Polarization-, Wavelength-, and Filter-Free All-Optical Clock Recovery in a Passively Mode-Locked Laser Diode With Orthogonally Pumped Polarization-Diversity Configuration

We proposed and demonstrated all-optical clock recovery system using a monolithic mode-locked laser diode (MLLD) that operated with less sensitivity to the polarization and the wavelength of the input data signals also with no bandpass filter to eliminate the input signal-components. The keys to this new technique are the MLLD integrated with a tensile-strained quantum-well saturable absorber and a new polarization-diversity setup by signal input orthogonally polarized to the lasing polarization of the MLLD. This approach was experimentally validated in the 40 Gbps clock recovery experiments. The results exhibited excellent performance of the clock recovery with low timing jitters (<0.3 ps) remaining small dependence on the wavelength and the polarization of the input data signals and input-signal suppression less than -30 dB with no use of the bandpass filter. We also succeeded in the stable clock recovery for the input of polarization-scrambled data signals.     

强经典驱动腔QED系统的量子纠缠演化特性

研究了强经典场驱动模型下原子间纠缠与光场间纠缠的演化特性,其中原子与光腔场发生非共振相互作用。在给定其中某一原子与其耦合光腔场的条件,通过调节另一原子与其相互作用光场的失谐量,来分析原子间纠缠出现猝死行为的区域,以及两光场纠缠相干态的产生条件。     

基于放大反馈激光器高速全光时钟提取的研究

为了研究放大反馈激光器全光时钟提取的性能,采用单边带相位噪声功率谱积分的方法,对40Gbit/s无恶化信号和噪声恶化信号分别进行了时钟提取实验,计算了所提取时钟的时间抖动。同时还测量了放大反馈激光器的锁定范围。通过实验取得了恶化前后所提取时钟的时间抖动分别为130fs和150fs,放大反馈激光器的锁定范围为234MHz。结果表明,基于放大反馈激光器的全光时钟提取方案对噪声恶化具有较强的容忍度,而且具有较宽的锁定范围。这一结果对于全光时钟提取技术的进一步发展具有重要意义。     

Reconfigurable All-Optical Logic Gates for Multi-Input Differential Phase-Shift Keying Signals: Design and Experiments

Differential phase-shift keying (DPSK) signals are promising candidate for the long-haul transmission systems. However, the development of the all-optical signal processing techniques for the DPSK signals is still in its infancy, especially the all-optical logic operations. In this work, a general scheme for reconfigurable logic gates for multi-input DPSK signals with integration possibility is proposed. Benefiting from the optical logic minterms developed by two kinds of optical devices, i.e., optical delay interferometers and semiconductor optical amplifiers (SOAs), target logic functions can be realized by combining specific minterms together. The scheme is reconfigured by changing the phase control of the delay interferometers or the input wavelengths. The latter approach was adopted in the experimental trials. Although the outputs of the scheme are on-off keying (OOK) signals, the data format is compatible with all-optical decision circuits where OOK format is preferred. Two- and three-input experiments are carried out at 20 Gbit/s with nonreturn-to-zero DPSK signals. Various logic operations are demonstrated, including full sets of two- and three-input minterms, AND, NOR, XOR, and XNOR logic operations where the AND and NOR logic are derived simultaneously and the XOR and XNOR logic are convertible. The optical SNR as well as the Q-factor of the two- and three-input results are measured and compared. It shows that the input powers to the SOAs are critical in achieving good extinction ratio and the Q-factor of logic results degrades when several minterms are combined. The recovery time of the SOAs need to be optimized as well. Finally, the scaling issues of the scheme are discussed.     

Optical signal processing based on self-induced polarization rotation in a semiconductor optical amplifier

We demonstrate novel optical signal processing functions based on self-induced nonlinear polarization rotation in a semiconductor optical amplifier (SOA). Numerical and experimental results are presented, which demonstrate that a nonlinear polarization switch can be employed to achieve all-optical logic. We demonstrate an all-optical header processing system, an all-optical seed pulse generator for packet synchronization, and an all-optical arbiter that can be employed for optical buffering at a bit rate of 10 Gb/s. Experimental results indicate that optical signal processing functions based on self-polarization rotation have a higher extinction ratio and a lower power operation compared with similar functions based on self-phase modulation.     

Spatially coherent beam formation and mode locking of an array of solid-state lasers

A study is reported on the spatially coherent beam formation from an array of four Nd-glass lasers and on mode locking their longitudinal modes. The results indicate a nearly 16 times increase in radiance. For mode locking, only a single modulator is required. A spatial filter in the optical cavity performs the spatially coherent beam formation and the precision synchronization of the mode-locked pulses at the output mirror of the optical cavity.     

Optical Noise Tolerance in a Polarization-, Wavelength-, and Filter-Free All-Optical Clock Recovery System Based on a Monolithic Mode-Locked Laser

We experimentally investigated optical noise tolerance of a polarization-, wavelength-, and filter-free all-optical clock recovery system based on a monolithic mode-locked laser diode. The results showed that for input signal degradation, the jitter of the recovered clock did not degrade to approximately 8 dB/nm of the optical SNR. We also compared the clock recovery performance as functions of the wavelength and the modulation format (on-off keying and phase-shift keying) of the input data signals. We revealed that no significant changes were measured in the clock recovery performance despite such changes in the parameters of the input data signals, indicating that noise-tolerable clock recovery is expected, retaining the polarization- and the filter-free operations, regardless of the wavelength and the modulation format of the input data signals, by using our new scheme.     

All optical signal regularizing/regeneration using a nonlinearfiber Sagnac interferometer switch with signal-clock walk-off

All-optical signal regularizing/regeneration using a nonlinear fiber Sagnac interferometer switch (NSIS) that employs signal-clock walk-off is investigated. The NSIS realizes all-optical signal regeneration, including timing and amplitude regularizing, by switching clock pulses with amplified input signals using a walk-off-induced, wide, square switching window and intensity-dependent transmittance of the device. First, characteristics (in both the temporal and spectral domains) of the all-optical signal regeneration achieved with the NSIS are investigated theoretically and experimentally. They certify that if clock pulses are within the square switching window obtained with signal-clock walk-off, the clock pulses can be modulated according to the data that the input signals carry and retain their temporal and spectral profiles. This means that if clock pulses can be prepared that meet the system requirements, the NSIS can convert input signals that may not satisfy system requirements into high-quality output signals. Limitations on the switching contrast due to the cross-phase modulation of counterpropagating reference pulses is also discussed. Second, two possible applications of NSIS-based all-optical signal regularizing/regeneration, 1) an all-optical multiplexer with an optical clock and 2) an all-optical regenerative repeater, are discussed. Preliminary experiments with ~10-ps pulses at bit rates of ~5 Gb/s that use locally prepared optical clock pulses, show that the NSIS provides an error-free regeneration function with a certain tolerance for pulse-period irregularity if a proper optical clock is obtained     

Performance and scalability of an all-optical clock recovery figure eight laser

A novel geometry for all-optical clock recovery using a semiconductor amplifier yields a strong locking mechanism in a short cavity. The recovered clock has a large locking bandwidth, low timing jitter, and fast lock-up time at a 2.5 GHz rate. Preliminary results at a 9 GHz rate also indicate a high quality recovered clock.     

All-optical clock recovery using a modelocked figure eight laserwith a semiconductor nonlinearity

A novel geometry for all-optical clock recovery is demonstrated using a semiconductor laser amplifier in a nonlinear optical loop mirror to modelock a figure eight laser. A clock signal can be recovered over a broad locking bandwidth of 0.5 MHz when random data at 1 Gbit/s are input to the system     

Photonic packet switches: architectures and experimentalimplementations

Photonic packet switches offer high speed, data rate and format transparency, and flexibility required by future computer communications and cell-based telecommunications networks. In this paper, we review experimental progress in state-of-the-art photonic packet switches with an emphasis on all-optical guided-wave systems. The term all-optical implies that the data portion of a packet remains in optical format from the source to the destination. While the data remain all-optical, both optical and optoelectronic techniques have been used to process packet routing functions based on extremely simple routing protocols. An overview of the design issues for all-optical photonic packet switching is given and contrasted with electronic packet switch implementations. Low-level functions that have been experimentally implemented include routing, contention resolution, synchronization, and header regeneration. System level demonstrations, including centralized photonic switching and distributed all-optical multihop networks, will be reviewed     

All-Optical Chromatic Dispersion Monitoring for Phase-Modulated Signals Utilizing Cross-Phase Modulation in a Highly Nonlinear Fiber

We propose and experimentally demonstrate an all-optical chromatic dispersion (CD) monitoring technique for phase-modulated signals utilizing the cross-phase-modulation effect between the input signal and the inserted continuous-wave probe. The probe's optical spectrum changes with the accumulated CD on the input signal, indicating that the optical power variations can be measured for monitoring. The experimental results show that this technique can monitor up to 120 ps/nm of CD for a 40-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) transmission system, with the maximum measured optical power increment of 16.5 dB. The applicability of this monitoring technique to higher bit-rate phase-modulated signals, such as 80-Gb/s RZ differential quadrature phase-shift keying and 80-Gb/s polarization-multiplexed RZ-DPSK, is also investigated via simulation.      

基于半导体光放大器非线性偏振旋转效应的全光采样

提出了一种新的基于半导体光放大器非线性偏振旋转效应的全光采样方法,利用速率方程对全光采样的理论机理进行了阐述.借助该速率方程模型对采样器的输入偏振角、偏振控制器的附加相移和偏振合束器的偏振方向等参数进行了优化设计.计算结果表明,采样器传输曲线具有较好的线性工作范围,能够实现模拟光信号的高速全光采样,且其输入泵浦光功率小于1mW.由于该全光采样的工作原理与全光波长转换类似,而目前的全光波长转换工作速率可达320Gbps,因此该全光采样的采样速率可望达到上百GS/s.     

Reshaping capability of cross-gain compression in semiconductor amplifiers

We introduce and experimentally demonstrate a novel scheme for all-optical regeneration. We exploit the reshaping properties of cross-gain compression between two logically inverted signals in a gain-saturated semiconductor optical amplifier. This technique performs wavelength-preserving signal reshaping and produces, as an additional output, a wavelength-converted copy of the input signal. We report experimental results showing apparent improvement of the eye diagrams and of the bit-error rate for degraded 10-Gb/s signals.     

All-optical switching by counterpropagating operation in cascadedsemiconductor optical amplifiers

We propose a simple, compact, integrative, flexible, power-efficient, and all-optical switch. The operation is based on self-induced gain modulation leading to nonlinear transmittance with a threshold level dependent on input powers of the data and control signals counterpropagating in cascaded semiconductor optical amplifiers. We demonstrate numerically the all-optical switch with small-signal modulation, low-power consumption, high-output power, and high-output extinction ratio     

采用SOA-Sagnac光纤干涉仪的AOWC研究与实验

对采用SOA—sagnac光纤干涉仪的全光波长变换器(AOWC)从理论上进行了较为详细的研究，首次根据光路合成法求出SOA—Sagnac光纤干涉仪的响应函数。并构成了一套实验系统，测量了SOA的增益、带宽与输入光功率的关系，测量了输出信号的消光比以及输入、输出信号的波形和眼图。并对它们进行了比较。     

基于半导体光放大器非线性偏振旋转效应的全光采样

提出了一种新的基于半导体光放大器非线性偏振旋转效应的全光采样方法,利用速率方程对全光采样的理论机理进行了阐述.借助该速率方程模型对采样器的输入偏振角、偏振控制器的附加相移和偏振合束器的偏振方向等参数进行了优化设计.计算结果表明,采样器传输曲线具有较好的线性工作范围,能够实现模拟光信号的高速全光采样,且其输入泵浦光功率小于1mW.由于该全光采样的工作原理与全光波长转换类似,而目前的全光波长转换工作速率可达320Gbps,因此该全光采样的采样速率可望达到上百GS/s.     

压缩态光场实验中的模式匹配与偏频锁定技术研究

光学参量过程是产生压缩光的关键环节,为了提高实验中光学参量振荡腔的稳定性,必须将激光与光学参量振荡腔进行模式匹配,并用锁定技术稳定光学参量振荡腔。理论分析了模式匹配效率对压缩度和偏频锁定技术精度的影响。经过模式匹配之后,在实验上实现了光学参量振荡腔的锁定,并对锁定后的光学参量振荡腔进行了稳定性测量。理论与实验结果表明:模式匹配效果越好,压缩光的压缩度和偏频技术的锁定精度越高;在较好的模式匹配条件下,光学参量振荡腔的腔长锁定精度为7.35 nm,稳定时间可达2 h以上,能够满足对压缩态光场的探测需要。     

40 Gbit/s全光异或门性能仿真

为了提高基于SOA-MZI结构的全光异或门的输出消光比,优化系统性能,将SOA和HNLF相结合,在光通信系统设计软件OptiSystem7.0仿真平台上搭建了基于SOA-MZI的全光异或仿真实验模型,对两路40 Gbit/s的RZ码数据信号进行了全光异或仿真实验。利用HNLF的非线性效应设计了一种优化结构对基于SOA-MZI的全光异或输出信号进行优化,并对优化前后的信号时域波形图和系统眼图进行了比较分析,通过多次反复实验得到一组最佳的系统参数,使得基于SOA-MZI的全光异或门的输出消光比从10 dB提高到约28 dB。实验结果表明:常规的基于SOA-MZI的全光异或门由于相消干涉不彻底造成输出消光比较低,而经过优化,很好地解决了这种问题,提高了异或输出消光比,优化了系统性能。     

基于光纤光栅外腔半导体激光器增益饱和效应的全光波长转换实验研究

对基于光纤光栅外腔半导体激光器增益饱和效应的全光波长转换器的静态与动态特性进行了实验研究。为消除反馈光与转换信号输出光对光源的不利影响及提高光输入、输出信号耦合效率 ,提出了采用环形器进行信号耦合的光学结构。实验结果表明 ,转换器件具有高于 30nm的波长转换间隔 ,并可实现波长上、下转换。进行了15 5Mbit/s伪随机码调制信号的动态波长转换实验。