Xuelei Fu

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.

Ultrawideband monocycle pulse generation based on delayed interference ofπ/2 phase-shift keying signal

We propose a scheme to generate ultrawideband (UWB) monocycle pulses using delayed interference of a π/2 phase-shift keying (PSK) signal. The PSK signal is generated with an optical phase modulator. A fiber-based delay interferometer is used to provide the delay together with a ±π/2 phase shift between the signals in its two arms before the interference. The two opposite phase shifts correspond to the generation of a pair of polarity-reversed UWB monocycle pulses. The full width at half maximum of the pulses is ~68 ps and the 10 dB fractional bandwidth is 168%.

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.

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.

Phase-sensitive four-wave mixing interferometer

A nonlinear interferometer is constructed using a dual-pump, dual-signal four-wave mixing (FWM) process. The generated idlers are categorized into phase-insensitive and phase-sensitive (PS) outputs according to whether the power is sensitive to the phase difference of the input signals. The PS idlers are obtained from the interference of the primary idlers and are regarded as the FWM interferometer output. Potential applications include photonic exclusive-NOR and exclusive-OR operations, photonic correlators, and photonic microwave filters.

Reconfigurable photonic ultrawideband pulse generation from an optically injected semiconductor laser

We demonstrate reconfigurable photonic ultrawideband (UWB) pulse generation by injecting a phase-modulated optical wave into a semiconductor laser. By adjusting the injection power level and phase modulation depth, the photonic UWB generator is capable of generating either a single-optical-carrier monocycle or power-efficient UWB pulses. A UWB pulse with spectral power efficiency (SPE) of 36.10% has been achieved by optimizing the injection parameters. Transmission in an 8.4 km single mode fiber results in a degradation of SPE to 27.55% without significant pulse distortion.

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.

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.

Bit-Rate Flexible Demodulation of DPSK Signals Based on Phase Sensitive Gain in Cascaded Four-Wave Mixing

We demonstrate bit-rate flexible demodulation of differential phase-shift keying (DPSK) signals in a linear structure. The demodulator utilizes a tunable optical delay based on the combination of wavelength conversion in a photonic crystal fiber and dispersion in a short section of single-mode fiber. Error-free demodulations for return-to-zero-DPSK signals at both 25 and 40 Gb/s have been successfully achieved.

Active control of gain saturation in fiber-optical parametric amplifier using stimulated Brillouin scattering

We have demonstrated the use of stimulated Brillouin scattering (SBS) to control the gain saturation characteristics of fiber-optical parametric amplification (FOPA). The saturation can be dynamically deferred or expedited without changing the input FOPA pump and signal parameters. It is observed that the input signal power at saturation can be increased or decreased by up to 6 dB. Experiments are performed to further investigate the role of the SBS-induced nonlinear phase on the power transfer efficiency in the FOPA.