Noise characteristics of dual-pump fiber-optic parametric amplifiers

The noise figure (NF) properties of an undepleted and lossless dual-pump fiber-optic parametric amplifier (FOPA) are theoretically and numerically investigated. The theoretical study takes into account the noise characteristics of the two pump waves that are considered to have parallel polarization states for gain maximization. It is shown that noisy pump waves degrade the amplifier's NF, especially when the amplifier is operating at high gain values and when the input signal is high. The theoretical observations are validated by Monte Carlo numerical simulations, and the agreement between them is excellent. Finally, a comparative study concerning the noise characteristics of dual-pump and single-pump FOPAs is performed.     

光纤光学参量放大器的增益特性研究

介绍了光纤光学参量放大器的理论,基于耦合波方程推导出光纤光学参量放大器的增益表达式.以增益表达式为基础,详细分析了在典型参数下光纤光学参量放大器的性能.在单泵浦情况下,对不同光纤长度、不同泵浦功率及不同泵浦波长的光纤光学参量放大器做了性能分析.在双泵浦情况下,对不同泵浦波长的光纤光学参量放大器做了性能分析.研究结果表明,在典型参数情况下的双泵浦光纤光学参量放大器具有较好的特性.     

Noise characteristic of dye-doped polymer optical fiber amplifiers

The noise in polymer optical amplifiers is mainly derived from the amplification of spontaneous emission （ASE）. ha this paper, the noise characteristic of dye-doped polymer optical fiber amplifiers is studied. The propagation equations of ASE power and the rate equations of dye molecular concentration are found based on the energy level transition of dye. The noise characteristic of optical fiber amplifiers is given by solving above equations numerically, and the relationship between noise figure and parameters of optical fiber amplifiers is investigated in detail. The result shows that the noise figure of dye-doped polymer optical fiber amplifiers will not exceed 5 dB.     

Investigation on noise characteristics of dual-pumped fiber optical parametric amplifiers based on photonic crystal fibers

The noise characteristics of dual-pumped fiber optical parametric amplifiers(FOPAs) induced by gain and loss in photonic crystal fibers(PCFs) are analyzed.A special photonic crystal fiber is designed.Its noise figure(NF) changes with structure parameters,and it decreases as the hole diameter decreases.Three factors including input-signal power,signal wavelength and pump separation which impact on the final noise figure are discussed with the designed PCF.     

Pump-to-signal transfer of low-frequency intensity modulation in fiber optical parametric amplifiers

This paper describes the theoretical and experimental investigation of the transfer of low-frequency intensity modulation (IM) from pump to signal in fiber optical parametric amplifiers (OPAs). It is first established that low-frequency IM of the pump remains unchanged over the length of the amplifier in spite of the presence of parametric gain. The pump-power dependence of the OPA gain is then used to calculate the instantaneous effect of pump IM on the signal and idler output powers. These calculations are performed for both one- and two-pump OPAs. The main predictions are that 1) the ratio /spl rho/ of the signal intensity modulation depth to that of the pump varies across the OPA gain spectrum and 2) for a 20-dB gain, /spl rho/ can exceed 10 at some wavelengths, which indicates that this effect can be detrimental. Experiments have been performed to verify these predictions. Using sinusoidal IM of the pump, the resulting amplified signal IM was measured, and the experimental results were found to be in good agreement with the theoretical predictions.     

Gain limitations in optical parametric amplifiers

Factors limiting the gain of parametric amplifiers pumped by the 266 nm harmonic of aQ-switched Nd:YAG laser have been investigated, and the advantages of combined parametric/dye amplifiers in the visible are discussed.     

Backward optical parametric oscillators and amplifiers

Degenerate backward optical parametric oscillators and amplifiers have been considered, for the first time, to the best of our knowledge. When the pump intensity is four times the threshold pump intensity, the conversion efficiency reaches a maximum value. On the other hand, for nondegenerate optical parametric oscillators, the conversion efficiency always increases as the pump intensity increases. This behavior is different from those for forward optical parametric oscillators. In either configuration, the oscillation can occur without an external feedback. There is, however, a distributed feedback provided through the opposite propagation directions of the signal and idler. The threshold pump intensities for the oscillators can be achieved by the lasers currently available based on quasi-phase matching in several structures. As the input intensity for the backward parametric wave increases, the gain for this wave decreases dramatically if the pump intensity is on the order of the threshold or higher. When the input intensity is much larger than the threshold pump intensity, there is almost no gain regardless of the level of the pump intensity     

All-optical regeneration in one- and two-pump parametric amplifiers using highly nonlinear optical fiber

We describe the operation of a two-pump parametric optical regenerator. It is shown that higher order parametric coupling provides optical regeneration with a high extinction ratio. Excessive spectral broadening is studied in a two-pump architecture and compared with that of the one-pump parametric regenerator. We show that the spectral widths of the higher order terms can be controlled in amplifiers by using counterphased optical pumps.     

Fibre optical parametric amplifiers with circularly-polarised pumps

A fibre optical parametric amplifier with orthogonal circularly-polarised pumps requires only half the pump power of an amplifier with linearly-polarised pumps to achieve a given gain. The gain is also independent of the polarisation of the input signal.     

Gain reciprocity in fibre optical parametric amplifiers

A fibre optical parametric ampifier operating in the small-signal gain regime can exhibit the same gain when amplifying in either direction. This is true even in the presence of random dispersion and birefringence variations along the fibre.     

超短光脉冲通过分布式光纤放大器的传输特性

为了探讨超短光脉冲在分布式光纤放大器中的传输放大特性及影响因素,建立了光脉冲在光纤放大器中的基本传输方程,以掺镱光纤放大器为例,采用分步傅里叶变换法对放大器中光脉冲的演变进行了模拟,讨论了初始啁啾和增益色散的影响。结果表明,当光脉冲在分布式光纤放大器中传输时,光纤的色散、非线性效应均会影响脉冲的形状和频谱,光脉冲初始啁啾也会对脉冲的传输状态产生影响;对于宽频谱光脉冲,增益色散相当于一种损耗机制,应该考虑其影响。相关结果对光纤放大器的系统设计和优化具有一定的参考价值。     

双泵浦光纤参量放大器光纤长度的选取研究

文章研究了在采用高非线性光纤的光纤参量放大器中,光纤长度的选取对增益谱性能的影响,结果表明,在其他参数固定不变的情况下,光纤长度选取的不同会在很大程度上改变增益谱的形状.最后,文章提出一种最佳光纤长度的选取方法,并通过数值模拟验证了该方法能有效地改善增益性能.     

Methods for full utilization of the bandwidth of fiber optical parametric amplifiers and wavelength converters

In fiber optical parametric amplifiers (OPAs), idlers are generated during the amplification process. For very wide and dense signal input spectra, idlers may overlap with signals, thereby interfering with proper operation as an amplifier. In this paper, filter-based methods to fully utilize the bandwidth of OPAs and wavelength converters in the presence of very broad signal spectra are investigated. In the basic filter setup, two parallel OPAs and two filters are used; alternatively, one can use a single OPA bidirectionally and a single filter. An interleaver-based arrangement, separating signals from idlers at the system output, with a crosstalk of below -20 dB and subdecibel bit-error-rate penalty, is experimentally demonstrated.     

Coherent reflectometry of optical fiber amplifiers

The reflectivity of commercially available erbium-doped fiber amplifiers (EDFAs) was measured with coherent optical frequency domain reflectometry (C-OFDR). Reflections at the output isolator as well as the distributed gain along the erbium-doped fiber could be observed thanks to the high amplified spontaneous emission (ASE) rejection due to the coherent detection. Gain figures obtained with the OFDR technique are in good agreement with single-pass direct gain measurements.     

Noise figure of vertical-cavity semiconductor optical amplifiers

The noise figure of vertical-cavity semiconductor optical amplifiers (VCSOAs) is investigated theoretically and experimentally. Limitations on the noise figure set by the reflectivity of the mirrors are studied. Highly reflective mirrors lead to increased output noise as well as lasing at moderate carrier densities, which imposes a limit on the obtainable population inversion. Expressions for the excess noise coefficient, which governs signal-spontaneous beat noise enhancement due to finite mirror reflectivity, are presented for transmission and reflection-mode operation. Experimental results from a VCSOA operating in the reflection mode at 1.3 μm are presented. The results, from optical as well as electrical measurement techniques, are analyzed and compared to theoretical values     

Noise characteristics of semiconductor laser amplifiers

Noise characteristics of Fabry-Perot (FP) cavity type AlGaAs laser amplifiers are studied theoretically and experimentally. Noise power dependencies on pumping rate and input signal level are measured. Multimode rate equations with McCumber's fluctuation operator are solved for the parabolic band and the exponential bandtail models, both with the no k-selection rule. Experimental results are in good agreement with theoretical predictions.     

Noise figure for erbium-doped optical fibre amplifiers

A rate equation model is used to calculate the excess noise figure for erbium-doped fibre amplifiers. It is shown that erbium amplifiers can operate with high gain and can have noise figures only 0.2 dB above the quantum limit     

Noise figure of erbium-doped fiber amplifiers in saturatedoperation

We have developed a simple electrical noise figure measurement technique for the characterization of optical amplifiers. By subtracting the results of noise measurements at identical detected power levels made with and without the amplifier present, we are able to achieve an accuracy of ±0.3 dB in measured noise figure. Using this technique we obtain an excellent agreement between electrically and optically measured noise figures for two 98O-nm-pumped, copropagating erbium-doped fiber amplifiers (EDFA's) operating in saturation     

Amplification of WDM signals in fiber-based optical parametric amplifiers

We demonstrate for the first time, experimentally, the performance of fiber-based optical parametric amplifiers in wavelength-division-multiplexed (WDM) applications. Both a 3 /spl times/ 10 Gb/s and a commercial 7 /spl times/ 2.5 Gb/s WDM system are investigated together with the parametric amplifier. Limitations due to pump depletion and four-wave mixing are quantified. Measurements showing the performance in terms of power penalty and gain versus input-output signal power are presented.