交叉相位调制提高半导体激光器混沌载波发射机带宽方法

提出半导体激光器混沌交叉相位调制(XPM)光反馈提高混沌载波发射机带宽方法,建立了有外腔光纤传输反馈XPM控制下的激光动力学物理模型.理论导出XPM作用下激光双反馈频率失谐公式,指出XPM产生的非线性相移影响了激光器增益和线宽增强因子,其光纤二阶非线性效应使激光振幅和相位变化更加丰富,而非线性相移的出现进一步增加了新的频率分量并使频谱展宽.数值结果表明,XPM使激光器混沌带宽增加到4倍以上,使激光混沌张弛振荡频率增加到2.85倍,其光纤长度、入纤光功率、面镜反射系数、光纤二阶非线性系数等都能影响激光混沌带宽.     

All-optical wavelength conversion based on cross-phase modulation

We have proposed and demonstrated an all-optical scheme of wavelength conversion based on cross-phase modulation (XPM). The frequency shift and broadening of a continuum wave induced by XPM in a dispersion-shifted fiber (DSF) is experimentally observed. Then, the wavelength conversion is achieved through the filtering by a fiber grating. The results indicate that wavelength conversion based on the cross-phase modulation of DSF is simple, efficient, and universal with wide conversion ranges and high rates.     

Suppression of Nonlinear Patterning Effect in Wavelength Conversion Based on Transient Cross-Phase Modulation in Semiconductor Optical Amplifier Assisted with a Detuning Filter

Nonlinear patterning （NLP） effect in wavelength conversion based on transient cross-phase modulation （XPM） in semiconductor optical amplifier （SOA） assisted with a detuning filter is theoretically investigated. A non- adiabatic model is used to estimate the ultrafast dynamics of gain, phase and electron temperature in the SOA. Simulation results show that the NLP can be greatly suppressed by introducing an assist light, especially for the probe wavelength distant from gain peak. Furthermore, the results also indicate that the improvement is more evident for long wavelength probe light and assist light in counter-propagating configuration.     

Multi-wavelength conversion at 10 Gb/s using cross-phase modulation in highly nonlinear fiber

In this paper we demonstrate a technique of signal wavelength conversion via cross-phase modulation (XPM)-induced nonlinear coupling among a 10 GHz return-to-zero (RZ) signal and a continuous wave (CW) carrier co-propagating in dispersion-shifted (DS) highly nonlinear fiber (HNLF). The wavelength conversion bandwidth up to ±20 nm was achieved experimentally and potential extension was verified by numerical simulations. The principle can easily be extended to 40 Gb/s and used as polarization insensitive all-optical wavelength converter.     

Efficient generation of high-power quasi-single-cycle terahertz pulses from a single infrared beam in a second-order nonlinear medium

It is shown that the coherence lengths for terahertz (THz) generation based on difference-frequency generation within an ultrafast infrared pulse can be sufficiently long for a wide bandwidth about each phase-matching wavelength owing to a slight dispersion in the THz region. As a result, quasi-single-cycle THz pulses can be efficiently generated. An efficient conversion for the parametric process is made possible not only by use of the wide phase-matching bandwidth but also by optimization of the pulse width for each peak THz frequency. I have investigated the strong-pump regime and found the limits to the conversion efficiencies to generate high peak intensities efficiently for THz waves with which to explore nonlinear regimes of the THz interactions.     

Cross-phase-modulation-based wavelength conversion using intersubband transition in InGaAs/AlAs/AlAsSb coupled quantum wells

We report an ultrafast cross phase modulation (XPM) effect in intersubband transition (ISBT) of InGaAs/AlAs/AlAsSb coupled quantum wells, where the ISBT absorption of a transverse-magnetic mode pump signal induces phase modulation of a transverse-electric mode probe signal. Using waveguide-type ISBT devices, we have achieved XPM-based 10 Gbit/s wavelength conversion with a power penalty of 2.53 dB. Also, we propose XPM-based signal processing circuits for gate switching and modulation format conversion.     

光纤非线性效应对10 Gb/s波分复用色散补偿系统的限制

对信道间距为１００ＧＨｚ的８倍１０Ｇｂ／ｓ波分复用色散补偿系统进行了计算机仿真,分析了光纤的色散和自相位调制（ＳＰＭ）、互相位调制（ＸＰＭ）、四波混频（ＦＷＭ）等非线性效应在具有级联光放大器系统中的作用。四种色散补偿方案是：ＳＭＦ（常规单模光纤）＋ＤＣＦ１（色散斜率为正的色散补偿光纤）、ＳＭＦ＋ＤＣＦ２（色散斜率为负的色散补偿光纤）、ＴＷ１（色散为正的非零色散光纤）＋ＴＷ２（色散为负的非零色散光纤     

All-optical wavelength multicasting exploiting cross-phase modulation in a dispersion-flattened nonlinear photonic crystal fiber

An all-optical wavelength multicasting scheme with tunable output wavelength and channel numbers has been proposed and demonstrated based on cross-phase modulation (XPM) in a dispersion-flattened highly nonlinear photonic crystal fiber. We show that the input signal wavelength can be simultaneously converted to four different wavelengths by filtering the broadened sideband of the continuous-wave (CW) probe beams. The experiments are carried out to investigate into the wavelength tunability, and exploit the dynamic characteristics with variable input signal powers, the ability of multicasting channels scalable, and the relationship between the multicasting signal qualities with variable optical band-pass filter (OBPF) bandwidth. The results indicate that the proposed wavelength multicasting scheme has the advantages of simple structure, efficient operation in a wide wavelength range, as well as transparent to bit rates. Moreover, the system can be upgraded to generate more multicasting channels by increasing the number of CW probe beams.     

Spectral Talbot phenomena of frequency combs induced by cross-phase modulation in optical fibers

Cross-phase modulation (XPM) of a frequency comb (finite-duration optical pulse sequence) by an intense, long Gaussian pump pulse is theoretically investigated, and new effects, namely, frequency-domain self-imaging phenomena (integer and fractional Talbot effects), are reported. The conditions favorable for observing spectral self-imaging phenomena by XPM are derived and numerically confirmed. The effects of nonidealities in a practical experiment (e.g., group-delay walk-off and dispersion) are also evaluated. One can use spectral self-imaging to tune the free spectral range of a frequency comb (without affecting the shape and bandwidth of the individual passbands) simply by adjusting the pump power in a fiber XPM scheme.     

基于光纤中交叉相位调制的波长转换器研究

波长转换器在未来的全光网络中将起到重要的作用.通过大量的数值仿真,研究了利用色散位移光纤中的自相位调制效应的波长转换器,首次对各参量,包括输入光信号脉冲的峰值功率,连续波的功率,两束光信号的频率间隔,光纤的色散,光纤的长度以及输入信号的比特率对此波长转换器的性能影响进行了数值研究.结果表明,光纤的色散和输入光信号脉冲的功率在这种波长转换器中起重要作用,而且这种波长转换器可以对高达200Gb/s的信号进行转换.     

光子晶体光纤中交叉相位调制光谱展宽特性研究

实验研究了超高速时分复用信号与探测光同向传输,在色散平坦高非线性光子晶体光纤中的交叉相位调制光谱展宽特性,从光谱学的角度分析了信号光波长漂移,泵浦光与信号光总功率及功率比,二者偏振态失配对交叉相位调制光谱展宽效应的影响,探讨了实现偏振不敏感交叉相位调制效应的可行性。研究发现,在36 nm波长范围,总功率大于23 dBm,泵浦光与信号光功率比合理,二者偏振态匹配时交叉相位调制效果最好,交叉相位调制的偏振相关性为11 dB,指出利用色散平坦高非线性光子晶体光纤中的残余双折射,调节泵浦光与光纤双折射主轴成45°,可以实现偏振不敏感交叉相位调制效应,随后的理论模拟和实验结果相一致。研究结果为实现基于交叉相位调制原理工作的超快全光信号处理器件作了充分准备。     

All-optical wavelength converter based on fiber cross-phase modulation and fiber Bragg grating

I present new method of phase modulation to amplitude modulation conversion (PM/AM conversion) that utilizes integrating capabilities of fiber Bragg grating (FBG). I found that the wavelength converter based on fiber cross-phase modulation (XPM) and new method of PM/AM conversion have an order of magnitude higher conversion efficiency then the wavelength converter based on sideband filtration method and up to 6 dB higher conversion efficiency then the converter based on the nonlinear optical loop mirror. Numerical analysis and experimental results are provided for bit rates up to 40 Gb/s.     

THE NONLINEAR SCHR?DINGER EQUATION AND THE CROSS-PHASE MODULATION IN ERBIUM-DOPED FIBER AMPLIFIERS

The nonlinear Schr$\ddot{o}$dinger equation(NLSE) in erbium-doped fiber(EDF) was obtained. The cross-phase modulation (XPM) in the erbium-doped fiber amplifiers (EDFA) was studied based on this NLSE and the rate equations. A more generalized form of the propagation equation in EDFA was obtained which included the phase shifts the EDFA induced. An analytical expression was given to the XPM in the EDFA. It was found that the XPM in the EDFA dose not change very much with the wavelength except at the neighboring wavelengths (around 1531 nm) where the absorption and emission cross-sections of the erbium ions reach their maxima, and the XPMs have opposite signs on the two sides around 1531 nm. Furthermore, it was found that the XPM increases with the increase of the length of EDF.     

A model to characterize the effect of cross phase modulation on polarization in an optical fiber transmission system

This paper presents a model that described the process of inter-influence between cross phase modulation (XPM) and polarization effects such as polarization mode dispersion (PMD) and polarization dependant loss (PDL) in an optical fiber communication system. Previous papers have discussed PMD-PDL and PMD-XPM effects in separate models, but in this work we developed a model that is capable of characterizing and evaluating PMD, PDL and XPM simultaneously. From the model, we found that PMD and PDL can be affected by XPM. The presence of XPM changed the vector directions of PMD and PDL in Stokes space.     

利用锁模光纤激光器在色散位移光纤中产生超连续谱的研究

采用主动锁模光纤激光器输出的重复频率10GHz、脉宽7．97ps的脉冲作为抽运光源,无需压缩后直接抽运4．2km的普通色散位移光纤(DSF)．利用色散位移光纤中自相位调制、交叉相位调制等非线性效应的联合作用,获得了20dB带宽达125nm、覆盖整个C波段、L波段和部分S波段的超连续(SC)谱。实验研究了抽运光脉冲峰值功率和抽运波长对超连续谱宽度的影响,结果表明抽运光脉冲峰值功率越高,得到的超连续谱的带宽越宽;通过对抽运波长的优化,可以实现最大程度的超连续展宽;分析了滤波器带宽对脉冲质量的影响;利用0．4nm带宽的可调谐滤波器对从超连续谱中滤出脉冲的特性进行了研究,在超连续谱的不同波长处获得了脉宽为8．90～9．80ps、时间一带宽积为0．44～0．49的稳定的窄光脉冲。     

Electronic properties of intersubband transition in (CdS/ZnSe)/BeTe quantum wells

In view of the fact that the bandwidth required in optical fiber communication systems will exceed 100 Gb s^-1, ultrafast optical switching and modulation devices with high efficiency must be developed. Given that intersubband transitions (ISBT) in quantum wells (QWs) are one of the important ultrafast phenomena, a numerical study of intersubband transition (ISBT) properties in (CdS/ZnSe)/BeTe QWs is considered. The structure modeled consists of a few monolayers of CdS embedded in a ZnSe/BeTe QW. A self-consistent analysis is made to achieve the desired properties and device applications. Variation of CdS well thickness leads to tailoring of the band alignment, achieving optical transitions in the wavelength range of 1.33–1.55 μm wavelengths for applications in optical fiber transmission. To analyze the optical behavior of the heterostructure under investigation, we have calculated the CdS well thickness-dependant oscillator strengths and electron emission energy of the intersubband transition between the two first states in the well. An attempt to explain our results will be presented.     

高速太赫兹探测器

太赫兹(terahertz,THz)技术在高速空间通信、外差探测、生物医学、无损检测和国家安全等领域具有广阔的应用前景.能响应1 GHz调制速率以上THz光的高速THz探测器是快速成像、THz高速空间通信、超快光谱学应用技术和THz外差探测等领域的核心器件.传统的THz热探测器难以实现高速工作,而基于半导体的THz探测器在理论上可实现高速工作.光导天线具有超快的响应速度,可实现常温和宽谱探测;肖特基势垒二极管混频器、超导-绝缘体-超导混频器和超导热电子混频器具有转换效率高、噪声低等优点,可用于高速THz空间外差和直接探测;基于高迁移率二维电子气的天线耦合场效应晶体管灵敏度高、阻抗低,可实现常温高速THz探测;THz量子阱探测器是一种基于子带间跃迁原理的单极器件,非常适合高频和高速探测应用,亚波长金属微腔耦合机理可显著提高器件的工作温度及光子吸收效率.本文对上述几种高速THz探测器进行了综述并分析了各种探测器的优缺点.     

All-optical NRZ-to-RZ format conversion with dual channel wavelength multicasting functions exploiting cross-phase modulation in a dispersion-flattened nonlinear photonic crystal fiber

All-optical single-to-dual channel format conversion from NRZ to RZ at 10 Gbit/s using cross phase modulation (XPM) in dispersion flattened highly nonlinear photonic crystal fiber (DF-HNL-PCF) is demonstrated. Format conversion with dual channels signal multicasting function is achieved by filtering simultaneously the blue- and red-chirped components of broadened optical spectrum induced by XPM between NRZ signal and clock light. Moreover, the wavelength tunability and dynamics characteristics of proposed format converter are also exploited experimentally by using NRZ signal light with different central wavelength and varying input power. Our results show that a wide wavelength operation range of 21.2 nm, extinction ratio (ER) and Q factor of over 10.9 dB and 6.1 are obtained. Furthermore, the influence of central wavelength offset of optical bandpass filter on converted RZ signal quality is investigated. The proposed scheme is simple, robust, and transparent to bit rate, which makes it very potential for application in future photonic networks.     

Study on the dynamic range of input power for wavelength converter based on cross-phase modulation in SOAs

In this paper, the dynamic range of input power for wavelength converter based on cross-phase modulation (XPM) in semiconductor optical amplifier (SOA) is studied. The dynamic range of input power is associated with the linewidth enhancement factor , which is influenced by optical wavelength and power. Shorter wavelength and larger power can induce smaller and lead to a larger dynamic range, while the gain modulation is more severe. Through dynamically controlling the current of the phase arm of the XPM wavelength converter by the detection of the input signal power level, the dynamic range of input power can be increased from 2 to 17 dB.     

Theoretical investigation of the input power dynamic range enhancement of XPM wavelength converter using a CW holding beam

The performance of pre-amplified cross-phase modulation (XPM) wavelength converter with a continuous wave (CW) holding beam has been theoretically investigated. To increase the input power dynamic range of the pre-amplified XPM wavelength converter, we apply a CW holding beam to the pre-amplifier of XPM wavelength converter. In our proposed scheme, the input power dynamic range with negative power penalty of 20dB was obtained.