Noise Figure of Silicon Raman Amplifiers

The noise figure of silicon Raman amplifiers in the presence of nonlinear losses is calculated. The impact of two-photon absorption (TPA) and free-carrier scattering on the noise figure is quantified using the quantum formulation of the Langevin approach. It is found that TPA-induced free-carrier loss degrades the noise figure by an amount that depends on the carrier lifetime. For example, in a 1-cm-long waveguide pumped at 200 MW/cm², the noise figure is 5.2 dB for a lifetime of tau = 1.6 ns and is reduced to 3.7 dB for tau = 0.1 ns. The reduction in the noise figure along with a concomitant increase in Raman gain from 2 to 8 dB suggests that lifetimes on the order of 0.1 ns or less are needed to create a useful silicon Raman amplifier that operates in the continuous-wave mode. It is also shown that in devices that use a p-n junction for carrier sweep-out, the screening of the junction field by generated free carriers results in a sharp increase in the noise figure at high-pump intensities. These results apply to operation in the near-infrared communication wavelengths. For mid-infrared wavelengths above the two photon absorption band-edge (2.3 nm), the absence of TPA and pump-induced free-carrier absorption ensures that the amplifier has a low-noise figure.     

Cascaded silicon Raman lasers as mid-infrared sources

It is shown by numerical simulations that cascaded silicon Raman lasers, in which the pump light undergoes multiple Stokes shifts in a silicon waveguide, can efficiently convert near-IR to mid-IR radiation. For pump wavelengths significantly below 2 mum, two-photon-absorption-induced free-carrier absorption degrades conversion efficiency, and the effective carrier lifetime determines the shortest possible pump wavelength     

Experimental and theoretical analysis of efficient erbium-dopedfiber power amplifiers

The efficiency of Er³⁺-doped fiber power amplifiers (EDFAs) pumped at 980 nm was experimentally investigated and quantum conversion efficiencies (QCE) up to 0.89 were achieved. The experiment was accurately simulated by a computer model using only measured input parameters. The model was further used in an analysis of power amplifiers pumped at 980 and 1480 nm that included waveguide optimization and Er³⁺ confinement. The QCE can be enhanced by increasing the numerical aperture (NA) and confining the Er³⁺ ions to the central region of the core. At pump powers typically used for packaged EDFAs (25-100 mW). QCE can be improved by up to 60% by increasing the NA from 0.15 to 0.25, and confined Er³⁺ doping can provide an improvement of up to 20%. However, NA and Er³⁺ confinement have insignificant effects on the noise figure when both the cutoff wavelength and the fiber length are optimized with respect to QCE     

一种新的SOI波导拉曼激光器模型及其应用

通过考虑腔中的自发拉曼散射,提出一种新的绝缘体上硅(SOI)波导拉曼激光器物理模型。仿真结果表明该模型能较好地描述其小信号输出特性,实现对该类激光器的快速分析、设计与优化。利用模型对基于多种SOI波导的拉曼激光器进行分析,结果表明室温下只有采用拥有较大拉曼系数,较小线性损耗和较短的有效载流子寿命的SOI波导才能使拉曼激光器达到阈值。提出采用优化SOI波导截面几何尺寸的方法来降低有效载流子寿命,进而提高整体拉曼增益。结果显示该方法可大幅提高SOI波导拉曼激光器的输出功率和能量转换效率。     

Broad-band erbium-doped fiber amplifier with double-passconfiguration

We demonstrate a broad-band silica-based erbium-doped fiber amplifier (EDFA) with double-pass configuration. The signal gain and noise figure are obtained more than 24 dB and less than 6 dB, respectively, for 1526-1562 nm and 1569-1605 nm. The same signal gain can be achieved with 53% less pump power and 45% shorter erbium-doped fiber length, compared to a conventional parallel type EDFA. Furthermore, the noise figure and power conversion efficiency are improved for the wavelength range     

Influence of Pump-to-Signal RIN Transfer on Noise Figure in Silicon Raman Amplifiers

The effect of the relative intensity noise (RIN), transferred from the pump to the signal, in 1-cm-long chip scale silicon Raman amplifiers is investigated in the presence of nonlinear losses. We show that due to the short waveguide length, the reduction in fluctuations that normally occurs due to “walk-off” between pump and signal waves in fiber amplifiers is inefficient in chip scale Raman amplifiers. In the counterpropagating pump configuration, which leads to minimum frequency RIN transfer, fluctuations up to 1.5 GHz are transferred from the pump to the signal. As a case study, the noise figure degrades by as much as 11 dB in the silicon waveguide with the free carrier life time of 0.1 ns, when it is pumped with a laser with a RIN value of $-$125 dB/Hz.      

用于喇曼放大的SOI脊形波导中自由载流子寿命的解析表达

研究了用于喇曼放大的绝缘硅(SOI)脊形波导中自由载流子寿命与非线性光学损耗的关系.通过理论推导结合二维数值模拟的方法,提出了带有零反偏pin结构的SOI脊形波导中自由载流子寿命的解析表达式,该解析表达式与他人的实验结果相符.结果表明,比起不带pin结构的波导,带有零反偏pin结构的波导中的自由载流子寿命最多可以缩短80%.同时,研究了pin结构外加反偏电压时,自由载流子寿命进一步缩短的原因,并从强场下自由载流子速度饱和的角度出发,得到了自由载流子寿命的理论极限值.最后,模拟了不同自由载流子寿命情况下SOI脊形波导的喇曼净增益随着输入泵浦光功率密度的变化曲线,为硅基喇曼放大器的进一步研究指明了方向.     

Performance of a high concentration Er/sup 3+/-doped alumino silicate fiber amplifier

We report the gain, noise figure, output saturation power, and conversion efficiency of a highly concentrated Er/sup 3+/-doped alumino silicate fiber amplifier. We obtain a gain per unit length of 1.0 dB/cm, which corresponds to the highest gain per unit length obtained in an Er/sup 3+/-doped fiber amplifier. The pump power threshold ranges from 2 to 5 mW, depending on the fiber length.     

Gain and noise penalty for detuned 980 nm pumping or erbium-dopedfiber power amplifiers

The impact of altering the fiber length and pump wavelength on the gain and noise performance of erbium-doped fiber power amplifiers pumped in the 980-nm band is examined. A gain penalty of <0.5 dB was experimentally observed over an 18 nm pump wavelength range. Theoretical analysis indicates that increasing the numerical aperture (NA) from 0.15 to 0.25 significantly improves the tolerance for a given gain penalty but has little effect on the noise figure. For a given fiber length, the noise figure increases by 0.1 dB for each 3 nm the pump wavelength deviates from 979 nm     

同向抽运喇曼放大器功率转换效率的数值分析

为了对同向抽运光纤喇曼放大器的功率转换效率进行研究,由耦合方程出发,采用龙格-库塔算法的数值模拟方法,详细分析了所有物理因素对同向抽运光纤喇曼放大器功率转换效率的影响. 结果表明,功率转换效率先随着光纤长度的增加而增加,当增加到最大值时保持数值不变;并且功率转换效率也随着初始信号光功率、光纤喇曼增益系数、信号光损耗系数的增加而增加,但随着光纤有效面积、抽运光损耗系数、抽运光与信号光的频率比的增加而减小;功率转换效率和初始抽运光功率呈抛物线曲线关系. 这对同向抽运光纤喇曼放大器功率转换效率的进一步研究以及光纤喇曼放大器的相关研究有一定参考意义.     

L-波段级联结构掺Er光纤放大器的优化设计

在前级Er光纤（EDF）长度和抽运功率确定的前提下，通过改变后级抽运功率，对L波段级联结构掺Er光纤放大器（EDFA）的两级光纤长度的比例进行了优化研究。当前级的抽运功率和光纤长度分别为60mW和5．4m时，通过对后级参数进行优化，小信号增益达到了30．1634dB，同时噪声指数仅为4．078dB。与其它设计方案相比，该方案更具有实用性：首先，可以通过选择适当的后级抽运功率使级联放大器得到足够大的增益；其次，可以充分利用抽运光能量，从而提高抽运利用效率。     

交叉增益型波长转换器的参数优化

在考虑放大自发辐射消耗载流子的前提下 ,运用放大器的分段模型和传输矩阵方法 ,理论分析了交叉增益(XGM)型波长转换器应用于通信系统中的误码率特性。基于误码率特性的分析 ,对波长转换器中放大器有源腔长度和内部损耗、转换波长间隔、探测功率和平均抽运功率等参数进行了优化。     

Comparison of the static and dynamic properties of single- and double-pass partially gain-clamped two-stage L-band EDFAs

We investigate the static and dynamic properties of partially gain-clamped two-stage L-band erbium-doped fiber amplifiers (EDFAs) in single- and double-pass configurations. While both amplifiers can be designed to provide the same gain-clamped performance, the double-pass configuration requires /spl ap/40% less pump power and /spl ap/22% shorter length of EDF in the second stage, and has a corresponding improvement in power conversion efficiency of 45%, but at the expense of an increase in noise figure (/spl ap/0.5 dB) and dynamic gain variation.     

All-optical efficient wavelength conversion using silicon photonic wire waveguide

We demonstrate efficient wavelength conversion using a four-wave-mixing (FWM) effect in a silicon photonic wire waveguide with spot size converters. Applying a continuously operated 160-mW pump, power density in the waveguide's core was increased up to around 430 MW/cm/sup 2/, and the FWM effect was remarkably enhanced. Internal conversion efficiency obtained in an experiment was -10.6 dB. The efficiency was significantly limited by the free-carrier absorption effect.     

Analysis of gain characteristics of bi-directionally pumped praseodymium-doped fiber amplifiers

Signal gain and noise figure in a bi-directional pumping configuration are investigated in the unsaturated and saturated region. Balanced and asymmetric bi-directional pumping configurations are effective in the unsaturated and saturated region, respectively. Especially, an asymmetric bi-directional pumping configuration with larger backward pump power than forward pump power increases the pump to signal conversion efficiency in the saturated region. An asymmetric pumping configuration is effective in constructing booster amplifiers.     

Four-wave mixing in silicon-nanocrystal embedded high-index doped silica micro-ring resonator

A nonlinear integrated optical platform that allows the fabrication of waveguide circuits with different material composition,and at small dimensions,offers advantages in terms of field enhancement and increased interaction length,thereby facilitating the observation of nonlinear optics effects at a much lower power level.To enhance the nonlinearity of the conventional waveguide structure,in this work,we propose and demonstrate a microstructured waveguide where silicon rich layer is embedded in the core of the conventional waveguide in order to increase its nonlinearity.By embedding a 20 nm thin film of silicon nanocrystal(Si-nc),we achieve a twofold increase of the nonlinear parameter,γ.The linear relationship between the fourwave mixing conversion efficiency and pump power reveals the negligible nonlinear absorption and small dispersion in the micro-ring resonators.This simple approach of embedding an ultra-thin Si-nc layer into conventional high-index doped silica dramatically increases its nonlinear performance,and could potentially find applications in all-optical processing functions.     

Noise analysis of conventional and gain-clamped semiconductoroptical amplifiers

We present a numerical study of the noise of conventional and gain-clamped semiconductor optical amplifiers (SOAs), using a detailed device model. The model makes use of a density-matrix gain calculation, and takes into account the forward and backward amplified spontaneous emission (ASE) spectra and the spatial carrier hole-burning. The device is longitudinally divided into M sections and a rate equation for averaged photon and carrier densities is used for each section. We demonstrate that the accuracy on the calculated noise figure strictly depends on the number of sections M. We obtain a good tradeoff between the results accuracy and the computational complexity with M=8. The model is then applied to study the noise in a distributed Bragg reflector (DBR)-type gain-clamped SOA for varying signal power, pump current, and lasing wavelength. We show that changes in the spatial carrier profile caused by the input signal significantly affect the noise figure, even when the gain is constant. A slight dependence of the noise figure on lasing wavelength is also foreseen, while the dependence on the pump current is negligible. A new method for gain-clamped SOA noise figure reduction is proposed, based on unbalanced Bragg reflectors. An improvement of noise figure (NF) as large as 2 dB is devised     

超短强激光作用下的CsLiB6O10晶体的光参量放大理论分析

对超短强激光抽运波长为355nm，脉冲宽度为10ps的CsLiB6O10。光参量放大器(OPA)的最佳晶体长度、能量转换效率和输出信号光脉宽进行了理论分析和数值模拟。得到了在IP(0)=300MW／cm^2，Is(0)=5MW／cm^2，Ii(0)=0的情况下，最佳晶体长度为27．0mm。随着抽运功率和信号光功率增大时，CsLiB6O10晶体作为光参量放大器的非线性晶体时，其作用的晶体长度变得更短。高转换效率的信号光输出取决于抽运光和初始信号光的强度及晶体长度的最佳优化值。     

Measurement of charge-carrier behaviour in PIN diodes using a laser technique

A measurement system for the determination of charge-carrier densities in operating power devices is described. The system is computer-controlled and uses the free carrier absorption at 3.39 μm wavelength to deduce charge densities as a function of space and time. Measurements of carrier distribution in PIN power diodes have enabled derivation of the ambipolar diffusion length, the carrier lifetime and the carrier mobility.     

基于SOA四波混频效应的慢光特性研究

根据行波SOA的四波混频效应,讨论了不同参数条件下的慢光时延特性。采用SOA分段模型,定量分析了光时延量与偏置电流、频率失谐、泵浦光功率的关系,以及泵浦光功率、载流子寿命的改变对工作带宽的影响。结果表明:可以通过调节频率失谐、偏置电流等参数对光时延量进行控制,增加泵浦光功率或抑制载流子寿命均可提高工作带宽。