G. Onishchukov

Dissipative solitons and their critical slowing down near a supercritical bifurcation

The existence of a novel kind of soliton in dissipative systems with competing, noninstantaneous nonlinearities has been predicted and experimentally verified. These subcritically bifurcating solitons exist near a supercritical continuous wave bifurcation. We show that their peculiarities originate from different saturation behavior of nonlinear loss and gain with regard to power and energy. Branches of stable and unstable solitary waves have been identified. For the first time to our best knowledge, we have experimentally proved critical slowing down of solitons.

Differential binary phase-shift keying transmission using cascaded semiconductor optical amplifiers

Recently the performance of Semiconductor Optical Amplifiers (SOA) in 1.3/spl mu/n fiber communication systems has been intensively studied and a 10 Gbit/s RZ - transmission over 500 km has been demonstrated in the field and over 1500 km in a re-circulating fiber loop set up using MQW-SOA. It turned out that the performance of such systems is primarily limited by three factors: the fast growth of Amplified Spontaneous Emission (ASE), the pattern effect and the nonlinear impulse-phase distortions in SOA which are caused by the low saturation energy of SOA, the gain recovery time comparable with the bit period and by the strong nonlinearity of SOA. The effects are also important in other systems where cascaded SOA are used, for example, as optical gates. With increasing bit rate in TDM systems and with number of channels in WDM, the effects became stronger and the maximum propagation distances decrease. So in the case of a 4/spl times/10 Gbit/s WDM system a 80 km transmission has been experimentally demonstrated and up to 200 km predicted from numerical simulations. The limiting effects and consequently the performance are similar in systems with both NRZ or RZ modulation formats. But using other modulation formats like Phase Shift Keying (PSK) or Frequency-Shift Keying (FSK), where the signal power is constant, it would be possible to avoid these specific for SOA, harmful effects and to approach the performance in the 1.5 /spl mu/m window. In this paper we present the results on a single channel 10 Gbit/s Differential Binary PSK - Direct Detection (DBPSK-DD) transmission in a 1.3 /spl mu/m system with in-line MQW-SOA amplifiers. The format has been chosen because of simplicity of the transmitter and receiver designs.

Optimization of signal transmission by an in-line semiconductor optical amplifier-saturable absorber module

A module consisting of a semiconductor optical amplifier and a saturable absorber is investigated with respect to gain, pulse and noise dynamics and their dependence on device parameters. Based on the analytical and numerical results optimization strategies were found regarding high-bit-rate signal transmission. The results are compared with recently reported experimental data.

Modulational instability in a transmission system with semiconductor optical amplifiers and in-line filters

Modulational instability of continuous waves in transmission systems with semiconductor optical amplifiers and in-line filters was theoretically and experimentally analyzed. Stable and unstable domains were identified. Even in the normal-dispersion region, modulationally unstable domains can exist for an appropriate filter detuning.

Fiber transmission systems with semiconductor optical amplifiers without in-line filtering

10 Gbit/s RZ signal transmission at 1.3 μm in a fiber transmission system with in-line semiconductor optical amplifiers is investigated using a recirculating fiber loop setup. We found that under certain conditions the system operates without in-line filtering and with strongly saturated amplifiers, provided the signal is extracted from the amplified spontaneous emission by means of a narrow optical filter in front of the receiver. These results are compared with a transmission scheme with in-line filtering.

Quantum dot (InAs/InGaAs DWELL) semiconductor optical amplifier

In this paper, InAs/InGaAs quantum dot SOA emitting at greater than 1300 nm with gain as high as 18 dB at low with 100 mA pump current was designed and manufactured. The gain recovery dynamics of the QD-SOA sample was studied using a pump-probe set up. Extremely low linewidth enhancement factor and fast gain recovery make the device perspective for deployment in communication systems. The position of the gain peak and the bandwidth are practically temperature independent.

Signal instability in a transmission system with cascaded semiconductor optical amplifiers

The transformation of phase into amplitude modulation, experimentally observed in a PSK system, can be explained by the action of an optical in-line filter. Furthermore it was shown that, caused by an interplay of in-line filtering and nonlinear effects induced by SOAs, arises for system parameters typical for an experiment. In conjunction with other noise sources this modulation instability has detrimental consequences for the system performance.

High bit rate 1.3-/spl mu/m transmission using semiconductor optical amplifiers in fiber link without in line filters

This work investigates a fibre link system without in-line filters for distances up to 1000 km using a fiber-loop recirculating setup and compares its performance with a system with narrow-band in-line filters. A polarization-insensitive MQW semiconductor optical amplifier was used.