Chapter Raman Fiber Laser–Based Amplification in Telecommunications

The chapter demonstrates a detailed study of Raman fiber laser (RFL)-based amplification techniques and their applications in long-haul/unrepeatered coherent transmission systems. RFL-based amplification techniques are investigated from signal/noise power distributions, relative intensity noise (RIN), and fiber laser mode structures. RFL-based amplification techniques can be divided into two categories according to the fiber laser generation mechanism: cavity Raman fiber laser with two fiber Bragg gratings (FBGs) and random distributed feedback (DFB) Raman fiber laser using one FBG. In addition, in cavity fiber laser–based amplification, reducing the reflectivity near the input helps mitigate the signal RIN, thanks to the reduced efficiency of the Stokes shift from the second-order pump. To evaluate the transmission performance, different RFL-based amplifiers were optimized in long-haul coherent transmission systems. Cavity fiber laser–based amplifier introduces >4.15 dB Q factor penalty, because the signal RIN is transferred from the second-order pump. However, random DFB fiber laser–based amplifier prevents the RIN transfer and therefore enables bidirectional second-order pumping, which gives the longest transmission distance up to 7915 km. In addition, using random DFB laser-based amplification achieves the distance of >350 km single mode fiber in unrepeatered DP-QPSK transmission

Raman Fiber Laser–Based Amplification in Telecommunications

The chapter demonstrates a detailed study of Raman fiber laser (RFL)-based amplification techniques and their applications in long-haul/unrepeatered coherent transmission systems. RFL-based amplification techniques are investigated from signal/noise power distributions, relative intensity noise (RIN), and fiber laser mode structures. RFL-based amplification techniques can be divided into two categories according to the fiber laser generation mechanism: cavity Raman fiber laser with two fiber Bragg gratings (FBGs) and random distributed feedback (DFB) Raman fiber laser using one FBG. In addition, in cavity fiber laser–based amplification, reducing the reflectivity near the input helps mitigate the signal RIN, thanks to the reduced efficiency of the Stokes shift from the secondorder pump. To evaluate the transmission performance, different RFL-based amplifiers were optimized in long-haul coherent transmission systems. Cavity fiber laser–based amplifier introduces >4.15 dB Q factor penalty, because the signal RIN is transferred from the second-order pump. However, random DFB fiber laser–based amplifier prevents the RIN transfer and therefore enables bidirectional second-order pumping, which gives the longest transmission distance up to 7915 km. In addition, using random DFB laserbased amplification achieves the distance of >350 km single mode fiber in unrepeatered DP-QPSK transmission

Raman fibre laser based amplification in coherent transmission systems

The thesis presents a detailed study of different Raman fibre laser (RFL) based amplification techniques and their applications in long-haul/unrepeatered coherent transmission systems. RFL based amplifications techniques were characterised from different aspects, including signal/noise power distributions, relative intensity noise (RIN), mode structures of induced Raman fibre lasers, and so on. It was found for the first time that RFL based amplification techniques could be divided into three categories in terms of the fibre laser regime, which were Fabry-Perot fibre laser with two FBGs, weak Fabry-Perot fibre laser with one FBG and very low reflection near the input, and random distributed feedback (DFB) fibre laser with one FBG. It was also found that lowering the reflection near the input could mitigate the RIN of the signal significantly, thanks to the reduced efficiency of the Stokes shift from the FW-propagated pump. In order to evaluate the transmission performance, different RFL based amplifiers were evaluated and optimised in long-haul coherent transmission systems. The results showed that Fabry-Perot fibre laser based amplifier with two FBGs gave >4.15 dB Q factor penalty using symmetrical bidirectional pumping, as the RIN of the signal was increased significantly. However, random distributed feedback fibre laser based amplifier with one FBG could mitigate the RIN of the signal, which enabled the use of bidirectional second order pumping and consequently give the best transmission performance up to 7915 km. Furthermore, using random DFB fibre laser based amplifier was proved to be effective to combat the nonlinear impairment, and the maximum reach was enhanced by >28% in mid-link single/dual band optical phase conjugator (OPC) transmission systems. In addition, unrepeatered transmission over >350 km fibre length using RFL based amplification technique were presented experimentally using DP-QPSK and DP-16QAM transmitter

Enhanced Transmission Performance Using Backward-Propagated Broadband ASE Pump

We propose a novel first order incoherent broadband ASE pump which can be used as a seed pump in dual order backward-pumped distributed Raman amplification. Using this broadband ASE pump mitigates the RIN transfer from the backward-propagated second order pump to the signal, and extends the reach of 10×120 Gb/s DP-QPSK WDM transmission to 7915 km, giving a minimum of 12% (833 km) increase, compared with using low RIN semiconductor laser diode and random distributed feedback (DFB) fiber laser

On the Mitigation of RIN Transfer and Transmission Performance Improvement in Bidirectional Distributed Raman Amplifiers

We develop a novel broadband first order Raman pump for use as a forward pump in transmission experiments. Our results show significant signal relative intensity noise (RIN) reduction, to a level comparable to backward only pumping. The corresponding optical signal to noise ratio can be improved in dual and first order forward pumped 83.32km bidirectional distributed Raman amplifiers by using the proposed broadband pump as a first order pump. A detailed experimental characterization of RIN, signal power evolution and performance of a 10-120Gb/s DP-QPSK coherent WDM transmission system are presented. We report ~10dB RIN reduction and 0.7dB Q factor improvement which allows a 1250km transmission distance increase compared with conventional low RIN and narrowband 1st order pump sources. We also demonstrate that, bidirectional pumping with only broadband 1st order forward pumping at 50mW shows the lowest RIN transfer from pump to signal. This extends the transmission reach up to 8332km with maximum distances increased by 1250km and 1667km compared with conventional backward only and 1st order semiconductor forward pumped bidirectional pumping respectively

RIN Transfer Mitigation Technique Using Broadband Incoherent Pump in Distributed Raman Amplified Transmission Systems

The paper reviews the recent advances on RIN transfer mitigation techniques used in distributed Raman amplified long-haul coherent transmission systems. The use of a broadband first order pump in substantial pump to signal RIN transfer mitigation has been demonstrated experimentally in both bidirectional and backward only pumping schemes. The generation process of a novel broadband, low RIN and incoherent pump is also reported in detail. In a 10×120 Gb/s DP-QPSK WDM transmission system, our proposed pumping schemes shows maximum transmission reach up to 8332 km and significant reach extensions compared with conventional low RIN and narrowband Raman pump sources

Transmission Performance Improvement Using Broadband Incoherent Counter-Pumped Distributed Raman Amplification

We propose a novel dual-order counter-pumped distributed Raman amplification technique using broadband incoherent 1st-order pump to suppress RIN transfer and improve Q-factor and transmission reach by 0.3dB and 833km respectively compared with conventional narrowband pumping

Symmetry Requirements for 34dB Nonlinearity Compensation in OPC Systems

We experimentally achieve compensation of nonlinearity of at least 34 dB when deploying Optical Phase Conjugation in an optimized 2 nd order distributed Raman system, and demonstrate that the required accuracy for span-to-span power misalignment is below ±1dB for 20dB compensation