Fig. 1. Schematic diagram of a microfiber

Fig. 2. Cross-section of step-index fiber

Fig. 3. (a) Effective refractive index of HE₁₁ and HE₁₂ mode for step-index fiber with varied diameter; (b) Cross-section mode field distribution of fiber with cladding diameter of 80 μm and 20 μm^[25]; (c) Variation of effective refractive index for high-order modes in microfiber versus diameter at wavelength of 800 nm

Fig. 4. Microfiber resonators. (a) Microfiber loop resonator; (b) Microfiber knot resonator; (c) Microfiber coil resonator

Fig. 5. (a) Natural coordinate system of MCR; (b) MCR under cylindrical coordinates; (c) Cross-section of adjacent microfibers

Fig. 6. Parameters of microfiber resonator. (a) Group delay; (b) Dispersion; (c) Transmission spectrum

Fig. 7. Roadmap of evolution in Q-factor of microfiber resonator

Fig. 8. (a) Schematic diagram of flame-brushing technique; (b) SEM image of a silica microfiber

Fig. 9. Fabrication of microfiber resonator. (a) Fabrication of MLR; (b) MKR’s cutting-end fabrication; (c) MKR’s complete fabrication; (d) Microscopic image of MKR; (e) Microscopic image of MCR; (f) Fabrication of MCR; (g) Fabrication of graphene-integrated MCR

Fig. 10. Temperature sensitivity as a function of the microfiber radius after package

Fig. 11. Sensors based on microfiber resonators. (a) Refractometric sensor based on MLR^[52]; (b) Graphene oxide deposited MKR for gas sensing^[62]; (c) Temperature sensor based on MKR^[64]; (d) Current sensor based on graphene-integrated MCR; (e) Hybrid-plasmonic MKR; (f) Soft and wearable HPMKR sensor; (g) Fiber hydrophone based on MKR^[39]; (h) Microfluidic sensor based on MCR; (i) 3D-stereo grating based on a microstructured rod with MCR

Fig. 12. Optical signal processing.(a) MCR broad band polarizer^[38]; (b) Graphene-integrated MCR all-optical modulator^[81]; (c) Polarization-dependent modulation of graphene-integrated MCR all-optical modulator^[81]; (d) Graphene-integrated MKR all-optical modulator^[82]; (e) WS₂-integrated MKR all-optical modulator^[83]; (f) MCR delay line^[84]

Fig. 13. Application of microfiber resonators in fiber laser.(a) Application schemes of microfiber-resonator-based fiber laser; (b) Operation regimes of microfiber-resonator-based fiber laser

Table 1. Performance comparison of 3 microfiber fabrication methods

Table 2. Sensors based on microfiber resonators

Table 3. Signal processing based on microfiber resonators

Table 4. Fiber laser based on microfiber resonators