Unidirectional reflectionlessness of a non-PT-symmetric system consisting of a MDM plasmonic waveguide side coupled to two MDM stub resonators with unbalanced gain and loss.
(A) Schematic of a perfect absorber unit cell consisting of an MDM plasmonic waveguide side coupled to two MDM stub resonators. (B) Reflection and transmission spectra for the structure of A calculated for light incident from both the forward and backward directions using FDFD (solid lines) and CMT (circles). Results are shown for w=50 nm, w1=10 nm, w2=25 nm, h1=67.5 nm, and h2=53 nm. The metal is silver and the dielectric is air. The left and right stubs are filled with SiO2 doped with CdSe quantum dots (εA=4.0804−j0.6) and InGaAsP (εB=11.38+j0.41), respectively. Also shown are the absorption spectra in the forward direction calculated using FDFD (green solid line). (C and D) Magnetic field amplitude profiles for the structure of (A) at f=193.4 THz (λ0=1.55 μm), when the fundamental TM mode of the MDM waveguide is incident from the left and right, respectively. All parameters are as in (B). (E and F) Magnetic field amplitude in the middle of the MDM waveguide, normalized with respect to the field amplitude of the incident fundamental TM waveguide mode in the middle of the waveguide, when the mode is incident from the left and right, respectively. The two vertical dashed lines indicate the left boundary of the left stub and the right boundary of the right stub. All parameters are as in (B) .