Fig. 1. (a) The cross-section and (b) the schematic of the waveguide amplifier proposed in this work with a low-loss GeSbS waveguide sitting on the erbium-doped lithium niobate film. The simulated fundamental TE mode distributions at 1480 nm (c) and 1531.4 nm (d), respectively. (e) The relationship between the waveguide width and effective refractive indices at 1480 and 1531.4 nm.

Fig. 2. (a) The experimental setup to characterize the gain performance of the heterogeneous waveguide amplifier. The inset pictures show the microscope images of the coupling region between the lensed fiber and chip when the 1480 nm pumping light is off (left) and on (right) with green color luminescence. (b) The microscope image of the waveguide bending region with a radius of 200 μm. (c) The cross-sectional SEM image of the Er3+:LN-GeSbS waveguide with vertical sidewalls. (d) The waveguide exhibiting strong green photoluminescence upon 1480 nm pumping.

Fig. 3. (a) The measured insertion losses at the signal wavelength of 1640 nm when the waveguide lengths are 1.2 cm, 4.6 cm, 6.6 cm, and 10.3 cm. (b) The dependence of propagation loss and absorption loss on the signal wavelength. The top edge of the bottom shaded region represents the propagation loss and the dots in the top shaded regime are the evaluated absorption losses at different wavelengths when on-chip signal power is −5  dBm. (c) The evaluated total waveguide loss per centimeter as a function of the launched signal power at wavelengths of 1640 nm (gray), 1550 nm (red), and 1531.4 nm (blue).

Fig. 4. The gain characteristics of the devices. (a) Measured internal net gain upon −14.4 dBm signal power input as a function of the pump power at 1531.4 nm for 4.8 cm (yellow), 6.6 cm (red), and 10.3 cm (blue). (b) The conversion efficiency varies with on-chip pump power. (c) The measured internal net gain versus launched signal power is excited by 1531.4 nm light waves with a fixed pump power of 55 mW. (d) The measured output power at 1550 nm with on-chip (black axis) and off-chip (red axis). (e) The dependence of the ASE optical power on the wavelength of the signal ranging from 1510 to 1630 nm with different waveguide lengths. (f) The signal enhancement as a function of signal wavelength upon 1480 nm pumping for a 10.3-cm-long waveguide.

Fig. 5. Noise figure as a function of on-chip signal power at 1531.4 nm.