Effective modes investigation of transmitted and reflective heterocore optical fiber surface plasmon resonance sensors

摘要

Two unexpected experimental phenomena in transmitted and reflective heterocore optical fiber sensors are observed. The surface plasmon resonance (SPR) wavelength of the reflective SPR (R-SPR) sensor redshifts about 100 nm to the transmitted SPR (T-SPR) sensor. The maximal extinction ratio is 0.60 for the T-SPR sensor and reaches 0.77 for the R-SPR sensor. For a further understanding of the generation mechanism of SPR in both sensors, the finite-element method is employed to calculate distributions of the electric fields. Accompanied with experiments, modal energy coupling among the modes as light transmits through the multimode-single-mode-multimode fiber sensor is demonstrated, and the length of the single-mode fiber (SMF) is the focus of interest. The initial dissipated energy of the higher-order TM modes breaks the dynamic coupling balance of modal energy in the SMF when SPR takes place as a significant perturbation. With increasing SMF length, extra energy couples from lower-order modes to higher-order modes, from TM modes to TM modes as well, which results in a deeper trough and a longer SPR wavelength and thus a more sensitive device. The results are promising for various applications of a broader spectrum, such as modulators and sensors. (C) 2019 Optical Society of America