Monolithic tunable single-frequency microlaser on erbium-doped lithium niobate on insulator

We present a monolithic, tunable single-frequency microlaser based on a dual-cavity structure fabricated on erbium-doped lithium niobate on insulator (Er:LNOI) by photolithography assisted chemo-mechanical etching (PLACE). The dual-cavity design consists of a microring coupled with a microdisk, the latter of which is integrated with a microelectrode. By exploiting the Vernier effect, single-frequency laser emission is achieved at 1551.2 nm, exhibiting a low threshold of 0.22 mW and a narrow linewidth of 2 MHz under 977-nm optical pumping. Furthermore, the strong electro-optic (EO) effect of lithium niobate combined with the Vernier effect, enables a high electro-optical tuning efficiency of 25.2 pm/V, representing an order-of-magnitude improvement over previously reported values. To extend the tuning range, the thermo-optic effect of lithium niobate is utilized, allowing the microlaser signal to be tuned from 1551.2 nm to 1551.9 nm with a tuning efficiency of 32 pm/°C. This monolithic tunable microlaser holds great promise for advancing low-cost, reconfigurable photonics research and applications.