Design and fabrication of a diffractive phase element for wavelength demultiplexing and spatial focusing simultaneously

The design of a diffractive phase element (DPE) that simultaneously implements wavelength demultiplexing and focusing is carried out on the basis of the general theory of amplitude-phase retrieval. The designed DPE is fabricated with optical contact lithography. Three masks are needed to produce the surface-relief structure of the DPE with eight quantized levels in depths. Experiments demonstrate that the designed DPE can successfully implement both the functions of demultiplexing three different-wavelength beams and focusing each component at a predesignated position simultaneously. Experimental measurements are in good agreement with the results of numerical simulations.     

基于光纤光栅的波分复用系统设计

设计了两种基于光纤布拉格光栅的波分复用(WDM)系统,一种为基于光纤光栅的四路波分复用系统,另一种为结合光分插复用器(OADM)的四路波分复用系统。给出了基于Opti System的波分复用光传输系统仿真模型,对复用及解复用后的光信号进行仿真得出了光谱图,对传输性能及Q因子、误码率、眼图等参数进行分析。在第二种结构中光纤光栅作为色散补偿器、光反射器和滤波器使用,可以实现任一波长的上载和下路。两种波分复用系统眼图张开良好,误码率均低于10e-9。证明了波分复用系统的正确性和设计方案的可行性。     

Design of phased-array wavelength division multiplexers using multimode interference couplers

Novel designs for phased-array wavelength-division multiplexers based on self-imaging properties of multimode interference (MMI) couplers are presented. These devices, which operate on N equally spaced wavelength channels, consist of two MMI couplers connected by an array of N monomode waveguides. The MMI couplers function as power splitters/combiners, and the waveguide array is the dispersive element. The excellent characteristics of MMI couplers offer the possibility of designing small-size devices with low loss and with high uniformity among different channels. A general theoretical formulation for an N-channel multiplexer is presented, and a simple procedure for finding an optimum set of lengths for the array guides is given. We show that these multiplexers can function as N x N wavelength-selective interconnecting components. The simulated performance of three variations of a five-channel device, designed in a rib waveguide system, is given. It is demonstrated that sidelobes in the multiplexer spectral response can be suppressed by weighting the power samples in the array waveguides through appropriate design of a nonuniform MMI power splitter.     

Compact wavelength division multiplexers and demultiplexers

Compact devices for wavelength division multiplexing and demultiplexing, believed to be novel, are presented. These devices are based on planar optics configurations, comprising multiplexed diffractive optical elements. The principle, design, and recording of these planar devices are described, including the fact that the recording is done at a single wavelength in the green region. Experimental procedures and results for planar devices that can handle three wavelengths in the visible as well as in the near infrared are presented.     

Design of 50 G nonpolarizing dense wavelength division multiplexer angle-tuning bandpass filter

Transmission characteristic differences of a narrow bandpass filter between p- and s-polarized light, especially the central wavelength separation, will corrupt the performance of the filter when the incidence is oblique. In this paper, by adding high-index materials asymmetrically to both sides of a low-index spacer, which tunes the equivalent index of the spacer, the central wavelengths of the two polarizations coincide perfectly when in 20° incidence; with different reflected layers on the two sides of the spacers and replacing some reflected layers with equivalent layers, the 0.5 dB normalized passband width is kept at 0.2 nm, which meets the requirement of the 50 G dense wavelength division multiplexer filter.     

Gain-clamped erbium-doped fibre amplifier for wavelength division multiplexed systems

Abstract

Amplification of multiwavelength signals by an erbium-doped fibre amplifier (EDFA) is becoming critical, due to the proliferation of wavelength division multiplexed systems. However, when a standard EDFA is employed, dissimilarities between signal gains may prove unacceptable. Thus, a novel gain-clamped EDFA is proposed here to tackle the issue of gain tilt, a measure of maximum gain difference. The suitability of the configuration is then investigated through a numerical model, which is developed based on the standard EDFA and fibre laser models.     

Toward tunable thin-film filters for wavelength division multiplexing applications

We provide a detailed analysis of the various problems connected with the development of tunable thin-film filters for wavelength-division multiplexing applications. We examine the relation between the change in layer thickness and the central wavelength shift for various configurations and point out the significance of the structure of the reflectors, the spacer thickness, and the location of the active layers. We describe and compare practical arrangements using either temperature or an electric field as the driving parameter.     

Bandpass filters for wavelength division multiplexing-modification of the spectral bandwidth

Dispersion of the phase shift upon reflection of the reflectors is used to narrow the spectral bandwidth of an all-dielectric bandpass filter for wavelength division multiplexing. The bandwidth is altered by the shifting of the order numbers of the spacer layers (of multiple half-wave optical thicknesses).     

Multichannel wavelength division multiplexing with photonic crystals

A multichannel wavelength-division-multiplexing system consisting of a two-dimensional photonic crystal is proposed. The system consists of two parts, a waveguiding element, realized by defects in a photonic crystal, and frequency-selective elements, realized by photonic crystal microcavities. Simulations, performed with a two-dimensional finite-difference time-domain technique with a perfectly matched layer absorbing boundary condition, showed the ability to filter an incident pulse into six spectral channels with a FWHM of 2 nm.     

Dispersion-optimized optical fiber for high-speed long-haul dense wavelength division multiplexing transmission

Four non-zero-dispersion-shifted fibers with almost the same large effective area (A(eff)) and optimized dispersion properties are realized by novel index profile designing and modified vapor axial deposition and modified chemical vapor deposition processes. An A(eff) of greater than 71 μm(2) is obtained for the designed fibers. Three of the developed fibers with positive dispersion are improved by reducing the 1550 nm dispersion slope from 0.072 ps/nm(2)/km to 0.063 ps/nm(2)/km or 0.05 ps/nm(2)/km, increasing the 1550 nm dispersion from 4.972 ps/nm/km to 5.679 ps/nm/km or 7.776 ps/nm/km, and shifting the zero-dispersion wavelength from 1500 nm to 1450 nm. One of these fibers is in good agreement with G655D and G.656 fibers simultaneously, and another one with G655E and G.656 fibers; both fibers are beneficial to high-bit long-haul dense wavelength division multiplexing systems over S-, C-, and L-bands. The fourth developed fiber with negative dispersion is also improved by reducing the 1550 nm dispersion slope from 0.12 ps/nm(2)/km to 0.085 ps/nm(2)/km, increasing the 1550 nm dispersion from -4 ps/nm/km to -6.016 ps/nm/km, providing facilities for a submarine transmission system. Experimental measurements indicate that the developed fibers all have excellent optical transmission and good macrobending and splice performances.     

Aberration properties in a chirped grating for coarse wavelength division demultiplexing

We studied the imaging performance of a chirped grating for a demultiplexer designed for coarse wavelength division multiplexing using a wavefront aberration analysis and the ray tracing simulation. The demultiplexer was composed of a chirped grating, cylindrical lenses, and a waveguide. The best image point and the spot shape focused by the chirped grating were effectively calculated with the wavefront aberration. We applied the aberration analysis to design a waveguide to connect branched beams to photodetectors, and we confirmed the demultiplexing performance experimentally.     

Athermalized low-loss echelle-grating-based multimode dense wavelength division demultiplexer

A high-density wavelength division demultiplexer (DEMUX) capable of demultiplexing eight-channel 200-GHz optically spaced signals into a 62.5-microm multimode-fiber array is reported. The wavelength range of operation is from 1549.32 to 1560.61 nm within the International Telecommunication Union grid. The measured wavelength accuracy is within 0.04 nm. The mean insertion loss of this DEMUX is 1.95 dB. Thermal analysis and temperature testing results are reported. The temperature test cycling from 20 degrees C to 60 degrees C indicates that the wavelength thermal drift is less than 0.8 pm/degrees C. Adjacent cross talk is measured to be better than -45 dB. The measured data transmission bit rate of this device is higher than 3.5 Gb/s.     

One-dimensional to two-dimensional channel formatting with micro-optics for wavelength division multiplexing networks

We present a method of interfacing a conventional wavelength multiplexing and demultiplexing device with a two-dimensional (2-D) array of surface-active elements, such as micro-electromechanical system devices or photodetectors. We use diffractive optical elements to transform wavelength division multiplexed signals spread along a line into a 2-D array. We applied this technique to build a device that is compatible with an arrayed-waveguide grating. The theoretical insertion loss predicted by combining beam propagation and rigorous coupled-wave analysis is 2.75 dB. However, the experimental loss is 10 dB. The difference is due to the poor quality of the diffraction gratings. Nevertheless, the formatting operation was performed successfully.     

Segmented chirped grating for coarse wavelength division demultiplexing with multimode optical fibers

A chirped grating segmented into partitions each having a constant blaze angle to use in a demultiplexer for coarse wavelength division multiplexing with multimode optical fibers is developed. Its designed configuration utilizes a resonance region to achieve high diffraction efficiency and large dispersion. The width, blaze angle, and diffraction order of each partition were optimized by vector diffraction analysis. The diffraction loss of the manufactured grating was less than 1.5 dB, and polarization-dependent loss was less than 0.6 dB within a wavelength width of at least 70 nm. It is confirmed that a demultiplexer with the developed chirped grating had a wide passband and low cross talk.     

All-optical crossbar switch using wavelength division multiplexing and vertical-cavity surface-emitting lasers

A design for an all-optical crossbar network utilizing wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) technology and a combination of free-space optics and compact optical waveguides is presented. Polymer waveguides route the optical signals from a spatially distributed array of processors to a central free-space optical crossbar, producing a passive, all-optical, fully connected crossbar network directly from processor to processor. The analyzed network could, relatively inexpensively, connect local clusters of tightly integrated processors. In addition, it is also believed that such a network could be extended, with wavelength reuse, to connect much larger numbers of processors in a multicluster network.     

Bandwidth reduction technique for multilayer wavelength division multiplexing (WDM) bandpass filters

The push to develop 100 GHz and smaller bandwidth WDM filters is at demanding levels. Currently, 200 GHz is the standard bandwidth for multilayer interference coatings with high efficiencies, and enormous processing effort is going into the development of standard 100 GHz filters. This paper outlines a simple design that will reduce bandwidth up to 40% when applied to 200 GHz bandpass filters. This design method can also be used in existing 100 GHz designs to achieve even smaller bandwidths.     

Scheduling advance reservation requests for wavelength division multiplexed networks with static traffic demands

Telecommunication and grid computing applications demand high bandwidth data channels that offer guarantees with respect to service availability. Such applications include: remote surgery, remote experimentation, video on-demand, teleconferencing and bulk transfers. Furthermore, by forecasting traffic patterns internet service providers attempt to optimise network resources in order to lower operational costs during peak periods of bandwidth consumption. Advance reservation for wavelength division multiplexed networks can address some of these issues by reserving high volume communication channels (i.e. lightpaths) beforehand. The authors develop a mathematical model to solve the problem of scheduling lightpaths in advance. The optimal solution is presented as a mixed integer linear program with the assumption that all traffic is static and the network is centrally controlled. Furthermore, we have developed two novel meta-heuristics based on: 1) a greedy implementation (local search) and 2) simulated annealing. The meta-heuristics have shown to produce good approximate solutions in a reasonable amount of time.     

双光纤波分复用网阻塞率研究

研究了双光纤波分复用互联网在不同网络容量使用率时的阻塞率,主要对单光纤网络使用波长变换器和双纤网络在波长数不同时对网络阻塞率的改善情况做了仿真比较,结果表明仅仅在低阻塞率时波长变换器给网络所带来的增益非常有限,双纤网络可以达到其效果。     

Multi-channel terahertz wavelength division demultiplexer with defects-coupled photonic crystal waveguide

Abstract

Terahertz (THz) wavelength division demultiplexer based on a compact defects-coupled photonic crystal waveguide is proposed and demonstrated numerically. This device consists of an input waveguide that perpendicularly coupled with a series of defects cavities, each of which captures the resonance frequency from the input waveguide. Coupled-mode theory and finite element method are used to analyze the transmission properties of the structure. It is found that the transmission wavelength centered around 1 THz can be adjusted by changing the geometrical parameters of defects cavities, which equals to THz waves generated by optical methods such as difference frequency generation and optical rectification. Applications in this frequency range are urgently needed. Furthermore, the highest transmission efficiency of 0.94 can be achieved when a perfect wavelength-selective mirror is set in the output waveguide.     

Holographic edge-illuminated polymer Bragg gratings for dense wavelength division optical filters at 1550 nm

We discuss the use of holographic photopolymer materials for use as dense wavelength division multiplexing filters in the C-band of the optical communication spectrum. An edge-illuminated hologram configuration is described that effectively extends the grating length to achieve narrow band filters operating near 1550 nm in photopolymers that are 100-200-microm thick. This configuration enables the formation of apodized and cascaded filter systems. Rouard's method is used to examine the properties of both apodization and cascaded gratings and indicates the potential for narrow spectral bandwidths (< 0.2 nm) and high side-lobe suppression (<-- 30 dB). Initial experimental results with a commercially available photopolymer are provided that verify narrowband spectral-transmittance properties (< 0.6 nm) and the ability to apodize the index profile. The primary limitation of the design is the absorption of existing photopolymer materials. Optimizing the polymer chemistry for filter design at 1550 nm may solve this problem.