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     

OTDM add-drop multiplexer based on time-frequency signal processing

A time-division add-drop multiplexer capable of high-extinction-ratio operation is presented both theoretically and experimentally. The approach used is based on time-to-frequency domain conversion of optical signals and relies upon the switching of linearly chirped optical pulses. By converting a 40-Gb/s optical time-division multiplexing (OTDM) signal to 4 /spl times/ 10-Gb/s wavelength-division multiplexing (WDM) channels and using fiber Bragg gratings for frequency-domain add-drop multiplexing, a timeslot suppression ratio in excess of 30 dB and error-free operation for the dropped, through, and added channels were achieved. A further stage of WDM-to-TDM signal conversion was used to map the resulting signal back into the time domain. Moreover, it is shown that it is straightforward to simultaneously operate on multiple channels by simply cascading gratings to make more complex filtering functions without the requirement for any further synchronization of the tributary channels.     

A broadcast-and-select OADM optical network with dedicated optical-channel protection

A metro-area optical-ring network based on a novel optical add-drop multiplexer (OADM) architecture using a wavelength blocker is proposed. We demonstrate experimentally the performance of the OADM and capability of optical channel dedicated protection in a two-fiber ring network with 24/spl times/10 Gb/s dense wavelength division multiplexing traffic capacity. The channel-by-channel optical protection of the network is enabled by using a liquid crystal-based wavelength-selective switch as the protection switch and erbium-doped fiber amplifiers (EDFAs) with fast transient-gain control. The bit-error rate performance of the network is studied for the normal operation and for the transition to the protection state from a failure. The network protection for all channels is provided within 5 ms on a cable-cut failure. Importance of transient-gain control during protection switching to reduce the network transients is also discussed.     

Eight-channel bidirectional WDM add/drop multiplexer

The authors propose and demonstrate an eight-channel reconfigurable bidirectional wavelength division multiplexed (WDM) add-drop multiplexer in which all channels can be added/dropped independently in either direction. The performance of the bidirectional WDM add/drop multiplexer is experimentally studied for a data rate of 10 Gbit/s per channel, providing an overall capacity of 80 Gbit/s. It is found that the performance of the add/drop multiplexer is not degraded by a backward propagating signal     

Experimental investigation of the cascadability of a cross-gainmodulation wavelength converter

The cascading characteristics of a wavelength converter based on cross-gain modulation (XGM) are studied experimentally using a recirculating loop at 10 Gb/s. The maximum cascaded number of the wavelength converter converting the signal to the same wavelength is improved from five to eight by adding a fiber grating-based optical add-drop multiplexer after the semiconductor optical amplifier (SOA) to enhance the high-frequency response of the wavelength converter. However, the low-frequency degradation of the signal together with amplified spontaneous emission (ASE) noise and jitter accumulation finally limits the wavelength converter to be cascaded for more times     

OTDM transmitter using WDM-TDM conversion with an electroabsorptionwavelength converter

An all-optical multiplexing technique using wavelength division multiplexing (WDM)-time division multiplexing (TDM) conversion with an electroabsorption wavelength converter has been proposed and demonstrated. The effectiveness of this WDM-TDM conversion technique for various pulsewidth settings was experimentally investigated. The fluctuation of the signal performance, which was inevitably caused by the coherent crosstalk between adjacent pulses in the conventional optical time division multiplexing (OTDM) technique, were successfully suppressed, even in the case of wide pulse duration. High Q-factor performance has been maintained for a wide range of duty ration from 36% to 74%. By introducing this technique to the optical time division multiplexer, a highly stable and high-quality 40-Gb/s optical signal can be effectively produced without generating the short pulse or setting two tributaries at orthogonal polarization states, and without introducing high-speed electronics for signal multiplexing. The WDM-TDM conversion with an electroabsorption wavelength converter was extended to 60-Gb/s operation by using three 20-Gb/s tributaries. A clear eye opening was confirmed for a waveform after the WDM-TDM conversion of the 60-Gb/s signal     

Dense wavelength-division multiplexing millimeter-wave-band radio-on-fiber signal transmission with photonic downconversion

Photonic downconversion (PDC) technique for dense wavelength division multiplexing (DWDM) millimeter-wave-band radio-on-fiber (ROF) uplink systems is investigated. The PDC technique is carried out for a lump of all uplink wavelength division multiplexing (WDM) ROF signals at a central station. Each channel is optically separated, photodetected, and demodulated individually without serious signal degradation due to the fiber dispersion effect. Error-free 25-GHz-spaced DWDM transmission and demultiplexing of two 60-GHz-band, 155-Mb/s differential phase-shift keying (DPSK) ROF signals over 25-km-long standard single-mode fiber (SMF) are experimentally demonstrated.     

A robust fiber-radio architecture for wavelength-division-multiplexing ring-access networks

In this paper, we propose a dynamic wavelength-allocation scheme for wavelength-division multiplexing (WDM) fiber-radio ring-access networks. This scheme can be used to improve the use efficiency of wavelengths at the burst traffic load on the fiber-radio networks. Moreover, a novel bidirectional wavelength add-drop multiplexer (B-WADM) is designed on the backboned ring, which can connect the working and standby sub-rings. It can provide the self-protected function that uses just a few optical devices under link failures. Furthermore, we carry out this study through the simulation and analysis for carrier-to-noise ratio (CNR), channel capacity, and spurious free dynamic range (SFDR) of the fiber-radio network. Finally, we set up an experimental network to demonstrate its performance. The experimental results illustrate that this fiber-radio architecture can provide the robust, flexible, and reliable characteristics for large radio terminals.     

A novel duplex WDM-PON with DPSK modulated downstream and re-modulation of the downlink signal for OOK upstream

We experimentally demonstrate and analyze a 10 Gbit/s full duplex wavelength division multiplexing passive optical network (WDM-PON) system. A non-return-to-zero differential phase shift keying (NRZ-DPSK) modulation technique is first utilized for downlink direction, and then the downlink signal is re-modulated for the uplink direction using intensity modulation technique of on-off keying (OOK) with a data rate of 10 Gbit/s per channel. An effective colorless WDM-PON full duplex transmission system is achieved for the data rate of 10 Gbit/s per channel with a channel spacing of 60 GHz over the distance of 25 km with low power penalty.     

基于光相位信号延时自相干的相位信息高速实时取样系统

提出了一种基于光相位信号自相干的高速光相位实时取样方案。利用时延为10ps的延时干涉仪(DI),将待测光信号的相位信息转换为强度信息;再在高非线性光纤(HNLF)中,利用四波混频(FWM)效应对强度信号进行取样。在接收端,利用不同中心波长的光滤波器(OBPF)即可滤出不同时间点的取样信号,从而在光域同时完成高速光相位信息的实时取样和取样信号的串-并转换。本文方案具有成本低、对测信号码率和波长不敏感的优点。实验中,对9GHz正弦调制以及10Gb/s非归零码调制的光相位信号实现了100G/s的高速实时取样系统,并转换为10路10G/s取样信号输出,最终恢复取样光信号的相位波形。     

基于马赫-曾德尔干涉仪和光纤光栅的光分插复用器

光分插复用器(OADM)是波分复用(WDM)系统中的关键器件之一。提出了一种结构新颖的基于马赫-曾德尔(M—Z)干涉仪和光纤光栅(FBG)的光分插复用器，它由两个三端口光环形器、一个光纤光栅和一个马赫-曾德尔干涉仪组成，马赫-曾德尔干涉仪起着光开关的作用。对光分插复用器的输出特性进行了实验研究，实验中调节干涉仪的臂长差，可以实现信号的上下载或直通功能，上下载时通道的隔离度大于20dB。这种结构的光分插复用器具有结构简单、体积小、价格低等优点，在波分复用技术中具有实际应用价值。     

Demonstration of Frequency-Domain Averaging Based Channel Estimation for 40-Gb/s CO-OFDM With High PMD

We experimentally demonstrate the intrasymbol frequency-domain averaging based channel estimation for a 40-Gb/s polarization-division-multiplexed coherent optical orthogonal frequency-division multiplexing signal with eight quadrature amplitude modulation under large polarization-mode dispersion, showing improved efficiency as compared to the time-domain averaging based scheme.     

Regenerative all-optical wavelength multicast for next generation WDM network and system applications

We experimentally demonstrate regenerative all-optical wavelength multicast by simultaneous multi-wavelength conversion of 10 Gb/s non-return-to-zero signals to four ITU 100 GHz spaced channels with a receiver sensitivity improvement of 1.84 dB and less than 0.14 dB difference among all the multicast channels, using a single commercial monolithically integrated SOA-MZI. The multicast device also exhibited about 22 dB optical signal-to-noise ratio enhancement for all the converted channels compared to the original signal channel without wavelength conversion. Our experiment for the first time revealed the regeneration properties of a SOA-MZI device for WDM wavelength multicast purposes, and proved the excellent performance of a simple scheme for various future network and system applications, such as all-optical wavelength routing and grid networking.     

光纤布拉格光栅耦合器型窄带上下话路滤波器的数值分析

从麦克斯韦方程组出发,通过将光纤波导扰动和光栅折射率调制扰动效应转换成等效的耦合系数,推导出光纤布拉格光栅耦合器的统一特征方程。采用打靶法并结合朗格-库塔(Runge-Kutta)数值积分对两种光纤布拉格光栅耦合器型上下话路滤波器的传输特性进行了详细的分析。结果表明,对于光栅破坏耦合器,利用光栅引入的强色散效应,滤波器的波长选择能力得到极大的提高,低于1 nm的带宽能够满足波分复用(WDM)系统的需求,并且当光栅调制的等效耦合远远超过两光纤消逝场间的耦合效率时,不仅有效地抑制了反射信号,使满足布拉格匹配条件的信号透射输出,还消除了旁瓣纹波;而对于光栅辅助耦合器,其非干涉本质使得器件性能更加稳定,并可通过调整光栅长度进一步改善滤波响应。     

A novel colorless WDM passive optical network delivering up/downstream signals and video broadcast signal simultaneously

A colorless wavelength division multiplexing passive optical network delivering up/downstream signals and video broadcast signal (VBS) simultaneously is presented in this paper. In this scheme, subcarrier modulation technique is adopted at the optical line terminal. Here un-modulated double-sideband subcarriers and optical carriers operating in different wavelength bands are used for downstream and video broadcast signal transmission, respectively. The use of differential-phase-shift-keying (DPSK) modulation for downstream transmission enables effective upstream transmission by direct re-modulation. The simulation results demonstrated with 2.5-Gb/s up/downstream signals and video broadcasting signal show this approach could work very well.     

A tunable wavelength conversion and wavelength add/drop scheme based on cascaded second-order nonlinearity with double-pass configuration

A selective and tunable wavelength conversion and wavelength add/drop scheme based on sum- and difference-frequency generation (SFG+DFG) is proposed, in which the concept of "double-pass" is introduced. An arbitrary channel can be dropped from a wavelength division multiplexing (WDM) signal and added to another WDM signal at arbitrary wavelength. The channel to be dropped is selected and depleted (dropped) by adjusting the pump 1 through sum frequency generation (SFG) during the forward propagation. Subsequently, the difference frequency generation (DFG), taking place during the backward propagation, is employed to convert (add) the dropped channel to another channel in another WDM signal by adjusting the pump 2. For the dropped and added channel, the phase matching of SFG and DFG are nearly perfect and the theoretical expressions are derived under the assumption that the two pumps are undepleted. The power of pump 1 is optimized to deplete the dropped channel completely, while that of pump 2 is chosen to maximize the output power of the added channel. Numerical calculations are performed to investigate the propagation of the other channels whose phase is mismatched. To suppress the crosstalk, the spacing of the WDM channels is chosen to be 0.2 nm (25 GHz). We have also compared our scheme with others (such as the single-pass scheme and the double waveguide scheme) and shown that ours possesses several distinct advantages.     

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.     

High-Bit-Rate Dense SS-WDM PON Using SOA-Based Noise Reduction With a Novel Balanced Detection

The major drawback of incoherent broadband sources (BBSs) is their inherent intensity noise. Semiconductor optical amplifiers (SOAs) can be exploited at the transmitter to mitigate this noise. Optical filtering at the receiver, however, leads to the return of most of suppressed noise. Wider filtering at the receiver is the best known strategy to maintain performance gains, at the price of reduced spectral efficiency due to the tradeoff between noise cleaning and adjacent channel crosstalk. We introduce a novel balanced receiver for wavelength division multiplexing (WDM) systems that maintains greater noise cleaning and leaves spectral efficiency unchanged. Unlike standard receivers, our balanced scheme does not filter the desired signal. In this paper, we first demonstrate that the newly proposed receiver is equivalent to standard WDM receivers when no SOA for noise cleaning is present at the transmitter. Although a 2.9-dB power penalty is incurred, network capacity is unchanged, i.e., bit error rate (BER) floors due to intensity noise are the same. When SOAs are employed to mitigate severe intensity noise, we show that our receiver outperforms the wide filtering strategy by two orders of magnitude. Dense WDM capacity is demonstrated up to 10 Gb/s using a thermal source, a saturated SOA, and the balanced detection scheme. A BER of 10^-6 is achieved at 10 Gb/s; further improvement is possible using low overhead forward error correction or a better SOA design. This demonstrates the ability of spectrum-sliced wavelength division multiplexing (SS-WDM) passive optical networks (PONs) to operate at 10 Gb/s at good spectral efficiency. Error performance better than 10^-9 is achieved up to 8 Gb/s with 30-GHz optical channel bandwidth and 100-GHz spacing.     

Dispersion of cascaded fiber gratings in WDM lightwave systems

Fiber gratings operating in the transmission mode can provide high dispersion at wavelengths close to the Bragg resonance. When multiple gratings are cascaded for wavelength division multiplexing (WDM) applications, the net dispersion between the stop bands of any two consecutive gratings is significantly modified. We discuss the dispersion characteristics of such cascaded fiber gratings and propose a dispersion compensator for simultaneous compensation of group-velocity dispersion (GVD) for multiple channels of a WDM lightwave system. We also discuss the impact of the dispersion possessed by cascaded gratings on grating based add-drop multiplexers     

Simultaneous Multichannel Photonic Up-Conversion Based on Nonlinear Polarization Rotation of an SOA for Radio-Over-Fiber Systems

A photonic frequency up-conversion scheme based on the nonlinear polarization rotation (NPR) arising in a semiconductor optical amplifier for wavelength-division-multiplexing (WDM) baseband signals is proposed and experimentally demonstrated. Error-free simultaneous up-conversion of 4 times 2.5 Gb/s WDM baseband channels with a 20-GHz local oscillator signal is experimentally demonstrated in the whole C-band. Compared with the cross-gain-modulation-based scheme, the proposed scheme is found to be almost independent of the wavelength separation between the probe and pump signals. Both the radio-frequency spectrum and the bit-error-ratio performance after electrical down-conversion have shown low distortion induced by the optical NPR-based up-conversion.