We　propose　a　feasible　and　efficient　scheme　to　generate　N-atom　W-class　states　in　spatially　separated　cavities　without　using　any　classical　driving　pulses.　We　adopt　the　model　in　which　the　couplings　between　different　atoms　are　mediated　only　by　virtual　excitations　of　the　cavity　and　fiber　fields,　so　the　scheme　is　insensitive　to　the　cavity　decay　and　fiber　photon　leakage.　We　carry　out　both　theoretical　investigation　in　a　decoherence-free　subspace　and　numerical　calculation　accounting　for　decoherence　due　to　the　atomic　spontaneous　emission　as　well　as　the　decay　of　cavity　and　fiber　modes.　The　theoretical　and　numerical　results　agree　in　the　large　atom-cavity　detuning　regime.　Our　scheme　proves　to　be　useful　in　scalable　distributed　quantum　networks.　(C)　2013　Optical　Society　of　America