AWG作光路分插复用器串扰对信道数的影响

研究了阵列波导路由器作光路分插复用器（OADM）串扰的影响,其路由器含有m个上路/下路信道和n个传输信道。理论分析表明:随着上路/下路信道m和传输信道n的增加,串扰使OADM的信噪比QCT,成非线性下降、由于在阵列波导路由器中存在串扰,限制了基于 OADM的网络复用信道数。     

Photonic crystal ring resonator based add-drop filter using hexagonal rods for CWDM systems

In this paper,theoretical analysis of two-dimensional photonic crystal ring resonator(2D PCRR) based add-drop filter(ADF) is presented for coarse wavelength division multiplexing(CWDM) system to drop a channel at 1511 nm using hexagonal rods that are positioned in the square lattice.The 2D finite difference time domain(2D FDTD) method and plane wave expansion(PWE) method are used for obtaining the filter response and band structure of the filter respectively.Close to 100 dropping and coupling efficiencies at 1511 nm and 16 nm of bandwidth are observed through simulation.This is very well meeting the requirement of ITU-T G.694.2 standard,which is specified for metro access and short haul optical networks.The overall size of the proposed filter is 11.4 μm×11.4 μm.It can also be used in integrated optics.     

Silicon-on-Insulator Microring Add-Drop Filters With Free Spectral Ranges Over 30 nm

We demonstrate highly compact optical add-drop filters based on silicon-on-insulator microring resonators. The microring resonators have a small radius of 2.5 mum and a very large free spectral range ~ 32 nm at the 1.55 mum communication band. The propagation loss in such small micoring resonators was experimentally determined and shown to be extremely important in designing microring add-drop filters with low add-drop crosstalk, low drop loss, and maximally flat drop passband. For box-like channel dropping responses, second-order optical add-drop filters with two coupled microring resonators are designed and demonstrated, and the simulation matches well with the experiment. Devices were patterned with electron-beam lithography. Two fabrication procedures utilizing different polarity of resists were introduced and compared, and the process with negative resist resulted in much smaller sidewall roughness of waveguides, thus reducing the propagation loss in microring resonators.     

A high-drop hole-type photonic crystal add-drop filter

Based on the effect of total internal reflection（TIR）and photonic band gap,a new type of hexagonal-lattice hole-type silicon photonic crystal add-drop filter is proposed with a large circular hole as inner ring.The single mode operation is realized by compressing the two rows of photonic crystal above and below the line defect waveguide.Two-dimensional（2D）finite-difference time-domain（FDTD）method is then applied to investigate the impacts of side length of inner ring and coupling strength on its drop efficiency.It is also fairly compared with the traditional inner ring structure composed of hexagonal-lattice holes.The results show that the proposed structure can offer higher spectral selectivity than the traditional one.Two channel wavelengths of 1.425μm and 1.45μm can be simultaneously dropped at corresponding ports with drop efficiency of more than 90%and quality factor of 900 in the proposed configuration when the width of bus waveguide,the side length of inner ring and the coupling strength are 0.8 3 a,4a and 0,respectively,where a is the lattice constant.     

Impact of crosstalk in an arrayed-waveguide router on an opticaladd-drop multiplexer

The impact of crosstalk in an arrayed-waveguide (AWG) router on the performance of an N-channel optical add-drop multiplexer (OADM), with m add/drop channels and n-pass channels is theoretically investigated. A single arrayed-waveguide router is simultaneously used for multiplexing and demultiplexing. This results in crosstalk not only from the incoming channels, but from the outgoing channels as well. We show that the performance of the OADM degrades as either N or m are increased, suggesting that the number of channels in a network based on OADM's is limited by crosstalk in the AWG router. When an optical filter is added at the output of the OADM the digital signal-to-noise ratio Q is independent of N and m, and within a few tenths of a decibel of the perfect filtering case     

High-performance operation of monolithically-integrated multipurpose reconfigurable optical add-drop multiplexer

WDM operation of a novel monolithically-integrated 16-channel reconfigurable add-drop multiplexer (ROADM), demonstrating high crosstalk suppression and cascadability to eight nodes for 10 Gbit/s NRZ signals, is reported. The device provides separate wavelength add/drop ports and a common wavelength-multiplexed add/drop port for high system functionality.     

光子晶体与光子准晶复合型上下载滤波器

基于二维正方晶格光子晶体与十二重Stamfli型光子准晶提出了单环形腔上下载滤波器及双环形腔串联上下载滤波器.分析并对比了两种上下载滤波器的传输效率随光子准晶介质柱半径及折射率大小的变化规律,且对比了两种上下载滤波器的品质因数随环形腔中心介质柱半径及折射率大小的变化规律.结果表明,双环形腔串联复合型上下载滤波器的性能优于单环形腔复合型上下载滤波器.研究结果将为设计及制备优良上下载滤波器件提供一定指导作用.     

WDM ring network using a centralized multiwavelength light sourceand add-drop multiplexing filters

We propose and experimentally demonstrate a wavelength division multiplexed (WDM) ring network employing a centralized multiwavelength light source to supply all nodes with optical carriers of precise wavelength spacing. This approach overcomes the problem of monitoring and controlling the wavelengths of optical sources dispersed throughout the network. A four-node test bed using optical lattice-type add-drop multiplexing filters and a multiwavelength light source based on resonant cavity-enhanced four wave mixing in a Fabry-Perot laser diode was constructed to demonstrate the feasibility of the proposed method. The effects of coherent crosstalk in such networks are analyzed, and methods such as phase scrambling or the use of a pulsed optical source are shown to significantly reduce the effects of coherent crosstalk. The use of four-port add-drop multiplexer (ADM) filters instead of 1:n optical wavelength multiplexer/demultiplexers to implement the wavelength add-drop function at each node is shown to lead to a broader transmission bandwidth for each channel and also easier compatibility with the coherent crosstalk suppression mechanisms described     

Optical add-drop multiplexers based on autocloned photonic crystals

We describe and demonstrate the operation of optical add-drop multiplexers (OADMs) based on photonic crystal (PC) structures fabricated by autocloning technology. In these OADMs, a three-dimensional PC structure was utilized as a Bragg reflector. We obtained a drop bandwidth of 2 nm at a wavelength of 1560 nm. We also demonstrate for the first time add and drop operations of the PC-based OADMs in a wavelength-division multiplexing optical transmission system.     

Fabrication of (Pb,La)(Zr,Ti)O/sub 3/ thin-film arrayed waveguide grating

The design and fabrication of an 8-ch, 500 GHz-spacing arrayed waveguide grating on (Pb,La)(Zr,Ti)O₃ has been successfully achieved for the first time. An insertion loss of 22.1 dB, including a 10 dB coupling loss, and an adjacent crosstalk of -23.1 dB have been obtained. The device is expected to be monolithically integrated into high-speed optical switches to form integrated chips such as a reconfigurable add-drop multiplexer     

基于内全反射微环空气孔型光子晶体光分插滤波器

提出一种基于内全反射微环和光子晶体带隙相结合的混合结构空气孔型二维三角晶格光子晶体光分插滤波器,通过压缩及移位围绕线缺陷波导的上下两排光子晶体阵列,实现空气孔型线缺陷波导单模的有效调控,进而影响信道的下路效率,并且利用二维时域有限差分法系统分析不同波导宽度以及不同移位量δ时滤波器的下路效率。模拟计算表明,当波导宽度为0.8槡3晶格常数,耦合强度为0个晶格常数,移位量为0.5个晶格常数,信道波长为1464nm时,下路效率为-0.11dB,品质因子Q为1100;当波导宽度为0.8槡3晶格常数,耦合强度为1个晶格常数,移位量为0个晶格常数时,下路效率为-0.89dB,品质因子Q为2100。     

Theory of loss and gain trimming of resonator-type filters

The characteristic response of resonator-type filters is determined by the mutual resonator-to-resonator coupling coefficients, which are not readily trimmed once a device is fabricated. We show that loss and/or gain is a mechanism which can mimic the role of the coupling coefficients, and which can therefore be used for post-fabrication tuning or trimming. By using loss-only trimming, the throughput crosstalk performance can be improved by several orders of magnitude while incurring only small signal attenuation     

All-Optical Label Extractor/Eraser for In-Band Labels and 160-Gb/s Payload Based on Microring Resonators

Photonic integration of an all-optical packet switch (AOPS) is a crucial issue since it leads to a great reduction of volume, power consumption, and costs. Recently, a 1 times 4 AOPS was successfully demonstrated by using an all-optical label extractor/eraser. The label extractor/eraser was implemented by means of fiber Bragg gratings and optical circulators that prevent the photonic integration of the AOPS. Here, we demonstrate a passive and asynchronous photonic integrated all-optical label extractor/eraser by using narrowband silicon-nitride add-drop ring-resonators. By exploiting the narrow bandwidth of the drop port and pass-through port error-free simultaneous separation/erasing of the in-band labels from the 160-Gb/s packet payload was demonstrated without noticeable pulse-shape distortions.     

All-fiber wavelength-tunable acoustooptic switches based on intermodal coupling in fibers

In this paper, we demonstrate a novel all-fiber wavelength-tunable acoustooptic switch utilizing intermodal coupling in a two-mode fiber (TMF). Its all-fiber configuration consisting of a fiber acoustooptic tunable filter and a mode-selective coupler results in the low loss (<2 dB) operation. The operating bandwidth >50 nm, the switching time of 40 /spl mu/sec, and the crosstalk of 20 dB were achieved. By controlling the design parameters of the two-mode fiber, the 3-dB bandwidth of the switched signal was varied from 2.5 nm to >35 nm. A novel all-fiber dynamic optical add-drop multiplexer is also demonstrated using two acoustooptic switches in series.     

OTDM add-drop multiplexer based on XPM-induced wavelength shifting in highly nonlinear fiber

In this paper, we study experimentally and numerically simultaneous time-domain add-drop multiplexing for high-speed optical time-division multiplexing (OTDM) networks based on cross-phase-modulation (XPM)-induced wavelength shifting in a 50-m highly nonlinear fiber. This scheme needs only a single-channel clock rate and does not alter the input signal wavelength. Simultaneous add and drop operations at 80 Gb/s have been demonstrated experimentally with less than 1-dB power penalty for the dropped channel and no distinct bit-error-rate (BER) degradation for the added channel. Numerical simulations show that the experimental results are only limited by the available signal pulsewidth, and simultaneous add-drop multiplexing at 160-Gb/s or higher bit rates is possible with this scheme by employing control and signal pulses with proper pulsewidths.     

Demonstration of the MEMS Digital Micromirror Device-Based Broadband Reconfigurable Optical Add–Drop Filter for Dense Wavelength-Division-Multiplexing Systems

For the first time, an optimized optical add-drop filter (OADF) for dense wavelength-division-multiplexing systems is demonstrated using the Texas Instruments microelectro-mechanical-system Digital Micromirror Device (DMDtrade). This OADF features a polarization-insensitive fault-tolerant broadband operation, low loss, and the ability to selectively add/drop with high-wavelength-resolution multiple channels in the C telecommunications band. The proof-of-concept OADF designed for the C-band demonstrates low insertion loss, 0.15-dB polarization dependent loss, 3-dB wavelength resolution of 0.4 nm, and an average crosstalk of better than 30 dB. With the use of a reference mirror, the OADF becomes a multiwavelength 2 times 2 routing switch     

Architectures with improved signal-to-noise ratio in photonicsystems with fiber-loop delay lines

In a class of photonic systems, the intensity of the noise component caused by crosstalk from internal signals is investigated. The relevant systems are those that use loops of optical fiber as reentrant delay-line memory elements. Three architectural variations are shown to improve the ratio of the intensity of an internal signal to the intensity of this noise component. These variations include providing one extra memory element, minimizing the number of switches in a memory element that a photonic signal must traverse, and designing large systems hierarchically from smaller ones. These architectures, and the detailed formulas used to evaluate them, pertain specifically to a photonic time-slot interchanger, but the concepts are believed to generalize to similar photonic systems with applications in computing and signal processing     

Evaluation of self-collimated beams in photonic crystals for optical interconnect

Self-collimated beams and photonic bandgap mirrors in photonic crystals are evaluated for applicability in an on-chip interconnect system. Simulations using the plane-wave expansion and finite-difference time-domain methods are utilized to design and evaluate the theoretical performance of these systems, called a virtual waveguide due to borderless confinement of the signal. The effect of systematic and random fabrication errors on the performance is characterized. Coupling efficiency is virtually unaffected by misalignment, but is found to be a strong function of the length of the waveguide and the frequency of light. Additional routing capabilities of sharp 90/spl deg/ turns and signal crossings with no crosstalk are demonstrated. Photonic crystal virtual waveguides are ideal structures for on-chip optical signal routing.     

An InP-Based Monolithically Integrated Reconfigurable Optical Add–Drop Multiplexer

We demonstrate an InP-based monolithically integrated reconfigurable optical add-drop multiplexer consisting of an array waveguide grating, a semiconductor optical amplifier, four 2x2 Mach-Zehnder optical switches, and four PIN photodetectors using the asymmetric twin waveguide technology. The total chip size is 10 x 6 mm, and each of the components in the circuit exhibited performance similar to that achieved in a discrete form. The add-drop functionality of the chip is demonstrated via the routing of the signal from the add port to the drop/output port.     

Performance of WDM ring and bus networks in the presence ofhomodyne crosstalk

This paper examines the effects of coherent and incoherent homodyne crosstalk in wavelength division multiplexed (WDM) ring and bus networks using reconfigurable optical add-drop multiplexers (OADM's). It is widely understood that incoherent homodyne crosstalk causes power penalties at the receivers in these networks. We show that coherent homodyne crosstalk causes a range of possible received powers, and that coherent and incoherent crosstalk together lead to a range of possible power penalties. A Monte Carlo simulation is used to examine the probability distribution of power penalties due to homodyne crosstalk under various conditions. We find that increasing the switch and multiplexer crosstalk within each OADM, and increasing the number of WDM channels, all produce increased probabilities of large power penalties. However, the number of nodes through which a signal is transmitted does not affect the power penalty distribution