Acoustically anti-guiding optical structures are provided. In an exemplary acoustically anti-guiding fiber, a suitable cladding size for ant guiding fibers occurs wherein the cladding size is determined such that the net material dampening in the cladding is large enough to dampen acoustic waves. In another embodiment, a cladding can be considered infinite if the round-trip time from a core to an outer cladding boundary (or interface) is greater than a coherence time of an acoustic wave.