Fig. 1. (a) Schematic fabrication processes of erbium-doped LNOI waveguides. (b) Optical micrograph of fabricated erbium-doped LNOI waveguides. (c) Simulation results of mode distributions regarding fundamental transverse electric modes at wavelengths of 974 nm (top) and 1532 nm (bottom).

Fig. 2. Experimental setup for gain characterization in erbium-doped LNOI waveguide amplifiers. VOA, variable optical attenuator; OC, optical coupler; PM, power meter; PC, polarization controller; WDM, wavelength division multiplexer; OSA, optical spectrum analyzer. The photograph of the erbium-doped LNOI chip clearly shows the generated green fluorescence propagating along the straight waveguide.

Fig. 3. Optical transmission spectra of Er-doped LNOI microring resonators on the same chip in (a) the 1550 nm band and (b) the 980 nm band. The Lorentz fit (red line) showing 9.78×104 and 2.42×105 loaded quality factors near 1531.5 nm and 974.5 nm, respectively.

Fig. 4. Gain characterization in erbium-doped LNOI waveguide amplifiers. (a) The dependence of net internal gain on pump power at a fixed signal power of ∼5 nW. (b) Measured signal spectra at ∼1531.47 nm with increasing pump powers of 0, 0.10 mW, 7.35 mW, 16.19 mW, 32.31 mW, and 64.02 mW. (c) The net internal gain as a function of increasing signal power at fixed pump power of ∼23 mW. (d) The amplified spontaneous emission (ASE) spectrum of the erbium-doped LNOI waveguide at pump power of 0.57 mW.