Abstract
In this paper, a novel polarization-independent hybrid plasmonic coupler based on a T-shaped slot waveguide is proposed and investigated by numerical simulations using the finite element method. The structure supports both the TE-polarized slot waveguide mode and the TM-polarized plasmonic mode, offering a greater possibility to achieve the polarization-independent operation. The simulation results show that with proper structural parameters, the waveguide coupler with high extinction ratios of 31.2 dB (TE) and 30 dB (TM) and low insertion losses of 0.38 dB (TE) and 2.04 dB (TM) can be achieved at a telecommunication wavelength of 1550 nm. An investigation of the influence of structural perturbations indicates that the proposed coupler also has a good tolerance to fabrication errors. The proposed structure has potential applications in the field of subwavelength integrated photonic circuits.
Highlights
Ultra-high-density photonic integrated circuits (PICs) and interconnects have attracted considerable research interest in recent years.1 Miniaturized waveguides for guiding and manipulating light at the diffraction-limited scale have been proposed and demonstrated by utilizing various technologies, such as photonic crystal waveguides,2 surface plasmon polariton (SPP, which is the electromagnetic wave coherently coupled to electron oscillations and propagating along the metal–dielectric interface) waveguides,3 and slot waveguides.4 Unlike dielectric waveguides, SPP waveguides can provide a deep subwavelength mode confinement far beyond the diffraction limit5 and potentially lead to photonic integration at a scale comparable to that of electronics
The schematic diagram of the proposed polarizationindependent directional coupler based on the T-shaped SDLSPP (TSDLSPP) waveguide is shown in Fig. 1, which consists of two identical parallel TSDLSPP waveguides with the interaction length of L and separated by a gap distance of D
The materials selected for the semi-infinite substrate, slot regions, and ridges are silver (Ag, with the dielectric constants selected from Ref. 21), silica (SiO2, with a refractive index of nSiO2 = 1.445), and silicon (Si, with a refractive index of nSi = 3.455), respectively
Summary
Ultra-high-density photonic integrated circuits (PICs) and interconnects have attracted considerable research interest in recent years.1 Miniaturized waveguides for guiding and manipulating light at the diffraction-limited scale have been proposed and demonstrated by utilizing various technologies, such as photonic crystal waveguides,2 surface plasmon polariton (SPP, which is the electromagnetic wave coherently coupled to electron oscillations and propagating along the metal–dielectric interface) waveguides,3 and slot waveguides (which possess a high refractive index contrast and a strong mode confinement in the low refractive index slot region).4 Unlike dielectric waveguides, SPP waveguides can provide a deep subwavelength mode confinement far beyond the diffraction limit5 and potentially lead to photonic integration at a scale comparable to that of electronics. To well balance this trade-off, recently, a novel type of hybrid plasmonic waveguide, referred to as slot-based DLSPP (SDLSPP) waveguide, has been intensively studied11 and it has shown promising potential in applications, such as ring resonators,12 power splitters,13 and directional couplers.14 Most of the SPP waveguides have been demonstrated to offer the subwavelength confinement for only TM polarization. Another feasible approach is to develop directional scitation.org/journal/adv couplers with polarization-independent properties, such as T-shaped dielectric slot waveguides18 and silicon-based hybrid plasmonic waveguides19 for efficient control of birefringence.
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