COLUMBIA, Md., Sept. 19 -- Essex Corp. announced that a Department of Defense (DoD) agency has purchased a 16-channel hyperfine WDM device with unsurpassed 6.25-GHz-spaced channels. According to several industry analysts, Essex is the first and only company selling sub-25 GHz WDM. The agency will use the device to develop high-capacity research networks. The unit will be delivered early in the fourth quarter of 2002.