Wavelength-spacing tunable multi-wavelength fiber optical parametric oscillator based on multiple four-wave mixing

We propose a wavelength-spacing tunable multi-wavelength fiber optical parametric oscillator (MW-FOPO) with a simple line cavity and one pump source based on multiple four-wave mixing (MFWM). Stable multi-wavelength lasing at room temperature is achieved due to the four-wave mixing effect and the broadband gain of the fiber optical parametric amplifier based on a highly nonlinear fiber. The wavelength spacing of the proposed MW-FOPO can be tuned by adjusting the wavelength of the pump light or the central wavelength of the fiber Bragg grating. Seventeen lasing lines with a wavelength spacing of 2.89 nm and an extinction ratio larger than 10 dB, which covers the wavelength region from 1540 to 1568 nm is demonstrated.     

光子晶体光纤四波混频光谱中相位匹配特性的研究

与传统光纤不同,光子晶体光纤可以具有多个零色散波长,在四波混频光谱中,具有更丰富的相位匹配特性。目前很多文献报道了光子晶体光纤非线性光学特性的实验结果,但对其产生机理及光谱的变化规律缺乏详细的理论分析。为此对光纤中四波混频原理进行了分析,给出了高增益的相位匹配条件。利用多极法计算了光子晶体光纤的非线性系数及色散特性。对具有多个零色散波长光子晶体光纤的相位失配特性进行了分析,得到了相位匹配波长随泵浦波长及泵浦功率的变化规律。给出了相位匹配曲线,分析了不同色散曲线的相位匹配波长特点,两个零色散波长光子晶体光纤,在四波混频光谱中将激发出四个新的波长。实验得到了两个零色散波长光子晶体光纤的四波混频光谱,与理论分析一致,验证了相位匹配理论的可靠性。多个零色散波长光纤,能产生丰富的相位匹配曲线,会出现更多的四波混频波长,可以有效的控制光孤子及超短脉冲的四波混频及共振散射产生的光谱特性。为光子晶体光纤中基于四波混频的波长变换及超连续谱的研究提供了理论指导。     

在单零色散微结构光纤中一次抽运同时发生两组四波混频的实验观察

采用可以减小纤芯面积的小气孔设计方案巧妙设计并成功拉制了一根高非线性的单零色散微结构光纤.利用有限元法模拟并计算得到了该光纤的基模有效折射率、色散系数和非线性系数等基本属性随波长的变化关系,然后利用四波混频的有效相位失配方程模拟了其相位失配曲线.模拟表明,在该光纤中可以同时发生两组四波混频.在位于微结构光纤的正常色散区的0.800,0.810和0.820μm三个波长处,分别采用不同的功率抽运,在实验上都非常明显地观察到了分列于抽运波长两侧的四个增益波带的产生.经与相位失配曲线比较,发现它们满足相位匹配条件,从而证明了两组四波混频过程的同时发生.实验结果与理论预言符合得很好.发生在正常色散区的四波混频效应的产生可归结于负的四阶色散对相位匹配过程的贡献.本文研究可对微结构光纤的结构设计和基于四波混频的多波长转移技术的发展提供经验与借鉴,同时也对非常见波段激光器和宽带光源的开发具有参考意义.     

利用交叉相位调制和四波混频制作的时间透镜的仿真分析

利用高非线性光纤中的交叉相位调制和四波混频分别在仿真中实现了时间透镜. 对基于交叉相位调制的时间透镜中的高非线性光纤中的非线性过程进行了仿真分析. 仿真结果表明, 该时间透镜的主要影响因素为色散、自相位调制与四波混频; 通过采用带有一定色散斜率的高非线性光纤可同时消除色散、自相位调制和四波混频的影响; 另外, 该高非线性光纤的色散零点最好选在信号脉冲和抽运脉冲波长的中心附近. 然后对基于四波混频的时间透镜的实现进行了仿真分析. 仿真结果表明, 该时间透镜的主要影响因素为色散、 自相位调制和其他的四波混频; 通过设定合适大小的信号脉冲和抽运脉冲的功率可消除自相位调制和其他的四波混频的影响; 另外, 通过在高非线性光纤中引入一定的色散可进一步提高信号脉冲和抽运脉冲的功率, 从而获得更高功率的输出脉冲. 最后对两种时间透镜系统做出了比较. 关键词： 光脉冲压缩 时间透镜 交叉相位调制 四波混频     

Nonlinear fiber-optic strain sensor based on four-wave mixing in microstructured optical fiber

We demonstrate a nonlinear fiber-optic strain sensor, which uses the shifts of four-wave mixing Stokes and anti-Stokes peaks caused by the strain-induced changes in the structure and refractive index of a microstructured optical fiber. The sensor thus uses the inherent nonlinearity of the fiber and does not require any advanced postprocessing of the fiber. Strain sensitivity of -0.23 pm/με is achieved experimentally and numerical simulations reveal that for the present fiber the sensitivity can be increased to -4.46 pm/με by optimizing the pump wavelength and power.     

色散位移光纤中零色散波长纵向分布对四波混频转换效率的影响

研究了色散位移光纤零色散区域附近的四波混频特性 ,讨论了当零色散波长彼此不同的多段光纤连接起来后对四波混频效率的影响。理论计算结果表明 ,在信号光和抽运光波长间隔较小的区域 ,各光纤对四波混频过程都有贡献 ,且互相调制 ,并出现增益现象 ,有着很复杂的效率图。     

Self-induced phase matching in stimulated four-wave mixing in a nonbirefringent single-mode optical fiber

Self-induced phase matching in stimulated four-wave mixing in a nonbirefringent single-mode optical fiber has been observed. It is shown that in a nonbirefringent single-mode fiber the phase matching that is necessary for stimulated four-wave mixing can be accomplished with a combination of self-phase modulation and cross-phase modulation induced by a pump-laser pulse.     

Retrieval of the zero-dispersion wavelength map of an optical fiber from measurement of its continuous-wave four-wave mixing efficiency

We present a novel algorithm for reconstruction of the longitudinal distribution of zero-dispersion wavelength in an optical fiber from low power, end-to-end measurements of four-wave mixing efficiency. It is based on a modified version of the error-reduction approach used in classic phase-retrieval problems. Experimental results demonstrate the validity of this algorithm.     

Reducing polarization sensitivity for all-optical wavelength conversion of the optical packets based on FWM in the HNL-DSF using co-polarized pump scheme

Polarization insensitivity is a fundamental requirement for wavelength conversion technique in the future all-optical networks. Our experimental results show that a co-polarization pump configuration based on four-wave mixing in high-nonlinear fiber can reduce largely the polarization sensitivity. We have theoretically investigated those experimental phenomena, and the theoretical analyses are in good agreement with experimental results.     

基于光纤四波混频波长转换和色散的慢光实验研究

对基于光纤四波混频（FWM）波长转换和色散的慢光实现进行了详细和系统的实验研究.首先,实验测定了高非线性光纤中FWM带宽约为40 nm,从而确定了慢光的可调谐带宽;接着,在普通单模光纤和色散补偿光纤（DCF）中针对500 MHz正弦信号和100 ps短脉冲信号分别实现了34和198 ns的脉冲延迟,在DCF中还实现了209 ns的脉冲提前.讨论了增大延迟量的方法,指出随着宽带FWM波长转换的实现和大色散光纤的应用有望获得微秒量级的大延迟量,从而为高性能光纤延迟线和全光缓存器等应用提供支持. 关键词： 慢光 四波混频 色散     

Observation of twin-beam-type quantum correlation in optical fiber

We report generation of pulsed twin beams of light through optical parametric amplification in a fiber Sagnac loop. By pumping the Sagnac loop with picosecond pulses at a wavelength near the zero-dispersion wavelength of the fiber, we achieve phase-matched nondegenerate four-wave mixing with gain. For a gain of 2.2, the intensity noises of the amplified signal and the generated idler (conjugate) pulses are found to be correlated by 5.0 dB, and the subtracted noise drops below the shot-noise limit by 1.1 dB (2.6 dB when corrected for losses). We have investigated the gain dependence of the quantum-noise reduction as well as of the intensity noises of the amplified signal and idler pulses. As the gain increases, we observe the onset of excess noise on the idler pulses.     

Spacing-tunable multi-wavelength fiber laser based on cascaded four-wave mixing in highly nonlinear photonic-crystal fiber

A multi-wavelength fiber laser based on the cascaded four-wave mixing in highly-nonlinear photonic-crystal fiber is proposed and investigated. The cascade operation is initiated by two strong pump waves boosted by multi-mode pumping erbium/ytterbium co-doped double-cladding fiber amplification technique. A segment of highly-nonlinear near-zero-dispersion-flattened photonic crystal fiber is employed to induce highly efficient cascaded four-wave mixing. The wavelength spacing can be continuously tunable by stretching the fiber Bragg grating. Experimental results show that multiple wavelengths with a high optical side-mode suppression-ratio of >30 dB are achieved. Furthermore, the proposed multi-wavelength fiber laser exhibits an excellent stability at room temperature.     

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.     

Evolution of first-order sidebands from multiple FWM processes in HiBi optical fibers

The generation of two idler waves inside a high birefringent (HiBi) optical fiber through three four-wave mixing (FWM) processes is studied theoretically. The coupled-equations for the field amplitudes are derived and analytically solved, in the co-polarized and orthogonal polarization schemes. The obtained solutions take into account the delayed Raman response of the medium. The polarization sensitivity of the generation of the idler waves is analyzed. Results show that the stimulated Raman scattering does not change the efficiency of the idler wave generation in the co-polarized scheme, whereas in the orthogonal polarization scheme that nonlinear process decreases the efficiency of the four-wave mixing processes. Results also show that this set of multiple four-wave mixing processes is physically quite different from the typical single or dual pump four-wave mixing configurations. Findings show that the power transfer from the pumps to the idler fields can lead to a monotonous growth, or a periodic evolution of the sidebands along the fiber. Results show that the process efficiency varies greatly with the angle between the two pump polarizations.     

Broadband cascaded four-wave mixing by using a three-pump technique in optical fibers

We present an optimized technique to generate frequency combs by four-wave mixing in highly nonlinear low-dispersion fibers. Three-pumps with unequally spaced frequencies (separation of 100 and 200 GHz) were used. The pumps were located relatively close to the zero-dispersion wavelength of the fiber. Using this three-pump technique we obtained a total of 275 FWM products experimentally, with a 100 GHz spacing and a spanning of over 220 nm.     

高非线性光子晶体光纤中飞秒脉冲的传输特性和超连续谱产生机制的实验研究及模拟分析

用实验和数值模拟两种方法研究了高非线性光子晶体光纤中飞秒激光脉冲的传输特性和超连续谱的产生机理，给出了抽运脉冲在三种不同中心波长情况下输出光谱展宽并形成超连续谱的实际测量及理论模拟结果.研究表明：在零色散波长抽运时，光谱展宽以自相位调制为主，同时三阶色散的影响明显，传输脉冲在时域内出现振荡次峰.而在反常色散区抽运时，光谱展宽的初期以自相位调制为主，随后根据抽运功率的不同孤子自频移、高阶光孤子的裂变和四波混频效应会逐渐增强，进而成为光谱展宽的主要原因.与此相应，在时域中能明显看到孤子的形成和红移，飞秒传输脉 关键词： 光子晶体光纤 高非线性光子晶体光纤 飞秒脉冲激光 超连续谱     

Numerical simulation of four-wave mixing efficiency and its induced relative intensity noise

Four-wave mixing,as well as its induced intensity noise,is harmful to wavelength division multiplexing systems.The efficiency and the relative intensity noise of four-wave mixing are numerically simulated for the two-wave and the three-wave fiber transmissions.It is found that the efficiency decreases with the increase of both the frequency spacing and the fiber length,which can be explained using the quasi-phase-matching condition.Furthermore,the relative intensity noise decreases with the increase of frequency spacing,while it increases with the increase of fiber length,which is due to the considerable power loss of the pump light.This investigation presents a good reference for the practical application of wavelength division multiplexing systems.     

Toward visible cw-pumped supercontinua

We report a 1 mum cw-pumped supercontinuum that extends short of the pump wavelength to 0.65 mum. This is achieved by using a 50 W Yb fiber laser in combination with a photonic crystal fiber with a carefully engineered zero-dispersion wavelength. We show that the short-wavelength generation is due to a combination of four-wave mixing and dispersive wave trapping by solitons. The evolution and limiting factors of the continuum are discussed.     

基于光子晶体光纤四波混频效应的波长转换研究

研究了光子晶体光纤中的四波混频效应及其波长转换.采用长度为25 m的高非线性色散平坦光子晶体光纤,当泵浦功率为19.8 dBm时,得到100 nm的转换带宽和－20 dB的最大转换效率.实验结果表明,当信号功率低于四波混频阈值时,两路不同波长的信号同时输入产生的四波混频效应互不影响.     

Four-wave mixing in dual wavelength fiber laser utilizing SOA for wavelength conversion

In this paper, a novel configuration of a wavelength converter is set forth by utilizing a semiconductor optical amplifier (SOA) as a nonlinear gain medium to generate a four-wave mixing (FWM) effect by using a dual wavelength bi-erbium-doped fiber laser that uses an Arrayed Waveguide Grating (AWG) together with two optical channel selector (OSC) as selective elements to function as a dual wavelength switchable pump power. The four-wave mixing (FWM) is produced with a wavelength detuning of 7 nm from the pump and signal which used is as the converted signal at wavelength 1532.8 nm or 1534.5 nm for transferring data from the input signal at wavelength 1547.0 nm. Thus, even though the conversion efficiency is as low as −43 dB, it is still possible for applications as a wavelength converter.