Abstract
Relative intensity noise transfer from the pump to the signal in 2nd-order ultra-long Raman laser amplifiers for telecommunications is characterized numerically and experimentally. Our results showcase the need for careful adjustment of the front FBG reflectivity and the relative contribution of forward pump power, and their impact on performance. Finally, our analysis is verified through a 10 × 30 GBaud DP-QPSK transmission experiment, showing a large Q factor penalty associated with the combination of high forward pumping and high reflectivities.
Highlights
Raman amplification schemes are capable of providing distributed amplification over tens of km as opposed to traditional EDFA based lumped amplification
This is especially true for second- or higher-order, bidirectionally pumped configurations [1] in which an equal amount of pump power should ideally be provided by the forward (FW) and backward (BW) propagating pumps in order to obtain the flattest possible signal power variation (SPV). 2nd-order, ultra-long Raman fiber laser (URFL) amplifiers have consistently proved to be an excellent option in terms of maximum reach for both unrepeatered and long-haul multichannel coherent transmission systems [2,3,4] using advanced modulation formats in combination with nonlinearity compensation techniques such as digital back propagation (DBP) or optical phase conjugation (OPC) [5, 6]
Recent works [10, 11] have shown that random distributed feedback laser amplifiers [12] can be suitable for overcoming relative intensity noise (RIN) impairments enabling transmission distances up to 7915 km for a 10 x 116 Gb/s DP-QPSK long-haul system by removing the fiber Bragg grating (FBG) at the input side of an URFL, essentially transforming a Fabry-Perot-like closed cavity into an half-open cavity, at the expense of an additional reduction of the FW pumping efficiency
Summary
Raman amplification schemes are capable of providing distributed amplification over tens of km as opposed to traditional EDFA based lumped amplification In these systems, gain distribution allows for a smoother variation of the signal power in transmission and, for a reduction of amplified spontaneous emission (ASE) noise and a significant improvement of the transmission distance. Gain distribution allows for a smoother variation of the signal power in transmission and, for a reduction of amplified spontaneous emission (ASE) noise and a significant improvement of the transmission distance This is especially true for second- or higher-order (i.e. when pump and signal are two or more Stokes shifts apart), bidirectionally pumped configurations [1] in which an equal amount of pump power should ideally be provided by the forward (FW) and backward (BW) propagating pumps in order to obtain the flattest possible signal power variation (SPV). We present the transmission performance of a WDM 10 x 30 GBaud DP-QPSK coherent transmission system, showing the Q factor as a function of the propagation distance when different cavity configurations are used as the core building block of a recirculating loop for emulating long-haul communication
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