Abstract-We propose and experimentally demonstrate a phase sensitive optical processor, capable of generating two co-directional and phase shifted phase sensitive amplifiers (PSAs) in a single device. Phase-sensitive operation is obtained by polarization mixing a phase-locked signal/idler pair generated in a degenerate dual-pump vector parametric amplifier based on four-wave mixing (FWM) in a highly nonlinear fiber (HNLF). We refer to this configuration as a polarization assisted PSA (PA-PSA) and demonstrate some of the applications that it may find. Firstly, we experimentally demonstrate the regeneration of a binary phase shift keying (BPSK) signal in a system that requires only a very low nonlinear phase shift (NPS) of 0.35 rad. Secondly, we decompose a quadrature phase shift keying (QPSK) signal into its in-phase and quadrature components. Whilst application to a QPSK signal is shown in our demonstration we demonstrate numerically that any complex modulation format signal can be decomposed using this approach. Finally, we use our processor to regenerate QPSK signals in a single non-linear device.Index Terms-Four wave mixing, nonlinear optics, phase sensitive amplifiers. I. INTRODUCTIONBoth phase insensitive and phase sensitive (PS) FWM schemes are often used as the basis for achieving optical processing of spectrally efficient modulation formats, which utilize both the phase and amplitude of the optical carrier. Some processing applications that have already been demonstrated include wavelength conversion [1][2][3][4][5][6][7], phase regeneration [8][9][10][11][12][13], electric field decomposition of phase shift keying (PSK) signals [14][15][16] and analogue-to-digital conversion (ADC) [17]. Single-and dual-pump configurations with the signal, idler and pump(s) being aligned either along the same polarization axis (scalar schemes) or on different polarization axes (vector schemes) and either non-degenerate or degenerate configurations (with the signal and idler being at either different or the same frequency, respectively) have been demonstrated [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. In many of the applications above, for example, both PSA-based regeneration of BPSK signals and electric field decomposition of, in principle, any advanced modulation format require an ideal binary step-like phase response. This is usually achieved by generating a complex conjugate copy (idler) of the signal through PS-FWM, and coherently adding the two together. The relative strength of the two waves determines the phase sensitive extinction ratio, PSER (defined as the difference between the maximum PS gain and the maximum PS de-amplification), and in turn the steepness of the steps in the phase response. For an ideal steplike response, the two components should have identical power [8][9]. Indeed, to generate phase conjugated copies of similar signal strength a large non-linear interaction is needed, requiring for example, Watt-level pump powers in a HNLF.It would be more energy-and cost-efficient, however, ...
Abstract:Adopting an exact solution to four-wave mixing (FWM), wherein harmonic evolution is described by the sum of two Bessel functions, we identify two causes of amplitude to phase noise conversion which impair FWM saturation based amplitude regenerators: self-phase modulation (SPM) and Bessel-order mixing (BOM). By increasing the pump to signal power ratio, we may arbitrarily reduce their impact, realising a phase preserving amplitude regenerator. We demonstrate the technique by applying it to the regeneration of a 10 GBaud QPSK signal, achieving a high level of amplitude squeezing with minimal amplitude to phase noise conversion.
Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc. ID XXXXX); published Month X, XXXX We investigate theoretically the benefits of using all-optical phase regeneration in a long-haul fiber optic link. We also introduce a design for a device capable of phase regeneration without phase-to-amplitude noise conversion. We simulate numerically the bit-error rate of a WDM optical communication system over many fiber spans with periodic re-amplification and compare the results obtained with and without phase regeneration at half the transmission distance when using the new design or an existing design. Depending on the modulation format, our results suggest that all-optical phase regeneration can reduce the bit-error rate by up to two orders of magnitude and that the amplitude preserving design offers a 50% reduction in bit-error rate relative to existing technology.
We propose and demonstrate a new phasesensitive (PS) scheme based on four-wave mixing followed by a polarizer to achieve an ideal binary step-like phase transfer function at nonlinear phase shifts as low as 0.3 rad by significantly increasing the parametric deamplification component. PS operation is obtained by polarization mixing the phase-locked and orthogonally polarized signal and idler, which is generated in a degenerate dual-pump vector parametric amplifier.Index Terms-Four wave mixing, nonlinear optics, phase sensitive amplifiers.
We demonstrate all-optical regeneration of both the phase and the amplitude of a 10 GBaud quadrature phase shift keying (QPSK) signal using two nonlinear stages. First we regenerate the phase using a wavelength converting phase sensitive amplifier and then we regenerate the amplitude using a saturated single-pump parametric amplifier, returning the signal to its original wavelength at the same time. We exploit the conjugating nature of the two processing stages to eliminate the intrinsic SPM distortion of the system, further improving performance.
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