The optical layout of erbium-doped waveguide amplifiers (EDWAs) based on spiral and folded spiral planar lightwave circuits is considered. It is shown that layouts may be ranked according to their ability to provide maximum gain within a given chip area and an optimum layout based on a spiral containing both straight and curved waveguide sections is identified from an initial set. The analysis is initially based on simple geometric principles. A detailed optical simulation is then carried out using an algorithm that links a five-level rate equation model with beam propagation by the method of lines. The results confirm the choice of optimum layout.
Daniel Lowe, Richard R. A. Syms, and Weibin Huang, "Layout Optimization for Erbium-Doped Waveguide Amplifiers," J. Lightwave Technol. 20, 454- (2002)