Ultrashort broadband polarization beam splitter based on an asymmetrical directional coupler

An ultrashort polarization beam splitter (PBS) based on an asymmetrical directional coupler is proposed by utilizing the evanescent coupling between a strip-nanowire and a nanoslot waveguide. In order to be convenient for integration with other components, mode converters between the nanoslot waveguide and the strip-nanowire are introduced and merged into S-bends to achieve an ultracompact PBS. As an example a 6.9 μm long PBS based on a silicon-on-insulator platform is designed, and the length of the coupling region is as small as 1.3 μm. Numerical simulations show that the present PBS has a very broad band (>160 nm) for an extinction ratio of >10 dB.     

A very short vertical directional coupler with polarization-insensitive high extinction ratios

We propose a very short vertical directional coupler with polarization-insensitive high extinction ratios. The structure of the coupler has two deep-ridge waveguide structures in the upper and lower parts which can be implemented using a double-sided wafer process. The coupling length and extinction ratios of the vertical directional coupler with symmetric structures decrease as the thicknesses of the inner cladding layer and core layer decrease. The extinction ratio is improved using a slight asymmetry in the refractive indices of two core layers. As the thicknesses of the inner cladding layer and core layer decrease, the length of the vertical directional coupler for extinction ratios greater than 30 dB of both TE and TM modes decreases. A vertical directional coupler with a very short length less than 100 μm and polarization-insensitive high extinction ratios greater than 30 dB can be implemented using the structure proposed in this paper.     

反相电极聚合物定向耦合电光开关的优化设计

为了消除单节电极定向耦合电光开关的工艺误差对器件性能的不良影响,应用耦合模理论、电光调制理论、保角变换及镜像法,优化设计了一种两节交替反相电极聚合物定向耦合电光开关.模拟结果表明,该器件具有良好的开关性能:在1 550 nm的工作波长下,器件耦合区的长度为4 753.5 μm,交叉态电压为1.22 V,直通态电压为2.65 V,插入损耗小于2.21 dB,串扰小于-30 dB.通过微调状态电压,可以很容易地消除工艺误差对器件性能产生的不良影响.本文方法的设计结果与光束传播法的仿真结果符合得很好.     

Design and analysis of a vertical directional coupler between a three-dimensional plasmonic slot waveguide and a silicon waveguide

The design of a vertical directional coupler between a three-dimensional plasmonic slot waveguide and a silicon waveguide is theoretically investigated in detail. It consists of two steps: the design of isolated plasmonic slot waveguide and silicon waveguide and the determination of the gap between the two waveguides and the length of a coupling region. The designed structure transfers 70.8% of the power carried by the silicon waveguide mode to the plasmonic slot waveguide mode when the gap is 150 nm and the coupling length is 2.14 μm. The wavelength dependence of our vertical directional coupler is also studied. The analysis shows that the amount of the transferred power changes slightly over a very wide wavelength range between 1.40 μm and 1.61 μm. Moreover, if we employ the fabrication technology for silicon photonics, it is quite tolerant to the variation of the length of its coupling section. Finally, the vertical directional coupler is considered for a polarizer.     

Photonic Crystal Polarizing and Non-Polarizing Beam Splitters

A polarizing beam splitter （PBS） and a non-polarizing beam splitter （NPBS） based on a photonic crystal （PC） directional coupler are demonstrated. The photonic crystal directional coupler consists of a hexagonal lattice of dielectric pillars in air and has a complete photonic band gap. The photonic band structure and the band gap map are calculated using the plane wave expansion （PWE） method. The splitting properties of the splitter are investigated numerically using the finite difference time domain （FDTD） method.     

Polariton propagation in coupled quantum wire waveguides

The propagation of the excitonic polariton along the directional coupler consisting of adjacent parallel GaAs quantum-wire waveguides is simulated by using a finite element method. It is found that the coupling length is as short as 2.5-4 μm, which is three orders of magnitude shorter than the conventional optical directional coupler made of bulk GaAs. Such short coupling length will make it possible to fabricate extremely small optoelectronic devices such as directional-coupler-type switches.     

定向耦合器光波导开关阵列研究

在Z-LiN_bO₃衬底上制做了Ti扩散定向耦合电光开关阵列。把光纤固定在我们自己设计的衬底上,就做成了2×2开关。 本文讨论了三种光电开关。着重论述了Ti扩散定向耦合器的原理和交替Δβ法。在1.3μm的光波下改善了器件特性。     

一种新型光子晶体波导定向耦合型超微偏振光分束器

将两个二维空气孔光子晶体波导平行放置,两波导之间由三排空气孔相隔,构成一个定向耦合器.数值分析了TE(磁场平行于空气孔)和TM(电场平行于空气孔)偏振态光波在该定向耦合器中的传播行为.结果表明,减小耦合区两波导间的一排介质柱的半径,TE模的耦合长度减小,而TM模的耦合长度不变.基于此结构,设计了超微偏振光分束器,整个器件的尺寸为10.1μm,与已报道的24.2μm的结果相比,该器件具有更小的器件尺寸和更高的输出效率.     

1.30μm／1.55μm SiGe多模干涉滤波器

用多模干涉原理分析和设计了光通信波长（１．３０μｍ～１．５５μｍ）的Ｓｉ１－ｘＧｅｘ／Ｓｉ滤波器，并用模的传播分析方法对其传输特性进行了研究。结果发现，在Ｇｅ含量ｘ＝０．０４时，干涉区的脊高和宽度分别为６．３５μｍ和８μｍ。如果多模干涉区长度ＬＭ＝２３０２．５μｍ，可滤１．３０μｍ而通１．５５μｍ的波长。且具有３１ｄＢ的对比度和０．０１ｄＢ的插入损耗；如果多模干涉区长度ＬＭ＝２５１２．５μｍ，可滤１．５５μｍ而通１．３０μｍ的波长。具有１６ｄＢ的对比度和０．０９ｄＢ的插入损耗。     

Ka波段宽带谐波抑制定向耦合器

为解决传统分支线定向耦合器带宽较窄,且应用到线性化器等微波元件中时受谐波信号影响较大的问题,提出了一个宽带且带有谐波抑制功能的定向耦合器。该定向耦合器在双支节定向耦合器的基础上增加一个支节,可有效地提高定向耦合器的带宽,同时将其传输线支节替换为低通滤波结构,以实现对高次谐波抑制的作用。仿真结果表明,该定向耦合器的反射系数和隔离度均小于-15 dB,传输损耗小于3.8 dB,波动范围0.5 dB,相位差为90°且与双支节耦合器相比增加1 GHz带宽。满足耦合器的设计指标,可应用到微波元件中,提高微波元件的性能。     

跑道型结构光子晶体波导定向耦合器

鉴于波导定向耦合器在集成光路以及光电集成方面的广泛应用,提出了一种基于光子晶体波导间高效耦合的光子晶体定向耦合器。通过主波导和耦合波导间的耦合,可以实现对波长为1 490 nm和1 550 nm电磁波的高效分光。在将器件长度控制在30 μm左右的同时,其总效率高达93.05%。另外,发现主波导和耦合波导间介质柱结构参数对电磁波的耦合周期有着极大的影响。并通过将介质柱沿z方向拉伸0.1a(a为晶格周期),设计了工作波长为1 530 nm和1 540 nm的光子晶体定向耦合器,器件长度仅为60 μm。通过拉伸介质柱的纵向长度,可以大幅减小耦合周期,这对缩小器件体积以及实现更为密集的波分复用有着重要的意义。     

Novel 0.98/1.55 μm dichroic coupler based on lithium niobate

A novel 0.98/1.55 μm dichroic coupler with high-extinction ratio and low insertion loss has been designed and implemented on LiNbO₃ for Erbium-doped fiber amplifier applications. The design of dichroic coupler is based on a modified directional coupler structure with a single bend in each channel. Beam propagation method is used to analyze the coupler performance to get the optimal parameters for device design, such as channel width, titanium thickness, channel gap, and interaction length. Samples with the signal coupling ratio as high as 100% and pumping power ratio as high as 95% have been obtained.     

激光熔融拉锥型微型光纤耦合器设计

采用聚焦红外激光光束进行熔融加热,针对激光熔融拉锥型光纤耦合器设计了一种熔融区域长度为200 μm的微型光纤耦合器.使用光束传输法对拉锥长度和耦合区域的宽度进行了模拟并与实验结果比较,在1320 μm的拉锥长度和14 μm的耦合宽度处找到了最优化且低损耗的耦合器尺寸配置.     

双枝节加载的L波段宽带高隔离度定向耦合器

提出了一种小型化双枝节加载的L波段微带线定向耦合器。使用功率相消技术提高定向耦合器的隔离度,并且采用两根长度不同的加载枝节分别在两个相近的频点上反射信号,从而实现耦合器的带宽扩展;同时采用缺陷地结构的慢波特性减小该定向耦合器的物理尺寸,并利用缺陷地结构产生的陷波,合并上述两根枝节反射抵消产生的的两个陷波,进一步提高定向耦合器的带宽和隔离度。该耦合器工作在L波段,耦合度约为10 dB,在整个L波段内的隔离度均优于?20 dB,最大约为?52.81 dB,相对带宽为60%。最后对设计的定向耦合器进行加工和测试,测试与仿真结果一致性较好,证明了该电路的可行性。     

Directional coupler design based on coupled cavity waveguides in photonic crystals

We propose a directional coupler design based on coupled cavity waveguide in photonic crystals. The plane wave expansion is used to give the dispersion of the coupled cavity waveguides and two parallel such waveguides. The couple length is got from the dispersion curves. Based on the research of the dispersion, we present a directional coupler and the transmission property is given. This structure is potentially important for highly efficient directional coupler in integrate optical circuit.     

一种定向耦合器型高聚物光开关设计

本文提出了一种基于定向耦合器型的高分子聚合物波导光开关设计,其突出特点是极低的波长相关性和耦合区几何尺寸敏感度,可采用橡胶成型工艺(Rubber Molding Process)实现高聚物波导在硅基底上的快速转印成型.利用BPM方法进行了器件的波导结构设计及性能模拟,插入损耗为0.4-0.6 dB,串扰<-32 dB,偏振相关损耗约为0.08 dB,电光系数r33＝14 pm/V时,器件的开关电压为42 V.     

Graphical Representation of the Supermode Theory of a Waveguide Directional Coupler

A novel graphical representation of the supermode theory of a waveguide directional coupler based on phasor analysis is described. Following this approach, dependence of the magnitudes and phases of the output fields on the splitting ratio of a directional coupler is discussed. Both the cases of phase-matched (identical) and non-phase-matched (non-identical) waveguides constituting a directional coupler are investigated. This approach directly illustrates the fact that the phase shift suffered by the coupled light relative to the throughput light is π/2, regardless of the splitting ratio for identical guides, which is not the case for couplers with non-identical waveguides. It also yields additional information about the phases of the output fields of a directional coupler. The usefulness of this approach in the context of wavelength-flattened couplers, wavelength division multiplexing couplers, and polarization effects in directional couplers is also discussed. This approach should also be helpful in the analysis of guided wave interferometric devices such as wavelength interleave filters and modulators, based on concatenated directional couplers.     

多波导定向耦合器耦合特性

利用拉普拉斯变换,将多波导定向耦合器的耦合模方程组变换为三对角线性方程组,并采用追赶法求出了该方程组的通解;进一步,给定初始条件,进行拉普拉斯变换反演,即可严格地求出该耦合模方程组的解。采用该方法研究了5波导定向耦合器光从一个波导入射和等光强从5个波导入射时的耦合特性,求出了耦合模方程组解的解析表达式,给出了每个波导中光功率变化规律曲线。利用该方法,可很方便地求出任意有限数目波导组成的定向耦合器在任意入射条件下耦合模方程组的解,因此对于多波导定向耦合器结构的合理设计,具有非常重要的意义。     

用于X波段模块化相对论速调管放大器在线测量的紧凑型定向耦合器设计

为实现模块化相对论速调管放大器功率、频率和相位的在线测量,对紧凑型高定向性高带宽的定向耦合器进行了仿真和实验研究。利用小孔耦合理论和相位叠加原理进行理论分析,设计了一种双孔紧凑型定向耦合器,在此基础上采用主、副波导正交连接,耦合孔沿轴向和角向二维分布的方法,进一步缩短了耦合器的长度。通过电磁仿真对耦合器各参数进行优化,模拟结果表明：当中心频率为10 GHz时,普通双孔定向耦合器对TM01模式的耦合度为-60.68 dB,在250 MHz的带宽内定向性大于20 dB,此时耦合区长度为3.49 cm。改进型定向耦合器对TM01模式的耦合度为-58.1 dB,在300 MHz的带宽内定向性大于20 dB,此时耦合区长度仅为1.8 cm（约0.6λ）。耦合器的冷腔实验测量结果与仿真结果符合较好。     

Compact triplexer in two-dimensional hexagonal lattice photonic crystals

We design a compact triplexer based on two-dimensional (2D) hexagonal lattice photonic crystals (PCs).A folded directional coupler (FDC) is introduced in the triplexer beside the point-defect micro-cavities and line-defect waveguides.Because of the reflection feedback of the FDC,high channel drop efficiency can be realized and a compact size with the order of micrometers can be maintained.The proposed device is analyzed using the plane wave expansion method,and its transmission characteristics are calculated using the finite-difference time-domain method.The footprint of the triplexer is about 12× 9 μm,and its extinction ratios are less than –20 dB for 1310 nm,approximately –20 dB for 1490 nm,and under –40 dB for 1550 nm,making it a potentially essential device in future fiber-to-the-home networks.