Very High Absorption of Traveling Wave Photodetectors in Superconducting Fiber Plasmon–Polariton Optical Waveguides

Abstract

By using a finite element method, we investigate a new, very sensitive, superconducting traveling wave photodetector made by an optical fiber, which includes a high index layer (LaAlO₃) with small losses, a number of metallic (gold) cylinders, and a single active superconducting layer (YBCO). Although in our structure of the fiber with 32 smaller gold cylinders, the number of the modes is large (3 nondegenerate modes and 16 twofold degenerate modes), the imaginary parts of the HE₁₁, TM₀₁, HE₁₂, and higher order plasmon modes and also the power absorption (0.93 for HE₁₁,0.91 for HE₁₂,0.95 for TM₀₁ and larger than 0.93 for all higher order plasmon modes) in the active superconducting layer are larger in comparison with that of a fundamental mode from a LaAlO₃–YBCO–Au planar waveguide or with that of the HE₁₁, TM₀₁, HE₁₂ modes from a model previously published where the gold cylinders are replaced with a single gold layer. The nondegenerate HE₁₁ mode and the highest nondegenerate plasmon mode are highly confined in the YBCO layer in the space between the neighboring gold cylinders. Also, the plasmon mode TM₀₁ is highly confined in the YBCO layer but on the exterior surface of the gold cylinders. The HE₁₂ and the higher plasmon modes are highly confined in the YBCO layer in the space between the neighboring gold cylinders or very close to their exterior surface. The confinement regimes of the light and the power absorption efficiency in the superconducting layer can be optimized by only acting on the fiber geometry.