Pump wavelength independent gain with bidirectionally pumped alumino-silicate erbium-doped fiber amplifiers in the 800 nm pump band

Using a comprehensive computer model, it was shown that the effects of excited state absorption (ESA), in the 800 nm pump band, in alumino-phosphate-silicate (APS) erbium-doped fiber amplifiers (EDFAs) can be reduced significantly by using bidirectional pumping. If a band optimum length (BOL) is selected, a near optimum small signal gain (SSG) can be constant over broad pump wavelength regions due to the combined effects of ESA and ground state absorption (GSA). Hence, multilongitudinal mode, high power, reliable and inexpensive GaAlAs laser diodes can be used as pumping sources for EDFAs having SSG > 40 dB, noise figures of <4 dB, and output signal powers approaching 100 mW. These fibre amplifiers could be used as line repeaters, preamplifiers, and power amplifiers in different lightwave systems.<>     

Implicit analytical solution for erbium doped fibre amplifier

An implicit analytical solution for the gain and output signal power of a realistic erbium doped fibre amplifier is given as a function of pump power, fibre length, input signal power and various fibre and materials parameters. This solution is shown to accurately predict the gain variation with fibre length and pump power, and the saturation behaviour with increasing signal power. It is a useful block for accurately modelling multiamplifier systems while minimising computation time.<>     

Attenuation and fluorescence characteristics of optical signalspropagating in an erbium-doped fiber

For a monochromatic input signal launched into an erbium-doped fiber (EDF), a broadband fluorescence spectrum will be generated with total power approximately 30 dB lower than input signal power. The forward fluorescence power decays slowly at long EDF length due to smaller absorption cross section for wavelength components away from absorption peak. Care must be taken when the conventional cutback method is used to measure the attenuation of the optical signals in an EDF. The backward fluorescence power is saturated to a constant level, and the spectrum does not change for long EDF     

Strong optical bistability in ytterbium-doped fibre laser with reabsorption

The strong optical bistability in a ytterbium-doped fibre (YDF) laser is demonstrated, which is due to the saturable absorption of the unpumped YDF stage. The bistable regions of both the signal output and residual pump light are 320 mW within an antiphase manner with respect to each other. The signal output and residual pump light also exhibit self-pulsing instability. A bifurcated laser cavity configuration for switchable dual-wavelength generation is predicted based on the optical bistability of the residual pump power.     

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.     

35 dB optical gain at 2.716 mu m in erbium doped ZBLAN fibre pumped at 0.642 mu m

An optical gain of 35 dB at 2.716 mu m signal wavelength has been measured in an erbium doped ZBLAN fibre. A pump-wavelength scanning determined the pump wavelength for maximum gain. This pump wavelength was found to be 0.642 mu m. The maximum absorption wavelength for this Er/sup 3+/ doped fibre is 0.649 mu m. It was deduced that the excited state absorption process improves the gain performance of such fibres at the signal wavelength considered.<>     

Transmission and saturation performance of dispersion-shifted distributed erbium fibre

The gain spectra for a bidirectionally pumped 30 km length of lightly doped dispersion shifted erbium fibre and the amplification performance in saturation of a 54 km length of similar fibre are presented. The longer length comprised six spliced fibres with an average erbium concentration in the core of approximately 60 p.p.b. and could be rendered lossless with 2*30 mW of pump power for low power signals. With 2*55 mW of pump power a peak fibre gain of 17 dB at 1536 nm was realised; as the input signal power was increased the gain was suppressed but the fibre remained transparent for signal powers up to -2 dBm.<>     

Effects of multiple scattering in optical-fibre transmission line

The authors estimate the magnitude of secondary forward scattering and its dependence on line length and absorption loss. They show that, for pulsed signals, the ratio of the direct signal to the background is increased in the proportion of the peak to mean power in comparison with c.w. behaviour.     

同向抽运光纤拉曼放大器功率转换效率的理论分析

为了对同向抽运光纤拉曼放大器的功率转换效率进行研究,由耦合方程出发,首先理论推导出功率转换效率的解析解,然后采用数值计算的方法详细分析不同物理因素对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和单位面积的拉曼增益系数增加而增加,当增加到最大值时保持数值不变;小信号时,初始信号光功率对功率转换效率的影响较小;大信号时,功率转换效率随着初始信号光功率增加而快速增加;功率转换效率和初始抽运光功率呈抛物线曲线关系;抽运光与信号光的频率比增加时,功率转换效率减小。     

Optical level equalisation based on gain saturation in fibreoptical parametric amplifier

Optical level equalisation operation based on gain saturation in an optical fibre parametric amplifier is reported. The signal output has been measured as a function of the signal input in a fibre parametric amplifier, with the result that the signal gain saturates as the input power increases and the output power reached a maximum value at a particular input level. Utilising this gain saturation property, optical level equalisation has been demonstrated     

背景光对恒虚警下APD探测性能影响评估方法

针对恒虚警工作方式下,噪声、信号及倍增因子之间相互作用的问题,分析了倍增因子、背景辐射对APD探测系统性能的影响以及恒虚警补偿方式的工作原理,建立了恒虚警下背景辐射与倍增因子的关系模型。通过求取有、无背景光时系统可探测到的最小信号功率,建立了APD性能的评估模型,设计实验对模型进行了验证,利用该模型分析了不同噪声对APD探测性能的影响。结果表明,随着背景光增强,其对APD的性能影响逐渐增大,且增大速率逐渐减缓;暗电流噪声较小时,背景光对APD作用较为明显,随着暗电流噪声的增大,背景光对系统影响迅速减小,最终趋于平稳;背景光对APD的影响随热噪声、放大电路噪声的增大而均匀增大。     

Characteristics of phase-matched sum-frequency light in optical fibres

Characteristics of phase-matched sum-frequency light in optical fibres is investigated to determine the input power dependence and fibre length dependence. The output power at 0.54 ?m increases in proportion to the square root of the input power, increasing almost exponentially with increases in the fibre length from 4 m to 17 m and becoming nearly constant above 17 m.     

抽运功率配置对双向喇曼放大器性能的影响

为了研究抽运功率配置对双向抽运光纤喇曼放大器性能的影响,基于已有的耦合方程,采用数值仿真方法,分析了不同抽运功率配置对双向抽运光纤喇曼放大器的增益、增益饱和以及抽运功率转换效率的影响。结果表明,双向抽运光纤喇曼放大器的增益、增益饱和以及抽运功率转换效率特性均介于同向和反向抽运光纤喇曼放大器之间,并且随着同向抽运功率在抽运总功率中所占比例的升高,增益、增益饱和功率和抽运功率转换效率的数值增加;大信号、抽运功率较大时,抽运功率配置对双向抽运光纤喇曼放大器性能的影响显著。这对双向抽运光纤喇曼放大器和光纤激光研究具有一定的参考价值。     

Gamma-ray induced pulsewidth broadening and power loss inmodelocked Er-doped fibre laser

A modelocked erbium-doped fibre laser (EDFL) exhibited a 9.7% decrease in its pump laser output power and pulsewidth broadening from 9.2 to 300 ps following a 10.14 kGy(Si) gamma-ray irradiation. A decrease in the EDFL intra-cavity power from the combined effects of the pump laser degradation, and colour centre induced absorption in the fibre segments and other EDFL components was responsible for the broadening and long recovery times required for restoration of modelocking     

Maximum single frequency input power in a long optical fibre determined by stimulated Brillouin scattering

The experimental results of stimulated Brilloum scattering in about a 4 km fibre are reported. The pumping wavelength is 0.71 ?m. The Brilloum shift frequency was measured to be about 25 GHz. The transmitted power was found to be constant, when the input power exceeds about 14.8 dBm. The saturated transmitted power was 0.5 dBm, which corresponded with the output when 14.8 dBm input power was coupled and only linear fibre loss (about 4.0 dB/km) was assumed.     

有序统计恒虚警率技术综述

在噪声或杂波环境中进行自适应雷达目标检测是每部雷达接收机中非常重要的设计。在几乎所有的检测程序中,都将接收回波信号幅度与某一门限作简单比较。目标检测的主要目的是在极低的恒虚警率(CFAR)约束条件下使目标检测概率最大化。噪声和杂波背景可以用一个统计模型来加以描述,如独立相同瑞利模型,或用已知平均噪声功率的指数分布随机变量进行描述。但是在实际应用中,平均噪声或杂波功率绝对是未知的,并且还会随着距离、时间和方位角发生变化。因此,对用于几种不同背景信号情况的某些距离CFAR技术进行描述。在这些背景信号情况下,平均噪声功率和另外一些统计参数都被假设是未知的。因而所有的距离CFAR技术都通过将幅度门限应用于检测单元内的回波信号幅度,把估算流程(用以获取噪声功率的精确值或估算值)与判定步骤结合起来。许多研究工作都分析了这种通用的检测方案,对这一课题投入了大量精力。对这些重要的距离CFAR检测方案中的几种作一简短描述,然后进行技术比较。     

Stabilisation of a modelocked Er-doped fibre laser by suppressingthe relaxation oscillation frequency component

A novel method is reported for stabilising an actively modelocked Er-doped fibre laser by controlling its cavity length to suppress the relaxation oscillation RF power of the laser output. This RF power is a good measure of laser instability. With this method, the RF power ratio between modelocking frequency and background noise is kept to more than 70 dB, and stable bit-error-free operation at 6.3 GHz is realised for over 6 hr     

Optical amplification at 0.54 /spl mu/m by Tb/sup 3+/-doped fluoride fibre

0.54 mum band amplification using Tb³⁺-doped fluoride fibre is demonstrated. Spectroscopic properties of Tb³⁺-doped fluoride glass are clarified. A gain of 5.3 dB has been obtained in a 1 wt.% Tb³⁺-doped fluoride fibre for a signal power of -30 dBm by forward pumping at a wavelength of 0.488 mum with power of 100 mW     

Optical amplification at 0.54 /spl mu/m by Er/sup 3+/-doped fluoride fibre

Demonstrated is a 16.5 dB all-fibre optical amplifier at 546 nm using Er³⁺-doped fluoride fibre for a signal power of -30 dBm by forward upconversion pumping of a 974 nm laser diode. Results show Er ³⁺-doped fluoride fibre is a promising candidate for 0.54 mum optical amplifiers     

30 dB optical net gain at 1.543 mu m in Er/sup 3+/ doped fluoride fibre pumped around 1.48 mu m

A 30 dB optical net gain and 12 dBm maximum output power for -1 dBm signal input have been measured at a signal wavelength of 1.54 mu m with an erbium doped ZBLAN fibre pumped at 1.47-1.48 mu m. The results confirm the great potential of ZBLAN fibres for hosting rare earth ions to generate optical amplification. The discussion points out the parameters to be studied to improve the fibre amplifier performance.<>