The Calibur arc is set in the Alfihem Online world and it's Sinon first appearance in Alfheim world . Like other girls Sinon also has neko avatar in Alfheim Online. The Calibur arc starts October 18.
Mother Rosario arc is definitely the best story of SAO light novels. If you have read the light novel you will probably agree with me. This arc starts from November 8.
Before these arcs, there is a recap episode #14.5 on October 11.