According to the Cisco XENPAK doc, LX4 uses WWDM. I couldn't find a whole lot of reference on WWDM.
My understanding is that with CWDM and DWDM, you need either a passive mux/demux or a OADM for wavelength aggregation. Does that apply to WWDM as well? In other words, can I take two switches with LX4 XENPAK and connect them via SMF without mux/OADM?