Fig. 1. Waveguides fabricated by multiscan technique in Ho∶YAG ceramics. (a) Microscopic image of end-face after multiple scanning for Ho∶YAG waveguide; (b)(c) mode profiles at wavelengths of 1.55 μm and 1.95 μm. Scale bar is 10 μm^[62]

Fig. 2. Dual-line waveguides in Nd∶GGG crystals. (a) Microscopic image of dual-line waveguide in Nd∶GGG crystals fabricated by femtosecond laser; (b) simulated refractive-index profile at end-face of waveguide; (c)(d) measured and calculated mode profiles at wavelength of 632.8 nm, respectively^[74]

Fig. 3. Cladding waveguides in Nd∶YAG crystals. (a) Schematic of cladding waveguides directly written by femtosecond laser in Nd∶YAG crystals; (b) microscopic image of double-cladding waveguide; (c)(d) microscopic images of single-cladding waveguides with diameters of 100 μm and 30 μm, respectively^[84]

Fig. 4. Beam-splitter composed of optical-lattice-like Ti∶Sapphire cladding waveguides directly written by femtosecond laser. (a) Prototype of beam-splitter with three different parts; (b) schematic and (c) microscopic images of three parts, respectively^[86]

Fig. 5. Fabrication of ridge waveguides in Nd∶GdCOB crystals. Schematics of fabrication process for (a) planar waveguide and (b) ridge waveguide in Nd∶GdCOB crystals; microscopic images of (c) surface and (d) end-face of ridge waveguide^[48]

Fig. 6. Dual-line waveguides in Nd∶YAB crystals. (a) Microscopic image of dual-line Nd∶YAB waveguide fabricated by femtosecond laser direct writing; (b) near-field intensity distribution at 1090 nm along TM polarization; (c) near-field intensity distribution at 632.8 nm along TE polarization^[24]

Fig. 7. Rhombic cladding waveguides in Pr∶YLF crystals. (a) Microscopic image of rhombic cladding Pr∶YLF waveguide written by femtosecond laser; (b) near-field intensity distribution at 632.8 nm along TE polarization (parallel to x direction)^[122]

Fig. 8. 8.8 GHz Q-switched mode-locked laser in Nd∶YAG cladding waveguide^[101]. (a) Output power as a function of launched power; (b) central wavelength of waveguide laser modulated by PtSe₂

Fig. 9. 1×2 and 1×4 beam-splitters with optical-lattice-like Nd∶YAG cladding waveguides fabricated by femtosecond laser^[45]. (a) Schematic and (b)--(e) optical microscope images of beam-splitters

Fig. 10. Second harmonic generation in Nd∶YCOB cladding waveguides fabricated by femtosecond laser^[25]. (a) Schemeof end-face coupling system; (b)(c) oscillation cavities for waveguide laser generation and frequency doubling,respectively

Fig. 11. Micro-luminescence maps on input end-face of Nd∶YAG cladding waveguide array^[78]. (a)--(c) Images of intensity, peak position, and peak width corresponding to 940 nm emission line of Nd³⁺

Fig. 12. Setup for amplifying mode-locked vertical external-cavity surface-emitting laser (VECSEL) in wedgedYb∶YAG dual-line waveguide^[67]