Variable Tunneling Excitation of Optical Surface Waves

A method for coupling an optical beam into thin films utilizing shaped tunneling regions is described. It is shown that in principle all of the power can be coupled into the film. For ease of fabrication, a uniform gradient structure is preferable, however, and yields coupling of over 90 percent for incident coherent Gaussian beams. Experimental coupling values with gradient tunneling regions are in excess of 50 percent. Good mode isolation and elimination of prism edge effects are major features of the coupler. The experimental coupling values are obtained from a transmission measurement utilizing two prisms.