C. E. S. Castellani

Multi-pump optimization for Raman+EDFA hybrid amplifiers under pump residual recycling

A new technique to optimize the gain profile of broadband hybrid amplifiers is here proposed. It is based on the equalization of Erbiums gain spectrum by adjusting the flexible gain profile of a multi-pump Raman amplification stage. However, for increased power pump efficiency, the residual Raman pump is recycled by the Erbium-doped section. This hybrid amplifier is assessed in terms of single-channel global gain, ripple, and noise figure. Ripple values below 1 dB have been found in a bandwidth of approximately 30 nm under two and three pump configurations.

Design methodology for multi-pumped discrete Raman amplifiers: case-study employing photonic crystal fibers.

This paper proposes a new design methodology for discrete multi-pumped Raman amplifier. In a multi-objective optimization scenario, in a first step the whole solution-space is inspected by a CW analytical formulation. Then, the most promising solutions are fully investigated by a rigorous numerical treatment and the Raman amplification performance is thus determined by the combination of analytical and numerical approaches. As an application of our methodology we designed an photonic crystal fiber Raman amplifier configuration which provides low ripple, high gain, clear eye opening and a low power penalty. The amplifier configuration also enables to fully compensate the dispersion introduced by a 70-km singlemode fiber in a 10 Gbit/s system. We have successfully obtained a configuration with 8.5 dB average gain over the C-band and 0.71 dB ripple with almost zero eye-penalty using only two pump lasers with relatively low pump power.

Gain profile optimization for Raman+EDFA hybrid amplifiers with recycled pumps for WDM systems

An approximated technique to quickly optimize the gain profile of multi-pump broadband hybrid amplifiers under residual pump recycling in WDM systems is proposed. It is based on the amplifier spectral equalization by adjusting the flexible gain profile of a multi-pump Raman amplification stage to compensate the Erbium-doped stage gain variation within the C-band. In order to increase the pump power efficiency, the Erbium-doped fiber section recycles the residual Raman pump. Three different cases considering, respectively, one, two, and three pumps are analyzed to demonstrate the effectiveness of the proposed technique. The characterization of the Raman+EDFA hybrid amplifier has been performed in terms of global gain, ripple, and noise figure. The proposed optimization method for the Raman pump sets allows ripple figures to be reduced by half of their original values in single pumped configurations. Our results also suggest that two pump lasers is the best configuration when the maximum gain, minimum ripple, and pump power efficiency are simultaneously considered.

Numerical comparison between conventional dispersion compensating fibers and photonic crystal fibers as lumped Raman amplifiers

In this paper we discuss the use of photonic crystal fibers (PCFs) as discrete devices for simultaneous wideband dispersion compensation and Raman amplification. The performance of the PCFs in terms of gain, ripple, optical signal-to-noise ratio (OSNR) and required fiber length for complete dispersion compensation is compared with conventional dispersion compensating fibers (DCFs). The main goal is to determine the minimum PCF loss beyond which its performance surpasses a state-of-the-art DCF and justifies practical use in telecommunication systems.

Envelope-based technique for liquid level sensors using an in-line fiber Mach–Zehnder interferometer

This paper proposes a sensor interrogation technique based on the analysis of the overall spectrum envelope of an in-line Mach-Zehnder interferometer structure with three different fibers. The interference pattern created by a level sensor of 120 mm was evaluated with both the traditional and the proposed interrogation techniques. The result shows that the technique here proposed improves the sensitivity of the sensor by more than an order of magnitude. Moreover, our new interrogation technique allows the length of an in-line Mach-Zehnder interferometer to be extended up to 470 mm while maintaining high linearity and sensitivity.

Analysis of a multi-pump optimization in Raman+EDFA hybrid amplifiers with pump recycling for WDM systems

This paper analyzes multi-pump Raman+EDFA hybrid amplifiers with pump recycling using an improved technique that optimizes the gain and ripple of the amplifier for wavelength division multiplexing (WDM) applications. This technique is based on the equalization of Erbiums gain spectrum by adjusting the flexible gain profile of a multi-pump Raman amplification stage. The residual Raman pump recycled by the Erbiumdoped section is used to increase power pump efficiency. Multi-channel simulated gain characterization of the hybrid amplifier recycling Raman pump, in terms of global gain, ripple, and noise figure, is presented. Different configurations of the Raman stage with single, two, three and four-pump lasers are analyzed. For 8 WDM input channels with two and three-pump lasers, ripple values have presented variation from 3 to 9 dB against 4.3 to 12.6 dB obtained with the previous method, depending on the input power and number of pumps. The ripple analysis have has shown that the proper selection of pump wavelengths and powers, enables the construction of broadband hybrid Raman+EDFA amplifiers with enhanced power conversion efficiency and high and flat gains.

Performance comparison for Raman+EDFA and EDFA+Raman hybrid amplifiers using recycled multiple pump lasers for WDM systems

This work extends the optimization of the gain profile for hybrid amplifiers by evaluating the performance of the configurations Raman+EDFA and EDFA+Raman considering multiple input channels simultaneously. An approximated technique to optimize the gain profile of multiple Raman pump lasers in order to obtain broadband hybrid amplifiers under residual pump recycling is applied to hybrid amplifiers with two stages, EDFA and Raman, for WDM systems. Multiple input channels allowed the gain characterization of the hybrid amplifiers of the two proposed configurations in terms of global gain, ripple, and noise figure. Results have presented global gain and noise figure values of approximately 40 dB and 4 dB, respectively, whereas obtained ripple values approximately of 0.8 dB, considering the EDFA+Raman hybrid amplifier configuration.

Fast optimization of multipump Raman amplifiers based on a simplified wavelength and power budget heuristic

Abstract. 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.

Optimization in Raman+EDFA hybrid amplifiers for WDM systems

An approximated technique to optimize the gain profile of multi-pump broadband hybrid amplifiers (EDFA+Raman) under residual pump recycling is applied to a WDM system. The optimization has been focused on the global gain and its ripple factor for the hybrid amplifier. The EDFA spectral gain profile is the one to be compensated by the Raman amplification. The results of gain, ripple and noise figure for 8, 16, 32, 64 and 128 WDM input channels, with - 20 dBm each, are presented. The increase in the level of input power reduces the overall gain of the amplifier, but the profile remains unchanged. The performance of this configuration presented better results that means high gain, lower ripple, and higher bandwidth than those found in the literature.

Performance analysis and comparison of multipump Raman and hybrid erbium-doped fiber amplifier + Raman amplifiers using nondominated sorting genetic algorithm optimization

Abstract. 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.