Abstract : The work carried out during this PhD deals with the impact of 2R optical regeneration in an optical transmission system. Simple and low cost 2R devices could indeed replace some of the present day optoelectronic repeaters to enhance the performance and reduce the cost of long haul and metropolitan optical links. For new devices of this type to be relevant, they have to be compatible with present day WDM links. As a consequence, most of the work of this PhD consisted of the study of a device based on a vertical microcavity saturable absorber, which indeed presented all of the requirements for the targeted application. Our work here relates phenomenon understanding and a transmission performance study. The PhD was realised within the framework of the national research program ASTERIX which deals with saturable absorption for terabit WDM optical regeneration.
After a presentation of some generalities of transmission systems and of the main sources of system degradations, we describe the principles of regeneration and give an overview of the main regeneration techniques found in the literature. Following this, we show the difficulty of characterising regenerator efficiency. We show, in particular, that a regenerator should be characterised in a transmission link to prove its ability to regenerate the signal.
In the fourth part of the work, the impact of a cascade of 3R regenerators in a transmission link is studied, both numerically and experimentally. This helps the reader to better understand, in the case where amplitude noise limits the transmission, how the power probability density functions evolve and how the bit error rate (BER) degrades.
The efficiency of an original 2R regenerator, composed of a vertical microcavity saturable absorber and a semiconductor optical amplifier, is then demonstrated in a recirculating loop experiment at 10 Gbit/s. A distance improvement ratio better than 9,5 is obtained at a BER of 10-8, allowing a propagation over 20 000 km for this level of signal degradation. An original study of the efficiency of this device over a spectral band as wide as 13 nm allows us to demonstrate the potential of this device for WDM applications.
This device finally allows us to carry out a more general study of the impact of a cascade of 2R regenerators. A numerical study clarifies the timing jitter accumulation in a 2R regenerated link. It should also be noted that an novel study of the impact of regenerator spacing is carried out with the aid of a two path recirculating loop. There is an optimal regenerator spacing, leading in the best performance, corresponding to the best compromise between timing jitter accumulation and amplitude noise accumulation. In addition, this study shows the distance gain when a long spacing is used : the distance is doubled compared to the non regenerated case after 6 regenerators cascaded and spaced by 600 km, for a BER of 10-8. Finally, the timing jitter limitation of the transmission is shown experimentally.