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Raman amplifiers (RAs) can be represented as one of the best solutions for transmission techniques, where they can compensate attenuation and transmit the optical signal to long-haul distances. This work proposes and investigates two cascaded models (multi-stages of RAs) for enhancing the received power and the overall gain. This study includes three fiber types: Dispersion Shifted Fiber, Truewave and Freelight fibers at 100 km distance and pumping powers of 500, 600 and 700 mW. The obtained results reveal that the best results gain is 46.46 dB and the power of output signal is 42.47 dBm achieved at 700 mW pump power with Truewave fiber. The models are compared with previously published work, where the gain and the output signal power are enhanced to more than 66.58–85.84%. [ABSTRACT FROM AUTHOR]

A broadband amplification that utilizes a serial hybrid fiber amplifier is experimentally demonstrated in this paper. Two fully double-pass configurations, namely, setups A and B, are implemented. The difference between these two configurations is that the position of the two amplifiers (erbium and Raman) is swapped. These two configurations are tested under the same input parameter conditions. Two laser pump power wavelengths with a total pump power of 375 mW (1495 nm with 350 mW for Raman and 1480 nm with 25 mW for the erbium amplifier) were used. Under the optimum condition and under a small signal power of −30 dBm, a wide flatness gain bandwidth of 80 nm (1530–1610 nm) with an average gain level of 28.5 and 24 dB is achieved for setups A and B, respectively. A wide bandwidth is achieved by avoiding the amplification overlap between these two amplifiers through choosing the proper pump wavelength. In addition, A gain dynamic range values of 3 dB and more than 15 dB were recorded for setup A and B respectively. [ABSTRACT FROM AUTHOR]

Present communication providesa hybrid amplifier that can find suitable applications in DWDM optical network. The proposed hybrid amplifier includes EDFA and Raman amplifiers to envisage high gain characteristics for 64 channels in both the S + C band and S + C + L wavelength band (1545–1570 nm). Various parameters of the hybrid amplifier, such as doping concentration, pump power, pump wavelength, and fiber length, is chosen to optimize the gain profile. Aside from this, simulation upshots for individual amplifiers infer that EDFA shows a high gain of 22.1 dB for co-directional pumping, and the Raman amplifier deduces a gain of 12.2 dB for counter-directional pumping, whereas the EDFA-Raman hybrid amplifier bestows a substantial-high gain of 23.03 dB for co-directional pumping configuration. Additionally, it has been inferred that the hybrid amplifier offers a very minimal gain ripple of 0.8 dB, which indicates the gain is almost flat. The pump power, length, and doping parameters of EDFA and Raman amplifiers are optimized to get the flat gain of the Hybrid amplifier. It has been demonstrated that a maximum gain of 23.03 dB for a 64 × 10 Gbps, 25 GHz system is attainable up to 100 km of transmission distance. Hence, considering the aforementioned high gain and flat gain characteristics, the suggested EDFA-Raman hybrid amplifier opens up an avenue for future optical dense wavelength division multiplexing systems. [ABSTRACT FROM AUTHOR]

In this manuscript, the gain of the EDFA-Raman hybrid optical amplifier (HOA) is maximized using a popular nature inspired Whale Optimization Algorithm (WOA). The dominating parameters of HOA, length of Raman amplifier and EDFA and its pump powers are optimized to get the maximum possible gain. Further, the performance of WOA is compared by using other metaheuristic techniques such as Real coded Genetic Algorithm, Differential Evolution, Particle Swarm Optimization, to optimize the same model of HOA. WOA proves to be a better optimization technique as it is able to find maximum gain, have a better convergence curve and box plot performance as compared to the other three techniques. Moreover, the gain flatness and noise figure performance of HOA is compared with EDFA and Raman amplifier. [ABSTRACT FROM AUTHOR]

A Widely flatness gainbandwidth with double pass parallel hybrid fiber amplifier is experimentally demonstrated in this study. The proposed design combines serial erbium–Raman fiber amplifier in one branch and Raman fiber amplifier in the second branch. Multiple Raman pump units with a maximum power of 800 mW (250 mW of 1410 nm, 225 mW of 1480 nm, and 325 mW of 1495 nm) are utilized. Pump recycling technique is applied to achieve acceptable pumping efficiency. A maximum flatness gain bandwidth of 80 nm (1525–1605 nm) and average gain level of 22.5 dB are obtained at a small input signal power of - 25 dBm and optimum pump power values. While, a wider flatness gain of 90 nm (1520–1610 nm) and average gain level of 11.5 dB are achieved at a large input signal power of - 5 dBm. [ABSTRACT FROM AUTHOR]

In this paper, an ultra-long distance transmission fiber link based on bidirectional Raman amplifier is studied by theoretical simulation and experimental verification. The power evolution of pump and WDM signals in optical fiber in 355 km transmission link is simulated theoretically. The performance of the ultra-long distance system based on co-pump/counter-pump/bidirectional-pump Raman amplifier (CORA/CTRA/BiRA) are simulated. And the power budget is also predicted by simulation. The performance of 10*100 Gb/s signal transmission in 355 km fiber link based on bidirectional Raman amplifier are tested experimentally. The theoretical and experimental results are in good agreement. [ABSTRACT FROM AUTHOR]

Extending the sensing range for monitoring the railways, pipelines, borders, long structures, etc., has great importance in distributed fiber optic sensors development. Phase-sensitive optical time-domain reflectometry (φ-OTDR) sensors are the best candidate for this purpose. Optical fiber amplifiers in φ-OTDR sensors have increased the sensing range. A φ-OTDR sensor using combination of Erbium and Raman amplifiers has been demonstrated with a sensing range of 128 km. In this paper, we presented a disturbance monitoring up to 150 km utilizing Erbium and bi-directional Raman amplifications. In the proposed sensor, disturbances at 30, 70 and 120 km distances are applied and Rayleigh backscattered signals are investigated. [ABSTRACT FROM AUTHOR]

A simple switchable multiwavelength Brillouin–Raman fibre laser (BRFL) was demonstrated. The laser was arranged in a half-open cavity configuration including a physical mirror device with an adjustable reflectivity at one side of the laser cavity. The impact of the feedback power adjustment on frequency switching was carried out by comparing the peak power difference between odd- and even-order Stokes lines. Up to 468 flat-amplitude lines with a 10 GHz frequency spacing and average optical signal to noise ratio (OSNR) of 33 dB were observed with mirror reflectivity values of ∼15% up to 60% at a 1534 nm Brillouin pump power of 7 dBm and 0.9 W Raman pump power of 0.9 W. – Under the same pumping conditions, setting the mirror reflectivity at its OFF state (where reflectivity is nearly 0%) allows for up to 242 lines with 20 GHz spacing to be realized, with ONSR values of ∼35 dB. [ABSTRACT FROM AUTHOR]

A novel hybrid optical amplifier is proposed for 100 × 10 Gb/s dense wavelength division multiplexed (DWDM) system. The amplifier consists of a combination of Er-Yb co-doped fiber amplifier (EYDFA) with backward-propagating multi-pump Raman amplifier. A flat gain of >26 dB is achieved, over a wavelength range of 1545–1565 nm. The scheme works at 1 mW optimum input power per channel. Gain ripple of 1.37 dB and noise figure (NF) of <4.5 dB is observed. Anyhow, for higher input powers up to 10 mW, an increase in gain ripple up to 7.59 dB and NF up to 12.04 dB is observed. The effects of varying various parameters, like EYDFA pump wavelength, EYDFA length, Er/Yb concentrations and Raman length are also investigated. The obtained high and flat gain, along with the low NF, lesser bit error rate and high Q-factor, justifies the usefulness of proposed amplifier for applications in long-haul DWDM systems. [ABSTRACT FROM AUTHOR]

Abstract A novel flat-gain L-band hybrid optical amplifier is demonstrated using a combination of Raman and Er-Yb co-doped fiber amplifier (EYDFA) for a high capacity 80 × 100 Gb/s dense wavelength division multiplexed (DWDM) system at 0.2 nm channel spacing. The parameters of the proposed Raman–EYDFA hybrid amplifier are optimized using numerical techniques based on genetic algorithms to achieve a flat gain of >22 dB, with a gain ripple of 0.89 dB. This is obtained over a wavelength range of 1571–1587 nm at 1 mW optimum input power per channel, without using any costly gain clamping technique. The obtained noise figure (NF) is less than 6 dB for the given wavelength range. The overall decrease in gain and increase in NF is observed with the increase in input power. The obtained high and flat gain, along with the low NF and good Q-factor and bit error rate, confirms the feasibility of proposed amplifier for applications in broad band long-haul DWDM systems. [ABSTRACT FROM AUTHOR]

In this paper, we have reported a very advanced hybrid optical amplifier (Raman-TDFF amplifier) for the 180 × 10 Gbps super dense wavelength division multiplexing system with the channel spacing of 100 GHz. The performances of the model have been evaluated in terms of gain and noise figures for the C-band (from 1525 to 1565 nm). Gain flatness (>21 dB) is recorded with the least variation of 2.5 dB without using any cost effective technique. Further, the effect of the proposed hybrid optical amplifier has also been analyzed with slightly shifting the wavelength spectrum for the same feature. [ABSTRACT FROM AUTHOR]

silicon photonic crystal (PhC)-based structure is proposed to efficiently couple power from two different wavelengths, targeted to the application of an integrable Raman amplifier. The coupler uses two asymmetrical PhC waveguides as input ports which are joined together and the coupled power is directed to a slotted photonic crystal waveguide-based output port. Coupling efficiency and the other performance metrics are evaluated using a three-dimensional full-vector finite-difference time domain simulation method, which is tested for accuracy using some existing experimental structures and corresponding results. The heuristic approach has been adopted to optimize the design for maximizing the coupling efficiency. Dependence of the coupling performance on different design parameters has also been investigated. Simulations exhibit ∼3-dB coupling losses for both arms in a small footprint as small as ∼54 μm2. [ABSTRACT FROM AUTHOR]

In this paper, we have reported a very advanced hybrid optical amplifier (Raman-TDFF amplifier) for the 180 × 10 Gbps super dense wavelength division multiplexing system with the channel spacing of 100 GHz. The performances of the model have been evaluated in terms of gain and noise figures for the C-band (from 1525 to 1565 nm). Gain flatness (>21 dB) is recorded with the least variation of 2.5 dB without using any cost effective technique. Further, the effect of the proposed hybrid optical amplifier has also been analyzed with slightly shifting the wavelength spectrum for the same feature. [ABSTRACT FROM AUTHOR]

In this paper, a modified construction for the traditional ϕ -OTDR fiber sensor sensitive for all of distance is presented, the related numerical simulation and experiment analysis results show that this construction can reduce the gain imbalance for all of the distance along the fiber caused by the Rayleigh scattering loss of the fiber and the gain imbalance of Raman fiber amplifier in this fiber sensor system. In order to improve further the vibration sensitivity of this system, the possible methods to restrain the influences of modulation instability effect, Stimulated Brillouin effect, reduce the amplified spontaneous emission (ASE) noises of Raman laser (RL) and Erbium 3+ -doped fiber amplifiers (EDFA), double Rayleigh backscattering noise in this system are discussed, which will offer a great reference value for the science research and engineering application in the field of fiber sensor as we believe. [ABSTRACT FROM AUTHOR]

A micron-scale all-silicon Raman amplifier has been proposed in this paper, exploiting the giant Raman gain of silicon nanocrystal material along with the extreme optical confinement of slotted photonic crystal waveguide. Light Emitting Diode (LED) has been considered here for low-cost optical pumping and the possibility of on-chip integration. At the same time, LED pumping eradicates the temporal impairment of output pulses which is otherwise unavoidable in case of continuous wave laser pumping. An overall gain of 3.22 dB has been achieved for a 400 Gbps input pulse train with a waveguide length of the amplifier which is as small as 4 μm. Moreover, the strong electroluminescence of silicon nanocrystal opens up the possibility of integrating the pump source on the same platform and, hence, expedites the future scope of realizing micron-scale silicon Raman laser without external pump source. [ABSTRACT FROM AUTHOR]

In this work, we develop a high-power optical-fiber transmitter for lidar applications. The device can be utilized for measurements of the methane concentration and determination of the parameters of methane absorption line at wavelengths near 1,650 nm. The transmitter is based on a fiber Raman amplifier with an active fiber length converting the pumping radiation with a wavelength of 1,540 nm to the desired wavelength region of about 1,650 nm. We conduct the theoretical modeling of the Raman amplifier operation and demonstrate the advantage of the two-stage amplifier design over the single-stage design. In the modeling, the total power of a single Raman amplifier in the twostage design is 4.5 W with a pumping power of 5 W and an active fiber length of 1,000 m. Then we experimentally investigate the developed single Raman amplifier and demonstrate a satisfactory agreement between its parameters and the results of the theoretical modeling. The achieved average power of the transmitter at the output stage is over 7 W with two single Raman amplifiers joined in parallel. The distributed-feedback (DFB) master laser utilized in the transmitter is modulated by a linear-frequency signal with simultaneous application of a nonsynchronous high-frequency signal to eliminate the noise due to stimulated Brillouin scattering. [ABSTRACT FROM AUTHOR]

Ever since the laser's invention, there has been great interest in increasing beam output power without detriment to its coherence. Despite great advances having been obtained through the use of a diverse range of approaches, steady-state beam powers above ten kilowatts remain a significant challenge for solid-state lasers due to the heightened impact of detrimental nonlinear effects such as thermal lensing. Multiplexing several lasers using beam combination represents a method for surpassing the power barriers of single lasers. Here we propose and demonstrate a novel approach to beam combination and power scaling based on Raman conversion in diamond. Power from multiple non-collinear pump beams is efficiently transferred onto a single Stokes beam in a single-pass amplifier. Using three mutually-independent nanosecond pulsed beams from a free-running-linewidth 1064 nm laser, 69% of the total peak pump power of 6.7 kW was transferred onto a TEM00 Stokes seed pulse at 1240 nm in a 9.5 mm long diamond crystal. Compared to other beam combination techniques, diamond beam combination has advantages of relaxed constraints on pump beam mutual coherence, while enabling narrowband output. Thermal considerations for extending from low duty-cycle to continuous wave operation and higher power levels are discussed. [ABSTRACT FROM AUTHOR]

This paper reports on the performance of multi-wavelength Brillouin-Raman fiber laser exploiting an optical reflector. The ring-cavity multi-wavelength Brillouin-Raman fiber laser is based on hybrid Brillouin-Raman gain supported by SBS and SRS. The multiwavelength Brillouin-Raman fiber laser is systematically analyzed at different values of Raman pump powers, Brillouin pump powers, and categorically based on single mode fiber length, and Raman fiber length which operated from 1460 nm to 1430 nm of BP wavelengths. The optical reflector at 90% of reflectivity acts as an optical mirror is used in this structure. There are 5 channels at 1500 nm, and 1510 nm of BP wavelengths observed at Raman pump power of 30 dBm, 8 km of Raman fiber and 4 km of single mode fiber. In addition, the Raman pump power of 30 dBm is able to produce high gain value and subsequently generate a large number of channels across S-band region. [ABSTRACT FROM AUTHOR]

This paper is focusing on simulation and analyzing of S-band multi-wavelength Brillouin–Raman fiber laser performance utilizing fiber Bragg grating and Raman amplifier in ring cavity. Raman amplifier-average power model is employed for signal amplification. This laser system is operates in S-band wavelength region due to vast demanding on transmitting the information. Multi-wavelength fiber lasers based on hybrid Brillouin–Raman gain configuration supported by Raman scattering effect have attracted significant research interest due to its ability to produced multi-wavelength signals from a single light source. In multi-wavelength Brillouin–Raman fiber, single mode fiber is utilized as the nonlinear gain medium. From output results, 90% output coupling ratio has ability to provide the maximum average output power of 43 dBm at Brillouin pump power of 20 dBm and Raman pump power of 14 dBm. Furthermore, multi-wavelength Brillouin–Raman fiber laser utilizing fiber Bragg grating and Raman amplifier is capable of generated 7 Brillouin Stokes signals at 1480 nm, 1510 nm and 1530 nm. [ABSTRACT FROM AUTHOR]

This paper presents a performance analysis and comparison of optimized multipump Raman and hybrid erbium-doped fiber amplifier (EDFA) + Raman amplifiers, operating simultaneously at conventional (C) and long (L) bands, using multiobjective optimization based on evolutionary elitist nondominated sorting genetic algorithm. The amplifiers performance was measured in terms of on-off gain, ripple, optical signal-to-noise ratio (OSNR) and noise figure (NF), after propagating over 90 and 180 km of single-mode fiber (SMF). Numerical simulation results of the first analysis show that only three pumps are necessary to generate optimal gains in both amplifiers. Comparing the results of the second performance analysis, we conclude that, after 90 km SMF, the two amplifiers has the same on-off gain, if the total pump power (1807.1 mW) of the Raman amplifier is approximately double (100 + 994.7 mW) of the hybrid amplifier, when the EDFA is operating at 1480 nm with 5 m of doped fiber. Furthermore, the Raman amplifier needs a single laser with at most 741.1 mW, against 343.9 mW of the distributed Raman amplifier (DRA) pump in the hybrid system. Finally, the results of the last analysis, which considers only the EDFA + Raman amplifier, shows that with on-off gain of 26.14 dB, ripple close to 1.54 dB over a bandwidth of 66 nm and using three pumps lasers in the DRA the achieved OSNR was 39.6 dB with an NF lower than 3.3 dB, after 90 km of SMF. [ABSTRACT FROM AUTHOR]

Taguchi's method is introduced to perform multiobjective optimization of fiber Raman amplifier (FRA). The optimization requirements are to maximize gain and keep gain ripple minimum over the operating bandwidth of a wavelength division multiplexed (WDM) communication link. Mathematical formulations of FRA and corresponding numerical solution techniques are discussed. A general description of Taguchi's method and how it can be integrated with the FRA optimization problem are presented. The proposed method is used to optimize two different configurations of FRA. The performance of Taguchi's method is compared with genetic algorithm and particle swarm optimization in terms of output performance and convergence rate. Taguchi's method is found to produce good results with fast convergence rate, which makes it well suited for the nonlinear optimization problem. [ABSTRACT FROM AUTHOR]

An Er/Yb co-doped fiber/Raman hybrid amplifier (HA) is proposed and studied theoretically and analytically to improve the gain and noise figure of optical amplifiers. The calculations are performed under a uniform dopant and steady-state conditions. The initial energy transfer efficiency for Er/Yb co-doped fiber amplifier (EYDFA) is introduced, while the amplified spontaneous emission (ASE) is neglected. The glass fiber used for both Er/Yb and Raman amplifiers is phosphate. Different pump powers are used for both EYDFA and RA with 1 μW input signal power, 1 m length of Er/Yb amplifier and 25 km length of Raman amplifier (RA). The proposed model is validated for Er/Yb co-doped amplifier and Raman amplifier separately by comparing the calculating results with the experimental data. A high gain and low noise figure at 200 mW Raman pump power and 500 mW Er/Yb pump power are obtained for the proposed HA as compared with the experimental results of EYDFA, Raman amplifier and the EDFA/Raman hybrid amplifier. [ABSTRACT FROM AUTHOR]

We investigate the utilization of semiconductor optical amplifiers (SOAs) and quantum-dot laserbased Raman amplifiers in high-capacity dense wavelength division multiplexed (DWDM) 1310-nm transmission systems. Performed simulations showed that in a 10 x 40 Gbit/s system, the utilization of a single Raman amplifier in a back-propagation scheme can extend the maximum error-free (bit error rate <10-9) transmission distance by approximately 25 km in comparison with the same system utilizing only an SOA used as a preamplifier. We successfully applied a Raman amplifier in an 8 x 2 x 40 Gbit/s 1310-nm polarization multiplexed (PolMux) DWDM transmission over 25 km. Conducted experiments showed that the utilization of a Raman amplifier in this system leads to 4-dB improvement of the average channel sensitivity in comparison to the same system utilizing SOAs. This sensitivity improvement can be translated into a higher power budget. Moreover, lower input optical power in a system utilizing a Raman amplifier reduces the four-wave mixing interactions. The obtained results prove that Raman amplification can be successfully applied in 1310-nm high-capacity transmission systems, e.g., to extend the reach of 400G and 1T Ethernet systems. [ABSTRACT FROM AUTHOR]

The gain characteristic of spontaneous Brillouin scattering in 50 km single-mode fiber with a Raman pump is investigated. The Brillouin signal source is an external cavity laser (ECL) with 1550 nm wavelength and 1 mW power, and it is amplified by a 1455 nm Raman laser with the tunable power of 0 – 1000 mW. The results show that Stokes Brillouin scattering signal is amplified by Raman amplifier and Brillouin amplifier simultaneously. The high gain of 46.5 dB and 53 dB for backward Raman pump configuration and forward Raman pump configuration are achieved, respectively. And the differences between two types of Raman pump configurations are also analyzed. [ABSTRACT FROM AUTHOR]

We demonstrate the wavelength conversion of return-to-zero differential phase-shift keying (RZ-DPSK) signal with the pulsewidth-tunable operation using a Raman amplifier (RA)-based ultrashort pulse compressor and a highly nonlinear fiber (HNLF)-based four-wave mixing (FWM) switch. The wavelength of the input RZ-DPSK signal is converted to new wavelengths owing to the FWM effect in HNLF. On the other hand, the pulsewidth of the wavelength-converted RZ-DPSK signal is tuned from 10 to 3 ps by using the ultrashort pulse source based on RA-based adiabatic soliton pulse compression. The bit error rate characteristics of the input RZ-DPSK and the wavelength-converted RZ-DPSK signals with different pulsewidths are measured and error-free operations are achieved in all cases. The optical spectra, autocorrelation traces, and clear and opening eye diagrams show high conversion performance with wide-range pulsewidth tunability. [ABSTRACT FROM AUTHOR]

This study demonstrates simulation and experimental validation of a wideband serial hybrid Raman/erbium-doped fiber amplifier. Two configurations are adopted; in type A, a Raman amplifier is the first stage, and in type B, an erbium-doped fiber amplifier is the first stage. At low input signal power, the average gain level is 20 dB with a flat gain bandwidth of 40 nm for both configurations. The noise figure in type B is dominated by the erbium-doped fiber amplifier and produces lower values and flatter spectra than in type A. The gain of the proposed hybrid amplifiers is affected more by the second amplification stage. [ABSTRACT FROM PUBLISHER]

Using particle swarm optimization method, an optimized gain ripple was found for two-sided coupled integrated spaced sequence of Si and Si1−xGexmicroring resonator Raman amplifier. This amplifier had two sides of ring resonators, each consisting of eight rings. On the one side, the microrings were made of Si, and on the other, they were constructed from microSiGe rings. Resonance frequencies of a ring in Si row were equal to those of a ring in the SiGe row; therefore, for a ring of the first row and a ring of the second row, only one pump was used. [ABSTRACT FROM AUTHOR]

Dynamic characteristics of a multi-wavelength Brillouin–Raman fiber laser (MBRFL) assisted by four-wave mixing have been investigated through the development of Stokes and anti-Stokes lines under different combinations of Brillouin and Raman pump power levels and different Raman pumping schemes in a ring cavity. For a Stokes line of order higher than three, the threshold power was less than the saturation power of its last-order Stokes line. By increasing the Brillouin pump power, the n th order anti-Stokes and the ( n +4)th order Stokes power levels were unexpectedly increased almost the same before the Stokes line threshold power. It was also found out that the SBS threshold reduction (SBSTR) depended linearly on the gain factor for the 1st and 2nd Stokes lines, as the first set. This relation for the 3rd and 4th Stokes lines as the second set, however, was almost linear with the same slope before SBSTR −6 dB, then, it approached to the linear relation in the first set when the gain factor was increased to 50 dB. Therefore, the threshold power levels of Stokes lines for a given Raman gain can be readily estimated only by knowing the threshold power levels in which there is no Raman amplification. [ABSTRACT FROM AUTHOR]

We report a simple budget heuristic for a fast optimization of multipump Raman amplifiers based on the reallocation of the pump wavelengths and the optical powers. A set of different optical fibers are analyzed as the Raman gain medium, and a four-pump amplifier setup is optimized for each of them in order to achieve ripples close to 1 dB and gains up to 20 dB in the C band. Later, a comparison between our proposed heuristic and a multiobjective optimization based on a nondominated sorting genetic algorithm is made, highlighting the fact that our new approach can give similar solutions after at least an order of magnitude fewer iterations. The results shown in this paper can potentially pave the way for real-time optimization of multipump Raman amplifier systems. [ABSTRACT FROM AUTHOR]

The Raman amplifier can be used to increase the range of 1310 nm transmission. In the paper, we present detailed studies regarding the design and performance of the 1310 nm Raman amplifier utilizing quantum-dot pumping lasers. We design and investigate performance of the QD laser based 1310 nm Raman amplifier with a single and double pump configuration, different fiber lengths and 1240/1310 nm coupler types (CWDM or circulator). The 1310 nm Raman amplifier gain as a function of wavelength is presented showing the amplification bandwidth of about 14-16 nm. Further, we achieved a gain of 17.7 dB and a noise figure of 4.5 dB in a QD-laser pumped 1310 nm Raman amplifier in a double pump configuration and 12.3 dB in a single pump configuration. Application of the 1240/1310 nm CWDM coupler allows for about 1-2 dB higher gain than circulator, however, with the potential trade off of the amplification bandwidth. We compare the 1310 nm Raman amplifier with the 1310 nm SOA, proving the comparable gain, higher saturation output power and lower noise figure of the Raman amplifier. Finally, we show that joined SOA-Raman amplifier can provide the bandwidth up to 85 nm. [ABSTRACT FROM AUTHOR]

Optical amplifiers are realised in a wide range of applications, such as metro -- dense wavelength division multiplexing and cable television networks. These applications require the amplifier to provide a maximum output power level by accepting an input power near the saturation level. To obtain an ideal amplifier according to several parameters, the erbium concentration in the composite core glass, the optimum length of the fibre, the pump saturation and the input signal signal-to-noise ratio must be critically studied and addressed. In this paper, we will review the types of optical amplifiers used in communication systems today as well as the parameters that limit the performance of optical amplifiers in the network, such as the noise figure, the gain saturation, the polarisation dependence gain and inhomogeneous broadening effects. Based on the performance limitation factor, we model the amplifier gain profile and the effect of the gain value on the network performance. Finally, we propose various configurations of an optical amplifier, and the advantages of each amplification technique are highlighted. [ABSTRACT FROM AUTHOR]

Raman threshold pump power and optical amplification band calculations adjusted for attenuation dispersion in the range of total S+C+L telecom window of silica fibers (roughly from 1.46 to 1.62 µm) are presented. It has been shown that wavelength nonuniformity of signal attenuation coefficient essentially effects on amplification bandwidth and leads to the bandwidth decrease from 0.9 to 2.5 THz depending on pump spectral position and fiber type. Offered has been the technique of analytical approximation of attenuation coefficient as a basis for pump power threshold determination and for preceding data correction with reference to an optical amplification band. Simulation results for three widely used fibers, namely, DCF, TrueWaveRS™ and SMF have been presented. However, the technique allows estimating the optimal pump power in fiber Raman amplifiers for other fiber types as well. [ABSTRACT FROM AUTHOR]

This study demonstrates a broadband gain-clamped and gainflattened dispersion-compensated Raman/erbium-doped fiber hybrid amplifier that recycles residual Raman pump power using a single fiber Bragg grating for wavelength-division multiplexing systems. The optimum gain-clamped wavelength was 1564 nm. A gain variation of less than 0.21 dB can be achieved from 1525 to 1625 nm, and the dynamic input power exceeds 18 dB, ranging from -20 to -2 dBm. Further, a gain ripple of ±1.75 dB can be achieved from 1530 to 1595 nm. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A novel twin-core photonic crystal fiber was proposed to reduce the complexity and cost of fiber Raman amplifiers. By means of a proper design, this fiber could acquire a higher and flatter Raman gain efficiency coefficient curve rR=gR/Aeff over a specified band of wavelength than a conventional fiber. A Raman amplifier was designed with this novel twin-core photonic crystal fiber to operate in C band from 1530 nm to 1565 nm. A remarkable improvement over a conventional fiber Raman amplifier was obtained. It was numerically demonstrated that when pumped with a single source, an average gain of 8.7 dB with a fluctuation of less than 0.9 dB is achievable. [ABSTRACT FROM AUTHOR]

An experimental comparison of the stability performance of two multiwavelength lasers, based on either an erbium- doped fiber or Raman amplification, is reported. Both systems employ fiber Bragg gratings to select the operating wavelengths within the resonant ring cavity. The aim of this study is to compare the output power stability of the lasers and also their optical SNR ratios. [ABSTRACT FROM AUTHOR]

Abstract: We propose a perturbation method for time division multiplexed (TDM) pumping fiber Raman amplifier (FRA). The method is based on the solution of Raman partial differential equations (PDEs) by a closed integral form. Taking the signals and pumps power as the interim solution and updating their values in an iterative process, Raman gain and pump/signal evolution can be calculated in any order of accuracy. In the first order of perturbation, some analytical formulas for the FRA dynamic control are obtained. Analytical formulas are employed for gain ripple minimization and also the gain clamping problem under channel reconfiguration. [Copyright &y& Elsevier]

Abstract: Based on Lagrangian multiplier method (LMM), the gain spectrum of distributed multi-pump Raman amplifier (DMRA) is optimized. Beside of governing rate equations in Raman amplifiers, we consider two applicable constrains on cost function for optimizing the gain spectrum. Because of more accurate and controllable designing of DMRAs, a maximum power for each input pump wave is considered as well as average gain value as two constrains. LMM reduces the optimization problem with constrains to solve a two-point boundary value problem for each solution. This method is applied to minimizing gain ripple of full bandwidth (60nm) a 100Km Raman amplifier for different number of pumps. [Copyright &y& Elsevier]

Abstract: In this paper, the variational method is employed for minimizing the gain ripple of multi-wavelength fiber Raman amplifiers. The variance of gain spectrum of the fiber Raman amplifier is regarded as the cost function, restriction on total pump power and average gain is given as the constraints of the minimization problem. It is shown that the minimization problem with any necessary constraints on the pump powers, average gain and signal to noise ratio, is reduced to a two-point boundary value problem. The method gives the entire possible local and global solutions. The method is applied to different examples of fiber Raman amplifiers with different lengths from 25km to 100km and different numbers of pumps from 4 to 20 to determine the pump powers and wavelengths for minimum gain ripple. It was obtained for a 100km fiber Raman amplifier the gain ripple can be about 0.1dB with on–off gain more than 20dB. [Copyright &y& Elsevier]

We propose a low-cost Raman based amplification scheme for coarse wavelength division multiplexing systems. We also present a mathematical model suitable to be used in the design, analyze and optimization of Raman amplification systems. We validate the mathematical model with extensive comparisons with experimental results. Good agreement is obtained between numerical and experimental results. An amplification system offering more than 18 dB of gain over more than 80 nm is obtained using only four low power (up to 500 mW) semiconductor lasers. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 297–301, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23075 [ABSTRACT FROM AUTHOR]

The influence of pump direction in all-optical gain-clamped fiber Raman amplifier using the directional couplers in feedback loop is demonstrated. The isolator direction decided the lasing direction in feedback loop. The comparison of performance in two lasing directions for both schemes is shown. It is concluded that the forward pumping configuration with forward lasing has better gain clamping performance and noise performance. [ABSTRACT FROM AUTHOR]

In the present paper, the highly efficient Raman amplification properties of a realistic and idealized dispersion compensating photonic crystal fiber (DCPCF) are described numerically. We have used an accurate full-vectorial finite element modal solver with hybrid curvilinear edge/nodal elements and anisotropic perfectly matched layers for an accurate modal characterization of the realistic as well as idealized DCPCF. A good agreement is observed between numerically evaluated and experimentally [P.J. Roberts, B.J. Mangan, H. Sabert, F. Couny, et al., J. Opt. Fiber Commun. Rep. 2 (2005) 435–461] measured dispersion values. A high peak Raman gain efficiency of 10.5 W−1 km−1 is obtained at 13.1 THz frequency shift for a 1455 nm depolarized pump. A DCPCF module of 1-km length can compensate for the dispersion accumulated over 70-km of conventional single mode fiber link with a residual dispersion of ±50 ps/nm and can provide an average gain of 7.6 dB with ±0.9 dB gain ripples over C-band. [Copyright &y& Elsevier]

This paper presents a numerical analysis and comparison on the performance of multi-pump gain-flat Raman amplifiers based on triangular photonic crystal fiber and conventional fiber. It is demonstrated that the extra 5.93 dB Raman net gain can be achieved in the L-band when PCF acts as Raman gain medium. The noise performance of the two amplifiers are also calculated and compared. Comparison with the data of published literature was also carried out to verify our analysis. The results showed that PCF is the appropriate candidate for high gain Raman amplifiers. [ABSTRACT FROM AUTHOR]

Abstract: Based on dual-order stimulated Raman scattering (SRS) of a single 1395nm Raman fiber laser in 75km single mode fiber and its corresponding dispersion compensation module, a hybrid Raman/Erbium doped fiber amplifier (EDFA) for long wavelength band (L-band) amplification is realized by inserting a segment of EDF within the span. By comparing the performance of gain and noise in four hybrid amplifiers with different span configurations, we find that the distribution of the secondary L-band amplification obtained from the EDF along the link has a great influence on the performance of the hybrid amplifier. Both gain and noise performance of hybrid amplifier can be improved significantly by optimizing the location of the EDF. Moreover, we can extend the flat gain bandwidth from L-band to central wavelength band (C-band) plus L-band by recycling the residual first-order SRS to pump a segment of EDF with proper length. [Copyright &y& Elsevier]

Abstract: We show experimentally and numerically that pump-to-Stokes transfer of relative intensity noise (RIN) makes a significant contribution to the output RIN of Raman fiber lasers (RFLs). We theoretically investigate the penalty in the signal-quality factor induced by a noisy RFL pump in a co-pumped Raman-amplified transmission span, where the noise on the RFL output is caused by pump-to-Stokes transfer of RIN. This penalty can be kept low by a proper design of the RFL, in particular by using high-reflectivity output couplers, high-gain Raman fibers and optimizing the RFL fiber length. [Copyright &y& Elsevier]

Abstract: By employing an output-power clamping technique, a dual-order Raman fiber laser (RFL) is theoretically presented with suppressed low-frequency relative-intensity-noise (RIN) transfer from pump sources to both first- and second-order Stokes output. Their powers can be easily tuned in a large dynamic range. Furthermore, the second-order output power can be individually controlled, which makes it flexible to adjust the ratio of the first- to second-order output power. In addition, the stabilization of low-power second-order output is also accomplished in the RFL setup. These properties fit the proposed RFL for use as dual-order pump sources in Raman fiber amplifiers. [Copyright &y& Elsevier]

In this article, a novel semi-analytical algorithm for calculating backward-pumped Raman amplifier is proposed. The algorithm does not need iteration and can greatly save computational time. Simulation results for Raman amplifiers with 25 km, 50 km, and 100 km fibers show that the accuracy of the method is quite satisfying in comparison with the shooting algorithm and the deviation is within 0.02 dB. [ABSTRACT FROM AUTHOR]

Abstract: We evaluated the effects of MPI noise on various modulation formats in a distributed Raman amplified system. The results show that RZ-DPSK is the most tolerant modulation format to MPI noise. [Copyright &y& Elsevier]

Abstract: We demonstrate the characteristics of the reflective type discrete Raman amplifier in the dispersion compensating fiber which is composed of a circulator and a Faraday rotator mirror. With the same dispersion compensation, the gain of the reflective type is higher than that of the conventional single-pass type. Moreover, the forward pumping is better than the backward pumping in the reflective type dispersion compensating Raman amplifier. We also show that, by using the reflective type configuration, the polarization mode dispersion of the dispersion compensating fiber can be almost compensated. [Copyright &y& Elsevier]

A discrete higher order pumped Raman amplifier served for dispersion compensation and amplification with a fiber Bragg grating (FBG) reflecting residual first-order pump power back into it is demonstrated. The on–off Raman gain differences are analyzed between with and without FBG. Noise performance analysis shows that the higher order pumped Raman amplifier with FBG is less susceptible to multipath interference noise than without FBG, reducing system penalties at high on–off Raman gain. At the same time, the Q-factor-lowering problem is alleviated when the FBG is tailed to reflect residual first-order pump power. [Copyright &y& Elsevier]