Metal-insulator-metal junctions are tunneling diodes able to operate at very high frequencies, arriving at the optical ones. The quantum tunneling is a stochastic event that depends very much on the insulator thickness. The insulator thickness is under the diffraction limit of the light that illuminates the diode. Particularly, in the mid-infrared, the insulator thickness is several orders of magnitude under the diffraction limit, and the electromagnetic field cannot penetrate into the structure. In all papers reviewed, the wave which illuminates the diode, inside the junction, is transformed in an evanescent one. The only way in which the electromagnetic radiation can be introduced into the structure is through a traveling wave of surface plasmon-polaritons. This work is focused on a procedure of light distributed, which by means of Kretschmann and Reather's prism-based configuration, allows introducing the electromagnetic field in the junction, biased the insulator all along its length. In this way, the technique presented here introduces an improvement that increases the diode responsivity considerably.