Wavelength and repetition rate tunable optical pulse source using a chirped fiber Bragg grating and a nonlinear optical loop mirror

We experimentally demonstrate a simple and novel scheme for tunable real-repetition-rate multiplication, based on the combined use of fractional Talbot effect in a linearly tunable chirped fiber Bragg grating (FBG) and cross-phase modulation (XPM) effect in a nonlinear optical loop mirror (NOLM). By tuning the group-velocity dispersion of the chirped FBG fabricated with the S-bending method using a uniform FBG, we obtain high quality pulses at pseudorepetition rates of 20/spl sim/50 GHz from an original 8.5-ps 10-GHz soliton pulse train. We subsequently convert this pseudorate multiplication into a real-rate multiplication using XPM effect in an NOLM. A wavelength tuning is also achieved over a /spl sim/15-nm range.     

抑制克尔非线性效应的RZ-DPSK色散管理方案研究

对基于40 Gbit/s 归零码-差分相移键控(RZ-DPSK)的密集波分复用(DWDM)系统,为抑制包括自相位调制(SPM)和交叉相位调制(XPM)效应在内的克尔非线性引起的光脉冲相位抖动,提出了4种色散管理方案:前置、后置、中间和平衡补偿方案.分析了这4种补偿方案在抑制克尔非线性效应方面的优劣.通过选择合适的方案,可使RZ-DPSK系统在抑制SPM和XPM效应上平均有2 dB的性能提高.     

10-GHz return-to-zero pulse source tunable in wavelength with asingle- or multiwavelength output based on four-wave mixing in a newlydeveloped highly nonlinear fiber

In this letter, a novel scheme for a wavelength-tunable pulse source (WTPS) is proposed and characterized. It is based on four-wave mixing (FWM) in a newly developed highly nonlinear fiber between a return-to-zero (RZ) pulsed signal at a fixed wavelength and a continuous wave probe tunable in wavelength. The corresponding FWM product acts as the WTPS, and is implemented in a 10-Gb/s, 160-km transmission experiment and in a 40-Gb/s multiplexing/demultiplexing experiment. The scheme can be expanded to a multiwavelength WTPS, which is demonstrated for two wavelengths. The introduced penalty using the WTPS compared to the original RZ pulses is negligible     

Long-haul WDM transmission using higher order fiber dispersionmanagement

We propose a fiber dispersion management scheme for large-capacity long-haul wavelength division multiplexing (WDM) transmission systems that considers not only second- but also third-order dispersion characteristics using transmission fibers with opposite dispersion signs. It eliminates the waveform distortion of WDM signals that originates from the existence of third-order dispersion, which is a constraint placed on WDM capacity in conventional dispersion management, while reducing the interchannel interaction caused by the interplay of fiber nonlinearity and second-order dispersion. Design concept of the scheme is discussed to show the feasibility of using actual fiber parameters. An experimental investigation on transmission performance regarding the signal pulse format, nonreturn-to-zero (NRZ) and return-to-zero (RZ), and interchannel interaction caused by four-wave mixing (FWM) and cross-phase modulation (XPM) is described for optimizing WDM system performance. It is experimentally shown that RZ pulse transmission is possible without significant spectral broadening over a wide wavelength range in dispersion managed fiber spans. Using these results together with a wideband optical amplifier gain-bandwidth management technique, yields long-distance WDM transmission with the capacity of 25×10 Gb/s over 9288 km     

All-optical address extraction for optical routing

This paper describes the optical circuit that enables to extract address from a transmitted cell in an all-optical manner. Nonlinear optical loop mirrors (NOLM's) are used as all-optical switches in order to confirm the operation of the proposed circuit. The control pulses synchronized with address bits are generated from the transmitted cell. The address bits are successfully extracted without any electronic control circuit. The factors that limit an attainable bit rate are discussed. If we use NOLM composed of a 2-km-long fiber, 110 Gb/s is attainable for the 4 ps FWHM input pulse with RZ format     

NOLM中反向交叉相位调制作用分析

提出了反向交叉相位调制(XPM)耦合方程,得出了非线性光学环路镜(NOLM)中正、反向信号脉冲在传输过程中共同作用的非线性相移,研究了高斯脉冲情况下NOLM的开关特性,NOLM作为解复用器时反向XPM的影响,及作为光路由选择单元时无放大联接的级数.最后讨论NRZ码情况下的开关特性.     

Theoretical study of all-optical NRZ to RZ format conversion with tunable pulse width based on XPM in a silicon waveguide

An all-optical format conversion from non-return-to-zero(NRZ) to return-to-zero(RZ) is presented based on cross-phase modulation(XPM) in a silicon waveguide with a detuned optical bandpass filter(OBPF).The simulation results show that the tunable bandwidth of the OBPF leads to RZ signals with tunable pulse width.The conversion efficiency(CE) and the pattern effect of the RZ signal are attributed to the parameters of the pump pulse and the OBPF.The converted RZ signal exhibits lower timing jitter than the NRZ signal.     

利用非线性光学环路镜实现非归零码脉冲到归零码脉冲的变换

利用非线性光学环路镜（ＮＯＬＭ）成功地实现了非归零（ＮＲＺ）脉冲向归零（ＲＺ）脉冲的变换。实验中采用 开关激光器产生的超短光脉冲作为控制光、锁模激光器输出光经外调制后得到的光轮训珧。对变换信号采用时分复用（ＴＤＭ）方式得到了２０ＧＨｚ光信号。     

On-the-Fly All-Optical Contention Resolution for NRZ and RZ Data Formats Using Packet Envelope Detection and Integrated Optical Switches

We present a packet-by-packet contention resolution scheme that combines packet detection, optical space switching, and wavelength conversion performed in the optical domain by integrated optical switches. The packet detection circuit provides the control signals required to deflect and wavelength-convert the contending packets so that all the packets are forwarded to the same output without any collision or packet droppings. We demonstrate the compatibility of the scheme with both nonreturn-to-zero (NRZ) and return-to-zero (RZ) modulation formats by recording error-free operation for 10-Gb/s NRZ and 40-Gb/s RZ packet-mode traffic     

Fast analytical assessment of the signal quality in transparent optical networks

Constraint-based routing (CBR) requires a fast and accurate assessment of the different physical degradation effects in optical communications systems. This paper deals with fast analytical approximation formulas describing the induced system penalty due to the dominant nonlinear effects in 10-Gb/s nonreturn to zero (NRZ) transmission systems. This paper concentrates on the multichannel effects of cross-phase modulation (XPM) and four-wave mixing (FWM).     

基于高SBS阈值的HNLF产生高重复频率超短光脉冲

基于光纤中的四波混频(FWM)产生高重复频率超短光脉冲的原理,并为抑制光纤中的受激Brillouin散射(SBS),采用非均匀掺杂高SBS阈值非线性光纤,通过FWM对双拍频信号进行整形压缩,实验上获得了100GHz的高重复率超短光脉冲序列,进而分析了入纤功率对输出光脉冲的影响。     

Analysis of optical DEMUX characteristics based on four-wave mixingin semiconductor optical amplifiers

We have analyzed the basic characteristics of all-optical demultiplexing (DEMUX) based on four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) by solving a modified nonlinear Schrodinger equation by the finite-difference beam propagation method. Amplified spontaneous emission noise was not included in our model. The optimum pump pulsewidth for obtaining the high ON-OFF ratio is 1~3 ps for 1 ps, 250 Gb/s probe pulses. The shorter limit of the pulsewidth is due to detuning between the pump and probe frequencies, which is determined by the gain bandwidth of the SOA. In order to achieve faster DEMUX operation, an SOA with broader gain bandwidth is required. We also simulated pattern effects in the FWM signal. Power fluctuation in the FWM signal can be reduced by using a strong energy pump pulse and/or weak energy probe pulse. The energy fluctuation of the FWM signal decreases to less than 1% for a 30-bit, 250-Gb/s input probe pulse train with a pulse energy of 0.01 pJ. This small fluctuation should not disturb DEMUX operation. We have also examined DEMUX from time multiplexed signals by repetitive pump pulses. Strong energy pump pulses decrease the FWM signal intensity. However, there is no pattern effect due to gain saturation because the pump pulses are injected continuously     

All-optical wavelength conversion of short pulses and NRZ signalsbased on a nonlinear optical loop mirror

Wavelength conversion of short pulses at 10 GHz based on a nonlinear optical loop mirror (NOLM) is experimentally and numerically investigated for the case of small group velocity dispersion and walkoff between the control pulses and continuous lightwaves. Experimental and numerical simulation results show that the pulsewidths of the converted signals at different wavelengths are almost the same, and the pulsewidths are compressed when the peak power of the control pulse is smaller than a certain value. An RZ optical source containing eight wavelengths having a high sidemode suppression ratio, equal amplitudes and almost the same pulsewidths is obtained by using wavelength conversion in a NOLM consisting of a common dispersion shifted fiber. 10 Gb/s NRZ wavelength conversion based on the NOLM is demonstrated for the first time and certain conclusions in some of the references are confirmed by our experimental results     

20-Gb/s All-Optical Format Conversions From RZ Signals With Different Duty Cycles to NRZ Signals

An all-fiber delay interferometer and narrowband filter based an all-optical format conversion scheme, which can convert return-to-zero (RZ) signals with variable duty cycles to nonreturn-to-zero signals, is proposed and demonstrated. The passive converter is independent of wavelength and input power. The operation principle is analyzed and simulated. Experimental results of 20-Gb/s RZ signals with three different duty cycles accord well with the simulation results. The bit-error-rate measurements show the good performance of the proposed scheme. The conversion performances of different wavelengths and parameters are also discussed.     

Impact of Channel Plan and Dispersion Map on Hybrid DWDM Transmission of 42.7-Gb/s DQPSK and 10.7-Gb/s OOK on 50-GHz Grid

We investigate experimentally the performance of 42.7-Gb/s return-to-zero (RZ) differential quadrature phase-shift-keyed (DQPSK) channels in a dense wavelength-division-multiplexed transmission system having 10.7-Gb/s nonreturn-to-zero (NRZ) on-off keyed (OOK) channels. Cross-phase modulation (XPM) from the OOK channels is found to be a dominating nonlinear penalty source for copropagating DQPSK channels in a dispersion-managed transmission link with multiple standard single-mode fiber spans. It is also found that the XPM penalty strongly depends on channel occupancy and residual dispersion per span (RDPS). Large RDPS effectively mitigates XPM even for the worst-case occupancy where a 42.7-Gb/s RZ-DQPSK channel is amidst several 10.7-Gb/s NRZ-OOK channels on a 50-GHz channel grid.     

Experimental Demonstrations of All-Optical Phase-Multiplexing Using FWM-Based Phase Interleaving in Silica and Bismuth-Oxide HNLFs

We propose an all-optical phase-interleaving technology based on dual-pump four-wave mixing (FWM) in highly nonlinear fiber (HNLF). The proposed all-optical phase-interleaving technology is applied in an all-optical phase-multiplexing scheme to successfully phase-multiplex 2x or 3$,times,$10-Gb/s DPSK-WDM signals to a 20- or 30-Gb/s DPSK in non-return-to-zero (NRZ) formats. The proposed all-optical phase multiplexing scheme is demonstrated using dual-pump FWM in highly nonlinear silica and bismuth fibers. In contrast with optical time-division multiplexing technology, the proposed all-optical phase-multiplexing technology does not require pulse-carving, thus offering a high spectral-efficiency. Differential precoder for each input tributary is operated independently, and no additional encoder or postcoder is required to recover the original data after demodulation on the receiver side.      

XPM对非线性光纤环镜微波光子开关的影响

为了研究交叉相位调制(XPM)对非线性光纤环镜微波光子开关的影响.基于耦合非线性薜定谔方程,彩分步傅里叶法建立考虑XPM在内的数值分析平台,获得了MOLM微波光子开关中XPM对微波调制光载波信号和NOLM功率舆函数的影响.数值计算表明:XPM导致调制波波形畸变,信号能量从主瓣泄露;并且随着调制带宽的增大,旁瓣泄露愈加严重.同时由于XPM效应的非互易性,NOLM功率传输函数扭变,在耦合器分光比f∈(0,0.5)区间减少而在f∈(0,0.5)区间增大.     

Superposition of DQPSK over inverse-RZ for 3-bit/symbol modulation-demodulation

We successfully demonstrated overwriting of differential quadrature phase-shift keying (DQPSK) on inverse return-to-zero (RZ) pulses for simple 3-bit/symbol operation at a 10-Gb/s symbol rate (30-Gb/s bit rate). We adopted cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) for inverse-RZ generation, which allows both low and high levels of RZ optical signal to have a finite pulse energy in a bit time slot. We verified a wide tolerance of 20% of the bit-slot for time slot alignment between amplitude-shift keying and differential phase-shift keying modulation in the proposed scheme. We also demonstrated wide dynamic range characteristics at the extinction ratio for both 2- and 3-bit/symbol operation, compared to the conventional scheme. The proposed scheme allows a cross-modulation penalty, due to the intensity to phase modulation, of less than 1.5 dB in 2-bit/symbol and less than 5 dB in 3-bit/symbol operation.