Abstract
A black-box polarization insensitive fiber optical parametric amplifier (PI-FOPA) is characterized for the first time using a commercial 127 Gb/s polarization-division multiplexed PDM-QPSK transponder within a multiplex of twenty-two equivalent DWDM signals across a 2.3 THz bandwidth portion of the C-band. The PI-FOPA employs a recently demonstrated diversity loop arrangement comprising two lengths of highly nonlinear fiber (HNLF) with the parametric pump being removed after the first HNLF in both directions about the loop. This arrangement is named the Half-Pass Loop FOPA or HPL-FOPA. In total, a record equivalent 2.3 Tb/s of data is amplified within the HPL-FOPA for three different pump power regimes producing net-gains of 10 dB, 15 dB and 20 dB (averaged over all signals). For the latter two regimes, the gain bandwidth is observed to extend considerably beyond the C-band, illustrating the potential for this design to amplify signals over bandwidths commensurate with the EDFA and beyond. Under the 15 dB gain condition, the average OSNR penalty to achieve 10-3 bit error rate for all twenty three signals was found to be 0.5 ± 0.3 dB. Worst case penalty was 0.8 ± 0.3 dB, verifying the use of the architecture for polarization insensitive operation. The growth of four-wave mixing signal-signal crosstalk is additionally characterized and found to be gain independent for a fixed output power per signal. A simple effective length model is developed which predicts this behavior and suggests a new configuration for significantly reduced crosstalk.
Highlights
A single-pump Fiber Optical Parametric Amplifier (FOPA) has recently been demonstrated offering exceedingly wide bandwidth (>100 nm) with low signal gain variation (GV) whilst amplifying optical data [1]
It is hoped that future research into strained highly nonlinear fiber (HNLF) [20], will reduce or eradicate this penalty source as currently it is unavoidable in a single pump FOPA employing pump phase modulation
A black-box polarization insensitive fiber optical parametric amplifier (PI-FOPA) employing a Half-Pass Loop architecture has been characterized for the first time using a commercial polarization-division multiplexed PDM-QPSK 127 Gb/s transponder
Summary
A single-pump Fiber Optical Parametric Amplifier (FOPA) has recently been demonstrated offering exceedingly wide bandwidth (>100 nm) with low signal gain variation (GV) whilst amplifying optical data [1]. Numerous techniques have been investigated for achieving polarization insensitive (PI) FOPA operation, such as propagating two orthogonally-polarized pumps at symmetrical frequencies about the zero dispersion wavelength (ZDW) of a highly nonlinear fiber (HNLF) [5,6] This scheme is experimentally complex, but has been shown to work well for optical phase conjugation (OPC) applications. The diversity loop has been successfully demonstrated using PDM signals for OPC applications [9,10], but is inherently limited for FOPA net-gain amplification due to pump distortions arising from Stimulated Brillouin Scattering (SBS) and Four-Wave Mixing (FWM) of bi-directional pump components [11]. The design employed dual HNLF lengths within a standard diversity loop, but importantly used WDM filtering to remove the pump in both directions after each first length of HNLF This limited the pump to just a single propagation direction within each HNLF, avoiding the SBS/FWM interaction. We characterize the evolution of FWM crosstalk growth in this HPL-FOPA as the gain and signal output power are independently varied
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