IDES have been realized in modulation doped AIGaAs/GaAs heterostructures by fabricating split-gate configurations and ultrafine etched structures with optimized lithography and etching techniques. With deep-mesa etching technique it is possible to prepare single and multi-layered quantum wire systems. From dc magnetotransport typical confinement energies of 2me V are determined. The FIR response is strongly governed by collective effects which give the resonances the character of local plasmon modes. In multi-layered quantum wire structures a splitting of the plasmon dispersion in...