Effects of shaded facets on the performance of metal-coated etched diffraction grating demultiplexer

A finite-difference time-domain (FDTD) method combined with a periodic boundary condition is used to analyze the diffraction efficiency of an etched diffraction grating (EDG) demultiplexer coated with a metallic film at the backside. The numerical results show that the diffraction loss is mainly due to the scattering effect of shaded facets of a metal-coated grating at both the polarizations. However, the same shaded facets can produce a higher loss for a TM polarization than that for a TE polarization, which induces a higher polarization dependent loss (PDL) of the demultiplexer.     

A Flattened AWG Demultiplexer with Low Chromatic Dispersion

A design method is introduced to obtain a flat-top arrayed-waveguide grating (AWG) demultiplexer with low chromatic dispersion. A multimode interference (MMI) section is connected at the end of the input waveguide, and a tapered waveguide is connected at the entrance of each output waveguide of the AWG demultiplexer. The design procedure is presented. A design example is given and shown to have a much better performance than the conventional flat-top design using only an MMI section. The insertion loss of the designed AWG demultiplexer is also reduced.     

低偏振相关损耗全息光栅波分复用器的设计

对基于掺杂铌酸锂材料的体光栅波分复用器主要结构和光栅记录参量提出了一种优化设计方法.采用严格耦合波理论,对两种偏振不同入射角和不同记录晶体厚度下的器件关键性能参量,如插入损耗和偏振相关损耗等进行了优化.数值结果证明采用优化设计的晶体厚度和光栅记录时的入射角,在获得相当低的偏振相关损耗的同时,也能够获得较低的插入损耗,实现了综合性能优化的波分复用器设计.实验结果证明用优化设计的参量能有效降低波分复用器件的插入损耗和偏振相关损耗.     

两点法设计平场型EDG波分复用器件

利用两点法(two stigmatic points method)对平场型蚀刻衍射光栅(EDG)波分复用器件进行了优化设计.与传统EDG相比,该方法以较小的性能损失为代价,极大简化了制作工艺.通过标量波动衍射理论对16通道的该型器件进行了数值模拟,结果表明:在用光探测器陈列接收的情况下,额外的功率损耗约为1dB,信道间的不均匀性小于0.3dB,串绕小于-30dB.     

A dual-channel wavelength multiplexer / demultiplexer based on the restricted-resonance self-imaging effect

The authors propose a high-performance 980 / 1550-nm wavelength multiplexer / demultiplexer based on the restricted-resonance self-imaging effect in a buried-type waveguide system. The device functions either as a multiplexer or a demultiplexer, depending upon the direction of light propagation. Using the modal propagation analysis (MPA), characteristics of the device are investigated. We carried out the design of the device and showed that the device performance can be optimized by appreciate selection of the coupler width. A demultiplexer with an insertion loss of 0.4 dB and contrast of 25.5 dB at wavelength 1550 nm and 32 dB at 980 nm is demonstrated.     

Reduced back reflection design for an etched diffraction grating based planar demultiplexer

A design for a planar etched diffraction grating (EDG) demultiplexer is presented to reduce the back reflection. By reducing the diffracted field at the input waveguide, the present design makes the best effort to reduce the optical return loss. A design example is given to verify the performance. The spectral response at the input waveguide is simulated and the results show that at the wavelengths that cause back reflection, the reduced back reflection design only receives –47.7 dB of the input power, whereas the design without reduced back reflection receives –3.7 dB of the input power.     

Optimal design for a flat-top AWG demultiplexer by using a fast calculation method based on a Gaussian beam approximation

Passband broadening of an AWG (array waveguide grating) demultiplexer with an MMI (multimode interference) coupler connected at the end of a tapered input waveguide is considered. An explicit formula based on the field propagation of an approximate Hermit-Gaussian beam is used to calculate quickly and reliably the spectral response of the AWG demultiplexer. The widths of the input waveguide, the output waveguides and the MMI coupler are optimized. The optimal design is verified with the experimental measurement.     

Etched-Diffraction-Grating-Based Planar Waveguide Demultiplexer on Silicon-on-Insulator

An optical wavelength demultiplexer with the etched diffraction grating (EDG) on the silicon-on-insulator (SOI) material is demonstrated. Fabricated by the wet-anisotropic-etching method, 90° turning mirrors are used to bend waveguides, and the size of the EDG-based demultiplexer is minimized to only 16×2.5 mm². The crosstalk is below −16 dB. The on-chip loss is about 9.97 dB, which is composed of about 8.72 dB excess loss and 1.25 dB diffraction loss. The polarization-dependent central wavelength shift is below 0.13 nm, and the polarization-dependent loss is about 0.35 dB. The sources of the crosstalk and loss are discussed in details, and the related measures to improve the performance are also presented.     

大角度蚀刻衍射光栅的模拟

研究了平面波导密集波分复用器件中很有发展潜力的蚀刻衍射光栅(EDG).小角度范围光栅的模拟通常采用高斯近似的输入光场,由于近轴的高斯光场接近实际光场,所以模拟结果很准确.但这种方法应用于大角度范围的光栅则有偏差.本文提出了大角度蚀刻衍射光栅的模拟方法,分析了这种偏差并给出了模拟结果.事实上这种方法也适合于实际任意输入光场的模拟.     

低插损平坦谱响应阵列波导光栅解复用器优化设计

通过在输入波导与输入平板波导之间加入一种模式转换结构,获得了一个具有平坦光谱响应,低插损,光谱响应对称的阵列波导光栅型波分复用器,该模式转换结构由一个与输入波导的输出端连接的第一锥形波导,一个与此锥形波导输出端连接的细直波导,一个与细直波导输出端连接的第二个锥形波导以及一个连接输入平板波导和第二个锥形波导的梯形波导组成,通过优化设计梯形波导和第二个锥形波导的形状可以获得较宽的1dB通带带宽和较低的插损,同时光谱响应具有非常好的平坦性,而且通过对第一个锥形波导和细直波导的优化设计,在不引入明显的额外插损的条件下,能大大减小由于输入波导的弯曲引入的光谱响应的不平坦.     

电光聚合物波导中的锥形结构

提出并设计了一种基于电光聚合物的锥形波导,可用于单模光纤与电光聚合物波导器件之间的连接.锥形波导中采用了宽度锥形和折射率锥形结构.宽度锥形采用劈形形状,通过宽度和折射率的缓慢变化实现模场转换.劈形形状的宽度锥形具有较小的损耗且易于制作,折射率锥形可采用灰度掩膜光刻技术制作.研究了锥形波导的传输损耗与锥形波导的长度、波导宽度和厚度、材料吸收损耗等参数的关系及其优化,分析了锥形波导中的功率传输、模场分布与模式转换效率.结果显示锥形波导的传输损耗小于0.37 dB,光纤-波导-光纤的连接损耗优于1.62 dB,对插入损耗的改善达到8.78 dB,模场转换效率达到了83.7%.     

8-信道MMI阵列波导光栅复用/解复用器的研制

本文首先详细分析了基于自镜象效应的MMIDMUX器件的基本工作原理,在此基础上,在GaAs/GaAlAs系材料上完成了对8信道MMIDMUX的具体设计.该器件的输入、输出单模波导和SIE多模波导采用离散谱折射率法进行优化设计,最后获得了当输入、输出单模波导宽度为3μm、SIE多模波导宽度和长度分别为40μm和1731.45μm时,该器件对8信道波长的隔离度为～26dB,理论传输损耗为～0.24dB.     

平场输入/输出蚀刻衍射光栅的设计

光通信中波分复用技术是解决通信网络瓶颈的有效手段，近年来得到很大发展。以平面波导波分复用器件为核心的密集波分复用技术已经得到成功商用。蚀刻衍射光栅是平面波导密集波分复用器件中很有发展潜力的一种。原有蚀刻衍射光栅采用罗兰圆设计，输入输出在圆弧曲线上由条形波导引出；而平场输入／输出的蚀刻衍射光栅在很多应用中可以省去制作输入输出波导，大大简化制作工艺，同时能够保持良好的线性色散和聚集效果。给出了平场输入和输出蚀刻衍射光栅的设计方法，并利用标量衍射理论对设计的结果进行模拟，验证了平场输出蚀刻衍射光栅具有很好的分波效果。     

Use of space-time coding in coherent polarization-multiplexed systems suffering from polarization-dependent loss

We evaluate the advantage of using space-time coding in order to increase the tolerance of fiber-optic communications systems to polarization-dependent loss (PDL). Focusing on three particular codes, the Golden Code, the Silver Code (SC), and the Alamouti Code (AC), we calculate the amount of average PDL that can be tolerated for a given signal-to-noise ratio margin that is designed into the system. The SC is shown to be optimal in the case of low to moderate PDL, whereas, in the case of extreme PDL, the AC shows the best performance.     

A Passband-Flattened EDG Demultiplexer with an Air-Trenched Taper

A novel passband flattening method for a planar waveguide demultiplexer based on an etched diffraction grating is presented. A strongly confined taper is formed by etching air trenches at both sides of the input waveguide. The geometric parameters of the taper are optimized by considering the figure of merit, ripple, and loss. Numerical simulation for a design example is given to illustrate the passband flattening method.     

A Passband-Flattened EDG Demultiplexer with an Air-Trenched Taper

A novel passband flattening method for a planar waveguide demultiplexer based on an etched diffraction grating is presented. A strongly confined taper is formed by etching air trenches at both sides of the input waveguide. The geometric parameters of the taper are optimized by considering the figure of merit, ripple, and loss. Numerical simulation for a design example is given to illustrate the passband flattening method.     

一种改善频谱性能的蚀刻衍射光栅输出结构新设计

对波分复用系统中一种重要的解复用器-衍射蚀刻光栅(EDG)的输出结构进行了研究,并提出一种新的采用渐变波导和空气槽相结合的结构设计,在保持器件原有的紧凑结构的前提下极大的提高了器件的频谱特性.该结构设计不需要额外的工艺过程,并且具有很好的工艺容差性.结构的有效性通过波束传播方法(BPM)和模式传播分析(MPA)得到了验证.在所给的数值模型中,-1 dB带宽和品质因素分别比传统设计提高了1.474和1.383倍.同时,相邻信道间的串扰降低了15 dB以上,而整个结构引入的功率损耗仅仅为0.65 dB.     

利用锥型换能器的宽带低损耗声表面波滤波器设计

分析锥型换能器的基本原则是把换能器沿孔径方向划分成足够多的通道来进行近似,设计制作的关键是加权技术和数据处理技巧。由于SPUDT的特性,把EWC型的SPUDT引入到锥型换能器对制作宽带、低损耗器件是十分有用的;我们在Y128°LN基片上采用一般型和SPUDT型锥型换能器制作了相对带宽约15%的声表面波滤波器,一个换能器采用“块加权”,另一个换能器采用抽指加权。文中给出了两种器件的实验结果,SPUDT型声表面波滤波器的插损仅7.5dB。     

Polarization-independent silicon photonic grating coupler for large spatial light spots

We design and demonstrate a one-dimensional grating coupler with a low polarization-dependent loss(PDL)for large spatial light spots.Based on current fabrication conditions,we first utilize genetic algorithms to find the optimal grating structure including the distributions of duty and periods,making the effective refractive index of transverse electric mode the same as that of transverse magnetic mode.The designed grating coupler is fabricated on the common silicon-on-insulator platform and the PDL is measured to be within 0.41 d B covering the C-band.     

Performance analysis of an eight channel demultiplexer using a 2D-photonic crystal quasi square ring resonator

Recent years, the design of photonic crystal (PC) based optical devices is receiving keen interest in research and scientific community. In this paper, two dimensional (2D) PC based eight channel demultiplexer is proposed and designed and the functional characteristics of demultiplexer namely resonant wavelength, transmission efficiency, quality factor, spectral width, channel spacing and crosstalk are investigated. The demultiplexer is designed to drop the wavelength centred at 1537.6 nm, 1538.5 nm, 1539.4 nm, 1540.4 nm, 1541.2 nm, 1541.9 nm, 1542.6 nm and 1543.1 nm. The proposed demultiplexer is primarily composed of bus waveguide, drop waveguide and quasi square ring resonator. The quasi square ring resonator and square ring micro cavity (inner rods) are playing a vital role for a desired channel selection. The operating range of the devices is identified through a photonic band gap (PBG) which is obtained using a plane wave expansion (PWE) method. The functional characteristics of the proposed demultiplexer are attained using a 2D finite difference time domain (FDTD) method. The proposed device offers low crosstalk and high transmission efficiency with ultra-compact size, hence, it is highly desirable for DWDM applications.