Fig. 1. Simulated mode field distributions of 500  μm×4.4  μm 2×2 MMIs at (a) 1060 nm, (c) 1030 nm, and (e) 976 nm, respectively. False-color infrared images generated via MATLAB at the two output ports of the actual fabricated MMI at (b) 1060 nm, (d) 1030 nm, and (f) 976 nm, respectively.

Fig. 2. (a) Optical microscope image of a Yb:TFLN FP cavity. (b) Zoomed-in optical microscope images of a complete MMI image that is 500 μm long. (c) Coupling region of the MMI with a width of 4.4 μm. (d) The gap between the two microelectrodes is 10 μm.

Fig. 3. (a) Experimental setup used to characterize the Yb:TFLN FP cavity. The inset shows the energy level diagram of Yb3+ ions, the absorption and emission spectra of Yb:TFLN. (Pump, pump source; WDM, wavelength-division multiplexer; CTL, continuously tunable laser; PC, polarization controller; PD, photodetector; OSA, optical spectrum analyzer.) Normalized transmission spectra and Lorentz fitting (orange curves) around (b) 1060 nm and (c) 1030 nm for the 1030-FP laser and at (d) 976 nm for the 1060-FP laser.

Fig. 4. Lasing characterization of the Yb:TFLN FP cavity under a bidirectional pump with two 976 nm pump lasers. (a) Output optical spectrum of the 1030-FP laser from 1000 to 1100 nm. (b) Enlarged spectrum around a wavelength of 1029.6 nm; the lasing peak is fitted with a Lorentzian line shape (orange); the inset shows an infrared image of the mode-field distribution at 1030 nm. (c) On-chip laser power of the 1030-FP laser versus the input pump power. (d) Output optical spectral signal over a wide sweep of 100 nm of the 1060-FP laser. (e) Spectral amplification near 1062.6 nm; the inset shows an infrared image of the output port of the 1060-FP laser at 1060 nm. (f) Plot of the on-chip output power versus the input pump power of the 1060-FP laser.

Fig. 5. Wavelength tunability with applied voltages through microelectrodes. (a) Normalized laser output at voltages of −6  V,−3  V, 0 V, +3  V, and +6  V; the inset shows the probes used to connect the microelectrodes and DC power supply. (b) Linear relationship between the difference in wavelength and voltage applied to the electrodes.