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

Abstract

Highly efficient second harmonic generation (SHG) bridging the mid-infrared (IR) and near-IR wavelengths in a coupled hyperbolic metamaterial waveguide with a nonlinear-polymer-filled nanoscale slot is theoretically investigated. By engineering the geometrical parameters, the collinear phase matching condition is satisfied between the even hybrid modes at the fundamental frequency (3,100 nm) and the second harmonic (1,550 nm). Two modes manifest the great field overlap and the significant field enhancement in the nonlinear integration area (i.e. the slot), which leads to extreme large nonlinear coupling coefficient. For a low pumping power of 100 mW, the device length is as short as 2.19 µm and the normalized conversion efficiency comes up to more than 6.37 × 10 5 W −1 cm −2 which outperforms that of the plasmonic-based structures. Moreover, the efficient SHG can be achieved with great phase matching tolerance, i.e., a small theoretical fabrication-error sensitivity to filling ratio and a broad pump bandwidth in a compact device length of 2.19 µm using 100 mW pump. The proposed scheme links the mature near-IR devices to the mid-IR regime and have a great potential for integrated chip-scale alloptical signal processes.

Shaping Light in Backward-Wave Nonlinear Hyperbolic Metamaterials

“…Phase matching of contra-propagating fundamental and backward second harmonic wave in a plasmonic metamaterial is reported in [45]. The described approach can be applied to layered metal-dielectric metamaterials, which include layers of highly nonlinear dielectric as was proposed in [46] for the case of co-propagating waves.…”

Theoretical study of bicharacteristic waveguide for fundamental-mode phase-matched SHG from MIR to NIR

“…where ε is the molar absorption, C is the methane concentration, α prop is the propagation loss of the first waveguide, and Γ is the evanescent power factor defined as [17] z gas z total P dxdy P dxdy Γ =   (12) where P z is the z component of the Poynting vector normal to the waveguide cross section. The evanescent power factor Γ, which indicates the overlap of the interactions between the gas and the mode field, has a significant influence on the sensing performance.…”

“…Furthermore, the conversion efficiency can be significantly improved by employing polymer material with much higher second-order nonlinearity [9,10].Phase matching conditions (PMCs) which ensure the continuous power transfer from pump to harmonic are vital to realize efficient SHG process. Currently, the frequently utilized PMC techniques are based on quasi-phase matching (QPM) or intermodal-phase matching (IMPM) [11][12][13][14]. However, the QPM usually relies on the iron exchange technology or grating structure which can complicate the fabrication process.…”

Artificial Electromagnetic Characteristics Analysis in Hyperbolic Metamaterials Slot Waveguides Based on Graphene

“…1(a), the hyperbolic metamaterial waveguide system is composed of two graphenedielectric alternative multilayers with height H and width W vertically aligned with a gap distance g. Here, SiO 2 (ε d = 2.2) is chosen to be the dielectric layer and constructed with graphene to form hyperbolic metamaterials. Because the incident wavelength at infrared frequencies is much larger than the period of multilayer structure (t = 10 nm), the hyperbolic metamaterials can be treated as a homogeneous effective medium, and the permittivity sensor of different directions can be defined as [21]:…”