C. Stephan

Phase-preserving amplitude regeneration for a WDM RZ-DPSK signal using a nonlinear amplifying loop mirror.

We propose a modified nonlinear amplifying loop mirror (NALM) for phase-preserving 2R regeneration of wavelength division multiplexed (WDM) return-to-zero differential phase-shift-keyed signals. As proof of principle the regeneration capability of this NALM setup has been investigated experimentally for two 10 Gbit/s wavelength channels. A significant eye-opening improvement and a negative power penalty of 1.2 dB have been observed in both channels.

2R-Regeneration of an 80-Gb/s RZ-DQPSK Signal by a Nonlinear Amplifying Loop Mirror

The performance of a nonlinear amplifying loop mirror as a 2R-regenerator for an 80-Gb/s return-to-zero differential-quadrature-phase-shift-keyed signal has been investigated experimentally. A significant eye-opening improvement and a negative power penalty of up to 2.6 dB were obtained.

Nonlinear Phase Noise Reduction in a DPSK Transmission System Using Cascaded Nonlinear Amplifying Loop Mirrors

The performance of a nonlinear amplifying loop mirror as a phase-preserving amplitude 2R regenerator in a differential phase-shift-keying transmission system with nonlinear phase noise as dominant limiting effect has been investigated in a recirculating fiber-loop setup. The experimental results show that cascaded regenerators can efficiently prevent the accumulation of nonlinear phase noise in such systems. It was possible to significantly increase the transmission quality; alternatively, a considerable increase of fiber launch power could be achieved for the same bit-error ratio. As a limiting effect, the amplified Rayleigh backscattering in the highly nonlinear fiber is identified when the regenerator is passed multiple times.

Phase-preserving amplitude noise suppression using an attenuation-imbalanced NOLM

A nonlinear optical loop mirror with a bidirectional attenuator has been used for regeneration of return-to-zero differential phase-shift-keyed (RZ-DPSK) signals. A 2.5 ps, 10 Gb/s signal with amplitude fluctuations of 28 % was regenerated with a negative power penalty of 2 dB practically back to the quality of the undistorted reference signal. Parameters limiting system performance and optimization possibilities will be discussed.

Tunable Ultrafast Effective Nonlinearity Using a Nonlinear Amplifying Loop Mirror

Nowadays the complete control of fibre properties, such as dispersion, is an indispensable technology. For the nonlinearity, however, possibilities are limited particularly due to the difficulty of creating a nonlinear phase response with sign opposite to the Kerr effect. Promising candidates are interferometric devices, such as modified Mach-Zehnder interferometers proposed for nonlinearity management [1] or nonlinear amplifying loop mirrors (NALM) for nonlinear phase-shift compensation in phase-encoded optical transmission systems [2].

Rayleigh-backscattering impact on performance of NOLM-based phase-preserving optical limiters

An additional four-fold increase of DPSK transmission distance was obtained by optimization of the regenerator design, especially of the highly nonlinear fiber used. Numerical simulations show that further improvement can be achieved by additional dispersion imbalance.

Optimization of dispersion-imbalanced loop mirror for phase-preserving amplitude regeneration

The adaptation and optimization of a dispersion-imbalance loop mirror for phase-preserving amplitude 2R regeneration is shown by numerical simulations. Its performance has been evaluated for DPSK transmission. A 4.8dB Q-factor improvement has been demonstrated.

Reduction of nonlinear phase noise in DPSK transmission using a NALM

Performance of a NALM as phase-preserving amplitude 2R-regenerator in a DPSK transmission system has been investigated experimentally and numerically. A 3dB improvement of eye opening or alternatively a 3dB increase of fibre-launched power are demonstrated.

Improvement of DPSK transmission by phase-preserving amplitude regeneration using cascaded nonlinear amplifying loop mirrors

Experimental results obtained on 10 Gb/s RZ-DPSK transmission in a recirculating fiber-loop setup have shown that nonlinear amplifying loop mirrors (NALM) can efficiently enhance system performance: cascaded phase-preserving amplitude regeneration can efficiently prevent the accumulation of amplitude and nonlinear phase noise components in such systems. It was possible to significantly augment the transmitted signal quality; alternatively a considerable increase of fiber launch power could be achieved. Amplified Rayleigh backscattering in the highly nonlinear fiber in the NALM has been identified as main limiting effect when the regenerator is passed multiple times.

Phase-preserving amplitude regeneration using a Nonlinear Amplifying Loop Mirror in a DPSK transmission system

With the implementation of differential phase-shift keying (DPSK) in optical transmission systems, phase-preserving amplitude regenerators become attractive to prevent the accumulation of nonlinear phase noise which is one of the major impairments in long-distance DSPK transmission systems [1]. We presented in [2] that a Nonlinear Amplifying Loop Mirror (NALM) can provide phase-preserving suppression of amplitude noise of a DPSK signal and, thus, suppress generation of nonlinear phase noise when a signal with deterministic amplitude fluctuations is transmitted. This work reports experimental results on the improved performance of a DPSK transmission system using a NALM when nonlinear phase noise generated by amplified spontaneous emission of optical amplifiers due to the fiber nonlinearity is the main limiting factor.