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     

Over 1 W fibre-coupled power from single semiconductor source forpumping of Raman fibre amplifiers and erbium-doped fibre amplifiers

For the first time, over 1W of optical power has been coupled into single-mode fibre from a single semiconductor laser diode operating at 1.45 μm. This device meets the need for a compact high power source for pumping of erbium-doped fibre amplifiers and for Raman amplification in fibres     

Gain control in erbium-doped fibre amplifiers by an all-optical feedback loop

An all-optical feedback loop is demonstrated which effectively suppresses slow, signal-induced gain fluctuations in Er-doped fibre amplifiers (EDFAs). Gain control is achieved by operating the amplifier in a ring-laser configuration. The working principle is shown theoretically and experimentally by coupling a selected wavelength of the ASE at the output of the EDFA back to the input. Such a feedback loop, which can be fabricated out of all-fibre passive components, could be easily implemented in any system using EDFAs.<>     

Simple dynamic model of all-optical gain-clamped erbium-doped fiberamplifiers

A simple dynamic model of laser-gain clamped erbium-doped fiber amplifiers (EDFAs) using ordinary differential equations is presented. The model not only provides a fast means of calculating EDFA gain dynamics, but also shows explicitly how the laser relaxation oscillation frequency and damping constant are affected by design parameters through analytical expressions. It is shown that the dynamic power excursion caused by relaxation oscillations can be reduced by increasing the oscillation frequency. The simplified model has two limitations: first, the amplified spontaneous emission (ASE) spectrum is not fully resolved and the noise figure can not be studied; second, the effect of spectral hole burning, which also causes gain excursion, can not be modeled. The first limitation can be removed by ASE-resolved modeling, where the concept of average inversion is also utilized to save computing time     

Simplified modeling of transients in gain-clamped erbium-dopedfiber amplifiers

A simple technique for modeling transients in erbium-doped fiber amplifiers (EDFAs) has been applied to a gain-clamped amplifier. Integration of the variables along the length of the amplifier allows the formulation of the problem as a single simple, ordinary, time-dependent differential equation. We demonstrate examples for a typical conventional EDFA and one in which internal out-of-band oscillation is used to clamp the gain     

Generalised formula for optical-amplifier noise and its application to erbium-doped fibre amplifiers

A rigorous treatment for calculating the noise performance of optical fibre amplifiers, which includes nonuniform distributions of the pump intensity, the gain coefficient, and the spontaneous emission factor is presented. The noise figure of erbium-doped fibre amplifiers is evaluated under various operating conditions using this method.<>     

Design of gain-clamped doped-fiber amplifiers for optimal dynamicperformance

This paper provides a detailed analysis of gain-clamped doped-fiber amplifiers and design guidelines in a wavelength division multiplexed (WDM) networking environment. A simple dynamic model of the doped-fiber amplifier allows us to derive explicit expressions for the small-signal response, which help identify and optimize the most critical parameters for best dynamic performance. The most important parameter is the pump power, which should be chosen 1-2 dB's above its required open-loop value, with all channels present, for the required signal gain. In an all-optical networking scenario with input power per channel as high as -3 dBm the required pump power may well exceed 20 dBm. Thus optimization of other parameters such as laser wavelength and loop loss are important. For best dynamic performance either the loop loss should be extremely small, implying a very large laser flux, or the laser gain variation in response to a perturbation should be large. Accordingly, the laser wavelength should be placed either close to the unity-gain region of the clamped gain profile, or at its peak. Finally, the small signal model for a chain of clamped amplifiers is provided, and it is shown that long chains are vulnerable to low-frequency input signal perturbations     

Modeling of spontaneous emission noise in erbium-doped fibre amplifiers using the Green functions method

This article describes a study of the main characteristics of erbium-doped fibre amplifiers based on a non-quantum approach to the phenomenon of amplification in spatially inhomogeneous structures. The noise figure in particular is assessed theoretically and numerically on the basis of various amplifier parameters, including the reflection coefficients at the fibre input and output. The results show the importance of monitoring reflectivity at the amplifier input and the power of the incoming signal.     

Characterization of an ASE reflector-based gain-clamped erbium-doped fiber amplifier

We develop a simulation tool for an all-optical gain-clamped erbium-doped fiber amplifier (GC-EDFA) based on an amplified spontaneous emission (ASE) reflector and thoroughly verify its validity by comparing simulation data with experimental ones. We carry out simulation work as changing conditions like reflection ratio and bandwidth of the ASE reflector, EDF length, and pump power. From this work, we have an exact understanding about the gain clamping principle that a reflected ASE acts like an intensity reservoir against input signal intensity variation. In general, as a reflected ASE power becomes higher, both a dynamic range and a noise figure (NF) increase; on the other hand, a clamped gain value decreases. The ASE reflector-based gain clamping scheme can be used for EDFAs with low NF characteristics at small input signal range in case a reflected ASE power is set at a level much lower than powers required for normal gain clamping function.     

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     

Investigation on gain characteristics in non-degenerate cascaded phase sensitive parametric amplifiers

We theoretically and experimentally show the impact of the ratio between the signal and idler generated from the PIA part on the gain characteristics in the continuous wave (CW) pump non-degenerate cascaded phase-sensitive fiber optical parametric amplifier (PS-FOPA). The results show that the length of highly nonlinear fiber (HNLF) used for generating the idler can cause the variation of power ratio between the idler and signal, which significantly affects the gain characteristics of the PS-FOPA under the small signal gain condition. To obtain high gain, it is better to choose long HNLF to generate idler. In our experiment, 5.5 dB gain and 18 nm bandwidth (on/off gain>10 dBm) in PS-FOPA can be achieved when 300 m-long HNLF instead of 200 m-long HNLF is used in PIA.     

Reduced intermodulation distortion in 1300 nm gain-clamped MQWlaser amplifiers

A 1300 nm gain-clamped DFB multiple quantum well laser amplifier with negligible pass band ripple, 20 dB fiber to fiber gain, and 10 dB reduction in gain saturation is demonstrated. The remaining gain saturation is attributed to longitudinal hole burning. After some modifications the reduction in gain saturation is improved to more than 30 dB for an input signal having the same polarization state as the lasing mode. From these experiments and a theoretical analysis it is concluded that there is a potential for realizing highly linear 1300 nm CATV semiconductor laser amplifiers using gain-clamping with less intermodulation distortion than today's directly modulated linear semiconductor lasers     

Study on noise characteristic of gain-clamped erbium-doped fiber-ring lasing amplifier

A simplified method to estimate the noise figure of the optically gain-clamped erbium-doped fiber amplifiers (EDFA's) is proposed. The simulation results indicate that the population inversion level at the signal input end dominates the noise performance of the entire amplifier. For a gain-clamped EDFA with ring-lasing configuration, the effects on the noise figure of the amplifier by the distributions of the pumping and lasing powers as well as the lasing wavelength are analyzed theoretically. The suggested noise-optimum configuration is co-pumping and co-traveling lasing oscillation at 1531 nm. Near quantum limit internal noise figure of 3.6 dB is achieved in the experiments under the best arrangement. The experiment results show perfect accordance with the theoretical analysis.     

Analysis of channel addition/removal response in all-optical gain-clamped cascade of lumped Raman fiber amplifiers

The effect of addition and/or dropping of wavelength-multiplexed channels in a network comprising three concatenated lumped Raman fiber amplifiers (LRFAs) have been analyzed by numerical simulation and verified experimentally. The first LRFA in the cascade is gain clamped using a ring-laser configuration, and the lasing power propagates through the cascade. A large-signal numerical model that incorporates time variation effects and the downstream propagation of signal, upstream propagation of pumps, and downstream and upstream propagation of amplified spontaneous emission spectral components has been used for the theoretical analysis. The LRFAs consist of 16 km of dispersion-compensating fiber counterdirectionally pumped at 1455 nm by a Raman fiber laser. Channel addition/removal is simulated by propagating through the cascade of LRFAs optical power from two laser diodes. One of them is square-wave modulated at 500 Hz, and power fluctuations of the second continuous-wave signal caused by the cross-gain saturation effect in LRFAs are monitored.     

宽带铋基掺铒光纤放大器的增益箝制研究

应用于动态通信网络中的光放大器需要恒定的信号增益.为此,设计了一个基于环形激光腔结构的宽带铋基掺铒光纤放大器(Bi-EDFA),进行了宽带Bi-EDFA信号增益箝制特性的理论研究.结果表明:通过将放大器输出的一个前向放大自发辐射(ASE)噪声光反馈到输入端,可以实现对1.53 μm波段传输信号的增益箝制.环路损耗越小,...     

Modulation instability in erbium-doped fiber amplifiers

The onset of modulation instability in erbium-doped fiber amplifiers (EDFAs) is studied through a stability analysis of the underlying nonlinear Schrodinger equation. The existence of gain in EDFAs lowers the threshold for modulation instability considerably compared with the case of undoped fibers. Modulation instability generates multiple pulses when a single pulse is amplified. It can also create multiple subpulses in mode-locked fiber lasers, a feature observed experimentally. Numerical simulations show that EDFAs can convert a continuous-wave optical signal into a train of high-repetition rate femtosecond pulses     

Modeling of gain in erbium-doped fiber amplifiers

An analytic method is described for fully characterizing the gain of an erbium-doped fiber amplifier (EDFA) that is based on easily measured monochromatic absorption data. The analytic expressions presented, which involve the solution of one transcendental equation, can predict signal gains and pump absorptions in an amplifier containing an arbitrary number of pumps and signals from arbitrary directions. The gain of an amplifier was measured over a range of more than 20 dB in both pump and signal powers. The measured theoretical results agreed to within 0.5 dB. Although the results described apply explicitly to EDFAs pumped in the 1480-nm region, they are also applicable to EDFAs pumped in the 980-nm region. The method is valid whenever the gain saturation by amplified spontaneous-emission noise can be neglected, which is typically the case for amplifiers with less than about 20 dB of gain     

Design of erbium-doped triangular photonic-crystal-fiber-based amplifiers

The amplification properties of erbium-doped triangular photonic crystal fibers (PCFs) are analyzed by varying the pitch, the hole diameter, and the dopant radius by means of a full-vector finite-element modal formulation combined with a population and propagation rate equation solver. Fiber designs which allow us to greatly reduce splice losses are presented and it is demonstrated that PCF amplifiers may deliver gains of more than 47 dB with splice losses lower than 0.3 dB.     

Performance of high-concentration erbium-doped fiber amplifiers

The full characteristics for two high-concentration erbium-doped fibers are reported. The comparison of the fibers characteristics indicates that design of fiber geometry can be used to partially compensate for the degradation of the amplifiers performance due to upconversion processes. For high NA fiber the 22-dB small-signal gain, and 3.5-dB noise figure are obtained from a 24-cm length of fiber. We report a photon quantum conversion efficiency of 28%, which corresponds to the highest efficiency obtained in heavily doped fibers     

Transient analysis of erbium-doped fiber amplifiers

The transient response of an erbium-doped fiber amplifier (EDFA) pumped at 1.48 μm, taking into account the gain-saturation effects due to the amplified spontaneous emission (ASE), is studied theoretically and experimentally. The theoretical model is used to predict the gain saturation and recovery times of an EDFA and its effects to the amplification of optical pulses