Optical multi/demultiplexers for single-mode fiber transmission

This paper describes two types of optical multi/demultiplexers using a single-mode fiber for a two-way transmission system. One type, the filter type, consists of four bandpass filters and a short wavelength pass filter or a long wavelength pass filter. The other, the filter-grating type, consists of two bandpass filters and a grating. The present multi/demultiplexers have four channels with 1.05, 1.15, 1.3, and 1.5 μm wavelengths. Total insertion losses are less than 2.3 and 3.2 dB for the filter type and the filter-grating type, respectively. Cross-talk between channels is less than -40 dB.     

温度不敏感阵列波导光栅

文章详细论述了温度不敏感平面阵列波导光栅(AWG)的设计原理和几种主要的实现方法,如针对硅基二氧化硅AWG,的负热光系数材料嵌入补偿方法、负热光系数材料上包层补偿方法、双金属片应力补偿方法和移动输入波导补偿方法等,并列举了采用这些方法的实际例子和补偿效果。     

Wavelength-division multi demultiplexers for two-channel single-mode transmission systems

Low-loss lensless 2-channel wavelength-division multiplexing (WDM) couplers may be produced on the beam-splitter principle with interference filters and three butt-coupled fiber ends not only for multi-mode Operation but also for single-mode transmission links. These devices are constructed with single-mode fibers-for bidirectional transmission only in the transmission channel, but for unidirectional operation in all channels. The interference filter, used in the experiment to separate the emissions of two LD's with wavelengths of 834 and 868 nm, may be implemented both as a longwave-pass (LWP) and a shortwave-pass (SWP) edge filter with high edge steepness and low polarization effects. WDM single-mode couplers exhibit very low insertion losses lying in the O.5-dB region. Their fat-end crosstalk attenuations attain values of between 15 and 30 dB and their near-end crosstalk attenuations are better than 65 dB.     

Systematic design of superprism-based photonic crystal demultiplexers

In this paper, design of photonic crystal demultiplexers based on superprism effect is discussed. Figures of merit for performance of these demultiplexers are defined and a systematic design procedure is presented. We consider different design schemes, based on equal angular separation between channels and equal frequency separation between channels, and find the optimum structures among conventional photonic crystal lattices for each case. Our results provide design solutions for a range of current applications.     

Optical frequency tuning by laser-irradiation in silica-based March-Zehnder-type multi/demultiplexers

Optical frequency tuning due to photoinduced refractive-index changes is described in Mach-Zehnder interferometer-type frequency division multiplexers (FDMs) which are composed of GeO/sub 2-/silica-based waveguides on Si substrates. A maximum refractive-index change of about 4*10/sup -5/ at 1.3 mu m is obtained at an Ar/sup +/ laser power of 20 W and an irradiation time of 1 h. This leads to frequency tuning of more than half a period in FDM with a free spectral range of 25 GHz. In addition, the annealing effects on the refractive-index change are investigated.<>     

Novel method for centre wavelength tuning of silica waveguide type Mach-Zehnder multi/demultiplexers

A novel method for tuning the centre wavelength of silica waveguide type Mach-Zehnder multi/demultiplexers (MUX/DEMUXs) has been devised. This tuning is achieved by irradiating a CO/sub 2/ laser beam onto either arm of the Mach-Zehnder interferometer. In a MUX/DEMUX for channel spacing of 20 nm, the centre wavelength is tuned about 3 nm and the results closely agree with the calculation.<>     

The effect of array periodicity on the filtering characteristics of metal/dielectric photonic crystals

We present a both theoretical and experimental investigation into the effect of array periodicity on the filtering characteristics of metal/dielectric photonic crystals(MDPhCs) with hexagonal arrays of subwavelength holes in gold/silicon dioxide films,varying the array periodicity from 6 to 8μm every 1μm while the ratio of hole radius to array periodicity is kept constant(1/4).The results indicate that the reflectance spectrum is highly dependent on the array periodicity.When the array periodicity increases,the reflectance spectrum exhibits a large redshift regularly.The finite difference time domain(FDTD) simulations agree well with the experimental results. By analyzing the relationship between the position of the reflectance minimum and the array periodicity,we find that the filtering characteristics of MDPhCs have an almost linear relationship with the array periodicity under the conditions of keeping the same ratio of hole radius to array periodicity(1/4).This finding provides an effective way to control the filtering characteristics of MDPhCs,which have potential applications in optical filters,plasmonic thermal emitters and so on.     

阵列周期对金属/电介质光子晶体滤波特性的影响

本文从理论和实验上研究了在圆孔半径与阵列周期的比维持不变（1 / 4）的条件下,每隔1微米改变阵列周期大小（范围从6至8微米）对金/二氧化硅薄膜正六边形亚波长孔阵列的金属/电介质光子晶体（MDPhC）滤波特性的影响。结果表明,其反射光谱与阵列周期有关。当阵列周期增加,反射光谱中出现有规律地红移。采用时域有限差分（FDTD）法数值模拟的结果与实验结果相吻合。通过分析反射率最小值的位置和阵列周期之间的关系,发现在圆孔半径与阵列周期的比维持1 / 4的条件下,MDPhC滤波特性与阵列周期几乎有一个线性关系。这一发现为调控MDPhC的滤波特性提供了一种有效的方法,其在光滤波器,等离子体热发射器等具有潜在的应用。     

Measurement of phase and amplitude error distributions in InP-basedarrayed-waveguide grating multi/demultiplexers

The authors have measured the phase and amplitude error distributions in an InP-based arrayed-waveguide grating (AWG) multi/demultiplexer using Fourier transform spectroscopy and signal data processing. The signal data processing technique was based on wavenumber scale transformation and was applied to reduce the effect of second-order dispersion in a measured interferogram. The results reveal that the main origins of the crosstalk and dispersion in an InP-based AWG are random and slowly-varying phase errors, respectively     

Chromatic dispersion and bandshape improvement of SOI flatband AWG multi/demultiplexers by phase-error correction

By measuring the phase and amplitude distribution of the optical paths in a flatband arrayed waveguide grating, the array mask was redesigned to correct for the slow varying phase errors within the array waveguides, leading to a reduction in both the chromatic dispersion across the passband of the device and in the transmission band tilt.     

Measurement of phase and amplitude error distributions inarrayed-waveguide grating multi/demultiplexers based on dispersivewaveguide

We measured the phase and amplitude error distributions in InP-based arrayed-waveguide grating (AWG) multi/demultiplexers using Fourier transform spectroscopy with interferogram restoration. The interferogram restoration was used to reduce the effect of the group-velocity dispersion of the waveguide. It was based on a wavenumber scale transformation or a dispersion balance between two arms in the interferometer. We derived a criterion for choosing the appropriate restoration method by estimating the worst-case measurement error in the presence of second order dispersion. After selecting a method using the derived criterion, we obtained isolated fringe patterns, from which we were able to obtain the phase and amplitude distributions in 50 and 200 GHz AWGs. Using the obtained distributions, we examined the origin of the crosstalk and chromatic dispersion in InP-based AWGs. The results revealed that the main origin is phase error as found with SiO₂ -based AWGs     

High-linearity 208-MS/s photonic analog-to-digital converter using1-to-4 optical time-division demultiplexers

This letter describes a demonstration of a photonic analog-to-digital converter operating at 208 MS/s and utilizing phase-encoded optical sampling to achieve an 87-dB two-tone third-order intermodulation-free dynamic range. A pair of LiNbO₃ 1-to-4 optical time-division demultiplexers with >35-dB channel extinction distribute the 30-ps sampling pulses to an array of photonic integrate-and-reset circuits followed by 12-b 52-MS/s electronic quantizers. Interleaving spurs due to temporal crosstalk currently limit the overall spur-free dynamic range to 65 dB     

Athermal silica-based arrayed-waveguide grating (AWG)multi/demultiplexers with new low loss groove design

A new low loss groove design for athermal silica-based AWG multi/demultiplexers is proposed. The insertion loss was <3.2 dB with an excess loss of 0.4 dB. The temperature dependence of the channel wavelength change was suppressed to be below 2.5 GHz in the 0-85°C range     

Systolic array designs for Kalman filtering

Systolic Kalman filter (SKF) designs based on a triangular array (triarray) configuration are presented. A least squares formulation, which is an expanded matrix representation of the state space iteration, is adopted to develop an efficient iterative QR triangularization and consecutive data prewhitening formulations. This formulation has advantages in both numerical accuracy and processor utilization efficiency. Moreover, it leads naturally to pipelined architectures such as systolic or wavefront arrays. For an n state and m measurement dynamic system, the SKF triarray design uses n(n+3)/2 processors and requires only 4n+m timesteps to complete one iteration of prewhitened Kalman filtering system. This means a speedup factor of approximately n²/4 when compared with a sequential processor. Also proposed for the colored noise case are data prewhitening triarrays which offer compatible speedup performance for the preprocessing stage. Based on a comparison of several competing alternatives, the proposed array processor may be considered a most efficient systolic or wavefront design for Kalman filtering     

Crosstalk reduction in N×N WDM multi/demultiplexers bycascading small arrayed waveguide gratings (AWG's)

This paper shows a new scheme which improves the crosstalk performance of large optical multi/demultiplexers, a key component in wavelength division multiplexing (WDM) systems. This scheme uses arrayed waveguide gratings (AWG's) of various sizes and requires no additional equipment. It is well known that a large multi/demultiplexer can be constructed by cascading small multi/demultiplexers. We have studied the impact of the number and size of AWG stages on crosstalk performance. This paper proves that to obtain a multistage multi/demultiplexer with minimum crosstalk, the total channel number of each AWG stage must be minimized. For example, cascading 10-channel AWG's and 11-channel AWG's improves the crosstalk performance of a 110-channel multi/demultiplexer by about 7.5 dB. Furthermore, the crosstalk performance degradation due to fabrication error is theoretically investigated taking channel bandwidth into account. Optimum design parameters of multistage AWG's are introduced: When the AWG suppression ratio is 30 dB and the ratio of channel bandwidth to channel spacing is about 0.24, the degradation in crosstalk performance due to fabrication error is minimized. The tradeoff between the crosstalk performance and the efficiency in terms of hardware and wavelength are also discussed. It is discovered that this simple scheme can yield a crosstalk-free WDM router. Crosstalk reduction obtained by this scheme allows the realization of flexible multiwavelength networks based on wavelength routing     

Thermo-optically tunable arrayed-waveguide-grating made of polymer/Si

Inthe future,optical communication systems will usemore exceptional optical fiber with high bandwidth.Dense wavelength division multiplexing(DWDM)isconsidered as a promising solution to the demand fortransportingterabits ofinformation viafibers[1].Arrayed…     

基于微波光子阵列的数字多波束测控系统构想

未来测控设备将向着多目标、高速率、平台多样性发展。数字阵列体制由于其独特的优势,逐步应用于测控领域。但是数字天线阵面功耗、体积、重量、电磁兼容、数据传输等瓶颈限制了其应用。文章给出了一种基于微波光子阵列的数字多波束测控系统构架,将有效提高测控系统的灵活性、平台适应性、重构扩展性、电磁兼容性,为我国未来海陆空天一体化测控系统提供了有效的技术途径。     

一种改进的具有半径滤波和RANSAC优点的点云图像去噪方法

为了剔除点云中离散点噪声和密集平面噪声且保留点云的特征,提出了一种改进的具有半径滤波和RANSAC优点的点云图像去噪新方法.首先利用体素下采样对原始点云数据进行精简,然后针对离散点噪声,使用半径滤波将其剔除,最后在保留原始RANSAC算法的基础上,引入高度信息参数对拟合出的平面进行区分,据此进一步剔除点云中的密集平面噪...     

Design and realization of polarization independent phased arraywavelength demultiplexers using different array orders for TE andTM

A method for designing polarization independent phased-array wavelength demultiplexers, using different array orders for TE and TM, is described and analyzed with respect to fabrication variations. Flattening of the wavelength response is shown to improve fabrication tolerances. A four channel phased-array wavelength demultiplexer with at least 0.2 nm of polarization independent flattened response for each channel (spacing 1 nm) has been made with an insertion loss of 1.5-3 dB and a crosstalk of -17 to -19 dB