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.