Fig. 1. Evolution of real saturable absorber (SA) technologies starting from conventional materials, such as organic dyes, colored glasses, chromium-doped crystals, and semiconductor SA mirrors (SESAMs), to nanomaterials, including zero-dimensional (0D) quantum dots (QDs), one-dimensional (1D) single-walled carbon nanotubes (SWCNTs), two-dimensional (2D) graphene, and graphene-like 2D layered materials, such as topological insulators (TIs), transition metal dichalcogenides (TMDCs), and black phosphorus (BP). Red dots denote the first, reported application of each technology in a pulsed laser.

Fig. 2. Schematic diagrams of different types of planar and channel waveguides.

Fig. 3. Common strategies of transferring SA materials on optical substrates on (a) transmitting glass plates, (b) reflecting mirrors, and directly on (c) exposed waveguide surfaces.

Fig. 4. Schematic diagrams of two typical end-pumping configurations of passively Q-switched and mode-locked waveguide lasers based on (a) direct-interaction and (b) evanescent-field-interaction schemes.

Fig. 5. Schematic diagrams of two commonly used strategies for dispersion management in mode-locked waveguide lasers based, respectively, on (a) extended cavities and (b) soliton formation mechanisms realized by adjusting the cavity length, i.e., by tuning the air-filled gap between the SA and waveguide end-facet.

Fig. 6. Figures of merit (FOMs) of pulsed waveguide lasers operating in the Q-switched and Q-switched mode-locked regimes with (a) planar and (b) channel geometries, as well as in (c) the CW mode-locked regime. The FOM errors in these diagrams are ±10%. The symbols’ colors represent waveguide fabrication methods, while the symbols’ appearance stand for different laser configurations in terms of operation regimes, waveguide geometries (circles, Q-switched; triangles, Q-switched mode-locked; squares, planar waveguide lasers operating in the CW mode-locked regime; stars, channel waveguide lasers operating in the CW mode-locked regime) and SA integration types (open markers, free-standing SAs inserted in cavities; filled markers, integrated SAs coated on waveguides).

Fig. 7. Schematic diagram of (a) a hybrid PLD chamber and (b) the graphene-covered Yb:Y2O3/YAG planar waveguide fabricated by PLD. (c) Measured modal profile of the graphene Q-switched Yb:Y2O3/YAG planar waveguide laser. Reproduced with permission from Ref. [49], ©2015 Optical Society of America.

Fig. 8. (a) Schematic diagram of an LPE arrangement. (b) SEM image of the end-facet of the Tm:KYW/KYW planar waveguide fabricated by LPE. (c) Measured modal profile of the SWCNT Q-switched Tm:KYW/KYW planar waveguide laser. Reproduced with permission from Ref. [59], ©2018 Optical Society of America.

Fig. 9. (a) Optical microscope image of the end-facet of the Ho:YAG channel waveguide fabricated by direct bonding. (b) Photograph of the Ho:YAG waveguide sample. (c) Measured modal profile of the Ho:YAG channel waveguide laser. Reproduced with permission from Ref. [66].

Fig. 10. (a) Schematic diagram of the YAG/RE:YAG/YAG planar waveguide fabricated by tape casting. (b) Measured modal profile of the SESAM mode-locked YAG/Yb:YAG/YAG waveguide laser. Reproduced with permission from Ref. [69].

Fig. 11. (a) Schematic diagram of mask-assisted ion implantation/irradiation for channel waveguide fabrication. (b) Reconstructed cross-sectional refractive-index distribution of the Nd:YAG channel waveguide fabricated by C5+ ion irradiation. (c) Measured modal profile of the Nd:YAG channel waveguide laser. Reproduced with permission from Ref. [72], ©2014 Optical Society of America.

Fig. 12. (a) Cross-sectional TEM image and (b) the superimposed element distribution of the Nd:YAG crystal embedded with Au nanoparticles realized by ion irradiation. The particle size distribution and the nonlinear absorption coefficient at 515 nm of the sample are shown in (c) and (d), respectively. Reproduced with permission from Ref. [83], ©2018 The Royal Society of Chemistry.

Fig. 13. (a) Schematic diagram of mask-assisted ion exchange for channel waveguide fabrication. (b) Measured modal profile of SESAM mode-locked Yb3+-doped glass channel waveguide laser fabricated by ion exchange. Reproduced with permission from Ref. [35], ©2013 Optical Society of America.

Fig. 14. Schematic diagrams of the fabrication procedure of fs-laser-written waveguides^[18]: (a) single-line waveguide based on smooth Type-I modification, (b) stress-induced double-line waveguides based on two parallel Type-II tracks, and (c) depressed-cladding waveguides. The shadows represent the fs-laser-induced tracks, and the dashed lines indicate the spatial locations of the waveguide cores. (d) Schematic diagram of the three-element 3D photonic-lattice-like cladding structures for the 1×4 beam splitter and ring-shaped transformer^[114]. The cross-sectional images of each element are indicated as insets. Reproduced with permission from Ref. [98], ©2015 SPIE.

Fig. 15. Wavelength ranges covered by solid-state waveguide lasers operating in the CW, Q-switched, Q-switched mode-locked, and CW mode-locked regimes.