Fiber Amplifier Gain Research Articles

Shooting algorithm and particle swarm optimization based Raman fiber amplifiers gain spectra design

An initial value determination method with a contraction factor for the counter-pumped Raman coupled equations is proposed. This method is used in conjunction with initial guess correction mechanism of Newton's method to construct a new efficient shooting algorithm for the solution of counter-pumped Raman coupled equations. The particle'swarm optimization is used to find the optimal wavelengths and powers for the pumps. By combining the new shooting algorithm and particle swarm optimization a powerful approach to the design of gain spectra for Raman fiber amplifiers is developed. Using this approach a counter-pumped broadband Raman fiber amplifier in C + L-band is designed and optimized. An average on–off gain of 9.3 dB for a bandwidth of 95 nm is obtained using only 4 pumps, with an in-band ripple level of ± 0.7 dB.

Stimulated Brillouin scattering in optical fibers

We present a detailed overview of stimulated Brillouin scattering (SBS) in single-mode optical fibers. The review is divided into two parts. In the first part, we discuss the fundamentals of SBS. A particular emphasis is given to analytical calculation of the backreflected power and SBS threshold (SBST) in optical fibers with various index profiles. For this, we consider acousto-optic interaction in the guiding geometry and derive the modal overlap integral, which describes the dependence of the Brillouin gain on the refractive index profile of the optical fiber. We analyze Stokes backreflected power initiated by thermal phonons, compare values of the SBST calculated from different approximations, and discuss the SBST dependence on the fiber length. We also review an analytical approach to calculate the gain of Brillouin fiber amplifiers (BFAs) in the regime of pump depletion. In the high-gain regime, fiber loss is a nonnegligible effect and needs to be accounted for along with the pump depletion. We provide an accurate analytic expression for the BFA gain and show results of experimental validation. Finally, we review methods to suppress SBS including index-controlled acoustic guiding or segmented fiber links. The second part of the review deals with recent advances in fiber-optic applications where SBS is a relevant effect. In particular, we discuss the impact of SBS on the radio-over-fiber technology, enhancement of the SBS efficiency in Raman-pumped fibers, slow light due to SBS and SBS-based optical delay lines, Brillouin fiber-optic sensors, and SBS mitigation in high-power fiber lasers, as well as SBS in multimode and microstructured fibers. A detailed derivation of evolutional equations in the guided wave geometry as well as key physical relations are given in appendices.

The Effects of Complex Energy Transfer Dynamics and Gaussian Profiles on the Performance of High-Concentration EDFAs

In this paper, we investigate the effects of complex energy transfer dynamics and Gaussian profiles on the gain and noise figure performance of erbium-doped fiber amplifiers (EDFAs) with high doping concentration. We use a two-level system to study the complex energy transfer dynamics that comes from the homogeneous up-conversion (HUC) and the pair-induced quenching (PIQ). In our model, the system is stimulated by a pump source at the wavelength of 1480 nm and operated with a signal source at the wavelength of 1560 nm. Assuming a uniform distribution of erbium ions in the fiber core, we approximate the fundamental mode distributions by Gaussian profiles which are commonly used to calculate the mode radius or spot size. Using the numerical calculations and analysis of the rate and power propagation equations for a two-level model under consideration, the most advantageous Gaussian profile is determined as the Whitley mode radius to obtain a high-gain and a low-noise figure per unit length of silica-based fiber amplifiers. The effects of the number of ions per cluster and the percentage of ions in clusters on the calculated gain and noise figure are compared for several pump powers. Results are discussed to achieve a desired gain and noise figure performance, and compared with the available experimental data to verify the feasibility of the model.

Synthesis method based on genetic algorithm for designing EDFA gain flattening LPFGs having phase-shifted effect

We propose a new synthesis method based on the genetic algorithm for the design of erbium-doped fiber amplifier gain flattening filters. Our genetic algorithm iterates starting with the long period fiber gratings structure constructed by inserting the phase-shifted long period fiber gratings in the middle of the structure, for the more accurately matched spectrum to the desired erbium-doped fiber amplifier gain flattening filter. To verify a synthesizing technique using the proposed algorithm, we have synthesized the long period fiber gratings structures according to the inverted gain spectrum of a commercially available erbium-doped fiber amplifier over the entire 1525–1570 nm range, theoretically. We have also obtained the synthesized structure was more accurate than the structure without phase-shifted section.

Gain and Noise Figure Performance of Erbium-Doped Fiber Amplifiers

Fiber loss is a fundamental limitation in realizing long haul point–to-point fiber optical communication links and optical networks. One of the advanced technologies achieved in recent years is the advent of erbium doped fiber amplifiers (EDFAs) that has enabled the optical signals in an optical fiber to be amplified directly in high bit rate systems beyond Tetra bits. In this paper, a simulation of an EDFA has been studied to characterize Gain, Noise Figure of a forward pumped EDFA operating in C band (1525-1565 nm) as functions of Er+3 fiber length, injected pump power, signal input power and Er+3 doping density. The simulation has been done by using Optisystem 5.0 software simulator (license product of a Canadian based company) at bit rate 10 Gbps.

Polarization independent thermally tunable erbium-doped fiber amplifier gain equalizer using a cascaded Mach-Zehnder coupler

A thermally tunable erbium-doped fiber amplifier (EDFA) gain equalizer filter based on compact point symmetric cascaded Mach-Zehnder (CMZ) coupler is presented with its mathematical model and is found to be polarization dependent due to stress anisotropy caused by local heating for thermo-optic phase change from its mathematical analysis. A thermo-optic delay line structure with a stress releasing groove is proposed and designed for the reduction of polarization dependent characteristics of the high index contrast point symmetric delay line structure of the device. It is found from thermal analysis by using an implicit finite difference method that temperature gradients of the proposed structure, which mainly causes the release of stress anisotropy, is approximately nine times more than that of the conventional structure. It is also seen that the EDFA gain equalized spectrum by using the point symmetric CMZ device based on the proposed structure is almost polarization independent.

铒镱共掺特性对光放大器增益和噪声系数的影响

铒镱共掺特性对光放大器增益和噪声系数的影响

A NOVEL DESIGN APPROACH FOR ERBIUM-DOPED FIBER AMPLIFIERS BY PARTICLE SWAM OPTIMIZATION

A novel design approach for erbium-doped fiber amplifiers is proposed based on particle swarm optimization algorithm. The main six parameters of the EDFAs including: pumping wavelength, input signal power, fiber numerical aperture, erbium-doped area radius, erbium concentration, and the fiber length are optimized utilizing a fast and efficient method called particle swarm optimization algorithm. In this paper, a combination of fiber amplifier bandwidth, gain, and flatness are taken into account as objective function and the results are presented for different pump powers. Our investigation shows that particle swarm optimization algorithm outperforms genetic algorithm in convergence speed, straightforwardness, and coping with high- dimensional spaces, when the parameters of EDFA are to be optimized. It has been shown that the required time for the optimization of the fiber amplifier parameters is reduced four times by using particle swarm optimization algorithm, compared to genetic algorithm method.

Design and analysis of dynamic erbium-doped fiber amplifier gain-clamping systems with feedback control

We present an accurate and quantitative design scheme for erbium-doped fiber amplifier (EDFA) gain control systems. The proposed design scheme is demonstrated through the design of an eight-channel EDFA gain-clamping system with an all-optical self-tuning feedback loop. The effect of the time delay in the feedback loop and the selection of feedback wavelength are theoretically analyzed. Compared with existing electrical-optical EDFA gain schemes, the proposed design scheme is free from the feedback loop response speed limitation and does not need any predetermined information of the network traffic variation or operation point estimation. It can efficiently enhance the static and dynamic performance of the whole system. Furthermore, since the design can efficiently suppress the relaxation oscillation transient, it provides a cost-effective solution for the gain-clamping problem of a long EDFA chain by combining it with a fast-link control method.

Characteristics of bandwidth, gain and noise of a PbSe quantum dot-doped fiber amplifier

Different from existing erbium-doped fiber amplifiers (EDFAs), PbSe quantum dot rather than conventional erbium ion is adopted as dopant in the fiber, due to its favorable emission–absorption spectra. A three-level system is proposed based on the observed emission–absorption spectra of the PbSe quantum dot. Scattering loss arising from its high refractive index and nanometer size is discussed thereafter. By a steady-state approximation, populations of the levels are expressed as an analytical function. Propagation equations of the light power with different frequencies are thereby solved by utilizing a numerical method in a single-doped case. The signal gain, bandwidth and noise of the PbSe quantum dot-doped fiber amplifier (QDFA) are estimated for different pumping powers in a single-mode condition. Depending on the emission-peak wavelength and the spectral width, the proposed QDFA can function on a long-wavelength band, with a wider bandwidth and lower noise than EDFAs.

Optimization of the power ratios of the bidirectional pumping at two wavelengths for erbium-doped fiber amplifiers

The gain and noise factor spectra of erbium-doped fiber amplifiers with pumped according to a copropagating three-level scheme and according to a counterpropagating quasi-two-level scheme in the regime of unsaturated gain in the C band have been simulated numerically. It has been shown that, at the total pump power up to 30 mW and at the optimized power ratio of the copropagating and counterpropagating pumps, the inhomogeneity of the gain in the C band does not exceed 0.25 dB at the noise factor of 4.2–4.7 dB.

Erbium-doped hole-assisted lightguide fiber: structural study and optimization

Erbium-doped hole-assisted lightguide fiber (EDHALF) is composed of a high-index core doped with erbium, a low index cladding and a small number of air holes surrounding the core. The finite element method is applied for solving the modal field of the EDHALF. The numerical calculation methods of the cutoff wavelength and mode field diameter are described in detail. The modified average population inversion iteration method is proposed for calculating the gain and noise figure of erbium-doped fiber amplifiers. The effects of the air holes on EDHALFs' cutoff wavelengths, mode field diameters and the gain coefficients of fiber amplifiers are studied. It's found that decreasing the relative hole-to-core spacing can make the cutoff wavelength move to shorter wavelength and decrease the mode field diameter. When the relative size of air holes is relatively large, further enlarging it only slightly changes the cutoff wavelength, mode field diameter and the maximum of the gain coefficient. Finally, four structural parameters, namely the EDHALF-core radius, the refractive index difference between the core and cladding, the relative hole-to-core spacing and the relative size of air holes are optimized in terms of the design criteria, which take into account the cutoff wavelengths of fundamental mode and the second order mode, the gain and noise figure of fiber amplifiers and the splice loss between the EDHALF and the conventional single-mode fiber.

Transient gain dynamics in long-haul transmission systems with electronic EDFA gain control

We report our investigations on the impact of transients stemming from channel reconfiguration or network failure. Erbium-doped fiber amplifier (EDFA) gain dynamics are considered by an average-inversion-level model. The simulation model is also verified by laboratory experiments. In extensive simulations, optimal sets of parameters for an electronic EDFA gain controller have been determined. We show that better results can be obtained if the gain controller is optimized for a chain of EDFAs and not a single amplifier only. Additionally, an efficient simulation methodology to calculate the combined bit error ratio (BER) is presented by coupling simulations of transient phenomena with bit-based simulations incorporating nonlinear fiber effects.

Broad-band EDFA gain flattening by using an embedded long-period fiber grating filter

An erbium-doped fiber amplifier (EDFA) gain flattening technique using an embedded long period grating (ELPG) is proposed. By bending the ELPG, due to different coupling strengths yielded from different bending curvatures, it can be used for both the static and dynamic gain flattening despite of the different pump currents of the EDFA. The experimental results demonstrate that the flattened gain region of 34nm can be achieved within 1dB ripple.

S-band thulium-doped fiber amplifier employing high thulium concentration doping technique

This paper details an approach for shifting the gain of an S-band thulium-doped fiber amplifier (TDFA) that employs a high thulium concentration doping technique. The technique can shift the gain from the conventional gain band to the promising longer wavelength region by forming a suitable population inversion between the /sup 3/H/sub 4/ and /sup 3/F/sub 4/ levels that results from cross relaxation between thulium ions. It has been shown that, unlike with an erbium-doped fiber amplifier, the interaction between thulium ions caused by the high concentration doping increases the efficiency up to a thulium concentration of 6000 ppm. The authors also describe the particular characteristics of Tm ions that appear when the fiber length and pump power ratio between the forward and backward pump powers in bidirectional pumping are varied. Furthermore, the authors optimized the thulium concentration, fiber length, and pump power ratio between the forward and backward pump powers, so that a high gain and a low noise figure (NF) in the S-band are obtained. As a result, the TDFA achieved a gain of 22 dB and NFs of < 6 dB in the 1477- to 1507-nm wavelength region at a thulium concentration of 6000 ppm.

Long-distance fiber Bragg grating sensor system with a high optical signal-to-noise ratio based on a tunable fiber ring laser configuration

A novel tunable fiber ring laser configuration with a combination of bidirectional Raman amplification and dual erbium-doped fiber (EDF) amplification is proposed for realizing high optical signal-to-noise ratio (SNR), long-distance, quasi-distributed fiber Bragg grating (FBG) sensing systems with large capacities and low cost. The hybrid Raman-EDF amplification configuration arranged in the ring laser can enhance the optical SNR of FBG sensor signals significantly owing to the good combination of the high gain of the erbium-doped fiber amplifier (EDFA) and the low noise of the Raman amplification. Such a sensing system can support a large number of FBG sensors because of the use of a tunable fiber Fabry-Perot filter located within the ring laser and spatial division multiplexing for expansion of sensor channels. Experimental results show that an excellent optical SNR of approximately 60 dB has been achieved for a 50 km transmission distance with a low Raman pump power of approximately 170 mW at a wavelength of 1455 nm and a low EDFA pump power of approximately 40 mW at a wavelength of 980 nm, which is the highest optical SNR achieved so far for a 50 km long FBG sensor system, to our knowledge.

Modelling consideration of praseodymium-doped fiber amplifiers for 1.3 μm wavelength applications

To obtain the temperature-sensitive rate equations, a new energy level diagram of Praseodymium ion (Pr3+) in a glass host is modelled. By solving the modified rate equations, an analytical expression is presented to investigate the temperature dependence of the signal gain of a praseodymium-doped fiber amplifier (PDFA). It is seen that a change in the signal gain slightly depends on the variation of the distribution of Pr3+-ions in transitions 3F4↔3F3 with the temperature. Numerical calculations are carried out for the temperature range which is changing from −20 to +60°C. Pr3+-doped ZBLAN fiber amplifier pumped at 1017nm and Pr3+-doped sulfide fiber amplifier pumped at 1028nm are selected as an application for the 1.3μm signal wavelengths. It is also seen that the prediction of the model is in good agrement with their experimental results.

Broadband parametric amplification in photonic crystal fibers with two zero-dispersion wavelengths

In this paper, the fourfold parametric enhancement over Raman gain of the total optical fiber-amplifier gain is analyzed. Such fiber-amplifier gain may be obtained with a relatively flat profile over a bandwidth in excess of 70 nm by using a microstructure or photonic crystal fiber with two zero-dispersion wavelengths. Optimal fiber-amplifier gain enhancement occurs whenever the pump wavelength is slightly shorter than the second zero-dispersion wavelength of a microstructure optical fiber.

Using Bipolar Codes in Non-coherent Optical CDMA Systems to Stabilize Decision Threshold for BER Performance Improvement

We use bipolar codes in non-coherent optical code-division multiple-access (O-CDMA) systems to stabilize decision threshold and improve system performance. The bipolar optical system also obviates the need for complicated threshold injection process. Theoretical error rate results under threshold instability are presented. Simulation results for an O-CDMA bipolar system using light-emitting diodes (LED) as the light sources and 21dB Erbium-doped fibre amplifier (EDFA) gain at 622 Mbit/s show that, for 10 -8 bit error rate (BER), the O-CDMA bipolar system can perform up to 15 km, a 7 km enhancement in comparison with the unipolar O-CDMA scheme.

Reduction of temperature-dependent gain in L-band EDFA using antimony-aluminum codoped silica EDF

We report a novel technique to suppress the temperature-dependent gain (TDG) of an L-band erbium-doped fiber amplifier. The composite optical gain block consists of conventional L-band erbium-doped fiber (EDF) serially concatenated with a special EDF in a ternary glass composition, antimony-aluminum codoped silica that showed an opposite TDG coefficient in the L-band. The TDG variation of the composite gain block was suppressed to less than /spl plusmn/1.5 dB for a saturated gain of 15 dB between 1565 and 1605 nm, measured over a temperature range of -40/spl deg/C to +80/spl deg/C.