Hybrid Plasmonic Modes in Multilayer Trench Grating Structures

Abstract

brings about a high potential application value in many fields such as plasmonic photocatalyst, [6,7] nonlinear optics, [8,9] surface-enhanced spectroscopy, [10,11] solar cells, [12,13] high integration optical devices, [14,15] and metamaterials, [16,17] etc. Among various basic plasmonic structures, the metal-insulator-metal (MIM) configuration that the insulator film is sandwiched between two symmetric metal films is one of the most common units. [18] In this structure, the electric field is strongly constrained, causing a stronger energy confinement effect in deeply subwavelength scale. [19,20] However, due to the presence of metal, a large Ohmic loss is inevitable in the individual plasmonic structures including the traditional MIM geometries, which results in difficulties to achieve strong confinements of electric field with a low loss simultaneously. [21,22] Generally, for the widely used Si-based plasmonic devices, it is an undesirable phenomenon. One of the main reasons is that silicon has a relative large thermo-optic coefficient and the temperature variety induced by Ohmic loss influences its properties seriously, [23,24] leading to the instability and limitations of integration. In addition, the large loss means the low efficiencies for Si-based plasmonic optoelectronic converters as well. [25] In this case, the enhancement of plasmonic mode coupling through engineering of multiple structures may realize a reduction of the Ohmic losses, [21,26] and some composite structures are constantly designed to achieve the mode coupling. Exciting surface lattice resonances (SLRs) is a line of thought for reducing losses, but it is usually supported by nanorods or nanoparticles, and coupled with localized surface plasmon resonances (LSPRs). [27][28][29] Thus, further investigations of novel microstructures based on propagating plasmon resonances are necessary.According to the contents above, first, we demonstrate a microstructure of multilayer grating including MIM waveguides inside. Alternate Al and Si layers are utilized to replace the traditional single material grating stripes on the Si substrate. Not only will SPPs be excited by the grating-shaped structure, but also the standing wave resonance will be formed by Fabry-Perot (F-P) cavities that consist of MIM waveguides. Then we demonstrate a microstructure of multilayer trench grating including both stripes and trenches. The section of multilayer grating stripes can also perform a narrowband F-P resonance through MIM structures. Meanwhile, the multilayer For common plasmonic structures, it is difficult to considerate both the abilities of confining light and reducing loss. Here, two plasmonic multilayer structures comprised of five alternate Al and Si layers are demonstrated. First, the multilayer gratings with near-infrared dual narrowband peaks are given in the spectrum excited by Fabry-Perot resonance. Through investigating the modes of electric field distributions, the frequency-sensitivity, and linear designable characteristic of its working bands are cl...

Microcavity electrodynamics of hybrid surface plasmon polariton modes in high-quality multilayer trench gratings

“…The five alternate Al and Si films formed two MIM waveguides in the multilayer grating stripe to sustain a gap plasmon mode with a relatively large propagation range 24 , 30 . Reflection was observed at the gap terminations due to the finite length of the waveguide, thereby resulting in the formation of an inner standing wave, which is a typical F-P resonance system with two distinct features, specifically, frequency sensitivity and multiple resonance orders 34 . The order of this F-P resonance mode is simply expressed as follows 35 , 36 : where φ r is the phase shift at the gap termination, which can be obtained by the linear fitting method, and β is the complex propagation constant, which can be calculated using dispersion equations derived from the symmetric waveguide theory with respect to the regular symmetric MIM waveguide, as carefully explained in our previous work 34 .…”

“…Furthermore, this IMI configuration can be simplified to the interface between Al and air because the light hardly penetrated the first Al film. In addition, the energy was largely concentrated in the cavity of the trench, thereby resulting in the presence of the cavity resonance mode, which is another SPP mode with multiple resonance orders 34 . However, the present study only observed the first order in the concerned waveband.…”

“…However, research on low-loss structures based on hybrid SPP modes is rarely reported. Very recently, our previous work demonstrated an SPP-mode hybridization phenomenon based on a multilayer trench grating geometry 34 , which led to the realization of a large absorption quality factor ( Q ) in the trench configuration but lacked a quantitative analysis and verification of the entire loss inhibition. Furthermore, the microcavity electrodynamic processes in the hybrid SPP modes, specifically absorption, radiation, and connections between various losses, which are significant to the design of the plasmonic devices, all remain unclear.…”

Optics with hyperbolic materials [Invited]

“…A Si grating structure coated with a multilayer HMM has been realized [73,74] as illustrated in Fig. 5(d).…”

“…(c) Ag/Al 2 O 3 multilayer HMM with grating and quantum dots layer embedded[72]. (d) Cross-section of a trench structure covered with Al/Si multilayer HMM[73,74]. The hypercrystals consist of small Λ 1 and large periods, Λ 2 , respectively.…”