The Routing and Wavelength Assignment (RWA) problem is an optical networking problem that aims to improve data transmission by eliminating optoelectronic conversions through the network. The RWA problem is in the set of NP-complete problems and thus, it is also an interesting problem from a computational point of view. It can be solved in different flavors, being the Static Lightpath Establishment (SLE) the one studied in this work. In this work we define different Answer Set Programming (ASP) encodings for the RWA-SLE problem and study their performance when solving the problem with a state-of-the-art conflict-driven ASP solver: clasp. We investigate the relation between the performance of the ASP encodings and two different characteristics of the encodings: the number of nogoods and loop nogoods generated during search and a new measure for their tightness that we introduce. We also compare the performance of our ASP encodings with the best performing pseudo-Boolean encoding that we presented in a previous work.