基于光子晶体多模波导的1．31／1．55μm双波长功分器的设计

设计了一种基于光子晶体多模波导的双波长光功分器,该器件能同时实现1.31 μm和1.55μm两种通信波长的光信号功率的平均分配,整个器件长度仅为15μm,是已报道的常规结构的182分之一.根据导模传输法,讨论了对称入射时光子晶体多模波导中的自映像效应,采用时域有限差分法模拟了光场在波导中的分布,入射场的单重像和二重像交替在波导中周期性地出现.并讨论了功分器的输出效率,及输出效率随位于单模波导与多模波导联结处的介电柱位置变化而产生的变化.     

光子晶体波导定向耦合光功分器的设计与优化

基于波导定向耦合原理设计了一种全新的光子晶体波导定向耦合光功分器.采用时域有限差分法对这种器件的光波传输特性进行了数值分析,结果表明:本征模色散曲线之间相交;器件的尺寸比传统光功分器更小;入射到光功分器的能量平均分配到输出端,且光波透射率高达95%.这些优异特性对于制造大带宽、高透射率和结构紧凑的光电器件具有极大的应用价值.     

一种可调能量输出比光子晶体波导耦合分束器

在完整三角形光子晶体中引入3条相互平行的单模波导形成定向耦合型分束器,非对称地改变波导间耦合区的介质柱的折射率,可实现能量输出端口能量比的改变.时域有限差分数值仿真结果表明,耦合区介质柱折射率在改变量较小时,能保证分束器有较高的能量透过率,且能实现输出端口能量输出比在一定范围内的调节.     

定向耦合型超微多路光分束器的设计

定向耦合器由多个光子晶体单模波导平行、邻近放置构成.在输入光场时称入射时,根据自映像原理数值分析了光在其中的传播行为.基于此结构,以3通道为例,设计了超微多路光分束器,仅仅通过对称地改变耦舍区中两个介质拄的折射率,使光场在横向发生重新分布,实现了输出能量的均分或自由分配.这种调制方法简单且输出效率更高.     

Coupling between photonic crystal waveguides

A calculation procedure for evaluation of the coupling length of two parallel coupled channel waveguides in a planar photonic crystal is proposed. The first step of the calculation is evaluation of the band structure of a photonic crystal containing two coupled linear defects. The eigenvalue corresponding to eigenstates localized in the linear defect (the waveguide) is split due to the coupling. This splitting is treated within the coupled-mode theory that yields a simple relation between the splitting and the coupling length. The MIT photonic bands code is used to evaluate the coupling between channel waveguides in silicon./sup 1/ These calculations show that in contrast to the finite-difference time-domain approach, the method is effective for three-dimensional light propagation.     

使用二维光子晶体设计极化分离器

设计了一种二维光子晶体的极化分离器,时域有限差分模拟和频率等高线图均用来显示这种器件是如何在给定的频率下工作的,其工作原理来源于二维光子晶体对TE和TM模式有着不同的色散特性,这种器件可以使用在集成光学和微波技术.     

一种实现超微光子晶体型定向耦合器的方法

在光子晶体定向耦合器中,通过减小两耦合波导之间介电柱的折射率来增大耦合系数,从而获得更短的拍长,形成超微的器件尺寸。耦合器的奇模场随调制折射率的减小变化不敏感,偶模场向更高频率的方向移动。在同一频率范围内,调制折射率减小,导致拍长随频率变化的函数曲线的斜率随频率增加而增大,这一特性可以在波分复用器中用来减小相邻信号频率差,在相同的器件长度下,可获得更多的信道。采用时域有限差分法验证了拍长随调制折射率减小而减小的变化规律。     

Topology optimisation of slow light coupling to photonic crystal waveguides

The slow light coupling efficiency in photonic crystal waveguides is enhanced by using the topology optimisation method. As much as 5 dB improvement in transmission can be achieved in the proximity of the spectrum cutoff. Moreover, the resemblance of the resulting two optimised spectra from different initial configurations indicates the possible convergence of the optimisations.     

光子晶体波导中慢光的实现

首先指出实现慢光的两种不同途径--改变材料色散和波导结构色散,并对利用结构色散产生慢光的光子晶体波导的原理、结构和特征作了说明.然后综述了目前光子晶体波导中产生慢光的新型结构和方法:啁啾结构、耦合结构和优化参数方法,并对它们做了比较.最后简要说明了慢光的研究意义和发展前景.     

Design and fabrication of silicon photonic crystal optical waveguides

We have designed and fabricated waveguides that incorporate two-dimensional (2-D) photonic crystal geometry for lateral confinement of light, and total internal reflection for vertical confinement. Both square and triangular photonic crystal lattices were analyzed. A three-dimensional (3-D) finite-difference time-domain (FDTD) analysis was used to find design parameters of the photonic crystal and to calculate dispersion relations for the guided modes in the waveguide structure. We have developed a new fabrication technique to define these waveguides into silicon-on-insulator material. The waveguides are suspended in air in order to improve confinement in the vertical direction and symmetry properties of the structure. High-resolution fabrication allowed us to include different types of bends and optical cavities within the waveguides.     

Low-loss silicon-on-insulator photonic crystal waveguides

Silicon-on-insulator-based 2D photonic crystal waveguides have been optically characterised. The measured total insertion loss is below 19 dB in the waveguides with unpolarised light. With the length mask technique, it is found that the photonic crystal waveguides show propagation losses below 4 dB/mm     

Wavelength switching by mode interference between longitudinally coupled photonic crystal channel waveguides

A wavelength switching mechanism of two longitudinally coupled and independently contacted photonic crystal channel waveguides is reported. The waveguides are coupled by a photonic crystal section of one period in /spl Gamma/-M orientation. The cavity lengths are chosen such that the cavity modes exhibit slightly different mode spacings and allow for a wavelength switching by mode interference between the two cavities.     

Dual grating-assisted directional coupling between fibers and thin semiconductor waveguides

A novel dual grating-assisted directional coupler (DGADC) for coupling an optical fiber with a thin semiconductor waveguide is proposed. As an example, a DGADC in silicon-on-insulator is discussed. Maximum coupling efficiency in excess of 90% can be obtained using this coupler, while the highest coupling efficiency previously reported was only 40%.     

Multiple-scales analysis of photonic crystal waveguides

The multiple-scales method is used to derive a scalar differential equation that describes the envelopes of photonic crystal waveguide modes. For a photonic crystal heterostructure waveguide and an air core photonic crystal waveguide, the mode frequencies calculated from the envelope approximation and full numerical simulations agree to 9% in the worst case when compared to the frequency difference of the band edges. The single-mode and cutoff width conditions for a photonic crystal waveguide are predicted and verified.     

Experimental demonstration of evanescent coupling from optical fibre tapers to photonic crystal waveguides

Experimental results demonstrating nearly complete mode-selective evanescent coupling to a photonic crystal waveguide from an optical fibre taper are presented. Codirectional coupling with 98% maximum power transfer to a photonic crystal waveguide of length 65 /spl mu/m and with a coupling bandwidth of 20 nm is realised.     

一种0.3 THz二维光子晶体定向耦合器的设计

设计了一种基于二维光子晶体的太赫兹定向耦合器,通过在2个平行的横向线缺陷中加入纵向线缺陷的方式,实现了良好的耦合结构,在太赫兹频段实现了较好的功率耦合特性。这种二维光子晶体带定向耦合器结构紧凑,可用于太赫兹系统中信号功率的检测与监控,具有良好的应用价值。     

Low-loss propagation in photonic crystal waveguides

The fabrication and characterisation of high-quality silicon membrane photonic crystals are reported. The etching process was carefully optimised to give holes with very smooth and vertical sidewalls, resulting in propagation, with a minimum loss of 4.1plusmn0.9 dB/cm in a single line defect (W1) waveguide     

Experimental demonstration of high coupling efficiency between wide ridge waveguides and single-mode photonic Crystal waveguides

The experimental demonstration of a high efficiency coupling technique based on setting a single defect within a photonic crystal (PhC) taper is reported. The samples were fabricated on a Silicon-on-insulator substrate and a 3-/spl mu/m-wide ridge waveguide was used to couple the light into and out of a single-mode PhC waveguide. Transmission efficiencies higher than 70% for wavelengths at 1.55 /spl mu/m are demonstrated which sharply improves the transmission efficiency achieved with butt-coupling and conventional PhC tapers.     

Out-of-plane losses of line-defect photonic crystal waveguides

A numerical model is presented for computing the out-of-plane losses of a general class of two-dimensional photonic crystals superimposed. onto a slab confinement structure. The usefulness of this model is demonstrated by calculating the propagation loss of a single-row-defect waveguide composed of hexagonal air holes etched into two different slab structures. The results are interpreted in terms of a simple coupled-mode-theory picture in which loss is due to resonant coupling between the fundamental and certain radiative slab modes. These calculations show that low-loss photonic crystal waveguides should be possible by carefully designing the slab waveguide     

Accurate modeling of line-defect photonic crystal waveguides

An accurate three-dimensional method to calculate the Bloch modes of photonic crystal (PhC) waveguides is proposed. Good agreement with available experimental and numerical data is obtained. The originality of the method lies in the fact that the Bloch modes are seen as the electromagnetic fields associated to the complex poles of an in-plane transversal scattering matrix. In comparison with previous approaches, the computational domain discretized is smaller and a higher accuracy for the losses of PhC waveguides is achieved.