Optical link design for minimum power consumption and maximum capacity

Using a well-established analytic nonlinear signal-to-noise ratio noise model we show that there are very simple, fibre independent, amplifier gains which minimize the total energy requirement for amplified systems. Power savings of over 50% are shown to be possible by choosing appropriate amplifier gain and output power

Minimising total energy requirements in amplified links by optimising amplifier spacing

We investigate the energy optimization (minimization) for amplified links. We show that using the using a well-established analytic nonlinear signal-to-noise ratio noise model that for a simple amplifier model there are very clear, fiber independent, amplifier gains which minimize the total energy requirement. With a generalized amplifier model we establish the spacing for the optimum power per bit as well as the nonlinear limited optimum power. An amplifier spacing corresponding to 13 dB gain is shown to be a suitable compromise for practical amplifiers operating at the optimum nonlinear power

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

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

Suppression of WDM four-wave mixing crosstalk in fibre optic parametric amplifier using Raman-assisted pumping

We perform an extensive numerical analysis of Raman-Assisted Fibre Optical Parametric Amplifiers (RA-FOPA) in the context of WDM QPSK signal amplification. A detailed comparison of the conventional FOPA and RA-FOPA is reported and the important advantages offered by the Raman pumping are clarified. We assess the impact of pump power ratios, channel count, and highly nonlinear fibre (HNLF) length on crosstalk levels at different amplifier gains. We show that for a fixed 200 m HNLF length, maximum crosstalk can be reduced by up to 7 dB when amplifying 10x58Gb/s QPSK signals at 20 dB net-gain using a Raman pump of 37 dBm and parametric pump of 28.5 dBm in comparison to a standard single-pump FOPA using 33.4 dBm pump power. It is shown that a significant reduction in four-wave mixing crosstalk is also obtained by reducing the highly nonlinear fibre interaction length. The trend is shown to be generally valid for different net-gain conditions and channel grid size. Crosstalk levels are additionally shown to strongly depend on the Raman/parametric pump power ratio, with a reduction in crosstalk seen for increased Raman pump power contribution

Broadband gain-spectrum measurement for fiber optical parametric and Raman amplifiers

We examine the use of a depolarized broadband probe to experimentally measure gain spectra of amplifiers comprising parametric and Raman gain. The suggested technique allows a quick and accurate characterization of gain spectra spanning more than 100 nm. We derive formulas for processing spectral data to address polarization dependent gain and idler generation, and consequently develop a measurement methodology for obtaining reliable results. We demonstrate the viability of this approach by performing an experimental comparison with results obtained using tunable lasers. We expect the technique described here to be useful for fiber optical parametric amplifier development and characterization

Bandpass switching in a nonlinear optical loop mirror

A novel device configuration is used to demonstrate wavelength-confined, a bandpass, switching in a nonlinear-optical loop mirror (WOLM). Demonstrated is a self-switching in the soliton regime using a partially reflecting Bragg grating as a wavelength-dependent loss element. Two wavelength operation in which a signal is switched through the use of cross phase modulation, are demonstrated. Observed is the operation of the device confined to wavelengths defined by the grating reflection band

Performance limits in optical communications due to fiber nonlinearity

In this paper, we review the historical evolution of predictions of the performance of optical communication systems. We will describe how such predictions were made from the outset of research in laser based optical communications and how they have evolved to their present form, accurately predicting the performance of coherently detected communication systems

First experimental demonstration of nonlinear inverse synthesis transmission over transoceanic distances

We demonstrate for the first time, the transmission performance of 10Gbaud nonlinear inverse synthesis based signal over transoceanic distances, showing a significant improvement in data capacity x distance product (x12) compared with other NFT-based systems

Limits of broadband fiber optic parametric devices due to stimulated Brillouin scattering

We experimentally find a practical stimulated Brillouin scattering (SBS) threshold for broadband high-performance fiber optical parametric devices relying on dispersion-stable GeO2-doped silica highly nonlinear fibers. We demonstrate that SBS limits the nonlinear phase shift in such fibers to ~0.3 rad per pump unless the SBS is mitigated in some way. We consequently derive corresponding limits on signal gain and conversion efficiency and find the required SBS mitigation factor for a range of fiber optic parametric devices’ applications. Finally, we examine the level of SBS mitigation using air gaps and fiber tapers for implementation in polarization-insensitive fiber optic parametric devices employing bidirectional loops. We observe that an air gap or fiber taper are not very efficient for SBS mitigation as they provided an increase in SBS threshold up to 0.7 dB attributed primarily to their excess loss

Suppression of WDM four-wave mixing crosstalk in fibre optic parametric amplifier using Raman-assisted pumping

We perform an extensive numerical analysis of Raman-Assisted Fibre Optical Parametric Amplifiers (RA-FOPA) in the context of WDM QPSK signal amplification. A detailed comparison of the conventional FOPA and RA-FOPA is reported and the important advantages offered by the Raman pumping are clarified. We assess the impact of pump power ratios, channel count, and highly nonlinear fibre (HNLF) length on crosstalk levels at different amplifier gains. We show that for a fixed 200 m HNLF length, maximum crosstalk can be reduced by up to 7 dB when amplifying 10x58Gb/s QPSK signals at 20 dB net-gain using a Raman pump of 37 dBm and parametric pump of 28.5 dBm in comparison to a standard single-pump FOPA using 33.4 dBm pump power. It is shown that a significant reduction in four-wave mixing crosstalk is also obtained by reducing the highly nonlinear fibre interaction length. The trend is shown to be generally valid for different net-gain conditions and channel grid size. Crosstalk levels are additionally shown to strongly depend on the Raman/parametric pump power ratio, with a reduction in crosstalk seen for increased Raman pump power contribution