Gain characteristics of a dual-pump fiber optical parametric amplifier with Raman effect

We investigate the pump-depleted model of a dual-pump fiber optical parametric amplifier(FOPA) with Raman effect.As bandwidth increases,the gain profile of the distorted FOPA would be impacted seriously.Under the widebands,especially when the pump separation is large,zero dispersion wavelength(ZDW) fluctuation is another factor which can not be neglected.Numerical simulations with these comprehensive factors are mainly analyzed to obtain their influence on gain characteristics.Saturated gain spectrum is also discussed in detail.     

Pump to signal RIN transfer in Raman fibre amplifiers

An analytical model and measurements of the pump to signal relative intensity noise transfer characteristics of co- and counter-pumped Raman amplifiers is presented. Quantitative analysis of noise averaging from chromatic dispersion in co-pumped systems, and from different propagation directions in counter-pumped systems is given     

RIN transfer in copumped Raman amplifiers using polarization-combined diodes

Pump-to-signal relative-intensity-noise (RIN) transfer in a forward-pumped Raman amplifier using polarization-combined diodes is measured and analyzed. For the first time, by means of experiment and simulations, we call attention to the impact of the polarized nature of stimulated Raman scattering on RIN transfer. We show that measuring the RIN at the output of a depolarized Raman pump and inserting this figure in the commonly used RIN transfer equation is not sufficient for good signal RIN prediction. Although depolarizing the Raman pump enables polarization-independent signal gain, proper modeling of RIN transfer should include the polarization dependence of the Raman effect and the polarization mode dispersion of the fiber.     

Pump to signal RIN transfer in Raman fiber amplifiers

We present an analytical model and measurements of the pump to signal relative intensity noise (RIN) transfer characteristics of copumped and counterpumped Raman amplifiers. We give a quantitative analysis of noise averaging from chromatic dispersion in copumped systems and from different propagation directions in counterpumped systems. It is shown that nondispersion-shifted fibers and other fibers with high dispersion between the signal and pump wavelengths give a greater potential for use in copumped Raman amplified systems     

RIN transfer measurement and modeling in dual-order Raman fiber amplifiers

A numerical analysis is presented that models the transfer of relative intensity noise (RIN) from the first- and second-order pump lasers to the signal radiation in dual-order Raman fiber amplifiers. Measurements are presented of the first- and second-order RIN transfer functions for co- and counter-propagating fiber amplifiers. The second-order RIN transfer function is similar to that found in single-order Raman fiber amplifiers and the first-order transfer function is approximately 15 dB less than the second-order transfer function. The impact of the RIN transfer from the first- and second-order pump lasers to the signal radiation on the system performance is examined and estimates for the required pump laser RIN levels are presented.     

Double-cavity Raman fibre lasers with suppressed pump-to-Stokes transfer of low-frequency RIN

Double-cavity Raman fibre lasers with two longitudinally concatenated Stokes cavities are shown to permit the suppression of low-frequency relative-intensity-noise (RIN) transfer from the pump laser to the Stokes output. This concept can provide low-noise Raman fibre lasers for use as pump sources in co-pumped Raman amplifiers.     

RIN transfer analysis in pump depletion regime for Raman fibreamplifiers

A numerical analysis is presented that models the relative intensity noise transferred from a Raman pump to a signal laser in an optical fibre. The analysis is valid in both the pump-depletion and nondepletion regimes. The RIN requirements for a 0.1 dB Q-penalty in the pump depletion regime are similar to those in the nondepletion regime, exhibiting a RIN requirement reduction of only 3-4 dB/Hz     

Output-power-clamped Raman fibre laser with suppression of low-frequency RIN transfer from pump sources

An optical approach is demonstrated for suppressing low-frequency relative intensity noise (RIN) transfer from pump sources to the author's proposed Raman fibre laser (RFL). Low-frequency RIN transfer suppression is accomplished by outputting not the second- but first-order Stokes, which output power is clamped by the lasing second-order Stokes in the cavity and can be easily tuned in a large dynamic range. Thus, this technique fits the RFL for use as pump sources in Raman fibre amplifiers.     

Regenerative gain in a Raman free-electron laser oscillator

A parametric study of gain in a millimeter-wave Raman free-electron laser oscillator and comparisons to linear theory are carried out. The intense (1 kA/cm²), relativistic (600-800 keV), cold [(deltagamma/gamma)_{parallel} < 1percent] electron beam employed is guided by a 9.45 kG magnetic field through a 1.45 cm period, 49.5 cm long uniform undulator. Operation at < 1 kG pump field results in a < 10 percent electron quiver velocity (upsilon_{perp}/upsilon_{parallel}) velocity. The laser power output has been mea sured at ∼ 3 MW corresponding to an efficiency of 4 percent, and tunability in the 90-170 GHz range has been achieved with a narrow linewidth (Delta lambda/lambda leq 1percent). Using a new technique, linear small-signal growth rates have been unfolded from the oscillator startup delays. Excellent agreement is found with three-dimensional small-signal calculations for both the spatial growth rate and the resonance frequency. One-dimensional theory was found to predict shorter wavelength laser output than that observed.     

Amplified spontaneous Raman scattering and gain in fiber Raman amplifiers

The spectrum of amplified spontaneous Raman scattering and gain in a fiber Raman amplifer has been calculated analytically as a function of distance and pump power. The model used makes no assumptions on the magnitude of the gain and considers the pump nondepletion region. From the results, the on/off ratio has been calculated and is found to have a variation with length that depends on frequency detuning. An enhancement in on/off ratio is also found for small fiber lengths but at limited gain. The use of a narrow-bandpass optical fiber leads to quite different behavior of the on/off ratio than for the unfiltered case.     

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.      

光纤拉曼放大器的最大拉曼增益特性

为了分析同向抽运与反向抽运光纤拉曼放大器的最大拉曼增益,基于耦合微分方程,采用理论推导的方法,根据不同抽运结构下信号光放大的不同实际情况定义并推导出同向抽运光纤拉曼放大器和反向抽运光纤拉曼放大器的最大拉曼增益公式。然后,详细分析了各个参数对两种抽运方式下光纤拉曼放大器的最大拉曼增益的影响。对两种抽运方式下相同参数引起的最大拉曼增益进行了比较。结果表明,同样的参数对同向抽运与反向抽运光纤拉曼放大器最大拉曼增益的影响有相同的地方,也有不同的地方。最后,将最大拉曼增益和常用的开关增益进行了比较。对光纤拉曼放大器的实验、成本估计和器件效率等研究有重要参考意义。     

Influence of the zero dispersion wavelength fluctuation on the gain and noise performance in dual-pump fiber parametric amplifiers

Because of the zero dispersion wavelength (ZDWL) random fluctuations, the gain and noise figures deteriorate in optical parametric amplifiers based on highly nonlinear fibers (HNLFs). The detrimental role of ZDWL fluctuations on the gain and noise performance in dual-pump fiber optical parametric amplifiers (FOPAs) is presented. Numerical investigations of noise figure (NF) for different fibers with random fluctuation are analyzed. The noise figures for different fibers are varying even if the random fluctuation is small. Through choosing HNLFs with low ZDWL fluctuation and large nonlinear coefficient, high-gain and low-noise performance can be obtained.     

拉曼增益对回音壁模式光学微腔的全光调制

基于光通信系统对于全光调制和全光开关等的需求,从理论上和实验上研究了拉曼增益对回音壁模式光学微腔系统共振模式的全光调制。理论分析表明,拉曼增益能够补偿回音壁模式光学微腔系统的损耗,进而改变微腔系统的耦合机制,在不对微腔系统做任何机械性移动的前提下实现对系统共振透射率的连续调制。实验中采用光纤锥耦合的二氧化硅微芯圆环腔,利用560W的低功率泵浦光引发的拉曼散射,波长为1 545.7 nm的信号光实现了13.5 dB的调制度,使得系统的耦合机制由欠耦合转化为临界耦合。     

Effect of a Raman co-pump's RIN on the BER for signal transmission using ON-OFF keying modulation format

This paper theoretically studies the effect of the relative intensity noise (RIN), which is transferred to the signal from a Raman co-pump, on the bit-error rate (BER). We show that a given amount of the transferred RIN degrades the BER by about an order of magnitude more than does the same amount of the amplified spontaneous emission (ASE) added to the signal. We investigate how this effect depends on such parameters as the duty ratio of the signal pulses and on the amount of the ASE that has been added to the output signal along the transmission line.     

Reduction of polarization-dependent gain due to signal-to-signal Raman interaction in fiber Raman amplifier

An excellent polarization-dependent gain (PDG) suppression technique using a polarization scrambler is proposed in this letter. Investigations on PDG due to signal-to-signal Raman interaction among 40 wavelength-division-multiplexer signal channels were carried out experimentally to evaluate the system performance after incorporating a polarization scrambler in the system. It was confirmed by experiment that the use of polarization scrambler is an effective way to reduce PDG caused by signal-to-signal Raman interaction.     

In situ design method for multichannel gain of a distributed Raman amplifier with multiwave OTDR

We demonstrate a novel approach for the measurement of pump/signal waves interaction in the Raman amplifier (RA), with the use of multiwave optical time-domain reflectometry. With the application of obtained pump-evolution profiles to algorithms based on effective length recalibration, the multichannel Raman gain can easily be predicted with excellent accuracy for the undepleted, distributed RA. As a further extension of this algorithm, an in situ semi-analytic Raman-gain design method is also demonstrated.     

Model for polarization-dependent gain due to pump depletion in a WDM system with forward-pumped Raman amplification

We study polarization-dependent gain (PDG) due to signal-induced pump depletion (SIPD) in a wavelength-division-multiplexing (WDM) system with forward-pumped Raman amplification. It is found that SIPD can polarize the pump significantly in fiber with very low polarization-mode dispersion (PMD). To quantify the impact of fiber PMD on SIPD-induced PDG for a practical WDM system with many signal channels and multiple Raman pumps, an approximate vector model has been developed. The developed model allows us to directly calculate PDG from both SIPD and signal-signal Raman interaction (SSRI) with greatly reduced computation time. Based on the developed model, detailed numerical investigations for two typical C-band WDM systems are presented. It is shown that significant PDG can be introduced by SIPD when the fiber PMD coefficient is lower than 0.01 ps/km/sup 1/2/ even if the pumps are fully depolarized. It is also shown that PDG due to SIPD and PDG due to SSRI are in phase at shorter wavelength channels but out of phase at longer wavelength channels.