Embedded whispering-gallery mode microsphere resonator in a tapered hollow annular core fiber

Abstract

We propose and demonstrate a tapered hollow annular core fiber (HACF) coupler for excitation of whisperinggallery modes (WGMs) of an embedded microsphere resonator. The coupler is simply fabricated by fusion splicing of a segment of HACF with the single-mode fiber (SMF), and then improved by tapering the splicing joint to reduce the cone-apex angle. Therefore, the coupling efficiency from the SMF to the HACF is enhanced to excite various WGMs via evanescent field coupling. Normal positive, negative symmetrical Lorentzian and asymmetric Fano line shapes can be obtained by varying the resonator size and location. Another interesting phenomenon is observed that a higher Q-factor mode in a lower Q-factor mode has a contrast as high as 58. Temperature sensing with good stability is also demonstrated. This embedded WGM microsphere resonator in the tapered HACF is expected to promote environmental adaptability in practical applications due to its simplicity and robustness.

Singlemode-Multimode-Singlemode Fiber Structures for Sensing Applications—A Review

“…The SHCS fiber structure can also be functionalized for sensing of magnetic field strength [114], humidity [115], hydrogen detection [116], displacement [117], liquid level with sub-micrometer resolution [118] and ultrahigh sensitivity thickness measurement with nanometer resolution [119]. A tailored SHCS fiber structure for RI sensing [120] and Fano resonance achieved by inserting a microsphere into the HCF have also been observed and studied recently [121][122].…”

Whispering Gallery Mode Optical Microresonators: Structures and Sensing Applications

“…proposed a temperature sensing coupler of a tapered hollow toroidal core fiber (HACF) for exciting the WGM of the embedded microsphere resonators. The device was complicated in preparation but enhances the coupling efficiency from SMF to HACF, as shown in Figure a . The sensitivity of the device was only 10.8 pm °C −1 .…”

“…a) Experimental device preparation schematic. Reproduced with permission . Copyright 2018, Chinese Laser Press.…”

In-Fiber Polymer Microdisk Resonator and Its Sensing Applications of Temperature and Humidity

“…In 2015, Shi et al fabricated a microdisk WGM resonator in an optical fiber by direct femtosecond (fs) laser ablation, while its Q factor is significantly limited by the surface roughness . In 2018, Wang et al realized a WGM resonator by directly embedding barium titanate glass microspheres into the air hole of a tapered hollow annular core fiber, and excited various WGMs via changing the resonator size and location . Subsequently, Mallik et al demonstrated two fiber-tip hybrid resonators based on silica microspheres coated with different polymer layers for multiparameter sensing, and their WGMs were excited simultaneously with the help of an external fiber taper .…”