【作者】 白冰；

【导师】 裴丽；

【作者基本信息】 北京交通大学 ， 通信与信息系统， 2021， 博士

【摘要】 近年来,以硅基光电子技术为代表的片上集成技术越来越受到学术和产业界的关注。尽管硅与包层材料之间的高折射率差显著减小了器件尺寸,但偏振态对硅基光电子器件和回路的性能产生了非常显著的影响。目前,大多数的硅基片上偏振调控器件都是介质波导结构。由于介质材料的双折射效应较弱,器件尺寸往往较大,且结构相对复杂。表面等离激元是一种存在于介质和金属界面的特殊表面波,可以将光场能量很好地限制在界面附近,具有亚波长尺度的光场限制能力。更为重要的是,表面等离激元是横磁模,具有天然的偏振敏感性,为超小型的硅基偏振调控器件的研究提供了全新思路。其与硅基光波导结合可以有效调控波导模式的有效折射率和光场分布,显著增强器件的双折射效应,有望实现超小型、高性能的片上硅基表面等离激元偏振调控器件。本论文围绕片上偏振调控技术,以硅基混合表面等离激元波导为基本结构,研究超小型片上偏振调控器件。通过引入金属结构增加设计自由度,探索硅波导与硅基混合表面等离激元波导光场模式分布的特点。在SOI(Silicon-on-Insulator)材料平台基础上,提出了两种混合表面等离激元波导偏振调控器件,并且探讨了利用偏振转换实现片上光子加法器的可能。本论文的主要创新成果总结如下:1.提出了一种基于中空型硅基混合表面等离激元波导的TM模式片上起偏器。通过优化锥形波导结构,并且利用TM模式的光场限制能力,有效阻断了TE模式的传播。由于硅波导上方的金属条宽度远大于波导宽度,该结构无需金属与波导的精确对准,增大了工艺容差,有效降低了工艺难度。分析结果表明,在整个C波段,器件消光比大于34 d B且插入损耗小于1 d B。当器件长度为4μm时,在1.55μm波长下消光比可达57.7 d B,插入损耗为0.145 d B/μm。2.提出了一种基于弯曲非对称定向耦合的超小型片上偏振旋转分束器。在表面等离激元与弯曲波导结构的共同作用下,交叉偏振耦合系数得到了显著增大。分析结果表明,器件耦合长度仅为5.21μm。通过表面等离激元调控光场分布和波导模式有效折射率,器件TM-TE模式的偏振转化效率可达99.9%。1.55μm波长下,TM模式和TE模式的消光比分别为20.6 d B和32.5 d B。在80 nm带宽范围内,偏振转化效率大于90%,通道串扰小于-19 d B。3.提出了基于硅基表面等离激元加法器的光子神经网络。面向双端口光子卷积神经网络,对其中的矩阵相乘部分进行了理论研究与实验验证,测试结果表明该结构具备10GOPS的光域矩阵乘加计算能力;利用同一波导中TM与TE偏振态良好的正交性以及不同波导之间的偏振交叉耦合,设计了双端口硅基表面等离激元光子加法器,对矩阵相乘部分的输出实现了稳定可靠的光域求和运算。面向多端口光子储备池计算网络,利于多个偏振模式的正交性,设计了多端口硅基表面等离激元光子加法器,对随机投影层的多通道输出实现了求和运算,且器件尺寸相对紧凑。更多还原

【Abstract】 In recent years,the on-chip integration technology represented by Silicon Photonic technology has attracted more and more attention from academia and industry.The high refractive index contrast between silicon and its cladding makes the devices compact,however,the polarization state has a significant impact on the performance of on-chip photonic devices and circuits.Currently,most on-chip polarization control devices are based on dielectric waveguide structures.Due to the weak birefringence effect of dielectric materials,the device footprints are usually relatively large and the structures are complicated.Surface plasmon polaritons(SPPs)is a kind of special surface wave existing at the interface between medium and metal,which can confine the energy of light near the interface and has the ability of limiting the light field in sub-wavelength scale.More importantly,the surface plasmon is a transverse magnetic mode with natural polarization sensitivity,which provides a new idea for the research of ultra small siliconbased polarization control devices.Combined with the silicon photonic waveguide,it can effectively control the effective refractive index and light field distribution of the waveguide mode,and significantly enhance the birefringence effect of the device.It is expected to achieve ultra small and high performance silicon-based surface plasmon polarization control device.This thesis focuses on the on-chip polarization handling technology and utilizes silicon hybrid plasmonic waveguide as the basic structure to study ultra-compact polarization controlling devices.By introducing metal structure to increase the degree of design freedom,the characteristics of the optical field mode distribution of the dielectric waveguide and the hybrid plasmonic waveguide are explored.Based on the SOI material platform,two silicon hybrid plasmonic polarization handling devices are proposed,and the possibility of using polarization conversion to implement on-chip photonic adders is also discussed.The main innovations achieved in this thesis are summarized as follows:1.A transverse magnetic(TM)-pass on-chip polarizer based on hollow hybrid plasmonic waveguide is proposed.With the optimized tapered structure and plasmonics induced optical confinement for TM mode,the propagation of the transverse electric(TE)mode is effectively blocked.Since the width of the metal strip above the silicon waveguide is much larger than the width of the waveguide,this structure avoids the precise alignment between the metal and the waveguide,which increases the process tolerance and effectively reduces the fabrication difficulty.The device length is only4 μm and the extinction ratio is as high as 57.7 d B at the central wavelength of 1.55μm with low insertion loss of 0.145 d B/μm.In addition,the extinction ratio >34 d B and insertion loss <1 d B are achieved within the whole C-band.2.An ultra-compact on-chip polarization rotating beam splitter is realized by using an asymmetric bent directional coupler.Benefitting from the large birefringence induced by the bent structure and plasmonic effect,the cross-polarization coupling coefficient is significantly increased.The coupling length of the device is only 5.21 μm,which is the smallest length reported in the known literature.By controlling the optical field distribution and the effective refractive index of the waveguide mode via plasmonics,the TM-to-TE polarization conversion efficiency of the device is as high as 99.9%.At the wavelength of 1.55 μm,the extinction ratios of TM mode and TE mode are 20.6d B and 32.5 d B,respectively.Furthermore,the polarization conversion efficiency is higher than 90% while maintaining cross talk below-19 d B within the bandwidth of80 nm.3.Photonic neural networks based on silicon surface plasmon adder is proposed.For two-port photonic convolution neural network,the matrix multiplication part is theoretically studied and experimentally verified.The test results show that the structure has the ability of 10 GOPs optical domain matrix multiplication and accumulation.Using the good orthogonality of TM and TE polarization states in the same waveguide and polarization cross coupling between different waveguides,a two-port silicon-based surface plasmon photonic adder is designed.The stable and reliable optical domain adding is realized for the output of the matrix multiplication part.For the multi-port photonic reservoir computing network,which is conducive to the orthogonality of multiple polarization modes,a multi-port silicon-based surface plasmon photon adder is designed to achieve the adding operation of multi-channel output of random projection layer,and the device size is relatively compact.更多还原