08/01/06: See the New Compact Frequency Extension Modules.
VDI recently introduced a new broadband 1.1-1.5 THz Frequency Extension Module (FEM). The design is all solid state using planar GaAs technology. There are no mechanical tuners and the FEM may be electronically swept to any frequency in the band. This system is mechanically and electrically robust with 400 GHz of bandwidth and peak power of 2-3uW. FEMs to nearby bands are under development.