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Ph.D. Thesis - Rasmus KjŠr - June 2008
Raman amplification in optical communication systems.
Ph.D. thesis, DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, Kgs. Lyngby, Denmark.
26 August 2008.
Supervisors: Palle Jeppesen, Leif K. Oxenl°we, Bera Pßlsdˇttir.

Rasmus KjŠr

In this thesis, fiber Raman amplifiers (FRAs) are investigated with the purpose of identifying new applications and limitations for their use in optical communication systems. To better understand the dynamics, gain and noise limitations of the amplifier, a numerical amplifier model is developed. The model is used to predict the performance of the amplifier in both static and dynamic cases and its results are shown to agree well with experimental amplifier measurements. Due to its high Raman gain efficiency and large deployment numbers, dispersion compensating fiber (DCF) is a highly suitable Raman gain medium and new applications of so-called dispersion compensating Raman amplifiers (DCRAs) are presented. These applications are: Terminal dispersion compensation using DCRAs, the extension of the dynamic and flat gain range of a commercial erbium-doped fiber amplifier (EDFA) to support longer spans, and the use of a hybrid wide-band DCRA/EDFA to obtain 60 nm gain bandwidth, noise figure of less than 4.5 dB and a total output power of 22 dBm. To extend the reach of future access networks, a long-reach passive optical network (PON) architecture is proposed and theoretically and experimentally evaluated. To compensate the fiber loss in the long-reach PON link, distributed Raman amplification (DRA) is used and different pumping schemes and their effect on the maximum reach and channel capacity are evaluated using a numerical model. A 120 km bidirectional link with sufficient output power for PON applications and no with additional penalty due to the bidirectional traffic is experimentally demonstrated. The dynamic properties of the PON link are tested with burst-mode traffic and the system is found to be a promising candidate for future long-reach access PONs with burst-mode traffic. Inter-channel crosstalk in saturated fiber amplifiers and the resulting output transients is a serious issue, particularly in high-speed (e.g. 40 Gbit/s) and reconfigurable networks. Output power transients can lead to burst errors during detection and in the worst case cause damage to vital system components. A new all-optical method for mitigating transients on a channel level is presented. The method is optimized using a numerical model and is simultaneously demonstrated on four 40 Gbit/s wavelength division multiplexed (WDM) channels. The result on the transient-induced channels is a sensitivity improvement in excess of 5 dB.

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Record created 2008-09-30, last modified 2008-10-15

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