Figure 4 . Demonstration of a plasmonic WG, (a) SEM image of the MIM WG coupled to a plasmonic mode converter, (b) E-field distribution in the plasmonic mode converter-full device (top), the E-field distribution in the different parts of the device (bottom).
The air gap width has a significant impact on the mode converter’s coupling efficiency (CE). Without the air gap, good CE cannot be achieved, but the CE is significantly increased by adding a tiny air gap of roughly 20 nm. But when the air gap width rises, the CE steadily declines until it reaches the same level as when there is no air gap at a width of 100 nm. Additionally, without the airgap, the metal portion of the mode converter absorbs or scatters most of the propagating light. Most of the light is scattered when the gap is large because the side lobes of the silicon ridge WG cannot be properly drawn to the metal.
Despite its apparent simplicity, the procedure detailed here is difficult due to the positional precision needed for fabrication at a scale of ca. 20 nm or less. With the use of NTT’s advanced nanostructure production methods, this procedure is feasible. The integration of WGs with a deep-subwavelength core to optical integrated circuits is made possible by the creation of the first extremely efficient 3D mode converter. This accomplishment not only reduces the size of traditional devices but also lays the path for the possible use of novel devices with never-before-seen features in conjunction with nanomaterials. It is expected that more experimental research groups will join hands to find a low-cost and easy solution for the realization of these exceptional plasmonic sensor designs which are extensively published without experimental demonstration.