Jean-Pierre Blondel

Network application and system demonstration of WDM systems with very large spans (error-free 32/spl times/10 Gbit/s 750 km transmission over 3 amplified spans of 250 km)

We present the network applications of WDM systems with very large spans. Enabling technologies are low loss fiber, large launch powers, Raman preamplification and forward error correction. An experiment using all these technologies is presented.

4.16 Tbit/s (104 /spl times/ 40 Gbit/s) unrepeatered transmission over 135 km in S+C+L bands with 104 nm total bandwidth

104 /spl times/ 40 Gbit/s unrepeatered transmission over 135.9 km is demonstrated on S+C+L bands (1492-1596 nm) using S-band lumped Raman amplifiers. The system implements distributed Raman pre-amplification over continuous bandwidth of 104 nm.

Erbium-doped fiber amplifier behavior in transoceanic links

We have investigated the signal and noise power evolution along cascaded erbium-doped fiber amplifier systems, in various configurations, with and without optical in-line filters. We showed what the key parameters are and what are the conditions to obtain a given signal to noise ratio performance.

25 GHz spaced DWDM 160/spl times/10.66 Gbit/s (1.6 Tbit/s) unrepeatered transmission over 380 km

Unrepeatered transmission of 160 25 GHz spaced channels at 10 Gbit/s over 380 km is demonstrated. The combination of recent advanced technologies, such as DWDM multiplexing/demultiplexing, large pump power, remote amplification, in-line filtering and FEC, allow this record transmission to be achieved.

Raman amplification in unrepeatered submarine systems pushes the limits of distance and bandwidth

Raman amplification is a key technology for unrepeatered transmissions as it allows to widely increase both span length and optical bandwidth in a very simple manner. We review in this paper recent record demonstrations and installed systems where Raman amplification fulfills its role as a mean to reach very long repeaterless distances and to expand into new spectral areas.

Relevant EDFA features for CATV applications

While low loss and large bandwidth have allowed optical fibers to become essential in a large amount of telecommunication systems, this has not yet been true for video distribution systems where the cost per subscriber must be as low as possible. First optical video distribution systems have been developped using 1.3 pm distributed-feedback (DFB) lasers. Up to now, the modulation format used in such systems is analog amplitude-modulation vestigial-sideband (AM-VSB) scheme since it provides direct compatibility with cable TV industry and present television sets. However, this modulation scheme requires a very high signal-to-noise ratio on the receiver side so that it is necessary to detect large optical powers (above -10 dBm) to ensure good picture quality. This means that the power budget (budget one can afford for optical fibers and splitters losses) for 1.3 im systems, even with powerful optical sources, is not very important; in turn, this means that it seems difficult to cut the cost per subscriber with this technology. With optical Erbium-Doped Fiber Amplifier (EDFA) breakthrough, many suppliers of cable TV transmission systems moved to 1.5 .tm technology. Whereas this new component is revolutionizing most of the telecommunication systems as optical fiber did 20 years ago, the use of optical amplifiers for analog systems is not so impressive as for robust digital transmission systems. This is due to the fragility of analog signal in respect with noise and distortion. Because of the noise generated by an optical amplifier, it is not possible to cascade a large number of them while reaching a realistic signalto-noise ratio at the network termination. Optical amplifiers may also distort the analog signal when the transmitter consists of a directly-modulated semiconductor laser, suffering from chirp (unwanted wavelength modulation when power modulation is achieved through current modulation). Moreover, shifting from 1 .3 .tm to 1 .5 pm wavelength brings new problems : 1 .5 tm DFB lasers are not yet as linear as 1.3 im DFB lasers and analog system designers have to cope with chromatic dispersion at 1 .5 .tm in standard fibers (i.e. non dispersion-shifted fibers). It is clear that many of the technical issues for 1.5 im analog systems are far from being resolved. In this paper, we investigate the way, and to what extent, erbium-doped fiber amplifiers may improve analog systems power budget. The organization of the paper is as follows. In Section 2, we discuss what is the relevant noise parameter for optical amplifiers to predict the signal-to-noise degradation they cause. We also show that the same overall noise performance can be reached with amplifiers featuring different noise parameter and output power combinations. This section is completed with experimental measurements. Linearity definitions and requirements for AM-VSB systems are presented in Section 3. Included is a discussion of some specific factors that degrade the signal linearity within an optical amplifier in respect with optical source characteristics. Finally, the still opened technical matters and potential evolution for 1.5 jim analog systems are briefly summarized in Section 4