We present optical investigations of rectangular surface plasmon polariton waveguides lithographically defined on GaAs substrates. The plasmon propagation length is directly determined using a confocal microscope, with independent polarization contro
l in both excitation and detection channels. Surface plasmon polaritons are launched along the waveguide using a lithographically defined defect at one end. At the remote end of the waveguide they scatter into the far-field, where they are imaged using a CCD camera. By monitoring the length dependence of the intensity of scattered light from the waveguide end, we directly extract the propagation length, obtaining values ranging from LSPP = 10-40 {mu}m depending on the waveguide width (w=2-5 {mu}m) and excitation wavelength (760-920 nm). Results are in good accord with theoretical expectations demonstrating the high quality of the lithographically defined structures. The results obtained are of strong relevance for the development of future semiconductor based integrated plasmonic technologies.
