Character analysis of slow light with communication waveband in fiber optical parametric amplifier

The comprehensive characters of delay time and delay bandwidth with distortion, signal wavelength dependence and delay bandwidth product in fiber optical parametric amplifier are investigated theoretically when the pump locates at anomalous dispersion region. The delay character of single pulse, data stream with certain bit pattern and pseudo random data stream are analyzed comprehensively. In this category of fiber optical parametric amplifier, the delay time and delay bandwidth product vary from signal wavelengths and bit rates. For the same nonlinear coefficient, pump power and fiber length, the diverse dependences of bit pattern in different signal wavelengths are found by numerical simulation. The impacts of pump power and fiber length on the delay character and distortion are also discussed. These relations are conductive to the design of slow light based on fiber optical parametric amplifier in telecommunication waveband.     

光纤参量放大增益谱边带快慢光特性研究

针对窄带光纤参量放大(FOPA),区别于以往增益谱的大增益斜率区域,研究了FOPA增益谱边带脉冲信号的快慢光特性.首先从理论上推导出了小信号增益条件下信号延时量的解析表达式;其次,在低抽运功率条件下(1 W),实验研究了10 Gb/s伪随机二进制序列脉冲信号在FOPA增益谱边带的延时特性,实验结果与理论计算基本符合;最后,通过分析研究抽运光功率、光纤色散及非线性系数等参数对信号延时量的影响规律,可以为FOPA增益谱边带的快慢光延迟线的设计提供参考.     

Theoretical study of gain distortions in dual-pump fiber optical parametric amplifiers

We study analytically and numerically the small signal gain in dual-pump fiber optical parametric amplifiers by including the phase modulation of the pump waves needed for practically increasing the stimulated Brillouin scattering threshold. As for the single-pump case, we show that large signal gain distortions are generated under co-phase modulation, which depend on the rise/fall time of the phase modulation and on the fiber dispersion slope. However, it is clearly confirmed that the counter-phase modulation scheme allows to efficiently suppress these gain distortions over the whole flat gain region. In addition, we demonstrate through realistic numerical simulations that this useful technique overcomes the additional impact of pump-phase modulation to amplitude modulation conversion and zero-dispersion wavelength variations.     

Slow and fast light based on SBS with the spectrum tailoring

In this paper, slow and fast light of a signal pulse of nanosecond duration are achieved in the same experimental device by using band-pass filters to tailor the spectra of spontaneous Brillouin scattering (SPBS) coming from 50 km single-mode optical fibers (SMF) as the pump light. The phase matching condition of slow and fast light is satisfied by changing wavelengths of band-pass filters .In our experiment, we obtain the tunable delay time for various signal pulses range from 1 ns to 20 ns. By increasing the power of the pump field to 16 mW, a 1 ns signal pulse is delayed 1.5 ns and is advanced 1.0 ns respectively, while the signal pulse almost has no distortion. The experiment has demonstrated that larger relative pulse delay of slow and fast light can be obtained in the same experimental setup when pump power is lower.     

室温掺铒光纤放大器中实现参量控制无损耗光速减慢传输

本文对掺铒光纤放大器中的光速减慢传输系统进行深入研究,提出一种直接利用掺铒光纤放大器中抽运光 强度和掺铒光纤长度,通过优化控制参量来降低信号光强度损耗系数,从而可以实现无强度损耗光速减慢传输, 研究结果表明:当抽运光功率为3.5 mW时,信号光强度损耗系数近似为零;当抽运光关闭时,掺铒光纤长度为 0.1 m时,信号光强度损耗系数近似为零.     

A systematic analysis of hole size,hole-type and rows shifting on slow light characteristics of photonic crystal waveguides with ring-shaped holes

A photonic crystal waveguide embedded in silica is proposed and the effects of number of defect rows adjacent to the line-defect, number of rows shifted in transverse direction to the light propagation and the types of holes in these rows on slow light properties are investigated without changing the line-width by plane-wave expansion method. We observe that the structure with one row of ring-shaped holes exhibits better slow light properties than the structure with two and three innermost rows of ring-shaped holes when outer and inner radius of the holes are considered as free parameters. Shifting the second innermost rows of holes is found to be preferable than shifting the second innermost rows of rings. Besides, shifting the second and third innermost rows together does not make considerable enhancement on the slow light properties as shifting only the second innermost rows, no matter the shifting holes are ring-shaped holes or only holes.     

光斑的形状因子及其在光纤定解问题中的应用

通过比较面光源与多极子点源两种辐射场,定义了光斑的形状因子,它决定于光斑上的源强分布.给出了形状因子的确定方法,求出了几种常见光斑的形状因子.把形状因子应用于光纤理论,补充了入射端面上的定解条件,完整地设定了定解问题.利用形状因子简单讨论了光纤端面的源强分布对光纤模式特性的影响 关键词： 光纤光学 多极子面光源 形状因子     

Amplification of 12 × 10 Gb/s WDM signals with negligible FWM crosstalk in a double-pumped fiber optical parametric amplifier

We report on the amplification of 12 × 10 Gb/s wavelength-division-multiplexed signals by a double-pumped fiber optic parametric amplifier (2P-FOPA). A gain of 10 dB is obtained using a 4.3 km-long conventional dispersion shifted fiber (DSF) as nonlinear medium. Our spectra show negligible generation of spurious FWM products, and we attribute this to the small variations of the zero-dispersion wavelength of the DSF. The 2P-FOPA performance is assessed through Q-factor measurements, and we show that for output powers per channel ranging from −15 to 3 dBm the power penalty is less than 0.5 dB.     

Phase and amplitude control of the group velocity in a two-level system with shelving state

We study the propagation of two weak light pulses with the same temporal shape, symmetrically detuned from a stronger cw pump, in a two-level system which decays via a shelving state. We show that the group velocity of the weak pulses can be controlled, with small distortion, by modifying either the relative amplitude of the weak pulses or the total phase Φ. The changes in the local group velocity on propagation are due to pump absorption, and to changes in the total phase on propagation which occur for all cases apart from the case where the amplitudes of the weak fields are equal and or π. Slow light occurs when the initial total phase but not when ; when one pulse is less intense than the other, it experiences the greater slowing down, and the effect is greater than in the case of equal intensities.     

Numerical analysis of stimulated inelastic scatterings in ytterbium-doped double-clad fiber amplifier with multi-ns-duration and multi-hundred-kW peak-power output

We investigate the stimulated Brillouin scattering (SBS) and the stimulated Raman scattering (SRS) in an ytterbium-doped double-clad fiber amplifier that outputs optical pulses with multi-ns-duration and multi-hundred-kW peak-power. The ytterbium-doped double-clad fiber amplifier is simulated by a model which is composed of a set of propagation-rate equations. The simulated results show that SBS and SRS will deform the output signal pulse in both the time domain and the spectral domain, and degrade the performance of the ytterbium-doped double-clad fiber amplifier seriously. It is shown in our simulation that the troublesome SBS can be effectively suppressed by broadening the signal linewidth to a critical value of 0.07 nm in our calculation, and the effect of SRS can be suppressed using a large-mode-area fiber with proper length. The model and the simulated results are very useful for designing an ultra-high-power ytterbium-doped double-clad fiber amplifier.     

利用白光干涉谱测定云母片的快慢轴

白光照射到透明云母薄片时,后侧内表面产生的反射光与入射光会在云母片的前表面发生干涉.利用光谱仪可以观察到由于干涉而形成的条状光谱.改变入射光的偏振方向,可以观察到由于云母薄片双折射特性引起的干涉条纹的移动.根据条纹移动的方向,可以判定出云母片两正交的光轴方向上折射率的差异,从而判定出其快轴和慢轴.     

Gain optimization of an erbium-doped fiber amplifier and two-stage gain-flattened EDFA with 45 nm flat bandwidth in the L-band

An erbium-doped fiber amplifier (EDFA) is simulated. The variation of gain with different parameters is obtained and the values of these parameters are optimized to achieve a maximum value of gain. A two-stage gain-flattened EDFA consisting of two EDFAs in series is also simulated. In the operating range of 1565-1610 nm, the flat gain of 46 dB is obtained.