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Phase manipulation is crucial for radio frequency (RF) and optical signal processing. In this work, we introduce an interferometric phase-reduction scheme to flexibly suppress the phase change while simultaneously amplifying the signal. We develop a numerical model to evaluate the characteristics of this processing scheme. The concept is further demonstrated with a proof-of-principle experiment that modifies the phase and gain profiles induced by stimulated Brillouin scattering in an optical fiber. This scheme provides an additional freedom to control the signal phase and amplitude in RF/optical processing functionalities. [ABSTRACT FROM AUTHOR]

Four-wave-mixing (FWM) crosstalk in frequency nondegenerate phase-sensitive fiber optical parametric amplifiers (FOPAs) applied for wavelength-division-multiplexed (WDM) signals is investigated experimentally and theoretically. We analyze significant FWM interactions that can generate crosstalk components in the signal band. Approximate expressions are developed for the FWM crosstalk to conveniently estimate how it scales with the system parameters. The analytical results agree well with the experimental results and simulations. The results show that the FWM crosstalk grows dramatically with the increase of the system parameters, including input signal power per channel, signal gain, the length of nonlinear fiber, and signal channel number. We also compare the FWM crosstalk in the phase-sensitive FOPA and the phase-insensitive FOPA experimentally and explain the difference of their crosstalk behaviors through theoretical analysis and simulations. The results show that, due to the presence of idlers at the input, the phase-sensitive FOPA produces higher crosstalk than the phase-insensitive FOPA even when they have equivalent signal gains. It indicates that the crosstalk in the phase-sensitive FOPA is more detrimental so that careful design of the amplifier to suppress the impact of the FWM crosstalk is necessary. The analytical solutions obtained in this paper are useful in the design of PS-FOPAs for amplifying WDM signals. [ABSTRACT FROM AUTHOR]

We experimentally show that the 1 dB compression point at the gain peak of a fiber optical parametric amplifier (FOPA) can be improved by 4.2 dB when it is assisted with a backward Raman pump to deliver an unsaturated gain of ~25 dB. We derive an efficient numerical model to describe gain saturation in a Raman-assisted FOPA (RA-FOPA). By scrutinizing the evolution of the optical fields, we find that the phase relation among the signal, the pump, and the idler can alleviate gain saturation in the RA-FOPA, instead of accelerating the saturation as in a conventional FOPA. Enhanced linear amplification is also demonstrated with a Nyquist-shaped 16-QAM signal, where the maximum signal power into the RA-FOPA can be 2.2 dB higher than that into the conventional FOPA within a 0.5 dB Q-factor penalty. This letter shows that the RA-FOPA has a superior dynamic range for linear operation, facilitating high-performance amplification for higher-order modulation formats. [ABSTRACT FROM AUTHOR]

We present a novel reconfigurable optical add-drop filter based on phase-sensitive amplifiers (PSAs). By manipulating the relative phase among an optical pump, signals, and idlers, spectral selectivity can be achieved along with low noise amplification. The use of backward Raman amplification enhances the phase-sensitive operation of the parametric process, enabling higher stopband isolation and lower intra-band crosstalk. A Raman-assisted phase-sensitive amplifier (RA-PSA) is characterized in detail, showing a 7.8-dB combined gain extinction ratio enhancement and 10.85-dB gain improvement. For the first time, we demonstrate an RA-PSA enabled optical add-drop filter with less than 0.4-dB penalty using three-channel QPSK signals. The novel scheme provides a simple way to enhance the extinction ratio of the PSA enabled add-drop filter, which can be an essential subsystem in optical links based on phase-sensitive amplification. [ABSTRACT FROM PUBLISHER]

We demonstrate the generation of a self-oscillating optical frequency comb using a Raman-pumped Brillouin optoelectronic oscillator. In this scheme, stimulated Brillouin scattering is utilized as a frequency selective component. Due to the narrow gain bandwidth of stimulated Brillouin scattering, which is ~30 MHz in a single mode fiber with about 11 GHz frequency shift, microwave signal with very low phase noise can be generated. Thus, the optical comb driven by this optoelectronic oscillator is highly coherent. In our experiment, a 7-line optical comb with 2.7 dB variation of 10.89 GHz spacing is obtained with a phase noise of -93 dBc/Hz at 10 kHz offset. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

We propose and experimentally demonstrate dynamic control of gain profile in a single-pump fiber-optical parametric amplifier (FOPA) assisted by gain-transparent stimulated Brillouin scattering. The FOPA gain can be enhanced/reduced through controlling the phase-matching condition without disturbing the initial parameters of the FOPA. Both the maximum and minimum gain profiles are obtained, offering operational flexibility in randomly synthesizing the profile to satisfy different requirements. Our synthesis can turn the conventional M-shaped profile into spectrally flat gain with 0.1-dB variation over 24 nm. This scheme can be potentially applied to dual-pump FOPA and can benefit other applications of parametric processes. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

We demonstrate a new technique of reconfigurable demultiplexing of optical time-division-multiplexing (OTDM) signal. The operation is achieved by pump depletion in an optical parametric amplifier using probe pulses from a time- and wavelength-interleaved laser source. Error-free operations have been achieved for both adjacent and alternate two-channel demultiplexing with power penalties less than 0.6 dB at 40 Gb/s. [ABSTRACT FROM PUBLISHER]