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From the advent of communication, there has been a constant demand for increasing communication capacity. In optical communications, capacity can be increased by implementing more fibers or can be increased by using the same fiber to transmit more than one signal. The process is known as the wavelength division multiplexing or WDM. Channels placed closer to each other in the wavelength scale leads to the process of DWDM or dense WDM networks. But with so many channels transmitted together over minimum distances of 10 km, the power of each channel decreases significantly within the fiber, hence a Raman amplification system has been incorporated within the network. The whole system is designed at the 1300 nm optical window which has shown the least dispersion among the other optical windows. Results from simulating a 16 channel network with 8 optical pumps, where all are configured in co and counter propagating directions. They have shown good amount of gain, relatively low noise and good SNR over the whole communication band of channels rendering the system to be a faithful communication network. [ABSTRACT FROM AUTHOR]

A hybrid optical amplifier (HOA) is designed and optimized for the transmission of 40 dense wavelength division multiplexed system (DWDM) channels modulated at 10 Gbps having 25 GHz spacing at the edge of the L and U wavelength bands over more than 250 km. Multi-parameter optimization process is used to achieve the highest gain and best gain flatness. Different power combinations distributed among four lasers of a total forward pumping power (1270 mW) and total backward pumping power of either 730 mW or 850 mW are investigated for their effect on the hybrid amplifier gain and flatness. The best power distribution among the pumps provides about 31 dB overall gain with a flatness about 0.8 dB and noise figure ∼5.7 dB. It is found that the red-shifted pumps' wavelengths should be used in the forward direction, while the blue-shifted pumps' wavelengths should be used in the backward direction. [ABSTRACT FROM AUTHOR]

The ever-increasing demand for the transmission capacity has stimulated intensive investigations, in terms of both new transmission window of standard single mode fiber (SSMF) and new fiber utilizing the spatial domain. Multi-band wavelength division multiplexing (WDM) transmission exploring the extended wavelength band, besides traditional C+L band, is an attractive solution for the rapid and cost-effective enhancement of transmission capacity. To this end, here we demonstrate the U-band WDM transmission over 125-km G.652.D fiber, when the C-band amplified spontaneous emission (ASE) source acts as the incoherent pump for Raman amplification (RA). Meanwhile, bidirectional long short-term memory neural network (BiLSTM-NN) is applied to inversely design the spectral shape of two C-band ASE sources. After the optimization through inverse design, the ROP variation at the U-band can be less than 1.2 dB under different net Raman gains. Consequently, we can experimentally achieve a net Raman gain of ∼15 dB over a 3 dB bandwidth of around 2.1 THz at the U-band, under the condition of distributed bidirectional Raman pump configuration. Finally, the performance of the U-band RA is experimentally verified by transmitting three-wavelength 20 GBaud DP-QPSK signals, when the threshold of 7% HD-FEC can be successfully reached.

Optical amplifiers are developed to boost up the performance of the communication systems. Amplifiers such as erbium doped fiber amplifier (EDFA), RAMAN and semiconductor optical amplifier (SOA) are used for this purpose. It is mandatory to use optical amplifiers for signal transmission to long distances. In this paper, the hybrid optical amplifier EDFA-RAMAN-EDFA is proposed to enhance the signal quality received at receiver end and to initiate the efficient transmission of 8 × 10 Gbps transmission speed for wavelength division multiplexed (WDM) system. The proposed mechanism is evaluated with respect to various parameters such as quality factor, eye-height, and bit error rate (BER) and eye diagram considering various values of transmission distance ranging from 100 to 200 km. The analysis shows that the proposed mechanism has better quality factor value and minimum BER value than the traditional approach. Wider eye opening for proposed technique represents that the distortions produced in the system are least. [ABSTRACT FROM AUTHOR]

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]

The study presents the average power model of optical Raman fiber amplifiers based on frequency spacing and amplifier section stage optimization technique. The amplifier section stage is taken from 25 to 75 km and frequency spacing is taken from 0.2 up to 1 nm. Input/output Raman signal variations are measured versus operating wavelength range and bit time period variations. The suitable input signal power for the optical transmitter is chosen to be −10 dBm and return to zero modulation code is applied with an available data rate of 10 Gb/s. Sixty-four channels are multiplexed to benefit a multi-number of users with suitable power levels. [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]

In this letter, we apply high-bandwidth silicon-based integrated coherent Transmit & Receive Optical Sub-Assembly (IC-TROSA) in long-haul fiber transmission systems. G.654E fiber and Raman amplifiers are employed in the fiber link to reduce the transmission loss and the nonlinear interference. In the experimental demonstration, the silicon-based IC-TROSA can provide similar performance as commercial coherent transceivers. In addition, G.654E fiber can achieve longer transmission distance than G.652D fiber. Moreover, 16 Tb/s ($80\times 200$ Gb/s) Nyquist DP-QPSK and 20 Tb/s ($50\times 400$ Gb/s) Nyquist DP-16QAM transmission over 10000 km and 4000 km fiber distance have been successfully achieved under the threshold of soft-decision forward error correction (SD-FEC) codes with 20% overhead, respectively. [ABSTRACT FROM AUTHOR]

Four wave mixing (FWM), Erbium doped fiber amplifier (EDFA), semiconductor optical amplifier (SOA), Raman amplifier, Bit error rate (BER), Erbium doped fiber amplifier (EDFA), optical spectrum analyzer (OSA) Q-factor and BER for amplifiers is obtained as 6.1, 10 SP -10 sp (EDFA-EDFA), 10.62, 10 SP -27 sp (RAMAN-EDFA) and 11.01, 2.1×10 SP -29 sp (SOA-EDFA) at 150 Km. Subsequent to this amplifier is SOA-EDFA that provides Gain less than EDFA-EDFA but more than Raman-EDFA. Keywords: Four wave mixing (FWM); Erbium doped fiber amplifier (EDFA); semiconductor optical amplifier (SOA); Raman amplifier; Bit error rate (BER); optical spectrum analyzer (OSA) EN Four wave mixing (FWM) Erbium doped fiber amplifier (EDFA) semiconductor optical amplifier (SOA) Raman amplifier Bit error rate (BER) optical spectrum analyzer (OSA) 303 309 7 07/05/22 20220701 NES 220701 1 Introduction Nowadays, technological development, a period noticeable by augmentation of multimedia services and wavelength division multiplexing based communication systems, has set increase to high capacity WDM optical networks. [Extracted from the article]

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]

A tunable multiwavelength Brillouin-Raman fiber laser (MW-BRFL) operated at an ultralong wavelength band (U-band) is presented in this work. The MW-BRFL was configured in a full-open linear cavity consisting of 11.2 km long dispersion compensating fiber that functioned as a Brillouin frequency shifter and Raman amplification gain medium. At Raman and Brillouin pump powers of 930 mW and 11.8 dBm, respectively, a stable multiwavelength generation with wavelength spacing of 0.17 nm was generated over a wavelength span of 53 nm. The generated channels covered a spectral range of 1630–1683 nm corresponding to 314 channels. The channels could also be tuned over 10 nm with an average optical signal-to-noise ratio greater than 26 dB. The laser system exhibited power fluctuation of less than 0.25 dB over 3 h. In a nutshell, the proposed MW-BRFL is promising with respect to its performance, simplicity and flexibility.

We provided a feasible solution for 800-Gb/s per carrier long-distance wavelength division multiplexing (WDM) coherent optical fibre transmission based on offline DSP. We experimentally demonstrate 5-carrier 125-GHz-spacing WDM coherent optical fibre transmission achieving 2000-km transmission distance and 800-Gb/s net bit rate per carrier. We utilized 100-Gbaud truncated probabilistically shaped (TPS) polarization-multiplexed 64QAM format in this work. In terms of advanced components, the high-speed digital-to-analog converter with 35-GHz 3 dB-bandwidth and Raman-amplified ultra-large-area fibre were utilized to achieve higher baud-rate and longer transmission distance. In terms of modulation format, we changed PS to TPS to obtain a more suitable shaping depth, and make the shaped signal better suited to the DSP process of coherent optical communication, including constant modulus algorithm (CMA) equalizer. Besides, our results show that the TPS-64QAM signal with 5-bit/symbol/polarization entropy outperforms the standard-32QAM with a same bit rate by around 1 dB sensitivity gain. Furthermore, we proposed a multiple-input multiple-output (MIMO) Volterra equalizer (VE), which consists of a 1st-order 2 × 2 MIMO complex-valued widely linear (WL) equalizer and a 2nd-order real-valued nonlinear equalizer. Our proposed MIMO VE can effectively resolve the impact of In-phase/quadrature (IQ) imbalance and IQ skew, and compensate linear and nonlinear impairments at the same time. We also utilized partial kernel VE to reduce the complexity by retaining part of the 2nd-order kernels. [ABSTRACT FROM AUTHOR]

The objective of current work is to design and analyzed 96×10 Gbps DWDM system taking EDFA, SOA, and RAMAN amplifier as an inline amplifiers up to a fiber length of 300 km. The performance of EDFA, SOA, and RAMAN amplifier is measured on the basis of power received, Q-factor, probability of error and BER for various values of fiber distance. In this paper it has been proved that for 96 channels DWDM system at 10 Gbps bit rate, EDFA reveals superior performance as far as the amount of power received is concerned. The value of quality factor (Q-factor) for RAMAN amplifier is almost identical to that of the Q-factor for EDFA and is higher than the Q-factor for SOA till a fiber length of roughly 80 km thereafter SOA reveals somewhat better Q-factor than EDFA and RAMAN amplifier. As far as BER is concerned EDFA and RAMAN amplifier show roughly identical and somewhat lower BER than SOA till a fiber length of roughly 80 km, afterwards SOA reveal somewhat lesser BER till the fiber length of 210 km. In relation to the probability of error P(E), It is analyzed that P(E) remains more or less same for the entire set of optical amplifiers(OAs) but beyond the fiber length of 240 km EDFA shows somewhat lower P(E) than the other two OAs. At the end the Eye diagrams for the three OAs are also figure out. [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]

Analysis is presented to evaluate numerically the combined effect of amplified spontaneous emission (ASE) and stimulated Raman scattering (SRS) on the bit error rate performance of a WDM transmission system with Raman amplifier using heterodyne receiver. The results are compared with those for a WDM system reported with direct detection receiver for different system parameters. It is observed that coherent heterodyne system is less affected by the crosstalk due to combined effect of ASE and SRS compared to direct detection. It is noticed that allowable transmission distance is 170 km, and 166 km of WDM channels for 8, and 16, respectively, when coherent heterodyne receiver is and with pump power of 10 mW and channel bandwidth of 12.5 GHz. The corresponding transmission distance is 60 km and 10 km, respectively, for direct detection system already reported. [ABSTRACT FROM AUTHOR]

The development of lightwave systems required large capacity communication networks in today's high-tech era. To fulfill these challenges required proper amplification of the signals. Hybrid optical amplifier made a remarkable change in present optical networks in order to amplify the signals for better performance of a system. In this paper, we have proposed different hybrid optical amplifier configurations [such as semiconductor optical amplifier (SOA)-erbium-doped fiber amplifier (EDFA), EDFA-EDFA, Raman-EDFA] at channel spacing of 0.8 nm for 8 × 10 Gbps for wavelength division multiplexed optical networks. The performance is examined on the basis of quality factor (dB), maximum output power (dBm), minimum bit error rate (BER), and minimum eye closure by varying the transmission distance from 20 to 180 km. It is demonstrated that Raman-EDFA configuration provides better results for the small distances up to 100 km as compared to EDFA-EDFA and SOA-EDFA configurations. The variation in Q factor for Raman-EDFA, EDFA-EDFA, and SOA-EDFA is 33.35–13.56 dB, 32.30–10.95 dB, and 18.52–25.03 dB, respectively. When distance is increased from 100 to 180 km, SOA-EDFA provides better results than Raman-EDFA in terms of BER, but it shows non-uniform gain spectrum. [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]

Optical networks were invented by the developing and developed nations in order to extend the capacity required for communication systems in a worthwhile way. In this paper, the attempt is done to improve the capacity and performance of semiconductor optical amplifier, Raman and erbium-doped fiber amplifier (EDFA) amplifiers used in optical networks. The potential of different optical amplifiers operating at 8×10 Gbps has been examined and their performance was compared on behalf of different parameters, viz. eye opening, eye closure, jitter, quality factor and transmission distances. It was observed that EDFA provided the consistent good quality of communication for long-distance transmission up to 150 km along with better eye opening and eye closure with acceptable jitter performance. Further, it is observed on the basis of quality factor and bit error rate that EDFA gives comparably better performance than Raman amplifier. Moreover, it is seen that as the data rate of the system increases, the quality of communication signals starts decreasing. [ABSTRACT FROM AUTHOR]

Distributed Raman amplifier (DRA) has been widely studied in recent decades because of its low noise figure and flexible gain. In this paper, we present a novel scheme of DRA with broadband amplified spontaneous emission(ASE) source as pump instead of discrete pump lasers. The broadband pump is optimized by machine learning based inverse design and shaped by programmable waveshaper, so as to realize the ultrafine, dynamic and arbitrary gain spectrum shaping of Raman amplification. For the target of flat gain spectrum, the maximum gain flatness of 0.1086 dB is realized based on the simulation results. For the target of arbitrary gain spectrum, we demonstrate four gain profiles with maximum root mean square error (RMSE) of 0.074 dB. To further measure the performance of arbitrary gain spectrum optimization, the probability density functions (PDF) of RMSE and Errormax are presented. Meanwhile, the numeral relationship between the bands of broadband pump and signal is also explored. Furthermore, this work has great application potential to compensate the gain distortion or dynamic change caused by other devices in communication systems.

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]

We describe a hybrid Raman-optical parametric amplifier (HROPA) operating at the O- and E-bands and designed for coarse wavelength division multiplexed (CWDM) passive optical networks (PONs). We present the mathematical model and simulation results for the optimization of this HROPA design. Our analysis shows that separating the two amplification processes allows for optimization of each one separately, e.g., proper selection of pump optical powers and wavelengths to achieve maximum gain bandwidth and low gain ripple. Furthermore, we show that the proper design of optical filters incorporated in the HROPA architecture can suppress idlers generated during the OPA process, as well as other crosstalk that leaks through the passive optical components. The design approach enables error free performance for all nine wavelengths within the low half of the CWDM band, assigned to upstream traffic in a CWDM PON architecture, for all possible transmitter wavelength misalignments (±6 nm) from the center wavelength of the channel band. We show that the HROPA can achieve error-free performance with a 170-nm gain bandwidth (e.g., 1264 nm–1436 nm), a gain of >20 dB and a gain ripple of

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]

The implementation of hybrid optical amplifiers has led to the emergence of DWDM in optical communication systems. By implementation of hybrid optical amplifiers, the performance of DWDM transmission can be enhanced. In this paper, different configurations of hybrid optical amplifiers are discussed which can be implemented at low cost and efficient performance of DWDM transmission system. Optical amplifiers can be used in different hybrid configurations to enhance the performance of the optical link and minimize the limitations of existing amplifiers. [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]

Optimal design of a Raman-amplified periodic cell depends strongly on the constraints set by overall system requirements. The best possible tradeoff in terms of cost-effectiveness, nonlinearity, pumping efficiency, optical signal-to-noise ratio (OSNR), and tolerance to relative intensity noise transfer varies depending on characteristics, such as total transmission length, desirable number of spans or power budget requirements. Here, we perform a thorough experimental and theoretical study of the best performing configurations for second-order amplification over a broad range of applications, with span lengths ranging from 10 to 150 km. Results highlight the presence of different regimes in which different contributions to noise become dominant. We find that ultralong Raman fiber laser cells with high forward pumping are to be preferred in unrepeatered transmission applications, whereas in long-haul transmission a shorter cell based on random distributed feedback lasing can be a better option as it enables low relative intensity noise transfer with a higher output OSNR at the cost of a reduced pumping efficiency. [ABSTRACT FROM PUBLISHER]

The effect of using distributed Raman amplifiers (DRAs) on the performance of DWDM networks is investigated. It was found that the network performance significantly improves since it reduces the noise figure (NF) by 6 dB and a bit error rate (BER) of 10-12 for 100 Km DWDM network is obtained. In addition, the amplified spontaneous emission (ASE) from Raman amplifier in DWDM network has been reduced by 9 dB successfully through the use of nonlinear optical-loop mirror (NOLM). However the output signal suffers for instability due to the frequency chirp. [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]

A theoretical model of noise—amplified spontaneous emission and Rayleigh backscattering—in few-mode fiber Raman amplifiers is presented in this letter. Based on this model, the equalization of the signal modal gain determines the equalization of the noise modal gain. The model can also be used to predict the mode-dependent optical signal-noise ratio. The theoretical results of this model are consistent with reported experimental results. [ABSTRACT FROM PUBLISHER]

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]

We propose a distributed Raman amplifier available for dual-order co-propagating configuration with low-relative intensity noise (RIN) transfer. The first-order and second-order pumps are composed of incoherent and coherent light sources, respectively. By using the incoherent light source as a first-order pump, RIN transfer can be reduced. A semiconductor optical amplifier-based first-order incoherent light source for the configuration has been developed. The results of the RIN measurement and 22.5-Gbaud polarization-division multiplexing 16 quadrature amplitude modulation (PDM-16QAM) transmission experiment over 2720 km in a re-circulating loop show that the proposed configuration will be effective for a practical low-noise co-propagating Raman amplifier. [ABSTRACT FROM PUBLISHER]

Analysis is carried out for a single span wavelength division multiplexing (WDM) transmission system with distributed Raman amplification to find the effect of amplifier induced crosstalk on the bit error rate (BER) with different system parameters. The results are evaluated in terms of crosstalk power induced in a WDM channel due to Raman amplification, optical signal to crosstalk ratio (OSCR) and BER at any distance for different pump power and number of WDM channels. The results show that the WDM system suffers power penalty due to crosstalk which is significant at higher pump power, higher channel separation and number of WDM channel. It is noticed that at a BER 10−9, the power penalty is 8.7 dB and 10.5 dB for the length of 180 km and number of WDM channel N=32 and 64 respectively when the pump power is 20 mW and is higher at high pump power. Analytical results are validated by simulation. [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]