Fig. 1. Basic optical waveguiding properties of a silica micro/nanofiber at 633 nm wavelength in the air^[7]. (a) Calculated propagation constant β, where D is the fiber diameter and V is the normalized propagation constant;(b) energy flow (Poynting vector) distribution along the axial direction (upper) and the cross-sectional field intensity distribution (lower) of the waveguided light

Fig. 2. Optical properties and applications of optical micro/nanofibers^[7]

Fig. 3. Preparation of high-precision optical micro/nanofibers based on high-order mode cutoff feedback control^[30]. (a) SEM image of a typical optical micro/nanofiber; (b) optical micro/nanofiber drawing results with a preset target diameter of 500 nm. The blue dots stand for diameter value of the experimental measurement, the dashed line stands for average value of the experimental measurement, and the solid line stands for the target value. 699 nm is the wavelength corresponding to the cutoff of TE01 mode of a 500 nm diameter micro/nanofiber

Fig. 4. On-top parallel coupling of an Er³⁺/Yb³⁺ co-doped high refractive index tellurite glass micro/nanofiber and one side of a silicon-based microring cavity^［48］.（a）SEM image of the coupling structure；（b）optical microscope image of the coupling structure，in which the green fluorescence of the tellurite glass micro/nanofiber comes from up conversion luminescence of Er³⁺ ions excited by a 976 nm light；（c）broadband photoluminescence spectrum of Er³⁺ ions in a tellurite glass micro/nanofiber coupled out from the bottom horizontal drop waveguide，after circulating in the silicon-based microring cavity around 1550 nm band

Fig. 5. Superconducting nanowire single photon detector (SNSPD) based on near-field coupling optical input of a micro/nanofiber^[51-52]. (a) Schematic of near-field coupling between a micro/nanofiber and a superconducting nanowire; (b) photo of a micro/nanofiber coupled on-chip SNSPD module; (c) optical microscope image of a micro/nanofiber on-top coupled superconductor nanowire

Fig. 6. Micro/nanofiber-based wearable "optical skin" tactile sensors^[68]. (a) Schematic of the sensor structure; (b) response test results of the sensor to 2.1, 1.3, 0.2, 0.1 Pa, respectively; (c) response test results of the sensor to mechanical vibration of 1, 4, 20 kHz, respectively; (d) photo of attaching the sensor on a wrist for pulse measurement; (e) pulse test results of 66 times per minute

Fig. 7. Pre-bent micro/nanofiber-based wearable "optical skin" sensors^[69]. (a) Schematic of the sensor structure; (b) comparison of the cross-section modal field intensity distribution of a micro/nanofiber before and after being stretched; (c) experimental results and real-device photo of attaching the sensor onto the forehead surface for body temperature measurement; (d) output spectra of the sensor measuring different temperatures in an oil bath

Fig. 8. All-optical ultrafast modulator based on hybrid "graphene-micro/nanofiber" structure^[87,90]. (a) Schematic of the graphene-coated micro/nanofiber (GCM) structure; (b) response time test results of pump-probe technique (the fiber diameter is 1.4 μm, the GCM length is 20 μm, and the response time is ~2.2 ps when the pump power is 200 nW), and the inset shows the dependence of the modulation depth on the pump intensity; (c) schematic of two types of all-optical modulation structures based on GCM (top: modulation structure based on absorption loss; bottom: optical phase modulation structure based on an all fiber Mach-Zehnder interferometer); (d) experimental results of all-optical modulation based on two types of GCM structures (top: pump pulse pairs with different intensities; middle: modulation results based on absorption structure; bottom: modulation results based on phase modulation structure)

Fig. 9. Mode-locked fiber laser based on micro/nanofiber dispersion management^[92]. (a) 1 μm mode-locked fiber laser based on intracavity micro/nanofiber dispersion management, extra-cavity dechirping micro/nanofiber and single-mode fiber; (b) comparison of extra-cavity autocorrelation curves after and before dechirping