Multiwavelength All-Optical Clock Recovery of Non-Return-to-Zero Data

A novel scheme of all-optical clock recovery from mutiwavelength non-return-to-zero （NRZ） data stream is proposed and demonstrated. The chirp induced by a chirped fibre Bragg grating and a semiconductor optical amplifier is used to enhance the clock. The clock is recovered after injecting the enhanced signal into the scheme based on the stimulated Brillouin scattering. The experiment is carried out and the dual-wavelength clock is recovered. This novel scheme can realize clock recovery of multiwavelength NRZ signal in the total wavelength range of 3.3nm. This clock recovery technology is transparent to the data bit rate and modulation format, also without pattern dependence.     

基于半导体光放大器的非归零信号时钟恢复

提出了一种基于半导体光放大器加窄带光纤光栅滤波器，将非归零信号转换为伪归零信号，再把伪归零信号注入到主动锁模环行腔激光器进行时钟提取的非归零信号时钟恢复方案.利用该方案实现了10 Gb/s伪随机非归零信号的全光时钟恢复，对工作原理和结果进行了分析和讨论.实验证明该方案具有结构简单，调整容易，输出波形好的特点.     

Novel scheme of clock recovery for high-speed OTDM signals based on stimulated Brillouin scattering

A new but simply implemented optical clock recovery scheme for optical time-division multiplexing （OTDM） systems based on stimulated BriUouin scattering （SBS） effect is presented and demonstrated experimentally. According to the unequal-amplitude even-multiplexed OTDM signals, the frame clock is extracted. In addition, the clock with multiple tributary rates is recovered from 160-Gb/s OTDM signal in simulation by utilizing the clock recovery module.     

基于UNI开关的40 GHz注入锁模全光时钟提取实验

基于超快非线性干涉仪UNI开关具有超过40 Gbit/s的开关速度，提出一种在锁模环形腔内利用UNI开关进行时钟提取的新方案.按此方案进行实验，对40 Gbit/s伪随机信号进行时钟提取，得到了清晰稳定的时钟脉冲.与利用SOA的交叉增益调制注入锁模时钟提取方案相比，在此方案中注入到SOA的信号功率仅0.5 dBm，降低了7 dB左右，对SOA的运行更安全.     

基于半导体光放大器和受激布里渊散射的全光非归零码时钟提取

利用半导体光放大器(SOA)的增益饱和特性、自相位调制(SPM)效应和啁啾光纤光栅(CFBG)的滤波和啁啾特性共同作用实现了10 Gbit/s非归零码(NRZ)信号的时钟分量增强。经过该结构的非归零光谱的时钟分量增强后,其时钟数据抑制比提高了12.9 dB。时钟分量增强后的信号经基于受激布里渊效应(SBS)的时钟提取结构后实现了对非归零信号的全光时钟提取。这种新型非归零全光时钟提取结构具有对数据速率及数据格式透明,低抖动,不受码型效应的影响等优点。     

All-optical clock recovery from 10-Gb/s NRZ data and NRZ to RZ format conversion

A non-return-to-zero (NRZ) to pseudo-return-to-zero (PRZ) converter consisting of a semiconductor optical amplifier (SOA) and an arrayed waveguide grating (AWG) is proposed, by which the enhancement of clock frequency component and clock-to-data suppression ratio of the NRZ data are evidently achieved. Alloptical clock recovery from NRZ data at 10 Gb/s is successfully demonstrated with the proposed NRZ-to-PRZ converter and a mode-locked SOA fiber laser. Furthermore, NRZ-to-RZ format conversion of 10 Gb/s is realized by using the recovered clock as the control light of terahertz optical asymmetric demultiplexer(TOAD), which further proves that the proposed clock recovery scheme is applicable.     

等幅均匀复用OTDM信号的单路和群路时钟提取

提出了针对等幅均匀复用的光时分复用信号进行全光时钟提取的一种新方案,理论上分析了该方案的可行性,并给出了各次谐波时钟频率分量大小的表达式.实验上利用该方案成功地从等幅均匀复用的8×2.5 GHz信号中提取出了2.5 GHz单路时钟和20 GHz群路时钟光脉冲.此技术可应用于高速OTDM信号的时钟提取.     

光时分复用系统中单路时钟的提取

提出利用复用信号的时候不均匀性,采用主动光纤锁模激光器,直接从复用后的信号中提取出复用前的时钟光脉冲。考虑到电的时分复用与光的时分复用在机理上的一致性,故初步复用时分复用信号进行实验,成功地从时分复用信号中得到了复用前的时钟光脉冲。此处电的时分复用所得的结论适用于光的时分复用。     

10、20、40Gb/s速率下恶化信号的光时钟提取

报道了一种全部由10GHz带宽的元件构成的、用于时钟提取的双环注入锁模光纤激光器.这种装置集光电振荡器(OEO)与注入锁模光纤激光器的优点于一体,利用它不仅从恶化的数据信号中实现了10Gb/s的位时钟提取,在采用了光电振荡器的分频、锁模光纤激光器的有理谐波锁模以及F-P梳状滤波器的频率倍乘技术以后,还从20Gb/s和40Gb/s的恶化信号中提取出了位时钟.该方案的另一个优点是无码型效应.     

Half baudrate electrical clock based demultiplexing scheme for OTDM-DQPSK signal using SOA and optical filter

A demultiplexing scheme based on semiconductor optical amplifier(SOA)and optical filter for optical time division multiplexing differential quadrature phase shift keying(OTDM-DQPSK)system is proposed and investigated experimentally.With only a common half baudrate electrical clock modulated 33%duty cycle return-to-zero(RZ-33)optical clock signal as pump,this scheme is cost-effective,energy-efficient,and integration-potential.A proof-of-concept experiment is carried out for the demultiplexing of a 2×40-GBd OTDM-DQPSK signal.Error-free performance is demonstrated,and the average power penalty for both channels is about 3 dB.     

Single AWG based clock extraction from WDM signals with mixed formats and mixed bit-rates

A simple and flexible simultaneous clock extraction for WDM signals with mixed modulation formats and bit-rates is proposed and demonstrated using a single commercial arrayed waveguide grating (AWG), which acts both detuned multi-channel filter and demultiplexer for the input signals. By using an AWG with 100 GHz spacing, clock extraction from transmitted multi-channel nonreturn to zero (NRZ) and NRZ differential phase shift keying (NRZ-DPSK) signals at mixed bit-rates from 10 to 40 Gb/s with 200 GHz spacing is achieved simultaneously. By cascading a clock recovery module, clock signal can be easily recovered from the preprocessed signals with enhanced clock tones.     

All-optical frequency multiplication/recovery based on a semiconductor optical amplifier ring cavity

A novel scheme for all-optical frequency multiplication/recovery based on a semiconductor optical amplifier ring cavity is proposed and investigated numerically. The results show, for a 2.5 GHz driving pulse train, it can be generated 5-25 GHz repetition rate pulse trains with low clock amplitude jitter, polarization independence and high peak power. Furthermore, the extraction of the clock signal from a pseudorandom bit sequence signal can be realized based on the proposed scheme.     

All-Optical Clock Recovery from NRZ-DPSK Signals at Flexible Bit Rates

We propose and demonstrate all-optical clock recovery （OR） from nonreturn-to-zero differential phase-shift- keying （NRZ-DPSK） signals at different bit rates theoretically and experimentally. By pre-processing with a single optical filter, clock component can be enhanced significantly and thus clock signal can be extracted from the preprocessed signals, by cascading a OR unit with a semiconductor optical amplifier based fibre ring laser. Compared with the previous preprocessing schemes, the single filter is simple and suitable for different bit rates. The clock signals can be achieved with extinction ratio over lOdB and rms timing jitter of 0.86 and 0.9 at 10 and 20 Gb/s, respectively. The output performances related to the bandwidth and the detuning of the filter are analysed. By simply using a filter with larger bandwidth, much higher operation can be achieved easily.     

相移干涉计量中相移器的原路相干相位检测标定

A new all-optical clock extraction scheme based on an asymmetric nonlinear optical loop mirror (NOLM) is proposed and demonstrated experimentally. The proposed scheme can operate at a relatively low switching power (only 0.3 Pπ is required for the clock pulse, where Pπ means the required switching power for the maximum switching in the asymmetric NOLM) and a relatively low input clock to data ratio (2～2.5). The proposed scheme is promising for clock extraction in the future ultrahigh-speed self-clocked OTDM network.     

40 Gb/s信号全光3R再生实验

提出一种新型40 Gb/s全光3R再生器方案。采用高精细度法布里-珀罗滤波器进行时钟提取。时钟提取前,通过高稳定光源对输入信号光波长变换实现信号光波长和法布里-珀罗滤波器梳状窗口对准;时钟提取后,接半导体光放大器(SOA)进一步消除时钟信号噪声。全光判决中,采用双半导体光放大器串联增大非线性性能,提高了判决门的响应速度。判决输出接窄带滤波器去除脉冲啁啾拖尾,减小码型效应。实验中,恶化40 Gb/s光脉冲信号通过全光3R再生器可以得到再生脉冲。输入恶化信号时间抖动大于5 ps,脉冲宽度大于16 ps,再生得到的信号时间抖动小于1.5 ps。再生信号相对于输入信噪比改善14 dB。连续稳定工作记录大于15 h。通过实验验证,这种全光3R再生器方案成功地实现了40 Gb/s信号的再生。     

Asymmetric Nonlinear Optical Loop Mirror for All Optical Clock Extraction in Self-clocked Optical Transparent OTDM Network

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A simple method for clock recovery

All optical bit clock recovery is one of the key technologies for all optical 3R recovery. In this paper, a simple method applying the combination of Fabry–Perot (F–P) filter and semiconductor optical amplifier (SOA) for clock recovery is proposed. The effect of the F–P filter finesse on the clock recovery and the reduction in the amplitude fluctuation of the clock pulse by the SOA are discussed theoretically. With this technology 10 Gbit/s clock recovery with equal amplitude and wavelength transparency was realized experimentally.     

Simple optical preprocessing for optical clock recovery using a single fiber Bragg grating filter

We propose a simple optical preprocessing for optical clock recovery using a fiber Bragg grating (FBG) filter. In the proposed scheme, the signal preprocessing is performed by suppressing the carrier component through the FBG filter, and experiment shows that the clock component is larger than about 10 dB compared with other rf components within a distance of from the clock frequency component.     

平行线偏光激发CPT共振方案实验研究

目前的相干布居囚禁(CPT)原子钟和CPT磁场计中普遍采用圆偏振光方案 (σ⁺-σ⁺)实现CPT共振, 该方案对原子的利用率较低. 为了提高原子的利用率, 本文实验研究了通过平行线偏振相干双色光与⁸⁷Rb原子作用实现CPT共振的方案(lin//lin). 与σ⁺-σ⁺方案相比较, lin//lin方案消除了极化暗态, 获得更多工作原子. 在相同的实验条件下, 开展对比实验研究获得了信噪比为σ⁺-σ⁺方案2倍, 微分线型信号的中心斜率为σ⁺-σ⁺方案1.65倍的CPT共振信号. 研究结果表明该方案是实现低功耗原子钟、磁场计等设备的理想候选.     

Trellis ternary line coding scheme for asynchronous optical CDMA systems

In this paper, we investigate the employment of a ternary line coding technique based on Ungerboeck's trellis-coded method in asynchronous optical CDMA systems. The ternary coding we use is predicated upon the equal-weight orthogonal (EWO) scheme. Each user transmits two mutually orthogonal signature sequences to represent “+1” and “−1”, respectively, and nothing is transmitted for “0”. The receiver employs a maximum-likelihood soft-decoder to select the path with minimum Euclidean distance as the preferred path. This trellis ternary coding scheme applies set partitioning with partially overlapping subsets to increase the free Euclidean distance, which considerably improves system performance. Furthermore, due to line coding technique, such scheme comprises sufficient clock information, and thus benefits for baseband timing extraction (i.e. clock recovery). Numerical results reveal that the proposed trellis ternary coding scheme can significantly reduce the error floor and allow more active users to be accommodated in the network.