Surface Plasmon-Enhanced Coupling of Optical Guided Waves to High-Temperature Superconducting Optoelectronic Structures

A novel technique is proposed for coupling near-infrared and visible optical power to high-temperature superconducting (HTS) optoelectronic structures, fabricated on a high-index substrate, by means of the excitation of surface plasmon polariton (SPP) waves at the interface of the HTS layer and a metal cladding. The modal characteristics of these guided waves differ from those of the SPP modes of a metal slab bounded by symmetric or asymmetric dielectric layers because of the presence of a high-index semi-infinite substrate at close proximity. The modal dispersion of the guided mode exhibits a cutoff with increasing HTS thicknesses. Inasmuch as the HTS layer possesses a large extinction factor, it absorbs most of the optical power, whereas in a conventional dielectric-metal structure, the power is virtually absorbed by the metal. Furthermore, the variation of the coupling efficiency as a function of the HTS thickness is examined, and it will be demonstrated that the surface plasmon-assisted coupling technique outperforms unguided illumination schemes. The proposed technique and structure are particularly useful for guided-wave superconducting optoelectronic devices, including superconducting photodetectors and photomixers.