Surface plasmon resonance (SPR) devices have been widely used in label-free biosensing applications due to their convenient surface wave configuration and the capability to optically detect biomolecule surface binding with a high stability and uniformity between different experiments. Meanwhile, integrating SPR nanostructures onto single-mode fiber (SMF) end facets provides unique advantages such as flexible geometry, compact sizes and in vivo monitoring capability. To improve the performance of SMF end facet SPR devices which are usually limited by guided mode diffraction, following our previous work on plasmonic crystal cavities , in this work we demonstrate a plasmonic distributed feedback (DFB) cavity with a phase shift section. The DFB structure contains a periodic array of nanoslits in a gold film, which provides a surface plasmon polariton (SPP) bandgap from 865 to 877 nm on the water-gold interface. A phase shift section is embedded at the center of the DFB structure to introduce an SPR defect state within the SPP bandgap. The devices were fabricated onto the fiber end facets by a glue-and-strip transfer process . To demonstrate real biosensing implementations, the reflection spectra of the SMF guided lightwaves were taken in real-time to detect refractive index change, adsorption of bovine serum albumin onto gold surface, and the association and dissociation between human immunoglobulin G (hIgG) and its antibody.
 X. He, H. Yi, J. Long, X. Zhou, J. Yang and T. Yang, "Plasmonic Crystal Cavity on Single-Mode Optical Fiber End Facet for Label-Free Biosensing," Applied Physics Letters 108, 231105 (2016)