光子晶体异质结耦合波导光开关

以二维三角晶格光子晶体为研究对象,在该光子晶体中引入两行平行的单模线缺陷波导,以一行耦合介质柱为间距,通过调节部分耦合介质柱的折射率,构筑了光子晶体异质结耦合波导光开关结构。利用平面波展开法和定向耦合原理计算了在不同入射光频率下,缺陷波导间耦合介质柱的折射率不同时的耦合长度,确定了合适的光子晶体异质结耦合波导光开关的结构参数。利用时域有限差分法研究了该光开关中耦合介质柱的折射率变化及异质结构介质柱的位置分布对光信号输出路径的影响。结果表明,通过改变该结构中耦合介质柱的折射率可以改变光的输出路径,可实现光的开关行为。并且异质结构介质柱位置的随机分布对该光开关的影响不大,有助于光子晶体新型滤波器、定向耦合器、波分复用器以及光开关等光子器件的研究。     

光子晶体定向耦合三波长功分器

以二维三角晶格光子晶体为研究对象,在该光子晶体中引入两行以一行耦合介质柱为间距的平行单模线缺陷波导.通过分析和研究光子晶体波导耦合结构的耦合和解耦合特性,发现在不同频率下耦合波导的耦合长度不同.利用平面波展开法和定向耦合原理计算了在不同入射光频率下,缺陷波导间耦合波导的耦合长度,设计了一种新型超微光子晶体波导耦合型三波长功分器,实现了归一化频率分别为0.369、0.394、0.435的光波的分束效果.采用时域有限差分法验证了该功分器具有很好的功率分配效果.本文结果有助于光子晶体新型滤波器、定向耦合器、波分复用器、偏振光分束器以及光开关等光子器件的研究.     

耦合腔光子晶体慢光波导结构

在单线缺陷结构中引入两个附加的相邻介质柱,构成一种新型的光子晶体耦合腔波导结构.通过平面波展开法对波导结构的的慢光特性进行了仿真分析,研究了平移线缺陷上下两侧介质柱,以及改变腔体的长度对器件色散特性和群速度的影响.结果表明:与平移缺陷上下两侧介质柱相比,通过改变腔体的长度,不仅可将光群速度低到0.03c(c为真空下的光速),而且器件的有效波长范围接近20nm.利用时域有限差分法得到波导结构的传输场分布图,研究波长的选取对入射激励光在光子晶体耦合腔波导中传输场的影响,发现结构参量优化后的光子晶体耦合腔波导仍然具有良好的传输特性.     

渐变空气孔双芯光子晶体光纤特性研究

为进一步开发新型光耦合器件,利用全矢量有限元法和平面波展开法分析了一种包层空气孔直径渐变的双芯光子晶体光纤,得到了其耦合长度、耦合系数以及色散系数随波长和结构参数的变化曲线。数值分析结果表明,与普通包层等空气孔结构光纤不同,此种结构的光子晶体光纤在一个极宽的波长范围内(0.4μm~2.4μm)耦合长度极短,耦合特性极强。当波长位于0.9μm~2.0μm之间时,具有近零超平坦色散特性。这种新型结构的双芯光子晶体光纤在光通信系统和光耦合器件的设计方面具有重要的应用价值。     

基于波导间能量耦合效应的光子晶体频段选择与能量分束器

基于波导间能量耦合效应的光子晶体功率分束器具有结构紧凑、带宽较宽、弯曲损耗低、分光角度大和不受外界电磁场干扰等优点.本文利用时域有限差分方法,理论研究了二维三角晶格光子晶体耦合波导的功率分束特性,设计得出了一种能够在宽频谱范围内针对不同频率区间实现不同分光比的功能器件.在此基础上通过改变耦合区介质柱形状以及输出分支波导与能量耦合波导的连接位置,最终针对三个相邻频率范围内的入射光信号,较好地实现了三均分、二均分、单一输出通道这3种能量分配输出模式.该功能器件具有透过率对比度高、结构紧凑等特性,对于发展全光功能器件在大规模全光复杂集成领域内的实际应用具有一定的促进作用.     

基于混合导光型光子晶体光纤的波分解复用器研究

设计了一种基于混合导光型光子晶体光纤的波分解复用器,该波分解复用器同时具有折射率导光型光子晶体光纤和带隙导光型光子晶体光纤的特点,可用于稀疏型波分复用系统中.设计的稀疏型波分解复用器由一段三芯光子晶体光纤组成,通过填充不同折射率的材料.形成了混合导光型光子晶体光纤.根据耦合模原理,在临近的波导中,当传播常数相等时,模式之间发生强烈耦合.能量在波导之间交替.由于填充的材料折射率不同,使得光功率在两个小同的波长上发生耦合,构成了两个不同响应波长的光滤波器.通过选择合适的光纤长度,使得在光纤的输出端,不同波长的光从不同的波导输出,实现波分解复用的功能.采用全矢量有限元法分析了光纤传输特性,计算了不同波长光的耦合长度.采用光束传播法仿真发现,长度为4.3 mm的光纤能实现波长为1.31μm和1.55μm光的解复用.     

基于二维光子晶体点缺陷可调谐光功率分配器

在二维矩形阵列结构硅光子晶体中去除中间一排硅柱形成线波导,在线波导右侧引入点缺陷。利用时域有限差分法(FDTD)模拟仿真以及数值分析研究线波导中光耦合特性,计算出两个通道的分光比,发现改变光子晶体的温度可以明显改变这两个通道的光功率比。基于此结构,提出了一种新的光功率分配器,可以获得大范围的光功率比值,从1∶1～90∶1都可以通过改变光子晶体的温度来实现,并且当温度从0℃～200℃就可以实现这一功能,最后设计了一款三通道可调谐光功率分配器,通过调节两个点缺陷区域内温度来实现光功率的分配。     

双光子吸收对光子晶体定向耦合全光开关的影响

 利用时域有限差分方法,在非线性条件下,考虑双光子吸收效应的同时,建立了分析2维光子晶体定向耦合波导光开关的模型。数值计算结果表明,对于长度较短的波导耦合器件,在强控制光和非线性条件下,双光子吸收效应会对波导的耦合作用产生一定的影响,从而改变入射光的透射特性,使光开关控制的动态过程发生变化。故而在设计全光开关器件时,对强控制光条件下的非线性双光子吸收效应有必要作为影响因素考虑进去。     

光子晶体波导定向耦合型1×3光分束器

将五光子晶体单模波导平行、邻近放置构成定向耦合器,依据自映像原理,数值分析了输入光场对称入射时,该系统中光的传播行为.基于此结构,设计了1×3光分束器,其器件长度可短至14.26μm.仅仅通过对称地改变耦合区中两个介质柱的有效折射率,使光场在横向发生重新分布,便可实现输出能量的均分或自由分配.通过非对称地改变耦合区中的一个介质柱,可实现3个输出端的输出能量的自由分配.该光分束器具有微小尺寸和各输出端输出能量的比例可自由调制的特点,在未来集成光回路中具有广泛的应用价值.     

基于热膨胀效应的可调光功率分束器设计

可调光功率分束器是集成光子系统中的重要功能器件,其光功率输出具有动态可调控特性,诸多光子系统对其有着广泛需求.本文基于空隙槽型Y分支波导结构,利用热膨胀效应,提出了一种新型可调光功率分束器实现方法,通过调控温度来改变分支处空隙槽的宽度,以实现其分支波导的光功率输出的动态变化.采用有限元方法,对其热膨胀形变和光学性能进行了模拟分析.其模拟结果表明,该器件能实现大范围光分束调控,且对波长和偏振态依赖性低;同时,该器件具有结构简单、易于设计和制作、易于调控等优点,这种新型器件在各种光子系统中具有重要应用前景.     

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。     

Fabrication of all-solid photonic bandgap fiber coupler

We report the fabrication of a tunable all-solid photonic bandgap fiber coupler based on the side-polishing technique. This device is believed to be the first demonstration of a photonic bandgap fiber coupler to eliminate the contamination of the open air holes. By adjusting the length of the interaction section, the tunable coupling ratio as much as 92.5% at 1550 nm is achieved. The investigation of the spectrum properties shows that the coupler has excellent tunability properties, for which the coupling ratio can be smoothly and continuously controlled.     

Kerr nonlinear switch based on ultra-compact photonic crystal directional coupler

In this paper, an all optical switch based on nonlinear photonic crystal directional coupler has been simulated and analyzed by the finite difference time domain (FDTD) method. The lunched pump signal increases the refractive indices of the central row of the coupler, due to nonlinear Kerr effect, hence the coupler works in the nonlinear conditions and lightwave guides to the other output port. We have tried to increase the coupling efficiency and reduce the required power in the nonlinear status by optimizing the bends structure and increasing the interaction between dielectric and lightwave signal. Therefore, the input signal beam can be controlled to be exchanged between two output ports to earn the highest output power ratio and the smallest amount of power required for nonlinear performance, the physical length of the coupler is determined to be 20a, where a is the structure lattice constant.     

Efficient coupler between chip-level and board-level optical waveguides

We propose an efficient optical coupler between a submicrometer-sized silicon waveguide on a silicon photonic chip and a multi-micrometer wide polymer waveguide on an optical printed circuit board for interchip optical networks. We show low coupling loss <0.4 dB with high lateral and angular tolerance to misalignment so that coupling can be done by automatic pick-and-place equipments with high throughput and low cost. The coupler has a wide optical bandwidth from 1470 to 1650 nm.     

Si-based two-dimensional photonic crystals coupled to one-dimensional Bragg mirrors

Planar two-dimensional photonic crystals can be combined with a one-dimensional Bragg mirror to control the quality factor and out-of-plane coupling of optical Bloch modes. We have investigated the optical properties of such structures fabricated on silicon. The photonic crystals are fabricated in the upper Si layer deposited on top of quarter-wave thick SiO₂-polycrystalline Si layers. The optical properties are probed by the room-temperature photoluminescence of Ge/Si self-assembled islands as an internal source. We show that an enhancement of the quality factor can be obtained by controlling the thickness of the silicon upper layer in which the two-dimensional photonic crystal is etched and by controlling the air filling factor of the photonic crystal. Quality factors of 2200 around 1100 nm are obtained by this method for defect-free photonic crystals with a square lattice pattern. The experimental results are supported by three-dimensional finite-difference time-domain (FDTD) calculations of the radiated modes for the investigated structures.     

Wavelength-selective coupling of dual-core photonic crystal fiber with a hybrid light-guiding mechanism

A novel class of wavelength-selective coupling photonic crystal fiber (PCF) that operates by a hybrid light-guiding mechanism has been proposed. Different from the traditional PCF coupler operating principle, this fiber coupler shares properties of both the total internal reflection index-guided and the photonic bandgap mechanism. This coupler allows highly accurate control of the filtering wavelength; both bandstop and bandpass filters can be easily implemented. The spectral transmission results demonstrate that the bandpass characteristic of the coupler is very narrow and free of sidelobes. Moreover, the operating wavelength and the coupling length can be continuously tuned by changing the refractive index of the filling material. This research gives a physical insight into the propagation mechanism in the PCF coupler and is crucial for future applications of the proposed device.     

Design and simulation of a switch based on nonlinear directional coupler

In this paper, we have analyzed a nonlinear photonic crystal directional coupler by the finite difference time domain method. We have tried to increase the coupling efficiency and also reduce the coupling length in linear and nonlinear states in this device. In this coupler, refractive index of the rods of the central row is tuned by input signal power due to nonlinear Kerr effect; therefore, input signal beam can be controlled so as to be exchanged between two output ports. Physical length is chosen to be 24a so as to have the highest output power ratio and also the smallest amount of power required for nonlinear performance.     

光子晶体波导定向耦合器

在完整二维光子晶体中引入线缺陷后，就形成了光子晶体波导；将时域有限差分方法(FDTD)用于光子晶体波导耦合研究，计算了不同耦合长度情形下的波导各个出口处的透过率，结果表明：光子晶体波导耦合遵循普通介质波导耦合的一般规律，也有定向耦合的功能。进一步的研究表明：对于不同的频率，光子晶体定向耦合器耦合系数是不同的，并且耦合系数和对应的频率之间近似直线关系。     

High efficiency,small size,and large bandwidth vertical interlayer waveguide coupler

Since the advent of three-dimensional photonic integrated circuits,the realization of efficient and compact optical interconnection between layers has become an important development direction.A vertical interlayer coupler between two silicon layers is presented in this paper.The coupling principle of the directional coupler is analyzed,and the traditional method of using a pair of vertically overlapping inverse taper structures is improved.For the coupling of two rectangular waveguide layers,a pair of nonlinear tapers with offset along the transmission direction is demonstrated.For the coupling of two ridge waveguide layers,a nonlinear taper in each layer is used to achieve high coupling efficiency.The simulation results show that the coupling efficiency of the two structures can reach more than 90%in a wavelength range from 1500 nm to 1650 nm.Moreover,the crosstalk is reduced to less than-50 d B by using multimode waveguides at intersections.The vertical interlayer coupler with a nonlinear taper is expected to realize the miniaturization and dense integration of photonic integrated chips.