Robust Spot-Packaged Microsphere-Taper Coupling Structure for In-Line Optical Sensors

We propose and realize a spot-packaged structure for the microsphere-taper coupling system by only encapsulating and solidifying the coupling region with low refractive index polymer as the package material. After spot-package, ultrahigh quality factor
$(>10^{7})$
is obtained with the microsphere diameters around 300
$\mu \hbox{m}$
. The robustness of the spot-packaged structure is also tested, demonstrating the remarkable anti-tensile strength ability with the bearable loaded force larger than 0.05 N for a packaged structure with the spot-package area larger than 30
$\mu \hbox{m}^{2}$
. In addition, the spot-packaged structure is integrated with standard fiber, promising in in-line optical practical evanescent field sensing applications, especially in harsh detecting environments demanding high overload resistance.