  All surface plasmon resonance (SPR) devices on single-mode optical fibers'
(SMF) end facets, as reported up to date, are limited by severely broad and
shallow resonance spectra. The consequent poor performance when they are used
as refractive index sensors, together with the challenge of nanofabrication on
fiber end facets, has prohibited the development of such devices for label-free
biosensing. Meanwhile, the planewave coupled, multimode fiber and fiber
sidewall SPR counterparts are extensively employed for label-free biosensing.
In this paper, we report the design, fabrication and characterization of a
plasmonic crystal cavity on a SMF end facet, which shows high performance
label-free sensing capability that comes from a steep cavity resonance near the
plasmonic bandedge. The experimental figure-of-merit is 68 RIU^-1, which is
over twenty times improvement to previous reports. The refractive index
detection limit is 3.5*10^-6 RIU at 1 s integration time. We also describe a
novel glue-and-strip process to transfer gold nano structures onto fiber end
facets.
