Waveguided optical switch in InGaAs/InP using free-carrier plasma dispersion

Waveguided optical switches using a carrier injection plasma dispersion are proposed. InGaAsP/InP four-port switches with two intersecting single-mode channel waveguides were fabricated by selective LPE and investigated at 1.5 ?m wavelength. Optical switching was observed, based on mode interference in the waveguide intersecting region.     

Channel capacity optimization of chirp-limited dense WDM/WDMAsystems using OOK/FSK modulation and optical filters

Frequency chirp in semiconductor lasers that are directly modulated through carrier injection not only induces dispersion in long-haul single-mode fiber communication systems, but also causes energy loss and signal distortion when frequency selective elements such as Fabry-Perot filters are present. This effect is significant for high-bit-rate channels in a dense wavelength-division-multiplexed system in a LAN/MAN environment which requires narrow-band filters to suppress crosstalk from adjacent channels. A simulation approach is used to determine the channel capacity in the presence of chirp and crosstalk. The results show that a minimal channel spacing of less than 37 and 10 GHz with each channel operating at 2 Gb/s using OOK and FSK, respectively, can be achieved by a dense wavelength division multiple access system. It is also shown that this system performance can be optimized through adjusting various parameters of the laser and the filter     

基于液晶光子晶体波导耦合的光开关特性分析

提出了一种基于液晶光子晶体波导耦合的光开关结构。采用平面波展开法(PWE)分析了光开关耦合区域的色散关系,分析表明可以通过设计适当的耦合区域长度使该结构对不同波长的光实现2×2光开关的功能。以工作波长1550nm和1565nm为例,用时域有限差分法(FDTD)对光开关的性能进行了仿真分析,结果表明开关具有低的插入损耗和高的通道隔离度,开光响应时间在毫秒量级。     

Experimental demonstration of layer-1 multicast for WDM networks using reconfigurable OADM

The feasibility of multicast-capable-reconfigurable optical add/drop multiplexer (MC-ROADM) based on broadcast-and-select switch is experimentally demonstrated. The MC-ROADM can support unicast connection as well as multicast connection, and can provide directionless switching and low insertion loss in path-through channel. We implement fully-reconfigurable multi-degree MC-ROADM based on wavelength selective switch, and evaluate multicasting performances by fully loading 40 × 10 Gbit/s wavelength division multiplexed (WDM) signals. For unicast and multicast operation, measured spectrum and bit-error-rate (BER) show good uniformity and no power penalty. After 1040 km transmission with 25 dB span loss, the measured BER is higher than forward-error-correction (FEC) limit for BER of 10⁻¹⁵.     

Non-blocking wavelength channel switch using TO effect of doubles series coupled microring resonator

A non-blocking wavelength channel switch (non-blocking tunable filter) using the thermo-optic (TO) effect of a double series coupled polymer microring resonator is demonstrated. This device can switch a wavelength channel without blocking other wavelength channels. An extinction ratio of more than 10 dB was realised.     

Reconfigurable Optical Add‐Drop Multiplexer Using a Polymer Integrated Photonic Lightwave Circuit

We have developed a fully functional reconfigurable optical add‐drop multiplexer (ROADM) switch module using a polymer integrated photonic lightwave circuit technology. The polymer variable optical attenuator (VOA) array and digital optical switch array are integrated into one polymer PLC chip and packaged to form a 10‐channel VOA integrated optical switch module. Four of these optical switch modules are used in the ROADM switch module to execute 40‐channel switching and power equalization. As a wavelength division multiplexer (WDM) filter device, two C‐band 40‐channel athermal arrayed waveguide grating WDMs are used in the ROADM module. Optical power monitoring of each channel is carried out using a 5% tap PD. A controller and firmware having the functions of a 40‐channel switch and VOA control, optical power monitoring, as well as TEC temperature control, and data communication interfaces are also developed in this study.     

Independent and Simultaneous Delay Control of Two 10-Gb/s Channels Using a Single Optical Delay Element

We demonstrate a single tunable delay element based on wavelength conversion and dispersion for independent dual-channel operation. The two signals are sent bidirectionally to a single piece of highly nonlinear fiber for wavelength conversion by four-wave mixing. The converted signals are then sent to a chirped fiber Bragg grating to utilize its wavelength-dependent delay characteristic. We demonstrate up to 400-ps delay for return-to-zero and nonreturn-to-zero modulated signals at 10 Gb/s. The amount of delay for each channel is controlled by the wavelength of a pump signal, and is completely independent of the presence of the other one. The quality of the delayed signals is also independent of the presence of the other; this is verified by bit-error-rate measurements.      

MOSAIC: a multiwavelength optical subcarrier multiplexed controllednetwork

The experimental demonstration of MOSAIC, a reconfigurable WDM add/drop network with subcarrier multiplexed control, is presented. The MOSAIC network implements the optical layer protocol to support bit-rate transparent multichannel lightpaths. Two types of add/drop multiplexers are implemented and combined in a three-node experiment. Multihop lightpaths are established giving an end-to-end bit error rate of better than 10^-9 at 1.2 Gbps. The reconfigurable add/drop multiplexer is based on a novel dilated 2×2 acoustooptic filter switch crossconnect and an analog optoelectronic crossconnect that drives a ten-wavelength laser array transmitter up to 2.5 Gbps per wavelength. The fixed wavelength add/drop multiplexer utilizes a fast digitally tunable laser transmitter. Both add/drop multiplexers support bit-rate transparent 2R optoelectronic regeneration as well as wavelength translation. Subcarrier multiplexing on each wavelength is used to support channel state monitoring and channel equalization as well as transmission of digital network control information. Systems experiments demonstrate cascaded 2R optoelectronic regeneration with wavelength translation and cascaded multichannel optical switching with up to seven hops. It is shown that combining cascaded 2R optoelectronic regeneration with cascaded multichannel optical switching can be used to balance jitter accumulation and amplified spontaneous emission generated amplitude noise to yield high signal-to-noise ratio for lightpaths     

Semiconductor monolithic wavelength selective router using agrating switch integrated with a directional coupler

A semiconductor monolithic wavelength selective router is proposed. An electrically tunable grating switch is monolithically integrated with a directional coupler. The effect of sidelobe on the demultiplexing characteristics of the router is investigated, and it is shown that the sidelobes degrade the wavelength crosstalk and introduce a power penalty for demultiplexing characteristics. A phase-synchronized sampled grating is introduced to suppress the sidelobes, and wavelength router switching is observed in this structure. The extinction ratio is over 10 dB at a current injection of 25 mA. Using this structure, power-penalty-free wavelength selective routing at a 2.5 Gb/s wavelength-division-multiplexed NRZ random pattern is demonstrated     

A 60 GHz Radio-Over-Fiber Network Architecture for Seamless Communication With High Mobility

We demonstrate a 60 GHz broadband picocellular Radio-over-Fiber network architecture that enables seamless connectivity for highly mobile end-users. Its seamless communication capabilities arise by the supported handover scheme that relies on a novel Moving Extended Cell (MEC) concept. MEC exploits user-centric virtual groups of adjacent cells that transmit the same data content to the user and utilizes a switch mechanism for restructuring the virtual multi-cell area according to the user's mobility pattern, so that a virtual antenna group moves together with the mobile user. We present the theoretical formulation for MEC and show that it can provide zero packet loss and call dropping probability values in high-rate wireless services for a broad range of mobile speeds up to 40 m/sec, independently of the fiber link distances. We also demonstrate the physical layer network architecture and switch mechanism both for a RoF network with a single 60 GHz radio frequency (RF) over each wavelength, as well as for a RoF configuration supporting simultaneous multi-RF channel transmission over each optical wavelength. The performance of the multi-RF-over-lambda network implementation is evaluated via simulations showing successful 100 Mb/s radio signal transmission over fiber links longer than 30 km. To this end, MEC can enable seamless connectivity and bandwidth guarantees in 60 GHz picocellular RoF networks being also capable of serving multiple users over the same wavelength in a RF frequency-division-multiplexed (FDM) approach.     

基于Fabry-Perot结构的可调波长选择光开关

本文提出波长选择光开关的概念,首次研制出一个基于Fabry-Perot结构的可调波长选择光开关,该开关为2×2光纤端口,每个端口携带N个波长,工作时可以选1个或多个波长,插入损耗小于3dB,波长调谐范围10nm,调谐机构为一对多层三明治结构的压电陶瓷,具有驱动电压低,小于5V的驱动电压可以达到3.3nm的调谐,最大开关时间为1毫秒,开关比优于30dB.最后还分析了其基本透射与反射光谱性能,并讨论其对光通信、光交换网络产生的重要应用价值.     

Application of super-DWDM technologies to terrestrial terabit transmission systems

This paper describes application areas, elemental technologies, and the feasibility of terrestrial terabit wavelength division multiplexing (WDM) transmission systems based on super-dense wavelength division multiplexing (DWDM) technologies with a channel spacing of 12.5 GHz. Numerical simulation results quantitatively show that the merit of super-DWDM transmission is the elimination of the need for dispersion compensation over the several hundreds of kilometers of standard single-mode fiber (SMF). To support super-DWDM transmission, the prototype of a multiwavelength generator, which consists of just an intensity modulator and a phase modulator, is developed as a small-size WDM light source with high-wavelength stability. We use this prototype to conduct a 1.28-Tb/s (512 channels /spl times/ 2.5 Gb/s) transmission experiment with a channel spacing of 12.5 GHz over 320 km (80 km /spl times/ 4 span) of standard SMF without dispersion compensation. The potential and the feasibility of super-DWDM transmission with a channel spacing of 12.5 GHz for terrestrial systems is confirmed by the numerical simulation and the transmission experiment.     

Design theory of long-distance WDM dispersion-managed transmissionsystem

This paper describes a novel design theory of long distance wavelength division multiplexed (WDM) dispersion-managed optical transmission systems. Assuming that the transmission distance, bit rate, and number of WDM channels are initially known, we investigate the optimum dispersion allocation and input power per channel to achieve the minimum channel spacing. Based on the design guidelines for single-channel and multichannel systems, we establish the optimal design strategy. Details of the design procedure are demonstrated for 2.5-, 5-, and 10-Gb/s 10000 km WDM systems by using computer simulations. Next, we study the impact of the fiber dispersion slope on the usable wavelength span, and show that the attainable capacity of the representative 5-Gb/s 10000 km WDM system employing the postcompensation scheme can not exceed 100 Gb/s. Finally, we propose several techniques to approach the ultimate capacity of the WDM system and show that up to 1 Tb/s (200×5 Gb/s) 10000 km system can be implemented without utilizing the in-line dispersion slope compensation scheme. We also discuss the 10 Gb/s-10000 km WDM system employing in-line dispersion slope compensation     

基于全光纤M-Z干涉仪的单通道光开关研究

为了实现高性能的光开关器件,提出了在马赫-曾德尔干涉仪的一端连上光纤布喇格光栅构成单通道光开关器件的方法,并针对该器件进行了理论模拟研究和实验验证,得出了该器件在波长1550nm处的光开关输出谱。结果表明,该器件具有结构简单、易于实现和性能良好等优点。     

Tunable Chirp Managed Laser

We demonstrate a compact tunable chirp managed laser (CML) comprising a radio-frequency switch, a directly modulated distributed feedback laser array, a microelectromechanical systems mirror, and an optical filter and obtain error-free transmission performance over 30 nm at 10.7 Gb/s up to 200 km without electrical dispersion compensation (EDC) or optical dispersion compensation. Transmission distance is stretched to 300 km over the same wavelength range by adding a standard EDC to the receiver.     

Benefits of wavelength translation in all-optical clear-channelnetworks

In this paper, we study the benefits of wavelength translation in all-optical networks providing clear channel circuit-switching among users. We first establish approximate analytical models for a static-routing circuit-switched network with an arbitrary topology, both with and without wavelength translation. We then study the performance of the nonblocking centralized switch, the mesh-torus network and the ring network, using the analytical models and simulation results. It is shown that the analytical models match the simulation results very well in the case of the centralized switch and the mesh network. The results of our study also show that the benefits of wavelength translation are modest for the centralized switch and the ring network. On the other hand, the results show that wavelength translation can significantly improve the performance of a large mesh-torus network     

Chromatic Dispersion Monitoring for High-Speed WDM Systems Using Two-Photon Absorption in a Semiconductor Microcavity

This paper presents a theoretical and experimental investigation into the use of a two-photon absorption (TPA) photodetector for use in chromatic dispersion (CD) monitoring in high-speed, wavelength division multiplexing network. In order to overcome the inefficiency associated with the nonlinear optical-to-electrical TPA process, a microcavity structure is employed. An interesting feature of such a solution is the fact that the microcavity enhances only a narrow wavelength range determined by device design and angle at which the signal enters the device. Thus, a single device can be used to monitor a number of different wavelength channels without the need for additional external filters. When using a nonlinear photodetector, the photocurrent generated for Gaussian pulses is inversely related to the pulse width. However, when using a microcavity structure, the cavity bandwidth also needs to be considered, as does the shape of the optical pulses incident on the device. Simulation results are presented for a variety of cavity bandwidths, pulse shapes and durations, and spacing between adjacent wavelength channels. These results are verified experimental using a microcavity with a bandwidth of 260 GHz (2.1 nm) at normal incident angle, with the incident signal comprising of two wavelength channels separated by 1.25 THz (10 nm), each operating at an aggregate data rate of 160 Gb/s. The results demonstrate the applicability of the presented technique to monitor accumulated dispersion fluctuations in a range of 3 ps/nm for 160 Gb/s return-to-zero data channel.      

8 × 10 Gb/s transmission system over 2 015 km with dispersion compensation by fiber Bragg Grating

The cascaded chirp fiber Bragg gratings（CFBGs） with ITU-T standard wavelengths and wavelength grid are applied to compensate the dispersion of 8×10 Gb/s WDM system. The ASE of the EDFA could be reduced, the OSNR of the transmitted signal can be increased and the fluctuation of the EDFA gain can be restrained in a certain scope by the CFBG employed in the system. Experiment of error-free 8×10 Gb/s 2015 km transmission without FEC and electric regeneration is demonstrated in this paper. In this system, only EDFA is used as amplifier,and no other form of dispersion compensator is adopted except CFBG. The experimental result showed that after 2 015 km transmission,the consistency of the dispersion compensating for each channel is perfect.     

Wavelength dependence of modal dispersion in graded-index optical fibres

We describe a method based on the selective mode excitation at different wavelengths for studying the profile dispersion influence on the modal dispersion. By using this technique, we are able to determine either the optimum wavelength at which the fibre should be operated or the correction needed for optimising the index profile at a given wavelength.     

1.6 Tbit/s(40×40 Gbit/s)光通信传输系统

在国家自然科学基金网(NSFCNet)上已实现由400 km×10 Gbit/s传输链路直接升级的一路400 km×40 Gbit/s光传输实验的基础上,采用自行研制的40×40 Gbit/s载波抑制归零(CS-RZ)码多波长光发送源,进行了160 km的1.6 Tbit/s(40×40 Gbit/s)波分复用(WDM)光传输实验。实验结果表明,对于常规中短距离10 Gbit/s传输链路可以直接升级至40 Gbit/s。但是由于40 Gbit/s传输系统的色散容限小于60 ps/nm,而且传输光纤与色散补偿模块的色散斜率不匹配,要实现40通道40 Gbit/s的传输,必须对40个信道分别进行精细的色散补偿。这也说明,对于宽带的40 Gbit/s多波长系统,有必要优化设计或更新传输链路。