Fiber Raman Amplifier Research Articles

Performance of Fiber Raman Amplifier due to Change in Refractive Index of Second Core of Dual Core Fiber Raman Amplifier

We vary the refractive index of second core of dual concentric cores of a single mode Fiber Raman Amplifier (FRA), having a step profile. Based on well known scalar analysis, we study crucially the effects of this variation on the performance characteristics of FRA for the first time. For practically important frequency shift band of 20 cm −1 to 700 cm −1 , our interesting observation is that values of refractive indices in a certain higher range show better flattening of effective raman gain in comparison to those in lower range with single pump; side by side, larger negative coefficient of dispersion is achieved in the operating range of wavelength with increase of refractive indices keeping the outer core radius, core gap radius and refractive index of the first core fixed. These promising criteria should attract the attention of system designers engaged in fabrication of FRA.

Experimental research on single-frequency fiber Raman amplifier

Single-frequency fiber Raman amplifier (SF-FRA) is known for the ability of all-band amplification, and it is very attractive for the amplification of single-frequency seed light at a special wavelength, such as 1178nm and 1271nm. The 1080nm single-frequency signal light is amplified by a 1031nm pump source, and the influences of seed power of single-frequency signal light, length of Raman gain fiber, pump scheme are experimentally investigated. The results show that the efficiency of SF-FRA increases with the enhancement of the single-frequency signal power and the length of Raman gain fiber. The efficiency of co-pump SF-FRA is higher than that of the counter-pump SF-FRA. The measure ments show that the linewidth of single-frequency signal light is not broadened obviously in the process of Raman amplification. The visibilities of the rapid-exposure pattern of far-field interference of single-frequency seed light and the amplified light are 0.814 and 0.719, respectively. The results show that the coherence of single-frequency signal light is affected by the SF-FRA more or less. These experimental results can provide a reference for designing other special wavelength SF-FRA.

Two-Section Fiber Optic Raman Polarizer

We report on a theoretical study of polarization impairments in periodically spun fiber Raman amplifiers. Based on the Stochastic Generator approach we have derived averaged equations to calculate polarization dependent gain and mean-square gain fluctuations. We show that periodically spun fiber can work as a Raman polarizer but it suffers from increased polarization dependent gain and gain fluctuations. Unlike this, application of a depolarizer can result in suppression of polarization dependent gain and gain fluctuations. We demonstrate that it is possible to design a new fiber Raman polarizer by combining a short fiber without spin and properly chosen parameters and a long periodically spun fiber. This polarizer provides almost the same polarization pulling for all input signal states of polarization and so has very small polarization dependent gain.

Two Models of Optical Pulse Self-Compressor Combined the Nonlinear Coupler with Backward Raman Fiber Amplifier

Based on the nonlinearity of the nonlinear optical coupler (NOC) and the amplifying capacity of the backward Raman fiber amplifier (PBRFA), two new optical systems to compress the optical pulse (Optical Pulse Self-Compressor: OPSC) are proposed. Using the expressions describing relationship between input and output intensities from ports of the NOC and the derived expression describing the amplification of the PBRFA, the compressing process of the optical pulse propagating through the OPSC is simulated. The results show that the peak of the optical pulse will be enhanced and the duration of the optical pulse will be reduced significantly. Consequently, the shape of input pulse is completely compressed with the certain efficiency. It means the optical pulse is self-compressed without the external pump pulse by proposing the OPSC.

Low Noise C-Band EDFA/DRA Hybrid Amplifier Using the Same Pump Laser

This paper presents the investigation of a hybrid amplifier consisting of Erbium doped fiber amplifiers EDFAs and a distributed Raman amplifier in the C-band. Our simulations take into account all the effects associated with transmitted signals and a pump laser in the optical fiber. The overall noise figure for the proposed hybrid amplifier was less than 10dB, as a limiting case for maximizing the span length and/or minimizing the impairments of fiber nonlinearities. The combination distributed Raman amplifier and EDFAs present better performance than conventional EDFA-only systems. This low noise figure will enable maximum transmission distance. The transmission is discussed of 16 channels spaced 1nm and 1mW of optical power through 100km of fiber. Full Text: PDF References S.K. Kim, S.H. Chang, J.S. Han, M.J. Chu,"Design of hybrid optical amplifiers for high capacity optical transmission", Electron. Telecom. Res. Inst. J. 24, 81 (2002) T.N. Nielson,"Raman Amplifiers in WDM Systems", 12th LEOS Annual Meeting, vol. 2, 471 (1999) T. Suzuki, M. Kakui, M. Hirano, M. Onishi, Y. Nakai, M. Nishimura,"Broadband discrete fiber Raman amplifier with high differential gain operating over 1.65 /spl mu/m-band", Optical Fiber Comm. Conf. MA3 (2001) S. Kawai, H. Masuda, K. Suzuki, K. Aida,"Wide-bandwidth and long-distance WDM transmission using highly gain-flattened hybrid amplifier", IEEE Photon. Technol. Lett. 11, 886 (1999) [CrossRef] W.Y. Oh, S.S. Lee, H. Lee, W. Seo,"16-Channel C-Band Hy-brid Fiber Amplifier Comprising an EDFA and a Single Diode Laser Pumped Dispersion Compensating Raman Amplifier", European Conf. on Comm. 4.4.5, (2000) H. Suzuki, J. Kani, H. Masuda, N. Takachio, K. Iwatsuki, Y. Tada, M. Sumida,"1-Tb/s (100×10 Gb/s) super-dense WDM transmission with 25-GHz channel spacing in the zero-dispersion region employing distributed Raman amplification technology", IEEE Photon. Technol. Lett. 12, 903(2000) [CrossRef] Y. Zhu, W.S. Lee, C. Scahill, C. Fludger, D. Wetly, M. Jones, J. Homan, B. Shaw, A. Hadjifotiou,"1.28 Tbit/s (32×40 Gbit/s) transmission over 1000 km NDSF employing distributed Raman amplification and active gain flattening", Electron. Lett. 33, 43(2001) [CrossRef] B. Zhu, P.B. Hansen, L. Leng, S. Stulz, T.N. Nielsen, C. Doerr, A.J. Stentz, D.S. Vengsarkar, Z.J. Chen, D.W. Peckham, L. Gruner-Nielsen,"800 Gbit/s (80×10.66 Gbit/s) transmission over 3200 km of non-zero dispersion shifted fibre with 100 km amplified spans employing distributed Raman amplification", Electron. Lett. 36, 1860 (2000) [CrossRef] H. Masuda, S. Kawai, K.-I Suzuki,"Optical SNR enhanced amplification in long-distance recirculating-loop WDM transmission experiment using 1580 nm band hybrid amplifier", Electron. Lett. 35, 411 (1999) [CrossRef] D.A. Chestnut, C. J. S. de Matos, J.R. Taylor,"Raman-assisted fiber optical parametric amplifier and wavelength converter in highly nonlinear fiber", J. Opt. Soc. Am. B- 19, 1901 (2002) [CrossRef] A. Carena, V. Curri, P. Poggiolini,"On the optimization of hybrid Raman/erbium-doped fiber amplifiers", IEEE Photon. Technol. Lett. 13, 1170 (2001) [CrossRef] G.E. Tudury, J. Hu, B.S. Marks, A.S. Lenihan, C.R. Menuk, G.M. Carter,"Gain characteristics of a 210 km hybrid Raman/erbium-doped fiber amplified loop", Opt. Comm. 264, 152 (2006) [CrossRef] H. Masuda, Raman Amplifiers for Telecommunications 2, Sub-Systems and Systems (New York, Springer-Verlag 2004) A.W. Naji, B.A. Hamida, X.S. Cheng, M.A. Mahdi, S. Harun, S. Khan, W.F. AL-Khateeb, A.A. Zaidan, B.B. Zaidan, H. Ahmad,"Review of Erbium-doped fiber amplifier", Int. J. Phys.Scien. 6(20), 4674 (2011) A. Sano, T. Kobayashi, E. Yoshida, Y. Miyamoto,"Ultra-high capacity optical transmission technologies for 100 Tbit/s optical transport networks", IEICE Trans. Commun. E94-B (2), 400 (2011)

Efficient and robust shooting algorithm for numerical design of bidirectionally pumped Raman fiber amplifiers

An efficient and robust shooting algorithm for the design of bidirectionally pumped Raman fiber amplifiers is proposed. First, a parameter S, new to our knowledge, called scaling vector, is introduced. This parameter is used in combination with the physical picture of stimulated Raman scattering to generate accurate initial guesses for the powers of backward pumps in the bidirectionally pumped Raman fiber amplifiers. Second, a modified Newton–Raphson method is developed. With an appropriate restriction for the adjustment of increments of initial guess attached, the modified Newton–Raphson method is used to correct the initial guesses to approach the true solution of the problem. By combining the method of initial value determination and the correction mechanism, 14 types of bidirectionally pumped Raman fiber amplifiers are designed. The simulation results show that the proposed shooting algorithm is more efficient and stable than most of the existing ones. Comparison with three other relevant methods reported in the literature is made to reveal the advantages of the new method.

Novel Design of Flat Gain Spectrum Raman Fiber Amplifiers Based on Ant Colony Optimization

In this work, a new metaheuristic called ant colony optimization (ACO) is introduced into the design of flat-gain-spectrum Raman fiber amplifiers (RFAs) for the first time. In this novel design method, the pump powers and pump wavelengths are optimized by ACO to obtain a flat gain spectrum with a prespecified maximum gain ripple under the given parameters of RFAs. The simulations show that the proposed method is efficient and stable. Finally, a <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> -band RFA with a gain ripple of 0.32 dB is designed to demonstrate the technique in detail.

Activated polarization pulling and de-correlation of signal and pump states of polarization in a fiber Raman amplifier

We report on a theoretical study of activated polarization pulling and de-correlation of signal and pump states of polarization based on an advanced vector model of a fiber Raman amplifier accounting for random birefringence and two-scale fiber spinning. As a result, we have found that it is possible to provide de-correlation and simultaneously suppress PDG and PMD to 1.2 dB and 0.035 ps/km(1/2) respectively.

Experimental investigation on amplification and coherence properties of a single-frequencyand dual-single-frequency narrow-linewidth fiber Raman amplifier employing a switchablenarrow-linewidth seed laser

We demonstrate a narrow-linewidth fiber Raman amplifier (NL-FRA) operating atsingle-frequency (SF) and dual-single-frequency (DSF) to study the amplificationand coherence properties. A switchable NL seed laser at a central wavelength of1079.7 nm is utilized to provide SF and DSF signal light for FRA. The signallight is Raman amplified to 791 mW and 1.07 W, respectively. Measurements ofspectrum and frequency spectrum indicate that there is no significant indication ofstimulated Brillouin scattering (SBS) and four-wave mixing (FWM). The experimentalinvestigation on coherence properties of SF and DSF NL-FRA indicates that theoptical-path-difference-control and control-servomechanism-system for coherent beamcombination (CBC) of DSF NL-FRAs are more strictly required, but still feasible.

Polarization Attraction in Counterpropagating Fiber Raman Amplifiers

Polarization attraction in counterpropagating, randomly birefringent, fiber Raman amplifiers is numerically investigated, including the effects of nonlinear polarization rotation, pump depletion and orthogonal Raman gain. The analysis determines the limitations of the pulling efficiency, and shows that the maximum achievable mean degree of polarization is a function of the mean gain.

Flat gain spectrum design of Raman fiber amplifiers based on particle swarm optimization and average power analysis technique

In this work, the modified particle swarm optimization is used as an optimization tool to determine the set of wavelengths and power levels of pumps that delivers a flat gain spectrum for Raman fiber amplifiers. The average power analysis technique is used as a numerical method to solve the coupled Raman amplifier equations. By combining the modified particle swarm optimization and average power analysis technique an efficient algorithm for the design of flat-gain-spectrum broadband Raman fiber amplifiers is constructed. Application of this algorithm to the design of flat-gain-spectrum broadband Raman fiber amplifiers shows that the design efficiency of the new method is improved by 1–2 orders of magnitude compared with similar implementations previously reported in the literature. A 4-backward-pump gain-flattened Raman amplifier with bandwidth of 100-nm and maximum gain ripple of <1.0 dB is designed to demonstrate the technique.

Raman Fiber Oscillators and Amplifiers Pumped by Semiconductor Disk Lasers

Optical pumping of Raman fiber lasers and amplifiers with semiconductor disk lasers represents novel advantageous approach as compared with conventional pumping techniques based on diode lasers and/or fiber converters. Short pulse generation and low-noise amplification are experimentally demonstrated using this pumping concept. High-power, low-noise, and diffraction-limited beam quality, naturally attributed to disk laser geometry, promises significant and positive impact on the optical amplifier technology.

Investigation on the suppression of stimulated Brillouin scattering in single-frequency Raman fiber amplifiers

High power operation of single-frequency Raman fiber amplifiers (SF-RFAs) is usually limited by the onset of stimulated Brillouin scattering (SBS). In this paper, we present our theoretical investigation on the suppression of SBS in SF-RFAs, based on the intensity equations combining SBS and stimulated Raman scattering (SRS). The effects of increasing the mode area of fiber and utilizing temperature and strain gradients along the fiber on the suppression of SBS are discussed. The simulation results suggest that it is not an advisable method to suppress SBS in SF-RFAs by increasing the mode area. Besides, although tensile strain and temperature gradients can suppress SBS in RFA singly, the conditions are too rigorous to realize. Based on the numerical simulation results, a feasible scheme for the suppression of SBS in RFA is proposed using the temperature gradients together with tensile strain gradients along the fiber length, resulting in an increase of ∼3 times of amplifiers output power.

Optimization of pump parameters for gain flattened Raman fiber amplifiers based on artificial fish school algorithm

In this work, a novel metaheuristic named artificial fish school algorithm is introduced into the optimization of pump parameters for the design of gain flattened Raman fiber amplifiers for the first time. Artificial fish school algorithm emulates three simple social behaviors of a fish in a school, namely, preying, swarming and following, to optimize a target function. In this algorithm the pump wavelengths and power levels are mapped respectively to the state of a fish in a school, and the gain of a Raman fiber amplifier is mapped to the concentration of a food source for the fish school to search. Application of this algorithm to the design of a C-band gain flattened Raman fiber amplifier leads to an optimized amplifier that produces a flat gain spectrum with 0.63 dB in band ripple for given conditions. This result demonstrates that the artificial fish school algorithm is efficient for the optimization of pump parameters of gain flattened Raman fiber amplifiers.

C + L band extended reach amplified next generation access networks

The feasibility of optical amplification solutions for extended reach next generation access networks in C + L bands is studied. Amplification schemes based on Raman fiber amplifier and their combination with remotely pumped erbium-doped fiber amplifiers are assessed and optimized. The results concerning a ring with 80 km for rural scenario demonstrate gain equalization over a bandwidth of 50 nm. The survey was complemented with experimental results

S-band multiwavelength Brillouin Raman Fiber Laser

In this paper we propose and demonstrate an S-band Brillouin–Raman Fiber Laser (BRFL). The S-band BRFL utilizes a Dispersion Compensating Fiber (DCF) as the non-linear gain medium in a linear cavity configuration and amplified by two 1425 nm, 380 mW pumped Raman Fiber Amplifiers (RFAs). A Brillouin Pump (BP) signal of 1515 nm at 12 dBm in power is injected into the setup to generate Stokes lines via the Stimulated Brillouin Scattering (SBS) process. The S-band BRFL is able of generating a Brillouin comb with 32 Stokes lines with a flat peak output power of − 18 dBm. The best BP to Stokes power ratio of the system is determined to be 50:50, while a ratio of 70:30 is observed to generate Stokes with a higher peak power, but at the expense of the number of wavelengths. The S-band BRFL has many potential applications as multiwavelength sources for communications and sensors.

Solid-core photonic bandgap fibers for cladding-pumped Raman amplification

Cladding-pumped solid-core photonic bandgap Raman fiber amplifiers are analyzed theoretically as possible candidates for power scaling. An example fiber design with a mode field diameter of 46 µm and a cladding diameter of 250 µm is calculated to exhibit 0.12 dB/km of confinement loss at the first Stokes wavelength and >10 dB/m at the second Stokes wavelength for a pump wavelength of 1.567 µm while maintaining low loss and large mode area in realistic coiling configurations. A Raman amplifier based on this fiber with 85 kW of output power, 78% optical conversion efficiency, a maximum heat load of 130 W/m, and a length of 235 m is simulated.

High-Power Narrow-Linewidth Continuous-Wave Raman Amplifier at 1.27 $\mu$m

A high-power narrow-linewidth continuous-wave (CW) Raman fiber amplifier at 1.27 μm is demonstrated for remote sensing measurements of atmospheric oxygen (O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). The amplifier uses phosphosilicate fiber in both a standard single-mode design and with the core size varying in the longitudinal direction for stimulated Brillouin scattering (SBS) suppression. The highest reported power level at this wavelength to date, a total peak power of 3 W, has been achieved for online (2.4 W) and offline (580 mW) spectroscopic measurements, in agreement with theoretical predictions. Additionally, it is shown that when 60-kHz sinusoidal amplitude modulation is applied to the amplifier seed signal, the modulated wave form is preserved at the amplifier output with 1.8 W total average power being obtained.

Bidirectional Dual-Wavelength Raman Fiber Ring Laser

A new stable dual-wavelength fiber ring laser based on Raman amplification, deploying a dispersion-compensating fiber (DCF) as gain medium, is introduced. The gain competition effects in the fiber Raman amplification are mitigated because the two emission lines, selected by fiber Bragg grating within the resonant ring cavities, travel in opposite directions through the gain medium. The experimental results confirm that the novel multiwavelength ring laser source is stable and it offers a high optical signal-to-noise ratio.

Low-noise Raman fiber amplifier pumped by semiconductor disk laser

A 1.3 µm Raman fiber amplifier pumped by 1.22 µm semiconductor disk laser in co-propagation geometry is demonstrated. Measured relative intensity noise of -148 dB/Hz over frequency range up to 3.5 GHz was measured at 900 mW of pump power. 9 dB gain was achieved with co-propagating pumping geometry with less than 2 dB additional noise induced by amplifier to the signal. Nearly shot-noise-limited operation of semiconductor disk laser combined with the diffraction-limited beam allows for efficient core-pumping of the single-mode fiber Raman amplifiers and represents a highly practical approach which takes full advantage of co-propagating pumping.