Crosstalk in double-pumped fiber optic parametric amplifiers for wavelength division multiplexing systems

We study experimentally inter-channel crosstalk in double-pumped fiber optic parametric amplifiers constructed with conventional dispersion shifted fibers (DSFs) having different lengths (L_A = 13.8, L_B = 6.8, L_C = 4.3, and L_D = 0.8 km). For long fibers (L_A and L_B), eye diagram measurements in a 5-channel (100 GHz spacing) system show that in order to have negligible crosstalk, the output signal power per channel, P_s, should be limited to P_s < 0 dBm. By decreasing the fiber length (to L_C) it is possible to increase the output signal power and/or the number of signals while keeping the crosstalk on negligible levels. This trend was further confirmed by using a very short DSF (L_D = 0.8 km).Finally, we experimentally demonstrate that a general trend in 2P-FOPAs is that spurious FWM increases with the number of signal channels up to a given number of channels when a saturation regime is reached. This saturation of the generation of spurious tones occurs when the bandwidth occupied by the signals exceeds ∼4-5 nm.     

Influence of guard band on performance of absolute polar duty cycle division multiplexing over a single wavelength and wavelength division multiplexing system

For the first time to the best of our knowledge the effect of guard band (GB) on the performance of 40 Gb/s Absolute Polar Duty Cycle Division Multiplexing (AP-DCDM) over a single wavelength and wavelength division multiplexing (WDM) are investigated and reported. It is demonstrated that the spectral width occupied by 40 Gb/s AP-DCDM with GB is 100 GHz (with minimum spectral efficiency of 0.4 b/s/Hz) whereas, this value can be reduced to around 80 GHz for AP-DCDM without GB (with minimum spectral efficiency of 0.5 b/s/Hz). In addition to better spectral efficiency, this amount of saving in the spectral width leads to ～60 ps/nm improvement in chromatic dispersion tolerance. In this paper, characteristics of AP-DCDM with and without GB over WDM system are compared at the speed of 40 Gbit/s per WDM channel, for the tolerance to narrow optical filtering and minimum allowed channel spacing. The AP-DCDM without GB has narrower spectral width than AP-DCDM with GB, which makes its implementation in WDM system advantageous.     

Pulsed digital micro-holography of femto-second order by wavelength division multiplexing

Wavelength division multiplexing (WDM) used in a pulsed digital micro-holographic system to record ultra-fast processing of the order of femto-second is reported for the first time, where a BBO crystal is used to generate harmonic wave of the incident laser wave, and both of the basic and the frequency doubled waves are time-delayed and introduced to a Michelson’s interferometer to record two sub-holograms with different spatial frequencies on a single frame of a CCD by WDM. In the experiment, an ultra-fast dynamic process of air ionization induced by a single femto-second laser pulse is holographic recorded by this system, and both of intensity and phase difference images digitally reconstructed are obtained through Fourier transformation and digital filtering, which shows clearly the dynamic process of formation and propagation of the plasma, with a time resolution of the order of femto-second.     

A new synchronization scheme based on time division multiplexing and wavelength division multiplexing technology for practical quantum key distribution system

Three clock synchronization schemes for a quantum key distribution system are compared experimentally through the outdoor fibre and the interaction physical model of the the clock signal and the the quantum signal in the quantum key distribution system is analysed to propose a new synchronization scheme based on time division multiplexing and wavelength division multiplexing technology to reduce quantum bits error rates under some transmission rate conditions.The proposed synchronization scheme can not only completely eliminate noise photons from the bright background light of the the clock signal,but also suppress the fibre nonlinear crosstalk.     

体相位全息光栅式波分复用器的研究

利用体相位全息光栅的优良特性,研制光栅式密集型波分复用器(DWDM)。准直后的信道波长通过体相位全息光栅两次衍射,在焦面上实现信道波长的分复用。阐述了体相位全息光栅的独特结构特点,给出了体相位全息光栅式密集型光波分复用器件的原理图,计算出各个信道的位置及间隔,用Zemax仿真出设计模型。相比于薄膜滤光片式器件而言,具有许多独特的优良特性,能够实现更密集更多信道数量的分复用。     

基于粗时分复用技术的光纤光栅传感系统研究

充分利用光纤光栅传感网络的频域和时域资源,综合考虑了光栅传感环境特点、传感点铺设和维护等因素,提出了一种新型的基于粗时分复用的TDM/WDM光纤传感网络设计方案。先按时分复用方式将光纤传感环境划分成不同时延的传感域,再将域内传感点按波分复用方式进行波分复用,并结合网络拓扑结构分析了网络中的影响测量结果的主要因素。方案引入了传感域和时延容差概念,可以放宽对传感点精确位置的要求,可对传感网进行分域管理,便于替换死亡的传感器,更加方便、简洁地实现大容量光纤光栅传感系统,可依据器件具体情况灵活分配传感域内域外的传感器复用数,使每个传感单元的传感成本显著降低。     

密集波分复用(DWDM)、光学交叉互连(OXC)和全光通讯网络(AON)

本文介绍了全光网（AON）的基本结构和特点，介绍了全光网的两种关键部件－密集波分复用（DWDM）和光学交叉互连（OXC），讨论了各种方案的物理模型、工作原理和应用，并展望了光通讯的发展趋势。     

Duty-cycle division multiplexing (DCDM)

A multiplexing technique, which is based on duty-cycle division, is proposed. The channel multiplexing and demultiplexing are performed electrically at the single user bit rate, which is very economic. In a three-user system (3×10 Gb/s), the simulation results show that the best receiver sensitivity value achieved is −30.1 dBm with an optical signal-to-noise ratio (OSNR) of 22.3 dB, while the chromatic dispersion tolerance ranges from 192 to 280 ps/nm. Migration from 30 to 120 Gb/s is achieved with the penalty of 6.4 and 5.2 dB in the receiver sensitivity and OSNR, respectively, for the worst user.     

Cross-channel interference due to wavelength switching events in wavelength packed switched WDM networks

An important characteristic of tunable lasers, that may affect system performance, is that they can generate light at various wavelengths as they tune between different wavelength channels. These spurious components could cause severe cross-channel interference if the tunable laser is used in a WDM network. In this paper, we investigate the effect of such interfering signals, generated by up to three tunable lasers during a switching event, on the BER of a data channel transmitted on the same wavelength as the spurious components. The results show that it is vital to attenuate the output of tunable lasers during their wavelength transition in order to prevent system performance degradation.     

高效异质结构四波长波分复用器的设计与优化

将两光子晶体单模波导平行、邻近放置构成一个光子晶体波导耦合结构.根据耦合和解耦合理论,设计了一种新型的高效异质结构四波长波分复用器.应用时域有限差分法模拟了该器件的效率,并通过改变一排介质柱的折射率,实现了较高的透射率.进一步发现在入射口处添加三对介质柱,可以有效地降低系统的反射,实现了四个波长的高效传输,四个波长的透射率均超过了90%.该器件不仅具有较高的透射率,而且其尺寸仅为36 μm×17 μm,在未来的光子集成回路中具有潜在的应用价值. 关键词： 光子晶体波导 耦合 异质结构 波分复用     

Polarization insensitive wavelength conversion based on dual-pump four-wave mixing for polarization multiplexing signal in SOA

We have theoretically investigated polarization insensitive all-optical wavelength conversion for polarization multiplexing signal based on dual-pump four-wave mixing (FWM) in a SOA. The simulation result shows that the polarization insensitive converted signal can be separated into two lightwaves without crosstalk when one of the two orthogonal data lightwaves is parallel with one pump and the SOA should be polarization insensitive. Several conditions which affect the conversion efficiency for polarization multiplexing signal are also discussed.     

Suppression of four wave mixing in wavelength division multiplexed system with hybrid modules

In this paper, two different configurations of optical phase conjugator, dispersion compensating fiber and fiber Bragg grating have been investigated. These configurations are further compared with the conventional schemes. Several link configurations have been compared and investigated the potential for inter-subcarrier four wave mixing suppression by means of midway fibers plus hybrid modules. The proposed schemes show improvement in performance by suppressing the four-wave mixing (>40 dBm). It strongly suppresses the four-wave mixing signal by introducing the destructive interference (due to OPC) between the first and second halves of the fiber optic link.     

A novel wavelength dispersive device with a dispersive element based on staircase-like straight and parallel arrayed waveguides

We propose a new type of arrayed waveguide grating (AWG) multiplexer/demultiplexer based on modified group refractive index. This device is composed by an array of straight and parallel waveguides of equal length and each waveguide consist of two sections with different width. The length of the two sections are changed from a waveguide to the adjacent one following a linear dependence resulting in a wavelength dispersive waveguide array. An example of the device design for silicon-on-insulator (SOI) platform is provided and numerical simulations have been carried out for various arrayed waveguide parameters. We demonstrate that the group index modification can be used for tailoring device dispersion properties, and that it can also result in new dispersion characteristics predicted numerically not observed in conventional AWGs. Additional advantages are that the demultiplexer does not necessarily require bending waveguide sections as in a conventional AWG (de)multiplexers, and thus yields highly compact devices with potentially very low insertion loss. Channel spacing of 1 nm have been predicted for sub-micron waveguides sizes. In this paper it is also proposed a novel wavefront converter based on waveguide array lens-like element with waveguides broadened sections. Numerical results for different input/output geometries are analized.     

Design of a device with wavelength multiplexing and routing functions using dynamic holography on SLMs

This work describes the theory and design of a generic multipurpose device that can operate as a tunable wavelength filter, wavelength multiplexer and wavelength router. This device could be especially useful in optical network applications based in both coarse and dense wavelength division multiplexing technology. The enabling component is a ferroelectric liquid crystal spatial light modulator (SLM) where dynamic holograms are implemented in real time. As a consequence, the device will be able to carry out different functions according to the hologram recorded onto the SLM. The great advantage of this device is a polarization insensitivity operation, allowing low crosstalk and simple handling.     

Performance comparison of wavelength shift keying WDM system and conventional on-off WDM system in presence of four-wave mixing

Performance of wavelength shift keying (WSK) wavelength division multiplexed (WDM) system is analyzed and compared to that of conventional on-off keying (OOK) WDM system in respect of four-wave mixing (FWM) effect. WSK technique employs symmetric wavelength assignment and balanced detection to cancel FWM interference to first order. WSK–WDM outperforms conventional OOK–WDM at all signal levels and permits higher allowable input power, lower power penalty and higher transmission distance for a given bit-error rate of 10⁻⁹. WSK–WDM is also found to be noise resistant.     

Reference-frame-independent quantum key distribution of wavelength division multiplexing with multiple quantum channels

Reference-frame-independent quantum key distribution (RFI-QKD) can allow a quantum key distribution system to obtain the ideal key rate and transmission distance without reference system calibration, which has attracted much attention. Here, we propose an RFI-QKD protocol based on wavelength division multiplexing (WDM) considering finite-key analysis and crosstalk. The finite-key bound for RFI-QKD with decoy states is derived under the crosstalk of WDM. The resulting secret key rate of RFI-QKD, which is more rigorous, is obtained. Simulation results reveal that the secret key rate of RFI-QKD based on WDM is affected by the multiplexing channel number, as well as crosstalk between adjacent channels.     

Intra-group principal modes in graded-index multimode fibers used for mode group division multiplexing transmission

By considering very strong intra-group mixing while neglecting inter-group mixing in mode group division multiplexing (MGDM) transmission, we theoretically introduce and describe the physical model of intra-group principal modes (IGPMs) in graded-index (GI) multimode fibers (MMFs), from the view of fiber transmission matrices for both cases of one- and dual-polarization. Proof-of-concept numerical calculations for an exemplary mode-group-channel with the two lowest-order degenerate mode groups (namely the three lowest-order fiber eigenmodes) show that IGPMs can exhibit potential possibilities of the MGDM channel with minimal mode mixing/dispersion-induced signal distortion over a GI MMF.     

基于少模光纤的模分复用系统多输入多输出均衡与解调

针对光纤模分复用传输系统中模式耦合串扰问题, 设计并制备了一种新型少模光纤, 其较高的模式差分群延时保证各模式信道独立传输.在此基础上, 提出一种级联多输入多输出(MIMO)延时均衡算法, 进一步减少源于模式复用器和解复用器的模式串扰, 提高基于少模光纤的模分复用传输系统的传输距离和传输容量.与传统MIMO均衡算法相比, 级联MIMO延时均衡算法在没有显著增加计算复杂度的条件下, 能够应用于模式差分群延时很大的模分复用传输系统.对单信道传输速率为 40 Gbps的四相相移键控两模复用传输系统进行仿真, 经40 km少模光纤传输后, 采用级联MIMO均衡算法较普通MIMO均衡算法有1.7 dB的质量因子的提升. 仿真结果证明, 使用少模光纤和级联MIMO延时均衡算法能够有效地消除模分复用信号间的串扰, 有望在下一代大容量光纤传输系统中获得 推广应用. 关键词： 模分复用 少模光纤 模式差分群延时 多输入多输出均衡     

All-optical regeneration of polarization division multiplexing signals in polarization nonlinear loop mirror

All-optical regeneration of 2 × 10-Gb/s RZ-OOK polarization-division-multiplexed (PDM) signals is demonstrated through a single polarization nonlinear loop mirror configuration. PDM signals with orthogonal polarization states are regenerated simultaneously and reassembled automatically. Up to 3.0-dB eye-diagram-based signal-to-noise-ratio (SNR) improvement is achieved for both channels with the input SNR of 6.7 dB. Such scheme is also capable of mitigating the polarization-mode-dispersion (PMD) effect for PDM signals in the presence of up to 6.3-ps DGD.     

基于时分复用技术的甚多束光脉冲产生系统

提出了一种基于时分复用技术的全光纤、全固化的用于惯性约束聚变驱动器的甚多路光脉冲产生系统.系统中采用单纵模振荡器输出连续激光信号,利用时分复用技术结合高速电光调制技术实现序列脉冲的产生和甚多束脉冲的独立整形.采用偏振无关的声光调制技术实现甚多束脉冲的独立输出.每个序列脉冲包含8个子脉冲,子脉冲间隔设置为120ns,对子脉冲独立整形和选单后将其传输放大至微焦耳量级输出.实验成功验证了采用时分复用技术完全可以实现序列脉冲输出,各子脉冲可以独立任意整形且最后的单束输出能量为1.275μJ.