20 dB net-gain polarization-insensitive fiber optical parametric amplifier with >2 THz bandwidth

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.

In-line and cascaded DWDM transmission using a 15dB net-gain polarization-insensitive fiber optical parametric amplifier

“…1). The pumps were phase modulated with three RF tones (100MHz, 320MHz and 980MHz) to mitigate SBS [14]. In operation, the pump and loop polarization controllers (PCs) of the HPL-FOPA were periodically adjusted to maintain the gain in each direction about the loop in a fixed ratio.…”

“…However, in some ways researchers have tended to highlight eye-catching FOPA results whilst struggling to accomplish some basic yet fundamental requirements. For example, polarization insensitive operation with substantial netgain (the topic of this work) has historically proven extremely difficult to achieve, but a recent breakthrough using a modified diversity-loop approach has highlighted a path forward [13,14]. Other FOPA issues remain persistent however.…”

“…1. The PI-FOPA used a half-pass loop (HPL) architecture with full details of constituent parts and operation given in reference [14]. The optical transmitter (Tx) of the testbed was a commercial (Oclaro) polarization-division multiplexed (PDM) QPSK transponder with line-rate of 127.156Gb/s, including ~20% overhead for forward error correction (FEC).…”

“…In this way, no ASE was added to the transponder signal itself at the transmitter. A set of Waveshaper spectral profiles were subsequently generated, allowing ftsp to be fully tuned on a 50GHz grid between 193.4THz (1550.12nm) and 195.6THz (1532.68nm), which was consistent with the FOPA gain bandwidth [14]. An additional set of Waveshaper shapes was also generated for each ftsp with the ASE blocked at ±200GHz spacing from ftsp in order to allow interpolation of the system noise floor at ftsp for received OSNR measurements, whilst retaining the nearest neighbors to the transponder.…”

Towards wide-bandwidth ultra-flat FOPAs

“…Thirdly, pump power is limited by stimulated Brillouin scattering (SBS), and techniques used to mitigate it (such as pump dithering) cause signal degradation [5]. Finally, it is difficult to obtain polarization insensitive gain, although recent progress has been made [6].…”