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Hybrid optical amplifiers (HOAs) are crucially important for broadband band amplification, and are widely deployed in high-capacity dense wavelength division multiplexed systems. We summarize the present state-of-the-art in this rapidly growing field. In addition, theoretical background and various inline configurations of optical amplifiers have been presented. Various issues such as gain flatness, gain bandwidth, transient effect, and crosstalk were presented in HOAs. Results show that the HOAs provide better gain flatness without using any expensive gain flattening techniques, and an acceptable range of gain, noise figure, bit error rate, and transience. [ABSTRACT FROM AUTHOR]

For the first time, a novel net gain analytical model of EDFA–Raman hybrid optical amplifier (HOA) is designed and optimized the various parameters using genetic algorithm. Our method has shown to be robust in the simultaneous analysis of multiple parameters, such as Raman length, EDFA length and its pump powers, to obtained highest possible gain. The optimized HOA is further investigated and characterized on system level in the scenario of 100×10 Gbps dense wavelength division multiplexed (DWDM) system with 25 GHz interval. With an optimized HOA, a flat gain of >18 dB is obtained from frequency region 187 to 189.5 THz with a gain variation of less than 1.35 dB without using any gain flattened technique. The obtained noise figure is also the lowest value (<2 dB/channel) ever reported for proposed hybrid optical amplifier at reduced channel spacing with acceptable bit error rate. [ABSTRACT FROM AUTHOR]

A simple genetic algorithm is implemented to perform multi parameter optimization of Raman Fiber Amplifier for 100 channel S band dense wavelength division multiplexed system at 25 GHz interval. A cost effective system using single Raman pump is investigated aiming at maximum average gain. The single counter propagating pump is optimized to frequency of 211.528 THz and 652.93 mW power level with optimum Raman fiber length of 44.064 Km. There is evidence to show that the optimum solution presents a small gain variation (less than 3 dB) over an effective bandwidth covering 197–199.475 THz. The optimized configuration enabled an adequate system performance in terms of acceptable Q -factor (19.52 dB) and BER (1.46 × 10 −21 ). [ABSTRACT FROM AUTHOR]

We propose a new optical data format based on simultaneously modulating nonreturn-to-zero and polarization-shift-keying for high-speed applications by means of efficient utilization of bandwidth. To the best of our knowledge, this article reports on the first investigation of a Raman erbium-doped fiber amplifier hybrid optical amplifier using a hybrid/orthogonal modulation technique in the scenario of 8- and 20-channel dense wavelength division multiplexed systems with high-data rates at 0.2 and 0.8 nm channel spacing, respectively. The results show that the proposed modulation format offers significant advantages in offering high-spectral efficiency values with acceptable quality factors and bit error rates. [ABSTRACT FROM AUTHOR]

We present a simple genetic algorithm implemented to perform multiparameter optimization of a Raman fiber amplifier for a 100-channel L-band dense wavelength division multiplexed system at a 25-GHz interval. The system is investigated for various cases with fixed pump frequency leading to 202.2-THz pump as the best choice with average gain above 19.5 dB. There is evidence to show that a single counterpropagating pump optimized to 588.2-mW power level and optimum Raman fiber length of 38.8 km presents a small gain variation (<2 dB) over an effective bandwidth covering 187 to 189.475 THz. The optimized configuration enabled an adequate system performance in terms of acceptable Q-factor (17 dB) and bit error rate (5.60 x 10-13). [ABSTRACT FROM AUTHOR]

Abstract: In this paper, four modulation formats including nonreturn-to-zero (NRZ), nonreturn-to-zero raised cosine (NRZ-RC), return-to-zero (RZ), return-to-zero raised cosine (RZ-RC) DWDM system with different hybrid optical amplifiers are introduced. We show that NRZ-DPSK and RZ-DPSK degrade the performance when Raman amplifier is considered. The obtained results reported that RZ and RZ-RC DWDM system with Raman-EDFA provide better results and cover 1512 and 1260km of transmission distance, respectively, with acceptable quality factor (>15dB) and bit error rate (<10−9). Further, it is also confirmed that using the hybrid optical amplifiers is a best alternative to increase the span distance. [Copyright &y& Elsevier]

Abstract: In this paper 10Gbps WDM systems at 16, 32 and 64 channels have been investigated with EDFA, RAMAN and SOA amplifiers individually and the performance has been compared on the basis of transmission distance and dispersion with and without nonlinearities. It is demonstrated that when the dispersion is 2ps/nm/km and the number of channels are less, then SOA provide better results because as we increases the number of channels, the gain saturation problem arises due to cross gain modulation, the cross phase modulation and four wave mixing. When dispersion is increased from 2 to 10ps/nm/km, EDFA provides better results than SOA in the term of BER and output power, but it shows non-uniform gain spectrum. We also observed that RAMAN amplifier provides better results for L band amplification and gain flatting issue because it can substantially reduce the impact of fiber nonlinearity. [Copyright &y& Elsevier]

Abstract: In this paper, we investigated the performance of multi terabits DWDM system consisting of hybrid optical amplifier RAMAN-EDFA for different data format such as non-return to zero (NRZ), return to zero (RZ) and differential phase shift keying (DPSK). We find that in 64×10 and 96×10Gbps, RZ is more adversely affected by nonlinearities, where as NRZ and DPSK is more affected by dispersion. We further show that RZ provide good quality factor (13.88dB and 15.93dB for 64 and 96 channels), less eye closure (2.609dB and 3.191dB for 64 and 96 channels) and acceptable bit error rate (3.89×108 and 1.24×109 for 64 and 96 channels) at the respective distance as compare to other existing modulation format. We further investigated the maximum single span distance covered by using existing data formats. [Copyright &y& Elsevier]

Abstract: In this paper, we investigated the post-, pre- and symmetrical power compensation methods for a different position of hybrid optical amplifier RAMAN–EDFA in fiber link. The effect of increase in signal input power for three power compensation methods is compared in terms of bit error rate, eye closure penalty and output received power. It is found that the post power compensation method is superior to pre- and symmetrical power compensation methods. Further, the effect of variation in length of the standard single mode fiber and dispersion-compensated fiber for three power compensation configurations has also been observed. We observed that RAMAN–EDFA as post power compensation method provides least bit error rate (10−40) and high output power (12dBm) at −15dBm signal input power at fiber link. [Copyright &y& Elsevier]

This article proposes various combinations of optical amplifiers for a dense wavelength division multiplexed system and investigates the impact of reduced channel spacing at high bit rates in terms of quality factor, bit error rate, eye closure, and output power. It is reported that the hybrid optical amplifier (Raman–erbium-doped fiber amplifier [EDFA]) provides better results with a maximum covered single span distance (220 km) at channel spacing of 6.25 GHz. The maximum acceptable bit rate for the 12.5-GHz channel spacing dense wavelength division multiplexed system is also investigated, and the recommendation is provided that for the Raman–EDFA, Raman–EDFA–Raman, EDFA–Raman–EDFA, and EDFA–semiconductor optical amplifier–EDFA, the operating bit rate should not be greater than 20, 16, 19, and 20 Gbps, respectively. [ABSTRACT FROM AUTHOR]

In this paper, two stage hybrid optical amplifier (HOA) composed of a single erbium doped fiber amplifier and Raman amplifier is proposed for dense wavelength division multiplexed (DWDM) system and investigate the impact of reduced channel spacing. The performance has been evaluated in the term of gain, gain flatness and noise figure. Also, using gain equalization technique, hybrid optical amplifier that has a gain flatness of 3 dB, and a noise figure of less than 7.4 dB is observed. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the performance of optical/hybrid optical amplifier for 64×10Gbps dense wavelength division multiplexed system has been compared. It is observed that hybrid optical amplifier (RAMAN–EDFA) provides better results as compared to conventional amplifiers. The impact of modulation formats (NRZ, RZ and DPSK) on hybrid optical amplifier has been further investigated and it is found that 64×10, RZ is more adversely affected by nonlinearities, where as NRZ and DPSK is more affected by dispersion. [Copyright &y& Elsevier]