Reinhold Ludwig

Four-wave mixing in semiconductor optical amplifiers for frequency conversion and fast optical switching

Four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is an important tool for frequency conversion and fast optical switching in all-optical communication networks. We review the main applications of SOAs as nonlinear optical components. Concentrating on FWM, we define general parameters that are of relevance for signal processing applications. We show, how basic experiments and general simulation procedures can be used to determine optimum operating conditions for the intended applications. Besides a comprehensive investigation of FWM among continuous waves, we present new experimental results on FWM with picosecond optical pulses. A comparison of both reveals a different behavior and demonstrates that new optimization criteria and advanced theoretical models have to be applied for the case of short optical pulses. Moreover, we discuss the possibility to extract the dynamical SOA parameters from our experiments.

Ultrahigh-Speed OTDM-Transmission Technology

This paper reviews ultrahigh-speed data transmission in optical fibers based on optical time division multiplexing (OTDM) transmission technology. Optical signal processing in the transmitter and receiver as well as the requirements on ultrahigh-speed data transmission over a fiber link are discussed. Finally, results of several OTDM-transmission experiments, including 160-Gb/s transmission over 4320 km, 1.28-Tb/s transmission over 240 km, and 2.56-Tb/s transmission over 160-km fiber link, are described

Comparison of interferometric all-optical switches for demultiplexing applications in high-speed OTDM systems

We have investigated three interferometric all-optical switches based on cross-phase modulation (XPM) in semiconductor optical amplifiers (SOAs), the semiconductor laser amplifier in a loop mirror (SLALOM) switch, the Mach-Zehnder interferometer (MZI) switch, and the ultrafast nonlinear interferometer (UNI) switch. Switching windows with different widths are measured under similar conditions for all three switching configurations. We introduce the integrated contrast ratio (ICR) as a measure to evaluate the performance of a switch from switching windows. Using the ICR, the switches are compared and their application is discussed as demultiplexer in optical time division multiplexing (OTDM) systems for data rates of 40, 80, and 160 Gb/s.

Transmission of Single-Channel 16-QAM Data Signals at Terabaud Symbol Rates

We present latest results for OTDM transmission systems in combination with digital coherent detection achieving record-high serial data rates in a single-wavelength channel. We show serial data transmission of 5.1 Tb/s (640 GBd) over 80-km and 10.2 Tb/s (1.28 TBd) over 29-km dispersion managed fiber (DMF). For 5.1-Tb/s transmission over 80-km DMF, the BER of all 128 OTDM-tributaries (both polarizations) is found to be below the hard-decision FEC-threshold, corresponding to an error-free net data rate of 4.8 Tb/s. In a 10.2-Tb/s experiment, the BER of all 256 TDM-tributaries (both polarizations) is found to be below the FEC-threshold in the back-to-back configuration. This translates to an error-free net data rate of 9.5 Tb/s. After transmission over a 29-km DMF negligible pulse broadening and a BER below the FEC limit is found.

160 Gbit/s optical 3R-regenerator in a fiber transmission experiment

A fiber-based, wavelength-shift free 3R-regenerating repeater was operated at 160 Gbit/s in a dispersion-managed fiber link for the first time. Error free 160 Gbit/s OTDM transmission over 186 km was demonstrated.

Noise analysis of frequency converters utilizing semiconductor-laser amplifiers

This paper deals with a general problem concerning semiconductor-laser amplifiers used for frequency conversion. The amplified spontaneous emission (ASE) of a saturated amplifier is investigated experimentally and theoretically. An analytical solution accounting for the spatial dependence of the inversion parameter as well as the spectral dependence of the ASE is derived. Hence, the results can be applied to arbitrary saturation conditions and frequency shifts. Our theory is applied to frequency converters based on four-wave mixing and is found to be in good agreement with both the numerical results and the experimental data. In order to quantify the performance of a frequency converter, a noise figure is defined and shown to be strongly dependent on the frequency detuning and the power of the input waves.

Single wavelength channel 10.2 Tb/s TDM-data capacity using 16-QAM and coherent detection

We present a serial 10.2-Tb/s transmission-system using a 1.28-TBd RZ-16-QAM signal, polarization multiplexing and ultra-fast coherent demultiplexing. Considering FEC-overhead, we achieve a record error-free net data rate of 9.5-Tb/s and transmission over 29-km.

Impact of fiber chromatic dispersion in high-speed TDM transmission systems

General guidelines for high-speed time-division multiplexing (TDM) data-rate transmission are essential for the increase of the overall transmission capacity. In this paper, general theoretical investigations concerning fiber chromatic dispersion in optical TDM systems are performed. Recent experiments that confirm the theoretical predictions are presented. Nonzero dispersion-shifted fiber and standard single-mode fiber are recommended for 40 and 160 Gb/s, respectively, independent of the chromatic dispersion compensation scheme.

Generation and coherent time-division demultiplexing of up to 5.1 Tb/s single-channel 8-PSK and 16-QAM signals

We have generated single-wavelength channel 8-PSK and 16-QAM RZ-data signals up to 5.1 Tb/s and subsequently extracted the time-division base rate channel using an ultrafast coherent receiver with time-division demultiplexing function and digital BER post-processing.

Integrated 100 Gbit/s ETDM Receiver in a Transmission Experiment over 480 km DMF

We report an integrated ETDM receiver for 100 Gbit/s, which comprises 1:2-demultiplexing and clock & data recovery on a single chip. The ETDM receiver was tested successfully in a 100 Gbit/s transmission experiment over 480 km dispersion managed fiber.