Abstract
The hybrid three-arm coupler, which consists of the middle long range
surface plasmon polariton (LRSPP) waveguide and two outside conventional dielectric
waveguides, is proposed and analyzed numerically with finite element method.
The characteristics, including coupling length, coupling loss, extinction
ratio and frequency dependence, are discussed in detail with different structure
parameters. Compared with the two-arm hybrid coupler, the coupling loss of
the three-arm hybrid coupler based devices can be reduced, especially with
wider middle LRSPP waveguide. Extra transmission loss on the metal strip can
be avoided because of the lossless input and output arms. Furthermore, different
from conventional three-arm dielectric coupler, we find that the three-arm
hybrid coupler with asymmetric structure can reach a much higher extinction
ratio by introducing a middle arm offset. Since the middle arm can only transfer
the TM mode from one dielectric arm to the other one within the TM mode coupling
length, this structure is promising for realizing integrated polarization
splitter or other functional devices.
© 2008 IEEE
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