Fig. 1. Structure diagram of heterogeneous integrated on-chip devices based on chalcogenide waveguides and X material (X means lithium niobate or erbium-doped Al₂O₃). They are erbium-doped waveguide amplifier, nonlinear parametric frequency conversion waveguide, and acousto-optic modulator from top to bottom, respectively. Inset shows cross section of integrated device

Fig. 2. Schematics of on-chip acousto-optic modulators based on lithium niobate. (a) Mach-Zehnder interferometer (MZI) and microring resonant acousto-optic modulator^[46]; (b) suspended MZI and microring resonators acousto-optic modulator^[47]; (c) suspended photonic crystal waveguide acousto-optic modulator^[48]

Fig. 3. Non-suspended ChGs-lithium niobate heterogeneous platform with integrated built-in push-pull acousto-optic modulator^[27]. (a) Structure diagram of device; (b) comparison of push-pull and non-push-pull photoacoustic S₂₁ spectra; (c) scanning electron microscope (SEM) diagram of device

Fig. 4. Structural diagrams of several acousto-optic modulators based on a ChGs-lithium niobate hybrid integrated platform. (a) Microring resonator acousto-optic modulator^[52]; (b) transmission spectrum of microring resonator^[52]; (c) optical-mechanical resonator acousto-optic modulator^[53]; (d) grating and π phase-shift grating acousto-optic modulator^[54]; (e) comparison of photoacoustic S₂₁ spectra of two grating acousto-optic modulators^[54]

Fig. 5. GeSbS/LN heterogeneous integrated waveguide for efficient parametric frequency conversion^[85]. (a) Cross-section schematic of waveguide. Inset shows SEM image of waveguide; (b) effective refractive indices of waveguide as a function of wavelength in communication and visible light bands. Insets show optical field (E_z) profiles of mode distributions for TE₀₀ mode at 1574.6 nm and TE₀₁ mode at 787.3 nm, respectively

Fig. 6. Measured second-harmonic generation (SHG) from GeSbS/LN waveguide with a length of 1 cm^[85]. (a) Measured SHG efficiency spectrum of waveguide (solid line). Dashed line shows calculation result using sinc² function; (b) spectrum of SHG at a pump wavelength of 1574.28 nm. Insets are bright- and dark-field microscope images showing SHG signals; (c) measured SHG power as a function of pump power

Fig. 7. Cascaded SHG/difference-frequency generation (cSHG/DFG) in GeSbS/LN heterogeneous integrated waveguide and phase-matched pump wavelength as a function of temperature^[85]. (a) Spectra of cSHG/DFG for signals from 1581 to 1611 nm. Inset shows principle of cSHG/DFG process; (b) measured and calculated conversion efficiency versus signal detuning from pump wavelength; (c) measured phase-matched (PM) pump wavelength λ_PM as a function of temperature. Linear fitting indicates a tuning slope of 0.18 nm/K

Fig. 8. Structure diagram of heterogeneous Er³⁺:Al₂O₃-GeSbS integrated waveguide amplifier^[117]. (a) Er³⁺ ions energy-level transition diagram upon 1480 nm pumping; (b) cross-section illustration of Er³⁺:Al₂O₃-GeSbS waveguide structure and TE mode distributions at 1480 nm and 1533 nm, respectively; (c) schematic of spiral optical waveguide amplifier

Fig. 9. Preparation and characterization of Er³⁺ doped Al₂O₃ thin film^[117]. (a) Deposition process of Er³⁺:Al₂O₃ thin film by atomic layer deposition technique; (b) photoluminescence (PL) spectrum ranging from 1450 to 1650 nm of sample with erbium ion concentration of 4.9×10²⁰ cm^-3 at 850 ℃ annealing temperature; integrated PL intensity responses for five samples under different annealing temperatures at wavelengths of (c) 1533 nm and (d) 1550 nm, respectively

Fig. 10. SEM images and gain characteristics of waveguide^[117]. (a) Cross-section SEM images of Er³⁺:Al₂O₃ thin film and Er³⁺:Al₂O₃-GeSbS waveguide; (b) microscope image of spiral waveguide with a total length of 4.6 cm; (c) waveguide rested in a compact footprint of 0.9 mm×0.9 mm and exhibiting strong green PL upon 1480 nm pumping; (d) dependence of internal net gain on wavelength of signal; (e) measured and simulated internal net gain as a function of pump power; (f) internal net gain versus signal power for signals at 1533 nm and 1550 nm