70 research outputs found
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
Impact of pump phase modulation on QAM signals in polarization-insensitive fiber optical parametric amplifiers
We examine mitigation of stimulated Brillouin scattering (SBS) in fiber optical parametric amplifiers (FOPAs) by pump phase modulation in the context of QAM signals and the state-of-art polarization-insensitive FOPA architecture. We characterize the impact of the pump phase modulation on QAM signals in the cases of single-polarization FOPAs and polarization-insensitive FOPAs, and study pathways to minimization of this impact. We find that the impact of pump phase modulation on signals is more complicated in polarization-insensitive FOPAs than in single-polarization FOPAs, and it can be mitigated by using the features of the polarization-insensitive FOPA architecture. We use the required optical signal to noise ratio (rOSNR) to evaluate the impact of pump phase modulation on QAM signals and find that the induced signal phase modulation makes significantly more contribution than the induced signal amplitude modulation. Our numerical and experimental study has revealed a distribution of the rOSNR penalty across the FOPA gain spectrum which is distinct from previously reported for on/off signals. We explore and optimize the pump phase modulation schemes to reduce the signal rOSNR penalty whilst providing more SBS mitigation at the same time. We demonstrate that a receiver digital signal processing plays a significant role in contribution to rOSNR penalty
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
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