Versatile hybrid plasmonic microfiber knot resonator.

A planar, all-optical fiber polarizer-based device based on a hybrid plasmonic microfiber knot resonator (HPMKR) is demonstrated in this Letter. A microfiber knot resonator (MKR) can be flexibly attached to the gold film, which forms the hybrid plasmonic mode with high propagation loss. Therefore, the device can be used not only as a broadband polarizer, but also as a high-quality resonator by tuning the geometry of the MKR. The polarizer has an extinction ratio of more than 15 dB ranging from 1200 to 1600 nm, and the Q-factor is more than 52,000 for one polarization state. For a chosen polarization, the resonator has an extinction ratio of nearly 15 dB, even though the diameter of the microfiber is more than 5 μm, which is unattainable for a normal MKR. By further optimizing and packaging, the device can be utilized as a weight sensor, with a sensitivity of 18.28 pm/g (51.2 pm/kPa) for the cavity resonant wavelength. Further, a vibration sensor on a HPMKR structure for detecting vibration from tens of hertz to several kilohertz is demonstrated.