Hybrid Amplifiers Part I Combining Raman Amplification with Amplification by EDFAs in Long Haul WDM Systems Outline 1. Overview of Raman and EDFAs combined amplification 2. Hybrid amplifier issues 3. Comparison of different amplified system configurations 4. Gain balance between Raman and EDFAs Overview of Raman and EDFAs Combined Amplification Why use Hybrid Amplifiers • Enlarges the transmission capacity of broadband systems • “Upgrading” the existing systems built with EDFA amplifiers with broader/flatter bandwidth • Ability to carry more wavelength-multiplexed optical channels at given spacing among the channels • Raman amplification gives flexibility to the selected band amplification • Less sensitive to nonlinear effects – systems’ point-of-view Basic Idea of Hybrid Amplifiers Principle of working / Operating Mode • Flatten EDFA gain by using Raman gain • Improve gain performance at longer signal wavelengths Typical Configurations Raman Amplifiers setup in different configurations: • discrete • distributed • backward-, forward- and bidirectional pumped • numerous types of fibers (DSF, DCF to be used as SRS active media) EDFAs setup considers: • single or multiple fiber stages • series or parallel configuration • C- and L-band regions Hybrid Amplifiers Issues The Hybrid Amplifiers studies are concerned with: • maximizing the span length and/or minimizing the impairments of fiber nonlinearities • enhancing the EDFAs’ bandwidth • designing “optimal” hybrid amplifiers in order to obtain flat and widest output gain performance Comparing Different System Configurations EDFA only RX TX EDFA + Raman TX RX Raman only TX RX Results Obtained After Comparing the 3 Types of Systems Considering in-line and pre-amplification functions: • Long-haul EDFA-only systems are limited by OSNR and NL effects • Raman-only systems tend to be limited by a reduction of SNR caused by double Rayleigh backscattering • Combination of distributed Raman and EDFAs present better performance than conventional EDFA-only systems • Raman complement EDFAs in terrestrial high capacity long haul applications Optimizing HFA in a System Evaluate the optimum gain balance between the RAs and EDFAs that enables maximum transmission distance* * Carena et al., IEEE Photon. Techn. Techn. Lett. Lett. Vol. 13, No. 11, pp. 11701170-1172, 2001. Gain Balance Between Raman and EDFAs 1. Complex problem with several degrees of freedom - optimization technique 2. Main considerations to determine the optimum gain balance between Raman and EDFAs 3. Most important parameters - OSNR, gain-flatness, bandwidth - number of channels, number of spans, maximum transmission capacity Focusing on Extending the Bandwidth • Increase the number of transmitted channels • Gain flatness • Optimize the hybrid amplifier performance (gain, NF, OSNR) Techniques that Enlarge Flattened Gain-Bandwidth of “Discrete” Fiber Amplifiers I. New host materials fluoride- and telluride-based EDFAs thulium-doped fiber amplifier II. Using EDFAs with GEQ + discrete Raman amplifier III. Different amplifier configurations two-gain band parallel/series configuration – multiple fiber stage gain-equalizing (GEQ) filters Typical Values Observed in Hybrid Amplifiers Bandwidth > 40 nm Gain 15 – 25 dB Gain Ripple < 11.3 % Noise Figure < 6 dB OSNR > 32 dB Examples of Wide Flattened Bandwidth for Discrete Raman/Hybrid Fiber Amplifier Bandwidth (nm) G Flatness (%) 64 76 75 40 11.3 4.7 3.7 3.2 Reference OAA 98, p. 103 OFC 98, paper PD7 Electron. Lett. 34, 897, 1998 IEEE PTL 9, 1343, 1997 Specifications EDFA 1 stage 2 stage Discrete Raman 2 stages 1 stage Nr. Pump 2 3 NF(dB) <6 <6 Part II Designing Hybrid Amplifiers Outline 1. Models required in the simulations 2. Hybrid amplifier designed to LAN 3. Gain and noise figure results 4. A hybrid amplifier setup in multiple fiber stages 5. Characterization and performance in a system Models Required in the Simulations EDFA Modeling: Solve rate and propagating equations for pump, signal, and ASE, considering non-linear effects present in the fiber propagation. Raman Amplifier Modeling: Solve the rate and propagation equations for pump, signal, and ASE in the Raman fiber amplifier. Hybrid Amplifiers Designed for Local Area Networks* • LAN and MAN applications - Gave ~ 20 dB - Net gain > 10 dB • Distributed Raman fiber amplifier in series with a remotely pumped discrete EDFA • C-band and L-Band • WDM signal input • Optimized design parameters * Karasek et al., IEE Proc.-Optoelectron. Vol. 148, No. 3, p. 150, 2001 Hybrid Amplifier Layout Pump Power Specification Co-propagating pump power Raman EDFA Signal Input Power Raman 51 channels, −17 dBm/ch EDFA Raman Amplifier – Fiber Specifications EDFA – Fiber Specifications Evaluating Results in the C-Band Wavelength Range 35 Hybrid 40 25 20 35 Hybrid EDFA Raman 15 10 30 5 0 1530 1540 1550 1560 Wavelength (nm) 1570 25 1580 OSNR (dB) Gain (dB) 30 Raman Output Power Spectra Forward Backward Total Powers Along the EDFA Signal Pump ASE+ ASE− 25 40 20 39 15 38 Hybrid EDFA Raman 10 37 36 5 35 0 1570 1580 1590 Wavelength (nm) 1600 34 1610 OSNR (dB) Gain (dB) Results in the L-Band Wavelength Range Additional Comments • Hybrid fiber amplifier simulated for multi-wavelength operation in LANs • Distributed RFA and remotely pumped EDFA • Net gain 10 – 20 dB • EDFA is excited by the pump power unabsorbed in the transmission fiber • C-band and L-band results Part III Simulating Gain-Equalized Hybrid Raman-EDF Amplifiers Outline • Simulating hybrid amplifier with no filter • Spectral gain results • How to flatten the gain spectrum • Conclusions Wide Band Gain-Flattening Hybrid Amplifier* • Wide and flatness bandwidth • Short EDF + discrete Raman amplifier • Two-stage Raman amplifier • Bidirectional pumped at 3 different λp • C-Band and L-Band signal wavelength * Masuda et al., IEEE Photon. Techn. Lett. Vol. 11, No.6, p. 647, 1999 Hybrid Amplifier with no Filter Pump Power Specifications Raman 1 Bidirectional EDFA Co-pump Raman 2 Bidirectional Signal Input Power Specifications 16 channels spaced by 5 nm Power (dBm) EDFA Signal Input Power Specifications Raman 2 Power (dBm) Power (dBm) Raman 1 Spectral Gain Along the C-Band and L-Band Wavelength Range 25 Gain (dB) 20 Hybrid EDFA Raman1 + Raman2 Raman1 Raman2 15 10 5 0 1530 1540 1550 1560 1570 1580 Wavelength (nm) 1590 1600 Spectral NF and OSNR to C-Band and L-Band 10 40 NF (dB) 38 6 4 36 2 1530 1540 1550 1560 1570 1580 Wavelength (nm) 1590 1600 OSNR (dB) 8 Hybrid Amplifier Output Pump Power (dBm) Signal ASE Hybrid Amplifier Output Transmitted Power (dBm) Pump Reflected Signal Pump Signal ASE ASE Comments • Raman amplifier increases the gain at longer wavelength signal; • Design can be optimized; • Considerable gain ripple which limits usefulness for high capacity transport systems; • Er doped fluoride fiber also presents the gain ripple observed for silica fiber. How to Flatten the Gain Spectrum • Use a passive filter device such as thin film, fiber grating, etc. Including a transmission filter in the design Gain Flattening Filter Specifications Wavelength Range Specifies how flat the filter will be Gain Flattening Filter Optimization Power (dBm) Power (dBm) Spectra Observed Before and After the Filter Filter Curve Filter Curve In/Out Signal Difference Intensity (dB) 8 6 4 2 0 1520 1540 1560 1580 Wavelength (nm) 1600 Comparing Gain Results 30 Gain (dB) 25 20 15 With Gain-Flattening Filter With No Filter 10 5 1530 1540 1550 1560 1570 1580 Wavelength (nm) 1590 1600 1610 Comments • Hybrid amplifier was simulated using one EDF stage and two Raman amplifiers cascaded in series; • C-Band and L-Band wavelength range; • Qualitative results’ analysis; • Hybrid amplifier configuration was used as an inline amplifier; • Low gain variation (3.1 dB) was observed under strong input signal variation (– 30 dBm to –20 dBm); • Gain bandwidth equal to 69 nm. Conclusions • Hybrid amplifiers simulations considered different amplifier configurations. • Pump wavelength selection, EDFA and Raman specifications, and the configuration / combination of both amplifiers are critical in the design of hybrid amplifiers. • Hybrid amplifiers compensate for the gain decay at longer signal wavelength.
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project