Distributed Fiber Raman Amplifier Research Articles

Transient Link Control Technique Applied to Optical Hybrid Amplifier (EDFA + DFRA) Cascades

For the first time to our knowledge, power transient control in hybrid amplifier (HA) cascades is analyzed by means of numerical simulation. Four hybrid configurations are investigated, considering distributed fiber Raman amplifiers (DFRAs) in both backward and forward pumping schemes, in front of and behind an erbium doped fiber amplifier (EDFA). The link control technique was applied to the best and the worst configurations in terms of power excursion. When 17 out of 20 channels were dropped/added, the steady-state power excursions of the surviving channels were reduced from 4.21 dB and 6.25 dB to 0.01 dB and 0 dB, for a single HA under configurations EDFA + backward DFRA and forward DFRA + EDFA, respectively. For a cascade of 12 HAs (1800 km), the steady-state output power excursions were mitigated from 8.66 dB to 0.07 dB and 0.60 dB, for the same hybrid configurations, respectively.

High performance efficiency of distributed optical fiber Raman amplifiers for different pumping configurations in different fiber cable schemes

Fiber Raman amplifiers (FRAs) are attractive for ultra wide dense wavelength division multiplexing (UW-DWDM) transmission systems due to their advantages of broad amplification bandwidth and flexible central wavelength. With recent developments of optical pump sources with high power near 1.4 μm wavelength and highly nonlinear fiber having a peak effective Raman gain coefficient, more than ten times that of conventional single mode fiber, distributed FRAs (DFRAs) are emerging as a practical optical amplifier technology, especially for opening new wavelength windows such as the short and ultra long wavelength bands. Optical pump powers required for Raman amplification were significantly higher than that for erbium-doped fiber amplifier (EDFA), and the pump laser technology could not reliably deliver the required powers. However, with the improvement of pump laser technology, Raman amplification is now an important means of expanding span transmission reach and capacity. In the present paper, we have deeply investigated the proposed model for optical DFRAs in the transmission signal power and pump power within Raman amplification technique in co-pumped, counter-pumped and bi-directional pumping direction configurations through different types of fiber cable media. The validity of this model was confirmed by using experimental data and numerical simulations. Key words: Distributed fiber Raman amplifier, signal power, pumping power, forward pumping, different fiber media, backward pumping, bidirectional pumping configuration.

Performance of Distributed Fiber Raman Amplifier Based on Hybrid Cladding Photonic Crystal Fiber

This article presents a feasibility study for using a hybrid cladding photonic crystal fiber as a distributed fiber Raman amplifier based transmission link with negligible confinement losses and flattened dispersion characteristics. The simulation results clearly indicate that a bit error rate of 10−9 can be maintained at the end of a (4 × 170)-km distributed fiber Raman amplifier link operating with 40 Gbps and 0.6 dBm transmit power if 20 dBm of pump power is used for each span.

分布式光纤拉曼放大对远程光纤水听器系统噪声特性的影响

分布式光纤拉曼放大对远程光纤水听器系统噪声特性的影响

Stimulated Brillouin scattering effect on gain saturation of distributed fiber Raman amplifiers

Stimulated Brillouin scattering effect on gain saturation of distributed fiber Raman amplifiers

Design of a flat-gain multipumped distributed fiber Raman amplifier by particle swarm optimization

The pumping scheme of multipumped distributed fiber Raman amplifiers is optimized by a powerful method called particle swarm optimization. By use of particle swarm optimization, we optimize both pump powers and frequencies of multipumped Raman amplifiers with a high number of pumps. Particle swarm optimization is a fast and effective method, and it surpasses other optimization methods, such as the genetic algorithm, for optimizing fiber amplifiers. It is shown that the computational efficiency of particle swarm optimization is significantly better than that of the genetic algorithm, reducing the time of computation to one third, and its implementation is more straightforward. A gain bandwidth of 92.1 nm and a gain variation of 0.49 dB in the range of 1524.5-1616.6 nm are obtained by this method, using ten backward pumps in a 60-km-long amplifier. The gain variation reduction is due to the inclusion of pump frequencies in the optimization process.

Redistribution of pump power and impairments in gain-equalized distributed fiber Raman amplifiers due to four-wave mixing and parametric amplification

In this work, by using a comprehensive numerical model which rigorously describes the interaction between stimulated Raman scattering (SRS) and four-wave mixing (FWM), we verify that FWM processes, including depletion and parametric gain, generate a redistribution of pump power in distributed fiber Raman amplifiers (DFRAs). As a consequence of pump–pump FWM, several FWM components can be generated, which act as new sources of SRS for Raman pumping. Due to new SRS–FWM interactions, a redistribution and exchange of pump power along the fiber also occurs, producing degradation in the performance of the amplifier. Numerical results show impairments in distributed amplified systems due to these interactions, such as loss of flatness on the spectral gain, reduction on the net Raman gain, and the presence of strong FWM products within the transmission band. We note that the localization of the zero dispersion wavelength (λZD) of the fiber is a critical factor in the occurrence of these impairments. A reduction of net Raman gain up to 3 dB and tilt up to 7 dB in the spectral gain profile have been found in different amplified systems as consequence of pump–pump FWM and parametric gain of Raman pumps.

Channel addition-removal response in a cascade of three distributed Raman fiber amplifiers transmitting 10×10 GE channels: experimentation and modeling

Feature Issue on Transmission in Optically Transparent Core Networks We present experimental results on the transmission of 10×10Gbit Ethernet (10 GE) channels over a 383km long fiber link composed of 133km nonzero dispersion shifted and 150km plus 100km of standard single mode fiber. Transmission is based on distributed Raman amplification in the three fiber spans. Susceptibility of the transmission quality to channel addition-removal has been investigated by replacing eight of the 10 GE small form factor pluggable module transceivers with signals from a WDM tester that were square-wave modulated at 500Hz with 50% duty cycle. Experimental results are extended by numerical simulation of surviving channel power transients in the cascade.

Theoretical Analysis on the PMD-Assisted Pump-to-Signal Noise Transfer in Distributed Fiber Raman Amplifiers

A theoretical analysis on the pump-to-signal noise transfer, in the presence of the polarization mode dispersion in the distributed fiber Raman amplifiers, is presented. We analytically show the impact of temporal fluctuations of the pump state of polarization on the relative intensity noise of the amplified signal. The system performance degradations are then estimated with analytical expressions.

Gain flattened distributed fiber Raman amplifiers

An S band and a C band distributed fiber Raman amplifiers (DFRAs) with flattened gain and compensated dispersion have been studied and implemented with 1 427 nm and 1 455 nm mono-wavelength fiber Raman lasers as the pumped sources respectively. The gain of single-wave pumped S band and C band can reach 10 dB and 15 dB respectively. And a 50 nm gain flattened width was successfully obtained by using a chirp fiber Bragg grating (CFBG) gain flattened filter with gain ripple of ±0.6 dB. The C band DFRA has been applied to CDMA wireless communication system successfully.

Distributed fiber Raman amplification in long reach PON bidirectional access links

Distributed Raman fiber amplification is proposed and experimentally demonstrated to support long reach passive optical network (PON) links. An 80 km, bidirectional, single fiber link is demonstrated using both standard intensity optical modulators at 10 Gb/s and up to 7.5 Gb/s using novel reflective semiconductor optical amplifier electro-absorption modulator.

Optimizing the incoherent pump spectrum of low-gain-ripple distributed fiber Raman amplifier for a given main pump wavelength

The method for designing the incoherent pump spectrum for the distributed fiber Raman amplifiers (DFRAs) of low gain ripple is studied, in which the wavelength of the maximum power spectral density can be assigned. The assigned wavelength is called the main pump wavelength. Incoherent pump spectrum is described with the power spectral density function (PSDF) that comprises a set of piece-wise continuous functions. PSDF is optimized for the minimum gain ripple with the least-square minimization method. An extremum pump wavelength condition is applied to PSDF. A proper initial trial PSDF is given so that the optimized PSDF converges to the desired result and the power spectral density at the extremum pump wavelength is the maximum. With this design method, we show the optimized PSDFs for the DFRAs using backward pumping and bidirectional pumping. The gain ripples of considered DFRAs are less than 0.1 dB for 20-dB ON-OFF Raman gain over 70-nm bandwidth. The reduction of average effective noise figure with shorter main pump wavelength is shown and investigated.

Full characterization of modern transmission fibers for Raman amplified-based communication systems

Telecommunication carriers have to estimate the Raman parameters of the fibers installed on their optical transport networks in order to facilitate the design of the next generation of high bit-rate Raman amplified-based transmission systems. This paper reports a very complete characterization of the most popular modern transmission fibers in terms of Raman efficiency, noise figure and double Rayleigh backscattering crosstalk. Our experiment is based on an averaged power analysis, applied to a counter-pumped long-haul distributed fiber Raman amplifier. We evaluate as well at 40 Gb/s for these different fiber types the double Rayleigh backscattering impact in terms of Q-factor penalty for various Raman gains and RZ modulation formats with different duty cycles.

Improvement in characteristics of a distributed Raman fiber amplifier by using signal-pump double-pass scheme

We have proposed and demonstrated a novel signal-pump double-pass distributed Raman fiber amplifier (RFA) by using a three-port optical circulator as a reflective mirror. This unique RFA architecture not only doubles the amount of dispersion compensation, but also enhances the pumping efficiency. In comparison with the conventional signal-pump single-pass scheme, the proposed RFA has a 2.0-dB gain improvement and a 3.7-dB equivalent noise figure suppression, measured at 1598 nm. The proposed RFA may find wide applications in long-haul transmission and optical networks, where dispersion compensation is of great concern.

Matrix algorithms for dynamic gain-spectrum adjustment of backward-pumped distributed fiber Raman amplifier

Two matrix algorithms aiming at a dynamic gain-spectrum adjustment in a backward-pumped distributed fiber Raman amplifier (B-DFRA) are developed based on the relation between changes in the pump power and the gain spectrum. Characteristic channels are chosen to reduce the dimension of matrices in the algorithm, which can be implemented by built-in microprocessors or DSP chips inside the B-DFRA module. Furthermore, as shown by the theoretical analysis and the numerical simulation, elements in the matrices can be directly and easily measured in deployed fiber plants without information on fiber parameters. These matrix algorithms are capable of adjusting the gain spectrum to fit the arbitrary profile desired in reality, while a wide dynamic range can be achieved by a multistage adjustment using matrices measured under several gain levels.

Design of the pump power spectrum for the distributed fiber Raman amplifiers using incoherent pumping

The method to design the incoherent pump power spectrum described with a set of piece-wise continuous functions (PWCFs) for the distributed fiber Raman amplifier (DFRA) is presented. The pump power spectrum is divided into a number of sub-bands, in which each sub-band is described with a polynomial. The power spectral density function (PSDF) is the absolute value of the set of PWCFs, in which the polynomial coefficients are optimized with the least-square minimization method for reducing the signal gain ripple. Two 100-km TW-Reach DFRAs using backward pumping and bidirectional pumping respectively are taken as examples. The numerical results show that the gain ripple of less than 0.02 dB over 70-nm bandwidth can be achieved. The spectral characteristics of the optimized PSDF for the ultra-low gain ripple are investigated. The optimized PSDF can be synthesized with multiple incoherent pumps. The synthesis examples using the multiple Gaussian incoherent pumps are shown, in which the gain ripples are increased to 0.3 dB due to the discrepancy between the optimized PSDF and the synthesized PSDF. The gain ripples can be reduced to 0.05 dB by further optimizing the parameters of the multiple Gaussian incoherent pumps.

Comparison of wavelength-division-multiplexed distributed fiber Raman amplifier networks for sensors

A novel distributed fiber Raman amplified star topology used for optical sensor wavelength-division multiplexing is proposed. The performance of this star configuration is compared to an optically amplified bus topology. The two different network topologies are compared and demonstrated experimentally and theoretically as means of gathering information from four wavelength-division-multiplexed photonic sensors. We report how the star configuration yields better signal-to-noise ratios than the bus topology. Furthermore, this improvement is made without increasing the complexity of the regular star topologies.

S-band gain flattened distributed fiber Raman amplifier with chirped fiber bragg grating filter

S-band gain flattened distributed fiber Raman amplifier with a bandwidth from 1 488 nm to 1 541 nm (53 nm in width), an averaged gain of 10 dB and a gain ripple of ±0.6 dB is obtained successfully, in which a single-wavelength high power fiber Raman laser with wavelength of 1 427.2 nm is used as the pump and the chirped fiber Bragg grating is used as the gain flattening filter. Besides, filter wavelength division multiplexer (FWDM) is used as the multi-signal multiplexer and 1 427 nm/1 505 nm coarse wavelength division multiplexer (CWDM) is used as the pump-signal coupler. The gain media are G652 fiber of 50 km in length and dispersion compensation fiber (DCF) of 5 km in length. Moreover, the location arrangements of different type of fibers and the effect caused by gain flattening filter as well as their solutions are discussed in detail. It is very significant to extend the range of optical fiber communication band and increase the capacity of fiber communication especially for ultra-long haul and ultra-high capacity communication system.

Distributed fiber Raman amplifiers with incoherent pumping

Distributed fiber Raman amplifier (DFRA) with incoherent pumping is investigated and its performance is compared to that with the conventional coherent pumping. It is shown that increasing the spectral bandwidth of incoherent pumping source can reduce the Raman gain ripple significantly, and degrade noise figure slightly at short wavelengths, compared to coherent pumping. To achieve the same gain flatness, the number of pumps for broad-band DFRAs with incoherent pumping can be significantly reduced compared to the coherent pumping.

16×42.8 Gb/s unrepeated transmission over 200 km of standard single-mode fiber by using an electroabsorption modulator

We demonstrate an unrepeated transmission of 16×42.8 Gb/s over 200 km of a standard single-mode fiber (SMF) using a commercially available electroabsorption modulator (EAM). In an optical link, a distributed fiber Raman amplifier, a remote pumped optical amplifier, an optical booster amplifier, and an optical preamplifier are used for signal amplification. After transmission of 200 km, Q-values of the 16 channels range from 11.5 to 12.3 dB. The experimental result reveals that the EAM can be used for STM-256 (OC-768)-based long as well as short reach applications.