通信波长频率一致纠缠光源的频谱测量

本文利用光栅单色仪实现了对超短脉冲抽运周期极化磷酸氧钛钾晶体产生的通信波长频率一致纠缠光子源的频谱特性分析.测量到双光子的联合频谱呈正关联分布,为频率一致纠缠光源.信号光、闲置光中心波长分别为1574.4 nm和1574.9 nm,频谱宽度分别为35.3 nm和37.6 nm,双光子符合包络宽度约为3 nm.根据单光子频谱宽度与双光子符合包络宽度的比值可以得到双光子的频率纠缠参量R约为12,表征了信号光子与闲置光子之间具有较高的频率纠缠度.     

Saturation of biphoton generation near atomic resonance

We have numerically investigated the biphoton generation rate as a function of several parameters in the spontaneous four-wave mixing in cold atoms.It has been found that the biphoton generation rate can easily reach saturation with the intensity of the coupling laser increasing.The saturation intensity is mainly dependent on the dephasing rate of the ground states,unrelated to the pumping laser.It implies that though the biphoton waveform can be manipulated by the coupling laser,the generation rate of the biphoton cannot increase markedly after the saturation.The saturation effect also suggests that there is an optimal coupling laser for obtaining the largest biphoton generation rate with a sufficiently long coherence time.     

Quantum entanglement of Fock states with perfectly efficient ultraslow single-probe photon four-wave mixing

We propose a method to achieve quantum entanglement of two Fock states with perfectly efficient, ultraslow propagation enhanced four-wave mixing. A cold atomic medium is illuminated with a two-mode cw control laser to produce coherent mixtures of excited states. An ultraslowly propagating, single-photon quantum probe field completes the four-wave mixing with 100% photon flux conversion efficiency, creating a depth dependent entanglement of two Fock states. We show that at a suitable propagation distance, a maximum entangled state is created with a single-photon wave-packet state that has 50% probability of being in each of two product-type Fock states.     

Pump-depleting four-wave mixing in supercontinuum-generating microstructure fibers

Four-wave mixing processes are shown to provide a high efficiency of non-linear optical frequency conversion and spectral transformation of ultrashort pulses in supercontinuum-generating microstructure fibers. Pump-depleting conversion of 800-nm radiation to the spectral range around 500 nm is achieved by phase-matching the parametric four-wave mixing process for 80-fs Ti:sapphire-laser pulses. The ways to use microstructure fibers for generating frequency-tunable radiation through four-wave mixing with the maximum efficiency of pump-field frequency conversion are discussed. PACS 42.65.Wi; 42.81.Qb     

飞秒激光脉冲在三能级有机分子介质中传播时的频谱分析

通过采用预估校正的时域有限差分法求解麦克斯韦-布洛赫方程,我们研究了飞秒激光脉冲在三能级有机分子(4,4-二甲氨基二苯乙烯分子)介质中传播时脉冲的频谱演化情况.在单光子共振情况下,即入射脉冲频率等于1、2能级之间的共振频率,对大面积入射脉冲,由于强的二次激发的作用,电场频谱中出现了在ω32附近振荡的频率成分,ω32是2、3能级之间的共振频率,说明对大面积入射脉冲二能级模型已经失效,需要采用多能级模型来描述分子介质.在双光子共振情况下,即入射脉冲频率等于1、3能级之间的共振频率的一半,由于介质中放大的自发辐射和四波混频的作用,部分入射脉冲能量转化为高频和低频电场成分的能量,分子介质表现出了很强的光功率限幅特性.     

阿秒和频相位共轭极化拍频的不对称色锁二阶相干控制

研究了级联三能级系统中孪生色锁随机光场的相位共轭阿秒和频极化拍频(ASPB)不对称新效应。从理论上分析了自关联单光子简并四波混频(DFWM)和双光子非简并四波混频(NDFWM)信号辐射场与物质间不对等效应、混合型太赫兹失谐振荡特性,及双光子非简并共振四波混频信号的延时不对称性;同时也分析了由干涉计两臂不平衡色散效应引起的阿秒和频极化拍频信号的延时不对称性,即阿秒和频极化拍频信号的最大值相对于零延时有一个小偏移,结果表明该不对称性并这不影响阿秒和频极化拍频零差探测两偶极禁戒跃迁能级分裂的总体精度。阿秒和频极化拍频作为一种消除多普勒增宽的超快调制过程,从理论上说它可以扩展到任何两偶极禁戒跃迁能级系统。     

基于半导体光放大器四波混频原理的光采样

建立了可研究强超短光脉冲放大特性且包含自由载流子吸收、受激辐射、双光子吸收、光谱烧孔和超快非线性折射效应的半导体光放大器理论模型,用以建立脉冲四波混频模型,并进一步仿真了基于半导体光放大器的光采样过程,重点讨论了自由载流子吸收、双光子吸收效应对采样特性的影响。仿真结果与实验结果相符。     

Manipulation of supercontinuum generation by stimulated cascaded four-wave mixing in tapered fibers

Tailoring supercontinuum generation is important for a number of applications. Stimulated four-wave mixing in tapered optical fibers can lead to modified initial conditions for the evolution of supercontinua. We experimentally show that synchronizing a pump pulse with an additional signal pulse induces cascaded four-wave mixing components. The spectral evolution and the interaction with the pump wavelength are investigated in detail upon increasing pump power. Furthermore it will be shown that four-wave mixing components provide the initiation for an altered shape of the spectral fiber output when soliton dynamics are involved. We finally demonstrate the altered evolution in a synchronized feedback configuration. This work can lead to a control over specific spectral components of supercontinua. PACS  42.81.-i; 42.25.Kb     

High speed optical path routing by using four-wave mixing and a wavelength router with fiber gratings and optical circulators

A novel all-optical-path-routing technique is described, which employs four-wave mixing in a dispersion-shifted fiber and a wavelength router with fiber gratings and optical circulators. The signal wavelength is converted to a specified channel by four-wave mixing, and is finally selected with the wavelength router. It offers good potential for enabling the number of output ports of a wavelength router to be extended as it provides a very sharp spectral edge and a low insertion loss.     

基于光纤中四波混频效应的全光串-并转换研究

 为了实现高速信号的降速处理,设计并通过实验演示了一种高速全光串-并转换系统。在方案中,利用时钟脉冲自身的频谱宽度和光纤中四波混频的高速响应特性,可以从一个光分频时钟脉冲出发,利用光纤中群速度色散（GVD）致脉冲展宽效应,把一个重复频率为10 GHz的时钟窄脉冲在时域上展宽,并通过光纤中的四波混频过程,将一路40 Gb/s 的归零（RZ）码信号转换成为4路10 Gb/s信号,完成串-并转换功能。该方案响应速率高,对波长和码率透明,并具有很大的转换路数可拓展性。     

Four-wave mixing and biphoton generation in a two-level system

We find that in a two-level system there are two kinds of four-wave mixing processes which destructively contribute to the third-order nonlinear susceptibility. In a paired-photon generation scheme by using a single retroreflected pump beam, these two processes occur with definite time orders. The biphoton temporal correlation, which is measured with a back-to-back geometry in a laser-cooled two-level atomic ensemble, shows a damped Rabi oscillation and photon antibunching. Without suppressing the background of Rayleigh scattering, the upper limit of Cauchy criteria is estimated.     

Propagation characteristics of biphotons in cold atomic vapor

We investigate the propagation characteristics of the narrowband Stokes/anti-Stokes photons in cold atomic vapor. The four-wave mixing process results from parametric amplification of the anti-Stokes photons. We find that the process of parametric amplification is very similar to the light pulse propagating through an anomalous dispersion gain medium. Finally, we obtain the general solutions of the Glauber biphoton correlation functions, which are in good agreement with the experiment results.     

Coherent optical spectroscopy of promising materials for solid-state optical processors

State of the art of optical coherent spectroscopy of doped solids that are promising as information carriers for optical processors is reviewed. Special attention is paid to optical echo spectroscopy of doped crystals classified as the Van-Vleck paramagnets where the long-lived stimulated echo is observed with the optical-memory time reaching several hours at low temperatures. Modern elaborations of optical echo processors based on this echo phenomenon are discussed. Physical principles of femtosecond echo spectroscopy and coherent four-wave mixing spectroscopy are formulated. The abilities of these methods in the diagnostics of fast processes at room temperature are illustrated using examples of a doped polymer films. The results of elaborations of a new branch of optical spectroscopy (biphoton spectroscopy) are also presented. The advantages and possible applications of this method are demonstrated using an example of two crystals (Er³⁺:YAG and Cr³⁺:Al₂O₃).     

Four-wave mixing of linear waves and solitons in fibers with higher-order dispersion

We derive phase-matching conditions for four-wave mixing between solitons and linear waves in optical fibers with arbitrary dispersion and demonstrate resonant excitation of new spectral components via this process.     

Experimental characterization of semiconductor optical amplifiers used as frequency converters by means of four-wave mixing

In this article we report extended measurements of four-wave mixing in bulk-semiconductor amplifiers using continuous wave sources. We demonstrate that four-wave mixing in semiconductor amplifiers permits realizing in the practice frequency conversion in the spectral range of utility for optical telecommunications. Efficiency larger than 1 have been demonstrated up to 1 THz with a low level of background noise. In addition, this technique has allowed us to investigate the carrier dynamics down to an equivalent time resolution of the order of few tens of femtoseconds.     

Demonstration of phase correlation in multiwavelength mode-locked semiconductor diode lasers

Wideband spectral phase correlation is demonstrated from a multiwavelength mode-locked semiconductor laser. By use of frequency-resolved optical gating techniques, significant phase correlation was observed between multiple intracavity oscillating wavelengths, with wavelength separations of ~1 nm . The resultant temporal characteristics show a substantial modulation owing to the spectral coupling induced by intracavity-generated four-wave mixing. This result may lead to novel methods for directly generating ultrafast subpicosecond optical pulse sequences with spectrally tailored amplitude and phase characteristics from actively mode-locked semiconductor lasers.     

Tunable single-longitudinal-mode SOA-based fiber laser based on the spectral narrowing effect in a dispersion-shifted fiber

A tunable single-longitudinal-mode(SLM) semiconductor optical amplifier(SOA)-based fiber laser based on a dispersion-shifted fiber(DSF) is proposed and successfully demonstrated. SLM operation is obtained due to the spectral narrowing effect resulting from inverse four-wave mixing in a DSF. A tunable optical filter performs wavelength selection function. By inserting a length of DSF in the laser cavity, SLM lasing can possibly be obtained when laser oscillation is stably established after traveling through the DSF many roundtrips. Stable tunable SLM oscillation with a signal-to-noise ratio as high as 65 dB over a wavelength range of about 35 nm is achieved experimentally, and each spectral linewidth is less than 6.5 kHz.     

在远离光子晶体光纤零色散波长的正常色散区入射飞秒脉冲产生四波混频及孤子效应的实验研究

在远离光子晶体光纤零色散波长的正常色散区入射飞秒脉冲,实验产生了一对由四波混频引起的信号波带和闲频波带,及一对由脉冲内拉曼散射和非孤子辐射引起的孤子和色散波带,并观察到功率饱和现象.利用有限元法理论模拟了光纤的色散和非线性特性,用四波混频的相位匹配条件模拟了光纤在满足相位匹配条件下所产生的信号波带和闲频波带出现的可能位置,并与实验结果符合得很好.结果表明:即使在光子晶体光纤的正常色散区抽运激光脉冲亦可以产生四波混频和孤子效应;研究发现四波混频的产生是由四阶色散参量引起的;并进一步从理论上解释了孤子及色散波的产生原因.     

Experimental Study of Four-Wave Mixing in Semiconductor Laser Amplifier and its Application to Dispersion Compensation in Mid-Span Spectral Inversion System

Properties of four-wave mixing (FWM) in the semiconductor laser amplifier are studied experimentally in this paper. The optical phase conjugation of the mixing wave is applied to compensate the chromatic dispersion of transmission fiber. It is presented experimental results of the transmission of short optical pulses with 12-ps width over 204 km standard single mode fiber. The results confirm that mid-span spectral inversion (MSSI) employing FWM in a semiconductor laser amplifier is one of potential dispersion compensation techniques for optical transmission over standard single mode fiber with bit rate beyond 40Gb/s.