Since the development of the first scanning near-field optical microscope great effort has been put into the development of nearfield optical probe tips that have both a good lateral resolution, in the range of several tens of nanometers, and a high power throughput. Several groups have proposed the use of scanning near-field optical tips with a coaxial structure. From electromagnetic theory it is well known that such structures can attain power transmissions of close to one and they do not have a cut-off frequency. In this paper we discuss some questions concerning the stimulation of optical coaxial modes and their propagation behavior.