Harry Gensler's book "Formal Ethics" deals with a few meta-ethical principles using deontological modal logic together with a linguistic gimmick (imperative sentences) due to H-N Castañeda. Computational to the extent that it provides pencil-and-paper algorithms for reasoning. Gensler is a theist, but that doesn't harm the book as long as you can tolerate a few exercises in which that unneeded hypothesis (Laplace) is assumed.

"Multiagent Systems: Algorithmic, Game-Theoretic, and Logical Foundations" by Yoav Shoham and Kevin Leyton-Brown is an outstanding resource for those like myself who think that ethics should be based on Game Theory.

A good free online textbook on game theory is Osborne and Rubinstein's "A Course in Game Theory". I haven't done much more than sample it, but the coverage seems complete and rigorous. Rubinstein also has a book named "Modeling Bounded Rationality". The importance of that subject in the context of computational ethics should be obvious. But if you are still dubious, check out the anonymous reader comment at the link.

Some researchers working in modal logics relevant to mechanized ethical reasoning are Wiebe van der Hoek, Peter Vranas, Johan van Benthem, Joseph Halpern, and Krister Segerberg.