Fig. 1. Geometry of (a) asymmetric planar waveguide (n2>n1>n3) and (b) symmetric planar waveguide with its refractive index profile and a propagating light ray in its core

Fig. 2. Thermal conductivity of (a) Nd∶YAG and (b) Yb∶YAG crystal and ceramics[39]

Fig. 3. Schematic of the light propagating and refractive index distribution in (a) mutational and (b) gradual waveguide structure

Fig. 4. Different types of channel waveguides. (a) Embedded; (b) strip; (c) rib or ridge; (d) strip-loaded

Fig. 5. Schematic of cylindrical waveguide

Fig. 6. (a) Schematic of the experimental setup for the heavy swifti ion C5+ ion irradiation with metal mask; (b) schematic of pulse laser oscillation experimental setup for Nd∶YAG ceramic waveguide, the inset shows the microphotograph of the graphene saturable absorber

Fig. 7. Four types of optical waveguide crystals fabricated by femtosecond laser writing technology[68]

Fig. 8. Optical microscope images of the end surface of (a) hexagonal, (b) circular, (c) trapezoidal cladding waveguides of Nd∶YAG ceramics

Fig. 9. Three kinds of femtosecond laser direct writing technology. (a) Linear translation, transverse to the laser medium; (b) helical movement, transverse to the laser medium; (c) helical movement, parallel to the laser medium

Fig. 10. Microscope photos of type III waveguide with the diameter of 100 μm fabricated by (a) traditional method and (b) end surface photos under low-pump level at 807 nm by helical movement method by using (c) traditional method and (d) helical movement method; luminescent spot diagrams under low-pump level at 807 nm by using (e) traditional method and (f) helical movement method

Fig. 11. Schematic of spinel/YAG/Er∶YAG/YAG/spinel strip waveguide structure with double-clad

Fig. 12. Schematic of double-clad spinel/YAG/Nd∶YAG/YAG/spinel double-clad planar waveguide and guided modes at the lasing wavelength

Fig. 13. (a) Physical photograph and (b) surface SEM micrograph of the ceramic casting tape; (c) physical photograph and in-line transmittance of the planar waveguide YAG/Nd∶YAG/YAG transparent ceramics; (d) schematic of the single-pass YAG/Nd∶YAG/YAG ceramic planar waveguide laser amplifier system

Fig. 14. (a) Setup schematic, (b) output power under different output couplers and (c) beam quality factors under different output powers of the ceramic planar waveguide laser. The inset in Fig. (c) shows the beam spot imaged by CCD

Fig. 15. (a) Schematic of YAG/Yb∶YAG/YAG ceramic waveguide laser setup; (b) average output power of three-mirror laser cavity with different transmissivity (5% and 10%), the inset shows the mode profile

Fig. 16. Relationship between the refractive index and Yb3+ doping concentration of Yb∶YAG

Fig. 17. (a) Schematic of experimental setup, (b) output performance with different output mirrors, (c) output spectrum of YAG/Tm∶YAG/YAG ceramic planar waveguide laser

Fig. 18. Laser performance and physical photograph of Nd∶YAG ceramic fiber

Fig. 19. (a) Schematic and (b) laser performance of the end-cap type Nd∶YAG ceramic fiber

Fig. 20. YAG green fiber extruded from the high pressure nozzle whose diameter is 125 μm

Fig. 21. (a) Micrograph of fiber prepared with unclassified and classified YAG powder; (b) physical photograph of looped YAG fiber

Fig. 22. SEM micrographs of SF57 glass cladding on YAG fiber. (a) 3000×; (b) 10000×

Fig. 23. SEM micrograph of the surface of the YAG ceramic fiber with different surface state. (a) After sintering; (b) after polishing