Fig. 1. Structure of NV color center.（a）Structure diagram of NV color center，black circle represents the carbon atom；（b）energy level diagram of NV color center

Fig. 2. Different physical quantity measurements with ODMR^[47]

Fig. 3. Schematic diagram of evanescent wave sensing^[55]

Fig. 4. Experimental equipment diagram of reflection type and transmission type。（a）Schematic diagram of the steps for making the fiber probe^［57］；（b）schematic diagram of silver-coated reflection film on diamond surface and microscope image without silver-coated film^［41］；（c）transmission of excitation light and collection of fluorescence are completed through two optical fiber cones^［59］；（d）structure diagram of tapered optical fiber^［60］

Fig. 5. Evanescent wave optical fiber sensing structure. (a) Tapered fiber tip^[64]; (b) tapered fiber probe (red crystal is diamond particle^[34]); (c) U-shaped fiber structure^[65]; (d) NV-photonic crystal fiber sensor^[66]

Fig. 6. Fabrication of optical fibers by F2 doped diamond particles^[68]

Fig. 7. Diamond-doped tellurite glass fiber. (a) Experimental device; (b) tellurite fiber schematic diagram; (c) image of side (α) and end (β) of the fiber under scanning microscope, and excitation light and fluorescence images under different filters (γ)^[78]

Fig. 8. Fiber cavity and NV color center coupling device. (a) Tapered fiber with GaP-NV color center cavity^[82]; (b) coupling system of fiber microcavity and diamond particle^[17]

Fig. 9. Sensitivity index of magnetic field measurement in recent ten years ^{[34,37-39,41,67-69,77,87-95]}

Fig. 10. Diagram of multi-physical quantity measuring device. (a) Structure of sensor probe^[91]; (b) configuration of time division multiplexing sensor^[97]

Fig. 11. Application of NV color center in cell temperature measurement. (a) Schematic diagram of thermal excitation neuronal cell temperature measurement structure^[36]; (b) fluorescence spectrum of NV-silk fiber in cells, the central circle is the cell, the solid line is silk fiber, the dotted line box indicates two NV centers with representatives, and the color band represents fluorescence intensity^[98]

Fig. 12. Applications in the field of materials science. (a) Optical fiber sensor measurement chip surface temperature^[41]; (b) tapered fiber probe to characterize microwave vector near field^[102]; (c) NV center sensing device is used for nondestructive testing^[43]

Fig. 13. (a) Parabolic lens^[30]and (b) micro concave mirror^[106] are respectively used to improve fluorescence collection efficiency

Fig. 14. Fiber optic integrated magnetometer. (a) Internal structure of magnetometer, including optical fiber, microwave antenna, excitation coil, and diamond sample^[37]; (b) internal structure of integrated magnetometer^[39]; (c) diamond excitation and fluorescence collection are achieved using step-index fiber, and microwave antennas are integrated on the diamond surface^[93]

Fig. 15. Photodiode and diamond fluid optical waveguide are fused into the optical fiber^[20]