Optical field enhancement in nanoscale slot waveguides of hyperbolic metamaterials

Abstract

Nanoscale slot waveguides of hyperbolic metamaterials are proposed and demonstrated for achieving large optical field enhancement. The dependence of the enhanced electric field within the air slot on waveguide mode coupling and permittivity tensors of hyperbolic metamaterials is analyzed both numerically and analytically. Optical intensity in the metamaterial slot waveguide can be more than 25 times stronger than that in a conventional silicon slot waveguide, due to tight optical mode confinement enabled by the ultrahigh refractive indices supported in hyperbolic metamaterials. The electric field enhancement effects are also verified with the realistic metal-dielectric multilayer waveguide structure.

Highly efficient second harmonic generation in hyperbolic metamaterial slot waveguides with large phase matching tolerance

“…1 shows the schematic of the proposed HM slot waveguides. Two identical HM waveguides composed of alternating metal-dielectric multi layers [25,26] with a square cross section of 250 nm × 250 nm are placed adjacent to the both sides of a nonlinear organic polymer in the slot (height g = 20 nm). The assumed polymer is a doped, cross-linked organic polymer with a nonlinear susceptibility of χ (2) 111 = 619 pm/V [15,27] and refractive index n = 1.68 at the wavelength of λ = 1,550 nm (n = 1.58 at λ 3,100 nm) [24].…”

“…The hyperbolic metamaterials were composed by alternate thin layers of silver (Ag, filling ratio f r ) and germanium (Ge) with a pitch thickness of 10 nm [24]. The metamaterial can be treated as a homogeneous effective medium [25,26]. The linear modal properties taking into the nonlinear coupling wave equations are the complex effective index and the field distribution in the slot.…”

“…The proposed HM slot waveguide supports the even hybridization of individual modes. The even hybrid modes (EHMs) not only inherit all of the advantages of individual modes listed above but also present some unique features [26], such as a greatly enhanced field in the low-index polymeric slot due to the slot effect [32,33]. To make the most use of the material nonlinearity, the EHMs with m x = 1 exhibiting a zero phase accumulation (a constant phase) along the x direction [25] are preferred.…”

“…So the HM waveguide enables the deep subwavelength confinement with ultrahigh effective index [25], which exceeds those of traditional plasmonic-based structures. Due to the normal electric displacement continuity, significant electric field enhancement occurs at the low-index slot region of the coupled HM waveguides [26]. In contrary, nonlinear optical processes associated with HMs remain relatively unexplored compared with their linear counterparts.…”

Dual-gated tunable absorption in graphene-based hyperbolic metamaterial

“…HMMs have been investigated for potential applications in negative refraction, 2,3 imaging hyperlens, 4 and as an optical waveguide. 5 HMMs exhibit exotic physical behavior such as the broadband Purcell effect, 6 nonlinear effect, 7 and perfect absorption. 8,9 Smolyaninov 10 found that HMMs display critical opalescence, indicating that they may emulate virtual microscopic black holes, an interesting feature of the real physical space-time.…”