Search

Optical frequency combs (OFCs) with programmable free spectral range and high optical carrier-to-noise ratio (CNR) play a crucial role in diverse research fields, including telecommunications, spectroscopy, quantum information, astronomy, sensing, and imaging. Unfortunately, the presence of stochastic noise often results in degraded optical CNR, leading to limited communication performance and measurement accuracy in comb-based systems. There is a lack of effective and flexible methods to improve the CNR of OFCs contaminated by broadband noise, hampering their widespread utilization. To address this challenge, we propose a four-wave mixing based spectral Talbot amplifier to purify OFCs flexibly. Our approach employs programmable spectral phase filters followed by a nonlinear Kerr medium to regenerate an OFC with superior CNR. In our experimental demonstration, we regenerated a 165-GHz spaced CNR enhanced OFC from a noise-dominated comb source spaced at 11 GHz, achieving up to ∼11-dB CNR improvement. The technique allows for a user-defined purification factor m to range from 7 to 15. Furthermore, our scheme demonstrates flexibility in adjusting the wavelengths of the regenerated comb lines via a tunable optical delay line without the need for a tunable seed laser. We also investigated the impact of the pump and signal on the regenerated comb experimentally and studied the influence of dispersion mismatch on the suppression of undesired sidebands numerically. Our proposed scheme presents a powerful alternative for programmable purification, manipulation, and detection of noise-dominated spectral waveforms. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate an optical phase conjugation (OPC) enhanced transmission system based on the Kramers–Kronig direct detection scheme. The single-sideband signal is modulated at 80-Gb/s 16-QAM with orthogonal frequency-division multiplexing. In the 180-km transmission experiment, the OPC surpasses digital chromatic dispersion compensation in Q factor, optimum launched optical power (LOP) and optical signal-to-noise ratio (OSNR) sensitivity. The improvement in Q factor, optimum LOP and OSNR sensitivity are 0.9 dB, 1.0 dB, and 1.7 dB respectively. The superiority of OPC over pure optical dispersion compensation is also analyzed by simulation. The results indicate that the OPC is an effective means to enhance the transmission performance of single-sideband signals. [ABSTRACT FROM AUTHOR]

In this letter, we propose a novel approach for optical single-sideband (SSB) generation by utilizing four-wave mixing Bragg scattering (FWM-BS). The scheme comprises three stages: the initial FWM-BS stage, the spectral phase control stage, and the final FWM-BS stage. Constructive or destructive interference can occur between the sidebands generated in the two FWM-BS stages, depending on the spectral phase mask applied between the stages. By applying an appropriate phase mask, one sideband can be eliminated by destructive interference, while the other sideband is magnified by constructive interference, thus realizing SSB generation. Both upconverted and downconverted SSB generations can be achieved. To verify the scheme, we experimentally demonstrate 50-GHz optical frequency upconversion and downconversion separately for multi-channel 16-Gbaud QPSK signals. [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]

Fiber-based wavelength multicast offers an attractive solution for efficient and flexible wavelength resource management in future optical networks. Unfortunately, most multicast approaches suffer from inevitable pump-to-pump beatings, generating undesirable products that take up bandwidth resources and result in serious degradation of the output signal quality. In this paper, we propose and experimentally demonstrate the Raman-assisted wavelength multicasting technique. The system performance is assessed through a one-to-seven multicast configuration for 10-GBd QPSK signal. Up to ∼16.8 dB power suppression has been achieved on the beating terms. Six newly generated replicas with Q factors all above the 7% forward error correction (FEC) threshold are obtained, despite their spectral overlap with the suppressed beating terms. Raman-assisted multicast further mitigates the performance penalty associated with signal power depletion, leading to a 0.8 dB Q factor improvement. Our proposed scheme enables more efficient utilization of the available spectrum in flexible bandwidth networks. [ABSTRACT FROM PUBLISHER]

We demonstrate all-optical manipulation of non-degenerate four-wave mixing (FWM) wavelength conversion bandwidth based on phase-matching control through gain-transparent stimulated Brillouin scattering (SBS). A 3-dB bandwidth of 26 nm is achieved when the conversion efficiency is maximized, corresponding to 44% increase from the original value. The bandwidth can also be shrunk to a minimum of 15 nm. The spectral dependence of conversion efficiency can potentially be synthesized randomly, leading to a large tunability in the bandwidth. The performance in bandwidth manipulation is also evaluated in the wavelength conversion of 10 Gbit/s non-return-to-zero (NRZ) on-off-keying (OOK) signal. [ABSTRACT FROM AUTHOR]

We propose and experimentally demonstrate dynamic control of phase-matching in fiber-based four-wave mixing (FWM) for wavelength conversion of communication signals. By introducing self-compensation of optical gain/loss with stimulated Brillouin scattering (SBS) pump and Stokes waves, the FWM phase-matching condition and hence the conversion efficiency (CE) can be flexibly controlled. The phase difference between the interplaying fields is manipulated by modifying the refractive index through SBS without disturbing the initial parameters of the FWM process. The scheme is first applied to wavelength conversion of 10 Gbit/s non-return-to-zero (NRZ) on-off-keying (OOK) signal. Its performance on phase-transparent wavelength conversion is subsequently examined using 10 Gbit/s NRZ differential-phase-shift-keying (DPSK) signal. Eye diagrams, FWM spectra and bit-error rate (BER) performances for the converted signals without SBS, with gain-transparent SBS for maximum CE and for minimum CE are analyzed. In the OOK/DPSK wavelength conversion with gain-transparent SBS, the CE has been reduced by 10.7/11.4 dB at a signal-pump spectral spacing of 1.9/1.94 nm; while it has been enhanced by 8.8/7.4 dB at a signal-pump spectral spacing of 4.1/4.07 nm. The pronounced enhancement of the CE at large signal-pump spectral spacing results in enlargement of the 3-dB FWM conversion bandwidth. Limitations in the extent of bandwidth enlargement and noise performance are discussed. Potential use of the scheme in other applications is also described. [ABSTRACT FROM PUBLISHER]

Abstract: We demonstrate polarization-insensitive wavelength multicasting of differential phase-shift keying (DPSK) signal based on four-wave mixing (FWM) in a highly nonlinear, birefringent photonic crystal fiber (PCF). The 10-Gbit/s RZ-DPSK input signal is copied to 8 wavelength channels through FWM with three optical pumps. The pump wavelengths are unequally spaced to avoid undesirable crosstalk from pump-to-pump beatings. The dependence of conversion efficiency on input signal polarization is suppressed by exploiting the PCF birefringence together with control of the pump polarizations. All pump polarizations are aligned at 45 degrees to the principal axes of the PCF. Open eyes and error-free results are obtained in all the 8 multicast channels for polarization-scrambled RZ-DPSK input signal. [Copyright &y& Elsevier]