Today, commercial fiber optical transmission systems are operated at a data rate of 10 or 40 Gbit/s per wavelength channel. The optical time division multiplexing (OTDM) technique allows for the investigation of the next generation TDM data rate of 160 Gbit/s while electrical signal processing at 160 Gbit/s is not yet available. In an OTDM transmission system, the key functions of the transmission system are realized using ultrafast all-optical or electro-optical network elements. In this paper, the recent progress in ultrafast technologies for 160 Gbit/s OTDM transmission systems is reviewed. The focus will be on techniques to realize optical pulse sources and ultrafast optical gates which operate on a time scale of a few picoseconds to a few hundred femtoseconds. They are the key elements of a 160 Gbit/s OTDM transmission system and are applied for various functions in the system. The paper focuses in particular on the application of ultrafast optical technologies for measurement purposes. In an optical communication system the quality of the data signal can be inferred from the optical eye diagram of the data signal. Presently, the measurement of optical eye diagrams at a data rate of 160 Gbit/s is inhibited by the limited bandwidth of photodetectors and electrical sampling oscilloscopes. By realizing an all-optical sampling system using the ultrafast technologies discussed before, the bandwidth of such an optical sampling system exceeds 400 GHz and allows for eye diagram measurements up to 320 Gbit/s.

The paper reports on optical signal processing for data transmission at 160 Gbit/s per wavelength channel using the DPSK-modulation format in connection with optical time division multiplexing (OTDM) technology.

A 10 GHz clock recovery from a 160 Gb/s data signal is demonstrated using a bidirectionally operated electroabsorption modulator (EAM). Employing a differential detection scheme, excellent locking stability is achieved. The recovered clock allows error-free 160 Gb/s to 10 Gb/s demultiplexing with no penalty.

The self cascading of an electroabsorption modulator (EAM) with commercially available components improves the switching performance of a single electroabsorption modulator. The improved performance is demonstrated in 160 to 40 Gbit/s demultiplexing experiments and 40 GHz pulse generation.

An electroabsorption demultiplexer was improved by operating it in a tandem-arrangement with an optically controlled SOA. An increase of the maximum data rate from 40 Gbit/s to 80 Gbit/s was experimentally demonstrated. The main drawback of the proposed scheme is the need of an additional optical control. In this experiment a mode locked laser was used to control the SOA. However, it should be sufficient to use a gain-switched DFB-laser. The advantage of this scheme is that no electronic devices for frequencies higher than 10 GHz are required and no additional RF-source or RF-amplifier is needed for the control laser. The set-up is very robust, especially because it does not base on interferometric or polarization sensitive effects.

Clock recovery from optical time division multiplexed data signals up to 160 Gbit/s is experimentally demonstrated using a phase-locked loop with a semiconductor optical amplifier in a loop mirror as a fast optical phase comparator. The timing jitter of the optical clock pulse extracted from a 160 Gbit/s data signal was < 0.3 ps.

We report on all-optical switches for high speed optical communication systems based on semiconductor optical amplifiers in an interferometric configuration, whereby the photon energy of the switched data signal is below the band gap energy.

The cascaded amplifier and saturable absorber is presented as a new all-optical switching scheme for optical signal processing applications. First demultiplexing experiments demonstrate the principle of operation of this scheme.

We demonstrate three techniques to measure the instantaneous frequency and intensity of optical pulses using semiconductor optical amplifiers (SOAs). Four-wave mixing, gain-saturation, and interferometric switching through a nonlinear optical loop mirror are three mechanisms by which sampling is done. We have experimentally measured the intensity and chirp profiles of pulses with energies as low as 10 fJ. Since the nonlinearity in the SOA is relatively slow, these measurement techniques are most appropriate for picosecond pulses often found in telecommunication applications. The temporal resolution of these methods are limited by timing jitter, which was ≈0.5 ps for the mode-locked laser diodes we used in our experiments, and by the width of the switching window

Summary form only given. Clock recovery (CR) is an essential part of any transmission system. In this paper, we propose a new type of optical clock recovery based on an optical PLL, where a SLALOM (Eiselt et al., 1995) acts as an ultrafast phase comparator. The scheme has been demonstrated successfully at bit rates up to 160 Gb/s.

Cross-absorption modulation in an all electroabsorption modulator is utilised to perform 80/10 Gb/s all-optical demultiplexing. An improvement in receiver sensitivity at 10 Gb/s is demonstrated when wavelength converting.

In this paper we describe experimental and numerical studies on high bit rate, single span transmission system over a length of 160 km without amplifiers in the link (unrepeatered). From these studies we revealed that the tolerance of the residual dispersion is very restrictive. Proper dispersion management and PMD compensation techniques are important topics in these and future systems.

We investigate the performance of a semiconductor optical amplifier (SOA) based Sagnac-interferometer switch in its application as time division demultiplexer. By performing dynamic switching window measurements with a time resolution of about 1 ps, the temporal width and the contrast of the switching windows are investigated for SOA lengths of 500, 1000 and 1500 μm. Operating the switch with a control pulse rate of 10 GHz (corresponding to all-optical demultiplexing to 10 Gb/s) the shortest switching windows, still retaining high contrast, are achieved with short SOAs. By increasing the control pulse rate to 40 GHz, the case of an SOA-based all-optical demultiplexer with a base rate of 40 Gb/s is investigated. Though the switching contrast deteriorates for the 40 GHz control pulse rate, the obtainable contrast is still up to 19 dB. This finding encourages the feasibility of SOA-based interferometric demultiplexers with base rates of 40 Gb/s. In particular, this feature will be crucial to future all-optical demultiplexers as the base rate of electronic signal processing is currently evolving to 40 Gb/s.

We present a novel algorithm to evaluate the performance of optical demultiplexers from standard switching-window measurements. Investigations of a SLALOM/TOAD demultiplexer for 80 Gb/s and 160 Gb/s show that biasing one arm of the interferometer by a constant phase offset significantly improves its performance.

Experimental and theoretical switching windows in an interferometric configuration with a gain-transparent semiconductor optical amplifier in a loop mirror (GT-SLALOM) are investigated. The amplifier gain and phase dynamics are analyzed in detail. For the gain dynamics, experimental and theoretical pump-probe results are presented. The phase dynamics is investigated theoretically. It is shown that the insertion of an optimized nonreciprocal phase shift in the GT-SLALOM configuration increases the contrast of the switching windows and, thus, improves the performance of the switch for demultiplexing applications. The influence of an asymmetric coupling ratio of the 3-dB input/output coupler on the switching contrast is also discussed.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text E. Hilliger, S. Diez, H. -. Ehrke, R. Ludwig, C. Schmidt, H. G. Weber, and J. Y. Emery, "80 Gbit/s All-Optical Demultiplexing using a Hybrid Mach-Zehnder-Interferometer Switch with Gain-Clamped Semiconductor Optical Amplifiers," in Photonics in Switching, P. Prucnal and D. Blumenthal, eds., Vol. 32 of OSA Trends in Optics and Photonics (Optica Publishing Group, 1999), paper 141. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Summary form only given. Various applications of all-optical signal processing, e.g, demultiplexing in optical time-division multiplexing (OTDM) systems or optical sampling, can be accomplished by all-optical switches based on semiconductor optical amplifiers (SOAs) in interferometric configurations. To optimize such switching devices, it is useful to have a model which describes the temporal characteristics of the switches accurately. The SOA model, which we present, takes the pulse propagation and the gain dynamics into account. The gain dynamics is determined by carrier density modulation (also called carrier density pulsation, CDP) and carrier heating (CH), calculated in separate rate equations.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text R. Ludwig, S. Diez, U. Feiste, E. Hilliger, C. Schmidt, and H. G. Weber, "Applications of SOA’s for Optical Signal Processing and OTDM," in Optical Amplifiers and their Applications, S. Kinoshita, J. Livas, and G. van den Hoven, eds., Vol. 30 of Trends in Optics and Photonics (Optica Publishing Group, 1999), paper ThC3. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

An advanced time-domain dynamical model for the investigation of semiconductor optical amplifiers (SOA) is presented. The model accounts for the ultrafast gain dynamics, the gain saturation and the gain spectral profile. It is also suitable for analyzing the amplifier in a system environment. As an example the model is used to investigate the gain dynamics of an SOA as well as the characteristics of an interferometer switch semiconductor laser amplifier in a loop mirror (SLALOM). Good agreement between modeling and experiment is shown. The model can be applied to the investigation of other optically time-division multiplexed (OTDM) applications, too.

Summary form only given. All-optical sampling of pulses is important for characterizing high-speed TDM systems. Many all-optical sampling techniques have been developed, but often measure only the intensity profile and not the wavelength profile. We demonstrate and compare three measurement techniques using semiconductor optical amplifiers to directly obtain the intensity and wavelength profiles (chirp) of an unknown optical pulse with resolution of about 1 ps and without extensive computation. The presented techniques have in common that a synchronized short probe pulse is used to sample a broader signal pulse. The interaction between these pulses is, however, mediated through different mechanisms, namely four-wave-mixing, gain saturation, and interferometric switching.