Xiaojie Guo

Gain saturation in a Raman-assisted fiber optical parametric amplifier

We investigate the gain saturation characteristics in a backward-pumped Raman-assisted fiber optical parametric amplifier (FOPA). It is experimentally observed that the onset of saturation occurs at a higher input power as compared to the case of a conventional FOPA with the same unsaturated gain. The output power under strong saturation is also enhanced. Simulations are performed on the power profile of the parametric pump to explain the distinct saturation behaviors. The monotonic increase of the parametric pump power in the Raman-assisted FOPA results in highly efficient power transfer to the signal while it suppresses the signal conversion to high-order idlers in the saturation regime.

Cross-Gain Modulation Suppression in a Raman-Assisted Fiber Optical Parametric Amplifier

We propose to use a backward Raman pump to suppress cross-gain modulation (XGM) during multiwavelength amplification in a fiber optical parametric amplifier (FOPA). The performances of two-wavelength amplification have been experimentally compared between FOPAs with and without the Raman pump under the condition of identical unsaturated gains. With Raman-assisted amplification, a larger range of input signal power is supported without causing significant depletion of the parametric pump. Consequently, the XGM crosstalk is effectively suppressed. The improvement is explained by compensation of the parametric pump power through the Raman gain. In our experiment, a 6.3-dB improvement has been obtained in the receiver sensitivity of a 10-Gb/s return-to-zero ON/OFF keying signal at the 10-8 bit-error rate level under simultaneous amplification of two data streams. The error floor has also been removed.

Raman-enhanced phase-sensitive fiber optical parametric amplifier

Backward Raman amplification is applied to enhance the performance of phasesensitive fiber optical parametric amplification. The gain extinction ratio and the maximum signal gain are increased by 9.2 and 18.7 dB, respectively.

Improving the Nonlinear Tolerance of Fiber-Based Optical Phase Conjugation

We demonstrate the use of Raman amplification to mitigate nonlinear distortion in optical phase conjugation (OPC) for a coherent optical orthogonal frequency-division multiplexing system. The OPC distortion is suppressed by lowering the input signal power. Meanwhile, the back-propagating Raman pump enhances the conversion efficiency, thus maintaining a comparable conjugated output signal power. The improvement in OPC signal quality by the Raman pump is numerically solved. Experimentally, the optimized output power can be enhanced by 10 dB and the maximum quality is improved by 1.2 dB. The input power dynamic range is also extended by up to 7 dB. This scheme is potentially applicable in mitigating the crosstalk among multichannel signals in a wavelength division multiplexing system.

Polarization-Insensitive Phase-Preserving Regenerator Based on a Fiber Optical Parametric Amplifier With Dual Orthogonal Pumps

We investigate the gain-saturation characteristics of a dual-orthogonal-pump fiber optical parametric amplifier. Nearly uniform power transfer functions have been obtained for various input signal polarizations by adjusting the total pump power. Based on this physical behavior, we demonstrate polarization-insensitive phase-preserving amplitude regeneration of 40-Gb/s nonreturn-to-zero differential phase-shift keying signals. The receiver sensitivity has been improved by a maximum value of 4.7 dB.

Raman-Enhanced Phase-Sensitive Fibre Optical Parametric Amplifier.

Backward Raman amplification is applied to enhance the performance of phase-sensitive fiber optical parametric amplification. The gain extinction ratio and the maximum signal gain are increased by 9.2 and 18.7 dB, respectively.

Crosstalk reduction by backward Raman pumping in multi-wavelength fiber optical parametric amplification

Reduction of four-wave-mixing crosstalk in multi-wavelength amplification is achieved using a backward Raman pump in a fiber optical parametric amplifier. The receiver sensitivity is improved by 1.6 dB in the amplification of three data channels.

Gain-saturated spectral characteristics in a Raman-assisted fiber optical parametric amplifier

We investigate the gain spectral characteristics in the course of saturation in a Raman-assisted fiber optical parametric amplifier (FOPA). It is experimentally observed that the saturated gain spectrum is modified with suppressed signal wavelength dependence as compared to a conventional FOPA. The gain at signal wavelengths on both farther and closer sides of the unsaturated gain peak from the pump saturates in a similar way. The modification of the saturated gain spectrum is explained by distributed nonlinear phase mismatch caused by the Raman effect.

Mitigation of nonlinear distortion in OPC module with backward Raman pumping

Nonlinear distortion is suppressed in Raman-assisted optical phase conjugation of CO-OFDM signals, resulting in improvement of 10 dB in optimized output power, 1.2 dB in Q factor, and 7 dB in input power dynamic range.

Investigation of Raman-Assisted Crosstalk Reduction in Multi-Wavelength Fiber Optical Parametric Amplification

Suppression of four-wave mixing (FWM) crosstalk during multi-wavelength amplification in a Raman-assisted fiber optical parametric amplifier (FOPA) is investigated theoretically and experimentally. The principle of crosstalk reduction by using a backward Raman pump is revealed by analytical expressions and verified by simulations. The crosstalk reduction is attributed to the unique power evolution of the signals caused by the monotonically increasing parametric pump power in the Raman-assisted FOPA. We obtain more than 7-dB reduction in FWM crosstalk initiated from both degenerate-FWM and nondegenerate-FWM processes in the Raman-assisted FOPA, as compared to a conventional FOPA with equivalent signal gain. The experimental results show excellent agreement with the simulations. We also discuss the effects of signal channel number and the powers of the parametric pump and the Raman pump on the FWM crosstalk. The simulation results indicate that under the same level of signal gain, the amount of crosstalk reduction can be increased by using a stronger Raman pump associated with a weaker parametric pump.