the PVP-co-PMMA and PMMA double-layer films can be peeled off by the ethanol solvent.This transfer method can transfer the graphene films onto substrates that are not resistant to acetone,such as electro-optic polymer films and organic semiconductor materials,and expands the application of graphene films.（4）In order to obtain mode switches with low voltage and broad bandwidth.The scheme of electro-optic mode switch designed by using graphene films and organic electro-optic polymer materials is proposed.Utilizing the property that graphene electrodes does not induce a significant loss to the TM waves in the low-index-contrast waveguide and the advantage that graphene electrodes can efficiently pole organic electro-optic polymer films,LP₀₁-LP_11a and LP₀₁-LP_11b1b mode switches based on graphene grating electrodes and electro-optic materials are designed.By optimizing the size of core,refractive indices of cladding and core materials and the design of grating electrodes,the mode switches with low voltage、low loss and high conversion efficiency are designed.And the ultra-broadband mode switch is designed by using length-apodized long-period grating electrode.更多还原