demonstrate the improved optical efficiency a finite difference time domain fdtd method was employed to simulate full wave electromagnetic coupling of the wg light into the pg structures the simulation model included the optical wave guide the plasmon generator the cladding material surrounding wg and pg and the air space at the abs two designs were evaluated the uniform edge plasmon generator with the same trapezoid cross section and the self focusing gap plasmon generator with a gradually shrinking trapezoidal cross section for the epg design the tm wg mode is the excitation source while for the gpg te wg mode it is the excitation source for the sake of simplicity the straight sections s 1 and s 3 of the sgpg design have not been included in the model fig7 a shows simulation results for a uniform plasmon generator structure as disclosed in the prior art the three figures show from left to right the time averaged electric field intensity distribution in the xz plane 20 nm above the top surface of the pg in the yz plane through the middle of the pg and in the xy plane at 20 nm from the abs the light wave coupling from the wg to the sp wave that forms a standing wave pattern due to reflection from the abs end can be clearly seen in the cross sectional views left and middle figures of intensity distribution the field intensity distribution in the xy plane corresponds to the confined optical spot around the tip of the pg the normalized peak.