Christian Stephan

Optimization of a Nonlinear Amplifying Loop Mirror for Amplitude Regeneration in Phase-Shift-Keyed Transmission

We present the numerical optimization of the transmission characteristics of a nonlinear amplifying loop mirror for amplitude regeneration of phase-encoded optical transmission formats. Adjusting the splitting factor, the amplifier gain and the phase bias, minimal phase distortions can be achieved while strong amplitude fluctuations are regenerated. The limiting effects of noise from the built-in amplifier and of amplified Rayleigh backscattering are also discussed.

Phase-Preserving Amplitude Regeneration in DPSK Transmission Systems Using a Nonlinear Amplifying Loop Mirror

A phase-preserving 2R regenerator based on a nonlinear amplifying loop mirror was implemented in a RZ-DPSK transmission system. Its performance has been investigated in numerical simulations and experimentally. The results show that amplitude regeneration using a NALM can efficiently prevent accumulation of nonlinear phase noise in a 10 Gb/s DPSK transmission system. In the experiments, significant improvements of eye opening and of BER as well as a 3 dB increase in fiber launch power have been demonstrated. Simulations at 10 Gb/s and 100 Gb/s indicated that the enhancement of the transmission quality is smaller at 100 Gb/s. The reason is that at 100 Gb/s nonlinear intra-channel effects rather than pure nonlinear phase noise are the main limiting factor and the NALM can only reduce the accumulation of amplitude noise in that case.

Effective negative nonlinearity of a nonlinear amplifying loop mirror for compensating nonlinearity-induced signal distortions

Conditions for realizing effective negative nonlinearity using a NALM are analyzed. Efficient compensation of SPM-induced nonlinear phase noise in a 100 Gb/s DPSK system is confirmed in numerical simulations.

Automatic extraction of runway structures in infrared remote sensing image sequences

Todays flight safety, especially during aircraft landing approach to an airport, is often affected by adverse weather conditions. One of the promising technologies to increase the pilots situation awareness is the Enhanced and Synthetic Vision System (ESVS): the combination of sensor vision and synthetic vision systems. In this paper we present one aspect of the sensor vision system, an algorithm that is using only a sequence of infrared images to detect possible runway structures and obstacles on it during the aircraft landing approach. No additional information from database, INS or GPS is used at this processing stage. The algorithm generates several runway and obstacle hypotheses and the final decision in ESVS is taken in the further processing stage: fusion of radar and IR data hypotheses and synthetic vision data. The functionality of the algorithm was tested extensively during several flight campaigns with landing approaches to different German and European airports in 2003 and 2004.

Nonlinear phase noise compensation using a modified nonlinear optical loop mirror

Nonlinear phase noise compensation with possibility of simultaneous amplitude noise suppression has been experimentally demonstrated in a DPSK transmission system using a modified NOLM. As main application quadrature and higher PSK modulation formats are expected.

DPSK Signal Regeneration Using a Nonlinear Amplifying Loop Mirror

Power characteristics and phase functions of a NALM are investigated in simulations and experimentally, showing a phase-preserving nonlinear characteristics suitable for amplitude regeneration of phase-encoded signals. A negative power penalty of -1.5 dB was obtained.

Experimental comparison of all-optical phase-preserving amplitude regeneration techniques

Performance of a nonlinear amplifying loop mirror and a fiber optical parametric amplifier in saturation used as phase-preserving amplitude limiters was investigated in a setup simulating a DPSK transmission system. The Q-factor improvement as well as the power penalty reduction have been compared under identical conditions. Both regenerators provide a similar Q-factor improvement, but the nonlinear amplifying loop mirror yields a better power penalty reduction.

Compensation of Nonlinear Phase Noise Using the Effective Negative Nonlinearity of a Nonlinear Amplifying Loop Mirror

The nonlinear amplifying loop mirror (NALM) has been explored for use as a nonlinear phase-shift compensator (NPSC). Operation conditions for a tunable effective negative nonlinearity are considered and the NALM parameter optimization is discussed for direct bit-error-ratio (BER) improvement by postcompensation after a nonlinear transmission line. In this configuration, the fundamental limits for NPSC are estimated for differential quadrature phase-shift keying (DQPSK) using a simplified model. Numerical simulations of a 20 Gb/s RZ-DQPSK transmission system confirmed the applicability of this model and showed a significant BER improvement in a realistic transmission line. Alternatively, the fiber launch power per span could be increased by 2 dB for the same BER.

Influence of Rayleigh backscattering on the performance of NOLM-based phase-preserving amplitude limiters

Design and fiber optimization in NOLM-type regenerators allow for a substantial decrease in excess noise originating from Rayleigh backscattering. Cascaded operation of up to 20 phase-preserving limiters in a DPSK transmission system is experimentally demonstrated.

Nonlinear phase-shift compensation for DQPSK signals using a nonlinear amplifying loop mirror

The application of a Nonlinear Amplifying Loop Mirror (NALM) as a nonlinear phase-shift compensator (NPSC) in phase-shift keyed transmission is investigated with emphasis on Differential Quadrature Phase-Shift Keying (DQPSK). The origin of the effective negative nonlinear phase shift in a NALM and the effects of the NALM parameters on the phase-shift compensation are discussed. Two possible application modes of the NALM as NPSC have been found: sole nonlinear phase-shift compensation up to 3 rad, and phase-shift compensation in a smaller range with simultaneous amplitude equalization. The points of operation for both modes and the limitations in their implementation are presented. Results show that the use of a NALM, optimized for phase-shift compensation, seems to be very promising, especially for the application as post-compensator in differential phase-shift-keyed transmission systems. To evaluate the performance of a NALM as post-compensator a simplified model of the NALM and a DQPSK transmission system was used. The BER with and without the NALM was calculated in dependence on the average nonlinear phase shift and on the input noise. The results show that with a NALM as NPSC the amount of nonlinear phase shift in a preceding transmission system can be approximately doubled for the same BER.